I have a firebird freedom that has a nasty tip stall characteristic at low speeds, like during landings. So i want to put stall strips on it. But i dont know how to[].

So could someone give me a better description on what they are and how to make them?

Thanks in advance!

Stall strips are usually wedges fitted to the leading edge of the wing which are designed to deliberately break up airflow, inducing a stall at high angle of attack.

The typical layout would be to fit them at the wingroots, to provoke the stall to develop at the wingroots rather than the tips thus, hopefully, giving a more predictable stall.

I have never tried them on a model and it would be interesting to see how they perform.

I have a sneaky feeling though that they'd be more trouble than they're worth on a model. They need to be positioned on the leading edge in such a way that they provoke the stall at a useful angle of attack. Fitted too high up the leading edge, they'll have the affected wing area stalled far too soon, reducing your lift and offering you little advantage. Too low on the leading edge and you'll still manage to stall asymmetrically before the breakers do anything at all.

My personal feeling is that washout is a more predictable and effective technique for our purposes, although including washout into an ARF wing is easier said than done...

I guess i might not put stall strips on my freedom. Sounds risky.

Not risky as such I wouldn't say, just that they'd take a bit of experimentation to make them work as you'd like. If you're not a confident flier if might be good to recruit the help of someone who is to do the test flying for you?

It's a case of getting the size and positioning right. On fullsize the designers wouls usually not include them in a design, but if upon test flying there were concerns about unsatisfactory handling at or near the stall, then the design engineers will have the required data to calculate how big a strip is needed and exactly where to put it for the desired effect. If they're present on fullsize aircraft, they are almost certainly the result of some sort of rectification or corrective work to address the handling. If you study photos of the fullsize F4U Corsairs, you'll see that some got a small stall strip on the leading edge of one wing only - the reason being that this aircraft had a tendancy to roll the other way during final stages of landing due to assymetric slip stream encountered from the prop. The little strip on the wing which rose stalled a small section of it, compensating for the roll. Definately not something the designers originally had in mind - just a correction to make the aircraft safer. The same usually goes even when they're symmetrical on aircraft - if during test flying the a/c tends to drop a wing at the stall, it may well get stall strips to see what happens. If that cures it, they get included on the production line

We don't have the luxury of data, so we need to do it by trial and error instead.

Your model shouldn't become significantly less predictable if you get it wrong - they just might not work as you hoped... experimentation would settle this one way or another

Here's a quick way to experiment with stall strips that you might want to consider.
Take some thin cardboard, such as the material in a postcard or a manila file folder. Cut a strip about 3/4 inch wide and with a length of about 1/3 of the span of one side of the wing. Fold the strip lengthwise with a sharp crease. Glue a small wedge of balsa (or foam) at each end of the folded strip to hold an fold-angle of about 45 degrees. Cut out the base of the wedge so it fits around the leading edge of the wing (precision isn't important) and allows the edges of the cardboard to rest against the top and bottom of the wing. Position the folded strip with one end against the side of the fuselage and with the folded edge aligned with an imaginary line that connects the front and rear of the airfoil-shape. Tape the folded strip to the wing ("Scotch" tape works fine). The sharp edge of the folded strip will protrude out beyond leading edge of the original airfoil.
Repeat with the second-side of the wing, with a structure that duplicates (as close as you can) the structure on the first-side of the wing.
Now you can fly the plane to see if the strips alleviate the tip stalling. If yes, you can replace the cardboard assembly with more permanent structure. If no, you can easily remove the experimental strips.

I pretty much agree with your earlier replies. I'd only add that you will also need to reduce your elevator travel or move the CG forward even if the stall strips work well. The reason for this is because you currently have enough control power to raise the wing angle of attack to a point where the wing stalls. The stall strips will make the inboard portions of the wing stall sooner, but the outboard sections will stall just as they do now unless you do something to reduce your maximum angle of attack.

Most prototype airplanes have their stall strips placed experimentally. That is, the strips were taped in place and the pilot went up and did a few stalls to see how it felt. When the pilot reported that stalling was satisfactory, then the strips were riveted on permanently. Modern, big dollar development programs such as F/A-18 or F-22 have enough technology to pretty much predict behavior at the stall. But that knowledge comes at a huge price. I suspect Cessna and Beech still do it the old fashioned way just as we modelers have to do: cut and try.

Dick Fischer

Something no one seems to have mentioned yet is that stall strips extended forward from the leading edge are used to force that area of the wing to stall. They don't delay the stall. So you want to install them on the center portion of the wing and not the tips. The idea being that you force the center to stall earlier to save the tips.

Another option instead of stall strips would be to add turbulator strips to the wing TIPS to try to delay the stall. What you want are span wise strips made from two layers of electrical tape stripes that are slit from the tape to be about 3/32 to 1/8 wide. Stick these double layer strips to the upper surface about 1/2 inch behind the leading edge for the outer 1/3 of the wings.

If niether of these works then you'll need to figure out a way to warp in some washout in the tips.

FWIW -Some of the European guys who fly indoor precision aerobatics -with flat foam models - have used various stall stips and dams and turbulators with some success - take a look at those - a real wake up!
These models seem to fly in the face of all the somber wisdom about airfoils -but actually are very well thought out.
The performance is simply amazing -smooth and dead accurate.