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When they started doing pitch testing on trucks...I wonder if anyone bothered to test any standard Rogallos (or John Lakes "Sailfeather"). Standards were pretty much phased out by then, but it might of resolved a few lingering questions.
This is a quote from Merlin back on April 4, 2012. I just ran across it.
Yes, I tested John Lake's Sailfeather and was so impressed that I made one (too cheap to pay $5 for his) for my Eipper Flexi Floater. It was on the glider at the recent 44th anniversary meet. May 23,2015 at Dockweiler Beach CA.
To test the concept built a 5' model of a "standard" Rogallo. Weight was added to the base tube of the control bar to ballast and set the CG. I also made a scale sized Sailfeather that I could attach and detach easily.
Without the Sailfeather: I made drops from my second story window into my back yard. With each drop I would release the model with decreasing angles to the ground. When the release angle got to a certain low point the model would go into full luff and dive straight to the ground. No sign of any pitch recovery action.
With the Sailfeather: Doing the same drops the angle could go vertical, into full luff, and the glider would still recover high enough above the ground to glide. Then I discovered I could even drop it at a negative angle and it would still rotate to a positive gliding angle. So in the latter case, the sail isn't just luffing, it is starting to invert and still rotates to a positive full sail.
I was convinced and after I made the one for my Eipper I never flew without it. It made the pitch much more docile at fast flying, low, angles. When Paul MacCready saw it on my Eipper Flexi Floater at the September, 2000, vintage HG meet at Dockweiler he told me he thought John Lake's Sailfeather was the single most important improvement ever made to the Rogallo type gliders.
Frank Colver
BTW - I think someday people will start flying "standards" again for sport fun flying when they can be made extremely light with newer materials. Image if you could run off a hill and fly with a 15 lb, large, airworthy, simple, glider. One with safe attitude recovery characteristics. Dreaming? Maybe.
Actually, of all the photos I have of my Flexi Floater I do have very few that are good shots of the "feather".
I almost stalled into Little Mountain CA because of that. I had my stomach against the base tube and my feet straight out on that occasion and on several others. I have no idea why I didn't re-rig the control bar. One of those stupid things that fortunately didn't kill me. It's still in that position today. 