There's another factor here which should not be overlooked. That is, it takes VERY little fuel to go from 'an inch below the neck' to 'over the top.' Because of the taper of the tank, that last inch just isn't much gas. Even less after you stop and spill the last of the fuel out of the spout to make sure you get all you paid for and to not trail it across the wing and tarmac.
Now, with the cross-over operating, the whole thing becomes a moving target. You think you have it right, but the gas pump isn't quite on level ground, and then you taxi off, and the left tank overflows as soon as you either level off or get left wing low. It's always the tank that's getting the overflow that is most vulnerable, of course. I know that about half the time, even when I think about it, I cogitate wrong, and if I don't leave a good inch and a half below BOTH necks, I can wind up spewing fuel out the left vent for about as long as it takes to fly the pattern twice. Probably because I've just taxied left-wing low for a while, and because that's where the header tank flows. Other times, it seems I get away with only about an inch of space. But I rarely try that any more, since that half inch amounts to about a quart of gas and I have no intention of flying 24 gallons non-stop! Some of it is probably the current state of the header tank. It, too, is a big flat 'pan' where a little change in attitude makes a big difference as to whether it is overflowing or not, or draining into the wings while on the ground, or not. Maybe you were just positioned so that it drained a lot into a wing tank, and so has a bit more 'headroom' the next time you get under way. Maybe you were positioned such that the fuel in the tank is tilted away from the overflow, and the first thing that happens when you taxi is that a big slug of fuel comes down into the wings from the header. What I'm saying I guess is that the fuel system is not a perfect design where you can fill both wing tanks with the header already full to capacity, and then assume any attitude and not have some overflow. It was good as they could get it before going to production, there were clearly some 'tweaks' done over the life of the design, and in 1945 a little fuel spillage out of a wing tank was not considered that big a deal. Oh, and by the way, I see 172s spewing from *their* vent pipes after filling up on a fairly regular basis. Seems to me that if you can get a gallon less than the rated capacity in each side and nothing horrible is happening, like the header spewing up like Ol' Faithful, you're doing pretty well in a situation where you have a bunch of interconnected, flat tanks in a machine that tilts from side to side. Greg __________________________________________________________________________ ______ To unsubscribe from this list please send mailto:[EMAIL PROTECTED] ___________________________________________________________ T O P I C A The Email You Want. http://www.topica.com/t/16 Newsletters, Tips and Discussions on Your Favorite Topics
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