US2918978A - Variable contour propeller blades - Google Patents

Description

Dec. 29, 1959 R. A. FANTI VARIABLE coNTouR PROPELLER BLADES Filed Feb. 11

ATTORNEY UnitedStates Patent O VARIABLE CONTOUR PROPELLER BLADES Roy A. Fanti, Springfield, Mass., assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application February 11, 1957, Serial No. 639,377

1 Claim. (C1. 17o-160.24)

This invention relates to propellers and more specically to propellers having variable contour blades.

It is an object of this invention to provide propellers having blades which achieve high lift at low angles of attack. l

It is another object of this invention to provide propellers having blades Ahaving improved stall flutter boundaries as compared to iixed contoured or cambered blades.

It is a still further object of this invention to provide exible boots over a substantial span of the blades on the upper and lower major surfaces near the trailing edge of the blade.

It is a still further object of this invention to provide flexible boots which can be selectively inflated to asymmetrically vary the prole of the trailing edge of the blade.

These and other objects of this invention will become readily apparent from the following detailed description of the drawing in which:

Fig. l is a partial showing of a propeller blade illustrating the varied contour of the trailing edge thereof;

Fig. 2 is an illustration in partial cross section of a propeller hub having a blade of variable contour;

Fig. 3 shows a typical cross section through the propeller blade of Fig. 2; and

Figs. 4, 5 and 6 illustrate the various propeller contours for different operative conditions.

Referring to Fig. l, a typical propeller blade portion is generally indicated at and includes upper and lower major surfaces 12 and 14. A typical expanded boot 18 is illustrated so as to change the contour as seen by the line 20 adjacent the blade trailing edge to improve or increase the lift of the propeller blade at low speeds. The boot 1S normally lies ush with the lower major surface 14 of the propeller blade as seen in Fig. 3, while another boot 22 normally lies llush with the upper major surface 12 of the blade. It is thus desired to have an on-off type of operation so as to improve the characteristics of the basic blade configuration.

Thus, as seen in Fig. 2, a propeller hub is generally indicated at 30 as having a propeller blade 32 carried thereby. The blade is shown in substantially feathered position for convenience of illustration of the inside thereof. The blade may be hollow or solid but includes a pair of pipes 34 and 36 (see also Fig. 3), respectively, which lead to a plurality of linger-like feed lines 38 and 40. The lines 38 open upwardly to the underside of the boot 22, while the pipes 40 lead to the underside of the boot 18. Fluid to the lines 34 and 36 is conducted from suitable sources of drain and pressure by means of valves 44 and 46, respectively, which are carried in from fixed part of the aircraft and mounted on nonrotatable structure. Fluid under pressure may be transferred from the valves 44 and 46 to the lines 34 and 36 in the rotating propeller hub by any suitable means as, for example, shown in Patent No. 2,296,288 issued September 12,

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1942, to Martin et al. or in Patent No. 2,338,483 issued January 4, 1944, to Beebe, Jr.

Thus, by contouring the valves 44 and 46, the boots 18 and 22 can be selectively inflated or deated to improve the lift characteristics and stall flutter boundary of the propeller for various operative conditions.

The stall flutter boundary may be best described in connection with the problem solved. The application of,

be used at the outerstations of the propeller blade.l

However, the use of these airfoil sections compromises the off-design operating conditions because of the inherent lower stall angles of these sections as compared to those of thick, high-camber propeller sections. Consequently, not only is the take-off thrust potential of the propeller reduced, but also the propeller becomes more susceptible to the single degree-of-freedom instability known as stall flutter. That is to say when the blade operates stalled during all or a portion of its cycle of oscillation, energy may be extracted from the airstream to maintain these oscillations. Experience shows that these critical conditions are functions of the mean angle of attack of operation of the blade and the flow velocity. rhe particular critical points at specified angle of attack and flow velocity combinations form the boundary between stable and unstable operating conditions-hence form the so-called Stall Flutter Boundary. Thus, as seen in Fig. 4, for normal high speed operation the relative air will be approaching the airfoil 48 in the direction of the arrow. In this condition both the boot 18 and the boot 22 are flush with the outer airfoil surface to provide low drag at the high speed position. On the other hand, as seen in Fig. 5, when the propeller blades are rotating at a relatively low speed and high positive thrust is desired, the boot 18 is expanded so as to vary the contour of only one of the major surfaces of the airfoil. It will be noted that although the effect of a ap is obtained, a ap when moved varies the contour of both the upper and major surfaces of the airfoil.

Then, as seen in Fig. 6, where the relative air is as shown by the arrow, reverse thrust or lift is being provided by the airfoil and the boot 22 is expanded to provide good low speed air ow conditions.

The particular profile desired may be obtained by providing prestressed or variable stiffness boot material; or

the material may have a variable thickness to provide the l difference in stretch at different chordwise positions.

It should be noted herein that by applying the contour varying mechanism to the trailing edge, we obtain a higher lift at low angles of attack so that the concept herein dilfers from devices which attempt to vary the camber of the leading edge of airfoils. Leading edge devices are intended to obtain higher angles of attack for the basic airfoil before a breakdown of liow occurs or stall ensues. Furthermore, higher angles of deflection of the contour can be obtained from this type of device as compared to leading edge mechanisms.

Furthermore, the reverse thrust stall flutter boundary of the device described herein will be much better than any leading edge camber modification. When the blade operates at negative values of lift, we say it operates in a reversed thrust condition. The flutter boundary curves so defined at these negative values of lift are called the reversed thrust Stall Flutter Boundary.

As `a. result of this invention it is apparent that a very simple, easily operated-meanshas been provided for practically Varying the contour of one of the major surfaces of a propeller blade adjacent the trailing edge of the blade. With this device good low speed, high thrust stall utter free characteristics-are*obtained at a minimum weight expense.

Although only one embodiment of this invention lhas been illustrated and described herein, it will become readily yapparent that various changes yand modifications may be made in the construction and arrangement of the various parts without departing from the scope of this novel concept.

What is desired by Letters Patent is:

` In a propeller having a hub, a plurality of blades carried by said hub having upper and lower major aerody` namic surfaces, means for varying the camber of each of said blades including inllatable resilient boots extending over a major part of the span of each of said blades and being located adjacent the trailing edges thereof, said boots being located on said upper and lower major surfaces of said blades and extending over only a minor portion of the chordwise dimension of said blades, said trailing edges normally being relatively sharp, said boots in the deflated position lying substantially flush with the remainder of said major surfaces, means for selectivelyy varying the contour of said boots and thereby selectively usV altering'the contour of either the upper or lower surfaces respectively of all the blades simultaneously whereby the trailing edge of each blade becomes relatively blunt and rounded for operation in positive or negative pitch posi- -ton respectively, said lasst-mentioned means including a source of fluid under pressure, a lsource of relatively low pressure, nonrotatable means operatively connected to said sources, and means connecting said nonrotatable means with the interior of said hub including valving for simultaneously conducting fluid to or from said boots on the same side of all the blades.

References Cited in thel le of this patent UNITED STATES PATENTS 2,011,902 Leigh Allg. 20, 1935 2,021,470 Upson Nov. 19, 1935 2,023,760 Dornier Dec. l0, 1935 2,296,288 Martin et al. Sept.y 22, 1942 2,338,483 Beebe Jan'. 4, v1944 2,400,388 Campbell May 14, 194.6 2,616,509 Thomas Nov. 4, 1952 FQREIGN PATENTS. 617,058 Germany Aug. l0, 1935

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