Patent Publication Number: US-3876334-A

Title: Variable pitch rate means

Description:
United States Patent 1 Andrews VARIABLE PITCH RATE MEANS [75) Inventor: Merritt B. Andrews, Westfield,  
 Mass.  
 [73] Assignee: United Aircraft Corporation, East Hartford, Conn.  
  221 Filed: Apr. 8, 1974 211 ApplNo.:459,2 14  
 1 1 Apr. 8, 1975 2.491.260 12/1949 Green 416/160 X 3.816021 6/ 1974 Lewis et a1 3.820916 6/1974 Agushev et a1. 415/152 FOREIGN PATENTS OR APPLICATIONS 70.616 2/1950 Denmark 416/160 1 103.512 3/1961 Germany n 1,143.223 2/1963 Germany 416/160 Primary Examiner-Everette A. Powell, Jr. Attorney, Agent, or Firm-Norman Friedland [57] ABSTRACT The pitch velocity of alternate and individual high solidity variable pitch blades of a bypass fan propulsor vary so as to pass through zero or flat pitch at different intervals, although ending at the same pitch at the extent of their traveI.  
 8 Claims, 4 Drawing Figures 3 m 1 or 2 PIJEIHEEAPR ems BACKGROUND OF THE INVENTION This invention relates to variable pitch fan blades of a bypass ducted fan propulsor and particularly to means for varying the blade pitch rates.  
  In blade pitch change systems it has always been desirable to provide variable blade pitch rates. Variable rates allow for rapid reversing with a minimum size pitch change power supply. This results in reduced power drain and associated reduced heat generation, reduced weight and envelope. To provide this feature, current blade actuation systems have nonlinear cams in the dome section of the actuator. More recent heretofore known actuators utilize a scotch yoke principle by attaching a roller trunnion to the blade. Here the effective moment arm of the trunnion is sequenced to vary essentially inversely with the blade moment reactions, thus affecting variable rate at constant power demand. Alternate systems have utilized such features as reduced actuator areas to low pitch. This affords dissimilar reverse increase pitch rates. Although this is not specifically tailored to the typical sinusoidal blade moment reaction load like the cam and scotch yoke some advantage can be gained.  
  This particular features, i.e., variable pitch rate, may be particularly efficacious for the type of propulsors known as Q-Fan being developed by the Hamilton Standard Division of United Aircraft Corporation. An understanding of this type of propulsor may be had by referring to US Pat. No. 3,747,343 granted to G. Rosen on July 24, 1973 and assigned to the same as signee, which is incorporated herein by reference.  
  This invention is particularly suitable in the event that the fan blades are designed to have a solidity factor greater than one resulting in the situation where adjacent blades will interfere with each other if they are passed through flat pitch at the same time, thus, making conventional reversing impossible.  
  I can obviate this problem, obtain the advantages enumerated above, by providing means to allow alternate blades to be reversed in sequence with their adjacent blades. Hence flat pitch reversing with blades of solidities greater than one can be effectuated. My invention contemplates a simple means of accomplishing variable pitch rate while achieving an improvement in power and envelope size.  
 SUMMARY OF THE INVENTION An object ofthis invention is to provide for a propulsor means for varying the pitch rate of fan blades.  
  A still further object of this invention is to provide for a variable pitch ducted bypass fan having blade solidi ties of greater than one, means for varying the pitch rate by a rotating ring-like gear having a predetermined wave-like shape mating with a noncircular pinion gear rotating the blades about their pitch changing axis.  
  Other features and advantages will be apparent from the specification and claims and from the accompany drawings which illustrate an embodiment of the inventron.  
 BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a perspective view partly in section schematically illustrating the invention.  
  FIG. 2(A) is a projected view showing the relationship of adjacent blades when in the take-off pitch position.  
  FIG. 2(B) is a projected view showing the relationship of adjacent blades in the transition from positive to reverse pitch.  
  FIG. 2(C) is a projected view showing the relationship of adjacent blades when the blades are in reverse.  
 DESCRIPTION OF THE PREFERRED EMBODIMENT Reference is now made to FIGS. I and 2(A), (B) and (C) which shows the preferred embodiment of this invention consisting of a plurality of fan blades of the type shown in U.S. Pat. No. 3,747,343, supra. In the O Fan installation as described above a plurality of fan blades are circumferentially supported in a hub for pitch change movement. This invention contemplates any of the well known systems that include a rotary type of actuator for effectuating the pitch change. Although there are numerous illustrations of a suitable rotating pitch change actuator, the type shown in U.S. Application Ser. No. 334,334 filed by me on Feb. 2|, I973 and assigned to the same assignee is exemplary.  
  As schematically shown in FIG. 1, shank or root 10 of fan blade 12 is rotatably supported for pitch change movement about axis 14 in rotating hub 16 in any suit able manner. In accordance with this invention. a non circular gear 18 is secured or connected to shank II) in any well known manner and meshes with ring gear 20. Ring gear 20 is connected to or apart of the rotating actuator( Not shown) and is moved in clockwise or coun terclockwise position relative to gear 18 for effectuating the rotation and hence pitch change movement.  
  Since the radius of gear l8 radiates from the pitch change axis, movement of gear 20 at a constant velocity will cause a variable pitch change rate. The mating surface 22 complimenting the shape of noncircular gear 18 is so shaped that the respective teeth are always in mesh. The shape of surface 22 is considered to be wave like or sinusoidal when viewed in a plane trans verse to its axis 24.  
  The relationship of the adjacent blades are best illustrated in FIG. 2(A), (B) and (C), showing a movement from the take-off(FlG. 2(A) through flat pitch (FIG. 2(B) and reverse (FIG. 2(C) It will be apparent from an inspection of FIG. 2 that the shorter radius of noncircular gear 18 meshes with the high point of ring gear 20. Thus, since adjacent blades are at different radii from the pitch change axis, the rate of pitch change will vary so that when the blades pass through flat pitch, adjacent blades will pass through at different points in time avoiding a leading edge to trailing edge contact (FIG. 2 (B) it being noted that the width of the blades overlap. The blade angles as indicated have the following relationship: B and B are not equal while (1 equals 0: and 6 equals 62 It will also be ap preciated tha the concept is only applicable when the number of blades are even.  
  This concept has the added advantage in that if there is a blade pitch actuation system failure that would inadvertantly let the blade angle drop to flat pitch, which is normal open system type failure, the resulting over speed which may be devastating will be limited by virtue of the fact that one half the blades generate a clockwise torque and the other half produces a counter-clockwise torque. As will be obvious to one skilled in the art this feature may be desirable to use on variable pitch fans of the type where reverse is through flat pitch even though the solidity may be less than one.  
  Thus. what has been shown by this invention is a simple means for effectuating varying pitch change rates of adjacent blades in a fan. The noncircular segment gear on each blade shank mate with a common ramped ring gear driven by a rotary actuator. Linear rotation of the ring gear causes nonlinear rotation of the blades in a simple and reliable manner.  
  It should be understood that the invention is not limited to the particular embodiments shown and described herein, but that various changes and modifications may be made without departing from the spirit or scope of this novel concept as defined by the following claims.  
 I claim:  
  1. Pitch change means for a propulsor having a plurality of blades circumferentially supported in a rotatable hub and means, including a pitch change actuator, for varying the pitch thereof. and additional means for varying the rate of change of alternate of said blades and means for imparting motion to said actuator.  
  2. Pitch change means as defined as in claim 1 wherein said pitch change actuator is rotational.  
  3. Pitch change means as claimed in claim 1 wherein the blades have a solidity factor of one or greater.  
 4. ln a propulsor for aircraft having a turbine type of power plant driving a variable pitch fan mounted in a power plant bypass duct, a hub supporting a plurality of fan blades that are so dimensioned that adjacent blades when in a given plane overlap each other, means for varying the rate of change of each and alternate blades so that adjacent blades pass through the plane where interference occurs at different intervals.  
  5. Pitch change actuating means for a bariable pitch propulsor having a hub supporting a plurality of circumerentially mounted blades for pitch change movement, said means including a ring-like gear having a nonuniform surface, a noncircular gear operatively connected to each of said blades mating with teeth formed in said nonuniform surface such that alternate nonuniform gears are spaced equidistant from a plane taken transverse through the axis of rotation of said ring-like gear and the center of rotation of said noncircular gears, means for imparting rotary motion to said ring-like gear for effectuating pitch change whereby the pitch rate of alternate blades will vary.  
  6. Pitch change actuating means as claimed in claim 5 wherein said noncircular gear is segmented.  
  7. Pitch change actuating means as claimed in claim 5 wherein said nonuniform surface takes a sinusoidal shape.  
 8. Pitch change actuating means as claimed in claim 5 wherein said blades have solidity greater than one.