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Strange "pulsing" Of Jet Engines

Fri Aug 13, 2004 1:17 am

retd from a spotting session at PNQ/VAPO this morning where I saw a number of fighters of various makes do their rapid takeoffs and landings.

Starnge thing i noticed: the engines had flames when seen from the rear (afterburners??) but they werent consistent , but rather kept varying in intensity as the aircraft (a Jaguar) picked up speed on the takeoff roll. Was this just an illusion or does it happen this way? And if yes why is this so? Shouldnt the thrust be consistent?

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Joined: Tue Jan 01, 2002 5:38 am

RE: Strange "pulsing" Of Jet Engines

Fri Aug 13, 2004 1:42 am

Two names for it are Multi-Staged-Afterburner or Staged Reheat.
On aircraft Afterburners since the early 70's the afterburner can be varied to produce more or less additional thrust. The P&W F-100 engine in 1971 had a five stage AB and the pilot could select any level he desired depending on how fast he wanted to be somewhere else and how much fuel he had to waste.
The rings you see in the flame are harmonic levels indicating the relative stage of afterburner selected.
That's the simple version...
One may educate the ignorance from the unknowing but stupid is forever. Boswell; ca: 1533

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