"PTOBO", question from a friend
 

Does anybody know what "PTOBO" would refer to?

This is in the Concorde Vol IIa flight manual.
Could stand for something like "Pre-Take-Off Balance-Offset", but solving this riddle would please both me, and the friend who asked me the question :ok:

CJ

Pre Take Off Burn Off

The fuel required to be burnt during taxy to allow txfr from tank 11 to tanks 5 & 7 to achieve TO CG (53.5% or 54%).

Used when ramp CG aft of TO CG (ie high fuel load)

Alternative was Pre Take off Transfer when ramp CG ahead of TO CG - fuel txfrd to tank 11. Much quicker and less hassle.

Many thanks, EXWOK !

That fully answers the question.

Cheers,

Christian

And it doesn't take a genius to work out that the limits you refer to (3300kg and 1800kg) are just another way of defining a max aft CG for taxying.

EXWOK,
Never had to do Concorde "fuel-and-CG math" myself, so I take your word for it.
(I helped to build 'em, not to fly 'em.)

I would assume that when you got up to the limits, a close watch was kept on what went into the rear baggage hold, as well.
Also, to start worrying about PTOBO, you'd probably already would have "over-filled", no?
(For those unfamiliar with the aircraft, it's a Concorde trick, where you "top off" each tank with a carefully metered dose of fuel after the "high level" indication comes on. Don't know if it's done on other aircraft.)

CJ

No need to overfill....you'll recall that tank 11 sits higher than all the others. So CG remains roughly constant until tanks 1-10 are full, then it starts to run aft as tank 11 continues to fill. So PTOBO vs PTOTR is a function of ZFCG and total fuel load.

We would sometimes encourage the loading of the aft hold in order to achieve a 54% take-off if heavy for its (small) fuel burn and performance benefits. Careful ZFCG management would minimise the Burn/txfr..

There was always more to the operation of this aircraft than first appearance suggested!