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There are several Zero-G airplanes to experiment briefly microgravity without going into orbit. One is the A310 from Novespace (F-WNOV):

enter image description here
Novespace A310 F-WNOV (source: Jonas Wirz at Airplane-Pictures.net)

When a Zero-G flight is executed, fuel should take the form of a sphere in the tanks, like demonstrated in the cabin for a beverage.

enter image description here
Advertisement in microgravity (source)

Thoughts:

  • This effect won't appear in negative G, subject to the design, fuel lines may still be immersed in tanks, this cannot be the case in micro-gravity.

  • The 0G segment is likely flown with power. First this is not a continuously descending flight as seen below. Second, friction will slow down the free fall anyway and must be compensated by some acceleration from the engines.

    enter image description here
    0G segment is not limited to the descent (based on source)

How does Airbus ensure the fuel is still delivered to the engines at the required pressure, without air?


Related: Are engines fed differently in reduced gravity aircraft?

Basically it says no modification is required because the lines are pressurized, and this is supported by a 1966 Nasa study (Use of aircraft for zero-gravity environment) which is not more detailed. The line being pressurized downstream of the pumps seems only one element of an adequate design. Upstream fuel will experiment the effect of micro-gravity and lines are no more immersed in the fuel. Air can enter and create a problem when reaching a pump or an engine. Pumps could be drained. Maybe the problem won't appear during the 0G segment, but it should appear later.

I'd like to have the details about how pumps, pressure, flow, or anything else contribute to maintain a good fuel supply to the engines.


This is the fuel system for the A310:

enter image description here

(Source)

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    $\begingroup$ An A310 uses 730lbs/hr in idle descent which equates to 117 gallons per hour. That's 2 gallons per minute. Since Zero-G only lasts 22 seconds, it only burns 0.75 gallons of fuel. I'm sure that there is enough in the lines to accommodate 22 seconds without starvation. $\endgroup$ – Ron Beyer Apr 1 '16 at 13:18
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    $\begingroup$ @DevSolar Fighter jets are designed to perform those kinds of maneuvers and have specially designed fuel systems to keep that from happening. $\endgroup$ – Ron Beyer Apr 1 '16 at 13:30
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    $\begingroup$ @RonBeyer, since Novespace flies their A310 specifically for the parabolic micro-G flights, they may well have modified the fuel systems to accommodate the expected flight regime. $\endgroup$ – FreeMan Apr 1 '16 at 16:24
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    $\begingroup$ A pressurized bladder tank would be an obvious solution, but I don't know if that's the actual answer. $\endgroup$ – Greg Taylor Apr 3 '16 at 9:44
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    $\begingroup$ Seems like a dupe of this question: Are engines fed differently in reduced gravity aircraft? $\endgroup$ – fooot Apr 4 '16 at 17:07
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I wrote an email to AirZeroG and asked them:

Other than the interior, are your aircraft modified in any way to handle zero-g flight?

Here is the response that they gave me:

Dear Sir,

Except free floating area cabin configuration, there are very few differences with a “standard aircraft”. The most significant one is installation of Zero-G meters in cockpit and a very simple installation on the wheels to help one pilot to lead the aircraft only in vertical axis, and the other pilot to lead only in horizontal axis.

Out of that, the biggest difference is maintenance program: each parabola performed to create Zero G onboard is considered as an aircraft cycle for the aircraft and its engines, and maintenance adjusted accordingly. Such consideration dramatically increases maintenance costs of the aircraft.

Kind regards

Gilles GOMPERTZ

I would say that if there were a fuel system difference they would say that is more significant than G-Meters in the cockpit. I'm assuming based on the response above that the fuel storage/delivery system is unmodified.

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    $\begingroup$ You deserve the bounty for the extra mile! +1 $\endgroup$ – TomMcW Apr 5 '16 at 17:35
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    $\begingroup$ With @TomMcW! Thanks a lot. Someone may later provide additional factual explanations about the procedure used or figures showing how this is possible with the unmodified fuel system. Anyway Ron this is a great idea of yours :-) I appreciate. $\endgroup$ – mins Apr 5 '16 at 17:42
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    $\begingroup$ That's pretty wild about the split controls. I guess with people floating around loose in back you'd have to fly that parabola pretty precisely. Wouldn't take much to slam them into the walls $\endgroup$ – TomMcW Apr 5 '16 at 17:54
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    $\begingroup$ I agree, @TomMcW. I'm not a pilot, but I'd imagine this would be similar to driving a car with one person steering and another working the gas/brakes. I wonder if the control split is only during the 0G segment or if it's a full-time engagement. That would make for some interesting landings until both pilots really got the hang of things! $\endgroup$ – FreeMan Apr 7 '16 at 15:43
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    $\begingroup$ @FreeMan would make it interesting indeed. With all the duties the PNF performs during approach and landing he needs his hands and attention free so I'd bet it's something that can be disconnected quickly after they finish the aerobatics. Might even just be some kind of handle that allows one of them to operate the yoke without holding the wheel $\endgroup$ – TomMcW Apr 7 '16 at 16:40
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Jet powered aircraft use feeder tanks to stabilize the flow of fuel to engines and APUs. These feeder tanks are pressurized and kept full to a specific amount to ensure fuel flow (for a certain period of time). The feeder tanks are fed by a system of transfer pumps from the main tanks, which in turn are pressurized (usually with an inert gas mixture). Unlike most gravity fed tanks, the tank is not drained via a single sump type arrangement, but a more complicated series of apertures for fuel to flow into the feeder (which may include in tank pumps).

While I cannot speak exactly to this aircraft, it is usually the case that special mission aircraft have fuel systems modified or designed to suit their needs. This aircraft may have a larger feeder tank or a different feeder tank design that allows for extended periods of low-g operation. Generally speaking, low-g operation does not have an affect on pressurized fuel systems.

Much of the information you seek is provided by the FAA here:

https://www.faa.gov/regulations_policies/handbooks_manuals/aircraft/amt_airframe_handbook/media/ama_ch14.pdf

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    $\begingroup$ Thanks for the answer, however this is a general one without actual details. Here is the fuel system for an unmodified A310, and this extract for the schematics. Could you please explain using these elements? $\endgroup$ – mins Apr 4 '16 at 18:14
  • $\begingroup$ @mins, now I am curious. The schematics you have clearly indicate that they are using isolatable wing and center tanks, each with independent pressurization and pumping sources. What are you looking to understand? Is it the position of the pumps/sumps in the tank relative to the liquid fuel? Take a look at the document you posted, it shows the use of baffles to restrict fuel movement, which prevents completely unconstrained movement (as shown in your picture). $\endgroup$ – tillmas Apr 4 '16 at 18:31
  • $\begingroup$ "it shows the use of baffles". I don't see baffles mentioned, what page? I don't see how baffles prevent the possible 0G starvation (in addition I imagine the tanks would be far from full for the 0G short flight). "they are using isolatable wing and center tanks": Again I don't understand whether you suggest the isolation valves are closed or left open during the 0G segment? Don't you want to include the pertinent elements from the schematics in the answer to clarify? Thanks. $\endgroup$ – mins Apr 4 '16 at 19:22
  • $\begingroup$ Baffles reference: 1.11.20, P.1, GENERAL. Baffles will reduce the fuel's ability to flow unconstrained, and as such will prevent it from forming its lowest energy state (a spheroid). They are there to prevent slosh, and will be more effective at preventing spanwise flow than chordwise, but will still have some value. 0G starvation is prevented by the pump being immersed in the fuel, or by using immersion lines. Without seeing the lines, it is not possible to know the mounting (nor will the general A310 fuel system design give you the answer if the 0G aircraft has been modified). $\endgroup$ – tillmas Apr 4 '16 at 19:26
  • $\begingroup$ Ok for the baffles. I'm less sure they would be sufficient to prevent fuel from leaving the pump inlets exposed, with the risk of air entering the line, causing problems during, or maybe after, the 0G segment. About the isolation valves you mentioned earlier, should they be closed or open? $\endgroup$ – mins Apr 4 '16 at 22:43

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