US2222444A

US2222444A - Airplane propeller

Info

Publication number: US2222444A
Application number: US324506A
Authority: US
Inventors: Leopold C Schmidt; Walter J Schmidt
Original assignee: Individual
Current assignee: Individual
Priority date: 1940-03-18
Filing date: 1940-03-18
Publication date: 1940-11-19
Anticipated expiration: 1957-11-19

Description

1940- c. SCHMIDT ET AL 12 2 AIRPLANE PROPELLER Original Filed Sept. 15, 1957 IN VENTOR.

AT'TORNEY.

Patented Nov. 19, 1940 UNITED STATES AIRPLANE PROPELLER Leopold C. Schmidt and Walter J. Schmidt, Jersey City, N. J.

Refiled for abandoned application Serial No.

163,516, September 13, 1937.

This application March 18, 1940, Serial No. 324,506

1 Claim.

The present application is a refile of our previous application filed September 13, 1937, Serial No. 163,516 and comprises an improved airplane propeller having aplurality of blades of different length, the length of each successive blade being in a definite relation to the one preceding it.

It is a well known fact that airplane propellers having more than one blade of equal length are very inefiicient. This is due to the fact that the high speed of one propeller blade will create an aerial void which will not have time to become equalized before the next propeller blade enters. The following propeller blade therefore has to operate in this void of wake from the preceding '15 one and it thus works in a partial vacuum or a rarefied air which would be equivalent to operating at a very high altitude. It is well known that no propellers are very effective at extremely high altitudes and it, is therefore readily seen that when the propeller speed exceeds a certain limit the effectiveness of a multiple blade propeller must necessarily be greatly diminished. For this reason it has been variously Suggested to use and try a single blade and while this is possible and gives higher efliciency it has several serious disadvantages due to the dynamic unbalance created. It is furthermore well known that due to the higher peripheral speed the above condition is only prevalent at the outer '30 ends of the propeller blades. The present invention proposes to eliminate all these difficulties by making the propeller blades of various lengths. w The object of our invention is therefore to provide an airplane propeller having a plurality of blades which are of different lengths and where the length of each shorter blade is a definite mathematical proportion to the length of the longer blade. A further object of our invention is to provide a propeller having a plurality of blades of unequal length where each blade is made of a difierent material and where the specific gra'vities of these materials are in a definite mathematical relation to the length of the blades. Still another object of this invention is to provide a multi-blade airplane propeller of higher efliciency and capable of giving increased power at lower speed thus being of smaller size fora given 'power. Other objects and' advantages of the invention will be apparent from the following specification and claim.

In the accompanying drawing, forming a part of this specification," and in which like numerals are employed to designate like parts throughout 5 the same:

Figure 1 is a front view of an airplane propeller having two blades of unequal length, and,

Figure 2 illustrates an airplane propeller having three blades of unequal length.

In the drawing, wherein for the purpose of illustration, is shown a preferred embodiment of our invention, the numeral I ll designates the hub of the propeller which has two blades l2 and I3. ,The blades l2 and I3 are fastened to the hub at I4 and IS. The radius to the tip of the longer blade is given the dimension RI while the radius to the tip of the shorter is given the dimension R2. R3 is the radius to the effective part of the shorter blade.

Referring to Figure 2, the illustrated three '15 blade propeller has a long blade I 6 a shorter blade I1 and a still shorter blade l8 equally spaced around the hub ID. The radius to the tip of the-longer blade is RI, the radius to the tip of the next shorter blade I1 is R2, the radius '20 to the tip of the shortest blade is R3 and the radius to the effective part of the shortest blade I8 is R4. It will be noted that in each case the radius to the tip of a shorter blade is always equal to the radius of the eflective part of the 25 next longer one.

The relation between the various blades can be shown mathematically as follows:

For the purpose of the mathematical treatment the following denotations are used: 30

R1=length of the longest blade R2=length of the next shorter blade R3=length of the next shorter blade I1 =moment of inertia of longest blade 35 I2 =moment of inertia of next shorter blade M1 =mass of the longest blade M2 =mass of the next shorter blade W1=welght of the longest blade Wz=weight of the next shorter blade Q1 =cross section of the longest blade 40 Q2 =cross section of the next shorter blade 'w1 =specific gravity of material used in the longest blade wz =specific gravity of material used in the next shorter blade 9 =acceleratio'n of gravity.

The moment of inertia may be expressed for each blade as follows:

Equation 2 may be further simplified by making Q1=Qz and we have then:

I1/Iz=w1R1 /w2R2 (35 To be dynamically balanced the above ratio of the moments of inertia for a two-bladed propeller must be equal to one. The speed is the same forboth blades, hence we may write:

w1R1 =w2R2 (4) From this equation it is possible to find the proper length of each blade for correct dynamic balance when the blades are made from materials of different specific gravity:

R =RN w /w 5) If for example the two blades of a propeller are made from Dow metal of spec. gr. 1.? and Dural of sp. g. 2.8 we have:

In other words the longest blade must be 18% longer than the shorter one. By using wood or metallic alloys of the desired specific gravities dynamically balanced propellers may be produced which have the proper graduations in blade length to give better efilciency for each blade and less noise and vibration. Propellers with three or more blades may be calculated in the same way. In the latter case the components of the moments of inertia of thetwo or more shorter blades must be equal to the moment of inertia of the longest blade. This may be expressed as follows for a three-blade propeller:

I1=I2.COS 60+13.005 60. hence: I1= /z(1'2+I3).

The ratio for dynamic balance must be one:

I 1 I w Rfi (6) 1 m i U: 3) E t- 2 a 'z Now cos 60=0.5 and From Equation 6 the length of the blades of higher efliciency and of higher power at lower speeds thus permitting a smaller over-all size..

The longer blade of the propeller will create a void in the space between R! and R2, the next shorter blade will work inside of the radius R2 and will thus not be afiected by the wake of the longer blade. the third blade in a three-blade propeller.

It is to be understood that the form of our invention, herewith shown and described is to be taken as a preferred example of same, and that various changes in the shape, size and arrangement of parts may be resorted to without departing from the spirit of our invention, or the scope of the subjoined claim.

Having thus described our invention we claim:

A propeller of the character described having a plurality of blades of unequal length, each shorter blade having its length determined in relation to the length of the next longer blade, by

and each blade being made of a difierent material in such a way that each shorter blade is made of a heavier material than the next longer one and that the specific gravities of these materials be related according to the following formula: w1=w2R2=/R1 LEOPOLD C. SCHMIDT.

WALTER J. SCHMIDT.

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