A few more thoughts related to centre tank pump inlets:
- Each OJ pump must be able to pump, while in climb and then cruise, 99% (as in (80t- 0.8t)/80t) of the fuel out of the centre tank before the inlets are free from the remaining fuel. The OJ pumps free of fuel, lose pressure and are subsequently switched off - the main tank boost pumps, which are permanently on, maintaining flow to engines in the meanwhile. In this case, the centre tank reduced to a little under 750kg indicated at its lowest at the time of the engines switch to main tank supply, before apparently increasing for some reason by 125kg or so to 800 kg indicated a few minutes later.
- Each OJ pump inlet is raised from the floor slightly and is in fwd part of the centre tank. What exact depth of liquid on top of floor (or liquid on top of ice on top of floor) immediately below the fuel pump inlet is required to submerge OJ pump inlet? How localised could that depth of water be given the geometry of the tank, position of ribs and the tank's shape during flight? Can anyone produce a diagram of exactly where everything is at the bottom of the tank near the OJ pump inlets?
- I assume that the fuel scavenge worked given drop from 800kg indicated to 0kg but ... given the knowledge that on cold flights like these that it is not uncommon for some of the fuel scavenge pipes to become blocked by ice, what would happen if the fuel scavenge lines local to the fwd positions on the left hand side and right hand side of the tank where the OJ pump inlets are were iced up, but the scavenge lines in the centre of the centre tank were working?
- I note from the rate of scavenge in Figure 1 the rate increased as the level of fuel indicated declined to 0kg. Could that suggest that as the level lowered: the rate of scavenge appeared to increase as less fuel/free water was accessible than expected as it was trapped where the scavenge lines were not working locally; and/or an expected increase given the vagaries and the geometry of tank?
Is it a red herring even to contemplate the boost pumps or centre tank pumps allowing the passage of fuel/water when they are selected OFF? I guess the premise of the suction feed test on the ground (as a pure test of the suction feed) would be flawed if it was a possibility that an engine-driven LP could draw fuel through any of the unpowered pumps from centre tank - and thus I would like to discount the idea completely. Yet as a Mad Hatter is drawn to a tea party, I am curious about the possibility given the suggestion in the interim report that air at least might possibly pass through the OJ/jettison check valve (and presumably therefore through the OJ pump when selected OFF too) ...
Last edited by dxzh; 12th Sep 2008 at 11:48.