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ACMIguy wrote:

The block 15's would dump fuel at shutdown, we had to put a bucket under the jet to catch it, now I noticed the block 25-52 no longer does that, why?

The F100-PW-100, PW-200 and PW-220 dumped fuel on shutdown. The PW-229 does not. I don't believe any of the GEs dump either. (They were designed later)

On jet engines there is a "pressurizing and dump valve" or P&D Valve that sits between the engine's fuel control and the manifolds that carry the fuel into the combustion chamber's fuel nozzles. This valve is responsible for sending the fuel into the engine while running, or away from the engine to shut it off.

Remember, a jet engine will run until you cut it's fuel source. While spinning the engine's fuel pump will continue to be driven from the gearbox until N2 reaches 0. This means the fuel in the system has to go somewhere when the pilot moves the throttle to OFF.

In older engines - J57, J75, TF-33, early F100s, etc; this fuel was simply dumped through one of the overboard engine drains. When the EPA and other regulations prohibited this sort of thing, it required this fuel to be caught. The CC needed to have a bucket to catch the offending fuel and properly deal with it. (Some units used special catch-cans that were pinned to underside of the jet prior to shut-down)

As the newer engines were designed the fuel dump line is simply plumbed back into the engine's fuel system so that it is "recycled" versus being sent to one of the engine's drains.

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That_Engine_Guy wrote:

For those who want to know what's all involved with nozzle ratios and positions, check out this graphic from NASA. Just to give you an idea what's involved to find the optimum Aj (Area Jet) for any given power setting. This is some of the magic worked by the engine's control computer a few times per second... Shocked

After looking at the diagram and reading about how the older open/close nozzles worked, I'm wondering if there were any jets that had manual control over the nozzle.

And one more loosely related question is if an engine loses its electronic control and has to go to manual control (like the BUC in the -200), does the nozzle follow a mechanical schedule or does it lock in a certain position?

DesignAndConquer wrote:

And one more loosely related question is if an engine loses its electronic control and has to go to manual control (like the BUC in the -200), does the nozzle follow a mechanical schedule or does it lock in a certain position?

PW-220 and PW-229 SEC mode drives the nozzle full closed. This provides the maximum amount of thrust possible at all throttle settings. Afterburner is also inhibited during SEC operation.

The BUC (Back Up Control) on the PW-200 had the nozzle "aerodynamically loaded" closed to obtain the maximum amount of thrust. As with the newer PWs the 'burner will not function in BUC mode.

You'll have to find a "GE engine guy" to answer to their nozzle operation, but I believe it is very similar. Shrug

Best thing in any case is to keep the engine in Primary Mode; that's what all engine guys/gals strive for!

Keep 'em flyin' Thumb

Here is a graphic so that you can all see what open versus closed looks like from inside the nozzle.

Enthusiast Joined: Apr 10, 2007 Posts: 73 Status: Offline

Not to get into thetech stuff, the gas laws must balance to keep proper t's and p's in the machinery. The nozzle has to adjust to help this along with the vgi vanes as well plus other techno gadgets that try to ooptimize out put. So the nozzle may close fully at sea level standard day, but tke it to reno and it may not on a standard day.

This is in response to ACMI Guy's question of Oct 11th:

The block 15 was closer kin to the F-105 and F-106 than to the block 25-32-42-52s! Elementary, my dear Watson!

I remember the good ole days when those ole Pratts would piss all over the ramp when they shut down--after a brief runup to scavange some oil pump somewhere. Fortunately, in the politically- and environmentally-correct '90s and 'oughts, I didn't have to listen to the tail feathers, runups, scavenge pumps, or anything like that because I was privileged to work on block 30s which had the superior engine.

Enthusiast Joined: Apr 10, 2007 Posts: 73 Status: Offline

I know what you mean, but blame that on the engine spo guy's when they started the PW-F100, I remember clearly that WP ENGINE SPO said no to the recycle design after coming out of the augmenter. There was a $$$ cost to add it and they wanted to get that F-15 off the ground on schedule and no more delays. Mad

Newbie Joined: Mar 26, 2008 Posts: 1 Status: Offline

Hi all,
I am an AMVI (Aeronautica Militare Virtuale Italiana) F-16 virtual pilot, we use OpenFalcon4.5 simulator.
I would like to learn more about the nozzle in a real F-16C block52.

In our simulator the "Nozzle Position" indicator works like this:

Full-AB: 100%
Military Power: 0%
Idle: about 1 or 2%
Idle with Landing Gear down: 90%

In real F-16C Block52, with throttle in idle position, the nozzle is always at 90%?
Or it is almost closed and 90% open only with the landing gear down?

Thank you all for your answers and for your fantastic forum.

PS: I know that my English is bad. Laughing

Enthusiast Joined: Apr 10, 2007 Posts: 73 Status: Offline

AMVI_Zakk wrote:

Hi all,
I am an AMVI (Aeronautica Militare Virtuale Italiana) F-16 virtual pilot, we use OpenFalcon4.5 simulator.
I would like to learn more about the nozzle in a real F-16C block52.

In our simulator the "Nozzle Position" indicator works like this:

Full-AB: 100%
Military Power: 0%
Idle: about 1 or 2%
Idle with Landing Gear down: 90%

In real F-16C Block52, with throttle in idle position, the nozzle is always at 90%?
Or it is almost closed and 90% open only with the landing gear down?

Thank you all for your answers and for your fantastic forum.

PS: I know that my English is bad. Laughing

I do believe that the WOW switch sends signal to DEEC that indicates if on ground or air. If on ground the NOZZLE needs to dump excess thrust at Idle so the nozzle will open to 90-95%. When off the ground the nozzle will set it self the pressures at the altitude to the fuel schedules so that flame out will not occur or gas law pressure balance to keep the flame intact again assuming your at idle.
I beleive this to be correct.

Enthusiast Joined: Jan 04, 2008 Posts: 44 Status: Offline

Watch from 3:05.
As the jet passes, you can clearly hear the 'zips' and 'whirs' of the engine nozzle:
http://www.youtube.com/watch?v=QMts5mKK ... re=related

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Question about engine nozzles