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Aviation History
1982
1982 - 2433.PDF
Rotaries for GA: Nasa gets serious Turbine-like smoothness, the ability to run on a range of fuels (even diesel) low weight, economy and quietness. The list of advantages claimed by Curtiss-Wright for the next genera tion of rotary (Wankel) engines goes on. There are still, it is admitted, a few technical barriers to cross before the full benefits of rotaries for light aircraft are realised, but there is no doubt that this type of engine is now being taken very seriously in the USA. The name Curtiss-Wright is synony mous with two of the most illustrious names in aviation. Wright-Cyclone was famous for radial piston-engines during the last World War, Curtiss with aircraft long before that. During the last 23 years Curtiss- Wright has staked its reputation on rotary engines. Its 750 h.p. BC2-350 ;s under development for US Marine Corps heavy armour and it is this engine which has served as the starting point for its general-aviation rotary engine study. Curtiss-Wright's rotary engine work began in 1958, when the company ob tained a licence for the NSU-Wankel design of rotary engine, and immediately embarked upon a major programme of design studies. Initially, attention focused on engines of about 500 h.p. but military interest led to a design for a 300 h.p. twin-rotor engine called the RC2-90. Designed speci fically for drone helicopters, it was not pursued because the US military dropped its requirement for such vehicles. But tests on the BC2-90 proved that rotaries were potentially extremely quiet, so Curtiss-Wright built another twin-rotor engine, the RC2-60, which was tested under US Navy sponsorship in a Lockheed Q-Star—the first aircraft ever to depend entirely for its motive power on a rotary engine. Again, the type demonstrated its neighbourly sound- levels and turbine-like smoothness. Examples were also installed in a Cessna Cardinal and in a Hughes TH-55A training helicopter. The latter benefited, Curtiss-Wright and Cessna have been working on a comprehensive study of stratifled-charge rotary engines for general-aviation aircraft. The results indicate that rotaries might well displace piston engines, and compete against low-cost turboprops In the Nineties. Julian Moxon reports. it turned out, from easier entry into autorotation, less vibration, and better accessibility. But the BC2-60 was des.igned primarily as an automotive engine and, although it proved the ad vantages of rotaries for flight, its power characteristics were unsuitable because of the kind of porting used. Curtiss- Wright did prove, however, that strati fying the incoming charge improved con siderably the engine's multi-fuel capa bility. Next, Curtiss-Wright talked to Cessna, Beech Aircraft, and Piper, and in 1977 Above A new shape in general-aviation propulsion? The RC2-75 encouraged Nasa to fund further development of rotaries for light aircraft. The turbocharger is seen at the right. Below the proposed RC2-32 with its accessories at the rear. No turbo- charger is shown—this would be further aft in the nacelle Propeller Reduction shaft gearing Rotor housing Air cond. compressor Starter Torsional isolator Mainshaft Rotor Coolant Oil pump pump came up with a design for a purpose- built general-aviation engine, the RC2-75. After some development this carburetted engine was judged competitive with con temporary reciprocating engines. Nasa had by then become sufficiently enthusiastic about rotaries to commis sion Curtiss-Wright and Cessna to carry out a design study for two versions of a much more ambitious kind of rotary engine. These draw on the combined benefits of stratifying and turbocharging the incoming mixture. The study, only recently released, is based on Nasa's objective of achieving 250 s.h.p. under cruise conditions at 25,000ft. A specific fuel consumption of 0-38 is demanded. The baseline engine is a flat-six Teledyne Continental TS10-550, regarded as one of the best current piston engines. Turbocharging this engine gives 298 b.h.p. at 25,000ft. The two rotary engines described in the report are intended for commercial introduction in the early Nineties, if the big three can be persuaded to move away from conventional power- plants. Curtiss-Wright is not, in fact, in tending to displace the engine manufac turers now in the business, rather to work alongside any which are seriously interested in rotaries, probably sharing production and support. The Advanced BC2-47 (the "2" means twin-rotor) is less ambitious than the RC2-32 Highly Advanced engine, which would need more development effort to FLIGHT International, 23 October 1982 1223
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