Engine failure due carb icing. Will it restart?
I thought about putting this on Instructor Forum due accent on training type aircraft, but feel that it might be more appropriate in Tech Forum. Part of the trouble check after engine failure in light singles (and twins)is to select carb heat on, presumably in case carb ice had caused the failure. The purpose being to get warm air into the carb system to melt any ice.
If the engine has stopped (ie not just rough running), then the warm air from around the exhaust muff will quickly dissipate. Does it become useless in 10 seconds, 30, or 40? I don't know, do you?
Therefore, is it not a waste of time following the time honoured cockpit drill of selecting carb heat to melt the ice?
And how do you know if the ice is melted anyway, unless you try an engine restart via the primer and electrical starter. Assuming the ice that caused the failure had accumulated around the throttle butterfly, then if the throttle is closed (which is standard procedure following engine failure - or is it?), would any remaining residual heat from the engine only reach one side of the butterfly valve and maybe not de-ice the other side?
And for any carb heat to be immediately effective in melting ice prior to restart drills, should you actually open the throttle wide before carb heat is selected, in order to get max residual warm air flow right down the throat of the carby past the wide open butterfly valve? Finally, how long should you wait after selecting carb heat on for it to work and before attempting a re-start?
As I see it, it is all very well to carry out these rote drills following engine failure, but are we fooling ourselves and the students to whom we give sage advice?
More to the point, is it just another myth that carb heat should be selected on as part of the trouble check following engine stoppage due carb ice, when the heat dissipates so quickly once the engine stops?