Spanners,
The air that I breath comes from the 12th stage of the HP comp. To get there it passes over the oil metering pump in the intake bullet. When engine a/icing is selected on, some of the 12th stage air is routed forward and then through small pipes inside the bullet before entering the LP comp and it occasionally induces oil out from the metering pump. This air/oil mix then ends up at the 12th stage and centifugal force throws it down the HP air outlets and it eventually gets up my nose. Then we have the cold air units with their syringe full of oil in the system as well.....
NG,
Ed, I seem to recall reading that the Tri-Jet is the fastest tanker, requiring higher power settings for Nimrod to keep up. Would the figure of 94% be about right, thus giving the 400 deg+ temp in the pipework?
Yes, as the BOI confirmed, XV230's engines were somewhere between 94% and 99% at the end of the bracket, so at least 400C would have been in the pipes. Perhaps, much higher.
Also, and I believe this is not uncommon, the Nimrod uses engine air to actually dump fuel in an emergency. This positive air pressure is used directly in the fuel tanks. I am a pilot with very limited engineering knowledge, but is there any concern about this procedure? Where is this air tapped from?
The air comes from the engine LP comps. It is reduced to a much lower pressure, with most air bled overboard, before it gets into the tanks. The vent system comes under spring relief pressure at 2.5 psi and backed up by the (in)famous blow-off valves if the vent valves fail. So, the fuel pressure in the dump lines/refuel lines, is very low and does not cause us any concerns. However, a loose coupling is a loose coupling and fuel without any pressure will leak through it. But, we are quite content that the lads are making sure that the couplings are not loose.
Finally, with a temp reduction of only 16 deg, surely the auto-ignition could have occurred anywhere the fuel was in contact with the damaged insulation?
Well, it is conjecture to say how much reduction is achieved by brand new, or very old, insulation. IMHO, regardless of the thickness, if the pipe has more than 400C air in it, the insulation wouldn't stop auto-ignition if the fuel is able to remain on top of it for a minute or two.
Regards
Ed Sett