On Mon, 28 Jan 2008 19:40:25 -0800 (PST),
wrote:

I had posted a link to a vid of a 701 weaving through the trees over
on .piloting.

At some point down the line I expressed interest in a VW powered 701.

One guy said he figured a VW would melt down in an aircraft cowling
when producing no more that 50HP.

He provided a link to Bob Hoover's blog, which had an entry "The
Christmas Engine", in which he states pretty flatly that:

1) No way to get 80 (let alone 100) HP out of an aircooled VW for any
extended period of time.
2) No way to cool an engine at those HP values if you could get them,
so you either get meltdown or very low time between overhauls.

Bob's blog looks as though he's talking direct drive. That pretty much
lines up with what I've read on the Great Plains website. GP says you
can only get higher HP from the VW by PSRU. That I can believe, on the
general principle that any engine has higher HP at higher RPM. Since
the VW wasn't designed to spin propellers, well, the best HP values vs
RPM don't align nicely for a direct drive VW and a propeller, do they?
That stands to reason.

So I'm asking this: for you VW people builders, what about cooling,
and is there some dyno data available from VWs spinning props with
PSRUs and direct drive available? Something somebody has been willing
to publish?

What about meltdowns? Because if what Bob Hoover says is true then it
seems to me there's no way Great Plains should be making a living --
unless their customers never have checked the numbers they GP claims.
GP has a lot of customers. You'd think they'd be screaming bloody
murder if they couldn't at least get close to 80 for takeoff.

I'm more concerned with thrust and cooling, though, than some HP
number.

What gives? What's "the truth"?

Doesn't matter what speed you run the V Dub, the stock cyl heads do
not have enough fin area to shed the heat of more than 40-50HP
longterm.. The mass of the heads allows short term higher output, but
the "thermal equalibrium" is reached just over 40HP.
If you thermal coat (ceramics) the combustion chamber and exhaust
ports, as well as the piston tops, you can likely push that 30% or
so..
You are still looking at a 50HP engine - and 50HP in a 701 is a
"ground hog". Just like the average dragonfly (although after off the
ground, a VW 'fly will REALLY go due to vastly superior aerodynamics.)

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