[NEED TRACK]External tanks fuel vanish

[Bananabrai]

Checklist states to not take off with external fuel (external transfer) switched on.

(The official F-14 checklist says that as well, so it seems to be common for some jets)

 

So I have the externals off all the time on the field, for take off and up until I leave the airfield area.

Sometimes it takes some time for start up and taxi (explaining the jet to other pilots).

Now, there seems to be a certain time span when the externals are just empty as soon as I switch them on.

Other pilots have the same problem/bug, so I have this confirmed by 4 other pilots, in multiplayer.

 

It happened only once that I switched the externals on directly after take-off and had no issue,

but I told my wing men a few minutes later to switch theirs on and they were empty immediately.

 

For the record, empty without filling the internals, I know that it feeds it to the internals if working correctly.

The actual fuel mass just disappears.

Edited November 17, 2020 by [ED]Obi

[RustBelt]

Yea I noticed that flying it the other day too, didn't think much of it, assumed I did something wrong when I loaded.

 

For reference you don't takeoff on externals because if you have a problem on takeoff and have to quickly clean up you don't want to drop the tanks you're drinking out of.

[[ED]Ben]

If you could get me a track of it happening, that would be great. Thanks

[Svend_Dellepude]

Yea I noticed that flying it the other day too, didn't think much of it, assumed I did something wrong when I loaded.

 

For reference you don't takeoff on externals because if you have a problem on takeoff and have to quickly clean up you don't want to drop the tanks you're drinking out of.

 

Engines are not fed directly from the external tanks. External fuel is pumped to internal tanks. As to why you shouldn't engage external fuel until airborne I seem to remember that it's a safety thing. IIRC it's in the manual somewhere.

[Frederf]

One reason for not using external fuel is that it can overfill the internal tanks and cause some to spill out of the vent. Fuel goes in circles around in the system and is dumped back into an internal tank. Engine takes fuel from this circulating path. If external fuel is introduced into the circuit without adequate capacity in the internal tanks then fuel overflow may occur. Without failures valves prevent this transfer and overfilling does not happen.

 

"During ground operation, delay or stop transfer of external fuel when either the left system indicates 1700 lbs or more, or the right system indicates 2300 lbs or more." The left and right systems hold 296 and 381 usable gallons total which is 1924 and 2476 lbs JP-4 or 1983 and 2553 lbs JP-8. This suggests that 34-42 gallons and 27-38 gallons should be empty in the left and right systems respectively before feeding external fuel.

 

Normal procedure is to takeoff on internal fuel only, during climb set transfer wing external until empty, transfer centerline external until empty, then use auto-balance as needed.

 

Immediately empty externals should not happen. Flight with external transfer switches off should result in no external fuel used. It's possible that your flight had unknowingly empty tanks at takeoff due to rearming which didn't replace empty tanks with full ones.

[Bananabrai]

Obi;n7142166]If you could get me a track of it happening, that would be great. Thanks

 

I will look for it.

 

To the topic of 'why': Thanks for the info, I knew the reason.

The jets were on the pad with full external tanks. I will try and do some tests for consistency inside an all new mission.

[Svend_Dellepude]

Are you on beta or stable? I seem to remember a bug where the fuel would still transfer to internal tanks if not full even if the external was not switched on. As soon as you then switched them on they would already have transfered all fuel and would show as empty.

 

At some point you could also just get new externals instead of refueling for turn around and they would insta refuel the internals on the ground. You could then dump them, reload new ones and off you went in a couple of minutes.

[Bananabrai]

Sorry for not reporting back.

 

I am on the OpenBeta. Just ran into the issue lately again and have a track now.

I basically provoked it by not turning on the externals for about 5 mins into flight after take off.

Where should I upload it? It is ~ 61 MB

 

Thanks in advance

[Svend_Dellepude]

You could upload to google drive or dropbox and paste the link here