GB2138507A

GB2138507A - Mounting end exhausting in turbo-propellor aircraft engines

Info

Publication number: GB2138507A
Application number: GB08406446A
Authority: GB
Inventors: Harry Wrighton Bennet
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1983-04-22
Filing date: 1984-03-12
Publication date: 1984-10-24
Also published as: GB2138507B; GB8406446D0

Abstract

In an engine (10) driving a pair of aft located, contra-rotating prop-fan propellors (28, 30) through a reduction gear-box (32), the engine exhaust gases are taken out through a duct (36) located in a strut (14), and a nozzle (38) adjacent a surface of an aircraft (12). The exhaust gas are fully expanded and are arranged to improve the flow over the aircraft fuselage. The strut wake can be reduced by a bleed of compressor air or exhaust gases through outlets (40). <IMAGE>

Description

SPECIFICATION Improvements in or relating turbo-propellor aircraft engines This invention relates to aircraft engines of the turbo-propellortype, commonly known as turbo-props.

These engines usually have a gas generator com prising a compressor, a combustion system, and a compressor driving turbine, a powerturbine driven by the exhaust gases from the compressor driving turbine and arranged to drive a propellor or propellors through reduction gearing.

The propellor or propellors are usually arranged at the upstream end ofthe engine which means that the air entering the engine gas generator has to pass through the propellor blading, before entering an annular or chin-type engine air intake. Because ofthe obstruction ofthe propellor blading and the tortuous flow path to gas generator, the inlet conditions are not ideal.

The intake problem can be solved by placing the propellor or propellors downstream of the gas gener ator,sothatthere is no obstruction to the gas generatorairinlet. However, the difficultythen arises of discharging the hot, high velocity engine exhaust gases so that they do not adversely affect the propelloror propellors and the associated reduction gearing. In our co-pending application U.K. 8204665, the reduction gearing is placed downstream of the propellor plane, andthe exhaust gases passthrough a convoluted mixer and hencethroughthe roots of the propellor blades, so thatthe blades pass through alternate flows or hot gas and ambient air.Thus the blade roots are subjected to variations of temperature oftemperatu re which are not desirable.

This difficulty can be overcome byducting away the exhaust gases from engine, and placing the reduction gearing and the propellor or propellors out of the way ofthe hot environment created bythese gases as shown in U.K. patent no.809811. The problem then arises of satisfactorily mounting such an engine in an aircraft.

The present invention seeks to provide a turbopropellor aircraft engine having an unobstructed air intake with the propellor or propellors at the downstream end ofthe engine, the exhaust gases from the engine being ducted away from the propelloror propellors and associated reduction gearing, and a means of mounting such an engine in an aircraft.

Accordingly,the present invention providesaturbo- propellorgasturbine engine associated with an aircraft, the engine comprising in flow series a gas generator comprising an unobstructed air inlet, compressor means, combustion means, and a compressor driving turbine means, a powerturbine driven by the exhaust gases from the compressor driving turbine, the power turbine driving a reduction gear box, and at least one propellor driven from the reduction gear box, the engine exhaust gases being taken through an exhaust duct which is inclined to the engine axis, the exhaust duct axis intercepting the engine axis between the powerturbine and the reduction gear box, the engine being mounted on a strut containing the exhaust duct which terminates in a nozzle adjacent a surface of the aircraft.

Preferably the aircraft is twin-engined, each engine being mounted on a strut adjacent the rear of the aircraft, the exhaust gases from the engines discharging overthetail oftheaircraftfuselage.

The strut will create a wake in which the propellor or propellors have to operate and the wake can be minimised by bleeding a small flow ofairfrom the gas generator compressor and exhausting through openings adjacent the strut trailing edge.

The exhaust duct can be insulated, and the exhaust gas heat can be used for strut de-icing. The exhaust gases are fully expanded so that they do not adversely affect the aircraft fuselage.

The engine can have a propellorora pair of contra-rotating propellors ofthe conventional type, or ofthe propfan type. This lattertype comprises about 8 to 10 blades, each blade being thin and having a high degree of sweep.

The present invention will now be more particularly described with reference to the accompanying draw ings in which Fig. 1 shows an aircraft powered by two turbo propellorengines having an exhaust arrangement according to the present invention.

Fig. 2 shows one of the tu rbo-propel lor engines of fig. 1 and part ofthe aircraft in more detail, Fig. 3 is a part plan view of a modified form of engine exhaust to that shown in fig. 2.

Fig. 4 is a section on line D-D in fig. 3.

Fig. 5 is a view on arrow E in fig. 4 and Fig. 6 shows another engine exhaust arrangement according to the present invention.

Referring to figs. 1 and 2, a turbo-propellorengine 10 is shown mounted on an aircraft 12 by means of a hollowstrut 14.

The engine comprises a gas generator 16 having an unobstructed air inlet 18, a compressor20, a combustion system 22, and a compressor driving turbine 24.

The exhaust gases from the gas generator drive a powerturbine 26 which in turn drives a pair of contra-rotating multi-bladed propellors 28,30, through a reduction gear box 32. The gas generator, powerturbine, reduction gear box, and the propellors all have a common axis of rotation A-A, though it is possible that the propellor axis can be offset from that ofthe reduction gear box.

The engine 10 is mounted in a nacelle 34which is attached to the strut 14, the strut containing an insulated portion ofthe length of an exhaust duct 36 to remove the exhaust gases from the engine.

The exhaust duct inlet is attached to the power turbine outlet and curves round to a straight length contained in the strut and terminates in a D-shape nozzle 38 to discharge fully expanded exhaust gases overthetail of the aircraft. The axis B-B ofthe exhaust duct in the strut intercepts the engine axis A-A at a point C between the powerturbine and the reduction gear box so thatthe reduction gear box and the propellorsarenotaffected bythe engine exhaust gases.

The propellors do have to operate in the wake of the strut 14, but this wake can be suppressed or its effect minimised by taking a smallflowofairfrom the gas generator compressor 20 and discharging through openings 40 adjacent the strut trailing edge 42.

Referring to figs. 3,4 and 5, the exhaust duct 36 is formed internally of the strut 14 towards the strut trailing edge and the hot engine exhaust gases exhaustto atmosphere through the nozzles 38 which are generally ofthe shape shown in fig. 5. Instead of a bleed ofcompressorairto reduce the strut wake as in fig. 2, some of the exhaust gases are taken out through openings 40, defined by upper and lower slots 44 and a series of curved outlet guide vanes 46. Such an arrangement is more efficient than bleeding a flow of compressor air.

In fig. 6, the arrangement is similar two that shown in figs. 3,4and 5, exceptthatthe exhaust gases exit through a nozzle 48 terminating generally downstream of the junction between the aircraft fuselage and fin. The nozzle 48 is generally circular in section and is divided in two by a vertical wall 50, each part of the nozzle receiving an exhaustflowfrom one ofthe engines 10.

The propelloraxis of rotation can be offset in the outboard direction to at least partially remove the propellorsfromthe strutwake. Only one propellor need be provided, and the or each propellor can be of the conventional type or of the propfan type, i.e. of thin section and highly swept to delay shock wave formation and having the ability to operate at at a high power loading.

Itwill be noted that with the engine layout described and the method of attachmentto an aircraft, the engine has an unobstructed air intake, the reduction gearboxoperates in a cool environmentandthe propellor or propellors are not affected by a hot gas flow. Also the flow of expanded exhaust gas over the aircraftfuselage can be directed to reduce drag, and the planeofthepropellors is such that the fuselage or the passenger containing compartment is notsubjected to pressure waves generated by the propellors.

The invention is not restricted to the type of gas generator, reduction gear box, propellor, number of propellors, or location of the engine relative to the aircraft. For example, it could be possible to mount the enginefromtheaircraftwing on a pylon and usethe exhaust gases for boundary layer control. In this latter case ofcourse, the noise reduction obtained would not be so great, taking into accountthefactthatthe wing mounted engine would befurtherfromthe fuselage.

Claims

1. Aturbo-propellor gas turbine engine associated with an aircraft,the engine comprising in flow series a gas generator comprising an inobstructed air inlet, compressor means, combustion means, and a com pressor driving turbine means, a power turbine driven bytheexhaustgasesfromthecompression driving turbine, the powerturbine driving a reduction gear box, and at least one propellor driven from the reduction gear box,the engine exhaust gases being taken through an exhaust duct which is inclined to the engine axis, the exhaust duct axis intercepting the engine axis between the powerturbine and the reduction gear box, the engine being mounted on a strut extending from the associated aircraft, the strut containing an exhaust ductwhich terminates in a nozzle adjacent a surface ofthe aircraft.

2. An engine associated with an aircraft as claimed in claim 1 in which a quantity of air is bled from the engine compressor and is exhausted to atmosphere through a numberofopeningsadjacentthetrailing edge of the strut.

3. An engine associatedwith an aircraft as claimed in claim 1 in which the strut has a number of outlets adjacentthetrailingedge,theoutletsbeing defined by a series of outlet guide vanes located in upper and lower slots in the surface ofthe duct, the slots being in communication with the exhaust duct.

4. An engine associated with an aircraft as claimed in claim 1, or claim 2 or claim 3 in which the duct terminates in a nozzle adjacent the surface ofthe rear ofthe aircraft fuselage.

5. An engine associated with an aircraft as claimed in any one ofthe preceding claims 1 to 2 in which the exhaust ductterminates in a two part nozzle which is also able to receive the exhaust gases from another engine,thetwo part nozzle being located downstream of the junction between the aircraftfuselage and fin.

6. An engine associated with an aircraft as-claimed in any ofthe preceeding claims in which the exhaust duct is insulated and a portion ofthe exhaust gases are ducted to de-ice the strut.

7. An engine associated with an aircraft as claimed in any one ofthe preceding claims in which the engine has a pairofcontra-rotating propellors,the propellors being ofthe prop-fan type.