Starting Combuster System
Thanks Jhieminga,
For the superb photo. What a lucky angle... Not sure I can see the Küchemann tip, though.
Quote from Speedbird48:
Didn't the BUA VC-10's have air bottles in the tail cone for starting where no external air was available??
Yes, according to my 1971 notes (ground school at Gatwick Bee Hive, instructor Pete Horscroft):
3 bottles of AIR (not, of course, nitrogen) at 3000psi. This was reduced to 300psi by a PRV, i.e., to "HP air" pressure.
But the amount of HP air was not itself sufficient to do the job of turning the normal pneumatic starter, so there was a combustor unit fitted between the PRV and the appropriate pneumatic engine starter (#3, but it could be refitted to #4). This stored and burned normal fuel, presumably to increase the mass flow (don't know what happened to the pressure) of air to the starter.
Sounds horrendous, and I don't think we used it very often (and that would have been the grizzled F/E's job, fortunately). Seems odd if the starter, which would normally use LP air at 25psi - 40psi, was also able to withstand HP air of at least 300psi? There is no PRV between the combustor and the starter, only a dump valve which dumps most of the air for the first 2 seconds, to give the starter a chance to start rotating before the full flow of air is introduced for a further 18 seconds.
According to my notes, Pete H also told us that the combustor burn is limited to 20 seconds to protect the starter from overheating by the hot air. (Amazing how much detailed, inside knowledge our ground-school instructors used to impart...) The RAF did well to specify an APU, I reckon.
(For the uninitiated, the remaining engines would subsequently be started by a conventional "crossbleed start", like most passenger jets, using LP air bled from the #3 engine, which has to be accelerated above idle rpm for the purpose.)