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Surge Tanks

Old 8th Feb 2019, 03:24
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Surge Tanks

Big planes have them, small planes don't. At what size does this become a necessity. What is the smallest aircraft type you know of with surge tanks?
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Old 8th Feb 2019, 05:11
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Itís not about size I think. More than Iíve seen fuel spilling through vents out of of a over fueled Cessna or some such...

I suspect surge tanks are required by CS25 specifications, thatís why big planes have them...
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Old 8th Feb 2019, 09:44
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Originally Posted by Sidestick_n_Rudder View Post
Itís not about size I think. More than Iíve seen fuel spilling through vents out of of a over fueled Cessna or some such...

I suspect surge tanks are required by CS25 specifications, thatís why big planes have them...
Thanks,

Maybe someone could let us know if there is a regulatory requirement.
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Old 10th Feb 2019, 03:14
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I would assume this be the regulatory requirement.
ß25.969 Fuel tank expansion space.Each fuel tank must have an expansion space of not less than 2 percent of the tank capacity. It must be impossible to fill the expansion space inadvertently with the airplane in the normal ground attitude. For pressure fueling systems, compliance with this section may be shown with the means provided to comply with ß25.979(b)
FAR 23 aircraft don't seem to have any explicit requirement. As SnR notes, you will see fuel coming from vents, usually after refuelling, the cold fuel expands under the influence of the sun on the wing warming. Have seen fuel venting in high wing Cessnas in flight in steep nose down conditions following refuelling.
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Old 10th Feb 2019, 13:37
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Thanks,

So it looks like every FAR 25 aircraft is required to have surge tanks.

I see from the ATR-42 manual that they follow the regulation for 2%...."An additional volume in each tank allows a 2% thermal expansion of fuel without spillage."

It would be interesting to know if there are surge tanks on an of the non-FAR 23 aircraft. I wonder how it worked for the large piston airliners back in the day.
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