Useable Fuel Capacity

[BrokenStraw]

What is the useable capacity of the 55 gallon fuel tanks?

[Nev]

On my 4-place B model, I measured only about 1 liter/quart each side to be unusable. However it's probably prudent to treat it as about 10 liters (2,5 gallons) each side particularly if you're in the habit of selecting an individual tank at lower fuel levels, and to account for an out-of-balance flight condition.

[rodsmith]

My tanks are home built, but built according to the original 4-place plans. On the B model they may be larger. I determined the unusable fuel to be 2 gallons for the main tanks and 1 gal for the aux. Before I filled them I put 4 gallons in each main and 3 gallons in the aux. I leveled the plane and pumped each aux tank into the main until the pumps lost suction. Could clearly tell by the sound of the pumps when that happened. Then I disconnected the fuel line at the servo and used the boost pump to drain each main tank into containers until the pump lost suction. Then I put the plane back in three point, drained each tank through the rear drain plugs and weighed the result. It was about 1.6, 1.7 gallons for the main, and .8, .9 for the aux tanks. I just round it to two and one gallons as unusable fuel.

[BrokenStraw]

Thanks guys. Sounds like estimating 2.0 to 2.5 gallons/main tank as unusable fuel will be safe assumption.

[jaredyates]

I think the safest plan is to test and find out?

[BrokenStraw]

Yes, understood. I was looking for expected range of unusable fuel as benchmark to check against my own results.

[svyolo]

My actual unusable fuel is extremely low, but I would never want to be flying when I got close. I did my fuel flow testing with <2 gallons per side.