Engine out practice

"Jay Honeck" wrote in message
ups.com...
As previously noted (in the thread about Paul's wife getting scared),
Mary and I had virtually stopped doing this kind of flying for fear of
harming our (very expensive) engine. A lively debate ensued as to
whether or not repeated high-to-low-to-high power applications would
wear out your engine any faster than would normal operations.


Jay, the cylinder barrels on your engine are steel with air-cooling fins
attached. Your pistons and cylinder heads are aluminum alloy. The two
metals will expand and contract at different rates when heated or cooled.
Think about the way the thermostat in your house works. A bi-metal strip
(strip of metal composed of one type of metal on one side and another type
on the other), when heated or cooled bends because of the different
expansion rates of the two metals. When I think of shock cooling I think of
the sudden removal of the heat source (abrupt power reduction) along with
the different metals contraction rate (steel with air blowing over it's
cooling fins versus aluminum inside the barrel with hot oil being sprayed on
it). It is easy for me to visualize the scuffing that can occur because of
the reduced clearances as the barrel contracts onto the piston. The same in
reverse would hold true for shock heating.

Whether any of this is true I don't know, but I am with you that gradual
increase or reduction of power seems less likely to cause damage to an
aircooled engine.

--
*H. Allen Smith*
WACO - We are all here, because we are not all there.