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umop apisdn
24th Feb 2017, 02:56
Hi.

I was wondering if anyone can shed some light on this. I'm likely missing something...

When a/my 210 is fitted with tip tanks, the MTOW reduces substantially, unless there is a minimum of 7GAL in the tips, then it increases back to 1724kg.

Presumably this is because of the extra lift created by the tips on the wing root, with the fuel then acting as a counter weight.

I'm just confused as to why this is not a function of zero fuel weight.

Say you loaded the plane up so that it was fuel restrictive, with 7GAL in the tips for max MTOW. As the fuel burns from the mains, the total weight of the aircraft would decrease to a point where it was permissible to pump the tips. With a light wing and a heavy fuselage, the wing root would be under more stress than it was at any other point of the flight. The only thing that allowed for the pumping of the tips was a decrease in weight as per the flight manual, but this doesn't make any sense, as it would put the extra pressure back on to the wing root.

DownWest
24th Feb 2017, 07:48
Might be C of G related?

Martin_123
24th Feb 2017, 10:20
your tip tank is a lot smaller in capacity than your main tank - let say your main tank is 45 gal and your tip tank is what - 14 gal? once your main tank starts to get dry you only pump up 14 gal max, as a result you never really go over the maximum mass and the stress on the wing root is nowhere near to what it is when your main tank is full

3wheels
25th Feb 2017, 09:57
Google "Wing Relief Bending Loads"...or "Wing Relieiving Loads".
A good simple explanation is here ...
https://www.bayt.com/en/specialties/q/72214/what-is-wing-relieving-fuel/