Gravity Refuelling

[LEM]

In the extremely remote case the refuelling station is not usable at all, we might still be able to refuel by gravity over the wings, like small airplanes.

Does anyone have experience of that?

How long would it take to refuel, say, 3000 litres on a, say, Boeing 737?

[mitzy69]

overwing refuel, would take longer than normal, as the refuel dispenser driver would have to find the hose and nozzle to do it, as it is a rare occurence on bigger airliners.
Refuel flow rate would be slower than normal as nozzle into tank top is small.
If it was raining would get water into the tank thru open hole.
Extra safety needed as operators could fall off top of tank,
3000 litres should take about 10 minutes.

[enicalyth]

All that I can remember is a "hasty" formula in said black book.
You can forget finesse because the pipe will "gloop" and effectively run half-full and will have very little pressure head to drive it.
The book said 11 UK gallons/min for a 3" armoured hose and 22 UK gallons/min for a 4" armoured hose. Call that 50 litres/min and 100litres/min respectively.
There are classical formulae and "deliberate" formulae as the Royal Engineers say but none of these are applicable to the sort of jury rig an old-fashioned gravity feed might suggest.
Nevertheless a proprietary 2" gravity feeder at RAF Gan could do 150 litres/min.
Therefore you are probably looking at a spread of 20mins-60mins under gravity, limited by frothing and glooping.

[primreamer]

Many years ago I had to overwing refuel the 2R tank on an L1011 in AGP. Can't remember the quantities or flow rates involved but the hose and nozzle were exactly like those found on a petrol station forecourt and seemed to take forever. I was concerned that the very ropey looking bonding lead and crocodile clip would detach and drop into the tank. Its also worth remembering to leave all the loose articles in your shirt/overall pockets somewhere else because if anything falls out, Sods Law will probably ensure that it will also drop into the tank. Seem to remember our procedures at the time required a duplicate insp to the filler cap when the refuel was complete.

[GOLF_BRAVO_ZULU]

enicalyth

That would still need feed pressure, even if hydrostatic. Was one quoted for those figures?