I have no first hand experience, but have been watching these auto conversio
ns for many years. My conclusion is that the gearbox is always the weakest l
ink. The Honda fit core for example is an amazingly durable engine (also use
d in their outboard marine engines). The issue with the geared engines is o
ne of harmonic resonance - but contrary to what most think the issue is not w
hen loaded, but rather when the prop is unloaded - typically at idle or on a
pproach. Regardless of the engine's HP, when resonance feedback peaks it ca
n be very destructive, needing to dissipate possibly hundreds of HP to dampe
n it back down. The simple rubber isolators used by Viking (and also aeromo
mentum) are IMHO totally inadequate...... indicated finally by a VIking in-f
light failure (I expect more to come). Rotax have dealt with the issue usi
ng dog-clutches etc., a high idle and other tricks? Could it be that the ai
rboat application mentioned is different in that the engine is either at idl
e (normally set above the resonance frequency to avoid the issue) or high po
wer.... no approach-no-prop-load conditions.
I concur that if one is only looking to save money: don't - go with the rot
ax, or a direct-drive non-geared engine, it will be cheaper in the long-run (
no bent airplane parts). As others have already mentioned an auto-conversio
n is an exercise in engineering ... which can be a fun and rewarding effort.
Cheers,
Pete
A239
PS - Looks as if the D-Motor folks are getting their act together and will s
oon have a very nice liquid cooled, light, direct drive, simple, durable eng
ine - the 6cyl will be about equivalent to the 914 (tho not normalized obvio
usly).
PPS- At osh now.... the place is looking good and the weather is great. B52 j
ust landed. Don't forget to drop by and grab a beer/pop :-)
> On Jul 19, 2017, at 11:11 AM, GTH <gilles.thesee@free.fr> wrote:
>
>
>> Le 19/07/2017 =C3- 12:37, graemeh a =C3=A9crit :
>> I realise that installing an alternative engine will be more work and tak
e more time. My challenge is to assess the extra build time vs how long it w
ould take me to save for the Rotax and also add in a risk factor to allow fo
r the extra risk in going for an alternative engine.
>>
>> [...]
>> Thanks again for all who have contributed and I'd appreciate hearing furt
her from anyone with direct experience in using alternative engines (on a Eu
ropa or other aircraft).
> Graeme and all,
>
> As one who made an alternative engine *installation* albeit with a proven e
ngine, I hope you'll allow me to express my opinion ;-)
> Devising a correct engine installation from scratch is not really the prob
lem. It takes time, research an lots of common sense, you'll find lots of in
fo on Contrails !
>
> The problem is with those alternative engines. The best way would be to in
terview several knowledgeable people with direct experience of a working ins
tallation, and a few hundred (preferably thousand) happy engine flight hours
in their logbook.
> But if those people did exist, then we would not be talking about an *alte
rnative* engine, but about a *proven* engine.
>
> Bottom line, if you have time and money, and are eager to help develop the
engine, by all means go for it. You'll be a pioneer, have lots of fun, lear
n lots of things, and discover there is no substitute for thousands of engin
eer hours, test cell time, destroyed engines, and thousands of flight hours b
efore you achieve a reliable aero engine.
>
> But don't trust the degree on the wall, the videos and the "we addressed t
he torsional" blah blah. Ask for the blueprints, the actual number of engine
s actually flying, the address of actual users atctually flying the engine, s
tudy the Service Bulletins - if there are none, caveat emptor, the engine ha
s no flight experience.
>
> On the other hand, if money, or time, or workshop equipment is key, then g
o for a Rotax (even a second hand one), devise a correct cooling installatio
n, and you'll soon be a member of the happy flyer-builder family.
>
> FWIW
>
>
> --
> Best regards,
> Gilles
> http://contrails.free.fr
> http://lapierre.skunkworks.free.fr
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