Asymmetric flap experiment of yore
I once had a very nice BL75 Funk, a pretty good STOL a/c as it was. But since making things faster or in this case, slower, is in my nature, I set out to put some of my NACA reading to practice.
Now, in this thread, the term Split Flap is used to describe an asymmetrical flap condition. Fair enough.
But in the design world a split flap is a type of flap such as on a DC-3 where where the upper wing surface remains intact and an aft bottom portion swings down. This type of flap is more effective than a plain flap but less so than a well designed slotted flap.
My split flap experiment consisted of a door skin plywood strip 1 foot wide and 8 feet long on each side supported by a vertical 6 inch strip supporting it at the trailing edge. This gave the geometry of a 30 degree 20 percent NACA split flap.
Results were out of the book, considerably slower stall but with a somewhat sharper break.
A group of friends there thought the experiment was a great success but one busybody stranger ranted that I might be in trouble if one side collapsed. So, thanking him for his concern and out of curiosity, I removed the support from one side. I then flew it carefully lifting off slightly and, somewhat surprised, was able to easily counteract the asymmetrical condition.
Had I simulated a split flap at 60 degrees, near full effect, I can't say whether that would be the case though.
\OT
For posterity, I should mention that this experiment was undoubtedly the nexus for the Gurney flap.
My close friend took a Polaroid of the flap setup. Then later that day, he went to a get together with Race drivers Phil Hill and Dan Gurney at Phil Hill's house. (My friend's brother was mechanic/houseboy/assistant for Phil Hill.)
My friend raved about how good this flap was, but the Polaroid from behind the plane only showed the vertical support at the trailing edge. So, since wings were already the thing with race cars, Dan, seeing only the flap vertical support at the trailing edge, tried out adding a vertical flap on a existing race car wing and it worked! Ta-da. The Gurney flap.
He tried to patent it but it was prior knowledge. NACA had tried every configuration of a vertical plate previously. Sadly, I discovered today that Dan, a local boy earlier, passed away in 2018. OT\
Ron