The Selig 1223 is a very high lift airfoil, however it doesn`t recover very well from a stall situation. This happens becouse an histresis cicle.
I`d like to have sugestions to avoid the hiteresis cicle.
Does anyone have an indeia about how to make shrak skin fished model wings?

I believe you want a "shark skin finish"?..
This could be achieved by using sandpaper with the grit side exposed to the airstream.
As to how much of the wing would need this or the size of the grit, I wouldn't hazard a guess.
If it's possible with your plane, the best way to use the qualities of the 1223 is to keep the airspeed high enough to avoid the seperation bubble responsible for the hysteresis. It's due to the Reynolds number.. airspeed is the best preventive.

Hi,
I`m realy glad someone answerd my question.
You told me I should avoid low flight speeds. Can you tell me how can I do that if I intend to use this profile on a plane to compete at SAE competion.

I'm going to run a bit counter to Paul's suggestion about air speed and say that you need to just keep the Reynolds number out of the lower end where the problems occur. Paul suggested speed as one way to do that and that is certainly valid. however wing chord is another way. Shorter aspect ratios that ensure the wing chord is a bit wider will produce a higher Reynolds number for any given airspeed.

So how wide do you go? Funny, this is a major topic in the RC sailplane world as well. Basically higher aspect ratios produce less induced drag and limit the tip vortex losses. However they force the wing to operate at lower Rn's and thus "eat away" the supposed performace gains from the high aspect ratio. The glider guys found that there is a "best" case where the Rn and the AR is balanced much like the best L/D of any wing. For models in the 100 inch range I believe the optimum aspect ratio is about 8:1 to 10:1. Open class likes to run 10:1 to 12:1 or even a bit higher. 2 meter is actually best at 6:1 to 8:1.

Also RELATIVELY higher speeds and SAE flying are not mutually exclusive. Use something like FoilSim to find out what your speeds are for various weights and Cl's and do the math to determine the Rn's. I suspect that with full loads the required airspeeds will be high enough that you don't really need to worry about the bad charactaristics of the bottom end of the range. But having said that you can find tune the flying by letting the model climb at a shallower angle as long as it meets the performance tasks. That will tend to keep the airspeed in the higher end of the model's range. Which is ALWAYS a good thing with a model loaded as these are. I don't think I'm making up stories is I suggest that most of the crashes of these types of models are due to the pilots getting greedy with the up elevator at the wrong times.

From what I've observed at 4 of the SAE AeroDesign West competitions, any plane attempting to fly near stall speed fails.
The stall angle for the 1223 is high enough that although the Cl to lift a large load is there, the Cd is too high for the limited power available.
There's not much more than 8 pounds of static thrust, which has to accelerate a plane weighing 30 pounds or more to 50 ft/sec minimum.
The Cl at that speed isn't anywhere's close to what a 1223 could deliver, were there power to handle the drag.
The best performers accelerate to flying speed at the 175 foot mark, and with a -minumum- of rotation, continue up. A big pitch change at rotation merely adds drag. And the plane doesn't take off at all, or tip-stalls in.
Designing for the max possible Cl isn't workable.
The successful plane's pitch angle is very low. Which also means alpha is low, relative to what the airfoil could do, with more power or a longer runway.
One of the area-limited planes in 2002 took off at 37 pounds AUW, with the aid of our usual afternoon head wind. That's not something you can depend on though.
Note the highest weight lifted this year in the open class used the same .61 motor the regular class uses. It wasn't a multi-motor thing at all, and...... the takeoff attitude is almost exactly the same as the ground attitude. With an all-up weight of 50 pounds, this is remarkable from what I've seen.
The 2005 wing span of 60 inches is going to be a real problem. The SAE designers might check out the AIAA DBF stuff.
Similar takeoff distance restriction, but more manuvering required in AIAA than SAE. Multi-wings are almost mandatory.

I noticed that the S1223 was all over the East competition this year. Planes not using it were in the minority.

However, I'm not sure that it's the right choice in a competition where the area is not limited, like this year. You can get more lift with more area as well as more Cl. It looked like some teams had wings that were actually too large for the engine - when using this airfoil.

My hypothesis is that the same wing planforms would have been more succesful with a less cambered airfoil. The price for the high max Cl on the S1223 is high profile drag at low angles of attack. Some teams had really big wings of high aspect ratio, that looked good on the ground, but didn't get out of ground effect. This is my explanation for that. Even when getting off the ground at high angle of attack, and letting the plane gain speed didn't help, because the drag stayed too high due to the airfoil drag.

At the very least, I'd hinge the whole TE and see if less camber and less drag would help.

I agree.. I compute the Cl at takeoff speed based on wing area, weight and speed, to see what angle of attack any airfoil might have at that time. The 1223 isn't being used to what it is capable of, due to the power limitation.
I'm not sure flaps will help, IF there is a profile which can deliver flapped Cls at the speeds to be flown, without flaps.

The other way to look at it is that with the S1223 you can ( and should) build a wing of restricted area. In this case a trade study would determine the wing area. That is what the ETS team that I flew for did. I'll have to re-read their report to see what factors they based it on, but it was a good sized wing, 14 ft x 18". It would get off the ground when I rotated it, then I'd let it speed up before trying to climb. It definitely would've pigged along in ground effect if I tried to fly it at liftoff speed the whole flight.

Funny thing was, with the highly cambered TE, the ailerons were overwhelming the servos, and floating upwards. They'd float high enough to easily see the problem hundreds of feet away. I wonder if that improved my climb Cd. It sure didn't help roll control, that's for sure.