Orbital Engines for Aviation?

Compact, Light And Powerful With A Torque Band That Lies Just Where An Aviator Needs It.

Three subsidiaries exist; they are the Orbital Engine Companies of Perth (research and development) and Michigan (manufacture); and, Orbital Fluid Technologies of Michigan (fuel systems). Orbital has been thorough in protecting its intellectual property by lodging 780 patents and patent applications in 26 countries, and continues to expand its patent portfolio. Millions of motorcycles are registered each year. It has been agreed that clean, OCP engines of 50cc (3hp/2.2kW) and 150cc (5hp/3.7kW) will power a range of motorcycles. An engine programme with Jaguar could be of particular interest to aviation. The engine is a 350hp (260kW), 3.2 litre V6 it is compact, powerful with plenty of low down torque and weighs only 170kg. All Orbital engines use the orbital combustion process (OCP). In essence it is a direct fuel injected, stratified charge, which, due partly to the consistently small fuel droplets of about six microns in diameter, promotes stable and efficient combustion through all power ranges. An electronically controlled, exhaust port valve and a tuned exhaust system containing a fast light off oxidation catalyst, ensures that efficient scavenging occurs; this allows precise control over exhaust gas levels. The benefits are light load fuel economy, high torque at low speed, and low emissions.

Like all good companies of the 90s Orbital is ‘green’ in its outlook. The company uses phrases like ‘social responsibility’ when referring to its own role. And it is not rhetoric – the figures support Orbital’s claims of an energy efficient, resource modest, clean output engine. Orbital engines surpass rival four stroke engines in the same class in weight, power, fuel economy and emissions of hydrocarbon (HC), carbon monoxide (CO) and oxides of nitrogen (NOx). The engine meets the tough Californian emission standards, and those set for Europe in 1996. As an example, the 1.2 litre OCP engine was 40% below the European limit for HC and NOx emissions and 93% below the CO limit. And as a result of the varied driving conditions – town and country – the OCP returned a consumption of 6.1 litres/100km (46mpg) for a 910kg (2000lb) vehicle. A similar 1.4 litres, four stroke vehicle returned 7.4l/100km (38mpg).

Of course the question in everyone’s mind: what about the engine’s durability? Orbital has achieved better than 700 hours high speed dyno running and is aiming at 1000 hours. A number of four stroke manufacturers use a 500 hour target. These tests are conducted with the engine under different loads – then for about 100 hours at 5000rpm without load, which really sorts the engine out. Orbital cites the engine’s comparative simplicity (fewer moving parts), its balance (low vibration) and its even fuel burn as the contributors to its impressive durability. The Orbital Engine Corporation recently toured Australia’s eastern states with two European Ford Fiestas fitted with 1.2 litre OCP engines. AA Managing Editor, Jim Thorn and AA author and correspondent Stewart Wilson both with long time motor racing backgrounds and this writer all test drove the vehicles at Goulburn’s Wakefield Park Speedway. We were then asked our impression on engine response, smoothness, vibration, noise and acceleration at varying speed ranges. The cars were fitted with five speed gearboxes and handled nicely. The test procedure involving a number of requirements for accelerate-stop regimes in order to simulate both city and open road driving impressions were that the engine felt much like a 1.8 litre four stroke. It was quiet, immediately responsive, and without any flat spots in throttle application and cornering; and it delivered impressive acceleration, especially from mid to higher speeds where many four strokes under 2.0 litres tend to trail off.

Also, there is no denying the much mentioned torque curve. During one exercise this writer deliberately placed the vehicle in fifth gear instead of second, yet the subsequent driveaway was still smooth and positive without shudder or valve bounce from as low as 20kph and 500rpm. And I hasten to add that this was at an uphill section of the track. The engine cannot be over revved, incidentally, as there is an automatic fuel cutout at 5900rpm, thus providing a sort of natural governor. Vehicles in this configuration are presently being test driven by British police units and Orbital says that the feedback is very satisfactory. The OCP Fiestas are normally aspirated and deliver in excess of 160kph on the motorways. Testimonials exist from the British press which indicate that officers prefer the OCP Fiestas for their patrols. Two hundred are also being imported into Australia in 1995 for local evaluation via various government agencies.

The 1.2 litre OCP engine’s standard power output is 80 hp (60kW), and 100hp (73kW) with a blower. It is reckoned that the engine consumes about 2.5 litre of oil for every 100 hours of mid rpm operation (5000km). Early research found that a three cylinder configuration was favourable with two stroke operation because of the positive tuning influence of the pistons to each other, resulting in low vibration. For this reason it is probable – though not definite – that most OCP engines will appear in three, six or twelve cylinder layouts. In aviation the 1.2 litre OCP’s application could possibly be in experimental and sports aircraft, gyrocopters and light trainers. As the engine’s optimum performance is at about 3500rpm, it is envisaged that the engine would drive an advance, low rpm propeller through a reduction gearbox. Orbital software and technology would negate the need for mixture control and the dreaded carby heat.

Orbital’s new inline, 2.0 litre six cylinder engine is currently being tested in large sedan vehicles again with impressive results. The engine is produced standard with an integrated blower and it is short enough to be mounted transversely – from the driver’s perspective – between the front wheels. It weighs just 100 kilograms (four stroke equivalent – 180kg) and outputs 160hp (120kW). This could be applied to new generation four seater singles, light twin trainers and light helicopters. However, the 350hp (260kW) engine developed with Jaguar is probably the most applicable to general aviation, especially in high performance singles and light twins of 6-10 seats. Pilots flying the latter would no doubt enjoy the luxury of comparatively more spare horsepower with the advanced, low drag airframes. Taking Orbital’s rule of thumb of about 50kW/litre, it’s realistic to predict that a 6.5 litre OCP V12 would deliver 700hp (520kW) and weigh 220kg. Weight does not double with the cylinders. A pair of such engines would easily power 12 seater executive and commuter aircraft to 25,000 feet with a clean and mean fuel burn and at airspeeds approaching the much more expensive gas turbines.

OCP engines are also excellent performers in the cold, and have been tested to -30°C. Orbital states that OCP engines can also be easily modified to run on a range of different fuels. Unfortunately all of this aerospace projection at present is supposition, although Orbital has hinted that it would develop such an engine as an OCP V12 if an airframe manufacturer demonstrated a commitment to it. Before retiring from the board of Orbital, Ralph Sarich (who apparently still tinkers) told this writer in 1988 that the concern with aviation was corporate liability, and it was thought in the short term that military aviation – remotely piloted vehicles and light observer aircraft – would probably be the first aviation application for OCP engines. One thing is clear however, and that is unless some sort of quantum leap occurs with four stroke technology, the OCP engine is the good neighbour engine of the future and its quiet hum will ultimately replace the chortling of the ageing Chieftains and Excalibur.