Ron Wanttaja wrote:

Probably your biggest worry, compared to a Lycosaur, is cooling. The air
cooling of your classic aircraft engine is extremely reliable...if it cools
properly when it's initially installed, there's very little that can happen
to it to make it NOT cool. If the oil cooler quits working, the engine
probably will last long enough to get you to a runway (other than if it
spews oil everywhere, of course).

You're not going to match that level of reliability; your airplane will
have a water pump, water hoses, and radiator that the Lycosaur lacks and
thus can't stop running if they quit. The lesson here is probably to use
the best quality parts you can find (race-type hoses, etc.) and to oversize
the system... if you develop a coolant leak in flight, it's nice if your
plane has to lose five gallons of coolant before it starts to overheat
rather than five quarts. Gauge the heck out of it, too...you want to be
able to detect problems as early as possible. I'd try put together some
sort of annunciator system rather than depend on the pilot's eyes to catch
a fading gauge.

All good suggestions. Another tack on the cooling system failure would be to
select an auto engine (or engineer its conversion) such that loss of coolant
does not cause a catastrophic failure. For example (and it's only an example!)
the Mazda Wankel engine will happily continue to run and produce usable power
without any coolant remaining. It will likely never start again, however,
without a major rebuild. Why is this? Because when overheating, the aluminum
rotor housings expand more than the cast iron rotors, which precludes seizing
(unlike most piston engines). Parts of the engine permanently deform however,
causing insufficient compression once the engine cools. Thus, no start.

I guess my point is: sometimes we should try to prevent the failure, and other
times we should try to minimize the effect of the failure. There's a balance
in there somewhere.

I wonder what could be done along the lines of emergency cooling, like the
emergency ignition? The AVweb article about flying the Hawker Hurricane
makes me wonder about a spray-bar system for auto-engine conversions.
Could you gain some flying time if you had a system that would spray the
engine itself with water? And/Or some emergency cowl flaps that would open
and expose the engine case directly to the slipstream?

The radiator's area is many times the surface area of the engine's water
jacket. Plus the now empty water jacket makes a real nice air gap blanket for
the cylinders. You'd do better to engineer a coolant-loss makeup system.
IMHO. Unfortunately, "make-up coolant" weighs 7.5 lbs. / gallon. Fly in the
rain with a big funnel? Secondary use for that "relief tube" ? :-)

Or perhaps have the pistons machined from some alloy with a low Cte (titanium?)
and make them as undersized (relative to the cylinder diameter) as the rings
will permit.

Russell Kent