F-15 Question.

[Hihonyr8811]

Does anyone know what causes the high pitched noise/squeal on take off and landing?

Someone has just asked me the question and I've no idea, I'm sure I've asked someone before and probably been given an answer but I can't remember


Here's an example of what I mean.

[Olicat]

Hydraulics i think, when the throttles are opened something happens to make that sound, but i dont know what!

[Thumper]

I dunno but I did find this:

The PW (Pratt & Whitney) engine uses an air driven motor within the Convergent Exhaust Nozzle Control, CENC, to vary nozzle exhaust area or "Aj" (Area, jet to be technical.)

I've heard it said the "whine" you hear during nozzle operation was the "cry" the F-15's made during early testing that gave them the name "Eagle"

[Olicat]

Yes; what you hear is the CENC "Convergent Exhaust Nozzle Control" that moves the actuators for the engine's exhaust nozzle.

If it 'zip-zips' (wistles) when the throttle is moved it is a F100-PW-2XX. The F110-GE-1xx engines use hydraulic (engine oil) actuators to move their nozzle, which is silent.

The CENC uses high-pressure air from the 13th stage of compression, the highest in the engine, to move the nozzle. The CENC is akin to an "air-motor" As the air moves through the CENC in one direction the nozzle is "driven" open by flexible-shafts that turn screw-jack type actuators. In less than a second, the CENC can turn 341 revolutions to fully open or close the nozzle. When air is directed through the CENC the opposite direction, the nozzle will close as everything spins in reverse.

The CENC controls "nozzle position" or Aj (Area Jet) which is the primary method of maintaining proper EPR (Engine Pressure Ratio) and N1 (Fan RPM) Whenever the pilot moves the throttle, or PLA (Power Lever Angle) the engine adjusts for the requested thrust, and Aj is the most evident adjustment made. (Nozzle opens/closes and the zip of the CENC is heard)

The CENC has an exhaust port that dumps the used air overboard. It is located about 5 o'clock on the engine just aft of the 'H-Flange' where the augmentor duct attaches to the aft-fan duct. On the Viper the exhaust port would be located between the ventrals, more towards the one on the right.

[Hihonyr8811]

Thanks you two

I think i'm juust going to direct them here, as I didn't understand any of that

Although I love that that's how they got the name eagle

[Xplumberlives]

Thanks you two

I think i'm juust going to direct them here, as I didn't understand any of that

Although I love that that's how they got the name eagle

Can you see the little piggies flying over!

I wonder how the F16 got the name Falcon and the F14 became Tomcat, oh and the F18 the Hornet, perhaps it was all down to funny noises the aircraft made!

[Hihonyr8811]

Thanks you two

I think i'm juust going to direct them here, as I didn't understand any of that

Although I love that that's how they got the name eagle

Can you see the little piggies flying over!

I wonder how the F16 got the name Falcon and the F14 became Tomcat, oh and the F18 the Hornet, perhaps it was all down to funny noises the aircraft made!

I dunno but I did find this:

The PW (Pratt & Whitney) engine uses an air driven motor within the Convergent Exhaust Nozzle Control, CENC, to vary nozzle exhaust area or "Aj" (Area, jet to be technical.)

I've heard it said the "whine" you hear during nozzle operation was the "cry" the F-15's made during early testing that gave them the name "Eagle"

I was commnting on what Thumper was quoting, you should take it up with who ever wrote the original quote, not me.

[Thumper]

You tell him H

[Xplumberlives]

[Molerat]

I was going to say it sounds like a nozzle air motor. Obvious really (to an ex sooty anyway) You probably don't notice it on old UK jets as we tend to have nozzles closed dry and open up when reheat lights (so the air motor is moving slower and the motor noise is masked by the burner noise) whereas the americans seem to like open nozzles, close them quickly then light the burners. Much the same type of noise as Tornado bucket motors.

[Stormcruiser2]

its also on the F16, but, it doesn't always squeek? its wierd....

[Thumper]

Yes, I have heard the F-16 make a similar noise as well as the Harriers when using nozzle to do a short take-off/landing.