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airfoil trade offs


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Davincy Technologoes, the makers of AirplanePDQ software, have a really neat program call Airfoil Optimizer. You input the baseline configuration of your airplane performance and airfoil and it allows you to compare peformance changes with other airfoils from an extensive library. :thumbsup:

 

I plugged in the Cozy MkIV as a baseline and found that while there are airfoils in the database that would improve cruise speed they hurt take off performance. Looks like Mr. Rutan made a very good choice/tradeoff. Imagine that. ;)

 

Still, it's fun to look... :)

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Can you get more takeoff performance by trading a bit of cruise speed?

 

Not sure I'd do it, I'm firming up on the ridgy-didge "as per plans" concept. It will still be my baby if it looks exactly like Nat's.

Mark Spedding - Spodman
Darraweit Guim - Australia
Cozy IV #1331 -  Chapter 09
www.mykitlog.com/Spodman
www.sites.google.com/site/thespodplane/the-spodplane

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Can you get more takeoff performance by trading a bit of cruise speed?

 

Not sure I'd do it, I'm firming up on the ridgy-didge "as per plans" concept. It will still be my baby if it looks exactly like Nat's.

...maybe...

 

A big part of the take-off performance airfoil problem appears to be reynolds number. The Eppler airfoil looks like it gives a lot better L/D at airspeeds around 60 kts than the low drag laminar sections. Thick sections and large leading edge radiuses (radii?) produce more lift at low reynold numbers and higher drag at cruise Cl and reynolds numbers. There might be some thick, large LE radius, highly cambered airfoil that would do it. But the design trade offs would be a lot more than just higher drag at cruise. Based on the library of airfoils available in this software it looks like Eppler has gone just about as far in that direction as worthwhile. So it looks to me like if you want better take off performance you need more thurst hp... (better acceleration, more power to overcome the drag associated with more lift, etc., etc.)

 

Even as "per the plans" there is still plenty of oppertunity to customize/personalize your baby. :)

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