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Rotax engines - more efficient than Lyco or Conti?

There are more and more Rotax engines popping up in 4 seater aircraft nowadays.
IMO 3 reasons
1/ Engine weight
2/ Cost of engine both new and to overhaul
3/ Fuel consumption
In the USA cost of fuel has been historically unimportant in GA aviation. This is not the case in Europe and with Avgas on and around €3/litre it is a significant portion of GA hourly costs.
Diesels are great for fuel consumption but they are expensive to purchase and to overhaul if you can overhaul them. Plus they are heavy. The women at our club will not pull the DA40D put of the hangar if there is not going to be someone there to help push it back up the slope into the hangar at the end of their flight.
An electric tow is on the club’s shopping list as soon as there is spare money.

France

4 seaters with negligible capability though; not enough HP. Especially for the average person’s weight today.

Administrator
Shoreham EGKA, United Kingdom

What negligible capability. I can’t see much difference if one makes like for like comparisons.
Eg the newTecnams v Cessna 172s or PA28s.

France

Silvaire wrote:

If I had a C172 (or a Tecnam P2010) with a six cylinder liquid cooled EFI turbocharged geared Rotax making 200 HP, I would be looking to replace it with something more like a four cylinder O-360 Lycoming.

gallois wrote:

What negligible capability. I can’t see much difference if one makes like for like comparisons.
Eg the newTecnams v Cessna 172s or PA28s.

A 140 HP 915 with turbo and CS prop will perform much better overall than a similar 150-160 320 with fixed pitch prop. CS and turbo obviously drastically increases the efficiency of the engine installation in an aircraft. But, they are also complex, expensive and adds maintenance time- and cost.

The elephant is the circulation
ENVA ENOP ENMO, Norway

Lycoming 320s are about €9000 -€10,000 more than the Rotax 915iS.
Average Fuel consumption in a APM41 Simba about 27l/p/h
Average fuel cosumption of the 320 in a Cessna 172 is around 30l/p/h IIRC.
An MCR4S with 915iS certainly looks to have better performance than both in all figures.

France

@LeSving, FWIW my choice in the Lycoming O-320 line for a new plane that is being optimized for fuel economy would be an IO-320 with a Whirlwind constant speed prop. The 160 HP IO-320 with 9.0:1 CR burns about 7.5 US GPH in cruise (or 28 liters per hour) and Whirlwind makes the most advanced props currently available for any engine IMO.

The specific fuel consumption of the IO-320 as I mentioned above is probably a bit better than the 135 HP Rotax and it makes more power, but it is heavier. I think it’s plenty small enough for a compact installation (the twin Comanche cowling below being a good example), and air cooling makes it better in that regard. It’s also notably easy to own and maintain by a private owner with a budget, there aren’t any better in the same power range: 2000 hr TBO followed by $25K engine overhaul for another 2000 hrs and so on, the engine core lasts likely 6000 hrs.

The application for which I would choose the turbo Rotax instead would be a high altitude focused operation in a plane designed specifically for that, hopefully operated by an organization that could maintain it and replace it every 1200 hrs or so. UAVs have been using the turbo Rotax in that role since circa 1988, although less so today than in the past due to limited power and the ever growing requirement to carry increased weight.

Last Edited by Silvaire at 03 Nov 15:12
26 Posts
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