Originally Posted by
Desert185
I have had more hot starts with JT9's during cold weather ops than with summer ambient temps. In that engine, at least, when you turn the fuel on (idle/rich) is dependent on EGT. Max motoring may go beyond just an N2 RPM if the EGT is above 100dC. The only influence reported temperature has is whether engine anti-ice is required after start.
Tailwinds, in my experience, didn't seem to have a big effect, if any, on JT9 starting temps, which was good with engine pneumatic air required for reverser deployment preventing reversers use during start. Hydraulic reversers are desired, at least for the placebo effect of blocking the tailwind during start and a quieter preflight experience (not only quiet, its also easier to preflight the fan blades when they aren't rotating at "max motor").
The Herc, as I recall, was more sensitive to strong tailwind starts. Lowering flaps to 100% in order to reduce wind up the tailpipe helped to control starting temps. A speed sense switch controlled the start sequence of fuel and ignition, so there wasn't much else the crew could do other than to release the start switch at the recommended RPM and hope for the best that everything worked as advertised.
Yes, the Allisons on the Herc were much more temp sensitive. On a hot day, especially at altitude, it could be a good idea to get positioned into wind and make sure the throttle was properly positioned for min blade angle. I have seen aborted starts due to stagnating rpm because they were at ground idle instead of ground start position. I suppose if you were using fuel enrichment, that could make a hotter start.
Flaps 100% is an interesting idea but how do you get them therefor the first engine start if this wasn't anticipated on the inbound leg. 9 port valve selector to interconnect systems?
As for the bigger engines you mention, I have seen a 40 gust 50 tailwind(at the end of a typhoon) on a warm day start on the CF-6 with its EEC's having no problem controlling temperature.
Originally Posted by
Old Fella
16% - 65% - 94% still sticks in the memory bank. The H model used a toggle switch to open the Starter valve, held in the open position manually against spring tension and released at around 60% RPM. Rather than just sit back and "hope for the best" if a hot start or stagnated start occurred it was simply aborted by using the condition lever to GROUND STOP. Strong tail winds did potentially lead to hot starts.
16-65 and 94 is correct but do you remember all the things done along the way.