GB1605270A - Aircraft power plants - Google Patents

Description

(54) IMPROVEMENTS RELATING TO AIRCRAFT POWER PLANTS (71) We, BRITISH AEROSPACE PUBLIC LIMITED COMPANY. a British Company organised under British Aerospace (Nominated Company) order 1980 and British Aerospace (Appointed Day) Order 1980, of 100 Pall Mall, London SW1Y 5HR, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:: This invention relates to jet engines of the type defined by being capable of providing both propulsive and lift thrust by means of angularly adjustable jet streams and which have a gas-turbine core engine and a front fan operatively associated therewith, the core engine supplying gases to at least one rearwardly disposed nozzle and the front fan supplying air to at least one forwardly disposed nozzle.

Fuel can be mixed with the air flow to the forward nozzle and with the gaseous flow to the rearward nozzle and burned to give increased jet thrust therefrom and thereby increase the total thrust of the engine. The former is known as plenum chamber burning and the latter is known as after-burning.

Where plenum chamber burning is used alone without after-burning, there is an accompanying large difference in the levels of thrust delivered between the forward and rearward nozzles which, in the lift phases of aircraft flight, can cause difficulties in aircraft control. One object of the invention is to at least reduce this imbalance.

Where both plenum chamber burning and after-burning are used there are differences in thrust due to the nature of the two burning processes since the plenum chamber burning is effected in cold air and the after-burning is effected in hot exhaust gases. A further object of the invention is to at least reduce any imbalance in thrust which results from the use of both plenum chamber burning and afterburning.

According to the present invention in a jet engine of the type defined the core engine has a by-pass duct which conveys air from the front fan around the core engine and into the exhaust gas stream of the core engine upstream of the rearwardly disposed nozzle.

Preferably the front fan also delivers air to the core engine in known manner.

A preferred embodiment of the present invention is described with reference to the accompanying drawings. In the drawings: Figure lisa side elevation of an engine slung under an aircraft wing.

Figure 2 is a plan view in diagrammatic section about the fore-and-aft axis of the engine.

An engine capable of providing both lift and propulsive thrust includes a core engine 1 having a compressor unit 2, combustion zone 3, and a turbine unit 4 coupled to the compressor unit 2 by means of a hollow shaft 5. A front fan 6 is mounted ahead of the core engine 1 on a shaft 7 which extends co-axially through the shaft 5 and carries a turbine unit 8 located aft of the turbine unit 4.

The engine has two jet nozzles 9, 10 disposed toward the front end of the core engine and on each side thereof and two jet nozzles 11, 12 disposed aft of the core engine again on each side thereof but closer together than the nozzles 9, 10. Each nozzle is of the known variable area multi-petal type and is capable of being directed both downwards and rearwardly in known manner.

The fan 6 supplies cold air both to the nozzles 9, 10, to the compressor unit 2 of the core engine 1, and also to a by-pass duct 13 which surrounds the core engine 1.

The rearward nozzles 11, 12 are in flow connection with the hot exhaust gases of the core engine 1 by means of a jet-pipe 14. The by-pass duct 13 discharges into this jet-pipe 14 downstream of the core engine I and the turbine unit 8. Thus cold fan air is delivered into the jet-pipe to be mixed with the hot gases therein.

To increase engine thrust, plenum chamber burning is provided in known manner by a colander arrangement 15 situated in ducts 16, 17 leading to the nozzles 9, 10 respectively. By this arrangement fuel is mixed with the cold air delivered by the fan and burned to increase the thrust of the jet stream issuing from the nozzles helps to optimise the thrust delivered.

Simultaneously, after-burning is effected in known manner by spray rings 18 situated in the jet-pipe 14 leading to nozzles 11, 12. By this arrangement fuel is mixed with the hot gases exhausting from the core engine 1 and burned to increase the thrust of the jet stream issuing from the nozzles 11, 12. The after-burning means 18 is situated aft of the discharge point of the by-pass air from duct 13 into the jet-pipe 14. Thus the hot exhaust gases are diluted by cold air prior to the point of mixing with fuel for after-burning. In this manner the thrust increases due to plenum chamber burning and to after-burning can be made more nearly equal. Thus the flight control forces on an aircraft resulting from the increase in thrust are minimised.

Figure 1 illustrates the engine mounted under the wing 19 of an aircraft. The nozzle pairs 9, 10 and 11, 12 are shown disposed equally fore-and-aft of the aircraft centre of gravity so that the centre of vertical thrust is coincident therewith. The centre of gravity is referenced 20. To achieve the optimum position for the nozzles relative to the wing, the jet-pipe 14 of the engine may be formed with one of a number of different lengths and the engine located accordingly.

In the embodiment shown the forward nozzles 9, 10 are under but adjacent the wing leading edge to minimise adverse lift effects due to the proximity thereof. Likewise. the rearward nozzles 11, 12 are under but adjacent to the wing trailing edge. Again, in this embodiment the rearward nozzles 11, 12 are positioned to exhaust near to the trailing edge of high lift flaps 21 so that the jet efflux can entrain and draw ambient air over the flap when extended to obtain an increased benefit from it.

With the engine described it is possible to provide 20,000 Ibs of thrust at the forward nozzles with plenum chamber burning and 14,000 Ibs of thrust at the rearward nozzles without after-burning. With after-burning the thrust from the rearward nozzles is increased to 21,000 Ibs to bring the thrust levels of the forward and the rearward nozzles sufficiently similar to enable the imbalance to be readily counteracted by the aircraft control means.

Because of the similarity of the thrust levels of the forward and rearward nozzles it is convenient to effect flight control of the aircraft about the pitch axis by utilising the engine and nozzle system in the following manner. When the nozzles are directed generally downwards, as in vertical take-off and landing pitch control can be achieved by varying the relative thrust of the forward and rearward nozzles. This is done by operating the plenum chamber burning differentially to the after-burning by varying the amount of fuel burned and/or by varying the nozzle areas.

When the nozzles are directed partly downwards and partly rearwards, that is to say in the transitional phase between horizontal and vertical flight, pitch control can be achieved by relatively varying the angles of the forward and rearward nozzles, respectively.

These methods of pitch control are effective for a multi-engined aircraft providing the engines being utilised for such control are positioned with their forwardly disposed nozzles forward of the centre of gravity of the aircraft and the rearwardly disposed nozzles aft thereof. This method is similarly effective for a single engined aircraft and in such a case additionally the engine and nozzles can be used for control about the other axes in the following manner: ROLL CONTROL When the nozzles are directed substantially downwards, the jet thrust to either side of the engine may be differentially varied by varying the area of the nozzles on one side compared with the other, or by varying the fuel burned on one side of the twin forward nozzles and on the same side of the twin rearward nozzles.

In the transitional phase of flight, where the nozzles are directed partly downwards and partly rearwards, the angular setting of the nozzles to one side of the engine can be varied in comparison with those on the other side to effect a rolling moment.

YAW CONTROL With the nozzles directed substantially downwards a yawing moment can be imparted to the aircraft by altering the angular setting of the two nozzles on one side of the aircraft in the opposite manner to the two on the other side of the aircraft.

During the transitional phase of flight when the nozzles are directed partly downwards and partly rearwards the yawing moment can be achieved by varying the thrust from the nozzles on one side of the engine relatively to the nozzles on the other side.

WHAT WE CLAIM IS: 1. A jet engine capable of providing both propulsive and lift thrust by means of angularly adjustable jet streams having a gas turbine core engine and a front fan operatively associated therewith, the core engine supplying gases to at least one rearwardly disposed nozzle and the front fan supplying air to at least one forwardly disposed nozzle, wherein the core engine has a by-pass duct which conveys air from the front fan around the core engine and into the exhaust gas stream of the core engine upstream of the rearwardly disposed nozzle.

2. A jet engine according to claim 1 in which fuel is mixed with the gaseous flow from the front fan to the forward nozzle and with the gaseous flow from the by-pass duct and the core engine to the rearward nozzle and burned to provide increased jet thrust therefrom.

3. A jet engine according to claim 1 or claim 2 having a pair of forward nozzles and a pair of rearward nozzles, the pairs of nozzles being so arrranged and the direction and/or the thrust of the efflux of each nozzle being variable such

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. known manner by spray rings 18 situated in the jet-pipe 14 leading to nozzles 11, 12. By this arrangement fuel is mixed with the hot gases exhausting from the core engine 1 and burned to increase the thrust of the jet stream issuing from the nozzles 11, 12. The after-burning means 18 is situated aft of the discharge point of the by-pass air from duct 13 into the jet-pipe 14. Thus the hot exhaust gases are diluted by cold air prior to the point of mixing with fuel for after-burning. In this manner the thrust increases due to plenum chamber burning and to after-burning can be made more nearly equal. Thus the flight control forces on an aircraft resulting from the increase in thrust are minimised. Figure 1 illustrates the engine mounted under the wing 19 of an aircraft. The nozzle pairs 9, 10 and 11, 12 are shown disposed equally fore-and-aft of the aircraft centre of gravity so that the centre of vertical thrust is coincident therewith. The centre of gravity is referenced 20. To achieve the optimum position for the nozzles relative to the wing, the jet-pipe 14 of the engine may be formed with one of a number of different lengths and the engine located accordingly. In the embodiment shown the forward nozzles 9, 10 are under but adjacent the wing leading edge to minimise adverse lift effects due to the proximity thereof. Likewise. the rearward nozzles 11, 12 are under but adjacent to the wing trailing edge. Again, in this embodiment the rearward nozzles 11, 12 are positioned to exhaust near to the trailing edge of high lift flaps 21 so that the jet efflux can entrain and draw ambient air over the flap when extended to obtain an increased benefit from it. With the engine described it is possible to provide 20,000 Ibs of thrust at the forward nozzles with plenum chamber burning and 14,000 Ibs of thrust at the rearward nozzles without after-burning. With after-burning the thrust from the rearward nozzles is increased to 21,000 Ibs to bring the thrust levels of the forward and the rearward nozzles sufficiently similar to enable the imbalance to be readily counteracted by the aircraft control means. Because of the similarity of the thrust levels of the forward and rearward nozzles it is convenient to effect flight control of the aircraft about the pitch axis by utilising the engine and nozzle system in the following manner. When the nozzles are directed generally downwards, as in vertical take-off and landing pitch control can be achieved by varying the relative thrust of the forward and rearward nozzles. This is done by operating the plenum chamber burning differentially to the after-burning by varying the amount of fuel burned and/or by varying the nozzle areas. When the nozzles are directed partly downwards and partly rearwards, that is to say in the transitional phase between horizontal and vertical flight, pitch control can be achieved by relatively varying the angles of the forward and rearward nozzles, respectively. These methods of pitch control are effective for a multi-engined aircraft providing the engines being utilised for such control are positioned with their forwardly disposed nozzles forward of the centre of gravity of the aircraft and the rearwardly disposed nozzles aft thereof. This method is similarly effective for a single engined aircraft and in such a case additionally the engine and nozzles can be used for control about the other axes in the following manner: ROLL CONTROL When the nozzles are directed substantially downwards, the jet thrust to either side of the engine may be differentially varied by varying the area of the nozzles on one side compared with the other, or by varying the fuel burned on one side of the twin forward nozzles and on the same side of the twin rearward nozzles. In the transitional phase of flight, where the nozzles are directed partly downwards and partly rearwards, the angular setting of the nozzles to one side of the engine can be varied in comparison with those on the other side to effect a rolling moment. YAW CONTROL With the nozzles directed substantially downwards a yawing moment can be imparted to the aircraft by altering the angular setting of the two nozzles on one side of the aircraft in the opposite manner to the two on the other side of the aircraft. During the transitional phase of flight when the nozzles are directed partly downwards and partly rearwards the yawing moment can be achieved by varying the thrust from the nozzles on one side of the engine relatively to the nozzles on the other side. WHAT WE CLAIM IS:

1. A jet engine capable of providing both propulsive and lift thrust by means of angularly adjustable jet streams having a gas turbine core engine and a front fan operatively associated therewith, the core engine supplying gases to at least one rearwardly disposed nozzle and the front fan supplying air to at least one forwardly disposed nozzle, wherein the core engine has a by-pass duct which conveys air from the front fan around the core engine and into the exhaust gas stream of the core engine upstream of the rearwardly disposed nozzle.

2. A jet engine according to claim 1 in which fuel is mixed with the gaseous flow from the front fan to the forward nozzle and with the gaseous flow from the by-pass duct and the core engine to the rearward nozzle and burned to provide increased jet thrust therefrom.

3. A jet engine according to claim 1 or claim 2 having a pair of forward nozzles and a pair of rearward nozzles, the pairs of nozzles being so arrranged and the direction and/or the thrust of the efflux of each nozzle being variable such

that aircraft flight control can be achieved.

4. A jet engine substantially as described with reference to the accompanying drawings.