Possibly one for KeithMac this one, being a Rhino fan I should have found this out ages a go but still, when RAF F-4s (I’m assuming RN F-4s were the same having never seen one take-off) ran there engines up prior to take-off, what is, and what is the reason for the white smoke which issues from the engine blow-holes on the sides of the rear fuselage? Its intrigued me for a long while so I hope someone can help.
Regards, Dazza.
By: Dazza - 10th November 2002 at 18:14
RE: Question about RAF/RN F-4s during engine run-up
Nice one Keith, superb info as usual.
Regards, Dazza.:-)
By: keithmac - 10th November 2002 at 14:49
RE: Question about RAF/RN F-4s during engine run-up
Dazza, Here’s a cutaway of a Spey showing all the various bearings etc which are pressurised and which end up venting hot smokey air overboard, most of it through the pipe which leads directly downwards in the diagram from the HP Turbine bearing.
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By: keithmac - 10th November 2002 at 14:27
RE: Question about RAF/RN F-4s during engine run-up
Di Dazza. All jet engines have parts which are pressurised internally by air drawn from the compressors, this helps to keep the oil in the bearings by pressurizing things called Labyrinth seals, it supplies cooling air to the Turbines and does a multitude of jobs. Most of it finds it’s way back into the main gas flow, some of it however has to be vented overboard. The smoke you see vented from the Phantom is some of this hot gas. It’s not directly related with the reheat, it’s just that when you go into reheat on the Phantom you’re already at the Max dry throttle setting (On the Phantom it’s called Max Mil or Max Military setting, a term inherited from the Americans) and there is a lot of this surplus hot gas to get rid of. There is also a lot of cooling air which is forced down between the outside of the Jetpipe and the fuselage inner skin to keep the fuselage from overheating, this also vents overboard.
Hope that answers your question.
KeithMac.
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November 9, 2002 at 10:06 pm