A diesel engine designed for light helicopter singles has been running on a test bench in Trappes, France since March as part of Europe’s Clean Sky, a €1.6 billion ($2 billion) research project. The 440-shp demonstrator is a tradeoff between car racing performance and aviation safety and durability requirements. It is planned to eventually power a Eurocopter EC120 for flight tests.
Compared to a turboshaft, the main benefit of a diesel is its fuel efficiency. Its main shortcoming is its power-to-weight ratio. The promoters of the diesel demonstrator – itself part of Clean Sky’s Green Rotorcraft “integrated technology demonstrator” – believe it may make sense to use a diesel on a light helicopter. Part of the weight penalty can be recouped thanks to an adapted airframe and the smaller amount of fuel needed, for a given range.
The V8 engine that is being tested is the HIPE AE 440 – the result of a collaboration between France’s Teos Powertrain Engineering and Austria’s Austro Engine. The former company, which specializes in car racing, designed the core engine. The latter manufacturer rather focused on components like the full authority digital engine control (FADEC) and, above all, airworthiness.
The engine has a total weight (including oil, accessories, etc.) of 528 lbs. For an equivalent level of performance, a turboshaft would weigh between 265 and 285 lbs. An equivalent level of performance does not mean equal power rating. A diesel retains its performance from sea level to 8,000 feet at ISA+20 temperature, which a turboshaft can’t do, according to Clean Sky officials. However, the demonstrator is not fully optimized, its designers concede. The starter is not a starter-generator and it has two batteries instead of one.
In September, the demonstrator will move from the test bench to an iron bird. It will then, in January or February, be integrated into the demonstration aircraft. Ground tests will last until April next year, when the first flight is planned. The flight test phase is expected to run through October 2014.
Prior to the trials, the engineers, with Eurocopter playing a major role, are using the test bench to address issues such as torque oscillation and vibration. A mechanical system will reduce vibration, otherwise a stronger main gearbox would have to be designed.
Some modifications have actually to be made to the EC120 airframe. They include engine attachments and the addition of a clutch. Thanks to the FADEC, the diesel’s behavior will be “as close as possible” to that of a turboshaft for the pilot to feel comfortable, engineers pledge.
The €20-million ($26-million) program aims at proving a fuel burn reduction of 30 percent can be attained on an existing helicopter airframe.