(Y)F-16 Engine - Nozzle blade movement factors

indigowarrior9 · by **indigowarrior9** » 25 Jan 2018, 09:33

: f16_nozzle_open.jpg (179.96 KiB) Viewed 7563 times

1. On the ground - when the engine runs at idle or is completely shut down - I often see the nozzle-blades "wide open".

: f16_nozzle_closed.jpg (200.57 KiB) Viewed 7563 times

2. On the ground - during takeoff (with afterburner) - I see the nozzle-blades "contracting" / "narrowing".

Which are the factors that determine the position of the nozzle blades:
- Is this only determined by the engines current output level (like throttle: close / idle / fully open / afterburner on)?
- Are there any other factors which have an effect on the nozzle blades position?

krorvik · by **krorvik** » 25 Jan 2018, 23:48

This page has a good explanation for the F-100 engines:

http://www.f-15e.info/technology/engines/pw2/pw2.htm

And here's a good vid showing it:

https://www.youtube.com/watch?v=tdczvix3EiE

bouliult · by **bouliult** » 27 Jan 2018, 10:21

On the pictures you show two different engines. Top one is a GE enginge and the lower one is a PW.

For the PW the nozzle is positioned by the DEEC. Digital Electronic Engine Control. It will have different inputs like static pressure in front and in the back of the engine. The Nozzle is positioned to maximize thrust. The DEEC commands the CENC (Convergent Engine Nozzle Control) to open or close the Nozzle. This is done with 13th stage compressor air converted to cables rotating the nozzle open or closed.

With the throttle at or near idle and gear down the nozzle opens to lose thrust to accommodate a landing.

krorvik · by **krorvik** » 29 Jan 2018, 14:18

I see you are asking other q's specific to the YF - note that the YF's, as far as I could dig up, had F100-PW100 engines (first production F16As had the PW200), which did not have the DEEC - that was introduced later on the PW220, mid 80s.

zhangmdev · by **zhangmdev** » 29 Jan 2018, 14:43

indigowarrior9 wrote:- Are there any other factors which have an effect on the nozzle blades position?

Ambient pressure into which the engine exhausts is an important factor. You don't want the gas to expand too much to cause its pressure drop way below the ambient pressure. That is why 1st stage rocket has engine(s) with short and small nozzle(s), while 2nd stage rocket engines (which work in close to zero ambient pressure) have long and large nozzles. Jet engines have variable nozzles can adjust to different ambient pressure.