AEROSPATIALE has formed a new enterprise with car and truck maker Renault to offer through its general-aviation subsidiary, Socata, a range of all-new horizontally opposed four-cylinder diesel engines for light aircraft.

A new company, Société des Moteurs Aeronautique, has been created to develop and produce the engines, which will be available for retrofit to existing Socata aircraft and to power new versions, says Socata president Jean-Marc de Raffin-Dourny. The first example, powered by the 186kW (250hp) MR250, is set to fly on a Socata TB20 Trinidad "before the Paris air show" in June, he adds, with certification set for early 1998.

By designing an all-new engine, the team hopes to avoid the problems which have plagued those attempting to use converted car engines for aviation, says Renault Sport president Christian Contzen. The use of a four-cylinder turbocharged diesel, which runs on kerosene (jet fuel) instead of specially prepared Avgas costing up to three times as much is the main contributor to the claimed 30% reduction in ownership costs over a conventional engine, he adds.

The new all-alloy engines are all built from the same common components, "reducing maintenance costs", says Socata's project director, Luc Pelon. The 185kW and 225kW versions have 90%parts commonality, the 135kW version, lacking the reduction gearing of the larger engines and having a smaller turbocharger being about 75% common. Pelon admits that the lower-powered engine is "about 10% heavier" than a conventional 135kW powerplant, but adds that this is "-compensated for by the lower costs of ownership and reduced fuel consumption".

The new 5-litre powerplants will cost "about the same as existing engines" says Raffin-Dourny. They will also be "around 10dB" quieter than traditional types because of the slower, 2,000rpm propeller rotation speed, he adds.

Other advantages claimed for the diesel are 3,000h time between major overhauls and better retention of power at altitude, with the MR250 producing 70% of its sea-level power at 25,000ft (7,600m) compared to 40% power for a piston engine.

Socata claims a two-year lead on the US NASA/Teledyne Continental effort to develop an aviation diesel engine, and adds that the French air force has already shown "strong" interest in re-engineing its fleet of Epsilon trainers.

Source: Flight International