US3893638A

US3893638A - Dual cycle fan jet engine for stol aircraft with augmentor wings

Info

Publication number: US3893638A
Application number: US442330A
Authority: US
Inventors: George S Kelley
Original assignee: Boeing Co
Current assignee: Boeing Co
Priority date: 1974-02-14
Filing date: 1974-02-14
Publication date: 1975-07-08
Anticipated expiration: 1992-07-08

Abstract

A dual cycle fan jet engine suitable for use in STOL aircraft with augmentor wings is disclosed. In a cruise mode of operation, primary air and fan air from a fan jet engine are axially exhausted rearwardly in a conventional manner. In an augmentor mode of operation, the primary air is diverted by valves through an augmentor turbine where it is expanded and exhausted at a relatively low velocity, and the fan air is diverted by valves through an augmentor compressor driven by the augmentor turbine. The supercharged output of the augmentor compressor is directed via wing ducting to the augmentor flaps of the associated augmentor wing.

Description

United States Patent [191 Kelley 1 DUAL CYCLE FAN JET ENGINE FOR STOL AIRCRAFT WITH AUGMENTOR WINGS [75] Inventor: George S. Kelley, Bellevue, Wash.

[73] Assignee: The Boeing Company, Seattle,

Wash.

[22] Filed: Feb. 14, 1974 [21] Appl. N0.: 442,330

[52] U.S. Cl 244/12 D; 60/225; 60/226 R; 60/229; 244/42 CC [51] Int. Cl. B64C 15/06 [58] Field of Search.... 244/12 D, 23 D, 23 B, 12 R, 244/12 A, 12 B, 42 CC, 42 CD, 6, 7, 23 R;

1 July 8,1975

3,761,042 9/1973 Denning 244/12 D FOREIGN PATENTS OR APPLICATIONS 1,273,332 8/1961 France 244/12 D Primary Examiner-Trygve M. Blix Assistant ExaminerGalen L. Barefoot Attorney, Agent, or FirmChristensen, O'Connor, Garrison, & Havelka [57] ABSTRACT A dual cycle fan jet engine suitable for use in STOL aircraft with augmentor wings is disclosed. In a cruise mode of operation, primary air and fan air from a fan jet engine are axially exhausted rearwardly in a conventional manner. In an augmentor mode of operation, the primary air is diverted by valves through an augmentor turbine where it is expanded and exhausted at a relatively low velocity, and the fan air is diverted by valves through an augmentor compressor driven by the augmentor turbine. The supercharged output of the augmentor compressor is directed via wing ducting to the augmentor flaps of the associated augmentor wing.

11 Claims, 8 Drawing Figures DUAL CYCLE FAN JET ENGINE FOR STOL AIRCRAFT WITH AUGMENTOR WINGS BACKGROUND OF THE INVENTION This invention is directed toward jet engines, and more particularly, toward jet engines suitable for use with STOL aircraft.

One of the problems with modern air travel, and in particular jet travel, is the cost of developing and maintaining airports. In general, modern airports are expensive because jet aircraft require relatively long runways for takeoff and landing. Because they are expensive, modern airports can only be justified when they are located near large metropolitan areas where there is a large demand for air travel. In these areas, the cost is even greater because the land values adjacent large metropolitan areas are considerably higher than they are in other, less densely populated, areas.

In any event, in recent years, attention has been directed toward developing aircraft which can land and take off from shorter runways. These aircraft are commonly known as short take-off and landing (STOL) aircraft. Because STOL aircraft use much shorter runways, the size of the airports associated with this type of aircraft is greatly reduced making small metropoli tan area airports more feasible.

One type of STOL aircraft that has been proposed utilizes fan jet engines and includes a diverter for diverting fan air from the jet engine into wing ducting. The diverted air exits from the wing ducting and exhausts through augmentor flaps which are retracted to form a portion of the wings during cruise. The flaps are movable and adjustable in a manner such that the fan air assists in lifting the aircraft at a considerably lower velocity than the aircraft can be lifted without the use of ducted fan air and augmentor flaps whereby the aircraft can land on and take off from shorter runways. By properly designing the augmentor wing, the noise output of the aircraft can be kept to a low level.

While STOL aircraft of the foregoing nature have been somewhat satisfactory in that they have a low noise output and improved lift capability, certain problems exist. For example, the pressure of fan air from a standard fan jet engine is inadequate for use with augmentor flaps. Thus, standard fan jet engines must be modified in order to increase the pressure of their fan air. Such modifications, however, decrease the efficiency of the engines under cruise conditions, when augmentor air is not needed.

Therefore, it is the object of this invention to provide a new and improved STOL aircraft engine.

It is a further object of this invention to provide a low noise fan jet engine suitable for use with a STOL aircraft that has good efficiency under cruise conditions.

SUMMARY OF THE INVENTION In accordance with principles of this invention, a dual cycle fan jet engine suitable for use in a STOL aircraft having augmentor wings is provided. In a cruise mode of operation, the primary and fan air outputs of a fan jet engine are axially exhausted to the rear in a conventional manner. In an augmentor mode of operation, the primary air output of the fan jet engine is diverted downwardly through an augmentor turbine. The augmentor turbine removes energy from this air and exhausts it at a relatively low velocity. Hence, this air has a low noise content. At the same time, the fan air is diverted upwardly through an augmentor compressor driven by the augmentor turbine. The compressed or supercharged output of the augmentor compressor is ducted through the wing in a manner such that it is exhausted through the augmentor flaps of the associated wing.

In accordance with further principles of this invention, the primary and fan air flow, either axially in the cruise mode of operation or to the augmentor turbine/- compressor in the augmentor mode of operation, is controlled by opening and closing valves.

In accordance with still other principles of this invention, one valve is opened and closed to control the axial flow of primary air, and a second valve is opened and closed to control the axial flow of fan air. A third valve controls the flow of primary air through the turbine blades of the augmentor turbine. and a fourth valve controls the flow of fan air through the compressor blades of the augmentor compressor.

It will be appreciated that the foregoing brief summary that the invention provides dual cycle fan jet engines suitable for use in a STOL aircraft for diverting and compressing fan air. The compressed fan air is exhausted through the augmentor flaps of the augmentor wings of the aircraft. The fan air is compressed by a compressor driven by a turbine which in turn is driven by the primary air exhausted by the fan jet engine. Be cause the air emitted from the turbine has a relatively low velocity, it has a relatively low noise content. The augmentor air also has a relatively low noise content because the augmentor wing can be designed such that augmentor air is emitted in a low noise content manner.

It will also be appreciated that. in addition to the low noise augmentor mode of operation, the dual cycle fan jet engine of the invention also has a cruise mode of operation suitable for high altitude flying where noise is no problem. The efficiency of the engine in the cruise mode of the operation is much better than in the augmentor mode of operation. Thus, the invention is flexible in that it allows the STOL aircraft to take off from or land on a short runway, yet cruise at relatively high altitudes in an efficient manner.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing objects and many of the attendant advantages of this invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a perspective view of a STOL aircraft;

FIG. 2 is a cross-sectional side view partially in section illustrating a dual cycle fan jet engine formed in accordance with the invention.

FIG. 3 is a perspective view of a vane valve suitable for use by the invention;

FIG. 4 is a front view of a vane valve of the type illus trated in FIG. 3 in an open state;

FIG. 5 is a front view ofa vane valve of the type illustrated in FIG. 3 in a closed state;

FIG. 6 is a side view of a vane suitable for use in a vane valve of the type illustrated in FIGS. 3 through 5;

FIG. 7 is a front view of an annular rotary valve suitable for use by the invention, and,

FIG. 8 is a perspective view of an annular rotary valve of the type illustrated in FIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT The STOL aircraft 11 illustrated in FIG. I comprises a fuselage 13; a vertical stabilizer I5; a horizontal stabilizer l7; wings l9; and, engines 21. The engines 21 are supported beneath the wings I) by struts 23. While only two engines 2] are illustrated in FIG. 1, additional engines may be utilized as necessary. The wings 19 are augmentor wings and include augmentor flaps 25. The augmentor flaps 25 are movable so that air generated by the engines and ducted through the wings can be exhausted through the flaps in a manner that increases the lift capability of the wings, as is well known in the art.

FIG. 2 illustrates a dual cycle fan jet engine 21, formed in accordance with the invention. hung from one of the Wings 19 by one of the struts 23.

The dual cycle fan jet engine 21 illustrated in FIG. 2 comprises a fan jet engine 33. In a conventional manner, outside air is received at the inlet 42 of the fan jet engine 33 and compressed to create primary air. The primary air 35 axially exits from the rear 37 of the front engine 33. During cruise, this air is exhausted rearwardly 36 via a horizontal duct 34 as hereinafter described. Other outside air also received at the inlet 42 of the primary engine 33 is compressed into fan air 44. The fan air 44 axially flows through an enclosed space 39 surrounding the horizontal duct 34 and exhausts from the rear of the engine nacelle 4], during cruise. Thus, in the cruise mode of operation, the primary and fan air axially flow in a conventional manner, ie. the outside air is compressed into primary and fan air and the compressed air is exhausted axially rearwardly in a conventional manner.

In addition to the cruise mode of operation, the dual cycle fan jet engine illustrated in FIG. 2 includes an augmented mode of operation. In the augmented mode of operation, the primary air 35 is diverted from its axial flow path. The diverted primary air 35 is applied to the blades 46 of a plural stage augmentor turbine 49 mounted in a lower vertical duct 50 located beneath and having access to the horizontal duct 34. Diversion ofthe primary air 35 in this manner is controlled by two valves, a primary air exhaust valve 47 and an augmentor turbine inlet valve 45. While the primary air exhaust valve 47 is illustrated as a vane valve and the augmentor turbine inlet valve is illustrated as an annular rotary valve, either of these valves can be formed in other manners, well known to those skilled in the art. Moreover, they can be reversed or both formed in a similar manner. That is, they both could be vane valves or they both could be annular rotary valves.

The primary air exhaust valve 47 is mounted in the horizontal duct 34 downstream from the rear 37 of the fan jet engine. The lower vertical duct is located between the rear 37 of the fan jet engine 33 and the primary air exhaust valve 47. The augmentor turbine inlet valve 45 is mounted in the lower vertical duct 50 between the horizontal duct 34 and the turbine blades 46. When the primary air exhaust valve 47 is closed and the augmentor turbine inlet valve 45 is opened, energy in the primary air 35 acting on the blades 46 rotates a ver tical shaft 53 in a conventional manner. Because en ergy is removed from the primary air 35, the air 48 ex hausting from the augmentor turbine 49 through a plurality of louvers 51 has a low velocity. Because it has a low velocity. it has a low noise content. Preferably, this air is exhausted downwardly and rearwardly so as to provide lift. However, it may be exhausted in other directions. if desired.

Also, forming part of the apparatus of the invention and used during the augmentor mode of operation is an augmentor compressor 57; a fan air control valve 55; and. an augmentor compressor outlet valve 58. The augmentor compressor 57 includes a plurality of blades 52 rotated by the vertical shaft 53 in a conventional manner. The blades 52 are mounted in an upper vertical duct having access from below to the fan air 44 exhausted by the fan jet engine 33. Mounted above the blades 52 of the augmentor compressor 57, as viewed in FIG. 2, is the augmentor compressor outlet valve 58.

The augmentor compressor outlet valve 58 may also take on a variety of forms. For purposes of illustration, it is illustrated as comprising a plate 59 rotatable about a hinge point 62 by a hydraulic cylinder 6]. When the augmentor compressor outlet valve is open, fan air compressed by the augmentor compressor 57 is allowed to flow into a duct '73 located in the strut 23. When the augmentor compressor outlet valve is closed, this flow is prevented.

Cooperating with the augmentor compressor outlet valve 58 is the fan air control valve 55. The fan air control valve 55 annularly surrounds the horizontal duct 34 and either allows fan air to flow past the outside of that duct or prevents such air flow. The fan air control valve allows such fan air flow when the dual cycle fan jet engine of the invention is in its cruise mode of operation and inhibits such flow when it is in its augmentor mode of operation.

In the foregoing manner, fan air is compressed and supplied to the strut and wing duct 73. The strut and wing duct 73 directs the compressed fan air through the strut 23 and wing I9 and emits it into a region between a lower flap 77 and an upper flap 8]. The strut and wing duct and its exhaust region are formed such that the exiting fan air has a low noise content. as is well know in the art.

As will be understood by those skilled in the art and familiar with augmentor wings, the fan air applied between the lower and upper flaps 77 and 81 tremendously increases the lift capability of the wing 19 and, thus, allows the STOL aircraft 11 to take off from and land on relatively short runways. This is the augmented mode of operation.

While the augmented mode of operation greatly improves the lift capability of the aircraft, it is relatively inefficient at cruise speed even if the flaps are moved so as to streamline the wing 13 as illustrated by the dashed lines in FIG. 2. In order to overcome this prob lem, as the STOL aircraft achieves altitude, the dual cycle fan jet engine of the invention shifts from its augmented to its cruise mode of operation. This shift is created by the augmentor tubine inlet valve 45 closing, the primary air exhaust valve 47 opening, the fan air control valve 55 opening and the augmentor compressor outlet valve 58 closing. The primary and secondary engines then operate in a conventional manner.

.ts previously indicated, the augmentor compressor outlet valve 58 may take the form of a plate 59 operated in a rotational manner about a hinge 62 by a hy draulic cylinder 61. The other valves may take on a va riety of forms. One such form is generally illustrated in FIGS. 3 through 6 and another is illustrated in FIGS. 7 and 8.

The valve illustrated in FIGS. 3 through 6 is an annular vane valve and comprises a coaxial hub 82 surrounded by a circular rim 83. Extending radially outwardly from the hub to the rim are a plurality of vanes 84. The vanes are aerodynamically shaped in crosssection and rotatable about their longitudinal axes 85 between two extreme positions. In one extreme position (FIG. 4), the vanes allow air to flow between the hub 82 and the circular rim 83 and create a minimum amount of restriction to such flow. When in this position, the longitudinal axes 86 defined by their aerodynamic shapes are aligned with the direction of the air flow. In the other extreme position (FIG. 5), the vanes 84 prevent the flow of air between the hub 82 and the circular rim 83. Positions in between the extreme positions provide a controlled amount of restriction to such air flow.

The vanes 84 are movable between their extreme positions by any suitable, well known, means. For example, the vanes may be gear coupled together by gears locked inside of the circular rim 83 in a manner such that movement of one gear will cause a simultaneous movement of all of the gears and, thus, their associated vanes. Moreover, the vanes can take on a variety of shapes. They can diverge outwardly, as illustrated in FIGS. 3 through 6. Or, they can be of constant width. Moreover, when the valve is closed, the vanes can overlap by either a small amount or a large amount. Further the amount of overlap can be the same or vary from the hub to the rim.

While a vane valve suitable for use as the primary air exhaust valve 47 has been illustrated in FIGS. 3 through 6, it will be appreciated that the same type of valve can be used for the fan air control valve. In this case, the hub will include a central aperture large enough to surround the outside of the horizontal duct 34.

The valve illustrated in FIGS. 7 and 8 is a rotary annular valve and comprises a pair of circular

vaned plates

89 and 91. Each of the vaned plates includes a plurality of radial vanes 87 separated by open regions 88. The vanes 87 and the open regions are of approximately the same size in area and shape.

The vaned plates are rotatable with respect to one another about a central axis 93 by any suitable means. One such means requires one of the plates to be fixed and the other to include a plurality of peripheral gear teeth 94. The gear teeth 94 coact with a gear 97 rotated by a suitable pneumatic or electrical motor 98 (FIG. 2). When the gear 97 is rotated for a short distance in one direction, the vanes 87 become positioned such that apertures are formed through the two plates. When the gear 97 is rotated in the opposite direction, the vanes become positioned such that no apertures exist through the plates. Alternatively, the vanes may be placed in a multitude of positions between these two extreme positions so as to control the size of the apertures formed through the plates. In a similar manner, a cylindrical annular rotary type valve may be utilized to form the fan air control valve 55 which surrounds the secondary engine 35. Also, as illustrated in FIG. 4, the shaft 53 passes through and lies coaxial with the center of a valve of this type when it is used to form the augmentor turbine inlet valve 45.

It will be appreciated from the foregoing description of the preferred embodiment that a dual cycle fan jet engine suitable for use in a STOL aircraft is provided by the invention. The engine can operate in a standard cruise mode or it can operate in an augmented mode. In the case of the cruise mode of operation. fan air is not applied to the augmentor flaps of the aircraft which are then in a streamlined position. In the augmentor mode of operation, compressed fan air is applied to the augmentor flaps. Also in the augmentor mode. the primary air from the fan jet engine is deflected downwardly to revolve the shaft of a turbine. The thusly driven turbine shaft drives a compressor which compresses fan air. It is this compressed fan air that is ducted to the augmentor flaps of the augmented wing of the aircraft so as to improve the lift capability of the wing.

Because the air exhausting from the turbine has a low velocity, it is a low noise content. The compressed air exiting from the compressor blades and ducted to the augmentor flaps also has a low noise content if the augmentor ducts and associated components are formed in a suitable manner. Thus. the engine of the invention generates a limited amount of noise in the augmentor mode of operation. On the other hand, it is highly efficient in its cruise mode of operation when its noise generation is of little consequence.

While a preferred embodiment of the invention has been illustrated and described, it will be appreciated by those skilled in the art and others that various changes can be made therein without departing from the spirit and scope of the invention. Hence, the invention can be practiced otherwise than as specifically described herein.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

I claim:

I. A dual cycle fan jet engine suitable for use in a STOL aircraft having ducted augmentor wings, said dual cycle fan jet engine comprising:

a fan jet engine adapted to generate primary air and fan air;

air driven means for extracting energy from airflow and generating mechanical power in accordance therewith;

air compression means for compressing air, said air compression means connected to said air driven means so as to be powered by the mechanical power generated by said air driven means;

a horizontal duct extending rearwardly from the primary air outlet of said fan jet engine;

a nacelle surrounding said fan jet engine and said horizontal duct for directing the fan air from said fan jet engine about said horizontal duct;

a first vertical duct connecting said horizontal duct to the inlet of said air driven means;

a second vertical duct connecting said nacelle to the inlet of said air compression means;

a first valve located in said horizontal duct, said first vertical duct being located between the rear of said fan jet engine and said first valve;

a second valve surrounding said horizontal duct, said second vertical duct being located between said fan jet engine and said second valve;

a third valve located in said first vertical duct between said horizontal duct and the inlet of said air driven means; and,

a fourth valve, located on the side of said air compression means remote from the side where said air compression means receives said fan air, for con trolling the flow of fan air from said nacelle to said air compression means.

2. A dual cycle fan jet engine as claimed in claim 1, wherein said first vertical duct is located beneath said horizontal duct and wherein said second vertical duct is located above said horizontal duct.

3. A dual cycle fan jet engine as claimed in claim 2, wherein said air driven means comprises an air turbine and wherein said air compression means comprises an air compressor.

4. A dual cycle fan jet engine as claimed in claim I, wherein said air driven means comprises an air turbine and wherein said air compression means comprises an air compressor.

5. in a STOL aircraft including ducted augmentor wings adapted to direct air energized by a jet engine to augmentor flaps, said augmentor flaps adapted to direct said air generally downwardly and, thereby, aug ment the lift provided by the aerodynamic shape of the wings of said STOL aircraft, the improvement comprising a dual cycle fan jet engine comprising:

a fan jet engine adapted to generate primary air and fan air;

air driven means for extracting energy from air flow and generating power in accordance therewith. said air driven means having an inlet in communication with the primary air of said fan jet engine;

air compression means for compressing air, said air compression means connected to said air driven means so as to be powered by the power generated by said air driven means and said air compression means having an outlet in communication with the duct of one of said ducted augmentor wings of said STOL aircraft;

duct means, mounted between the rear of said fan jet engine said air driven means and said air compression means. for ducting primary air from said fan jet engine between an axial exhaust and said air driven means. and for ducting fan air from said fan jet engine between an axial exhaust and said air compression means; and,

control means for selectively controlling the flow of primary air between said axial exhaust and said air driven means. and for selectively controlling the flow of fan air between said axial exhaust and said air compression means.

6. The improvement claimed in claim 5 wherein said air driven means comprises an air turbine and wherein said air compression means comprises an air compressor. the shaft of said air turbine being connected to the shaft of said air compressor so that said air compressor is mechanically powered by said air turbine.

7. The improvement claimed in claim 5 wherein said duct means comprises:

a first vertical duct connecting said horizontal duct to the inlet of said air driven means; and,

a second vertical duct connecting said nacelle to the air inlet of said air compression means.

8. The improvement claimed in claim 7 wherein said control means comprises:

a third valve mounted so as to control the flow of primary air from said horizontal duct to said air driven means; and,

a fourth valve mounted so as to control the flow of air from said horizontal duct to said air compression means.

9. The improvement claimed in claim 8 wherein said third valve is located in said first vertical duct between said horizontal duct and the inlet of said air driven means; and, wherein said fourth valve is located on the outlet side of said air compression means.

10. The improvement claimed in claim 9 wherein said first vertical duct is located beneath said horizontal duct and wherein said second vertical duct is located above said horizontal duct.

ll. The improvement claimed in claim 10 wherein said air driven means comprises an air turbine wherein said air compression means comprises an air compressor, the shaft of said air turbine being connected to the shaft of said air compressor so that said air compressor is mechanically powered by said air turbine.

Claims

1. A dual cycle fan jet engine suitable for use in a STOL aircraft having ducted augmentor wings, said dual cycle fan jet engine comprising: a fan jet engine adapted to generate primary air and fan air; air driven means for extracting energy from airflow and generating mechanical power in accordance therewith; air compression means for compressing air, said air compression means connected to said air driven means so as to be powered by the mechanical power generated by said air driven means; a horizontal duct extending rearwardly from the primary air outlet of said fan jet engine; a nacelle surrounding said fan jet engine and said horizontal duct for directing the fan air from said fan jet engine about said horizontal duct; a first vertical duct connecting said horizontal duct to the inlet of said air driven means; a second vertical duct connecting said nacelle to the inlet of said air compression means; a first valve located in said horizontal duct, said first vertical duct being located between the rear of said fan jet engine and said first valve; a second valve surrounding said horizontal duct, said second vertical duct being located between said fan jet engine and said second valve; a third valve located in said first vertical duct between said horizontal duct and the inlet of said air driven means; and, a fourth valve, located on the side of said air compression means remote from the side where said air compression means receives said fan air, for controlling the flow of fan air from said nacelle to said air compression means.

4. A dual cycle fan jet engine as claimed in claim 1, wherein said air driven means comprises an air turbine and wherein said air compression means comprises an air compressor.

5. In a STOL aircraft including ducted augmentor wings adapted to direct air energized by a jet engine to augmentor flaps, said augmentor flaps adapted to direct said air generally downwardly and, thereby, augment the lift provided by the aerodynamic shape of the wings of said STOL aircraft, the improvement comprising a dual cycle fan jet engine comprising: a fan jet engine adapted to generate primary air and fan air; air driven means for extracting energy from air flow and generating power in accordance therewith, said air driven means having an inlet in communication with the primary air of said fan jet engine; air compression means for compressing air, said air compression means connected to said air driven means so as to be powered by the power generated by said air driven means and said air compression means having an outlet in communication with the duct of one of said ducted augmentor wings of said STOL aircraft; duct means, mounted between the rear of said fan jet engine, said air driven means and said air compression means, for ducting primary air from said fan jet engine between an axial exhaust and said air driven means, and for ducting fan air from said fan jet engine between an axial exhaust and said air compression means; and, control means for selectively controlling the flow of primary air between said axial exhaust and said air driven means, and for selectively controlling the flow of fan air between said axial exhaust and said air compression means.

6. The improvement claimed in claim 5 wherein said air driven means comprises an air turbine and wherein said air compressioN means comprises an air compressor, the shaft of said air turbine being connected to the shaft of said air compressor so that said air compressor is mechanically powered by said air turbine.

7. The improvement claimed in claim 5 wherein said duct means comprises: a horizontal duct extending rearwardly from the primary air outlet of said fan jet engine; a nacelle surrounding said fan jet engine and said horizontal duct for directing the fan air from said fan jet engine about said horizontal duct; a first vertical duct connecting said horizontal duct to the inlet of said air driven means; and, a second vertical duct connecting said nacelle to the air inlet of said air compression means.

8. The improvement claimed in claim 7 wherein said control means comprises: a first valve located in said horizontal duct, said first vertical duct being located between the rear of said fan jet engine and said first valve; a second valve surrounding said horizontal duct, said second vertical duct being located between said fan jet engine and said second valve; a third valve mounted so as to control the flow of primary air from said horizontal duct to said air driven means; and, a fourth valve mounted so as to control the flow of air from said horizontal duct to said air compression means.

11. The improvement claimed in claim 10 wherein said air driven means comprises an air turbine wherein said air compression means comprises an air compressor, the shaft of said air turbine being connected to the shaft of said air compressor so that said air compressor is mechanically powered by said air turbine.