LeSving wrote:
No. All this stuff is there to: Increase reliability (by optimizing the core engine running parameters)
Are you saying that having more than ten separate fluid hose sections connected with engine, radiators etc. with clamps – where failure of even one hose or clamp makes the coolant or oil go away – means that they wanted to increase reliability?
I think – they had to do it – otherwise the engine would be either much heavier or produce half of the current power in order not to overheat.
Well, yes, if you want all the “hot” bits to remain more or less the same size, you have to provide water cooling 
And that introduces a major failure mode. In terms of R&D and “engineering for reliability”, GA is roughly in the 1970s
and back then, when you drove along any major road, the roadside would be lined with these, with steam coming out of the engine compartment Especially the uphill parts.
In cars, this has been solved, cheaply, with lots of engineering, and in GA it has been addressed with varying degrees of success, and done better on say a DA42 than on a Eurofox (better quality pipes and fittings).
if you want all the “hot” bits to remain more or less the same size, you have to provide water cooling.
That’s not actually correct. I have for example several air cooled motorcycle engines that run under 0.0015
inch (0.03 mm) diametric piston to cylinder clearance when cold and that small clearance is maintained when the pistons are heated and expand. The reason they can do that is that the cylinders are made of the same material as the pistons, and are coated with a very thin layer of hard nickel/silicon to make them last. Purely air cooled aircraft engines aren’t made that way, except for some experimental engines. Production air cooled aircraft engine cylinder technology predates the possibility to reliably hard coat aluminum cylinders.
In principle, the reason for liquid cooling is to increase power density and operating speed, as I mentioned above, particularly in applications where introducing a gearbox on the output is not an issue. Also, for e.g. cars and motorcycles it provides a secondary benefit in noise reduction and ability to idle for long periods in traffic that is irrelevant to aircraft, and it makes implementing digital fuel injection easier because one coolant temperature probe tells the story for all the cylinders.
Regardless, air cooling is a technically valid solution for light aircraft, especially if you want an engine that is ‘industrial’ is its ability to operate without much attention, and accordingly doesn’t have much fussy ancillary hardware. I am happier with that kind of engine for my service in my aircraft.
Silvaire wrote:
Air cooling is a good solution for light aircraft, especially if you want an engine that is ‘industrial’ is its ability to operate without much attention, and accordingly doesn’t have much fussy ancillary hardware. I am happier with that kind of engine for my service in my aircraft.
Most Rotax engines are non certified. For a certified installation (of any engine), part of the certification is to make sure the engine parameters are within specs under normal operation. This is obviously not required for a non certified installation. Some manufacturers still do a good job, others don’t. This translates to a certified installation (of any engine) can be operated without much attention. If special attention is needed, this is duly communicated in the POH. For a non certified installation, the default state so to speak, is to always pay attention to what is going on with the engine. It takes longer to know the aircraft.
Experience with Rotax engines installed in Sportcruiser aircraft has illustrated that the MAJOR reliability issue is the quality of the flexible rubber hoses.
Using cheap hoses just because they look the same as the original hoses is a bit like fitting a chocolate pin to a hand grenade. There is a very good reason that Rotax & the airframe manufacturer puts a life on hoses.
“Using cheap hoses just because they look the same as the original hoses is a bit like fitting a chocolate pin to a hand grenade. There is a very good reason that Rotax & the airframe manufacturer puts a life on hoses.”
Even for a Rotax 912 in a ULM this is stressed in the POH, or at least it is on the Super Guepard.
I am a life long sceptic on these sort of statistics without being able to study the methodology behind them.
Here there is a largish market these days whereby owners of certified Rotax powered aircraft will, when the engine reaches TBO or when a 2nd TBO becomes due, sell the engine into the ULM or experimental. I wonder how these figures have been treated in these statistics.
Without the methodology its database we could define our own statistics. As an example of this I would invite you to look at engine failures over the last few years on this very forum.
You might well get the impression that Cirrus engines are the most unreliable. Are they? Or is it because the reports are more publicised. As in the media are fascinated by the fact that a aircraft can safely return to earth under a parachute, whereas the Bonanza or PA28 which a pilot manages to land safely back on the airfield or even some other field, gets no attention at all.
