View Single Post
Old Mar 10, 2011, 06:01 AM
John235 is offline
Find More Posts by John235
Registered User
John235's Avatar
Sydney, Australia
Joined Mar 2006
1,315 Posts
Quote:
Originally Posted by canard addict View Post
John 235
John, Sorry for the slow response. I appreciate your interest and challenging questions. It was fun to see the video again and I have contacted the same gentleman to see if he will do a rerun. I was sold on the high lift flat bottom airfoils for years and noted their stall characteristics and inability to do things such as inverted flight and outside loops. The symmetrical airfoils seem so smooth for models that it makes me wonder what purpose that anything in between the two styles would serve.
From your comments, the Duck 2 sounds like a very enjoyable flyer. I can't wait to see the video. The gent who shot the first video certainly did a great job of it.

I think the symmetrical airfoil is perfect for the Duck style model because of the low aspect ratio main wing. Low aspect ratio makes it harder to stall the main wing, so you are less likely to come into issues with the stall characteristics of the symmetrical airfoil. If you increase the aspect ratio of the main wing with all else being equal you will push the main wing towards the AoA where it will stall. That is the reason why I expected the 36" span Duck 2 to spin more easily than the 30" version.

Applying the same reasoning to a symmetrical airfoil on the George Goose style model without other changes might suggest the possibility of problematic stall characteristics. So I think this is one case where it might be good to compromise between the fully symmetrical and flat bottomed airfoils. A semi-symmetrical airfoil, eg. NACA2412 as shown in several examples from Andy Lennons book might be one to consider. Not really a compromise, but the best of both worlds perhaps?

Quote:
Originally Posted by canard addict View Post
At present, I am toying with the thought of making a twin motor taildragger with swept back in-line wings similar to the Georgia Goose with a prominent rudder and no horizontal tail. What do you all think it should look like?
Charles
Should I visualise something like this? Or maybe you would prefer to use a longer tail moment.
John235 is offline Find More Posts by John235
Reply With Quote