In article t,
Richard Lamb wrote:

Orval Fairbairn wrote:
In article .com,
wrote:


Richard Lamb wrote:

RapidRonnie wrote:


Bottom line is that if you use an auto engine made in the millions you
can research the failure rate, particularly if you pick an engine used
in motorsports run to destruction you can see where they fail first. I
would pay a premium, a big premium, to be able to fly a small block
Chevy in terms of a bigger airframe than you otherwise would, just for
that huge knowledge base.


Gently disagree, Ron.

The reason is that the prop loads are far different from anything you'll
see on the race track.


If I may be forgiven (or not) for reading about the Corvair crank
failures with rectal vision, they should not have surprised anyone.

I have never heard of anyone breaking the crankshat in their family
car,
that includes VWs. That tells me that auto manufacturers in general
and VW in particular have sucessfully designed their cranks to last
indefinately under nominal and even somewhat more adverse than
nominal conditions.

One supposes, however, that auto manufacturers do not make the
crank a whole lot stronger than needed to achieve that result.
A part that lasts indefinately is not improved by making it last
longer than indefinately when doing so would add weight which,
especially to a high RPM moving part, is generally a bad idea.

There are a lot of VW powered airplanes, and it is not uncommon
for the crankshaft to break in those.

If we make the unremarkable assumption that GM did not over-
design their Corvair crankshats any more than VW did theirs then
the Corvair crankshaft failures are quite predictable.

It is highly unlikely that any auto manufacturer is going to put
a crankshaft that is a whole lot stronger than needed into a
standard engine, don't you think?


Automotive crankshafts are designed to take loads in predominately
torquing modes, while aircraft crankshafts have to take bending and
thrust loads, due to the fact that they have a very large flywheel
hanging on the end, which resists changes in direction.

Either engine will work quite nicely for the purpose for which it was
intended. It is when you change the mission that you had better
understand how the mission changes the operating environment vs the
design parameters.

And, as Orval had likely experienced himself,
(dam long limber chain drives?)
PSRU's may take the gyroscopic forces out,
but can add harmonic resonance issues that
may be even tougher to deal with than a simple
broken crank shaft...

It all looks so easy on paper...

I didn't experience it myself, but I have witnessed a few less than
spectacular results. One was a Ford V-6 in a Mustang II -- very poor
job, V-belt broke and took out the ignition -- fatal.

Another two were in Stewart 51s: one was a Ford V-8 with full electronic
fuel injection, etc. The computer took awhile to set up for high power,
then took awhile for low power. It got some bent valves. Owner replaced
it with a Walther turbine after only four flights.

Another S-51 had a chain drive PSRU, which started eating up the PSRU
housing because of chain slop -- there were no tensioners on the chain.

I have also seen a few successes, too. One was the late George Morse's
Olds V-6 in his Skybolt and later in the Prowler. He found that you need
an AN water pump instead of the automotive one and that you also need a
coolant pressure indicator, in addition to temperature.

Another success (so far) is an S-51 with a V-8 (geared PSRU) that ahs
been flying here for about a year. I don't know what problems (if any)
he has had, but he is taking small steps.

As I posted earlier, you CAN fly, successfully, on automotive
conversions, but it is not for the novice and technically-inexperienced.