Dec 02, 2013, 08:32 AM
Tossing planes into the snow
Joined Nov 2011
2,557 Posts
Quote:
 Originally Posted by Rockin Robbins Hey, I'm also glad to see this thread up and running healthily! I will be putting another Radian together just as soon as I get my flying wing mojo exercised. As far as the wing trailing edge goes, don't forget that the Wright Brothers found out in 1903 that for the struts of their Flyer, a rounded rectangular shape had less drag than a teardrop. I believe that we'll find the same thing with the Radian, that the blunt trailing edge will be so close to the best possible profile that just about anything else will make the situation worse. Also interesting as all heck is Horizon's choice of the Gottingen 398 airfoil. Lately we've had the great research in low Reynolds Number airfoils by Michael Selig over at the University of Illinois at Urbana-Champaign and Mark Drela at MIT. And lots of high falutin special low Reynolds Number soaring airfoils have hit the RC sailplane competition circuit. But what do we have here, slugging it out to a draw with the high dollar boys? We have the Gottingen 398 airfoil, designed in.........1919. And now you know the rest of the story. Our plane is a testimony to the value of inspiration when wind tunnels, high mathematics and PhDs just aren't available.
Thank you for this info. I guess I will just leave the trailing edge as it is.

Thank you as well, Thoren, for all your great info.
Dec 02, 2013, 06:01 PM
Registered User
Joined Feb 2007
9,411 Posts
Quote:
 Originally Posted by FabFlight Well, I'm more thinking in the line of a fixed extension. At first, I was tempted to extend the TE by some 17 mm and finish with a sharp edge, but after reading Baker and van Dam, I'm now sure. Perhaps a flow seperator would be better. Their work was based on an airfoil with a very thick butt end (17%) much more pronounced than the Radian's (2.5 - 2%). The gain in lift/drag might not be as dramatic. Construction-wise, the trailing edge is 4-5 mm so it would involve the construction of a submillimeter thick flow seperator sticking out about 4 mm out from the center of the trailing edge, ideally to a 10 degrees up angle. The same apparatus could be installed on the rudder.
Hello FabFlight,

Comment ca va a St-Remi? Est-ce St-Remi de Napierville?
Je suis un peu intrigue par les dimensions dans votre ecrit.

I guess the 17% is the max thickmess of the wings.
I am not sure what you mean by "butt end".

The trailing edge of my Radian does not exceed 2 mm.

Zor
Dec 02, 2013, 07:32 PM
Registered User
Joined Sep 2013
76 Posts
Quote:
 Originally Posted by Zor I guess the 17% is the max thickmess of the wings. I am not sure what you mean by "butt end". The trailing edge of my Radian does not exceed 2 mm. Your clarification would be appreciated. Zor
Bonjour Zor,

The trailing edge of mine is 5 mm and it tapers to 3,6 mm toward 3/4 of the wing to the tip.

For the thickness, yes I was referring to the 17% designed thickness of the airfoil as shown on airfoiltools.com
 Dec 03, 2013, 09:27 PM Registered User USA, CA, Chico Joined Feb 2011 2,553 Posts I'm not QUITE sure this incidence mod,,, makes QUITE the difference your thinkin,,, At our club down at SVSS,, SEVERAL VERY experienced glider guiders have tried it,,,,, Their conclusion : " if you like that style of flying,, go for it!!!",,, but they personally didn't find it helped THAT much,, but,,, YMMV. One of those guys has pretty consistantly been beating the guys with the high dollar molded planes, with a UNMODDED radian. So,,,, you decide