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Old 10-12-2017, 11:35 AM   #1
mytai01
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Default Question for real life F-15 maintainers

What is the high frequency buzzing noise I've heard Eagles make during some maintenance procedures? The engines are off...
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Old 10-12-2017, 05:43 PM   #2
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Not an F-15 maintainer, and not sure if this is something you can do without the engines running, but are you talking about the nozzle test?
https://youtu.be/tfNeAr8ix10?t=107
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Old 10-13-2017, 04:07 AM   #3
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The sound of something else other than an engine running after engine shutdown.

https://www.youtube.com/watch?v=o9zA0v5yrPs

https://www.youtube.com/watch?v=Ho-JzqjOdWY

https://www.youtube.com/watch?v=ksPO2zYvOT8
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Old 10-13-2017, 06:58 AM   #4
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I'm not an Eagle guy but I think what you are trying to point out is the avionics cooling fans shutting off when the power from the generators shut's off. When engine RPM goes below a certain percentage the generators will stop delivering power to the aircraft systems. Shutting off fuel flow to the engines stops the combustion process but the engine is still spinning keeping the generators running until the engine spool's down enough that the generators will no longer deliver electricity to the aircraft systems to run things like avionics cooling fans.
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Old 10-14-2017, 02:51 AM   #5
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Quote:
Originally Posted by Vampyre View Post
I'm not an Eagle guy but I think what you are trying to point out is the avionics cooling fans shutting off when the power from the generators shut's off. When engine RPM goes below a certain percentage the generators will stop delivering power to the aircraft systems. Shutting off fuel flow to the engines stops the combustion process but the engine is still spinning keeping the generators running until the engine spool's down enough that the generators will no longer deliver electricity to the aircraft systems to run things like avionics cooling fans.
Well, I want that in my DCS Eagle and any other aircraft with a similar setup...
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Old 10-14-2017, 05:45 AM   #6
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Auxiliary Power Units (APU). Once the engines are shut down, the Auxiliary Power Units disconnect from the electrical busses and that's when the APU winds (whines) down.

Source
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Old 10-14-2017, 07:54 AM   #7
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Originally Posted by VZ_342 View Post
Auxiliary Power Units (APU). Once the engines are shut down, the Auxiliary Power Units disconnect from the electrical busses and that's when the APU winds (whines) down.

Source
I assume these APU are not like the kind airliners have and you're not meaning the JFS, right?

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Old 10-14-2017, 08:03 AM   #8
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I think we should wait for someone that has actually work on the F-15.

The F-15 does not have an APU, it has a JFS which is only used for the start and AFAIK, has nothing to do with the shutdown procedures. It could be the sound of the AMADS spooling down but I do not know since my experience on the F-15 is very limited.


Of all the things the FC3 F-15 could use, why bother with something so trivial?
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Old 10-15-2017, 12:31 AM   #9
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Quote:
Originally Posted by mvsgas View Post
I think we should wait for someone that has actually work on the F-15.

The F-15 does not have an APU, it has a JFS which is only used for the start and AFAIK, has nothing to do with the shutdown procedures. It could be the sound of the AMADS spooling down but I do not know since my experience on the F-15 is very limited.


Of all the things the FC3 F-15 could use, why bother with something so trivial?
What do you want to see?
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Old 10-15-2017, 12:48 AM   #10
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If you are referring to just after engine shut-down, then the sound you hear is the emergency generator that comes on-line when the generators go off-line. The emergency generator is driven by hydraulic power and there is enough hydraulic pressure to drive it until the engines spool down.

Eagle Keeper for 12 years. McDonnell Douglas and Boeing for 7 years.
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