Alternative GA Powerplants

Porsche returns to aviation

Not many readers would be aware that Porsche is no newcomer to aviation. In fact the West German car and engine manufacturer was building powerplants for airships back in 1909. Porsche is presently working closely with Mooney on a Porsche-powered production version of the 231. The aircraft is already flying and has successfully completed several hundred hours testing though a production decision to build a launch batch of around fifty aircraft won’t be made till the overall GA market improves.

Porsche are also working with Socata who are using a Trinidad as a test bed and a German group who have provided a privately sponsored Cessna 182. Both types are flying to plan though at present are being used purely as a source of engine evaluation data.

The Porsche engine in question is from the 911 sports car and is a flat six rated at 197bhp continuous power and is normally aspirated. This is similar to the unit used in the Airship Industries Skyship 500 and 600 airships. Designated PFM 3200, the unit comprises an aluminium block with fuel injection and a 28 volt electrical system. The unit weighs in at 190kgs and naturally uses mogas. Porsche are said to also be looking at a 300bhp turbocharged version of this engine. Porsche hope that if put into production the PFM 3200 would be around 10% cheaper to purchase and run compared with the present generation of GA engines. On the surface this does not appear to be a very big saving and so it may be some time before Wichita swings away from its traditional suppliers in favour of the flat-six from Germany.

A new era from Teledyne Continental

Who would have thought that one of GA’s major announcements at the 1985 Paris Air Show would have been that Continental’s engines were going to revert from air-cooled to liquid cooling? On the surface, the proposition sounds like a step back in time yet the logic is that by using modern metals and coolants the engine can operate at higher temperatures, burn less fuel and produce more power for a given capacity at a higher altitude.

Teledyne Continental have so far developed two liquid-cooled engines, the 110hp IOL-200 and the 170hp IOL-300. Both are derived from their 0-200 and 0-300 air-cooled cousins. These are the forerunners of a whole new family of engines that TC will have available by 1989 including a 450hp turbocharged unit that will rival turbines at altitude and at less than half the acquisition cost. The IOL-200 is a four-cylinder, liquid-cooled, 200cu in engine of 110hp at 2750rpm. Incorporating a new lightweight cylinder design and combustion chamber the unit has a compression ratio of 11. 4:1 for minimum fuel consumption. The larger -300 is a six-cylinder unit producing 170/190hp at 2700/3000rpm and also features fuel consumption consistently below its air-cooled version. At altitude, particularly, the liquid cooling is more fuel efficient as basically the coolant is being used to disperse engine heat in place of fuel.

Both engines are equipped with a high-performance lightweight centrifugal pump, gear driven on the rear accessory case. Integral coolant manifolds are included with high-integrity aerospace-type fluid connectors. In short, both engines offer improved fuel consumption, reduced wear, longer TBOs and better high-altitude capability.

TC is not putting all its eggs in one basket however and has also embarked on an ambitious programme of rotary engine development. The first line of engines in this class though might well be better suited to military RPV use though the technology they prove will ultimately flow onto GA engines in the future.

On the small rotary side TC has developed two units, a single rotor unit of 40hp at 7,000rpm and a dual rotor unit of 85hp at 2300rpm. The latter engine could be adapted for very lightweight trainers of the Robin ATL class. Both rotaries are liquid cooled and weight a mere 23kg and 47kg respectively. Both engines run on a variety of fuels including Mogas and TC hope to have both units fully FAA certificated by mid-1986. A 120hp rotary is also under study but won’t be available till the smaller units are fully developed.

Avco Lycoming launch the stratified charge rotary.

Not willing to let primary competitor, Teledyne Continental, steal the future GA engine market, arch-rival Avco Lycoming has offered a challenge by way of the stratified charge rotary. Avco Lycoming recently teamed with John Deere Technologies to pursue a $US30m R&D programme on obtaining FAA certification for their revolutionary engine by the end of this decade. .

In a recent interview with Australian Aviation,· Howard Knutson, President of Avco Lycoming Williamsport division, said the rotary will combine the best of both piston and turbine engine technologies. Compared to present-generation piston engines, the rotary will have a higher power-to-weight ratio, run smoother and have a smaller frontal area permitting improved aerodynamics and reduced airframe drag. The rotary will cost less than a turbine engine of comparable power, be superior in high altitude performance and have lower fuel consumption at all power settings.

Knutson said one of the rotary’s biggest advantages is its multi-fuel capability which even includes LPG, Mogas, methane and diesel fuel in addition to avgas and avtur. “The engine to be developed initially will be liquid cooled and aimed for the 350- 400hp GA market” Knutson said. This includes the top end of the personal aircraft market, the middle segment of the business aircraft category and the lower end of the commercial and commuter aircraft market Ultimately though Avco Lycoming will be able to scale the engine to the market and so offer a complete range of rotaries from -100hp through to as much as 1000hp.

Knutson noted that the decision to invest $US30m in developing the rotary engine for aviation applications came after intense study of alternative technologies during the past three years. “The rotary, with a stratified charge, turbocharged configuration offers the most advantages,” he said.

The advantages of stratified charge, turbocharged rotary aircraft engines are outlined in further detail –

Stratified Charge: This combustion system can best be explained by following the rotor through the combustion cycle. As the rotor begins the combustion phase of its revolution, a ‘rich’ fuel/air mixture is injected into a small combustion area so that combustion can occur. This ‘rich’ fuel mixture eliminates the need for high octane fuel. As the rotor continues to turn, the combustion area becomes much larger and a ‘lean’ fuel mixture is injected (by a second injector) to complete the combustion phase. Because of the leaner fuel mixture, fuel efficiency is greater than that achieved in a piston engine. And since combustion is more complete and a low lead fuel is being used in the first place there are fewer exhaust emissions.

Multi Fuel Capability: Because of the stratified charge, the rotary can be certified to burn either avtur, avgas, Mogas, LPG, alcohol, methane or diesel, but not interchangeably. Current aircraft piston engines can only burn high-octane avgas with a few engines approved for Mogas. Turbine engines can only use, avtur or its equivalents. The capability to burn a variety of fuels including avtur and Mogas will ultimately be a significant advantage for aviation since these fuels are less expensive and more plentiful. Avtur is universally available and will be for many years to come while crop dusters and some remote operators could find it desirable to use either LPG, diesel or methane.

Low Fuel Consumption: The rotary’s stratified charge results in lower fuel consumption per horsepower extracted. Unlike a turbine, but similar to a piston engine, the rotary will have significantly lower fuel consumption at reduced power settings or when idling. Rapid Descents: The rotary engine more closely resembles a turbine in its ability to permit aircraft to make rapid descents from altitude because of its liquid cooling. Sudden and dramatic changes in engine temperatures resulting from rapid descents can damage an air-cooled piston engine.

Other general improvements to be found with the rotary include an improvement in reliability through a reduced number of moving parts, quieter running, low airframe drag due to its small frontal area, low engine weight, and simple maintenance with overhaul costing less than half the equivalent cost of a turbine.

Avco Lycoming and John Deere have already put much time and money into their rotary development and hope that by January 1990 the unit will be in mass production for a whole new range of aircraft possibilities.

Closer to home is the well-documented efforts of Ralph Sarich and his Perth-based Orbital Engine Technology group. This R&D centre has been heavily backed by BHP for nearly a decade and the fruits of their endeavours are soon to be realised as a massive licence engine contract build is rumoured to be ready for signing with one of the ‘Big Three’ US automobile manufacturers. Basically, the definitive Sarich unit is less than half the size and weight of a comparable automobile production engine while at the same time producing double the torque with an overall reduction in fuel burn to boot. Sounds too good to be true but the units are now being road tested in GMH Camira vehicles and their application to aviation in the longer term must surely be obvious.

So there it is, years of inactivity by the GA engine suppliers has finally swung around to the point where a number of new technologies are being meshed with the established piston engine in an attempt to reduce the cost of ownership and operation of tomorrow’s General Aviation aircraft.