Nacelle fins?

[swashplate]

I have noticed on various aircraft (737s, A320s) that the Engine nacelles have small fins attached to them.

What is the purpose of these devices?

Is it to reduce drag (burn less fuel)?

Or are the manufacturer's trying to use the nacelles to provide extra lift?

Possibly to help the aircraft achive extra stability in roll/pitch/yaw?

Or to alleviate loads on the wing that has to carry the engine....??


As usual, I look forwards to fascinating, detailed, informative replies.

Also, to the sarcasm, flaming etc.........

[This message has been edited by swashplate (edited 10 May 2001).]

[AffirmBrest]

Erm... don't really know for sure but my best guess is that they would perform a function similar to wing fences - ie. prevent separation of the airflow from the nacelle surface as it flows around and up the inside of the engine. Separation would create unwanted drag, and possibly unstable airflow over the slats/intake

Passengering with a window seat on cold, humid days I have noticed that condensation trails form above and behind the fin, indicating a pressure drop - I suspect this is a vortex forming behind the fin to 're-energise' the airflow and preventing laminar separation.

Or not?

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...proceeding below Decision Height with CAUTION...

[Cuban_8]

All,

Have been thinking about his one myself following a recent trip on a BMI A321. I initially though that AB might have hit the nail on the head. However, I don't think that the nacelle reaches a great enough incidence for the airflow to separate significantly. However, at incidence, cylinders shed vortices from their upper surfaces, and a guess of mine was that the fins may be present to modify the form of these vortices.

Otherwise, they may be present to control some flow characteristic due to the interaction of the fusalage/nacelle/wing in that area. Either way, i'm going to quiz one on my departments academics to see if they can enlighten us!

Regards,

Cuban_8