Combined Noise Shield and Thrust Reverser

This invention concerns improved noise suppression means for aircraft.

Low community noise is a major design consideration for new aircraft development, particularly in the commercial jet transport field. It is known to protect the community from noise emanating from the aircraft engines by suitably positioning them relatively to the airframe such that the airframe will constitute a shield either to absorb a percentage of the noise or deflect a substantial part of it away from the community. It is an object of the present invention to achieve this noise suppression requirement by improved means, in the form of a novel aircraft and engine-installation arrangement.

According to the invention, there is provided an aircraft with a fuselage at or near the rear end of which are located jet propulsion engines mounted on top of said fuselage and/or laterally disposed at opposite sides of its longitudinal axis, each engine air intake being located at a level above the aircraft wing trailing edge and not significantly aft of it such that the fuselage and wing surfaces provide a downward and partial sideways shield against noise emanating from the intakes.

Each engine is, for preference, partially recessed within the fuselage profile to provide an engine fairing or nacelle of reduced surface area for drag reduction and in addition an air intake and exhaust which may be of flattened form to increase noise shielding effectiveness. Also in the preferred arrangement, intake noise may be further shielded by the provision of flaps rearwardly extendible from the wing trailing edge in the take off and landing modes, permitting a reduction in nacelle length with associated reduction in surface area and in-cruise drag when noise shielding is of little consequence.

Each engine exhaust nozzle discharges into a common noise shielding duct or channel formed by a substantially horizontal structure and a pair of spaced-apart substantially vertical fins and rudders. The horizontal structure constitutes a fixed-incidence portion of the tailplane, while variable incidence portions lying outboard of the vertical fins are isolated by the fins from the effect of the engine exhausts and varying throttle settings.

In a preferred embodiment, an upstream portion of said fixed-incidence horizontal structure is deflectable in conjunction with a portion of the engine nacelle to form a thrust reverser common to all the engines. There is considerable advantage in this arrangement in that the reversed thrust exhausting close to the aircraft longitudinal axis will impart no significant asymmetric loadings to the aircraft in the event of an engine-out condition.

One embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings, in which

FIG. 1 is a plan view of an aircraft in accordance with the present invention,

FIG. 2 is a front view of the aircraft of FIG. 1,

FIG. 3 is a rear view of the aircraft of FIG. 1,

FIG. 4 is a longitudinal section through the aircraft rear end looking outboard,

FIG. 5 is a similar view to FIG. 4 but with the thrust reverser operative, and

FIG. 6 is a pictorial arrangement of the reverse thrust installation.

Referring to the drawings, in the aircraft configuration shown three jet propulsion engines are mounted upon and close to the rear end of a fuselage 1. A central engine 2 is mounted on top of the fuselage, the remaining pair 3 being disposed on either side of the aircraft longitudinal centre line such that their own longitudinal centre lines 4 are rearwardly convergent.

The fuselage rear end profile 5 is such that each engine is, in effect, partially recessed within the basic fuselage profile 6. This permits the engine fairings 7 to be of reduced surface area and the air intakes 8 of flattened form, both of which features promote noise attenuation by increasing the ratio of the shielding length to the depth of the noise source.

Each engine fairing 7 extends forward of its respective engine, the outer two terminating when the air intake is just behind the trailing edge 9 of the wing 10; downward the sideways noise, emanating from the air intakes, is thus shielded by the fuselage and wing. This shielding may be further increased by the provision of flaps 11 rearwardly extendible in the take-off and landing modes from stowed positions within the wing trailing edge 9. This latter feature enables the engine fairing length to be suitably reduced, within the scope permitted by the extendible flaps. The flaps are slidably mounted at their ends on the fuselage sides and on faired cantilever beams 12 on the wing. This is both a weight saving arrangement and a means of reducing in-cruise drag.

The rearward convergence of the engine axes provides that the effluxes, exhausting through nozzle fairings 13 and 14, can discharge into a common noise shielding channel 15 formed by a horizontal structure 16 and a pair of spaced-apart substantially vertical fins 17 to provide both sideways and downwards shielding. A condition of efficient noise shielding is the combination of flattened nozzle depth with a maximum possible shielding length. This is further enhanced by providing each engine 2, 3 with a multi-lobe nozzle 18. It is known that this type of nozzle can reduce engine noise and fuel consumption. In relation to the present arrangement these nozzles provide increased noise shielding effectiveness. Since jetnoise emanates at a line source downstream of the nozzle, whereas other noise emanates from the nozzle itself, the use of multi-lobe nozzles to increase mixing of jet and by-pass air will reduce the jet noise content of the noise spectrum.

The horizontal structure 16, in addition to performing its noise shielding function, acts as a fixed-incidence portion of the tailplane; variable incidence portions 19 extend laterally outboard of the vertical fins 17. They are thus advantageously isolated from the effect of the engine exhausts and throttle variations.

A further advantage of this present arrangement resides in the provision of thrust reversal. It would be possible to apply conventional thrust reversers to the outer engines but with conventional arrangements the application of thrust reversal to a centre engine would normally be difficult to achieve. However, the horizontal structure 16 incorporates at its upstream end a flap 20 having pivotal attachment to the fixed structure at 21 and movable from a closed position as shown in FIGS. 4 and 6 where it forms the forward upper surface of the horizontal structure 16 to an open position as shown in FIG. 5 where it reveals a duct or ducts 22 extending down between the vertical fins 17. The lower duct exit is similarly closed by movable lower flaps 23 when not in use, which flaps open in conjunction with upper flap 20 to lie substantially in alignment with or parallel to the flow direction through the duct 22. To complete the thrust reverser an upper rear portion 24 of the engine fairing rotates up and back to form in combination, with flaps 20 and 23, a multi-directional duct for thrust reversal upward and downward as indicated by the arrows 25 in FIG. 5. The thrust reverser assembly is acted simultaneously by two screw-jacks 26, operated by electrical actuators and which are pivotally mounted at 27 within the forward extensions of, and close to the base of, the fins 17. To allow for a failure condition the electrical actuators may be duplicated with an over-ride device. Alternatively, the thrust reverser system may be motivated by interconnected hydraulic jacks, for example, or pneumatic jacks by air bled from the engines and incorporating integral locks.

The jacks 26 operate directly on quadrants 28 through a pivotal connection 29, the quadrants forming side supports for the upper rear portion 24 of the engine fairing and being pivotally mounting at 37 on the fixed aircraft structure. Adjustable struts 30 provide interconnection between the quadrants 28 and the flap 20, having pivotal attachments 31 and 32 to the quadrant and the flat, respectively, whilst adjustable struts 33 and 34 have pivotal attachment to lever extensions 35 of the lower flaps 23 and provide interconnection to lever extensions 36 of the quadrants 28. Therefore, actuation of the screwjacks simultaneously opens or closes the thrust reverser system as a whole to ensure substantially symmetrical flow upward and downward.

In this arrangement the thrust lines of the engines are biased nose down so that the thrust line passes near the Centre of Gravity. When the thrust reverser is extended the drag line is inclined slightly nose-up. This is sufficient to provide a down load on the main wheels to increase wheel braking efficiency, without offloading the nose wheel to an undesirable extent.

Other features may be provided to improve still further the noise shielding characteristics.

A sheet of low velocity air may be interposed between the engine exhausts and the structure. This air can be ducted from the boundary layer on top of the fuselage ahead of the engine intakes. Thus it acts as a boundary layer bleed energised by the engine exhausts. Such a downstream air sheet has the multiple effect of:

a. reducing scrubbing drag

b. reducing scrubbing noise

c. reducing temperature effects on the aircraft structure

d. reducing structural fatigue

The invention is not limited to three-engine designs. Noise shielding can be used either to reduce the overall noise nuisance experienced by the community to levels lower than otherwise possible with the same engines, or to make possible the use of inherently noisier engines, or to avoid the need for special acoustic treatment.