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mark17
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 Subject: F15 noise 2009-07-13, 12:14 |
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Hi all,
Just got back from Lakenheath and 30 mins at Cottesmore.
Will post pictures after a shower!! What a cracking day.
Can anybody tell me what the strange noise is on the the Eagles just before they roll for take off and again just before touch down please.
I presume its some sort of brake,just curious really!
Thanks
Mark
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dinger
Location : Lincolnshire
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| Subject: Re: F15 noise 2009-07-13, 12:44 |
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Your strange noise is the exhaust nozzle actuation system which controls the nozzle area.
Dinger.
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stigorige
Location : norfolk
Spotter Watch Member : no
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| Subject: Re: F15 noise 2009-07-13, 13:19 |
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Absolutely correct Dinger, I believe the high pitched whistle is caused by by-pass air from the turbofans used to power the nozzle actuators.
Stig.
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dinger
Location : Lincolnshire
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| Subject: Re: F15 noise 2009-07-13, 14:07 |
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Dont think it will be by-pass air Stig as it wont be at the right pressure. My guess would be air tapped from the HP compressor, however, I stand to be corrected.
Dinger.
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stigorige
Location : norfolk
Spotter Watch Member : no
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| Subject: Re: F15 noise 2009-07-13, 14:29 |
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You could well be right, I think it powers a turbine which provides hydraulic power to the actuators.
Stig.
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spiritwalker
Location : Thurston, Bury St Edmunds
Spotter Watch Member : no
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| Subject: Re: F15 noise 2009-07-15, 08:43 |
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Whatever it is, it's a chuffin brilliant noise!!! 
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Blackcat1
Location : Aberdare, South Wales, Southern edge of LFA7
Spotter Watch Member : No
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| Subject: F15E 2009-07-15, 09:19 |
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I did an impression of that noise when talking to an F15E pilot at Mildenhall Air Fete a few years ago, he laughed his head off and said it was an awesome impression lol. 
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old_git
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| Subject: Re: F15 noise 2009-07-15, 10:05 |
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The noise is HP air bled off the compressor.
this air is then fed into a recirculating ball screw linear actuator.
the actuator has a little turbine like the air gun used to tighten your wheel nuts too hard at a well known brand of tyre fitters.
so this little turbine goes very fast making the whining noise.
the turbine is geared into the ball screw to give the linear push / pull to close the nozzles as the burner comes in.
apparantly the reason the nozzles are now left exposed rather than being covered by the "turkey feathers" previously fitted is because they tended to fall off rather a lot.
Geoff
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stigorige
Location : norfolk
Spotter Watch Member : no
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| Subject: Re: F15 noise 2009-07-15, 13:10 |
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I knew someone would have a definitive answer, I am correct that it's the turbine that makes the noise.
You can hear it several miles away when the a/c are on approach.
Stig.
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