Ldalmas

I am building a stol model of my invention and i got stuck on the wing tips any idea on what should do best?
laurence

Jimmbbo

If appearance is not an issue, the most wingtip with the least loss of efficiency is a flat endplate.

da Rock

Do a Google on "Hoerner wingtip", you'll get things like this windtunnel comparison between tip plates and Hoerners.

http://www.jefflewis.net/aerodesign.html

A number of fullscale stols use downturn tips.

Rotaryphile

Use a smoothly rounded wingtip. This will reduce induced drag by about seven percent compared to that of a square wingtip.

Ed_Moorman

My Feedback: (1)

I know what the full scale books say about Hoerner wing tips and end lates, but they don't know beans about Sport RC flying. I have flown both Hoerners and plates for over 30 years and for sport flying, you want plates. They work in both directions, upright and inverted.

I have tried fancy carved Hoerner's and just downward end plates and couldn't tell and difference. I will tell you this. Hoerners and downward plates will decrease your dihedral or add in an anhedral component. I use them on high wing planes like Sticks to compensate for the high wing location, stopping roll due to rudder.

As for block tips vs. flat tips, I ran some home made wind tunnel test many years ago. A friend of mine made a tunnel and glued threads on the leading edge of the wing. His wing had plug in tips so we could try different types. We didn't have and lift or force measurements, but we could see the path of the threads. These gave an indication of the outward flow and the tip vortex.

The big rounded, 1920's-1930's type tips were the worst, having the most outward flow and threads curling around the tips.
Stick type tips were next worst. Fairly good amount of outward flow.
Block wing tips were next. Some flow.
Flat ends were next to the best. Very little outward flow.
End plates or Hoerners were the best. No outward flow.

End plates also increase the roll rate, slow the landing speed and make it harder to snap and spin.

This wasn't very scientific, but is was enough for me to quit wasting my time carving any more tips. Pretty was not the best.

Rotaryphile

Tip plates work well to reduce induced drag at lift coefficients of over 0.5, but they increase total drag at lower lift coefficients, and are seldom used now, except in the form of NASA winglets. I have experimented quite a bit with them on a competition fun-fly airplane, and found that they reduce aileron yaw, due to the additional yaw resistance supplied by their additional lateral area up forward, and help extend good lateral control deeper into stall territory. They also result in a smaller minimum turning radius, due to the reduction of induced drag at high lift coefficients, but hurt top speed a bit.

Rotaryphile

A little add-on note regarding NASA winglets: Experiments were conducted to determine the best angle for winglets - straight up and down, or some angle other than 90 degrees. The best angle was STRAIGHT OUT, in line with the wing. In other words, a little more wingspan works better to reduce induced drag than winglets can manage. I heard that Boeing considered increasing the wingspan of their 747 to reduce drag and thus save fuel, and went to winglets simply because the additional wingspan would cause space problems at the ramp.