On a car they put the fuel intake at the lowest point. But on an airplane that frequently goes upside down and sideways so a lowest point fuel tank wouldn not work.
I am not an engineer, but the solutionbs I can up with was putting the gas in a plastic bag and compressing the bag with air, but that is a possible solution, I doubt that is what they actually do.
Or using a gas take with lots of fuel intakes.
But what do they really do to ensure a constant fuel supply.
I´m not sure how is it done; but in RC planes the fuel tank has a flexible hose inside with a weight on the tip, that way the intake is always pointing in gravity´s direction, so to speak.
I WAG that aircraft that have to perform airbatics could be equiped with a small intermediate tank with the flexible intake. I suspect that because I´ve read in some airbatic specs that the fuel system suports X seconds of inverted flight.
How would that work with non sphirical tanks?
Also, what does WAG mean?
Riddle me this: how often do you see a plane, even a jet, that spends a significant time - minutes rather than seconds - inverted in level flight?
Oops hit enter too soon.
Because with a non sphirical tank there would be an area that the hose couldn;t reach, or the hose would be diagonal when the plane is horizontal
But a fighter jet in dog fight would be maneuvering rapidly (at least according to my computer game education) and changing direction rapidly would cause the fuel flow to change, and I would assume that the fighter jet jockeys would want a constant fuel supply therefore a constant power supply.
Also acrobatic aircraft like the snowbirds spend a lot of time inverted.
In the battle of britain, the spitfires would lose power when inverted, and this was mentioned as a serious problem, so apparently inverted flight is important to a fighter plane. (AFAIK they lost power because they had a carbirator but that is beside the point)
The forward most tank is kept mostly full. The other tanks empty by feeding into the forward tank. If your forward tank is less than full, you should be nearly back to base and not maneuvering/inverted. If you are at negative G for a prolonged period, you can cavitate your fuel pumps, but this is a limitation of the pumps, not the fuel transfer system.
So the other tanks do not suck gas when the plane is maneuvering/inverted?
Does the forward tank have the clunk that Ale was talking about?
or does it have four or five holes in it to ensure that at least one hole is covered by gas at all times? Because for there to only be one hole the tank would have to be absolutely full at all times, but you said that only the forward tank sucks gas all the time, so when maneuvering, the forward tank would start to empty (as the other tanks are unable to fill it) it would start to empty, and we are back to the original problem.
Are there valves that can differentiate between gas and air for when the pump is sucking, ie only open when the pipe the valve is blocking is covered with gas. (when the gas tank starts to empty do they replace the void with air?)
Also, you sounded like an authority, I asume you are a mechanic or a pilot or something. What are/were you?
I bolded all my new questions in the hope that they get noticed + answered.
I’m no expert on the fuel system, but did pick up on some stuff sitting next to the fuel guy in the control room. I can try to answer these as best as I remember:
All tanks I´ve seen in RC planes are polihedrical, a box with rounded edges, plus a small “bubble” near the clunk attachment. The fuel line tip doesn´t, indeed, reach all corners of the tank, but should work fine while the tank remains at least 10.15% full; in any case with so little fuel remaining it would be ill advised to keep flipping around with the plane, it´s already time to land and refill the tank.
A WAG is a Wild Ass Guess. 
Thanks, but what guarentee’s the fuel flow (that is the only remaining question I have) (^Thanks you were really helpful on the related questions^) ?
The gas goes into the tank, but what is it about the tank that guarentee’s that the pumps can always suck fuel?
In a chain saw there is a float that is on top of the gas that guarentee’s fuel flow, and the clunk rotates towards gravity so that the tip of the nozzle is always in gas, but what exactly does it on a fighter jet/acrobatic aircraft? There has to be some opening in some tank somewhere that is always covered by gas so the the engines can run.
Umm … in both cars and plane there is a fuel pump that pumps gas to the engine. Some plane like the small Cessnas have gravity fed engines …
You know ignore my post … I miss read the question and I obviously have lost my ability to type …
Here is start …
so some airplanes do have a clunk (they call it in that article a flop), but according to my flight degree from the Sony Playstation Institute, Fighter Jets maneuver for more than 2 minutes, or are the short periods of time when the airplane is not inverted/pulling some sort of G inducing maneuver enough to keep the header tank full?
Well, I just flew the Extra 300S (Aerobatic) inverted for 15 minutes with no engine problem.
Fear the Turtle explained how the fuel system works.
I should mention, I was flying in MS FS2004. :eek:
I am not an an exciting airplane engineer, just a boring power plant engineer, but I think I can answer this question based on the information provided by Fear the Turtle. The rear tanks that empty first have a gravity feed from an outlet in the bottom of the tanks into fuel pumps. If you are inverted, these fuel pumps cannot operate. The rear fuel pumps pump into the forward tank that actually feeds the engine.
The forward tank is pressurized by the rear fuel pumps. The pressure in the forward tank allows it to flow under pressure into the fuel pump that feeds to the engine. Since it is pressurized going into the engine fuel pump, it can flow out the bottom of the tank even if the plane is upside down (thus really now going out the top of the tank), the pressure forcing it against gravity just like water pressure forces the water up into your shower.
If you are inverted for extended periods, the rear tanks cannot drain into the rear gravity fed pumps. The forward tank can force fuel into the engine fuel pumps, but as it does so, the pressure stored in the forward tank slowly drains off. Eventually the pressure in the tank reaches a point where it is no longer enough to push hard enough against gravity or the g forces of your maneuver. The pump attempts to draw more fuel, and as it does so the fuel right in the pump inlet drops to a pressure below which some of the liquid fuel vaporizes into small bubbles in the liquid fuel. As the pressure increases through the pump, the bubbles are driven back into liquid form. (That is the cavitation mentioned by the scary shelled water dweller). Cavitating pumps have a greatly reduced flow, and cavitation will eventually eat away the metal of the pump from the force of the bubbles collapsing. (Each bubble makes a tiny high velocity jet of fluid as it collapses). If the loss of power from the reduced fuel flow doesn’t warn you to right yourself, the pressure will rapidly drop off until you have no flow and you make a nice impact crater.
Well, like I said, they keep the the forward most tank full. This tank feeds the engine(s). Momentary hiccups of fuel flow into that tank won’t disrupt flow to the engines. On the program I was on, we had 3 fuel pumps located top/bottom/center of that tank to feed the engines. At most one pump might be momentarily uncovered. That tank was maybe 10% (at most) of our total fuel weight. If you were down to just this tank (and it was emptying), you were pretty low.
Ah crud. That’ll teach me to guess. Well, maybe it won’t.
Ahh so there are multiple holes in a gas tank for the gas to go through, and the pumps get assistance from the pressurized N2 gas? By centre you mean on the side, if the tank were football shaped (for lack of another easly recognizable shape with a feature) the centre pump (with matching hole) would be where the stiches are.** By centre, would there be two centre holes for the one centre pump to suck gas through?**
Thank you in advance, this is exactly what I was looking for.
Not sure how many holes/lines go thru the tank (these would correspond with the outlets of the pumps), but there are multiple “pickup points” (inlets), corresponding to the 3 pumps (each pump could have multiple pickup points for all I know). The forward tank is kept full, so no N2. Pressurized N2 helps the rear tanks transfer fuel to the forward tanks (and to the multiple rear tanks)
I’m not sure where exactly the pumps were located. By center I meant located vertically between top and bottom. How they are laid out horizontally, I’m not sure. Also - the pumps do not “suck fuel thru”; they are located in the tanks and only the outlet lines run through the tank wall. So technically they “push fuel out”.
I’ll be out of town for a couple days, so may not be able to pick this up again for a while.