SNAFlyboy
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Posts: 62
Joined: Thu Oct 18, 2007 5:42 pm

Gap Between Inlet And Fuselage

Fri Nov 30, 2007 2:38 am

Fellow A.netters,

I've often wondered: why is it that, on some aircraft, there is a gap between the engine inlet and the fuselage? For example, both the F-16 and F-4 Phantom II...


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Are the aerodynamics more favorable when the inlet is not flush with the fuselage, or is there another reason for this gap? Other fighter aircraft seem to have it as well, such as the Eurofighter and the Mirage 2000..

What's the deal here?  confused 

~SNAFlyboy
 
avt007
Posts: 1989
Joined: Mon Jul 10, 2000 4:51 am

RE: Gap Between Inlet And Fuselage

Fri Nov 30, 2007 2:43 am

I'd say they are trying to keep some linear airflow along the skin, in other words,a smooth, clean layer to flow back and keep the rest of the fuselage and empennage in smooth air.
 
Fly2HMO
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RE: Gap Between Inlet And Fuselage

Fri Nov 30, 2007 2:46 am

It prevents turbulent airflow from the fuselage boundary layer to be ingested by the engines. which could lead to a compressor stall.

Jet engines really don't like turbulent air.
 
MissedApproach
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RE: Gap Between Inlet And Fuselage

Fri Nov 30, 2007 2:50 am

I believe it has to due with turbulent air near the fuse, or coming off the nose. Air further from the airplane will be "clean". Most airplanes have intakes placed slightly away from the fuselage-

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tdscanuck
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RE: Gap Between Inlet And Fuselage

Fri Nov 30, 2007 6:54 am



Quoting FLY2HMO (Reply 2):
It prevents turbulent airflow from the fuselage boundary layer to be ingested by the engines. which could lead to a compressor stall.



Quoting MissedApproach (Reply 3):
I believe it has to due with turbulent air near the fuse, or coming off the nose.

It's not so much turbulent as stagnant. The gap is there so the engine doesn't ingest the stagnant boundary layer on the fuselage. It may or may not be turbulent, depending on the operating condition.

Tom.
 
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IFixPlanes
Posts: 239
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RE: Gap Between Inlet And Fuselage

Fri Nov 30, 2007 11:48 am

There is also a diverter in front of the A320 APU inlet.
The AMM (49-16-00) is telling why:
...
Its primary purpose is to improve the ram air recovery during in-flight APU operation. This is accomplished by positioning the inlet some 50mm into the airstream, thus the lowest energy portion of the aerodynamic boundary layer is prevented from entering the air
inlet.

...
never tell an engineer he is wrong ;-)
 
SNAFlyboy
Topic Author
Posts: 62
Joined: Thu Oct 18, 2007 5:42 pm

RE: Gap Between Inlet And Fuselage

Sat Dec 01, 2007 1:46 am

Thanks for your replies everyone, I hadn't considered compressor stalls and such, though it makes perfect sense now...

Did the Concorde exhibit the same kind of gaps between the engine inlets and the wing surface? In the picture below, there appears to be space between the inlet and wing, albeit a very small one...maybe my eyes are just playing tricks on me. Was stagnant/turbulent air ever much of a consideration at that location during any stages of flight?


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~SNAFlyboy
 
soon7x7
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RE: Gap Between Inlet And Fuselage

Sat Dec 01, 2007 3:31 am



Quoting SNAFlyboy (Reply 6):

Airflow considerations on the Concorde are performed inside the nacelle, not outside...and as the nacelles are located under the wing a psitive airflow is a constant...( I read that somewhere, can't quote at this point, but I do remember that)...j

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