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.