ARC radius airfoils question....long

From: <nmonllor_at_tampabay.rr.com>
Date: 30 Oct 2013 06:19:33 -0700

Hello everyone,
  
 I've come across many plans where two differnt percentages of arc have been presented for different cieling heights. An example of this would be in Ron Williams' book Dennis Jaeck's Pennyplane #2 on page 91. There have been others too.
  
 On this particular model plan it states:
 high cieling: 4% arc
 low cieling: 6% arc
  
 The first time I saw this, I figured it had to do something with lift, Bernoulli's law and so on. At the time, I didn't give it much thought as I just wanted to build a plane that flew. Since then though, I've come across it again and again on other plans and thought I'd take a look at why this was so.
  
 Well, my daughter Gabby is doing her science fair project on how differnt arc radius airfoils affect the flight of her Pennyplane. BAM, right between my eyes!!! The question arises again, but this time with a purpose.
  
 I thought it had to do with lift but, does it?
  
 A smaller percentage would create a higher hump in the air foil increasing lift according to Bernulli, but yet it is suggested for a lower cieling. Whyis this?
 What am I not seeing?
  
 Please help me understand.
  
 Thank you,
  
 Ren
Received on Wed Oct 30 2013 - 06:19:33 CET