GB1581048A

GB1581048A - Aircraft

Info

Publication number: GB1581048A
Application number: GB5110776A
Authority: GB
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1977-11-09
Filing date: 1977-11-09
Publication date: 1980-12-10

Description

(54) AIRCRAFT (71) We, RoLLs-RoYcE LIMITED, formerly RoLLs-RoYcE (1971) LIMITED, a British Company formerly of Norfolk House, St. James's Square, London, SW1Y 4JR, England, and now of 65 Buckingham Gate, London, SW1E 6AT, 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 propelled aircraft and in particular it relates to silencing the jet effluxes of jet propulsion engines in such aircraft by means of socalled " ejector silencers It has been proposed to effect silencing of the jet effluxes of turbo jets and turbo fan engines by discharging the jet efflux through an ejector.For the purposes of this specification, an ejector is defined as a device for entraining ambient air in the jet efflux, comprising a duct which surrounds and extends downstream of the discharge nozzle of the engine, there being an annular space between the duct inner wall and the engine nozzle through which ambient air is drawn by ejector action.

The ambient air mixes with the jet efflux, thus reducing the shearing effect between the jet and the atmosphere. Further silencing the jet is achieved because the duct intercepts noise emanating from the jet efflux, and this can be enhanced by lining the duct with noise absorbent materials and making it as long as possible.

It is possible to design fixed-position ejectors which give large reductions in jet noise, but unfortunately when fitted to an aircraft they increase the drag experienced by the aircraft, particularly at flight cruising speeds. The increase in drag at cruising speed can be partly overcome by designing the ejector to be translatable between a non-functional position adopted at cruising speeds in which the ejector is faired into the engine cowling and a functional position adopted at low 'levels in which it is extended out of its stowed position. This solution entails mechanical complication and additional weight and also limits the length of the ejector because of the pro blein inherent in translating and stowing a long ejector.

The present invention reduces the drag penalty associated with the fiting of fixedposition ejector to aircraft without entailing mechanical complicaion and weight penalties and whilst allowing good sound absorbing characteristics.

According to the invention, an aircraft is powered by at least one jet propulsion engine mounted on the fuselage of the aircraft forwardly of a fixed aerodynamic surface of the aircraft, the engine being positioned and configured to discharge into an ejector (as hereinbefore defined) which forms part of the fixed aerodynamic surface. The aircraft may advantageously be powered by two engines, each engine being associated with a respective jector forming part of a respective fixed aerodynamic surface.

In a convenient arrangement, the aircraft is powered by two gas turbine jet engines, each of which is mounted on the rear of the fuselage just forward of a re respective tail plane, an ejector being incorporated in each tail plane and forming part of both the upper and the lower surface of each tail plane.

In one possible arrangement, the tail planes are set into the fuseelage at an angle above the horizontal to form a V-shaped tail assembly. This arrangement eliminates the requirement for a vertical stabiliser fin, and may therefore reduce the overall stabiliser surface area and hence offset the added internal drag of the ejector.

Control surfaces such as flaps on the trailing edges of the fixed aerodynamic surfaces (e.g. the tail planes) may be operable td deflect the efflux from the ejectors to aid in control of the aircraft. Alternatively, each ejector may have a swivelling discharge nozzle capable of discharging the efflux over a. range of angles from the ejector centreline.

An embodiment of the invention will now be described by way of example only with reference'td the accompanying drawings, in which: Figure 1 is a side elevation of an aircraft incorporating structure according to the invention; Figure 2 is a view of the aircraft from underneath; Figure 3 is an end elevation looking forward from the rear of the aircraft, Figure. 4 is an enlarged part-sectional view taken in the direction of arrow 'A' in Figure 3;.

Figure 5 is a view similar to Figure 4 but showing a further embodiment of the invention.

Referring to Figures 1 to 4, a jet propelled transport aircraft 1 is powered by two gas turbine jet engines 2,4, for example, low bypass ratio turbo-fan engines.

The engines 2,4 are mounted on the rear of the fuselage 6 and each is positioned forwardly of a respective fixed aerodynamic surface 8,10. In this case the fixed aerodynamic surfaces 8,10 are tail planes, engines 2, 4 being mounted just in front of them on support structures 12,14 which blend aerodynamically into the base of the tail planes 8,10.

The aircraft structure forward of engines 2,4 is conventional and needs no description, but the aircraft structure to the rear of the engines differs from the norm for this type of aircraft because each engine 2,4 is associated with a respective ejector 16,18 which is incorporated in a respective tail plane 8,10 and forms part of both the upper and lower surfaces 8a, 8b, 10a, lOb of the tail planes 8,10; i.e. the ejectors form part of the aircraft fixed aerodynamic surfaces, being "submerged" in the tail planes. As best seen in Figure 3, the ejector casings 32,34 project from both upper and lower surfaces of tail planes 8,10.This configuration has the advantage that the total area over which air flows when the aircraft is in flight is reduced relative to a configuration in which the ejector are separate components, and therefore the aerodynamic drag caused by the ejectors is correspondingly reduced.

Another feature of the present embodiment is that the tail planes 8,10 are set into the fuselage 6 at an angle 0 above the horizontal H (see Figure 3), giving a "V"shaped tail assembly and eliminating the need for a vertical stabiliser fin, which again reduces drag as compared with a conventional arrangement, owing to re duced junctions. A "V"-tail also has the advantage that the pilot has better control of the aircraft in the event of a stall at a high angle of attack, since there is no vertically positioned rudder to be shielded from the airstream by the tail planes. Tail planes 8,10 are themselves provided with control surfaces as flaps 20,22 (seen best in Figures 2 and 4) which perform the func tions of normal tail plane flaps and of a rudder.

The purpose of ejectors 16 to 18 is to help in silencing the jet effluxes of engines 2,4. To this end the final nozzles 24,26 of engines 2,4 (Figure 4) discharge the jet efflux from the engines 2,4 into the ejectors 16,18 via the inlets 28,30. In Figure 4.

ejector 16, which is similar to ejector 18, comprises an approximately cylindrical double-wall casing 32 defining a substantially cylindrical duct. The space between the walls of casing 32 is preferably filled with sound absorbing honeycomb and/or fibrous materials to aid in silencing of the jet efflux. The casing 32 is of greater internal diameter than the maximum external diameter of engine nozzle 24 -and an annular inlet space 36 is thereby defined between them through which ambient an is drawn to mix with the jet efflux.

It will be noticed that the downstream end of the ejectors 16,18 are placed for ward of the trailing edges of flaps 20, 22.

The arrangement, best seen in Figures 3 and 4, is that flaps 20,22 are provided with respective thinner -flat portions 35,37 at their inboard ends, which project into the effluxes from ejectors 16,18. Thus, when the flaps 20,22 are raised or lowered, some jet deflection occurs, giving greater control forces and aiding in control of the aircraft.

As shown in Figure 4, each flap portion 35,37 is " cutaway " at 38 to prevent fouling of the end of the ejector.

An alternative arrangement is shown diagrammaticaly in Figure 5. Only the parts which are different from Figure 4 will be described. Here, the downstream end of the ejector 40 is provided with a swivelling discharge nozzle 46 of known type which 'operates. in conjunction with flap 44 of tail plane 42 to discharge the efflux at the angle to which the flap is set.

Flap 44 does not project into the efflux from the ejector 40 as does flap 20 in Figures 4, but is shaped to avoid contact with the efflux. Drag is therefore reduced relative to Figure 4, but control force is increased since the swivelling nozzle 46 directs the efflux more efficiently than flap portion 35.

Referring to both Figures 4 and 5, it should be noted that the centre-lines 48, 50 respectively of the engines and the ejectors are offset from each other. This is because the air intake for engine 2 must be far enough outboard of the fuselage to be completely within the free air stream, whilst it is preferable to discharge the propulsive jet closer to the fuselage centreline and parallel to it.

WHAT WE CLAIM IS: - 1. An aircraft powered by at least one jet propulsion engine mounted on the fuselage of the aircraft forwardly of a fixed aerodynamic surface of the aircraft, the engine being positioned and configured to discharge the jet efflux into an ejector (as hereinbefore defined) which forms part of the fixed aerodynamic surface.

2. An aircraft according to claim 1 powered by two engines, each engine being associated with a respective ejector forming part of a respective fixed aerodynamic surface.

3. An aircraft according to claim 2 in which each engine is mounted on the rear of the fuselage just forward of a respective tail plane, an ejector being incorporated in each tail plane and forming part of both the upper and the lower surface of each tail plane.

4. An aircraft according to claim 3 in which, in order to eliminate the need for a stabiliser fin, the tail planes are set into the fuselage at an angle above the horizontal to form a V-shaped tail assembly.

5. An aircraft according to any one of the preceding claims in which, in order to aid in control of the aircraft, the fixed aerodynamic surfaces associated with the engines and ejectors are each provided on their trailing edges with a flap operable to deflect the efflux from the ejector.

6. An aircraft according to any one of claims 1 to 4 in which each ejector has a swivelling discharge nozzle capable of discharging the efflux over a range of angles from the ejector centreline.

7. An aircraft according to any one of the preceding claims in which the engines are gas turbine jet engines.

8. An aircraft substantially as described in this specification with reference to and as illustrated in Figures 1 to 4 of the accompanying drawings.

9. An aircraft substantially as described in this specification with reference to and as illustrated in Figures 5 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. should be noted that the centre-lines 48, 50 respectively of the engines and the ejectors are offset from each other. This is because the air intake for engine 2 must be far enough outboard of the fuselage to be completely within the free air stream, whilst it is preferable to discharge the propulsive jet closer to the fuselage centreline and parallel to it. WHAT WE CLAIM IS: -

1. An aircraft powered by at least one jet propulsion engine mounted on the fuselage of the aircraft forwardly of a fixed aerodynamic surface of the aircraft, the engine being positioned and configured to discharge the jet efflux into an ejector (as hereinbefore defined) which forms part of the fixed aerodynamic surface.