Originally Posted by
wilycoyote4
I quote from other websites explaining the sound-----
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' (whistles) 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.
Every PW F100 engine has used a CENC to drive it's nozzle. Even the prototype F100-PW-100 made this sound. Some rumors say that this sound is the "screech" that gave the F-15 the name "Eagle"
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One is the PW nozzle showing the Speed Break open. The "Turkey Feathers" are the External Nozzle Segments. The parts that run horizontal around the nozzle and say "NO PUSH" at the aft end and "NO STEP" at the forward end. The newest PW-229 engines have black carbon-fiber Turkey Feathers.
The sound in the videos posted above reminds me of the leading edge mechanisms of a Boeing 747 which aren't exactly similiar, of course. But the noise of the mechanism is a screech-whirr at high pitch and very very loud. If you stand under the wing of a parked 747 when the leading edge is extended you can watch the "flexible-shafts that turn screw-jack type actuators" turning. Not that the comparison is perfect. But the sound will make you jump out of your denim jeans ----if it is new to you and you have no ear protection.
A Chinese girl I once knew, helping her learn English, described denim jeans as cow trousers. Love that girl, miss her.
Where was I? Oh yup, that noise should be added to aircraft such as the F-16 but how? Proper engine of course.