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Like Alex said, the fuel sloshes around and some of it comes out the fuel vent and may or may not get into your cockpit. This happens as you go through the knife edge in the T. If you watch somebody with a full fuel tank doing acro down low, you can often see the small spray of vapor coming off the fuel overflow or the little oil puffs coming out the overflow tube.

On Caps and some other aircraft the fuel overflow was moved down onto the gear leg, presumably to reduce the periodic smell of gas, but that led to an aircraft burning down when its venting gas ignited on the hot brakes and also I believe mud/grass/bugs plugging the overflow.

Obviously though the smell should not be anything more than a wiff, if the smell is persistent then there is something wrong and it should be checked carefully. Obvious things that can cause problems are old fuel lines which have a tendency to crack underneath the metal sheathing and cracked fuel tanks. Fuel lines are especially prone to problems if they were recently removed and reinstalled in a slightly different configuration. There is lots of good stuff on fuel system problems in the IAC technical tips books which you can get from the IAC.


© Dr. Günther Eichhorn
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