Quite a few Rotax engines are water cooled, and some of those are
certificated.

FAA rules stipulate that a homebuilt must complete a 40 hours testing
phase before it can be operated as a "normal" airplane. Before you can
even begin that it has to be approved by an FAA inspector who will
confirm that it's airworthy.

So if you can do that, it does't matter if you want an "airplane", car,
motorcycle, lawnmower, or boat engine powering it. If it will fly and
fly safely, then you're good to go.

Personally, I'll be using a Corvair auto conversion in my project when
the time comes.

Michael Gaskins
Stuart Grey wrote:
Okay, I don't know diddly; I've just caught the airplane bug. So, I'm
asking...

My buddy went out and spent multi tens of thousands of dollars on an
airplane engine. Lycoming, I think it was. Seems kinda pricy, but I
understand that most of that cost is testing, no iron.

I note that there was a lot of talk in the newsgroup and some books out
on Amazon.com on using non-certified engines.

How wise is that? The FAA really allows that, huh? If I had a noose in a
tree, and called it an experimental airplane, would the FAA let me fly
it? Probably not if the nose was over a populated area, huh? Just wondering.

VW engines are mentioned, I suspect because water cooled engines would
be too heavy for small airplanes, and it would introduce additional
cooling failure modes.

I guess I'm not smart enough to even know what questions to ask. So,
please discuss engines, so I can read the thread.

Is there a FAQ for this newsgroup?