Posts about: "Ullage (Fuel)" [Posts: 2 Page: 1 of 1]¶

@Lancman

Not so on several counts

1. The phenomenon of structural damage arising from internal pressure waves in fuel tanks was unknown when Concorde was designed. Consequently the design made no specific provision for it.
2. 17% ullage is ludicrous on an aircraft for which fuel capacity is of vital importance. The correct value for tank 5 on Concorde is 6%.
3. Tank 5 was filled to 94% capacity at start of roll which would have been normal for any long distance flight. No more fuel was added to it; on the contrary, a very little might have been pumped into tank 1. The fuel transferred forward from tank 11 was put into the engine feeder tanks 1 to 4. This of course was not enough to compensate for the demands of OL593s operating at TOP with afterburner, so these tanks were running down and would have been topped up (tanks 1 & 2) from tank 5 at some point.
5. What actually happened was that the take off acceleration threw the fuel to the back of the tank so that the free surface volume was confined to a small zone in the upper forward region of the tank. When the rubber struck the rear part of the tank undersurface the fuel above it was constrained by a solid wall, which was enough to generate the reflected shock waves.

@ CliveL

Thanks for that detailed and very interesting description of the fuel handling on Concorde and I agree that 17% ullage does seem to be very high, I've never come across a figure that high, ever. But your paragraph 5 seems to indicate that it was a jolly good idea from a flight safety point of view. The risk of tank rupture was increased because of the limited free surface volume. I'm just interested in what the circumstances were that allowed this restriction to be over-ridden.