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Gap Between Inlet And Fuselage  
User currently offlineSNAFlyboy From United States of America, joined Oct 2007, 86 posts, RR: 0
Posted (6 years 7 months 3 weeks 5 days 13 hours ago) and read 3518 times:

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

7 replies: All unread, jump to last
 
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 1, posted (6 years 7 months 3 weeks 5 days 13 hours ago) and read 3513 times:

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.

User currently offlineFLY2HMO From , joined Dec 1969, posts, RR:
Reply 2, posted (6 years 7 months 3 weeks 5 days 13 hours ago) and read 3511 times:

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.


User currently offlineMissedApproach From Canada, joined Oct 2004, 713 posts, RR: 2
Reply 3, posted (6 years 7 months 3 weeks 5 days 13 hours ago) and read 3507 times:

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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Can you hear me now?
User currently offlineTdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 4, posted (6 years 7 months 3 weeks 5 days 9 hours ago) and read 3462 times:



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.


User currently offlineIFixPlanes From Germany, joined Feb 2005, 239 posts, RR: 0
Reply 5, posted (6 years 7 months 3 weeks 5 days 4 hours ago) and read 3420 times:

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 ;-)
User currently offlineSNAFlyboy From United States of America, joined Oct 2007, 86 posts, RR: 0
Reply 6, posted (6 years 7 months 3 weeks 4 days 14 hours ago) and read 3319 times:

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


User currently offlineSoon7x7 From , joined Dec 1969, posts, RR:
Reply 7, posted (6 years 7 months 3 weeks 4 days 12 hours ago) and read 3299 times:



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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