I believe you can shock cool if you do a long climb at MCP, then level in very low OAT with low power setting. Opening cowl flaps during climb helps mitigate the high temperature that the block and head would reach, and closing them when leveling mitigates the rush of very cold air on an engine running at low power after having been very hot.
I don’t think they’re ever supposed to be open for extended periods in cruise, maybe with exceptions on especially hot days where you can’t keep the temperatures down otherwise.
POH should indicate precisely in which conditions they should be open / closed (as this is heavily airframe-dependent).
As for “too cold is bad”, I believe this only makes sense in the context of either:
Yes too cold exists.
And no, it’s not possible to give cowl flaps values in the POH. It depends a lot on OAT and altitude (air density), at least if you try to get the engine settings right. If you go ROP you can just add say a Gallon per hour of fuel or so and then the temps stay low enough. That’s however neither good for the engine, nor for the pocket or environment.
In the school 172 that I flew lately we had it very simple: cowl flaps open on ground and climb, closed for the rest.
I adjust it much more in detail on my plane. To achieve most miles per Gallon.
UdoR wrote:
In the school 172 that I flew lately we had it very simple: cowl flaps open on ground and climb, closed for the rest.
A 172 with cowl flaps? Do you mean 182?
A 172 with cowl flaps?
C172RG
Exactly
We open them on the ground and during climbs. Closed for cruise and descent.
I’d leave them open for pattern work, but I don’t really do circuits in the 182 except when I first got it.
Cylinder 1 might be lower temp as it may have a difference probe type depending on which cylinder the Cessna panel CHT sensor is on.
