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Old 11-09-2017, 06:10 PM   #1
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Default Aircraft with tip tanks question.

I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?

Anyone?
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Old 11-09-2017, 06:57 PM   #2
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probably not the right forum for that question... but maybe some previous corporate drivers can chime in..
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Old 11-09-2017, 09:16 PM   #3
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Quote:
Originally Posted by astroglider View Post
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?

Anyone?
Tip tanks burn first.
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Old 11-10-2017, 07:42 AM   #4
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Quote:
Originally Posted by astroglider View Post
I'm doing some research on fuel balancing procedures for various aircraft. I have no experience with aircraft equipped with tip-tanks and was wondering what the fuel burn procedure is for them? Say a Learjet. I know you have to add fuel to the tanks in a certain order...but what about when you burn the fuel?
Tip tanks, external tanks on wings and center line of fighters......generally speaking the gas inside them usually gets transferred out first, so they are empty first. Notice I didn't say "burned first". The fuel in the tank or tanks supplying the engines is always burned first. Those primary tanks get constantly replenished from the tanks that need to be empty first (tip tanks, etc.) It's unlikely that there is plumbing directly from the tip tanks to the engine itself.
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Old 11-10-2017, 08:50 AM   #5
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Generally...

Fuselage tanks get emptied first, to reduce wing loading. If you burned the wings first, you have a heavy fuselage supported by light wings. The wings would be subject to more severe bending forces in turbulence due to low inertia, especially with a heavier, higher intertia, fuselage resisting movement... ie the wings would move, the fuselage not so much resulting in more severe forces at the wing/fuselage interface.

By emptying fuselage tanks first, you leave the wings heavier with more inertia to resist bending forces. When the wings do move, the lighter fuselage has less tendency to stay put.

Tip/outer wing tanks are usually emptied first to avoid creating a high rotational inertia. If all the wing/fuselage fuel was burned, but you still had fuel in the tips it would be harder to both start yaw/roll motions, as well as stop them. The former is of concern for adequate control authority, the latter is of particular concern for spin entry.

Some airbuses empty outer wing tanks late in flight, but that's because the inner wing tanks are often full at T/O. Once the inners burn down, the outers empty to the inners, with a typical fuel load this happens prior to descent and arrival.
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Old 11-10-2017, 10:06 AM   #6
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Only tip tank aircraft I have experience with was the T-2 Buckeye. Tips transferred and were emptied first.
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Old 11-10-2017, 11:38 AM   #7
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Lear 35: similar in principle to what Adler said. No center-point refueling; it was over-the-wing hoses in the tip tanks. As you fueled, it drained by gravity to fill the wings first, then the tips would fill.

The wing joined it mid-tank, so all the fuel above the wing transferred by gravity. It just kept the wing tank full.

Inflight, once the tip level got below the wingline, there were jet pumps to transfer the fuel to the wing.

As I recall, the jet-pumps relied on fuel-flow from a running engine. If you were engine out, you might get trapped fuel in the tip, which would make roll control dangerous for landing.

As such, there is a big jettison pipe at the back of the tip tank for gross imbalances.

(It could also be used for chemtrails).
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Old 11-10-2017, 12:29 PM   #8
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On my 310, burn off the tips for an hour then burn the aux (tips were the mains). After the auxiliary's empty go back to mains, if you forgot it got quieter.
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Old 11-14-2017, 05:24 AM   #9
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Thanks everyone...good stuff.
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