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Newbie Joined: Dec 14, 2006 Posts: 2 Status: Offline

Can someone authoritatively tell me if F-16 has to run its engines at idle for some time after landing before it can safely shut them down? 10 minutes?
I need to know for sure since it is about some wager .... Razz

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Elite 2K Joined: May 13, 2004 Posts: 2945 Location: Utah

No...no such thing (least not a real time per say) we normally just let the engine idle to steady the system then shut it down, after many Hush house runs, it would be shut down almost at once in many cases.

Newbie Joined: Dec 14, 2006 Posts: 2 Status: Offline

Meathook wrote:

after many Hush house runs.

What's that if I may ask Question

Thanks for your answer (I meant to say "egine" not "engines" - I am of course aware that F-16 has one engine).

Elite 2K Joined: May 13, 2004 Posts: 2945 Location: Utah

The hush house is a building where the aircraft is tied down so full operational checks including afterburner runs can take place...your welcome

Elite 1K Joined: Jan 31, 2004 Posts: 1561 Status: Offline

michal wrote:

Can someone authoritatively tell me if F-16 has to run its engines at idle for some time after landing before it can safely shut them down? 10 minutes?
I need to know for sure since it is about some wager .... Razz

Well...don't know if the taxi-back after exiting the runway would count. Depending on ground traffic I suppose it could take 10 or so minutes to get back to the ramp and the motor doesn't go very far above idle power on the trip. Just enough to keep the jet movin' at a reasonable taxi speed. All depends on how far ya need to taxi I suppose.

Use to be, on the original PW100s anyway, the engine was revved for a quick moment before being shut down. Had something to do with oil scavenging or something like that. An engine guy could expand on that better than I.

Elite 2K Joined: May 13, 2004 Posts: 2945 Location: Utah

Yep, that was true now the fuel is just recycled...no need for that event anymore

Meathook wrote:

The hush house is a building where the aircraft is tied down so full operational checks including afterburner runs can take place...your welcome

Most of the times they are tied down.

Laughing

Elite 2K Joined: May 13, 2004 Posts: 2945 Location: Utah

Yes, except when a young airman makes a simple mistake that goes really wrong (as in your photo above).

By the way, that aircraft was assigned to my squadron back then....bad night for all involved

The "scavenge" or "rev up" at engine shut-down for the -200 and -220/-220E engines was to recover more oil from the engine's bearing cavities and pump it to the tank. At idle, oil would tend to gather in the bearing cavities. While not harmful to the engine, the oil would tend leak from the cavities after shut-down when the breather or "head-pressure" on the system was removed.

Many pilots would not scavenge properly (yes they do have faults) and engine troops were often called to leaking aircraft where the scavenge was re-accomplished to eliminate the possibility of a "real" oil leak. If the timing of the procedure wasn't followed CONSISTENTLY, it would not work as intended and leakage or bad oil level recording would result. This was key to not over-servicing the engine's oil tank and cause more leakage.

This became very evident in the late 90's as the engines aged and prior to the installation of an "anti-siphon" tube during a modification or TCTO to the engines. This would help break a suction that would form on the #5 bearing cavity and cause leakage from that area. (I think there were 3 variations of the mod before they got it right)

The "fuel-dump" at shut-down was the result of moving the throttle from idle to cut-off. The resulting motion of the throttle linkage, on the main fuel control, would cause a signal pressure line to cut fuel pressure to the open side, of the pressurizing and dump valve on the engine. This valve was responsible for dumping the fuel, when cut-off was selected, there-by diverting the fuel flow from the main fuel pump (which is still spinning with the engine) overboard so that the flame was exhausted inside the combustion chamber.

This dump can even be seen during old movies of early jet airliners when engines were shut down. J-57s, J-75, and most others all dumped fuel at shut-down. This was no longer acceptable with EPA (and other) regulations, and ground-crews had to catch this fuel in buckets or fabricated "catch-cans" pinned to the F-16's tail-hook area. These were later dumped in the proper recyclable or disposal areas near the flight line.

Newer -229 models of the F100 engine still "dump" fuel, but it is sent into a fuel manifold on the engine that is lower in pressure, so that the fuel is by-passed internally and recycled into the fuel system.

The "scavenge" of the oil system is no longer required on the -229 as the oil system has been redesigned and does not require the additional RPM to perform the job.

Moral: "The -229 isn't your Father's F100...." to coin a famous phrase.
Very Happy

Some of us still have the 220s and have to run up before shut down. My ANG unit is still block 25s until we upgrade to 30s after the BRAC kicks in at other bases.

Thanks for the indepth explanation! Smile

I did forget to mention something in my first post on this issue.

During test-cell operation, and installed power runs, the engine has to be at idle for 5 minutes prior to shut-down.

It allows the enigne to cool after higher power settings.

There is also a warm-up period prior to testing the engines to allow them to "normalize"

Any start after the first should only be performed after a 1 minute "motor-to-cool" period on start. This helps the hot top parts of the enigne match the temperature of the cool low parts, prior to start-up.

If you've ever had a flame-out from high power (esp MAX) you'd know how tight an F100 gets. Such conditions can occur when power to the test-cell is lost, or something inturrupts the fuel supply to the engine. The Core will lock up and can-not be turned by any means. (and shouldn't to preclude damage)
Even the "emergency" motoring of the engine with the -60 or -95 doesn't cool it enough to keep it from locking up.

After an overnight stay in the Hush-house they will be OK in the morning...

that was my favorite thing about running 220/220E's. running it up for scavenge... although it was not much, it was always fun!

Enthusiast Joined: May 09, 2006 Posts: 21 Status: Offline

That_Engine_Guy wrote:

The "scavenge" or "rev up" at engine shut-down for the -200 and -220/-220E engines was to recover more oil from the engine's bearing cavities and pump it to the tank. At idle, oil would tend to gather in the bearing cavities. While not harmful to the engine, the oil would tend leak from the cavities after shut-down when the breather or "head-pressure" on the system was removed.

Close. The problem was actually that the scavenge system would actually create a vacuum in the bearing cavity. After shut down cool oil would siphon (hence anti-siphon tube) from the tank and fill the cavity with too much oil. And when the oil would heat up it would push the carbon seal open and the oil would leak.

CCAF wrote:

That_Engine_Guy wrote:

The "scavenge" or "rev up" at engine shut-down for the -200 and -220/-220E engines was to recover more oil from the engine's bearing cavities and pump it to the tank. At idle, oil would tend to gather in the bearing cavities. While not harmful to the engine, the oil would tend leak from the cavities after shut-down when the breather or "head-pressure" on the system was removed.

Close. The problem was actually that the scavenge system would actually create a vacuum in the bearing cavity. After shut down cool oil would siphon (hence anti-siphon tube) from the tank and fill the cavity with too much oil. And when the oil would heat up it would push the carbon seal open and the oil would leak.

You know JR?

Enthusiast Joined: May 09, 2006 Posts: 21 Status: Offline

falconfixer860261 wrote:

You know JR?

I work for JR.

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F100 shutting down after flight