View Single Post
Old Jan 19, 2013, 07:39 PM
kcaldwel is offline
Find More Posts by kcaldwel
The answer is 37
kcaldwel's Avatar
Joined Jan 2007
3,851 Posts
Since you brought up the Cessna 150, I'll use it's airfoil as an example. The NACA 2412 works reasonably well at low Re, so this shows how much the performance changes just because of Re.

At an airspeed of 100kph, which would be near minimum power required for a 150, the Re would be about 2.8M. A scale model with a 30" span would be flying at about an Re = 90k. For the airfoil alone (infinite span), the best L/D goes from about 118:1 down to about 48:1. So the best L/D decreases by a factor of about 2.5. That would be reasonably representative of the whole airplane. So if the full-sized Cessna 150 had a glide ratio of 7:1, a scale model with a 30" span might have a best L/D of about 2.8:1.

Your model sounds much cleaner than a scale Cessna 150 so it might have a best L/D of 6:1 as a wild guess, not even having seen a photo.

Kevin
kcaldwel is offline Find More Posts by kcaldwel
Reply With Quote