Choosing airfoils based on calculated polars  
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All Forums >> RC Airplanes >> Aerodynamics >> Choosing airfoils based on calculated polars
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Choosing airfoils based on calculated polars - 7/5/2003 6:33:55 AM   
yclui


 

Posts: 43
Joined: 10/13/2002
From: Hongkong,
Status: offline 		Hello,

I have just download the Profili and after getting acquainted with the functions, the first thing I did was to compare the polars of HN354 and S4083 at Re = 216K which is typical for 60” slope racers in moderate lift conditions.

These are the polars of HN354 and S4083 plotted by Profili. HN354 is the airfoil used in my 60” slope racer http://www.euro-sailplanes.co.uk/uk/html/sport-hlg/mini-nyx.htm and the S4083 is used in my 60” HLG http://www.euro-sailplanes.co.uk/uk/html/sport-hlg/highlight.htm . The polars indicates that HN354 performs poorer than S4083 at high Cl and I wonder why it is still chosen for my slope racer as one of the major requirements for racers is that it won’t loose speed in tight turn.

I am trying to learn the basics of model design and if someone can kindly shed some light on this, I will appreciate it.

Thanks,

Y C Lui

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Choosing airfoils based on calculated polars - 7/8/2003 5:50:31 AM   
Ben Lanterman



Posts: 1284
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		You would need to calculate the turn rate (load factor) which can give the lift needed and then the CL needed to achieve the turn and see where it falls on the polars. The CL needed to turn might still be in the low CL area where the drag is a little lower. But keep in mind that although aerodynamics is rocket science that it isn't always applied with precision. You are headed toward a good start in your learning quest though.


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Ben Lanterman

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