Bret Ludwig wrote:
J.Kahn wrote:
snip

Exactly right Clare. The soob has a bulletproof interior but the use of
liquid cooling plus a drive system adds two complete failure modes that
aren't there at all with the Corvair. With the Corvair if you take care
of the systems design aspect, basically by using sound aircraft design
practices for carburation and ignition,


I question whether LyCon practice, which is actually derived from
small flathead gasoline burning farm tractors- a big single barrel
updraft carb and two farm tractor magnetos- is intrinsically "Sound
design practice".

Remember when the Continental, Lycoming and Franklin engines were
introduced they were not considered sound aircraft design! Real
airplanes used P&W or Wright radials or Allison or Curtiss liquid
cooled inlines-the E-2/J-2 Cub and similar planes were considered the
ultralights of their day, and before WWII one could fly an airplane
without a license if it wasn't registered and flown only within one
state (until the states, except Oregon, outlawed it-which is why the
early homebuilders often moved there.) Nothing smaller than a Waco was
considered a real airplane.


Simple, light, reliable is the Prime Directive, regardless of how old
the technology is. When it comes to airplanes, that is sound design
practice, when considering ass pucker levels while in climbout over a
builtup area or over a tree line. I don't care if it's made of rocks.
If it's simple, light and reliable, the fact that it's derived from
tractors is irrelevant. The big radials of the old days, when you look
at it, were also very simple, light reliable designs in relative to the
alternatives in view of the power requirements. You will note that the
"more sophisticated" liquid cooled aircraft engines never survived in a
significant way past WWII in commercial service, with one unusual
exception, the Canadair North Star airliner, which used Merlins.
Everything else was radials because relatively speaking they were the
simplest and lightest and most reliable solutions before jet engines,
even if their air cooling and pressure carbs were "crude".

This is the point. If you want to take advantage of technology like
electronic control, you have to design for complete redundancy if your
control system has a sudden potential failure mode. Not practical for
the homebuilder. The farm tractor technology engine can have its
components built with sufficient inherent robustness, or have a very
gradual failure mode, to provide the required safety without needing
duplicate systems, (like a crude but simple carb) or at least a minimal
level of redundancy.

I am a fan of auto conversions, but believe that those conversions to be
viable must be as close as possible to a traditional aircraft engine
from the standpoint of simplicity and overall design, and the Corvair
using a Stromberg aircraft carb and a dual primary points ignition comes
closest to fitting the bill of any conversion I have seen besides a
Great Plains VW. Now that the crankshaft strength issues are known and
a way forward is clear, the Corvair engine's potential is even better
than before as a conversion IMHO.

Cheers

John Kahn
Montreal