CA1038711A - Engine vibration dampener means - Google Patents
Engine vibration dampener meansInfo
- Publication number
- CA1038711A CA1038711A CA234,641A CA234641A CA1038711A CA 1038711 A CA1038711 A CA 1038711A CA 234641 A CA234641 A CA 234641A CA 1038711 A CA1038711 A CA 1038711A
- Authority
- CA
- Canada
- Prior art keywords
- engine
- cooling fins
- portions
- fins
- lug
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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- Cylinder Crankcases Of Internal Combustion Engines (AREA)
Abstract
ABSTRACT
A vibration dampener for an engine with cooling fins on its cylinders is an integrally formed resilient material member with a first portion having lug portions mountable on opposite sides of cooling fins and between adjacent cooling fins. The lug portions in their outer end portions are of reduced size relative their inner portions, and are wider in their inner end portions than the distance between the fins. Connected ends of the first portion traverse ends of the cooling fins. The vibration dampener is constructed and adapted to be mounted and held in place on an engine solely by friction with the lug-like portions compressed between cooling fins. It reduces the vibrating frequency to which the cool ing fins on the cylinders can be forced by normal operation of the engine to prevent the engine from reaching a resonant frequency A method of dampening vibrations of cooling fins of an engine having same on its cylinders includes providing a wedge-like member to temporarily spread the cooling fins, inserting a tooth of a comb-like resilient member between the spread fins and removing the wedge-like member to release the cooling fins so they compressibly hold the resilient member.
1 and 2
A vibration dampener for an engine with cooling fins on its cylinders is an integrally formed resilient material member with a first portion having lug portions mountable on opposite sides of cooling fins and between adjacent cooling fins. The lug portions in their outer end portions are of reduced size relative their inner portions, and are wider in their inner end portions than the distance between the fins. Connected ends of the first portion traverse ends of the cooling fins. The vibration dampener is constructed and adapted to be mounted and held in place on an engine solely by friction with the lug-like portions compressed between cooling fins. It reduces the vibrating frequency to which the cool ing fins on the cylinders can be forced by normal operation of the engine to prevent the engine from reaching a resonant frequency A method of dampening vibrations of cooling fins of an engine having same on its cylinders includes providing a wedge-like member to temporarily spread the cooling fins, inserting a tooth of a comb-like resilient member between the spread fins and removing the wedge-like member to release the cooling fins so they compressibly hold the resilient member.
1 and 2
Description
~3~7~
ENGINE DAMPENER ~vEANS
The invention is generally related to dampeners for reciprocating air-cooled engines and the method of applying the dampener to the engine. The invention is specifically related to resilient cooling fin dampeners for aircraft engines and modifications of the intake manifold and propeller servo control system for the purpose of reducing the forced vibrational frequency of the engine to prevent damage to the engine by self-induced vi~rations.
In general, aircraft engines are prone to have vibration problems, -as they must be light in weight and have a relatively high horsepower, 10 as well as being air-cooled. The problems of vibration are particularly a¢ute in reciprocating type air=cooled aircraft engines, d~ to the reciprocating firing motion of the engine. In the prior art, little has been done tO prevent or overcome excessive vibration problems in reciprocating air-cooled aircraft engines, except by way of strength-enL~g the damage-prone parts of the engine and spreading the operational frequency of the engine by operating engine-driven pumps, -and other accessories, at speeds whi~h are fractionally propor~ionally different from the crankshaft speed or firing or the frequency of the , , engine. In strengthening of the engine structure to prevent damage 20 fin dampeners have been constructed to be mounted between and on the end portion of the cooling fins, primarily to prevent the fin from `~
being broken off. The prior art fin dampeners and strengthening structures have a single strip of resilient material, specifically rubbex7 which is pressed into th0 outer portion of ~he cooling fins and i9 attached to the fins by the heat OI the engine which cures or sets the material. Other known fin dampener structures include a comb-like structure, having the teeth extending between the fins with a clasp encircling the teeth and tightenable to compress them circum-ferentially thus expanding it between the fins to hold it in place. A
30 prior axt fln dampener structure i9 known which extends from the . .
3~
~` outer portion of the fins completely to the attachment point of the fins with such being retained in place by an adhesive material. No ~ ;
prior art device or devices are known which are specifically constructed for use with an air-cooled multi-cylinder aircraft type engine to control the vibrational characteristics or natural operating ~requency of the engine in an atcempt to prevent the operating frequency ~om becoming resonant or causing substantial structural damage to the engine.
Reciprocating type internal combustion aircraft engines are inherently a vibration generating body in an aircraft due to the inherent reciprocating or oscillating motion~ Reciprocating type aircraft ,~ ......
engines are balanced internally so they will perform their operation ;
with a minimum of unbalance; however, in practice the engines do vibrate considerably and produce a quantity of often objectionable noise. Engine vibration and noise affect engine fatigue, airframe fatigue and ~i!lot fatigue. A great many engine failures and pilot failures or malfunctions can be attributed to engine vibration and .:
noise associated with the operating the reciprocating type of engine. `
The speci~ic engine failures or malfunctions which can be substantially attributed to vibrationally induced factors include9 cooling fin -~
fract~es, engine cylinder Eractures, piston ring fractures, and crankshaft and connecting rod fractures. It is well known in the art that fatigue, due to noise and vibration, will crack and propagate cracks in -materials subjected to such forces, and it is these Eorces which cau~e fracture or other failure in the identified parts OI an engine or other parts of an engine connected with these components.
The problem of engine failure and malfunction has long been a ~;
critical problem in aviation and it has been studied in depth. One such study was conducted by the United States National Transportation Safety Board and documented in the report entitled, "Special Study 3~7~
Accidents Involving Engine Failure/Malfunction, U. S. General Aviation, 1965-1969. " This report is publlshed by the National Transportation Safety Board as report nurnber NTSB-AAS-72-10, it was adopted November 29, 1972. This special studypresents a recor~ of engine failure/malfunction accidents for fixed-wirlg air-craft, all of which occurred in all operations of U. S. general aviation, during the period of 1965-1969. It includes a complete comparison of engine-failure accident rates ~or single-engine and mul~i-engine air~raft. Analysis are included concerning cal:ses and related factors of engine-failure accidents by selected ~nakes and models of aircraft and engines. It includes tables, comparing cause/factors for the accidents and severi~y OI the accidents for all fixed-wing aircraft along with single-engine and multi-engine fixed-wing aircraft.
The inventiorl disclosed herein is a result of studies of and experiments made with a Continental IO-470 and IO-520 series - .
erlgines. The IO-470 and IO-520 series of engines are manufaçtured ~ ~
. , .
in several models for different alpplications however they are basically structurally the same. These engines are essentially `~ ~;
20~ structurally identical with the IO-520 series having a larger dis-placement and horsepower rating. The following are exerpts from the identified report, from the portion related to analysis of engine ~ailure/malfunction for these particular engines. A close examination of the special study report indicates that these identified engines had a significantly higher-than-expected involvement in individual power plant cause/factor-citations. It is to be noted that the power ;~
plant of an aircraft was cited as a probable cause/related factor in over 44 percent of the engine-failure accidents. The predominant power plant cause/factor citation include in part; master and 30 connecting rods, cylinder assembly, piston and piston rings, and 3~
crankshaft. In regard to the I0-470 model engine, the cause/factor citations were specific tO the engine cylinder assemblLes, master and connecting rocls, crankshaft, fuel system lines and fittings. In regard to the Continental I0-520 engine, the cause/factor citations were specific to the piston, piston rings and crankshaft. The specific engine elements cited are the elements of the engine which would obviously be the most likely to have vibration and fatigue clamage because they are so closely related to the rotating and reciprocating motion of the engine. In use, the two identi~ied engines are normally -used in the following aircraft: Beechcraft Model 35; Cessna 180;
Cessna 182, Cessna 206, Cessna 188, and Navion Model L-17. In the special study report, detailed cause/factors for par~icular air-craft make and model are compared with those of other aircraftO ~-In this comparison a normal approximation the binomial technique was used~ wherein the accounts of a cause/factor for a particular assembly, engine, aircraft, etc~, is comparable to same appearance for all aircraft involved in the study. The special study report -reveals that most of the engine-failure accidents for each aircraft make and model were caused by a pilot-in-command error, such as inadequate preflight preparation and/or planning, mismanagement of fuel, and improper operation of power plant controls. Explaining why a particular aLrcraft has a higher than expected percentage of engine failure accidents for a specific power plant cause/factor involves an inspect;ion of the engines installed in those particular aircraft. In regard to the identified engine, the frequency of piston and piston ring problems are significantly higher than expected for the Navion L-17 and the Cessna 210 than in the Beechcraft. The Navion L-17 uses the Continental I0-470 model engine and the Cessna 210 is equipped with the Continental 10-470 and the Conti-nental L0-S20 engine. The I0-470 engine in the Beechcraft Model . .
~3~7~
35 aircraft experienced a higher than expected involvement in the fuel system pumps area. In regard to the Cessna 210 aircraft, the following engine elements and percentages are the parts of the engine structure which were cited as a cause/factor in the respective percent of total accidents: piston, piston rings--6.
cylinder assembly--5.2%, crankshaft--3.4~, and master and con-necting rods--3.4~. The expected percentage of engine structure failure or malfunction for the noted elements is 2%, 2%, 1.8~, ;
and 2.5'~, respectively. It is to be noted that the actual per-.":
10 centages are significantly higher than the actual percentages ~-~
in this instance substantially higher than the expected percent- ; ~ ;
a~es. ' In the special study, a total of 3,312 engine-failure accidents were considered. The accidents studied do not include home-built or experimental category of aircraft. The pilot was the cause~factor in the majority (64.31~ of the accidents and the power plant was a cause/factor in 38.82~ of the accidents.
Summerizing these comparisons of power plant cause/factors, some ; ` ;~
of them appeared to be significantly higher than expected in percentage of involvement to be vibration induced or caused.
, . .: . .
These two identi~ied engines, according to reports, appear to be more seriously a~fected by vihrations of normal engine operation -than do the other engines of the group studied. No prior art device is known which is operative to reduce the vibrational `
characteristics of a reciprocating type aircraft engine, ... .
particularly the identified engines so the vibrational response of the engine is effectively lowered to prevent damage and failures of the type outlined in the report on the special study.
The present invention provides in an engine having a plurality of cooling ~ins mounted in a spaced relation, that improvement of a cooling fin vibration dampener in con~ination ~3~
therewith, comprising: a member o resilient fully cured material having a first portion and a second portion, ~aid first portion ~ :
having at least two lug-like portions being mounted on opposite sides of an engine cooling fin and in compression between cooling fins adjacent to said first-named cooling fin, said lug portions being longitudinally elongated substantially, having a length substantially greater than any transverse dimension, and having their outer end portions being wider than the distance between said first-named fin and said fins adjacent thereto, said lug~
10 like portions when mounted extending inward into the outer edge ~ .
portions of said cooling fins with said outer end portions being essentially rounded in external shape; said second portion ~:
connects end portions of said first portion to when mounted traverse ends of said cooling fins, said first portion i5 integr~ ;~
wlth said second~portion, and said dampener is constructed and adapted to be mounted and held in place on an engine solely by ;;~
- . -friction with said lug-like portions compressed between said : fins, said cooling fin vibration dampe~er is constructed and adapted to in use reduce the normal operating natural frequency : 20 to which said cooling fins can be forced by normal operation of ~:
:
said engine thereby reducing the overall normal operating naural ~ .
frequency of said engine to prevent said engine from reaching a ;~
re~onant frequency~
: . ~
From another aspect, the invention provides a method of dampening vibrations of the cooling fins of an engine having cooling fins on the cylinder thereof, including the steps of: ;
inserting a wedge-like member or the like between adjacent cool-ing fins thereby spreading the cooling fin~ from their normal spaced relation; inserting a tooth of a cross sectionally comb-like resilient member having a width greater than the normal spaced gap between the cooling fins between the outer portion of , . . . .
.~ , . . .
.
~3~
the cooling fins; removing said wedge-like member from between the cooling fins thereby releasing the cooling fins to com-pressibly hold said tooth of said resilient member between the cooling fins; and repeating the above steps until all of the teeth of said comb-like resilient members are received between the adjacent cooling fins. ~ -Various other objects, advantages and features of the invention will become apparent to those skilled in the art from the following discussion, taken in conjunction with the accompany-ing drawing, in which~
Figure 1 is a top plan view of a cylinder portion of anair-cooled aircraft type engine having fin dampeners in place on the cooling fins thereof, with the cylinder being shown mounted on a port.ion of the engine crankcase; ;. .
Figure 2 is a bottom plan view of the cylinder shown :
in Figure 1 with the fin dampeners in place thereon;
Figure 3 is a cross-sectional elevation view of a finned segment of a cylinder havîng a segment of the fin dampener mounted therewith,
ENGINE DAMPENER ~vEANS
The invention is generally related to dampeners for reciprocating air-cooled engines and the method of applying the dampener to the engine. The invention is specifically related to resilient cooling fin dampeners for aircraft engines and modifications of the intake manifold and propeller servo control system for the purpose of reducing the forced vibrational frequency of the engine to prevent damage to the engine by self-induced vi~rations.
In general, aircraft engines are prone to have vibration problems, -as they must be light in weight and have a relatively high horsepower, 10 as well as being air-cooled. The problems of vibration are particularly a¢ute in reciprocating type air=cooled aircraft engines, d~ to the reciprocating firing motion of the engine. In the prior art, little has been done tO prevent or overcome excessive vibration problems in reciprocating air-cooled aircraft engines, except by way of strength-enL~g the damage-prone parts of the engine and spreading the operational frequency of the engine by operating engine-driven pumps, -and other accessories, at speeds whi~h are fractionally propor~ionally different from the crankshaft speed or firing or the frequency of the , , engine. In strengthening of the engine structure to prevent damage 20 fin dampeners have been constructed to be mounted between and on the end portion of the cooling fins, primarily to prevent the fin from `~
being broken off. The prior art fin dampeners and strengthening structures have a single strip of resilient material, specifically rubbex7 which is pressed into th0 outer portion of ~he cooling fins and i9 attached to the fins by the heat OI the engine which cures or sets the material. Other known fin dampener structures include a comb-like structure, having the teeth extending between the fins with a clasp encircling the teeth and tightenable to compress them circum-ferentially thus expanding it between the fins to hold it in place. A
30 prior axt fln dampener structure i9 known which extends from the . .
3~
~` outer portion of the fins completely to the attachment point of the fins with such being retained in place by an adhesive material. No ~ ;
prior art device or devices are known which are specifically constructed for use with an air-cooled multi-cylinder aircraft type engine to control the vibrational characteristics or natural operating ~requency of the engine in an atcempt to prevent the operating frequency ~om becoming resonant or causing substantial structural damage to the engine.
Reciprocating type internal combustion aircraft engines are inherently a vibration generating body in an aircraft due to the inherent reciprocating or oscillating motion~ Reciprocating type aircraft ,~ ......
engines are balanced internally so they will perform their operation ;
with a minimum of unbalance; however, in practice the engines do vibrate considerably and produce a quantity of often objectionable noise. Engine vibration and noise affect engine fatigue, airframe fatigue and ~i!lot fatigue. A great many engine failures and pilot failures or malfunctions can be attributed to engine vibration and .:
noise associated with the operating the reciprocating type of engine. `
The speci~ic engine failures or malfunctions which can be substantially attributed to vibrationally induced factors include9 cooling fin -~
fract~es, engine cylinder Eractures, piston ring fractures, and crankshaft and connecting rod fractures. It is well known in the art that fatigue, due to noise and vibration, will crack and propagate cracks in -materials subjected to such forces, and it is these Eorces which cau~e fracture or other failure in the identified parts OI an engine or other parts of an engine connected with these components.
The problem of engine failure and malfunction has long been a ~;
critical problem in aviation and it has been studied in depth. One such study was conducted by the United States National Transportation Safety Board and documented in the report entitled, "Special Study 3~7~
Accidents Involving Engine Failure/Malfunction, U. S. General Aviation, 1965-1969. " This report is publlshed by the National Transportation Safety Board as report nurnber NTSB-AAS-72-10, it was adopted November 29, 1972. This special studypresents a recor~ of engine failure/malfunction accidents for fixed-wirlg air-craft, all of which occurred in all operations of U. S. general aviation, during the period of 1965-1969. It includes a complete comparison of engine-failure accident rates ~or single-engine and mul~i-engine air~raft. Analysis are included concerning cal:ses and related factors of engine-failure accidents by selected ~nakes and models of aircraft and engines. It includes tables, comparing cause/factors for the accidents and severi~y OI the accidents for all fixed-wing aircraft along with single-engine and multi-engine fixed-wing aircraft.
The inventiorl disclosed herein is a result of studies of and experiments made with a Continental IO-470 and IO-520 series - .
erlgines. The IO-470 and IO-520 series of engines are manufaçtured ~ ~
. , .
in several models for different alpplications however they are basically structurally the same. These engines are essentially `~ ~;
20~ structurally identical with the IO-520 series having a larger dis-placement and horsepower rating. The following are exerpts from the identified report, from the portion related to analysis of engine ~ailure/malfunction for these particular engines. A close examination of the special study report indicates that these identified engines had a significantly higher-than-expected involvement in individual power plant cause/factor-citations. It is to be noted that the power ;~
plant of an aircraft was cited as a probable cause/related factor in over 44 percent of the engine-failure accidents. The predominant power plant cause/factor citation include in part; master and 30 connecting rods, cylinder assembly, piston and piston rings, and 3~
crankshaft. In regard to the I0-470 model engine, the cause/factor citations were specific tO the engine cylinder assemblLes, master and connecting rocls, crankshaft, fuel system lines and fittings. In regard to the Continental I0-520 engine, the cause/factor citations were specific to the piston, piston rings and crankshaft. The specific engine elements cited are the elements of the engine which would obviously be the most likely to have vibration and fatigue clamage because they are so closely related to the rotating and reciprocating motion of the engine. In use, the two identi~ied engines are normally -used in the following aircraft: Beechcraft Model 35; Cessna 180;
Cessna 182, Cessna 206, Cessna 188, and Navion Model L-17. In the special study report, detailed cause/factors for par~icular air-craft make and model are compared with those of other aircraftO ~-In this comparison a normal approximation the binomial technique was used~ wherein the accounts of a cause/factor for a particular assembly, engine, aircraft, etc~, is comparable to same appearance for all aircraft involved in the study. The special study report -reveals that most of the engine-failure accidents for each aircraft make and model were caused by a pilot-in-command error, such as inadequate preflight preparation and/or planning, mismanagement of fuel, and improper operation of power plant controls. Explaining why a particular aLrcraft has a higher than expected percentage of engine failure accidents for a specific power plant cause/factor involves an inspect;ion of the engines installed in those particular aircraft. In regard to the identified engine, the frequency of piston and piston ring problems are significantly higher than expected for the Navion L-17 and the Cessna 210 than in the Beechcraft. The Navion L-17 uses the Continental I0-470 model engine and the Cessna 210 is equipped with the Continental 10-470 and the Conti-nental L0-S20 engine. The I0-470 engine in the Beechcraft Model . .
~3~7~
35 aircraft experienced a higher than expected involvement in the fuel system pumps area. In regard to the Cessna 210 aircraft, the following engine elements and percentages are the parts of the engine structure which were cited as a cause/factor in the respective percent of total accidents: piston, piston rings--6.
cylinder assembly--5.2%, crankshaft--3.4~, and master and con-necting rods--3.4~. The expected percentage of engine structure failure or malfunction for the noted elements is 2%, 2%, 1.8~, ;
and 2.5'~, respectively. It is to be noted that the actual per-.":
10 centages are significantly higher than the actual percentages ~-~
in this instance substantially higher than the expected percent- ; ~ ;
a~es. ' In the special study, a total of 3,312 engine-failure accidents were considered. The accidents studied do not include home-built or experimental category of aircraft. The pilot was the cause~factor in the majority (64.31~ of the accidents and the power plant was a cause/factor in 38.82~ of the accidents.
Summerizing these comparisons of power plant cause/factors, some ; ` ;~
of them appeared to be significantly higher than expected in percentage of involvement to be vibration induced or caused.
, . .: . .
These two identi~ied engines, according to reports, appear to be more seriously a~fected by vihrations of normal engine operation -than do the other engines of the group studied. No prior art device is known which is operative to reduce the vibrational `
characteristics of a reciprocating type aircraft engine, ... .
particularly the identified engines so the vibrational response of the engine is effectively lowered to prevent damage and failures of the type outlined in the report on the special study.
The present invention provides in an engine having a plurality of cooling ~ins mounted in a spaced relation, that improvement of a cooling fin vibration dampener in con~ination ~3~
therewith, comprising: a member o resilient fully cured material having a first portion and a second portion, ~aid first portion ~ :
having at least two lug-like portions being mounted on opposite sides of an engine cooling fin and in compression between cooling fins adjacent to said first-named cooling fin, said lug portions being longitudinally elongated substantially, having a length substantially greater than any transverse dimension, and having their outer end portions being wider than the distance between said first-named fin and said fins adjacent thereto, said lug~
10 like portions when mounted extending inward into the outer edge ~ .
portions of said cooling fins with said outer end portions being essentially rounded in external shape; said second portion ~:
connects end portions of said first portion to when mounted traverse ends of said cooling fins, said first portion i5 integr~ ;~
wlth said second~portion, and said dampener is constructed and adapted to be mounted and held in place on an engine solely by ;;~
- . -friction with said lug-like portions compressed between said : fins, said cooling fin vibration dampe~er is constructed and adapted to in use reduce the normal operating natural frequency : 20 to which said cooling fins can be forced by normal operation of ~:
:
said engine thereby reducing the overall normal operating naural ~ .
frequency of said engine to prevent said engine from reaching a ;~
re~onant frequency~
: . ~
From another aspect, the invention provides a method of dampening vibrations of the cooling fins of an engine having cooling fins on the cylinder thereof, including the steps of: ;
inserting a wedge-like member or the like between adjacent cool-ing fins thereby spreading the cooling fin~ from their normal spaced relation; inserting a tooth of a cross sectionally comb-like resilient member having a width greater than the normal spaced gap between the cooling fins between the outer portion of , . . . .
.~ , . . .
.
~3~
the cooling fins; removing said wedge-like member from between the cooling fins thereby releasing the cooling fins to com-pressibly hold said tooth of said resilient member between the cooling fins; and repeating the above steps until all of the teeth of said comb-like resilient members are received between the adjacent cooling fins. ~ -Various other objects, advantages and features of the invention will become apparent to those skilled in the art from the following discussion, taken in conjunction with the accompany-ing drawing, in which~
Figure 1 is a top plan view of a cylinder portion of anair-cooled aircraft type engine having fin dampeners in place on the cooling fins thereof, with the cylinder being shown mounted on a port.ion of the engine crankcase; ;. .
Figure 2 is a bottom plan view of the cylinder shown :
in Figure 1 with the fin dampeners in place thereon;
Figure 3 is a cross-sectional elevation view of a finned segment of a cylinder havîng a segment of the fin dampener mounted therewith,
2~ Figure 4 is a sectional view o~ the ~inned segment and cooling fin dampener taken on line 4-4 of Figure 3; ;~
" : ~ ' .., _g_ , ., ' . . ' , ~38~
Fig. 5 is an enlarged side elevation view of a segment of the cooling fin dampener;
Fig. 6 is a plan view of the bottom side o~ an opposed cylinder, aircraft engine, the engine having the fin dampeners and the tuned intake manifold of this invention; ancl Pig. 7 is a perspective view of the propeller pitch control system including the governor pump, the propeller and propeller servo and a portion of the engine s~ructure with portions of the pump propeller servo and engine cut away for clarity.
The following is a discussion and description of the preferred speciîic embodiments of the engine dampener structure ancl rnethod oi this- invention, suchbeing made with reference tO the ~rawings, whereupon the same reference numerals are used to indicate the ,, same or similar parts and/or structure. It is to be understood that such discussion and description is not tO unduly limit the scope ~f ~ ~ .
the invention.
The engine dampener means of this invention includes several elements which operate as a system to dampen the vibration of an , ~
air-cooled reciprocating internal cornbustion aircraft type engine.
20 The general func~ion of the dampening means is to reduce the natural normal operating frequency of the ~ngine to prevent it from reaching an e~sentially resonant frequency. This type;~of engine has several vibrating elements which are ~oupled by the structure of the engine and vibrate as a complete system when the engine ls in normal operation, The dampening means of this invention includes several elements which operate to reduce the coupllng effect of ihe several vibrating elements of the engine and generally function to dampen the vibration of the engine. An element of a cylinder dampener structure includes a cooling fin and dampener mountable with the 30 co~lng flns of the engine. Another element is the cylinder dampener (~
~, . , ,, ~. . . .
includes a tuned intake mani~old. Another element is the propeller system dampener including a variable pitch propeller servo pump which is dampened, and of a propeller dampener with resilient members mountable onto blades of the propeller.
A study of the engine cylinder cooling fins reveals the fins to be easily excitable vibratable members. The cylinders of the subject type of aircraft engine generally have radially-disposed cooling fins extending from the cylinder structure between what is ~ ~
the compression chamber por~ion of the cylinder ard the portion - ;
10 of the cylinder mounted with the er~ine crankcase. Figs. 1 and 2 sho~iQ` top and bottom views respectively of such a cylin~er.
The compression chamber portion of the cylinder also has generally radially-disposed cooling fins extending therefrom with outwardly extending cooling fins on the end thereof. The force which normally excites the cooling fins during the operating of the engine is the combustion explosion in the cylinder. The Erequency in which -the cooling fins are excited depends upon the speed of ~he engine, the number of cylinders the engine has9 and the frequency at which ~ the fins of a particular cylinder are excitecl relative to the frequency 20 of other portions OI the engine depend upon the number of cylinders on a particular engine.
In the development of this invention, the two above-identified Continental make of engines were studied and the dampening means of this invention was developed specifically for those engines;
however, it i8 to be understood ~hat the general characteristics of this engine are similar to other similarly constructed engines, and the dampening means of this invention can be used with other .
similarly constructed engines. These identified engines have six (6) cylinders, three (3) on each side, in an opposed relation with 30 the crankshaft being in ~he center. The engines studied were - .
~ ~3~
equipped with variable pitch propellers ancl a normally aspirated fuel injection systenn. Figs. I and 2 show top and bottom views of one cylinder for such an engine attached to a portion of the crankcase. The combustion chamber intake and outlet ports are on what is normally the bottom side of the engine. The cylinder 12 is bolted to the crankcase 14 in a rigid position, by bolts extending through the flange on the cylinder barrel 16. A plurality of cooling fins 18 ext~nd from the cylinder barrel portion 16 in a regular spaced relation as shown. The outer end portion 12 is a combustion 10 chamber portion thereof, indicated at 20, and it has a plurality of coollng fins 22 extending radially therefrom as shown. A
valve assembly rocker arm cover 24 is attached to the outer end ~ ~-vf the cylinder 12. Spark plugs 2 6 and 28 are mounted in the ;
con~bustion chamber portion of the cylinder on the top and bottom sides thereof respectively. The fuel inject~r 27 is adjacent to the spark plug 26. A cylinder head tem~erature gauge probe 30 is mounted in the lower side of the cylinder 12 adjacent to the spark plug. A plurality of longitudinally disposecl cooling vanes, 32 and 34, extend from the spark plug portion of the coTnbustisn 2V chamber portion of the cyllnder to its outer end portion as shown on the upper and lower sides of the cylinder respectively. On the lower side of the cylinder 12, the intake port 36 is located on the opposite side of the cylinder relative to the exhaust port indicated at 38. The longitudinally disposed cooling fins 34 extend essentially between the intake port 36 and the outlet port 38. The structure of the cylinders for the IO-470 series engines and the IO-520 series engines is essentially the same with the cylinder barrel ;
portion 16 and combustion chamber portion 20 being constructed separate pieces of material and the separate portions being perma-30 nently joined. The natural frequencies of the cooling fins on the , ~ . , .
~ L~D31!~7 cylinders for th~se two series of engines is essentially the same, although the cylinders di~fer slightly in bore diameter. Additionally, the cylinders for the two series of engines are constructed in an original version and a heavy version; the heavy version has slightly thicker cylinder walls; however9 the cooling fins thereof having essentially the same natural frequencies. The heavier version of the cylinders is now required on U. S. Registered aircraft as per ~ederal Aviation Administration Airworthiness Directive . ~ -, : , ., Revision 72-20-2. In studying the cylinders of the IO-470 engine ~ 8 10 in the lightweight version, the cooling fins indicated at 40 on the exhause side of the cylinder are found to have a fundamental frequen , of approximately 880 cycles per second, (cps), with second, third, fourth, and fifth harmonics at 1760 cps, 264û cps, 3520 cps, and 7040 cps. On the intake side of the cylinder, the cooling fins indicated at 4~ are found to have a fundamental ~requency of approxi~ tely 1320 ~ps, wi~h a second harmonic at 26~0 cps. At this point, it is to be noted that the complete cylinder apparently exhibits charaeteristics of having a fundamental natural frequency of 44û cps, because the observed vibratable frequencies of the cooling fins on the cylinder ~o range between the second and the sixteenth harmonic of that ~undamental ~requency. In practi~e, the vibrating features of the cooling fins ; `~
were determined using an electronic piano tuner. The piston rings of a piston assembly for the IO-470 series engine have been studied using a sound generatorl~ induce vibration. In studying the compression rings, they were found to exhibit the 6-node vibrating node at ~40 ;~
cps~ the rings fundamental frequency, and harmonics 1-13 upward -therefrom~ A maximum amp~itude was observed at 880 cps with a ~-signlficant amptitude at 440 cps and 1760 cps, the firs~ and fourth harmonics respectively. The oil ring is observed to have a fundamental 30 frequencyo~ approximately 440 cycles per second. When the ,
" : ~ ' .., _g_ , ., ' . . ' , ~38~
Fig. 5 is an enlarged side elevation view of a segment of the cooling fin dampener;
Fig. 6 is a plan view of the bottom side o~ an opposed cylinder, aircraft engine, the engine having the fin dampeners and the tuned intake manifold of this invention; ancl Pig. 7 is a perspective view of the propeller pitch control system including the governor pump, the propeller and propeller servo and a portion of the engine s~ructure with portions of the pump propeller servo and engine cut away for clarity.
The following is a discussion and description of the preferred speciîic embodiments of the engine dampener structure ancl rnethod oi this- invention, suchbeing made with reference tO the ~rawings, whereupon the same reference numerals are used to indicate the ,, same or similar parts and/or structure. It is to be understood that such discussion and description is not tO unduly limit the scope ~f ~ ~ .
the invention.
The engine dampener means of this invention includes several elements which operate as a system to dampen the vibration of an , ~
air-cooled reciprocating internal cornbustion aircraft type engine.
20 The general func~ion of the dampening means is to reduce the natural normal operating frequency of the ~ngine to prevent it from reaching an e~sentially resonant frequency. This type;~of engine has several vibrating elements which are ~oupled by the structure of the engine and vibrate as a complete system when the engine ls in normal operation, The dampening means of this invention includes several elements which operate to reduce the coupllng effect of ihe several vibrating elements of the engine and generally function to dampen the vibration of the engine. An element of a cylinder dampener structure includes a cooling fin and dampener mountable with the 30 co~lng flns of the engine. Another element is the cylinder dampener (~
~, . , ,, ~. . . .
includes a tuned intake mani~old. Another element is the propeller system dampener including a variable pitch propeller servo pump which is dampened, and of a propeller dampener with resilient members mountable onto blades of the propeller.
A study of the engine cylinder cooling fins reveals the fins to be easily excitable vibratable members. The cylinders of the subject type of aircraft engine generally have radially-disposed cooling fins extending from the cylinder structure between what is ~ ~
the compression chamber por~ion of the cylinder ard the portion - ;
10 of the cylinder mounted with the er~ine crankcase. Figs. 1 and 2 sho~iQ` top and bottom views respectively of such a cylin~er.
The compression chamber portion of the cylinder also has generally radially-disposed cooling fins extending therefrom with outwardly extending cooling fins on the end thereof. The force which normally excites the cooling fins during the operating of the engine is the combustion explosion in the cylinder. The Erequency in which -the cooling fins are excited depends upon the speed of ~he engine, the number of cylinders the engine has9 and the frequency at which ~ the fins of a particular cylinder are excitecl relative to the frequency 20 of other portions OI the engine depend upon the number of cylinders on a particular engine.
In the development of this invention, the two above-identified Continental make of engines were studied and the dampening means of this invention was developed specifically for those engines;
however, it i8 to be understood ~hat the general characteristics of this engine are similar to other similarly constructed engines, and the dampening means of this invention can be used with other .
similarly constructed engines. These identified engines have six (6) cylinders, three (3) on each side, in an opposed relation with 30 the crankshaft being in ~he center. The engines studied were - .
~ ~3~
equipped with variable pitch propellers ancl a normally aspirated fuel injection systenn. Figs. I and 2 show top and bottom views of one cylinder for such an engine attached to a portion of the crankcase. The combustion chamber intake and outlet ports are on what is normally the bottom side of the engine. The cylinder 12 is bolted to the crankcase 14 in a rigid position, by bolts extending through the flange on the cylinder barrel 16. A plurality of cooling fins 18 ext~nd from the cylinder barrel portion 16 in a regular spaced relation as shown. The outer end portion 12 is a combustion 10 chamber portion thereof, indicated at 20, and it has a plurality of coollng fins 22 extending radially therefrom as shown. A
valve assembly rocker arm cover 24 is attached to the outer end ~ ~-vf the cylinder 12. Spark plugs 2 6 and 28 are mounted in the ;
con~bustion chamber portion of the cylinder on the top and bottom sides thereof respectively. The fuel inject~r 27 is adjacent to the spark plug 26. A cylinder head tem~erature gauge probe 30 is mounted in the lower side of the cylinder 12 adjacent to the spark plug. A plurality of longitudinally disposecl cooling vanes, 32 and 34, extend from the spark plug portion of the coTnbustisn 2V chamber portion of the cyllnder to its outer end portion as shown on the upper and lower sides of the cylinder respectively. On the lower side of the cylinder 12, the intake port 36 is located on the opposite side of the cylinder relative to the exhaust port indicated at 38. The longitudinally disposed cooling fins 34 extend essentially between the intake port 36 and the outlet port 38. The structure of the cylinders for the IO-470 series engines and the IO-520 series engines is essentially the same with the cylinder barrel ;
portion 16 and combustion chamber portion 20 being constructed separate pieces of material and the separate portions being perma-30 nently joined. The natural frequencies of the cooling fins on the , ~ . , .
~ L~D31!~7 cylinders for th~se two series of engines is essentially the same, although the cylinders di~fer slightly in bore diameter. Additionally, the cylinders for the two series of engines are constructed in an original version and a heavy version; the heavy version has slightly thicker cylinder walls; however9 the cooling fins thereof having essentially the same natural frequencies. The heavier version of the cylinders is now required on U. S. Registered aircraft as per ~ederal Aviation Administration Airworthiness Directive . ~ -, : , ., Revision 72-20-2. In studying the cylinders of the IO-470 engine ~ 8 10 in the lightweight version, the cooling fins indicated at 40 on the exhause side of the cylinder are found to have a fundamental frequen , of approximately 880 cycles per second, (cps), with second, third, fourth, and fifth harmonics at 1760 cps, 264û cps, 3520 cps, and 7040 cps. On the intake side of the cylinder, the cooling fins indicated at 4~ are found to have a fundamental ~requency of approxi~ tely 1320 ~ps, wi~h a second harmonic at 26~0 cps. At this point, it is to be noted that the complete cylinder apparently exhibits charaeteristics of having a fundamental natural frequency of 44û cps, because the observed vibratable frequencies of the cooling fins on the cylinder ~o range between the second and the sixteenth harmonic of that ~undamental ~requency. In practi~e, the vibrating features of the cooling fins ; `~
were determined using an electronic piano tuner. The piston rings of a piston assembly for the IO-470 series engine have been studied using a sound generatorl~ induce vibration. In studying the compression rings, they were found to exhibit the 6-node vibrating node at ~40 ;~
cps~ the rings fundamental frequency, and harmonics 1-13 upward -therefrom~ A maximum amp~itude was observed at 880 cps with a ~-signlficant amptitude at 440 cps and 1760 cps, the firs~ and fourth harmonics respectively. The oil ring is observed to have a fundamental 30 frequencyo~ approximately 440 cycles per second. When the ,
3~
compression rings are placed in a cylinder without a piston and the ~ -cylinder is vibrated the rings will vibrate in the 6- node pattern and crawl or move itl the cylinder bore in the direction of the combustion chamber end portion c~f the cylinderO The piston rings were studied at room temperature, and temperatures up to250~, with a small re-:
duction in natural frequency vibration noted at the elevated temperature.
At ~his point, i~ is to be noted that ~he piston rings of a piston assembly for the identified series of engines apparently exhibi~s the same har-monic frequencies as the cylinders for the engines as described lO supra In the general structure of an aircraft engine, the internal bore of the cylinders thereof are tapered with ~he barrel portion , - . , o~` the cylinder being larger than the compression end portion of ~ -the cylinder, so that adequate compression is maintained in the . . .
cylinder as it is heated during engine operation. When the cylinder , of such an engine is heated, the combustion chamber portion thereof is obviously heated significantly more than the barrel portion thereof, ;
due to the combustion process, and expanded significantly. The tapering of the cylinder bore of the cylinder is referred to as 20 ~ ~ "choklng". In studying the cylinders of the 10-470 series engines, the choked condition of the cylinder bore is found to be essentially relieved at approximately ~501~. It is to be noted that until the .
cylinder has reached approximately 250~, in operation of the engine of the cylirlder operates in a choked condition wherein the clearance between the piston and the cylinder wall is significantly leæs than would be encountered in normal operation. In studying operation of the 10-470 series engine, it has been found that the two cylinders on the forward end of the engine or the end thereof which mountæ the propeller and is normally forward when mounted 30 unbaffled will opexate at approximately lOO ~, below the .. . . . . .
, .
~ 3~
normal operating temperature of the rearmost pair ~ cylinders.
In examination of several I0-470 series engines ~nen dismantled after being run a substantial length of time indicates that the relatively cool temperature of the forward cylinders prevents the piston rings ~;
. . -:
from properly seating in the piston cylinder bores, and in some cases, causes scoring oE the piston and the cylinder bore. It is to be noted that when a pi~ton has moved in the choked cylinder, it requires s~stantially more force to move the piston than when it is moved in a heated and unchoked cylinder because the compression -;~
. .
rings move in a substantially cylindrical bore rather than a tapered bore as when the cylinder is in the choked condition.
The cylinders on the identified series of engines are mounted on the crankcase in a staggered and opposed relation as s hown in ~ig. 6 so the connecting rods properly line up with the appropriate throws on ~he crankshaf~. The cylinders are numbered from the rear of the engine to the front or output end of the engine with cylinder ~1 being the rearmost cylinder on one side of the crankcase~ and cylinder ~2 being on the opposite side thereof with the piston rods thereof mounted Otl the same crankshi~t throw. Cylinders l, 3, 20 and 5, are on one side of the crankcase, and cylinders 2, 4, and 6 are on the opposite side of the crankcase specifically the leEt and right respectively as shown in Fig. 6. The firing order of these series of engines is by cylinder nurnber as follows: l-6-3-2-5-4.
It i6 to be noted that in observing the firing order of the cylinders that combwstion on cylinex ~1 at the rear of the engine irnmediately precedes firing on cylinder ~6 at the forwardmost end and the opposite side of the engine, and in this order of firing, the cylinder which normally operates in an unchoked condition is fired immediately preceding a cylinder which normally will operate in a choked 30 conditlon.
. ' -15- `
.. , . . , , , .
~3~''7 a.~
` In normal operation of the identified series ~f engines, the intake maniold poxtion thereoE operates with pressure the atmospheric pressure. In these series of engines, the difEerential press~e between Lhe forward portion of the intake manifold which is connected with the forwardmost cylinders and the rear portion of the intake mani~ld, which is connected with the rearmost cylinders, indicates there is a differential pressure between these two points~ which will in normal operatlon of the engine vary from approximately 3 inches of mercury to approximately 4. 5 inches of mercury. The 10 horsep~wer OULpUt of an internal combustion engine is in part dependent upon the intake manifold pressure for a particular engine ~ ~;
speed. Examination of maximum power data for alti~ude per~
formance of the IO-470 series engines indicates that ~or an engine speed of approximately 2, 600 rpm9 a di~fexential pressure of ~. 5 inches of mercury has a differential power of approximately 51 horsepower or on a per cylinder basis, apF~roximately 8. 5 horsepower pex cylinder. In view of this, it is obvious that the forward cylinders of the engine are producing less horsepower than the rear cylind~rs . .
of the engine because the intake maniEold pressure at the rear oE
the engine is higher than it is at the forward portion of the engine. ;
study of constant speed operation of this engine revealed the described intake manifold pressure distribution; however, rapid opening and closing of the engine throttle drastically changes the manifold pressure distribution.
Figs. 3-S show in detail the structure o~ the cooling fin dampener alone and mounted with a finned segment of a cylinder.
The c~ooling fin dampener i,s prefereably a cross-sectionally comb~
like structure, indicated generally at 50, having a first portion 52 mountable between adjacent fins on a finned segment, and an integral ,~econd portion 54 connecting the ends of the first portion 52. The ~3~
.
cooling fin dampener 50 is preferalbly construct~d of a resilient material in a strip-like segmen~ with the teeth or lug-like portions of the first portion 52 a-ppropriately spaced to be inserted between the adjacent cooling fins. The firs~ portion 52 has a plurality of teeth or lug-like members with each having a reduced size outer encl portion 56, and each having a mounted end portion 58. The lug-like portions are tapered and preferably pointed on their outer end portion as shown in Pig. 5 when in an uncompre~ sed state and , they assume an essentially rounded shape as shown in ~igs. 3 and 10 4 when mounted. The lug-like portions have essentially parallel adjacent edges 60 between the outer end portions 56 and the mounted or inner end portions thereof 58. The fin dampeners second portion 54 is an elongated relatively narrow strip integrally Eormed with the ` ~ -fin dampeners first portion 52 at the mount~d portions 58 with the teeth-like portions of the second portion 520 The second portion 54 traverses the mounted end 58 of the teeth or lug-like members ;
of the first portion 52. ~ig. 3 shows a finned segment indicated ' generally at 66 with the cooling fin dampener 50 mounted thereon. ~ -The finned segment 66 illustrates the cylinder of an engine which 20 has a plurality of cooling fins 68, extending therefrom. The cooling fins 68 are essentially parallel to each other and generally perpen-dicuLar to the cylinder wall support segment 70. Eiig. 4 shows the finned segment 66 and dampener 50 in section taken through one of the cooling fins with portions of t.le cooling finned segment and the dampener shown in dashed lines. The dampener 50 is rnounted with the teeth-like portions thereof between adjacent eooling fins 68 and the second portion 62 thereof closely adjacent to or in contact with the outer peripheral edge of the cooling fins. The dampener ~ -50 has the teeth thereof extending in to the outer peripheral portion 30 of the cooling fins. The lug-like portions of the dampener's first /
, ., : , :
3!517~
`` portion 52 are preferably cons~ucted having a thickness or width greater than the gap or distance between the coollng fins so when they are mounted they are retained solely by friction between the cooling fins in a compressed condition.
In installing the cooling fin dampener 5û of this invention~ a pair oE adjacent cooling fins are separated by inser~ing a wedge-like member between same, then a tooth or lug-like portion of the dampener member is inserted between the fins in a desired position, ~ -~
then the wedge-like member is removed, releas~ng the cooling 10 fins to contact and compressibly retain the tooth-like member there between. Once a tooth of a fin dampener strip member has been inser~ed, the process is repeated on the next tooth, then the `
next, until the strip is mounted in the cooling fin in the position as shown in Fig. 3. A lubricant can be used to aid in inserting the teeth between the cooling fins. In practice a liquid detergent, such as a household di~hwashing detergent, has been successfully used to assist in placing the teeth-like portions of the fin dampener 50 ` ~;~
in a cooling fin. ;
In using the fin dampeni~S0 with the identified series of engines, 20 the first portion 52 of the dampener is consaructed with the teeth~
like p~rtion thereof spaced tO correspond with the cooling fin spacing of the engine. The cooling fins on the identified series of engines are approximately . 05 inches in thickness, and . I inches in spacing.
Preferably, the fin darnpener has the teeth or lug-like portions thereof cons tructed being . 15 inches in thickness and . 05 inches in spacing and approximately . 25 inches in width. In practice, fin dampeners constructed as described have been used with cooling fins in the identified engine and operated for a substantial length of time without failure of the fin dampeners or a substantial loss in resiliency.
30 Preferably, the fin dampener 50 is constructed of a neoprene ,........... ..
composition material~ because of its oil and hydrocarbon resisting properties. The fin dampener 50 is preferably cons~ructed by molding ~he neoprene composition material wi~h the teeth or lug-like portions sized and spaced so ~hey will fit the cooling fins of an engine in the described manner. It is obvious the resilient material of the fin dampener can be constructed of materials other than a neoprene ~;
composition material, for example, synthetic rubber, or a silicon ~ ;
. - ~
composition material or any other suitable resilient material can be -used.
Another portion of the dampening means of this invention is related to a cylinder dampener in the form of a tuned intake manifold for the engine. In regard to the tuned intake manifold, its function `~
is to cause the engine to operate with a uniform or substantially even normal operating manifold pressure. As described above, in ,,, ~;
the normal operatîon of the identified series o~ engines, the cylinders opera~e at a non uniform temperature with the forwardmost cylinders being the colder, and the rearmost cylinders being the hotter. ~or the 10-470 series engines, the temperature distribution between t~e orwardmost cylinders and the rearmost cylinders is approxi-mately 100E~. Normally, the cylinder head temperature of an air~
craft englne is mon~tored by a cylinder head tempera~ure gauge ~ ~ ~
probe by a cylinder head temperature gauge on one of the center ;;
cylinders. It ~s recommended by aircraft manufacturers that in normal operation of an aircraft it not be flown until the engine has - -reached the normal operating temperature. However, it is to be ~ ;
observed that when the englne has reached this temperature, the `
forward cylinders of the engine are still below the normal operating temperature so they are operating in the choked condition, as described above.
l~ig. 6 shows a plan view of the underneath side of the engine, -.. . . . , . . ~ , . . .
` ~3~7~ :
clearly exposing intake manifold. The intake manifold for the engine i9 indicated generally at 80 and includes a looped conduit s$ructure having an inlet and connected with the intake ports on the engine's cylinders. The conduit inlets are indicated a~ 82 at the rear of the engine~ On the right side of ~ig. 6, the conduit outlets are indicated at 83, 84 and 85 which serve the cylinders ~ 33 and ~5, respectively.
On the left side of ~ig. 6, the conduit outlets are indicated at 86, 87, and 88, and they serve~ cylinders ~ 4, and #6, respectively.
A flow-balancing condui$ 90 is communicably connected between ~he conduit segments of the intake manifold 80 for balancing the flow through the manifold. As described above, normal operation of the engine results in a pressure distribution thrvugh the intake manifold having a differential pressure or approximately 4. 5 inches of mercury between the outlets 83 and 86, on the rear of the engine and the outlets ``
85 and 88 on the forward of the engine. In practice, the press~re dis~ribution between the several outlets of the in~ake manifold 80 have been made essentially uniform by reducing the internal cross-sectional a~ea of the outlet segmen~s of the intake manifold, this causes the engine to operate with esse~ially intake manifold pres- ~;
sure and essentially the same cylir~ler head temperature on all cylillders. Inpractice, it has been found practical to crimp the ~-intake manifold to reduce the cross sectional area. The manifold's crimped sections are indicated at 92 and 94 in l~ig. 6. In practice, the intake manifold conduit segments adjacent toth~outlets 83, 84, 86, and 87, have been crimped by selectively placing a dent in an easily accessible portion o~ the manifold at a point closely adja-cent to the outlet end of the conduit segments. In crimping the conduits, the specific amount OI the crimp or dent determines the amount of reduction in cross sectional area this reduction is speci-3~ f~cally dependent upon the distance between the outlet segments and -20~
3~7~
The change in pressure differenti~l which must be accomplished. In .
practice, it has been found tha~ the rearmost conduits having crimps 92 must have a cross sectional area sligh~ly less than the center conduits having crimps 94, because they are nearer ts) the intake manifold inlet 82. In the intake manifolds for the above- identified series of engines, they are constructed of a lightweight material which is easily bent, and in practice i~ has been crimped by uæi ng a blunt objeet to force a dimple in the condui~ segments thereof in a curved outlet end portion closely adjacent to the outlets of the intake manifold. In practice on the 10-470 series engine, it has been operated with the intake manifold thereof modified as described, and will ~`
operate normally with the cylinder~ea-~{temperature for all the cylinders in the range are 350-380. The actual normal operating tempera~ure of the engine, of course, depends on ~utside air telnperature and the type o~ flying being done. In practice, the modified engine has been operated full power in low-level flight for extended periods of ~ime wath the outside air temperature approximately looQ~ and greater, at altitudes varying 1500 and 2500 fee~ above sea level, withou~ encount-ering any engine overheating, and with~ut signfflcant variance in the -cylinder head temperatur~ distribution.
Another p~tion of the dampening means of this invention `~
is related to a propellor dampener apparatus which includes a dampener for the propeller blades of the engine. l~ig. 7 shows in detail a two~
bladed propeller asæembly w~th dampeners thereon. The propeller assembly lO0 whl~h is normally used on the identified seraes of engines and on a great many other light alrcraft-type engines. The propeller assembly lO0 has a variable pitch propeller with a pair of blades 102 rotatably mounted on a hub lO'L that is attached to the engine crankshaft 106. The propeller blades 102 are rotated about their longitudinal axis at the hub 104 by a hydraulically powered servo 108. An engine , . .
~ ~3~
d riven hydraulic pump 110 a governor pump iB communicably connected with the servo 108 through the crankshaft 106 and used to control the pitch of the propeller blades 102. A pair of resilient propeller dampening members 112 are mounted on the forward side of the propeller blades 102 as shown. The propeller dampening members 132 are secured to tne propeller blades 102 by a suitable adhesilTe or by other sui~able means of attachement. In the propeller assembly 100 the servo 108 is connec~ed by a linkage with the individual propeller blades 102 and changing the hydraulic fluid pressure in the propeller servo 108 changes the pitch of the blades 102 relatively to the plane of rota~ion of the propeller. Servo-controlled variable pitch propellers use hydrauli~ pressure from the engine driven pump to change the pitch of the blades by applying pressure to increase the pit~h of the blades or applied pressure to deerease the pitch of the blades, depending upon the specific constru~tion of the system. The propeller assembly 11~ shown in ~ig. 7 is the type of system wherein flu~
pressure in the servo 108 is increased to increase the propell~r blade pitch.
It has been foun~ that vibra~ion in~ucing ~orces are transmitted 20 from the piston and cylinder assembly and governor pump to the propeller through the engine crankshaft. These forces transmitted to the propeller through the crank~haft are dependent upon the speed of the engine, and frequency of hydraultc fluicl pressure pulses from the pr~peller and governor pump. l~orces are also induced in the propeller by what is normally called "P-factor". The P-factor forces ~ -induced on the propeller are present when the aircraft is making a climbing turn. These forces are cuased by the difference in the angle of attack of the propeller blades as they move from one side of the engine to the other and are subjected to differential loading. The 30 P-factor induced vibrational forces are transmitted from the propeller - 1~3~
~o the engine through the crankshaftO The P-factor forces are believed to be a significant factor in causing engine failures during a climbing turn, particularly a climb Erom low altitude such as a takeoff7 where ;~
relatively high power is being developed by the engine. When a propeller blade is on the side of its swing, having the highest angle of attack, it produces a greater force on the engine crankshaft than it does when it is on the opposi~e side where the angle of attack is less. This variation in force is ~ransmitted directly ~o ~he engine crankshaft at a frequency dependent on the rotating speed of the 10 crankshaft and number of propeller blades. P-factor vibrating induced forces are particularly acute when u3ing a three-bladed propeller or a single-bladed propeller, as the forces on opposed sides of the aircraft are exlreme. When using a two-bladed propeller ,..... .
the P-~actor induced forces are less extreme than with a one- or three-bladed propeller because of the balancing effec~ of the second ~ -~ ~
blade being directly opposite to the crankshaft. Obviously9 the natural ,~
frequency and frequency response of a propeller depends upon many factors such as its resiliency, momRnt of inertia, etc. In practice, -~
it has been found that a metal propeller will readily transmit vibrational ~ -~
20 forces ~rom its tips to the crankcase, and through the entire engine~
with absence of any other forces.
The propeller dampener portion of the engine dampener structure of this invention includes a pair of resilient members 112 ~;
mounted on the interior portions of the propeller, as shown in ~ig. 7.
Preerably, the resLl~ent members 112 are constructed of a resilient material having high dampening properties, such as neoprene, which can be attached to the propeller blades by a suitable adhesive. In practice, neoprene composit~on electric de-icing boots have been applLed to a variable pitch servo-controlled propeller on the above-30 ic~enti~ied series of engines, and operated for a considerable ~ime.
,, .. . .
~ 3~
lq this practice, the propeller clampeners ~ve been found to, in combination with the other elements of this invention, substantially dampen the vibrational fvrces and vibrations of the engine. Preferably, the resilient propeller clampen~rs are applied to the propeller and cover approximately 30 to 40 percent of the propeller's radi~us, originating at a point adjacent to the propeller hub. In practice~ the propeller dampener members 112 were applied over approxima~ely 33 percent of the propeller's blade span originating at a point close to the propeller hub. Although the propeller dampeners are shown and 10 described as mounted on a variable pitch servo ~ontrolled tw~bladed propeller, it is to be understood that such can be applied to other propellers such as fixed pitch propellers and nonservo-controlled variable pltch propellers to achieve a similar result.
. ~ .
Another portion of the dampening means of this invention is related to a hydraulic dampener for the governor pump of the propeller pitch changing apparatus. In ~ig. 7, the propeller assembly 100 is shown with the governor pump 110 and with the hydraulic dampener apparatus indica~t ed generally at 120. The function of the hydraulic dampener is to dampen the pulsations and the hydraulic fluid discharged 20 from the gove~nor pump and to prevent these pulsations from being transferred to the other engine comp~ner~s into the propeller. The governor pump 110, shown in ~ig. 7 Is typical of governor pumps used in light aircraft in that it has a housing 1227 which is secured to a mount ;124 on the crank~ase of the aircraft engine. The governor pump 110 is driven from the englne crankshaft 106 by a pair of gears 126 and 128 as shown. Engine oil is supplied to the governor pump 110 through an inlet indicated at 130 and discharged through an outlet conduit 132 into a trans~er gland 134 on the engine crankshaft 106. The end portion of the englne crankshaft 106 is hollow to allow oil to pass to and from the propeller servo 108. In the propeller servo 108, oil pressure on ' ' ' ~;
t~e piston 136 moves the piston against the force of return springs 138 which in turn rnoves the linkage connected with the propeller blades 102. The oil flow in the outlet conduit 132 is controlled by a pilot valve indicated generally at 140 so that oil can flow into and out of the propeller servo 108 as required. A speed-adjusting apparatus on the upper portion of the governor pump 110 has a flyweight assembly 142 and a speed adjusting lever 144 to control motion of the pilot valve 140 and thus control the oil flow in the outlet conduit 132. The actual pump portion of the ~g~vernor pump llû is a gear type pump ; ~ -assernbly 148. A pressure relief valve assembly 146 is connected w ith the outlet of the gear pump assembly 148 in the lower portion .. . , . ~
of the governor pump housing 122. The gear pump 148 is driiven directly from the engine crankshaft by gears 126 and 128, as shown.
High pressure oil flow from the gear pump 148 to relief valve 146 ~ -~
is through a conduit indicated at 150~ The relief valve assembly ~ ~;
146 has a return to the gear pump 148 and an outlet to the pilot valve , ,, assembly 140. The gear pump assembly 148 is by its basic nature ~ ~ ~
. ~ . , a pump w~ich will provide a substantially high-pressure output flow with pulsations in the ou~?ut -flow because of the geared construction.
These pulsations In the output from the gear pump assembly 148 `
provide a substantial source of vibration which is transmitted to the engine throu~ the governor pump housing 122 to the pump mount 124 on the engine crankcase, and through the oil supply to the propeller assembly 100.
The hydraulic dampener apparatus 120 is connected with the outlet of the gear pump assembly 148, to dampen the pulsations - `
in its output oil flow. A conduit 154 is connected with the condult 150 that joins the outlet of the gear pump assembly 148 to ~he inlet of rellef valve assembly 146 for connecting the hydraulic dampening device. In practlce, a hydraulic accumulator has been used suc-,. . . . . . . .
~ 033!37a~
c essfully as a hydraulic dampening device as shown in :F ig. 7. In such practice, the accumulator housing 156 is provided with brackets for mounting it on the aircraft structure, with the conduit 154 beirlg a high-pressure flexible hose~ The hydraulic accumulator has a piston 160 mounted in the hous~ng 156 between an oil chamber 162 and an air chamber 164. The piston 160 is freely movable within the housing and it is provided with sealing rings to keep the oil and air separated. Air under pressure is manintained in the air chamber 164 in order to maintain the piston 160 in a balanced condition against 10 the oil in the oil chamber 162. During operation o~ the engine, the pulsations from the gear pump 148 cause the oil in the oil chamber 162 to pulsate thereby oscillating the pist~on slightly against ~he force of the air in the air chamber 164, thus dampening the pulsations in the oil fl~w as it is received by the relief valve assembly 146 and in t~.~n as it is~ received by the pilot valve 140 and propeller .
assembly 100~ The overall result of adding the- hydralic dampener in the form of the hydraulic accumulator is to dampen the pulsations in the.oil flow as it passes through the cranksha~ 106 and further .: .
into the propeller servo 108. ; . ` :~ .
20 - . Inpractice, in experimenting to determine the signi:ficance of the effects of the hydralllic darnpener for the governor pump, a i governor pump crankshaft and propeller assembly were mounted :
on the crankcase of an 10-470 series engine and operated by an auxiliary `- ~ ~ .
power source, In the identified series of engines the governor purnp operates at the crankshaft speed of the engine and it has a twelve (12) tooth gear in the gear pump assembly. At an engine speed of 2200 rpm, the pulsations of ~he oil flow from the governor pump ~ -have a frequency of 440 cps which is observed to be the same as the first harmonlc of the engines cylinders~ Upon changing the pitch 30 of the propeller blades with the governor pump operating at 2200 rpm 9.~13~3~
The second, third, and fourtl1 harmonics of 440 cps were detected in the propeller blacles with the fourth harmonic of 1760 cps being the most pronouncecl. In the cooling fins of a cylinder mounted on the engine crankcase substan~ial vibration was noted with the intensity thereof reaching approx~mately 1~0 db. Cycling of the governor :
pump llO to vary the pi~ch of the propeller blades was found to transfer a substantial vibration to the propeller blades through the engine crankshaft as the governor pump was operated at spee~3 comparable to cruise and takeo~ conditions. With the hydraulic dampener apparatus 10 120 connected in the fluid circuit as shown in ~ig. 7, the pronounced vibrational transfer which was noted previously it was observed to `
be markedly decreased. It is to be noted that a hydraulic dampener other than a hydraulic accumulator can be used as this portion of ~ -~he dampener means of this invention without departing from the ~-scope of ~he invention. One example of a suitable equivalent hydraulic accumulator is a bladder-type reservoir with a resilient bladder operating to dampen the pulsa~ions in the oil flow. ~ ~ ;
The following is a summary of results and observations made during practice OI ~his invention on use with two separate Cessna 210 model aircraft, one of wnich was equipped with an 10-470 series Continental engine, and the other equipped with an 1~520 series engine. The engines of both aircraf~ were modified, then operated for specified periods of time. The 10~520 was torn down for inspection. The Cessna 210 is a lightweight high wing monoplane .
having a retractable landing gear. Both o~ the enginæ involved in these tests were originally of standard manufacture equipped with standard fwel injec~ion systems and two bladed variable p~tch propellers.
In practice a Cessna 210 aircraft, having a remanufactured IO-470 series engine, has been operated with the fin dampeners, the tuned inta~se manifold, the propeller pitch control system having the , ~03B7~ :
hYdraulic dampener and propeller with the dampener members thereon.
This engine was operated for approximately four hundred (400) hours, engine time, after being remanufactured to the manufacturer's suggested specifications and before being modified as descxibed above. During operation of this aircraft, several observations were made regarding its vibrational characteristics. First, the overall sound level due to vibration in the cabin of the aircraft was significantly lower for both takeoff ancl cruise conditions than it was prior to modiîicatioff of the engine. Second, the cooling fins on the engine l~ibrated considerably 1() less than before. It was observed that one could place their hand on the cooling fins of a cylinder and feel only a slight fin movement, whereas with the unmodified engine a substantial fin movement or vibration was -felt when the cooling fins were touched. Third, the operating sound level of the engine outside of the cabin of the aircraft was noted to be --substantially less. Typically, the identified s~ries of engines have a recognizable sound in the form of an engine noise or crack that can be ~` `
heard as the aircraft flies low overhead. Thi~l noise has a cracking ~ ~
~, .
sound of approximately 8 cps which can be easily heard and readily de~eeted by an observer on the ground as an aircra~L having such an : . .
20 ~ engine is flown low oYerheadr W~th the engine modified as described~ ~;
this characteristic observable noise is not present. Fourth, a decrease in fuel and oil consumption has been noted. During operation of this aircraft, it was engaged in private utilityflying, and it was observed that the oil consurnption dropped from one quart per three hours to one quart per six hours.
, In practice, a new Cessna 2lO model aircraft, having a 75 hour 10-520 series engine was tested with the engine dampener structure of this invention. It is to be noted that the engine was purposely equipped with the lightweight cylinders in place of the 30 norrnally equipped heavyweight cylinclers. The engine was fitted . .
.
. . .
~3~
` with the fin dampeners, the hydraulic dampener and the propeller was fitted wi~h the resilient members. During operation of thls aircraft, ~ "
it was flown considerably at 75 percent power ancl an engine sp~ed ; '~
of 2, 480 RPM. In the operation of this aircraft, the ~our (4) obser~
vations enumerated above in E3xample I were each confirmed. During operation, it was observed that fuel consurnption was approximately 1, 13. 3 gallons per hour and oil consumption was 7.1 hours per quart at approximately 75 percent power and 190 mph ias. During normal ~ ;
operation of an aircraft of this type operating in the same area in similar type flights with unmodified engines, it was observed that such aireraft normally have a fuel consumption of approximately -~
17 to 20 gall~ns per hour at approximately 75 percent power an~
180 mph ias. `
It is to be noted that the suggested overhaul time for this engine is 1200 hours, engine time. ~fter operating this engine ;
~r 2, 271 hours (more than 1, 000 hours over the suggested ~ver~
haul time) the engine was dismantled for mspection. It is to be noted that du~ing operation of the engine, only routine maintenance, oil changes evexy 400 hours and tune~s were performed. ~t the time the engine was dismantled, the compression was ~und to be 79/80, ~ -~
which i8 to be compared with 80/80 for a new engine, and 60/80 as the minimum usable compression rating. Inspection of the bearings indlcated that all the bearings of the en~ine were in tolerance, with the maximum wear o~ . 00301 in the two forwardmost main bearings on the crankshaft where . OOS i8 the service limit. Inspection of the pistons revealed they were all within tolerance and were reusable.
X-ray photographs of the crankshaft assembly~ the piston assemblies;
and the cylinders indicated that no craeks were present. Inspection OI the plston rings indicated an essentially uniform wear pattern and particularly dld not exhibit any wear pattern that could be attrlbuted ~ L03B711 to the multi-node vibrations described above. The engine was reassembled with new piston rings and returned to use. To date this engine has r-m approx mately 4,000 hours (total engine tin e) without a single cylinder failure on the above described light weight cylinders and the compression is holding at 79/80 with the same low oil ;~
consumption of one quart per seven hours. ;~
In the manufacture ~ the engine dampener means of this invention including the several structures th~reof, it is obvious that it can be easily constructed to achieve the end product. The 10 mechanical apparatus of the invention can be constructed by the same technique currently used in manufacturing parts for aircraft -engines. The meth~d of dampening the ~ngine can be accomplished ~ -as described with the described apparatus or with suitable equivalent apparatuses or materials.
In the use and operation of the engLne dampener means of this invention, it has been seen through the example that the engine dampener apparatus does operate as described, and it has a substantial effect on the operation of internal con~ustion reciprocating air-cooled aircraft engines to extend the useful life thereof and to increase 20 the safety thereof. In carrying out th~ method of dampening the engine of this invention, it is seen that same can be accomplished easily and with significant useful results.
As will become apparent from the foregoing description of the engine dampener means, relatively simple and i~?iexpensive apparatus has been provided to dampen the vibra~ional characteristics of aircraft engine and the method of dampening the engine is also inexpensive and relatively easily accomplished. The engine dampener structure includes several elements which are easily attachable to or replaceable on an aircraft by an appropriately skilled mechanic 30 to have the effec~ of improving the operation of the engine, The -30 ~
' . ' ' ', , '' ' , .
method of dampening the engine of this invention can be accomplished by a nominally skilled aircraP~ engine mechanic.
, ' ,.~ ,',,, . ':
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compression rings are placed in a cylinder without a piston and the ~ -cylinder is vibrated the rings will vibrate in the 6- node pattern and crawl or move itl the cylinder bore in the direction of the combustion chamber end portion c~f the cylinderO The piston rings were studied at room temperature, and temperatures up to250~, with a small re-:
duction in natural frequency vibration noted at the elevated temperature.
At ~his point, i~ is to be noted that ~he piston rings of a piston assembly for the identified series of engines apparently exhibi~s the same har-monic frequencies as the cylinders for the engines as described lO supra In the general structure of an aircraft engine, the internal bore of the cylinders thereof are tapered with ~he barrel portion , - . , o~` the cylinder being larger than the compression end portion of ~ -the cylinder, so that adequate compression is maintained in the . . .
cylinder as it is heated during engine operation. When the cylinder , of such an engine is heated, the combustion chamber portion thereof is obviously heated significantly more than the barrel portion thereof, ;
due to the combustion process, and expanded significantly. The tapering of the cylinder bore of the cylinder is referred to as 20 ~ ~ "choklng". In studying the cylinders of the 10-470 series engines, the choked condition of the cylinder bore is found to be essentially relieved at approximately ~501~. It is to be noted that until the .
cylinder has reached approximately 250~, in operation of the engine of the cylirlder operates in a choked condition wherein the clearance between the piston and the cylinder wall is significantly leæs than would be encountered in normal operation. In studying operation of the 10-470 series engine, it has been found that the two cylinders on the forward end of the engine or the end thereof which mountæ the propeller and is normally forward when mounted 30 unbaffled will opexate at approximately lOO ~, below the .. . . . . .
, .
~ 3~
normal operating temperature of the rearmost pair ~ cylinders.
In examination of several I0-470 series engines ~nen dismantled after being run a substantial length of time indicates that the relatively cool temperature of the forward cylinders prevents the piston rings ~;
. . -:
from properly seating in the piston cylinder bores, and in some cases, causes scoring oE the piston and the cylinder bore. It is to be noted that when a pi~ton has moved in the choked cylinder, it requires s~stantially more force to move the piston than when it is moved in a heated and unchoked cylinder because the compression -;~
. .
rings move in a substantially cylindrical bore rather than a tapered bore as when the cylinder is in the choked condition.
The cylinders on the identified series of engines are mounted on the crankcase in a staggered and opposed relation as s hown in ~ig. 6 so the connecting rods properly line up with the appropriate throws on ~he crankshaf~. The cylinders are numbered from the rear of the engine to the front or output end of the engine with cylinder ~1 being the rearmost cylinder on one side of the crankcase~ and cylinder ~2 being on the opposite side thereof with the piston rods thereof mounted Otl the same crankshi~t throw. Cylinders l, 3, 20 and 5, are on one side of the crankcase, and cylinders 2, 4, and 6 are on the opposite side of the crankcase specifically the leEt and right respectively as shown in Fig. 6. The firing order of these series of engines is by cylinder nurnber as follows: l-6-3-2-5-4.
It i6 to be noted that in observing the firing order of the cylinders that combwstion on cylinex ~1 at the rear of the engine irnmediately precedes firing on cylinder ~6 at the forwardmost end and the opposite side of the engine, and in this order of firing, the cylinder which normally operates in an unchoked condition is fired immediately preceding a cylinder which normally will operate in a choked 30 conditlon.
. ' -15- `
.. , . . , , , .
~3~''7 a.~
` In normal operation of the identified series ~f engines, the intake maniold poxtion thereoE operates with pressure the atmospheric pressure. In these series of engines, the difEerential press~e between Lhe forward portion of the intake manifold which is connected with the forwardmost cylinders and the rear portion of the intake mani~ld, which is connected with the rearmost cylinders, indicates there is a differential pressure between these two points~ which will in normal operatlon of the engine vary from approximately 3 inches of mercury to approximately 4. 5 inches of mercury. The 10 horsep~wer OULpUt of an internal combustion engine is in part dependent upon the intake manifold pressure for a particular engine ~ ~;
speed. Examination of maximum power data for alti~ude per~
formance of the IO-470 series engines indicates that ~or an engine speed of approximately 2, 600 rpm9 a di~fexential pressure of ~. 5 inches of mercury has a differential power of approximately 51 horsepower or on a per cylinder basis, apF~roximately 8. 5 horsepower pex cylinder. In view of this, it is obvious that the forward cylinders of the engine are producing less horsepower than the rear cylind~rs . .
of the engine because the intake maniEold pressure at the rear oE
the engine is higher than it is at the forward portion of the engine. ;
study of constant speed operation of this engine revealed the described intake manifold pressure distribution; however, rapid opening and closing of the engine throttle drastically changes the manifold pressure distribution.
Figs. 3-S show in detail the structure o~ the cooling fin dampener alone and mounted with a finned segment of a cylinder.
The c~ooling fin dampener i,s prefereably a cross-sectionally comb~
like structure, indicated generally at 50, having a first portion 52 mountable between adjacent fins on a finned segment, and an integral ,~econd portion 54 connecting the ends of the first portion 52. The ~3~
.
cooling fin dampener 50 is preferalbly construct~d of a resilient material in a strip-like segmen~ with the teeth or lug-like portions of the first portion 52 a-ppropriately spaced to be inserted between the adjacent cooling fins. The firs~ portion 52 has a plurality of teeth or lug-like members with each having a reduced size outer encl portion 56, and each having a mounted end portion 58. The lug-like portions are tapered and preferably pointed on their outer end portion as shown in Pig. 5 when in an uncompre~ sed state and , they assume an essentially rounded shape as shown in ~igs. 3 and 10 4 when mounted. The lug-like portions have essentially parallel adjacent edges 60 between the outer end portions 56 and the mounted or inner end portions thereof 58. The fin dampeners second portion 54 is an elongated relatively narrow strip integrally Eormed with the ` ~ -fin dampeners first portion 52 at the mount~d portions 58 with the teeth-like portions of the second portion 520 The second portion 54 traverses the mounted end 58 of the teeth or lug-like members ;
of the first portion 52. ~ig. 3 shows a finned segment indicated ' generally at 66 with the cooling fin dampener 50 mounted thereon. ~ -The finned segment 66 illustrates the cylinder of an engine which 20 has a plurality of cooling fins 68, extending therefrom. The cooling fins 68 are essentially parallel to each other and generally perpen-dicuLar to the cylinder wall support segment 70. Eiig. 4 shows the finned segment 66 and dampener 50 in section taken through one of the cooling fins with portions of t.le cooling finned segment and the dampener shown in dashed lines. The dampener 50 is rnounted with the teeth-like portions thereof between adjacent eooling fins 68 and the second portion 62 thereof closely adjacent to or in contact with the outer peripheral edge of the cooling fins. The dampener ~ -50 has the teeth thereof extending in to the outer peripheral portion 30 of the cooling fins. The lug-like portions of the dampener's first /
, ., : , :
3!517~
`` portion 52 are preferably cons~ucted having a thickness or width greater than the gap or distance between the coollng fins so when they are mounted they are retained solely by friction between the cooling fins in a compressed condition.
In installing the cooling fin dampener 5û of this invention~ a pair oE adjacent cooling fins are separated by inser~ing a wedge-like member between same, then a tooth or lug-like portion of the dampener member is inserted between the fins in a desired position, ~ -~
then the wedge-like member is removed, releas~ng the cooling 10 fins to contact and compressibly retain the tooth-like member there between. Once a tooth of a fin dampener strip member has been inser~ed, the process is repeated on the next tooth, then the `
next, until the strip is mounted in the cooling fin in the position as shown in Fig. 3. A lubricant can be used to aid in inserting the teeth between the cooling fins. In practice a liquid detergent, such as a household di~hwashing detergent, has been successfully used to assist in placing the teeth-like portions of the fin dampener 50 ` ~;~
in a cooling fin. ;
In using the fin dampeni~S0 with the identified series of engines, 20 the first portion 52 of the dampener is consaructed with the teeth~
like p~rtion thereof spaced tO correspond with the cooling fin spacing of the engine. The cooling fins on the identified series of engines are approximately . 05 inches in thickness, and . I inches in spacing.
Preferably, the fin darnpener has the teeth or lug-like portions thereof cons tructed being . 15 inches in thickness and . 05 inches in spacing and approximately . 25 inches in width. In practice, fin dampeners constructed as described have been used with cooling fins in the identified engine and operated for a substantial length of time without failure of the fin dampeners or a substantial loss in resiliency.
30 Preferably, the fin dampener 50 is constructed of a neoprene ,........... ..
composition material~ because of its oil and hydrocarbon resisting properties. The fin dampener 50 is preferably cons~ructed by molding ~he neoprene composition material wi~h the teeth or lug-like portions sized and spaced so ~hey will fit the cooling fins of an engine in the described manner. It is obvious the resilient material of the fin dampener can be constructed of materials other than a neoprene ~;
composition material, for example, synthetic rubber, or a silicon ~ ;
. - ~
composition material or any other suitable resilient material can be -used.
Another portion of the dampening means of this invention is related to a cylinder dampener in the form of a tuned intake manifold for the engine. In regard to the tuned intake manifold, its function `~
is to cause the engine to operate with a uniform or substantially even normal operating manifold pressure. As described above, in ,,, ~;
the normal operatîon of the identified series o~ engines, the cylinders opera~e at a non uniform temperature with the forwardmost cylinders being the colder, and the rearmost cylinders being the hotter. ~or the 10-470 series engines, the temperature distribution between t~e orwardmost cylinders and the rearmost cylinders is approxi-mately 100E~. Normally, the cylinder head temperature of an air~
craft englne is mon~tored by a cylinder head tempera~ure gauge ~ ~ ~
probe by a cylinder head temperature gauge on one of the center ;;
cylinders. It ~s recommended by aircraft manufacturers that in normal operation of an aircraft it not be flown until the engine has - -reached the normal operating temperature. However, it is to be ~ ;
observed that when the englne has reached this temperature, the `
forward cylinders of the engine are still below the normal operating temperature so they are operating in the choked condition, as described above.
l~ig. 6 shows a plan view of the underneath side of the engine, -.. . . . , . . ~ , . . .
` ~3~7~ :
clearly exposing intake manifold. The intake manifold for the engine i9 indicated generally at 80 and includes a looped conduit s$ructure having an inlet and connected with the intake ports on the engine's cylinders. The conduit inlets are indicated a~ 82 at the rear of the engine~ On the right side of ~ig. 6, the conduit outlets are indicated at 83, 84 and 85 which serve the cylinders ~ 33 and ~5, respectively.
On the left side of ~ig. 6, the conduit outlets are indicated at 86, 87, and 88, and they serve~ cylinders ~ 4, and #6, respectively.
A flow-balancing condui$ 90 is communicably connected between ~he conduit segments of the intake manifold 80 for balancing the flow through the manifold. As described above, normal operation of the engine results in a pressure distribution thrvugh the intake manifold having a differential pressure or approximately 4. 5 inches of mercury between the outlets 83 and 86, on the rear of the engine and the outlets ``
85 and 88 on the forward of the engine. In practice, the press~re dis~ribution between the several outlets of the in~ake manifold 80 have been made essentially uniform by reducing the internal cross-sectional a~ea of the outlet segmen~s of the intake manifold, this causes the engine to operate with esse~ially intake manifold pres- ~;
sure and essentially the same cylir~ler head temperature on all cylillders. Inpractice, it has been found practical to crimp the ~-intake manifold to reduce the cross sectional area. The manifold's crimped sections are indicated at 92 and 94 in l~ig. 6. In practice, the intake manifold conduit segments adjacent toth~outlets 83, 84, 86, and 87, have been crimped by selectively placing a dent in an easily accessible portion o~ the manifold at a point closely adja-cent to the outlet end of the conduit segments. In crimping the conduits, the specific amount OI the crimp or dent determines the amount of reduction in cross sectional area this reduction is speci-3~ f~cally dependent upon the distance between the outlet segments and -20~
3~7~
The change in pressure differenti~l which must be accomplished. In .
practice, it has been found tha~ the rearmost conduits having crimps 92 must have a cross sectional area sligh~ly less than the center conduits having crimps 94, because they are nearer ts) the intake manifold inlet 82. In the intake manifolds for the above- identified series of engines, they are constructed of a lightweight material which is easily bent, and in practice i~ has been crimped by uæi ng a blunt objeet to force a dimple in the condui~ segments thereof in a curved outlet end portion closely adjacent to the outlets of the intake manifold. In practice on the 10-470 series engine, it has been operated with the intake manifold thereof modified as described, and will ~`
operate normally with the cylinder~ea-~{temperature for all the cylinders in the range are 350-380. The actual normal operating tempera~ure of the engine, of course, depends on ~utside air telnperature and the type o~ flying being done. In practice, the modified engine has been operated full power in low-level flight for extended periods of ~ime wath the outside air temperature approximately looQ~ and greater, at altitudes varying 1500 and 2500 fee~ above sea level, withou~ encount-ering any engine overheating, and with~ut signfflcant variance in the -cylinder head temperatur~ distribution.
Another p~tion of the dampening means of this invention `~
is related to a propellor dampener apparatus which includes a dampener for the propeller blades of the engine. l~ig. 7 shows in detail a two~
bladed propeller asæembly w~th dampeners thereon. The propeller assembly lO0 whl~h is normally used on the identified seraes of engines and on a great many other light alrcraft-type engines. The propeller assembly lO0 has a variable pitch propeller with a pair of blades 102 rotatably mounted on a hub lO'L that is attached to the engine crankshaft 106. The propeller blades 102 are rotated about their longitudinal axis at the hub 104 by a hydraulically powered servo 108. An engine , . .
~ ~3~
d riven hydraulic pump 110 a governor pump iB communicably connected with the servo 108 through the crankshaft 106 and used to control the pitch of the propeller blades 102. A pair of resilient propeller dampening members 112 are mounted on the forward side of the propeller blades 102 as shown. The propeller dampening members 132 are secured to tne propeller blades 102 by a suitable adhesilTe or by other sui~able means of attachement. In the propeller assembly 100 the servo 108 is connec~ed by a linkage with the individual propeller blades 102 and changing the hydraulic fluid pressure in the propeller servo 108 changes the pitch of the blades 102 relatively to the plane of rota~ion of the propeller. Servo-controlled variable pitch propellers use hydrauli~ pressure from the engine driven pump to change the pitch of the blades by applying pressure to increase the pit~h of the blades or applied pressure to deerease the pitch of the blades, depending upon the specific constru~tion of the system. The propeller assembly 11~ shown in ~ig. 7 is the type of system wherein flu~
pressure in the servo 108 is increased to increase the propell~r blade pitch.
It has been foun~ that vibra~ion in~ucing ~orces are transmitted 20 from the piston and cylinder assembly and governor pump to the propeller through the engine crankshaft. These forces transmitted to the propeller through the crank~haft are dependent upon the speed of the engine, and frequency of hydraultc fluicl pressure pulses from the pr~peller and governor pump. l~orces are also induced in the propeller by what is normally called "P-factor". The P-factor forces ~ -induced on the propeller are present when the aircraft is making a climbing turn. These forces are cuased by the difference in the angle of attack of the propeller blades as they move from one side of the engine to the other and are subjected to differential loading. The 30 P-factor induced vibrational forces are transmitted from the propeller - 1~3~
~o the engine through the crankshaftO The P-factor forces are believed to be a significant factor in causing engine failures during a climbing turn, particularly a climb Erom low altitude such as a takeoff7 where ;~
relatively high power is being developed by the engine. When a propeller blade is on the side of its swing, having the highest angle of attack, it produces a greater force on the engine crankshaft than it does when it is on the opposi~e side where the angle of attack is less. This variation in force is ~ransmitted directly ~o ~he engine crankshaft at a frequency dependent on the rotating speed of the 10 crankshaft and number of propeller blades. P-factor vibrating induced forces are particularly acute when u3ing a three-bladed propeller or a single-bladed propeller, as the forces on opposed sides of the aircraft are exlreme. When using a two-bladed propeller ,..... .
the P-~actor induced forces are less extreme than with a one- or three-bladed propeller because of the balancing effec~ of the second ~ -~ ~
blade being directly opposite to the crankshaft. Obviously9 the natural ,~
frequency and frequency response of a propeller depends upon many factors such as its resiliency, momRnt of inertia, etc. In practice, -~
it has been found that a metal propeller will readily transmit vibrational ~ -~
20 forces ~rom its tips to the crankcase, and through the entire engine~
with absence of any other forces.
The propeller dampener portion of the engine dampener structure of this invention includes a pair of resilient members 112 ~;
mounted on the interior portions of the propeller, as shown in ~ig. 7.
Preerably, the resLl~ent members 112 are constructed of a resilient material having high dampening properties, such as neoprene, which can be attached to the propeller blades by a suitable adhesive. In practice, neoprene composit~on electric de-icing boots have been applLed to a variable pitch servo-controlled propeller on the above-30 ic~enti~ied series of engines, and operated for a considerable ~ime.
,, .. . .
~ 3~
lq this practice, the propeller clampeners ~ve been found to, in combination with the other elements of this invention, substantially dampen the vibrational fvrces and vibrations of the engine. Preferably, the resilient propeller clampen~rs are applied to the propeller and cover approximately 30 to 40 percent of the propeller's radi~us, originating at a point adjacent to the propeller hub. In practice~ the propeller dampener members 112 were applied over approxima~ely 33 percent of the propeller's blade span originating at a point close to the propeller hub. Although the propeller dampeners are shown and 10 described as mounted on a variable pitch servo ~ontrolled tw~bladed propeller, it is to be understood that such can be applied to other propellers such as fixed pitch propellers and nonservo-controlled variable pltch propellers to achieve a similar result.
. ~ .
Another portion of the dampening means of this invention is related to a hydraulic dampener for the governor pump of the propeller pitch changing apparatus. In ~ig. 7, the propeller assembly 100 is shown with the governor pump 110 and with the hydraulic dampener apparatus indica~t ed generally at 120. The function of the hydraulic dampener is to dampen the pulsations and the hydraulic fluid discharged 20 from the gove~nor pump and to prevent these pulsations from being transferred to the other engine comp~ner~s into the propeller. The governor pump 110, shown in ~ig. 7 Is typical of governor pumps used in light aircraft in that it has a housing 1227 which is secured to a mount ;124 on the crank~ase of the aircraft engine. The governor pump 110 is driven from the englne crankshaft 106 by a pair of gears 126 and 128 as shown. Engine oil is supplied to the governor pump 110 through an inlet indicated at 130 and discharged through an outlet conduit 132 into a trans~er gland 134 on the engine crankshaft 106. The end portion of the englne crankshaft 106 is hollow to allow oil to pass to and from the propeller servo 108. In the propeller servo 108, oil pressure on ' ' ' ~;
t~e piston 136 moves the piston against the force of return springs 138 which in turn rnoves the linkage connected with the propeller blades 102. The oil flow in the outlet conduit 132 is controlled by a pilot valve indicated generally at 140 so that oil can flow into and out of the propeller servo 108 as required. A speed-adjusting apparatus on the upper portion of the governor pump 110 has a flyweight assembly 142 and a speed adjusting lever 144 to control motion of the pilot valve 140 and thus control the oil flow in the outlet conduit 132. The actual pump portion of the ~g~vernor pump llû is a gear type pump ; ~ -assernbly 148. A pressure relief valve assembly 146 is connected w ith the outlet of the gear pump assembly 148 in the lower portion .. . , . ~
of the governor pump housing 122. The gear pump 148 is driiven directly from the engine crankshaft by gears 126 and 128, as shown.
High pressure oil flow from the gear pump 148 to relief valve 146 ~ -~
is through a conduit indicated at 150~ The relief valve assembly ~ ~;
146 has a return to the gear pump 148 and an outlet to the pilot valve , ,, assembly 140. The gear pump assembly 148 is by its basic nature ~ ~ ~
. ~ . , a pump w~ich will provide a substantially high-pressure output flow with pulsations in the ou~?ut -flow because of the geared construction.
These pulsations In the output from the gear pump assembly 148 `
provide a substantial source of vibration which is transmitted to the engine throu~ the governor pump housing 122 to the pump mount 124 on the engine crankcase, and through the oil supply to the propeller assembly 100.
The hydraulic dampener apparatus 120 is connected with the outlet of the gear pump assembly 148, to dampen the pulsations - `
in its output oil flow. A conduit 154 is connected with the condult 150 that joins the outlet of the gear pump assembly 148 to ~he inlet of rellef valve assembly 146 for connecting the hydraulic dampening device. In practlce, a hydraulic accumulator has been used suc-,. . . . . . . .
~ 033!37a~
c essfully as a hydraulic dampening device as shown in :F ig. 7. In such practice, the accumulator housing 156 is provided with brackets for mounting it on the aircraft structure, with the conduit 154 beirlg a high-pressure flexible hose~ The hydraulic accumulator has a piston 160 mounted in the hous~ng 156 between an oil chamber 162 and an air chamber 164. The piston 160 is freely movable within the housing and it is provided with sealing rings to keep the oil and air separated. Air under pressure is manintained in the air chamber 164 in order to maintain the piston 160 in a balanced condition against 10 the oil in the oil chamber 162. During operation o~ the engine, the pulsations from the gear pump 148 cause the oil in the oil chamber 162 to pulsate thereby oscillating the pist~on slightly against ~he force of the air in the air chamber 164, thus dampening the pulsations in the oil fl~w as it is received by the relief valve assembly 146 and in t~.~n as it is~ received by the pilot valve 140 and propeller .
assembly 100~ The overall result of adding the- hydralic dampener in the form of the hydraulic accumulator is to dampen the pulsations in the.oil flow as it passes through the cranksha~ 106 and further .: .
into the propeller servo 108. ; . ` :~ .
20 - . Inpractice, in experimenting to determine the signi:ficance of the effects of the hydralllic darnpener for the governor pump, a i governor pump crankshaft and propeller assembly were mounted :
on the crankcase of an 10-470 series engine and operated by an auxiliary `- ~ ~ .
power source, In the identified series of engines the governor purnp operates at the crankshaft speed of the engine and it has a twelve (12) tooth gear in the gear pump assembly. At an engine speed of 2200 rpm, the pulsations of ~he oil flow from the governor pump ~ -have a frequency of 440 cps which is observed to be the same as the first harmonlc of the engines cylinders~ Upon changing the pitch 30 of the propeller blades with the governor pump operating at 2200 rpm 9.~13~3~
The second, third, and fourtl1 harmonics of 440 cps were detected in the propeller blacles with the fourth harmonic of 1760 cps being the most pronouncecl. In the cooling fins of a cylinder mounted on the engine crankcase substan~ial vibration was noted with the intensity thereof reaching approx~mately 1~0 db. Cycling of the governor :
pump llO to vary the pi~ch of the propeller blades was found to transfer a substantial vibration to the propeller blades through the engine crankshaft as the governor pump was operated at spee~3 comparable to cruise and takeo~ conditions. With the hydraulic dampener apparatus 10 120 connected in the fluid circuit as shown in ~ig. 7, the pronounced vibrational transfer which was noted previously it was observed to `
be markedly decreased. It is to be noted that a hydraulic dampener other than a hydraulic accumulator can be used as this portion of ~ -~he dampener means of this invention without departing from the ~-scope of ~he invention. One example of a suitable equivalent hydraulic accumulator is a bladder-type reservoir with a resilient bladder operating to dampen the pulsa~ions in the oil flow. ~ ~ ;
The following is a summary of results and observations made during practice OI ~his invention on use with two separate Cessna 210 model aircraft, one of wnich was equipped with an 10-470 series Continental engine, and the other equipped with an 1~520 series engine. The engines of both aircraf~ were modified, then operated for specified periods of time. The 10~520 was torn down for inspection. The Cessna 210 is a lightweight high wing monoplane .
having a retractable landing gear. Both o~ the enginæ involved in these tests were originally of standard manufacture equipped with standard fwel injec~ion systems and two bladed variable p~tch propellers.
In practice a Cessna 210 aircraft, having a remanufactured IO-470 series engine, has been operated with the fin dampeners, the tuned inta~se manifold, the propeller pitch control system having the , ~03B7~ :
hYdraulic dampener and propeller with the dampener members thereon.
This engine was operated for approximately four hundred (400) hours, engine time, after being remanufactured to the manufacturer's suggested specifications and before being modified as descxibed above. During operation of this aircraft, several observations were made regarding its vibrational characteristics. First, the overall sound level due to vibration in the cabin of the aircraft was significantly lower for both takeoff ancl cruise conditions than it was prior to modiîicatioff of the engine. Second, the cooling fins on the engine l~ibrated considerably 1() less than before. It was observed that one could place their hand on the cooling fins of a cylinder and feel only a slight fin movement, whereas with the unmodified engine a substantial fin movement or vibration was -felt when the cooling fins were touched. Third, the operating sound level of the engine outside of the cabin of the aircraft was noted to be --substantially less. Typically, the identified s~ries of engines have a recognizable sound in the form of an engine noise or crack that can be ~` `
heard as the aircraft flies low overhead. Thi~l noise has a cracking ~ ~
~, .
sound of approximately 8 cps which can be easily heard and readily de~eeted by an observer on the ground as an aircra~L having such an : . .
20 ~ engine is flown low oYerheadr W~th the engine modified as described~ ~;
this characteristic observable noise is not present. Fourth, a decrease in fuel and oil consumption has been noted. During operation of this aircraft, it was engaged in private utilityflying, and it was observed that the oil consurnption dropped from one quart per three hours to one quart per six hours.
, In practice, a new Cessna 2lO model aircraft, having a 75 hour 10-520 series engine was tested with the engine dampener structure of this invention. It is to be noted that the engine was purposely equipped with the lightweight cylinders in place of the 30 norrnally equipped heavyweight cylinclers. The engine was fitted . .
.
. . .
~3~
` with the fin dampeners, the hydraulic dampener and the propeller was fitted wi~h the resilient members. During operation of thls aircraft, ~ "
it was flown considerably at 75 percent power ancl an engine sp~ed ; '~
of 2, 480 RPM. In the operation of this aircraft, the ~our (4) obser~
vations enumerated above in E3xample I were each confirmed. During operation, it was observed that fuel consurnption was approximately 1, 13. 3 gallons per hour and oil consumption was 7.1 hours per quart at approximately 75 percent power and 190 mph ias. During normal ~ ;
operation of an aircraft of this type operating in the same area in similar type flights with unmodified engines, it was observed that such aireraft normally have a fuel consumption of approximately -~
17 to 20 gall~ns per hour at approximately 75 percent power an~
180 mph ias. `
It is to be noted that the suggested overhaul time for this engine is 1200 hours, engine time. ~fter operating this engine ;
~r 2, 271 hours (more than 1, 000 hours over the suggested ~ver~
haul time) the engine was dismantled for mspection. It is to be noted that du~ing operation of the engine, only routine maintenance, oil changes evexy 400 hours and tune~s were performed. ~t the time the engine was dismantled, the compression was ~und to be 79/80, ~ -~
which i8 to be compared with 80/80 for a new engine, and 60/80 as the minimum usable compression rating. Inspection of the bearings indlcated that all the bearings of the en~ine were in tolerance, with the maximum wear o~ . 00301 in the two forwardmost main bearings on the crankshaft where . OOS i8 the service limit. Inspection of the pistons revealed they were all within tolerance and were reusable.
X-ray photographs of the crankshaft assembly~ the piston assemblies;
and the cylinders indicated that no craeks were present. Inspection OI the plston rings indicated an essentially uniform wear pattern and particularly dld not exhibit any wear pattern that could be attrlbuted ~ L03B711 to the multi-node vibrations described above. The engine was reassembled with new piston rings and returned to use. To date this engine has r-m approx mately 4,000 hours (total engine tin e) without a single cylinder failure on the above described light weight cylinders and the compression is holding at 79/80 with the same low oil ;~
consumption of one quart per seven hours. ;~
In the manufacture ~ the engine dampener means of this invention including the several structures th~reof, it is obvious that it can be easily constructed to achieve the end product. The 10 mechanical apparatus of the invention can be constructed by the same technique currently used in manufacturing parts for aircraft -engines. The meth~d of dampening the ~ngine can be accomplished ~ -as described with the described apparatus or with suitable equivalent apparatuses or materials.
In the use and operation of the engLne dampener means of this invention, it has been seen through the example that the engine dampener apparatus does operate as described, and it has a substantial effect on the operation of internal con~ustion reciprocating air-cooled aircraft engines to extend the useful life thereof and to increase 20 the safety thereof. In carrying out th~ method of dampening the engine of this invention, it is seen that same can be accomplished easily and with significant useful results.
As will become apparent from the foregoing description of the engine dampener means, relatively simple and i~?iexpensive apparatus has been provided to dampen the vibra~ional characteristics of aircraft engine and the method of dampening the engine is also inexpensive and relatively easily accomplished. The engine dampener structure includes several elements which are easily attachable to or replaceable on an aircraft by an appropriately skilled mechanic 30 to have the effec~ of improving the operation of the engine, The -30 ~
' . ' ' ', , '' ' , .
method of dampening the engine of this invention can be accomplished by a nominally skilled aircraP~ engine mechanic.
, ' ,.~ ,',,, . ':
,, , "., ~-,, ~, ,' :,'.,' ~'' ~
,. . ,. ~ . . .. .
"
,'~'~ '^ ' ~ ' ' `'~; ~' ' , -31-,, , ,;
,,,~ .
Claims (7)
1. In an engine having a plurality of cooling fins mounted in a spaced relation, that improvement of a cooling fin vibration dampener in combination therewith, comprising:
(a) a member of resilient fully cured material having a first portion and a second portion, said first portion having at least two lug-like portions being mounted on opposite sides of an engine cooling fin and in compression between cooling fins adjacent to said first-named cooling fin, said lug portions being longitudinally elongated substantially, having a length substantially greater than any transverse dimension, and having their outer end portions being wider than the distance between said first-named fin and said fins adjacent thereto, said lug-like portions when mounted extending inward into the outer edge portions of said cooling fins with said outer end portions being essentially rounded in external shape;
(b) said second portion connects end portions of said first potion to when mounted traverse ends of said cooling fins, (c) said first portion is integral with said second portion, and (d) said dampener is constructed and adapted to be mounted and held in place on an engine solely by friction with said lug-like portions compressed between said fins, said cooling fin vibration dampener is constructed and adapted to in use reduce the normal operating natural frequency to which said cooling fins can be forced by normal operation of said engine thereby reducing the overall normal operating naural frequency of said engine to prevent said engine from reaching a resonant frequency.
(2) The vibration dampener of Claim 1, wherein:
(a) said second portion is elongated; and (b)said member has a comb-like section.
(a) a member of resilient fully cured material having a first portion and a second portion, said first portion having at least two lug-like portions being mounted on opposite sides of an engine cooling fin and in compression between cooling fins adjacent to said first-named cooling fin, said lug portions being longitudinally elongated substantially, having a length substantially greater than any transverse dimension, and having their outer end portions being wider than the distance between said first-named fin and said fins adjacent thereto, said lug-like portions when mounted extending inward into the outer edge portions of said cooling fins with said outer end portions being essentially rounded in external shape;
(b) said second portion connects end portions of said first potion to when mounted traverse ends of said cooling fins, (c) said first portion is integral with said second portion, and (d) said dampener is constructed and adapted to be mounted and held in place on an engine solely by friction with said lug-like portions compressed between said fins, said cooling fin vibration dampener is constructed and adapted to in use reduce the normal operating natural frequency to which said cooling fins can be forced by normal operation of said engine thereby reducing the overall normal operating naural frequency of said engine to prevent said engine from reaching a resonant frequency.
(2) The vibration dampener of Claim 1, wherein:
(a) said second portion is elongated; and (b)said member has a comb-like section.
32
3. The vibration dampener of Claim 2, wherein:
(a) said lug-like portions have pointed outer end portions, and (b) said lug-like portions have a rectangular cross section.
(a) said lug-like portions have pointed outer end portions, and (b) said lug-like portions have a rectangular cross section.
4. The vibration dampener of Claim 1, wherein said member is constructed of a neo-prene composition material.
5. The vibration dampener of Claim 1, wherein:
(a) said member has a comb-like section with said second portion being elongated, (b) said lug-like portions are rectangular and have pointed outer end portions, and (c) said vibration dampener is constructed of a neoprene composition material.
(a) said member has a comb-like section with said second portion being elongated, (b) said lug-like portions are rectangular and have pointed outer end portions, and (c) said vibration dampener is constructed of a neoprene composition material.
6. A method of dampening vibrations of the cooling fins of an engine having cooling fins on the cylinder thereof, including the steps of:
(a) inserting a wedge-like member or the like between adjacent cooling fins thereby spreading the cooling fins from their normal spaced relation:
(b) inserting a tooth of a cross sectionally comb-like resilient member having a width greater than the normal spaced gap between the cooling fins between the outer portion of the cooling fins;
(c) removing said wedge-like member from between the cooling fins thereby releasing the cooling fins to compressibly hold said tooth of said resilient member between the cooling fins; and (d) repeating the above steps until all of the teeth of said comb-like resilient members are received between the adjacent cooling fins.
(a) inserting a wedge-like member or the like between adjacent cooling fins thereby spreading the cooling fins from their normal spaced relation:
(b) inserting a tooth of a cross sectionally comb-like resilient member having a width greater than the normal spaced gap between the cooling fins between the outer portion of the cooling fins;
(c) removing said wedge-like member from between the cooling fins thereby releasing the cooling fins to compressibly hold said tooth of said resilient member between the cooling fins; and (d) repeating the above steps until all of the teeth of said comb-like resilient members are received between the adjacent cooling fins.
7. The method of claim 6 further including the step of applying a lubricant to the outer portion of the adjacent cooling fins after they are spread by said wedge-like member and before said tooth is inserted therebetween.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA234,641A CA1038711A (en) | 1975-08-29 | 1975-08-29 | Engine vibration dampener means |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA234,641A CA1038711A (en) | 1975-08-29 | 1975-08-29 | Engine vibration dampener means |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1038711A true CA1038711A (en) | 1978-09-19 |
Family
ID=4103957
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA234,641A Expired CA1038711A (en) | 1975-08-29 | 1975-08-29 | Engine vibration dampener means |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1038711A (en) |
-
1975
- 1975-08-29 CA CA234,641A patent/CA1038711A/en not_active Expired
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