I tried winglets on prop back in the middle 1980s on gas engines. As I recall, I did 18" ones for the G-38 and Webra Bully I was flyng and also a 22" for a Sachs-Dolmar 60cc.

I used Zinger wood props. I sanded the finish off the back side ofr the blade for a half inch or so then 30-minute epoxied on 3/8x1/2 maple motor mount stock. After the epoxy cured, I drilled and inserted small dowels or toothpicks with epoxy. Next, I used a Dremel sanding drum to sand the inside to a nice round shape. After shaping, I soaked the wood with thin CA. Some light sandng and I painted the prop in color with K&B epoxy paint. I used red and yellow.

Ground rpm was not much difference and I don't remember what it was. In the air, I did notice a good increase in climb and the prop seemed to bite more. As I recall, the rpm was lower, but the climb was better. This told me the prop was hangng on to more air, giving better performance.

Soon after I started flying mine, I saw some made from carbon fiber in pattern sizes. These didn't catch on. I think it was the cost vs. breakage factors.

I was always afraid to try them on small glow engine sizes because of the high rpm and the chance of slinging one off. I always made sure the sides were clear before starting and running up.