US2625047A

US2625047A - Pneumatic engine starter device

Info

Publication number: US2625047A
Application number: US101371A
Authority: US
Inventors: Homer J Wood
Original assignee: Garrett Corp
Current assignee: Garrett Corp
Priority date: 1949-06-25
Filing date: 1949-06-25
Publication date: 1953-01-13
Anticipated expiration: 1970-01-13

Description

Jan. 13, 1953 H. J. woon 2,625,047

PNEUMATIC ENGINE STARTER DEVICE Filed Jun'e- 25. 1949 4 Sheets-Sheet l @y H13 A fray/Veys Jan, i3, 3953 H. J. wooo 6253347 PNEUMATIC ENGINE STARTER DEVICE Filed June 25. 1949 4 Sheets-Sheet 2 Jan. 13, 1953 H. J. wooD 2,625,047

PNEUMATIC ENGINE STARTER DEVICE Filed June 25.. 1949 4 Sheets-Sheet 3 d.7A/VEN Top.- /VOMER [f1/000 By H/ls A anvers Jan. E5, 1953 H. .1. woon PNEUMATIC ENGINE STARTER DEVICE 4 Sheets-Sheet 4 Filed June 25. 1949 Patented Jan. 13, 1953 PNEUMATIC ENGINE STARTER DEVICE Homer J. Wood, Sherman Oaks, Calif., assignor to'The Garrett Corporation, Los Angeles, Calif., a corporation of California Application. June 25, 1949, Serial No. 101,371

Claims.

Thisv invention relates generally to the power plant art and more particularly to a pneumatic starter devicey adapted for use in starting the operation of a power plant, especially one of an aircraft type.

Among the many acute problems in the operation of modern aircraft power plants is the accomplishment of what erroneously appears to be a relatively simple operation, namely, that of starting turbo-jet and turbo-propeller engines. The problem of star-ting reciprocating enginesA is a relatively simple one, and many starter devices have been developed which are suitable for the purpose. The problem of starting such engines is simplified by the fact that the reciprocating engine starts at a relatively low cranking speed and, under normal conditions, a few revolutions are suiiicient tostart the firing of the engine. On the other hand, the turbine engine must be rotated at a relatively high speed before it is capable of taking over under its own power. It is thus apparent that it is necessary to overcome initial inertia of the rotatable parts, accelerate them to the speed necessary to. fire, and then assist the engine in further accelerating approximately twice this speed to a threshold to permit the turbine to satisfactorily accelerate itself from that point to operating speed, the successful completion of this starting operation within a practical period of time requiring the expenditure of much more energy than is necessary in starting reciprocating engines. Moreover, in the case of turbo-jet and turbo-propeller engines, to insure efficient, dependable performance, starting power desirably should be availyable under all conditions and from a source capable of providing an unlimited number of starts without the need for additional equipment or supplies. As a further prerequisite, when this source of power is to be airborne it must be very light in weight and occupy a minimum of space in the aircraft.

Various systems are now in use or being studied with a view toward accomplishing satisfactory starting of turbine engines under all conditions, these systems being classified generally as:

(a) Electric (b) A small auxiliary reciprocating engine (c) A small steam turbine (d) Solid propellant (e) Pneumatic (f) Hydraulic Of the six systems mentioned above, the electric and pneumatic are considered most practical and of the two last-named systems, the pneumatic system is believed more feasible from the engineering standpoint, the reasons for such conclusion being outlined hereinafter.

Systems (b), (c). (d), and (f) present additional supply problems, maintenance problems, or both. The light weight reciprocating engine presents its own starting and maintenance problems, especially at low ambient temperatures. A steam turbine system must necessarily include boilers, piping, etc., and requires additional maintenance and attention.

Solid propellants have been proposed for the purpose of starting power plants and while such means have been reasonably successful in connection with certain small reciprocating engines, when they are employed for starting turbo-jet engines their size is prohibitive. In addition, the solid propellant is costly and each charge delivers a single start and the large bulk and weight of each individual charge sharply limit the number that can be carried `aboard the aircraft.

Hydraulic starter systems are relatively heavy, subject to leaks with their ever-present nre hazard, and require much plumbing capable of conveying the hydraulic medium under high pressure. In addition, such systems must include hydraulic pumps driven by some source of power in the form of a small gas turbine or reciprocating engine. A tank must be provided for the hydraulic fluid and the use of a cooler is necessary for maintaining the temperature of the fluid within practical operating limits. The

combining of all these components results in a heavy, bulky, and complicated system which requires much attention and servicing and is subject to various other disadvantages.

While both electric and pneumatic starting systems for turbo-jet and turbo-propeller engines are considered more practical than other systems Aproposed for this purpose, the pneumatic system provides the most satisfactory performance. The

electric starting system, as used at present, is not entirely satisfactory from a military point of view. Such starters are very heavy and of relatively low power. Besides the weight of the electric starter itself, all airplanes so equipped must carry heavy battery equipment and be further reinforced by ground power plants weighing from 500 to 1500 pounds each, or rely entirely upon the ground power plants for starting.. Obviously, such airplanes must remain close to the bases where such ground power plants are available, and in case of a forced landing remote from such a base the airplanes must remain immobile until a ground power plant is available. In military operations, the starting of a number of aircraft presents a serious problem, especially in the case of the movement of an entire organization from one base to another. In extremely cool climates the power available from all battery sources is greatly reduced, thus further complicating the starting problem. In view of these disadvantages and those previously'discussed, there are obvious advantages in the use of a light airborne system, and the pneumatic starter forming the subject matter of the present application is particularly adapted for use in such a system.

It is an important object of this invention to provide a starter device whichV is particularly adapted for use in starting a turbo-jet or turbopropeller engine and capable of quickly accelerating the turbine to the high speed necessary to start the operation thereof.

Another object is to provide a starter devic of the character referred to, which is of the pneumatic type and which includes an air turbine driven by compressed air supplied from a suitable source, such as the compressor of a small auxiliary power plant of the hot gas turbine type. By this arrangement, a relatively small, lightweight, self-powered, air-borne source of energy is utilized to great advantage and the necessity for providing a non-airborne source of power outside the airplane, such as an auxiliary ground power plant, is obviated. Consequently, engines of the turbo-jet or turbo-propeller types can be readily started at any time, regardless of the location of the airplanes in which they are installed. This is an extremely important advantage since by this means military airplanes of these types can be quickly propelled into the air from any field of operation and for this reason it is unnecessary that the airplanes return to the base from which their ight is started. In addition, a pneumatic starter which derives power from an airborne auxiliary power plant of the hot gas turbo-compressor type is capable of effecting an unlimited number of starts since it is not dependent upon storage batteries or other similar sources of stored-up energy.

Another object is to provide an engine starter for aircraft of the turbo-jet or turbo-propeller types which is extremely light in weight and occupies very little space in the aircraft, and one which is highly efficient and dependable in operation and requires little attention on the part of the airplane crew except to operate the controls thereof.

Another object of the invention is to provide a small, compact starter device of the type indicated capable of delivering high torque and one which may be conveniently installed on and removed from the aircraft engine.

A further object is to provide a starter unit of the class referred to in which is incorporated a releasable driving connection between the output shaft of the starter and the jet engine, this, Y

power plant.

connection being of a centrifugally-actuated type and functioning to automatically disengage the starter shaft from the turbo-jet shaft when the latter attains a speed capable of sustaining full continuous operation of the engine being started.

A still further object is to provide a pneumatic starter unit of the classdiscussed above which includes a planetary speed reduction gearing and a friction clutchA inits power transmitting mechanism, said clutchjbeingiadapted to slip upon the occurrence of unusual drag or resistance to the free rotation ofthe" starter output shaft.

Another object is to provide a pneumatic starter of the character referred to which may, if desired, be operated by a mobile ground power plant capable of being moved into proximity with an airplane located on a eld and readily connected to the engine or engines thereof to start the same. In this respect, the present invention also contemplates a starter system in which a source of compressed air, such as a small hot gas turbocompressor, is carried by a mobile ground power plant which can be readily moved into position adjacent an airplane to supply compressed air to a pneumatic starter mounted on and adapted, when operated, to start the airplane engine. It is also proposed to provide a quick disconnect means for attaching the pneumatic starter device to an aircraft engine so that after the engine has been started, the device can be readily detached therefrom and retained with the ground power plant. Such an arrangement wherein the starter device is retained on the ground has the advantage of conserving weight in the airplane and, in the case of a high speed military airplane, the exclusion of even this small Weight may be extremely important. The present invention further contemplates the provision of a ground power plant in which the turbo-compressor is capable of supplying suflcient compressed air to the starter devices of several engines, as in the case where the aircraft is of the multi-engine type.

The present invention is directed to the starter device per se and reference made above, and subsequently, to preferred sources of compressed air for operating the device, and to the quick disconnect means therefor is merely for the purpose of illustrating the adaptability of the starter in connection with aircraft engines.

Further objects will appear from the following description and from the accompanying drawings, which are intended for the purpose of illustrating only, and in which:

Fig. 1 is a longitudinal sectional view through an engine starter device constructed in accordance with the present invention;

Fig. 2 is an end view of the turbine end of the device shown in Fig. 1;

Fig. 3 is an end view of the power output end of the device;

Fig. 4 is a cross-sectional view, taken on line 4-4 of Fig. 1;

Fig. 5 is a cross-sectional view, taken on line 5 5 0f Fig. 1;

Fig. 6 is a cross-sectional view, taken on line 6-6 of Fig. 1;

Fig. 7 is a cross-sectional view, taken on line 1-1 of Fig. l; and

Fig. 8 is a perspective view of a pair of turbojet aircraft engines, illustrating the present pneumatic starter applied to use in starting the engines and connected to be Operated by cornpressed air derived from an airborne auxiliary The present pneumatic starter device, while capable of starting engines of various types. is herein illustrated and described, by way of example, as arranged to start one or more aircraft engines of the turbo-jet type. Referring to Fig. 8, the turbine engines l5 and I6 are adapted to be started by means of identical pneumatic starter devices l1 and I8 which are connected to the engines, by means to be later described, and which are operated by compressed air supplied from a suitable source, such as the auxiliary by a tubular spacer 58. Y ball bearings48 and 49 is a turbine wheel shaft l 52 -which is provided with a pinion gear 53 at its inner end, this gear being hereinafter referred' to assthe-sun gear of a planetary gear system to be -later described. TheV forward end of the shaft 52 is disposed within the turbine housing section 'V24 and mounted on this end ofthe shaft isa turbine-wheel 55 having curved, generally radially power plant illustratedv generally at in Fig. 8 and described in more detail hereinafter.

'engine starter together with its source of compressed air, may be completely airborne and will The 'be'rst described in this connection, although the starter unit may be operated by a mobile ground servicing power plant, to be referred to later in `-the specification.

Referring now to Figs. 1 tov 7 of the'drawings,

" theengine starter device |1 includes a housing 2| which is'composed of an inner section 22, an

' intermediate section 23 andan 'outer' section 24, the section 22 enclosing a coupling means 25, the section 23 enclosing Aa planetary speed'reduction and power transmission means 26,'and the section 24 providing the housing of' an air turbine 21. The linner and'inte'rmediate sections have vnfiatching peripheral flanges which' are detachably secured together by means" of bolts 28. In a sim- Ail'ar manner, the outer'section 24 is detachably connected to the 'intermediate section '23 by -vmeans of bolts 29.

' "The intermediate housing section 23 isprovided with -an inner, annular flange 36 to which is secured, by screws 3|, a cup-like holder 32 which receives the outer raceof a ball bearing 33, an annular seal member 34 also being retained in place against the flange 38 bythe screws 3|.

The inner housing section 22 is also provided with .aninternal flange which defines an axial opening in which a ball vbearing 38 is disposed. An internal'driving element 49 is composed of axially `aligned components 4| and 42 which are secured together by studs 43 and nuts 44. The'ends of the components 4| and 42- are reduced in diameter tol adapt them to be received in the inner' races of the respective ball bearings 33 and 36. Held v-w-ithin the end of the component 42 of the driving element 40 by a transverse pin 45 is one element 46 ofthe coupling means 25.

The forward end ofl the component 4| of the vdriving element 49 is provided with a bore'in which is held a pair of ball bearings 48 and 49 which are retained in axially spaced relationship Rotatable within the extending blades 56 on the forward face of the Wheel adjacent its periphery. AS shown in Fig. 1,

the turbine wheel 55 is keyed to the shaft 52 as indicated at 51 and is held axially in place by nut means 58 screwed onto the forward threaded end ofthe shaft, a spacer ring 59 beingdisposed bef tween the rearward side of the wheel and the ball bearing 48.

As shown in Figs. l and 2, the forward housing section 24. has a central annular portion 82 which is joined to a circular wall 83'. Extending radially outward'from the portion 62. is an inclined circular wall'64 which is provided at its periphery with an annulariiange-like portion 85. Provided inthe portion 65 is a plurality of substantially tangential nozzles having nozzle openings 96 which, as shown in Fig. 4, are defined in part by` inclined partitions or vanes 61. "63,64, 65 of the turbine housing section 24, together with thev forwardannular wall of the in- The walls 62,

termediate housing section 23, define ahelical or scr'oll'pas'sage', a'tangentialtubular portion 691 providing an air'inietcommunicating 'with-fthe passage.v By this construction, compressedair introduced into the scroll passage 68'by wayiof the vinlet 69 passes through the inclined nozzle openings 68 and impinges against the-blades56 of the turbine wheel 55 to rotate the latter, the air, after performing l its work, discharging through'an'axial passage19, defined by the annular portion 62, and through a screen 1-l in this passage. The turbine unit thus is of the substantially radially inward, axial discharge flow type, this form of turbine having been found' to be highly efficient in operation and especially suiti able for lthe present starter device.

1 The outer component 4| of the driving element 46 has a flange 13 provided with three bores in -which ball bearings 14 are disposed and retained by rings 15. Planetary gear shafts 16 have 'one of their ends rotatably disposed in the ball bearings 14 and their opposite endsl rotatable in :roller bearings 11 positioned in apertures 18 of the inner component 42. The shafts 16 are providedwith integral gears 19 and flanges. Carried by the shafts 16 between the flanges 88 and the inner races of the ball bearings 14 are larger gears 8|, thel teeth of which mesh with the teeth ofz the f sun gear 53. Each pair of gears 8| and 19 -constitutes a compound planetary gear since each is carried by one of the shafts-15 and rotatable therewith.

As thusfar'described, vrotation` of theturbine wheel shaft 52 and sun gear`53 will merely impart rotation to the gears 8|, shafts 16 and gears However, in order to transmit power from the wheel shaft 52 to the driving element 40 and the element 48 of the coupling means 25, preferably at a reduced rate of speed, means are embodied in the starter device for causing the shafts 16 to revolve in anorbit around the sun gear 53. This means consists of a ring gear 85 having inv ternal gear teeth with which the teeth of the ends engaging the rings 9| and 92. Yapparent that normally the ring gear is'held planetary gears 19 mesh. The orbit gear 85 is rotatable in a circular opening 86 in the intermediate housing section 23 and has an annular ange81, a side of which is disposed against a plurality of friction discs 88 fast within the section.

A friction clutch 99 is disposed within the housing section 22 and includes a pair of rings 9| and 92, the latter being disposed in an annular recess 93- ofthe section. The rings 9| and 92 are joined by pins 94 and the clutch 99 is held against rota- :tion` by lugs 95 on the ring 9| (Fig. 1) engageable in slots 98 in the inner face of the housing section 23 (Fig. 6). The ring 9| is provided with a plurality of friction discs 91 which normally engage against the inner face of the flange 81`of the orbit gear 85 as shown in Fig. 1, the ringl 9| being urged in a direction to maintain such engagement by means of compression springs 98 Surrounding the connecting pins 94 with their It is thus stationary so that during rotation of the sun gear 53 the compuond planetary gear 8|, 19 is caused to travel around the ring'gear to thus transmit power to the driving element 48 and coupling element 46 at a speed of rotation which is considerably less than that of the turbine wheel shaft 52. It is also to be noted that when the couplingelement 46 is subjected to a loadin excess of a predetermined value, suicient torque maybe applied by the shaft 52 through the compound planetary gears' 8|,"19 t0 the ring gear 85 to cause the latter to "completely or partially' overcome frlctional resistance of the discs 88 and 91 to produce slippage. When this condition prevails, the compound planetary gears 8|, 19 will merely rotate on their own aXes and may or may not revolve about the sun gear 53, depending upon the degree of slippage occurring between the orbit gear 85 and the friction discs 88, 91.

The coupling device 25 includes, in addition to the element 46, an outer element which is disposed coaxially with the element 46, the element |00 being hereinafter referred to as a drive shaft since it is adapted for connection with the engine to be started. The drive shaft |00 is provided with an intermediate portion |0I which is rotatable in .a bearing plate |02 secured to the end of the inner housing section 22, a sealing ring |03 being employed to prevent escape of lubricant from the housing 2|. The drive shaft |00 has a reduced outer end |04 which projects from the housing section 22 and which has a uted periphery (Figs. l and 3). The inner end |05 of the drive shaft |00 is annular and surrounds the inner end |06 of the coupling element 46. The end |05 is provided with a pair of bosses I I0 having bearing holes in which weighted pawls III are pivotally mounted (Figs. l and 7). The pawls III have pointed ends ||2 which are adapted to be disposed in recesses II3 formed on the periphery of the inner end |06 of the element 45 as shown in Fig. '7, the recesses providing shoulders II4. The pawls normally are retained in this position by means of leaf springs I6 which have one of their ends secured within the end |05 and their free ends engaging the pawls.

The entire starter device I1 is adapted to be detachably secured to an end of a turbo-j-et or turbo-propeller engine I5, the inner housing section 22 being provided with a peripheral ange I8 having holes I I9 through which bolts |20 can be inserted and screwed into holes in the end of the engine I5. The fluted end |04 is adapted to enter a splined end of a shaft |2I of the engine I5 to provide a positive driving connection therewith so that when the drive shaft is driven by the turbine wheel 55 of the shaft of the engine is likewise rotated. While the starter device I1 is herein illustrated as attached to the engine I5 by the bolts |20, it may be detachably connected thereto by means of a suitable quick disconnect means, such means providing for quick removal of the starter device from the engine for inspection, repair, etc. In some airplanes, particularly those of the high speed military types, it may be highly desirable to conserve even the relatively small weight of the starter device. In this case, the starter device may be attached to the engine by the quick-disconnect means only until the latter is started and quickly disconnected therefrom after continuous operation of the engine is assured, the device then being removed from the airplane and retained on the ground. In other words, the starter device may be either airborne or incorporated with a. mobile ground servicing power plant. As previously pointed out. the quick-disconnect means forms no part of the present invention and for this reason is not herein disclosed in detail.

It has been stated that the starter devices I1 and I 8 are adapted to be operated by compressed air introduced into the scroll housing section 24 by way of the inlet passage 69, the motive air then being directed substantially radially through the inclined nozzles 66 where it impinges against the blades 58 of the turbine Wheel 55 to rotate Y the latter at a high rate of speed, the air then discharging from the starter device in an axial direction through the exhaust opening 10. Rotation of the turbine wheel 55 and its shaft 52 and sun gear 53, causes rotation of the compound planetary gears 8|, 19. As rotation of the coupling element 46 is started, the shoulders I|4 thereof, acting against the ends II2 of the pawls III, transmit torque to the drive shaft |00 and thence to the engine shaft I2| to rotate the same.

The strength of the clutch springs 98 is so calculated that complete fixation of the orbit gear Occurs immediately in the engine starting cycle and thus during the starting operation full power is transmitted to the engine and high speed of the latter is rapidly attained, that is, the speed of the engine is increased to a point at which the jet engine can satisfactorily accelerate itself to operating speed. When this latter speed of the engine is attained, centrifugal force and torque of sufficient magnitude is imposed on the weighted driving pawls III to cause them to pivot outwardly, as indicated by the broken lines in Fig. 7, against the action of the leaf springs I I8. Consequently, the transmission of power from the turbine wheel 55 to the engine shaft |2| is automatically disrupted and, since the starter then performs no further work, it can be stopped.

As previously mentioned, the pneumatic starter device is adapted to be operated by compressed air derived from any suitable source. It has been determined, however, that a small light weight auxiliary power plant of the type illustrated at 20 in Fig. 8 is especially suitable for the purpose. The auxiliary power plant 20 is preferably of the same type as that fully disclosed in my co-pending application titled Gas Turbine Auxiliary Power Plant, Serial No. 42,934, filed August 6, 1948, to which reference is made for a detailed description thereof. Suffice it to state herein that the auxiliary power unit 20 includes a hot gas turbine unit |25 which drives an air compressor unit |25 disposed in alignment with the unit |25. Air is drawn into the multi-stage air compressor unit through an inlet |21, the compressed air then passing through combustion chambers |28 wherein the enthalpy of the compressed air is increased by the combustion of fuel therein, the hot gas then passing through ducts |20 to enter the turbine scroll housing |30 and being directed through nozzles against the blades of a turbine wheel which is operatively connected to drive the compressor unit. The ow of air through the cycle referred to above is indicated by full line arrows in Fig. 8.

A portion of the air compressed in the unit |26 is bled therefrom at points |33 and, when the power unit 20 is installed in an airplane, this air may be diverted to the airplane pneumatic power system or to other pneumatically operated mechanisms through branch tubes I 34 and a duct |35. In the pneumatic starter system disclosed in Fig. 8, a portion of the compressed air flowing through the duct |35 is adapted to be diverted to either or both of the two engine starter devices II and |8 by way of respective ducts |31 and |38 connected between th-e duct |35 and the inlet tubes 69 of the starter devices. Valves |40 and 4| are disposed in the respective ducts |31 and |38 and adapted to control the flow of the compressed air to the pneumatic starters. When the valves |40 and |4| are opened, the flow of air bled from the compressor |26, through the starters, is as indicated by the broken arrows in Fig. 8.

As thus far described. the entire starter system whichincludes the starters- I1. and 1.8, the auxilis4 adapted for iinstallationin, an aircraft and, Where-Wholly feasible, suenan airbornearrange- `ment :is obviously preferable. "By' installing the systemin the aircraft `so vthat it is a component thereof, many advantagesareattained. Forexample, a major advantage resides in the fact vthat the starter system-'isfalways available for use so that the aircraft engines can be started at any time, regardless ofthe'location ofthe craft, and it is unnecessary toy return the airplane to the base from whenceit flew in order ltha-tits engines may be subsequently re-started. Thus, by this arrangement itA is possible to quicklyy start the individual engines of a groupof airplanes without relying upon. an outside sourcel. of` power 'forfoperating. the starters thereof, and; the takerofl 'of the; group-of airplanesV isl greatlyv expedited; 'As

'will beV apparent, this isof extreme importance especially when combat airplanes-must "leave` the liield quickly to intercept .enemy/craft. Shoulda forced landingV becomeY necessary, the engine or engines of the airplane 'may'r be subsequently started at the location where-the airplane lands, it Abeing unnecessaryto lawait -the arrivar-of a. mobile ground power plant for the purpose.

In most airplanes, the installation of the instant starter devices and auxiliary power plant is wholly practical since both units are compact and extremely light in weight. In this respect, it is pointed out that the weight of a single pneumatic starter of the type disclosed herein and having a horse power rating of 35 is approximately 15 pounds and that of the auxiliary power plant is approximately 68 pounds so that the major components of the airborne system weigh approximately 83 pounds. Compared to, for example, an electric starter system, this represents a material saving in weight since an electric starter of comparable horsepower Weighs approximately 45 pounds and storage batteries for operating the starter weigh approximately 160 pounds, the total weight of the major components of an airborne electric system thus being approximately 205 pounds or substantially 21/2 times that of the present pneumatic system. It is thus seen that the pneumatic starter system, illustrated herein by Way of example, at least partially solves the problem of weight and provides a highly eflicient and practical means for effecting an unlimited number of engine-starting operations without assistance from an outside source of power such as a ground power plant. Moreover, the auxiliary power plant which supplies compressed air for operating the starter unit or starter units may also serve various other functions such as providing (l) a pneumatic or direct mechanical drive for an aircraft alternator, (2) providing hot gas for wing dei-icing purposes, (3) providing compressed air for operating an air-cycle refrigerating unit for conditioning aircraft cabins on the ground, and (4) providing, with proper heat exchangers, means for heating aircraft engines, cabins, etc. It is thus seen that by the system described above a portion of the available compressed air from the auxiliary power plant may be utilized for operating the engine starter devices. In other words, when the auxiliary power plant is installed in the airplane, an adequate supply of compressed air is always available.

While the engine starter has been described as embodied in a system of an airborne type, i-t may also be advantageously employed in connection with a system in which the auxiliary power plant 1:0 is not installeddn the' airplane but rather is a mobileground power plant. As' previously indicated, in "the casel'ofhi'gh speed turbo-jet and turbo-propeller airplanes, the over-all weight of the craft may be extremely critical and it may be highly desirablefto omit such accessories as the auxiliary power plant,A and even the starter'devices,` from the airplane.` In otherwords, it may be'deemed moreexp'edient to sacrice the convenience and other desir-'abilities of having the starter system 'installed' inthe airplane for the saving. in weight,` even though the' present system is of. considerablylighter weight than other systemsV heretofore.- proposed. `In such case, the auxiliary power plant 'isadapted to be mounted on a mobile servicing cart'which can` be readily propelledto a` location adjacent the turbineengine to ber started, compressed-air then 'being forced through a. flexible'renforced hose to the inlet of the? air 'turbinefof the starter device. A servicing cart of this typem'ay also-bev employed for preheatingthe airplane engine and the cabin or cockpit of the craft. Such aservicing unit is comparatively light in weight and therefore-is v`more conveniently moved into operative position than 'similar units employed in conjunction'with electric starter `devicesand employing electric generators driven by large, heavy, internal combustion engines.

I claim as my invention:

l. In a prime mover actuated engine starting device: a housing; a hollow driving element Within said housing; spaced main outer bearings respectively supporting said element at its ends for rotational movements; spaced inner bearings at one end of said element; a prime mover shaft extending into said element, and being supported for rotational movement in said spaced inner bearings; a rotatably supported drive shaft at the other end of said element adapted to be operatively connected to a shaft of said engine; transmission means interconnecting said prime mover shaft and said element; and coupling means for connecting and disconnecting said drive shaft and said element.

2. In a turbine actuated engine starting device: a housing; a hollow driving element within said housing; spaced main outer bearings respectively supporting said element at its ends for rotational movements; spaced inner bearings adjacent one end of said element; a turbine wheel; a shaft extending from one side only of said wheel into said element, said shaft being supported for rotational movement in said spaced inner bearings; a rotatably supported drive shaft at the other end of said element adapted to be operatively connected to a shaft of said engine; transmission means interconnecting said turbine wheel shaft and said element; and coupling means for connecting and disconnecting said drive shaft and said element.

3. In a prime mover actuated engine starting device: a housing; a hollow driving element Within said housing; spaced main outer bearings respectively supporting said element at its ends for rotational movements; spaced inner bearings at one end of said element; a prime mover shaft extending into said element, and being supported for rotational movement in said spaced inner bearings; a rotatably supported drive shaft at the other end of said element adapted to -be operatively connected to a shaft of said engine; transmission means interconnecting said prime mover shaft and said element; and coupling means normally connecting said drive shaft and said element for unitary movement, said coupling means having parts centrifugally actuatable to disconnect said drive shaft and said element at a predetermined speed of rotation.

4. In a prime mover actuated engine starting device: a housing; a hollow driving element within said housing; spaced main outer bearings respectively supporting said element at its ends for rotational movements; spaced inner bearings adjacent one end of said element; a prime mover shaft extending into said element, and being supported for rotational movement in said spaced inner bearings; a drive shaft rotatably supported on the other end of said element adapted to be operatively connected to a shaft of said engine; torque limiting transmission means interconnecting said prime mover shaft and said element; and coupling means for connecting and disconnecting said drive shaft and said element.

5. In a prime mover actuated engine starting device: a housing; a hollow driving element within said housing; spaced main outer bearings respectively supporting said element at its ends for rotational movements; spaced inner bearings at one end of said element; a prime mover shaft extending into said element, and being supported for rotational movement in said spaced inner 12 bearings; means for drivingly connecting the other end of said element to a shaft of said engine; a sun gear carried by said prime mover shaft; an orbit gear surrounding said element intermediate its ends; planet gears carried by said element interconnecting said sun gear and orbit gear; and a friction clutch connecting said or-bit gear and adjacent portion of said housing.

HOMER J. WOOD.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS