Wierd F15 noise

[TankerPuke]

This is going to to sound a little wierd, but my sister was in Goldsboro, NC watching the planes land at Seymore Johnson AFB when she claims to have heard a sound similar to humming when you trim a boat engine. What the heck could that be? She heard it every time a plane came in to land and was on short final and she tells me she could hear it over the jet noise. I have no idea what it is. Do F15's do something extra special before landing?Anyone help me out here?

PUKE

 

[av8raaron]

Don't know what a boat engine trimming sounds like, but my guess is it's the gear coming down. You can hear this whirring noise from the ground (assuming jets are in the pattern) just after the gear lowers (time delay given the distance from the jets)

 

[Flaco]

F100 CENC makes the noise

She's likely hearing the nozzle on the F100 engine opening a bit and closing a bit as slight throttle changes are made on short final. The nozzle on the F100 is controlled by the CENC (Convergent Exhaust Nozzle Control) which is driven by bleed air from the compressor section of the engine. It makes a very distinctive high-pitched "whirring" sound when it is in use.

Flaco
F100 Grease Monkey

 

[CCDiscoB]

Not Exactly

close, but not quite right.

The F-15E is powered by the F100 PW-220 or 229. Not the -100. The difference is in the nozzle controller. The -220s and -229s have a DEEC (Digital Electronic Engine Control). Nozzle position is positioned by bleed air, but scheduled by throttle position. So when the trottles are thrown to idle, like on landing, the nozzles make a whirring sound. It is very distinctive. You can grade throttle technique based on how much the throttles are moving on landing.