Feathers McGraw
On a related note, what changed in the engine parameters if the Contingency mode was entered on take-off? And what would trigger that mode? Oh yes, and once engaged, is there a time limit on how long it can be maintained? I'm assuming in an engine out case that at heavy weight the reheats have to remain engaged on the remaining engines until the speed has built up to get off the back of the drag curve.
Contingency mode could be either manually or automatically selected during take-off. It would automatically be selected if an engine dropped below 58% N2, PROVIDED that the take-off monitor button was set, and reheat was selected. (A small yellow CTY light on the centre dash panel would flash in this case also). OR it could be manually selected by moving the 4 reheat selector switches through a clever little gate, from RHT to CTY. In this case, the yellow CTY light would illuminate steadily.
Actually at entry into service, contingency had a real problem, in that when selected the reheat flame would burn very fiercely, become unstable and extinguish altogether. (So instead of getting more power, you ended up with less; with just the increase in dry thrust, and no reheat at all
). It seems that the reheat flame holder was too small to support the bigger contingency flame, which effectively would just fall over. What we had to do in the early days of service was to isolate the wire that provided the contingency discreet to the reheat amplifier, ensuring that the reheat would hopefully still operate normally when contingency was invoked, so at least you got a small increase in power from the dry engine. The solution was the welding of 7 small 'fingers' to the outer part of the reheat flame holder, this made the flame holder 'appear' bigger than it really was to the flame. It worked perfectly, and we could therefore re-connect our wire again.
(Just making the flame holder physically bigger would have had a detrimental impact on the operation of the dry engine).
Dude
