Aircraft with tip tanks question.
#1
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?
Anyone?
#3
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Joined APC: May 2012
Posts: 1,418
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?
Anyone?
#4
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?
#5
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.
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.
#7
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).
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).
#10
While I believe that the OP is referring to tip tanks like a Lear 35, some aircraft that have fuel tanks within the wing structure, but outboard toward the tip. Douglas aircraft often would use the tip fuel last because the fuel filled structure was stiffer and less prone to twisting.
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