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Rotary engine technology takes off in general aviation

The EUREKA E! 2743 KERO project is driv-ing key Federal Aviation Authority (FAA) certification for Wankel rotary engines in general aviation. Swiss project leader Mistral Engines plans to supply a range of such engines for original equipment and retrofitting in all types of light airplanes and helicopters. Advantages include excellent reliability as there are few moving parts, a high power-to-weight ratio, compactness and smooth running compared with conventional piston engines. Moreover, the engine will run on widely available jet fuel. Oth-er potential applications include marine engines as well as light industrial ap-plications such as portable generators, compressors and pumps.

The four-stroke piston engine

technology used in the majority of light

airplanes involved in general aviation

dates back 60 years to the Second World

War. So, while designs are well proven,

motors require some 70 or 80 moving

parts and still run on 100-octane low-

leaded (100 LL) avgas fuel that has long

been displaced by heavier kerosene-

based jet fuel for commercial aircraft.

Moreover, 100 LL fuel is mostly limited

to North America and Europe; even

there it is becoming increasingly scarce

– and is soon to be banned completely

for environmental reasons.

Mistral Engines therefore saw a major

market for a safer, more reliable motor

that could be easily adapted to any

model of light aircraft and able to run

on industry standard jet fuel. The design

is based on the Wankel rotary engine

pioneered originally in Germany in

the 1930s but which emerged at the

wrong time. So far, it has only really

been developed and commercialised by

Japanese car maker Mazda in its RX-8

models and previous models.

Few moving parts

Safety and reliability are key factors in

aviation. The Wankel engine has a rotor

instead of reciprocating pistons, doing

away with any need for crankshafts,

pistons, valves and springs and reducing

the number of moving parts to only two

or three very robust ones. With so few

moving parts, the engine is extremely

reliable and safe. However, the rotary

engine is difficult to run in a fuel efficient

manner. Recently, the availability of

modern automotive electronics has

made it possible to overcome timing

and injection control complications,

resulting in fuel consumption similar to

that of piston engines.

Rotary engines for small planes are not

completely new. Many amateurs in the

USA have adapted car engines for this

purpose. It is actually a technology

particularly well fitted to aviation

applications. “We therefore decided

to take the Mazda rotary engine block

and to build an aero engine around it

that could be retrofitted to all aircraft,

explains Claude Geles, one of Mistral

Engines co-founders.

“Mounting an engine in an aircraft is a

delicate process and very expensive. We

also had to design a suitable gearbox.

Modern electronics now make it possible

to have exact timing for fuel injection

and ignition. The resulting engine looks

like a turbine; it is not really a turbine but

EUREKA labelling enabled us to find the 10 million euro in private equity financing that we needed to see the project safely through to a fully certified product ready for manufacture.

Claude Geles - Mistral Engines, Switzerland

Advances in combustion chamber design and electronic management systems are making it possible to develop a reliable rotary engine for small planes running on standard kerosene jet fuel

Shaping tomorrow’s innovations today

has many of its advantages, including a

very low level of vibration, it is light-

weight, compact and it is water cooled

– making it possible to change power

output very quickly without thermally

stressing the engine.”

Several partners involved

Several partners are involved in

the EUREKA project. The Ecole

Polytechnique Fédérale de Lausanne

(EPFL), where research was funded by

the Swiss Innovation Promotion Agency,

CTI, is studying the best combustion

conditions for the kerosene in terms

of combustion-chamber design,

injection and ignition. “We are also now

developing a special exhaust silencer

with the EPFL to limit the noise, using

active and passive noise- reduction

technologies able to work at very high

temperatures,” adds Geles. “This has

not been done before.”

The necessary electronic management

system was developed with French

partner DEM Electronique. The resulting

digital engine-control system features

full redundancy – essential for aircraft.

The heart of the system consists of

two separate computers which check

each other’s operations continuously.

In the unlikely event of one failing, the

remaining calculator immediately takes

over the entire engine management.

Full system redundancy extends to fuel

injectors and spark plugs.

Mistral Engines has been collaborating

with the Embry-Riddle Aeronautical

University in Florida, USA for flight

testing. The university will also help

in introducing the engine to the US

market. “We have had lot of discussions

with the FAA and we are certain that our

engines can be certified,” says Geles.

General aviation is presently in a high-

growth phase and is desperately looking

for new aircraft engine technologies.

About 65% of this market is in the USA

and the Americans are not developing

suitable new engines. The results

of KERO are expected to be already

marketable in 2010, as soon as FAA

certification is available. Petrol-fuelled

versions are already in production and

the kerosene version will use many of

the same parts. Parts are manufactured

by a range of companies, mostly in

Europe.

Labelling key to funding

EUREKA labelling played a key role

in obtaining funding for the Mistral

Engines’ development. “While we

managed to start the work with ‘pocket

money’,” explains Geles. “EUREKA

labelling enabled us to find the 10

million euro in private equity financing

that we needed to see the project safely

through to a fully certified product

ready for manufacture.” Most of the

technical problems have already been

overcome – one problem still being

tackled is pushing away the detonation,

or pre-ignition, limit. Nevertheless,

Geles predicts full FAA certification

within 18 months of the project ending.

The sky is then literally the limit!

We decided to take the Mazda rotary engine block and build an aero engine around it that could be retrofitted to all aircraft.

Project participants:Switzerland, France

Budget: 3.8 MEuro

Duration: 85 months

ContactMistral Engines S.AChemin Jacques-Philibert De Sauvage, 371219 Geneva, SwitzerlandClaude GelesTel.: +41 (22) 920 03 58 Fax: +41 (22) 920 04 09Email: geles@bluewin.chwww.mistral-engines.com

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www.eureka.be