Has anyone ever experimented with vortex generators on models? I would think that, if they work at model scale, VG's would be good for models that are prone to tip stalling.

Vortex generators are just one form of turbulator. The effectiveness of turbulation to delay the stall is dependent on the airfoil's separation bubble charactaristics.

I've had good luck with two sailplanes that I used turbulators on and in another case they didn't help at all. So do not be surprised if adding turbulation is not a general solution. In some situations they will help and in some others they won't.

vortex gen are use to increase the boundry layer thickness thus prolonging stall and give better control at slow speeds.

Heybwd, I am not sure you understand boundary layer term correctly, or maybe you do but you simply described youself wrong here. Boundary layer over the wing airfoil is the extremely thin layer or air which sticks t the airfoil and the one which is the main layer to create lift. Usually, boundary layers are laminar and they detaach from the wing at close to the midpoint of the airfoil. The trailing edge of the wing thus does not create lift and neither is it very useful for the wing. The trailing edge cretes wake drag, it is turbulent, and is a place for stall areas on the wing. Although, the trailing edge we need for LESS wake drag, since it's sharp edge which serves as the final point back along the airfoil provides a good detachment point for the air.

I think what you mean by "the boundary layer is amde thicket with turbulators" is the boundary layer is PROLONGED, thus increasing the wing efficiency- which is especially important to sail planes as BMatthews pointed out there- with a wing of better efficiency the sail plane would be more likely to stay at an altitude during no wind or rising current, but relying only on it's speed and the gravity.

Correct me if I am wrong, but I am pretty sure I am right since I read this boundary layer stuff from a good aerodynamic book written by a well experienced aerodynamicist and engineer.

Yishht87.

You're on the right track Yissht but not quite there. Most wings start as laminar like you say but there's a transition to turbulent. But the transition doesn't suddenly jump away in most cases. Instead it just stays as a thin turbulent layer.

On some wings where there's a funny pressure gradient change the laminar flow can suddenly separate from the surface instead of doing the usual conversion to turbulent flow. If this happens and it doesn't re-attach then it's a stall. But even then it's not what you think. During a stall the wing is still producing lift and it may or may not be as much as just before the sudden stall. However it also has a lot more drag than before and that slows the plane down and makes it lift less so it suddenly sufferes a rapid loss of lift until it can't fly and then it does the classic nose drop.

There's also another option that is far more common than a sudden laminar separation stall. This is where the laminar flow breaks away but then re-attaches further back and continues as the proper thin turbulent layer. However when this happens the separation bubble reduces the wing's lift and adds a lot of drag but the model will still fly. It just seems "doggy".

The various turbulator options of all sorts are intended to trip the laminar flow earlier before it has a chance to turn turbulent on its own. By using the trips to force it to go turbulent early you can often avoid the sudden separation bubbles and extend the higher lift coefficient flying up to the point where the normal stall finally happens. It's a trade off. You add a small amount of drag with the trip devices and earlier turbulent flow but you gain by extending the higher efficiency mode of airflow further into the low speed or high loading flight regimes. Like most things it's a trade off.

ok what you said is fine. But ask yourself as to what happens with the center of pressure when a wings stalls with out v/G as to one that does have them. We spent many hours testing in the wind tunnel at Boeing. Which at that time involved the 737and 767. As the boundary layer is does not move over a wing it remains fairly stationary.so placement of the VG was critical. To prove this.Go wash your car then take it for a drive to dry it off. The water will remain. on the surface. The Vg generators are soley to increase the blounary layer thickness which will give added control at slow speed. Thus delay air flow seperation. Which in fact has an effect on the center of lift and the center of pressure. Period.

OK, great, but do they work at the scale of models of, say, 50" wingspan?

if you are trying to cure tip stall you are better to go with a wing tip fence. Like those in use on airbus.

I know, but do vortex generators work at the scale of models of, say, 50" wingspan?

You keep saying vortex generators rather than turbulation devices. The little angled tab VG's seen on a lot of full sized aircraft. However by now you should know that not everything used on the big stuff scales down well to our sizes.

Will adding turbulation work to reduce tip stalling? In many cases yes in some cases no. What sort should you use? It depends on the airfoil and model's size. I've had excellent results using a double and triple thickness of automobile pin striping tape to produce a 1/8 wide by 2 or 3 layer thick trip strip on two of my past gliders.

Will those angled tabs work for the model you're trying to modify? Only testing will tell. The size of the tabs, spacing between them and chord wise location all will require testing and modification. Just adding turbulators is not a sudden gaurantee of delaying tip stalling. But it's likely safe to say that trying a strip turbulator is a lot less work and makes it much easier to modify the chordwise location. To try it for reducing a tendency to tip stall you should only use the trip strips out on the outer third of the wing. And I'd suggest starting with the location of the strip at 15% chord. And to ensure they are thick enough to do the job go for three layers of the stripping tape. Auto body paint stores have 1/8 wide masking tape that could be used 3 to 4 layers thick as an excellent test.

Finally - an answer. Thank you for your time and effort, I appreciate it.