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I've been reading about fuel tanks in aerobatic planes such as the Extra 330, Edge 540, XA41 and I don't really understand why in the Extra 330 there are separated center tanks and an acrotank instead of a single bigger acrotank like in the Edge and XA41.

I guess it's something related with balance and center of the aircraft but the Extra has two center tanks and their relative positions between them and with the acrotank are small.

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A long time ago aerobatic aircraft had just a single tank with a flop tube inside it.

This works "OK", but when you're doing something complicated with a half-empty or mostly-empty tank, it's too easy for the flop tube to ingest air instead of fuel. This leads to performance problems with both the engine and the pilot.

The solution is to have a very small "acrotank" with a flop tube and an arrangement of fuel line plumbing such that the tank remains 90% full, 90% of the time.

In my Laser, there's a very large tube (2" to 3" diameter) that feeds from the bottom of the main tank to a tube at the top of the acro tank (with that tube extending inside the tank to near the bottom). There's a small vent/return line.

When I'm right-side-up, the acro tank fills from the main tank in seconds. When I'm inverted, the tube arrangement prevents most of the fuel from returning to the main tank. Some returns via the vent/return line, but I still have about 5 minutes of sustained inverted flight fuel.

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