Tip Stall. Which wing drops?

[hkowalczyk]

I've been practicing stalls with my Herr Cloud Ranger, and have noticed that it always seem to drop the left wing when I do stalls, and it gets into a spin.

So I'm trying to figure out if this is usually the case. Does the engine rotation maybe cause this? It does seem to happen mostly with power on stalls. Or could it be I have a little too much left side weight? Its hard to tell because I've tried balancing it and it seems ok, but maybe just a little bit off could cause this? I know that the wings are level because I've got the FMA copilot which will keep them level through the stall. I've also tried it without the co pilot and the same thing.

Is there a simple fix that I could do to relieve this tendency? I know washout would help, but I was thinking of maybe adding stall strips to the wings? Anyone done this before?

[joey221]

As far as I can tell, dropping the left tip is more common than dropping the right, probably due to torque reaction and all kinds of other factors.

You slow that right tip down slow enough, and at a certain AoA, it will stall first, though.

I've only suffered one tip stall, ever, but have seen many, many planes piled in from them. In most cases (including mine!), the pilots seemed to be trying to force the plane skyward without sufficient airspeed, or slowed down too much on the final turn to a landing approach.

Best bet is to keep the AoA reasonable and keep the model's speed up. Washout and other contrivances have their aerodynamic costs, too.

[hkowalczyk]

I definetely try to keep the speed up, but when you're coming in dead stick ... you definetely don't want any bad tendencies in the plane, I can do plenty of damage through pilot error I don't need any extra help :D

[Ben Diss]

Try your stall while making a shallow right turn. Continue the experiment, increasing the bank until the plane doesn't drop a wing or drops the right wing.

-Ben

[hkowalczyk]

I tried that yesterday. It took quite a bit of right turn to get it to come down straight.

What I'm trying to accomplish is make the plane more docile. Basically I'm trying to figure out if this is a true tip stall, or just my left/right balance is off and then when the plane stalls it drops the heavy wing. Previously I had the fore/aft cg off a little bit and managed to whack it into the ground 4 or 5 times when it would suddenly stall and snap hard left into the ground.

I tried some stall strips last nite made out of 1/4" triangle stock but it did not seem to make any difference.

[Pierre Audette]

Maybe it's a northern hemisphere thing, like water down the sink (just kidding :D )

You may want to see if your wing is balanced left to right, and if there is any difference in twist between both sides.

You should be able to induce washout by carefully twisting the wing and reheating the covering. works for me.

Just curious about your stall strips. Did you create a drooping leading edge on the outer wing tips? The usually need to go about 1/3 of the wing, and basically create a similar effect to washout.

[Ben Diss]

I'd bet that your left wing is warped so that leading edge is up compared with the rest of the wing. Look at the plane from the tail and see if there is any twist in the wing.

-Ben

[hkowalczyk]

Ben,

I was looking at the wings this morning, and it looks like the left wing was warped slightly... but I wasn't sure if I was trying to convince myself of that. So tonight I'm going to try to take it off the plane and put it on a table to see if it is.

Pierre,

I just added stall strips to the root as shown in this article.

http://www.ont.net/nrmf/flightline/may00/nrmfcMay00.PDF

[astroboy]

I think maybe I'm a little confused on the subject of tip stalls. It's a little hard to tell for sure from the Cloud Ranger picture on the Herr site, but it looks like the wing isn't tapered. If the chord and airfoil are constant through the whole wing, and there's no washout, how can the angle of attack or other aerodynamic properties be any different between the root and tip? In other words, how can it tip stall?

Thanks,
Jeff

[hkowalczyk]

Jeff,

mmm.. good question. You're right that the wing is the same all the way through. I would guess if the tip is actually stalling it would be due to some effective angle of attack, since the airflow is 3-d as opposed to just 2-d.

Having said that, I was doing some more research on the web and came across this article

http://www.djaerotech.com/dj_askjd/dj_questions/tipstalls.html

which discusses the fact that I may just be having a stall , but due to many factors it drops a wing.... interesting... of course the question still remains, what do I do to fix this tendency :confused:

[Ben Diss]

Have you tried all of this without the autopilot?

[hkowalczyk]

Yup, tried it with and without the autopilot.

Well I think I managed to drop the right wing today..... I don't really know since I was too concerned about missing the trees. :eek:

Could it be that I don't have enough right thrust built into it?

[Mike Taylor]

Try adding washout to the wing tips; this will prevent the tips from stalling first.
You could also add 'tubulators' to the wing leading edges. I have used lengths of thread doped to the top leading-edge (run along the wing's top L/E at 5% - 10% of the chord), and also had luck with striping tape laid parallel to the leading edge.
The turbulence these tiny stripes produce seems to prevent the air flow from separating prematurely. The theory is that they 'add more energy' to the air flow...
HTH,
Mike

[aft_cg]

I don't know if your problem is a tip stall. It sounds like the same thing that happens to students during their first few power on stalls. The Cessna will drop the left wing due to the students lack of right rudder. The 152 and 172 trainers are definitly not known for tip stalling. But if enough yaw is present during the stall, then a tip drobs and it can lead to a spin. Keep the plane coordinated. The cure that you are asking for sounds like right rudder.

[Tony Oliver]

It's almost certainly a warp as mentioned in earlier posts.
However as most wings are not too accurately built, you'll always find one wing stalls slightly before the other. The reality of it is that if you slow the model down to around stalling speed while flying straight ahead, the moment you give any slight turn command with rudder, you are speeding up the wing on the outside and slowing the wing on the inside of the turn. Guess what! - the inside wing stops flying - it has dropped its speed to below stall speed, and the outer is lifting more. In addition to that, if you use ailerons, the downgoing aileron momentarily causes an increase in drag, so that in this case the turn you attempt is having the unexpected effect which we see as 'aileron reversal' - it's only a stall, but the wing drops instead of rising. This is usually to cries of 'I've lost it' or 'The aileron servo's not working' and 'Oh, sh**'

Tony

[Sparky Paul]

The airframe in question is so small that an unobservable difference between right and left sides can be the cause of the problem.
Some mismatch that in full-scale would be obvious but "insignificant" at model size.
Plus the Reynolds number effect. The plane is not so much flying as surfing thru the atmosphere, due to its size.
The wing is more of a flat-plate than an airfoil.
Any disturbance to the flow can create the departure..