CA1253479A - Compound helicopter and power plant therefor - Google Patents

Abstract

ABSTRACT OF DISCLOSURE

COMPOUND HELICOPTER AND
POWERPLANT THEREOF

A compound helicopter shown in Figure 1 of the drawings has wings 12 in addition to a helicopter rotor 14 and has twin powerplants 16 each including a low pressure compressor 18, a gas generator 20, a power turbine 22 driven by the gas generator and connected through a gearbox 32 to drive the helicopter rotor, and a variable area final propulsion nozzle 24 which receives the exhaust from the power turbine.
Augmentor wing flaps 28 are provided on the wings and fed with air from the low pressure compressor for providing additional lift and thrust from the wings.

In operation, at take-off the nozzles 24 are fully opened and all of the power produced by the power turbines 22 is used in driving the helicopter rotor for producing lift. In addition, the augmentor wing flaps 28 are directed downwardly to provide lift for forward flight the nozzles 24 are closed down reducing the power to the rotor and slowing it down, while at the same time generating, forward thrust. Additional forward thrust is derived from the flow of compressed air through the augmentor wing flaps 28.

Description

:12S347~
.

COMPOUND HELICOPTEI~ AND
POWERPLANT THER~FOR

The presen-t invention relates to compound helicopters and powerplants therefor. The term compound he:Licopter is used to denote a helicopter having wings in addition to the norrnal helicopter rotor, Cornpound helicopters are not new, and several different approaches have been used in their Aesign r'or example, it has been proposed to use separate :LO engines -to provide power ~or driving the rotor and for producin~ hori~ontal pro~ulsion. This approach has -the disadvantage tha-t durin~ the cruise mode of opera-tion, -the engine drivingthe rotor is throttled back or even shut down, and then becomes dead weight, ~nd the cruise en~,ines clo not contribute -to the lift a-t talse-off.

~ n alternative approach, therefore, has been to make -the same engine or engines perform the tasks of clrivin~, the rotor and ~rovi~ing for-~ard propulsive thrust rlhis entails -the probleln of swi-tching froM
one func-tion -~o the other, and several different proposals l~ ve l)eer~ de for doin~r -this, none of whicn llave yt` t l'OUIIU accept;ance, r~xamples O.r various colTlpound helicoptt?rs and powerpl~ ts are (lisclosecl in UK Pi~tents Nos. 1,024,9~9, 1,lOc3,l~ nd 1,120,65c~. These pa-tent specifications dis(;lose twin-engined helicoE)ters and various methods 3 ~y wllich -the two en~ines are switched from drivinar the helicop-t*l rc)tor or rotors to providinOr horizontal `" lZ53479 ~'- 2 -thrust. In all of these proposals the engines are either used to provide lift or forward thrust, and the disadvantage of this arrangement is that the engine is slow to change over from one mode of operation to the other.
An arrangement which does not suffer from this disadvan-tage is disclosed in U.K. Patent No. 980,608. In this arrangement a variable pitch fan is provided, and both the fan and the heli-copter rotor are driven at all times through gearing from the engine low pressure turbine. The amount of power going to the heli-copter rotor is varied by changing the pitch of the blades toincrease or decrease the power required for driving the fan. How-ever, in this arrangement, as in the other arrangements referred to above, the engine is specifically designed for use as a compound helicopter powerplant. Also the variable pitch fan is of relative-ly large diameter and this puts a limitation on the type of air-craft installation in which it can be used.
It is an object of the present invention to provide a powerplant for a compound helicopter which consists of a standard engine adapted to provide the power for vertical lift and horizontal propulsion with a minimum of modification.
According to the present invention there is provided a power-plant for a compound helicopter which has a main lift rotor and at least one wing provided with one or more lift augmentation devices for producing llft in addition to that normally produced by the wing in forward flight, the powerplant comprising one or more gas turbine engines which have a low pressure compressor, a core engine which drives the compressor, a power turbine driven by fA

i'Z5~7~

- 2a -the exhaust of the core engine and connected to drive an output shaft for connection to the helicopter rotor, ducting for conveying ~A

--` iZS~ 9 at least part of the air compressed by the low pressure compressor to the, or each, wing, and a variable area propulsion nozzle downstream of the power turbine, said nozzle receiving the exhaust from the power turbine and being operable to vary the power absorhed by the power turbine and simultaneously vary the propulsive thrust produced by the nozzle.
By this means the variable area nozzle can be used to control both the power generated by the power turbine for producing lift from the helicopter rotor, and the propulsive thrust generated by the engine for forward propulsion The variable area final nozzle is a relatively simple modification to make to a standard engine for providing the variation in power between lift and forward propulsion, ~in additionJ that is, to the drive shaft and gearbox for driving the helicopter rotor which is essential in all helicopter powerplants). This proposal also avoids the problems of the above-mentioned prior proposals in that the helicopter rotor is driven at all times, while the power split between lift and forward propulsion from the powerplant is variable over a wide range of values.
An example of the invention will now be more particularly described with reference to the accompanying drawing in which:
Figure 1 shows the top part of a twin-engined compound helicopter of the invention with its helicopter rotor, augmentor wing, and gas turbine engine powerplants, and, Figure 2 is a view on arrow A of Figure 1.

Referrirlg now to the drawings, there is shown a compound helicopter 10 having wings 12, one on each side, and a helicopter rotor 1l~. Two gas turbine engine powerplan-ts 16 are provided each having a low A 5 pressure compressor 1~, a core~'gas~generator 20 which drives the lo~/ pressure colnpressor, a po~er turbine 22 which is driven froln the exhaust of the core engine, an~ a variable area final nozzle 21~.

The arrange~llent of the parts of f~ach of the ~owerplall-ts are as follo~"s: At least a part of th~? air flow compressed by each core engine is passed -to the wings 12 via c~uc-till~r 26, and the wings hlve auglnerltor flaps 2a at the trailinLr edges thereof.
The augmentor win-~ is l;nown per se and its operation is not descriljed here in detail. It is sufficient -to say -that the air fr~ln the ducting 26 passes to atlliosphere thro-lgh th~ t`laps 28 and induces air flowing over tllc aircraft wing to pass between the rlaps and -to s-ticlc to the top flap to incre,~se the wirl, lift. 'rhe flaps 28 are also pivotable be-twee the position snown in full lines, which provides addition,ll do~nwardly direc-ted thrust to add to the lift gerlerated by the rotor 1l~, and the position s~owrl in dotted lines which provides forward thrust.
'L'I-lc col~ resseil air t`ro~ the two en~ines is supplied to opposite si(1es o~` a diaphraglrl 27 which dividec the ducti~lg 2t~ lorigi-tudinally. ~l~hus both enrines supply air t.) tlle ~'la~s 2a along the whole lengtl 3o ol tlle win~ arld, failure of one engine will not ~I`I ec~ -the ~`low from the other one, The core gras r~ne(ator 2() produces power to drive the colnpressor 18, a~ld the exhaust froln the gas generator passes through 12S3~79 the power turbine 22. A shaft 30 and gearbox 32 interconnect ~o-th of the power turbines 22 with the helicopter rotor lll to drive the rotor. The exhaust froM each of the power -turbines passes to atmosphere through the variable area final nozzle, which,in this exarnple, is shown pointing rearwards all of the time, ~u-t which could, if desired, be vectorable to direct the exhaus-t gases downwardly, for increasing lift, or sideways for attitude control.
The operation of the compound helicopter is as follo~"s:

For talce-off each of the gas turbine powerplants is run at maximulll power with -the variable area final nozzle in its rnaxilnum area l~osition. This provides the greatest pressure drop across the power turbine and hence maxim-lnl drive to the ro-tor 14 which Oenerates rnost of the ]ift, and minilnum propulsive thrust from the final no7~1e. ~dditional lift is generated by the compressed air from the low pressure compressor passing througl-l the augmentor flaps 28 which are pivoted to dire.ct the air downwardly. Thus the helicopter can taLce off vertically with only a very Ininor part of the energy remainin~ in the exhaust gas.?s creatirlg virtually no forward thrust from the variabLe area final nozzles 2~. Clearly, i.f the variable area final noz~les 21.~ are made -to be vec~orable to direct the exhaust gases downwardly, 3~ any erlerOy remaining coulcl be directed to provide still further lift.

i253479 Once airborne, if a conventional tilting helicopter rotor is used, forward flight can be initiated in the normal way. Alternatively the area of the final nozzles can be adjus-ted -to produce some forward thrust which will provide son~e ~orward velocity so that gradually the win~s will star-t to produce lift. This process can be hastened by radually pivoting the aUcrmentor flaps ~8 to~ards the horizon-tal position which provides a ~radua]ly increasin~ t`or~1ard thrust. When the ~in~s have st~r-ted to con~ri~ute to the lifting force necess~ry to keep the helicopter in the air~ the variable area final nozzles 2JI are closed down to off-load the power turbine 2.' th-Is reducinr-t~Ie power to the helicopter ro-tor 11I aIld increasing still fur-ther -the forward thrus~
on -the helicop-ter.

The reduc-tion Or po~er to, and consequent slowing down ot`, the helico-p-ter rotor is such as to enable relatively higrh forward speeds of -the order of 250 mph -to be achieved wi-thout the rotor the tip mach number of the advarIcing rota-tin~ blades becoming excessive.

The advantages of -the au~men-tor wing as par-t of the colllbination ~re tha-t i-t h~s a hioh lift coefficient an.i produces lo~ drag nt nIediuln speed. It also allo~/s -the win- pla(I area to be mirlimised which reduces -the efI(-?ct oI -tl-Ie ro~or dowr~ asl-l on the wingr lift.

~ Curth?r advarIta-re of a conIpound helicopter as de;criljed a~ove is -~hLit by simply choosing an appropriate nozzle aro~ erIoul1h l`orwarcl thrust can be produced ~ithou-t a significant :loss of lift from -the rotor, -to cn~ )le -the ~lelicoF~t?r to perform a shor-t take-off if overloale(l by runnir~r for~ard on the ground until the 1253~7g wing lift is sufficient to provide lift-off, ~his can significantly increase the range of the helicopter by increasin6 the amount of fuel carried at take-off, ~or the ~oidance of doubt the terln low pressure compressor used throu~hou-t this specification is to be understood to include the widely used alternative ~
term a fan.

Claims (4)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A power-plant for a compound helicopter which has a main lift rotor and at least one wing provided with one or more lift augmentation devices for producing lift in addition to that normally produced by the wing in forward flight, the power-plant comprising one or more gas turbine engines which have a low pressure com-pressor, a core engine which drives the compressor, a power turbine driven by the exhaust of the core engine and connected to drive an output shaft for connection to the helicopter rotor, ducting for conveying at least part of the air compressed by the low pressure compressor to the, or each, wing, and a variable area propulsion nozzle downstream of the power turbine, said nozzle receiving the exhaust from the power turbine and being operable to vary the power absorbed by the power turbine and simultaneously vary the propulsive thrust produced by the nozzle.

2. A power-plant as claimed in Claim 1 wherein the variable area nozzle of the, or each, engine is vectorable to provide either lift thrust or forward propulsive thrust.

3. A power-plant as claimed in Claim 1 wherein two gas turbine core engines are provided and the power turbines of each engine are coupled through a gearbox to drive a common output shaft.

4. A power-plant as claimed in Claim 3 wherein the ducting is divided longitudinally of the or each wing by a diaphragm and the air compressed by one engine is directed to one side of the diaphragm and the air compressed by the other engine is supplied to the other side of the diaphragm, the diaphragm and ducting being constructed and arranged so that failure of one of the engines does not affect the supply of compressed air by the other engine to the, or each wing.