Subaru engines

[highwingloader]

I have picked up a rumour that Subaru engines are bad news. Most people I have spoken to tell me that if it's not a Rotax then don't bother. What is the background to this view? People with Subaru engines all tell me they are fine and don't know what all the fuss is about.

Grateful for any views.

[slim_slag]

Ah, thought I was on JetBlast...

Wouldn't put one in an aircraft, best bang for the buck is to buy a mid time used Lycoming. Car engines produce all the power at the wrong rpms (way high) so you need a massive piece of kit to reduce the rpm to what a propellor works best at (way low).

Car engines are not designed to produce power at 5000rpm for very long. I wouldn't go anywhere in a plane behind a subaru engine unless I knew I could glide to an airport. In a car, they are superb, probably because they are horizontally opposed so can keep cool.

[FlyingForFun]

Highwingloader - do I know you? You posted this question the day after a friend of mine asked me exactly the same thing. My friend uses a different PPRuNe alias, so unless you've got two aliases, it must just be coincidence!

I asked around on behalf of my friend, and got an e-mail from one of the guys who built my Europa. On the assumption that you're not the same person who asked me about Subarus over the weekend (in which case, check your e-mail!), here's the reply I got:FFF,

You're correct about the negative aspects of the Subaru. Tell your friend not to touch it and to stick with Rotax 912 engines., preferably 912S or 912 with a wobbly prop.
The Subaru had a number of mechanical problems as well as being heavy. I know of no one installing them in Europas now!

RegardsHope that helps!

FFF
-----------

[Oscar Duece]

So Subaru engines are no good because: they only produce the required power at high rpm (5000) and need to use a reduction gear (psru).
Well isn't that the case for the Rotax (aka Austrian hand grenade).
At least the Subaru will only cost 25 % of a Rotax unit.

What's is it in ? or going in ?

Alternatives: small Lycoming or Cont., Wam 120, Limbach etc...

[slim_slag]

Oscar,

Yep rotax need the reduction gear too, but at least they are certified (or can be). Never heard of a sooby certified engine, heard of several which have blown up when taken to places the original designers never intended them to go. It's an old argument, just one opinion of many, and I wouldn't dream of stopping people putting them in their homebuilts.

[Brooklands]

There seems to be something of a following for them in the US for RV and Glastar kit planes. Look here (http://www.eggenfellneraircraft.com/) for somebody who is 're-manufacturing' them for kitplanes. The downside is that they look as they're only available in the US.

[LowNSlow]

The revs in the ad were quoted as being in the high 3,000 to low 4,000 for cruise settings. Isn't this similar to the Rotax 4-strokes? Scooby's have a reputation for pretty bullet proof engines in their cars where a lot of them spend a large part of their time in upper reaches of the rev range ie; 'normal' cruise rpm is around 4,000 rpm @ 100 mph.

I don't know, but think it could it be safe to assume that there have been a few less than professional conversions of the Scooby flat 4. How many were lifted from scrapyards rather than converted from factory new engines, I have read the articles written by people who have changed the oil and determined from the cleanliness that the engine was OK. Anybody who takes such a cavalier attitude to their engine are asking for a failure IMHO.

As a further comment, gearbox design can have a significant effect on engine reliability due to the vibration and bending loads transmitted back to the crankshaft from the prop / gearbox combination. Isn't Rotax up to the C model of gearbox in a relatively short space of time?
Adapting a gearbox to suit an engine may give you the speed reduction you're looking for but it may transmit unacceptable vibrations and loads which in the medium to long term will wreck your engine.

[FlyingForFun]

LowNSlow - re Rotax RPMs, I can only speak for my Europa, which is fitted with a Rotax 914 and variable pitch prop. With the prop at its full coarse setting, it cruises at around 120kt at 4600rpm, or 100kt at 4000rpm. I tend to use somewhere roughly in the middle, but I would guess that your quote of "high 3,000 to low 4,000 for cruise settings" may be slightly on the low side compared to my experience, although not by much.

I don't know how this would compare to a Subaru engine/gearbox combination.

FFF
--------------

[highwingloader]

Thanks for all that guys - good stuff. And for the benefit of FFF, I think you should apply for the diplomatic service (not for your performance at Gatwick on Sat night but for your abilities as a spy!!!!!)

Thanks for the trip in your Europa - great fun. Must get you Caravanning soon!