VARIABLE PITCH AFT PROPELLER VANE SYSTEM

Abstract

A propulsion system includes a rotationally fixed variable pitch vane system located axially aft of a propeller system.

Description

BACKGROUND

The present disclosure relates to a vane propeller system, and more particularly to a straightened slipstream which recovers swirl energy.

Turboprop propeller systems that include a single set of blades which rotate in one direction and in one plane of rotation are known as single rotation propellers. Pitch angles ranging from a fully feathered minimum drag angle to pitch angles which provide reverse thrust are typically provided for propeller speed and power management along a propeller axis of rotation. Turboprop propeller systems provide a relatively high level of propeller efficiency. However, a certain significant amount of efficiency may be lost to the swirl energy that the propeller imparts to the slipstream.

SUMMARY

A propulsion system according to an exemplary aspect of the present disclosure includes a rotationally fixed variable pitch vane system located axially aft of a propeller system.

A flight control method for an aircraft according to an exemplary aspect of the present disclosure includes collectively changing a pitch of a rotationally fixed variable pitch vane system located axially aft of a propeller system.

BRIEF DESCRIPTION OF THE DRAWINGS

Various features will become apparent to those skilled in the art from the following detailed description of the disclosed non-limiting embodiment. The drawings that accompany the detailed description can be briefly described as follows:

FIG. 1 is a general perspective partial fragmentary view of an exemplary gas turbine turboprop engine; and

FIG. 2 is a schematic block diagram of a rotationally fixed variable pitch vane system.

DETAILED DESCRIPTION

FIG. 1 illustrates a general perspective view of a propulsion system 10 that includes a propeller system 20. It should be understood that although a propeller system typical of a turboprop aircraft is illustrated in the disclosed embodiment, various rigid prop/rotor systems including tilt rotor and tilt wing systems will also benefit herefrom.

A gas turbine engine (illustrated schematically at 22) which rotates a turbine output shaft 24 at a high speed. The turbine output shaft 24 drives a gear reduction gearbox (illustrated schematically at 26) which decrease shaft rotation speed and increase output torque. The gearbox 26 drives a propeller shaft 28 which rotate a propeller hub 30 and a plurality of propeller blades 32 which extend therefrom about an axis of rotation A. Axis A is substantially perpendicular to a plane P which is defined by the propeller blades 32.

The plurality of propeller blades 32, in the disclosed, non-limiting embodiment are variable pitch in that each propeller blade 32 may be pitched about a pitch axis B defined along the length of the propeller blade 32. Pitch change of the plurality of propeller blades 32 may be accomplished through a pitch change system 34 operated in response to a blade module 36 to change the pitch of each propeller blade 32. The blade module 36 typically includes a processor 36A, a memory 36B, and an interface 36C (FIG. 2). The processor 36A may be any type of known microprocessor having desired performance characteristics. The memory 36B may include various computer readable mediums which store the data and control algorithms described herein. The interface 36C facilitates communication with a higher level control system such as the flight control computer (FCC) 38 as well as other avionics and systems. The blade module 36 operates to accomplish speed governing, synchrophasing, beta control, feathering, unfeathering and other collective control of the propeller blades 32 as generally understood.

A rotationally fixed variable pitch vane system 40 is located aft of the propeller system 20. The vane system 40 includes a multiple of vanes 42 which may be of approximately the same diameter as the propeller blades 32, however, the number, size, and shape of the vanes 42 may be selected based on a combination of aerodynamic, cost and weight analyses for each specific application.

The vane system 40 includes a vane pitch change system 44 operated in response to a vane module 46 to change the pitch of each vane 42. The vane pitch change system 44 may be of various forms, but is relatively less complicated than that the propeller system 20.

The vane module 46 typically includes a processor 46A, a memory 46B, and an interface 46C (FIG. 2). The processor 46A may be any type of known microprocessor having desired performance characteristics. The memory 46B may include various computer readable mediums which store the data and control algorithms described herein. The interface 46C facilitates communication with a higher level control system such as the flight control computer (FCC) 38 as well as other avionics and systems. It should be understood that the blade module 36 and the vane module 46 may be integrated with each other as well as with the FCC 38.

The pitch angle of the vane system 40 is set by the vane module 46 to straighten the flow, thereby recovering the swirl component from the propeller system 20. In additional, the pitch angle of the vane system 40 is set by the vane module 46 to provide the most thrust at a particular operating point, e.g., take off. The variable pitch provides maximum propulsive efficiency at each operating point but may result in increased weight, and complexity. The pitch angle of the variable pitch vanes 42 may be related as a function of the flight condition to maximize efficiency gains. Alternatively, the vanes 42 may be fixed pitch in which the vane pitch angle is fixed for a particular flight condition that provides the most fuel savings which, in one non-limiting embodiment may be a cruise condition.

In operation, the pitch angle of the vane system 40 is set by the vane module 46 to increase propulsive efficiency to provide significant fuel savings; increase thrust at a given condition and power setting to provide improved take-off climb and cruise performance. Alternatively, the same thrust is achieved at a lower power setting which also increases engine life and fuel savings.

During landing, the pitch angle of the vane system 40 is set by the vane module 46 to flat pitch which increases drag, reduces landing distance and reduces aircraft brake wear. That is, the vane system 40 operates as a speed brake in conjunction with, for example, the propeller blade 32 pitch angle set to reverse pitch.

Furthermore, for other aircraft such as a tilt-rotor aircraft, the pitch angle of the vane system 40 is set by the vane module 46 to a pitch based on an operating point flight condition such as hover flight to increase the efficiency of hover and low speed flight operations.

It should be understood that relative positional terms such as “forward,” “aft,” “upper,” “lower,” “above,” “below,” and the like are with reference to the normal operational attitude of the vehicle and should not be considered otherwise limiting.

It should be understood that like reference numerals identify corresponding or similar elements throughout the several drawings. It should also be understood that although a particular component arrangement is disclosed in the illustrated embodiment, other arrangements will benefit herefrom.

Although particular step sequences are shown, described, and claimed, it should be understood that steps may be performed in any order, separated or combined unless otherwise indicated and will still benefit from the present invention.

The foregoing description is exemplary rather than defined by the limitations within. Various non-limiting embodiments are disclosed herein, however, one of ordinary skill in the art would recognize that various modifications and variations in light of the above teachings will fall within the scope of the appended claims. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described. For that reason the appended claims should be studied to determine true scope and content.

Claims

1. A propulsion system comprising: a propeller system which rotates about an axis of rotation; anda rotationally fixed variable pitch vane system located axially aft of said propeller system.

2. The propulsion system as recited in claim 1, wherein said propeller system includes a plurality of propeller blades and said rotationally fixed variable pitch vane system include a plurality of vanes.

3. The propulsion system as recited in claim 2, wherein said plurality of propeller blades is equal to said plurality of vanes.

4. The propulsion system as recited in claim 2, wherein each of said plurality of propeller blades define a diameter generally equal to a diameter of each of said plurality of vanes.

5. The propulsion system as recited in claim 1, further comprising a vane module operable to collectively change a pitch of each of said plurality of vanes.

6. A flight control method for an aircraft: collectively changing a pitch of a rotationally fixed variable pitch vane system located axially aft of a propeller system.

7. A method as recited in claim 6, further comprising: changing the pitch of the rotationally fixed variable pitch vane system to recover a swirl component generated by the propeller system.

8. A method as recited in claim 6, further comprising: changing the pitch of the rotationally fixed variable pitch vane system to provides maximum propulsive efficiency at a particular operating point.

9. A method as recited in claim 8, further comprising: defining the operating point at a cruise flight condition.

10. A method as recited in claim 6, further comprising: changing the pitch of the rotationally fixed variable pitch vane system to a flat pitch during a landing condition.