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RE: What are these little fences for? - 4/19/2012 11:19 PM   
mithrandir



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Status: offline 		the fences can never be truly aligned with the flow....

the flow has a spanwise component that changes as the wing AOA changes... so there is always a little vorticity shedding
from these little guys....

though the effectiveness of the control surface might be improved, it is not without penalty...Prolly a net loss on a racer....

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RE: What are these little fences for? - 4/20/2012 12:52 AM   
rmh



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Status: offline 		Fences make a huge difference in stability when flying high alpha stuff (I know - there is no such thing)
Lotsa theory about this stuff - IF you get in there and fly more you will see the differences
I doubted the effectiveness til I got the right positioning and size of the fences -about mid half span and really not all that high- works very well

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RE: What are these little fences for? - 4/20/2012 5:36 PM   
Von Ohain


 

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Status: offline 		I agree that they are probably to there to stop parasitic airflow around the edges when the control surfaces is being deflected.
However, they do not add much any extra drag because they are just substituting rudder surface for sideways stability. A fact I believe the aircrafts designer has taken into account, and reduced rudder surface accordingly.

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RE: What are these little fences for? - 6/5/2012 5:30 AM   
TexasAirBoss



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Status: offline 		I'm going to take a guess and say this : This is a race plane. And deflecting control surfaces creates drag which might slow you ever so slightly. I guess these devices might cause the ailerons and elevator to work slightly more effeciently so that less deflection is required and therefore less speed is lost by deflecting them.

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RE: What are these little fences for? - 6/5/2012 10:25 PM   
BFoote


 

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Status: offline 		Fences are there to increase spanwise flow and conversely decreasing induced drag. Pylon racers require a huge amount of lift in a turn and a higher CL. When ailerons are deflected, increasing the CL over part of the wing, the higher CP(coefficient of pressure or coefficient normal), will stop spanwise flow and tend to exit it inwards where the discrepancy occurs. This effectively decreases the aspect ratio of the wing. Induced drag is effectively increased by the aspect ratio and the square of the Cl. When one goes into a turn, 1) your lift needs to increase and 2) Spanwise flow decreases initially due to deflected ailerons.

As was stated up thread, in a pylon turn, one wants to rotate to the desired angle and then hold a constant turn radius. In practice its easier to hold a near constant turn radius where the ailerons are not deflected much if at all.

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