A wing will stall when the angle of attack becomes greater than some critical value that depends on the airfoil and Re. The distribution of lift coefficient for a wing with lots of taper is higher at the tip so when the wing stalls the tip section stalls first - tip stall. Reducing the wing loading lets the plane fly at a lower angle of attack at a given speed. It will still stall if slowed enough and the tip will stall first - UNLESS the slowing speed gets down to Renolds no. where the stall gets so mushy its not important.
From what you aerobatic guys are saying I get it that you want a wing with a lot of taper so the tips stall first, and land fast enough to not get into stall while landing. That will work.

17, to me a person worrying about tip-stalls to the point where serious modifications are considered doesn't have a clear view of what flying is about or for.
To never have a tip-stall problem, don't fly.
Get a car or a boat.
Or take up sculpture.
Airplanes when pushed out of the envelope do things like tip-stalls and spins and crashes.
When the flier learns where the corners of the envelope are, tip-stalls go away, without doing anything to the airplane.
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ao8's leading edge slat idea is one doo-hickey... Ever pulled on the slats on a Bf-109? They move in and out with mere finger pressure. Intended to cure the tip-stall of the highly tapered highly loaded wing... but in practice, one would operate and the other wouldn't... If the pilot was shooting at an enemy, his aim would be thrown off.
What's more important in combat, safety of flight, or killing the enemy?
And other than wiring/taping the slats closed, the alternative is to pay attention to what you're doing.
Same thing with our models. Pay attention to what you're doing. Tip-stalls will go away with flight experience.
And I'd shudder to see a Giles with a 24% thick tip! Ug-o-lee!!!!

Paul,

Well, I dunno. Why tolerate things like squirrelly ground handling, tip stalls and yaw instability, (PBY) when all it takes is good design philosophy? If an airplane, model or full size, has nasty habits, then they're nasty habits. Spoils your afternoon or kills pilots. Why put up with it if all it takes is to add toe-in and camber, make it lighter (very doable in most cases ) and make the vertical fin big enough.

I actually don't HAVE to worry about dangerous and unwanted tip stalls. I prefer to eliminate them so that I can enjoy my airplane and do neat stuff, low, slow and close and not have to sweat it when it comes time to land. I actually NEVER have a tip stall problem and I build and fly, a LOT. I also have a car, (the brakes work) and I have a boat, (that I don't have to bail out.) Sculpture? Actually I do a lot of that when I'm carving wing tips, nose blocks and the like.

About that envelope. Why have a teensy, itty bitty envelope so that you're always wary of the edges when you can, with good design, make it bigger so that you can have more fun, and do more inside of it.

I agree that fat, 24% tips would be ugly. But, say you tried them, they worked real well, provided some unforeseen benefit and you learned something along the way. And hey, had fun doing it. Ain't that what it's supposed to be all about? Isn't that what our kind of flying is about,,, and for? We sure as heck aren't hauling freight or taking out nasties like Saddam.

Get that Giles out of that box and build it. Work real hard to make it light and I'll bet you'll start having fun too.

a088,

Interesting idea. I like your inventive and adventuresome spirit. Bet you'll have fun trying it out. Keep us posted, I'd really like to know how well they work.

Anyone know WHY the ME 109 needed automatic slats when the Spit had none, and did just fine? Could it be that the Spit had lots of washout and the 109 didn't? If so, why didn't it?


Jack Hyde,

Thanks for the explanation. I kind of figured that it was reduced angle of attack that helped.

The way I see it, you want asymmetric stalling ONLY when called for. This would mean two inputs. Elevator AND rudder. This gives you CONTROL. If you get a tip stall with JUST elevator input, when all you wanted to do was go up, then flipping over, SUDDENLY, and UNPREDICTABLY, will definitely spoil your day.

Not to be picky but another point. We really should't be referring to the fact that the tips stall. Yes they stall but what if they both stalled at exactly the same time. No big deal, the loss of lift on each wing panel would be equal and the plane would just mush over. This is good. The problem really is that one wing tip stalls BEFORE the other. With one wing tip stalled, and the other still lifting, whoops, the plane flips over when least expected, or wanted.

With a light aircraft, we have both tips flying even at extreme angles of attack because the entire wing, (including the tips), isn't working so hard to keep the plane in the air. However, both tips are near the edge of a stall without actually stalling. When we also apply rudder, the resulting yaw will give that extra bit of speed on the one tip, and a bit less on the other, causing one tip to stall first and we now have a very predictable and repeatable situation. This was something the Wright Brothers worked very hard to achieve. Control and predictability. Lack of control and predictability is NOT what flying is about and for.

Andy, try as I do, I can't reduce the plane count here enough to make room for one more!
I have planes hanging in the lobby of the local FBO, at the LHS...
Went out today and smacked 3 in on the slope in 10 minutes.. and they're still repairable!
This one is a cutey! And fun.... HOB 1/12th scale.
Nope, can't open the Giles box yet..

I don't know why anyone has not suggested (I guess the mere fact that you want to modify an aerobatic plane erks some people) this yet, but here is another thought.

If you were to add flaps, and deploy them when attempting to land it would solve the tip stall problem. Here is why. The flaps (deflected downwards) would increase the camber of the wing on the inboard section (as long as they are not full length). This would mean that the inboard section has a lower stall AOA and would stall before the tips. An added benefit would be that the lift would also increase with flaps deployed and drag as well. This would mean you can fly slower and the plane would slow down more quickly when you reduce throttle. Your glide angle could also be steeper, without increased airspeed, since the increased drag would prevent you from accelerating.

Sound reasonable? (and it certainly is not a doo-hickey! )

-Q.

Paul,

That's a great looking ME 109. Did it tip stall? :devious: Did it have slats?

Just kidding. Say, you're a real sport for putting up with my techno-babble. I seem to take these things way too seriously. Its just that I've been instructing for 30 years and have always tried to make it fun, not work. I related somewhere on this board about the beginner who was having a devil of a time learning. Turns out his instructor was a full size pilot who didn't believe in downthrust. After we put some in, (actually lots) he was amazed as to how well the plane handled. All this time he thought that he just had no talent and that this game we play just might be too much for him. We mighta lost him for good. He went on to university to take a business degree so he wasn't no dummy.

I kind of think that a lot of the problems of sport flying can be traced to high wing loadings. Reminds me of a piece in RCM many years ago about a product called helium filled micro balloons. Apparently, you'd fill up the wing with these and you could reduce your aircraft weight by 30 to 40 %. You had to be real careful though, to open the jar upside down. Don't know why it never caught on. Wish I had got some back then. Anyone know if they're still available? :bananahea

Flaps is interesting. Controliners use them coupled to the elevator. Any 3D or extreme aircraft use them? Imagine this kind of mixing. Flaps coupled to the elevator. Split elevators coupled to the ailerons to work together with them.

No doo-hickey required,,, just a very agile computer radio. We sure have it good today. Remember when you had to take a servo apart and resolder wires to reverse the servos?

Andy, I had problems with those helium micro-balloons myself. I always cover the bottom first.. then poured in the balloons, and by the time I got the top covered......
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The Me. does tip stall! Being a sloper it crashes a lot... twice yesterday, so it gets repaired a lot, which puts stuff back on out of kilter from the last time. I'd washed out the wings back when I built it. probably 2 years ago but that appears to have gone away. And the c.g. is a bit aft. Tons of fun though. Looks super making a low close fast pass and pulling into a Chandelle to come back the other way.
Wingloading is 12 oz.... I found that's the minumum needed yesterday to get past the increased wind speed at the slope lip.
Lighter planes got blown back into the ground.
While looking for some stuff to repair it between flights yesterday I uncovered a simliarly sized HOB P-51 which was going to be glow powered, but didn't get finished.. now it's gonna be a sloper.
Basically the same airplane as the Me, except for the top plastic part.
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I have a couple of planes with flaps. Scale, BT-13 and PT-19.. they don't need them but they work, and are neat to use in the wind, to have the plane hover in place.
I've tried coupling flaps with the elevator on fun-flies, but could get into trouble faster than I could get out of it.
Flaps on the lower wing on my Kadet bipe make it a super-turner, and popping them when starting a loop tightens it up a LOT.

Paul,

I envy you. I enjoy slope flying a lot but around here, we've got a little ground pimple we call a mountain and much of the wind is simply deflected around it. Still, I've managed some decent flights on a small sloper on a small hill. That's where you've got me though. I concede. Healthy wing loadings definitely required on a windy slope.

Just thought of this though. I wonder if putting in some reflex via a little up in both ailerons might not help. Hmmm, how would that affect the CG?

But, I'd bet lots of washout and a real forward CG might help. Or turbulators, or slats, or flaps, or uh, doo-hickeys. Nah, sounds like you're having too much fun.

All the best,

I certainly second the reflex suggestion. Mix in some reflex and deploy it only when landing. A good computer radio will do this, no problem. This is a sure way to make the tips stall proof. You just need to add to enough reflex. If you then also mix in flaps when landing you could turn a tiger into a little kitty-cat when landing.

One thing to bear in mind, sometimes tip stalls occur because a pilot is using too much aileron on a final approach. You need to learn to use the rudder more effectively. Don't ask me, I don't know where the rudder stick is on my radio ( ). The reason for rudder is that you are changing the camber of the wing tips due to aileron deflection. Ailerons can sometimes be enough to cause a tip stall all by themselves. Another sugesstion is to mix in differential on your ailerons for landings (again, a computer radio is required). Have them setup with only upward deflection and stay neutral when they normally would deflect downward. This method worked for me on an aerobatic plane with full span flaperons that would have such a scary tip stall my hair eventually turned white.

-Q.

Ao88,

Some interesting ideas. This stuff would also be beneficial, I'll bet, for heavily loaded scale aircraft of the WW2 variety. Come to think of it, going back to the Spit compared to the ME 109. The Spit had a very unique aileron design. They were hinged at the top in such a way that when deflected upwards, the bottom of the aileron would stick out into the slip stream creating drag on that wing panel. In other words, when going left, the right aileron is down and the airflow is cleanly deflected down. The left aileron though, not only deflects the air up, but the drag at the bottom causes a yaw effect to the left that minimizes the need for co-ordinated rudder. This, along with lots of washout, could be what made the Spit a *****cat and the ME a b*%#h requiring a doo-hickey like automatic slats.

Maybe that's my point. If a plane does something that makes your hair go white, the design is faulty. That any design could be improved so as to make the plane easier to fly, safer, more enjoyable and perform better is certainly a worthwhile enterprise.

Some airplanes pitch with rudder! My 1/6th Ziroli Stearmann drops the nose alarmingly with rudder, so much so landings (where I use rudder a lot) are "interesting" with that particular airplane. It will do a sloppy barrel roll with only the rudder also.
Other planes have been noted as rudder-pitchers.
The Spit ailerons are Frise types... the Zero has them also.. )and the most exquisite castings you'd never expect on an airplane for the hinges. Superb, but look way too delictate for a military airplane).
Frise BTW did the Blenheim/Beaufighter series.
Many planes of the WWII era use the Frise system of countering adverse yaw. Others use differential. I was astounded to read the Tiger Moth is rigged with almost no down aileron at all!
I've used Frise ailerons on some of my Kadets.. I get better roll rates with full-span strip ailerons.

1705493, you are mostly correct in saying that there is a design fault if a plane that has bad tip stall characteristics, but aerobatic plane are not normal. They are made to flip, flick, etc. and other stuff that would make mere mostals weap and toss their cookies. I think it is better to view this bread of plane as something to be tamed (for landings) using flaps, aileron reflex, aileron differential, etc. yet keep it's spirit in tact when up there.

Paul, as for the rudder-pitch coupling I shudder to think of it. I wonder why this is? Maybe you need more rudder below the thrust line, or your CG is so close to neutral that the plane amplifies any coupling that may exist, even though it is small compared to other planes. Have you tried a computer radio with rudder-elevator mixing? I would be very interested to know how easy it would be to do this kind of mixing and how finely tuned you need it for workable results.

-Q.

I was reading a British flight test report on the full-scale Bf-109 tonight, and it had pitch-coupling with rudder!
On my Stearmann it is more intrusive than any of the other planes I've noticed with it. I fly it with caution when landing,but otherwise exploit the snap capablity it gives. I loves snaps!
The odd thing about the Stearmann is it appears to be nicely balanced area wise relative to vertical position and area, but that nose drop with rudder can be alarming.
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I flew a Ulitmate I'd crashed several years ago and slooooooowly repaired, Friday. 44" span, Saito 50. It's much more manuverable than the SIG Ultimate Fun-fly about the same size.
The SIG has more wing area (but a much thicker wing) and less weight, yet it's not as active as this one is. Even with 4 ailerons instead of 2 as on the Saito plane, which used to have a nifty 540 degree hammerhead turn, I'm hoping it still does.
It's been sloping weather more often than not this month.
Flying, repairing, flying, repairing...
Got the HOB 1/12th P-51 ready to fly tomorrow (oops..this morning) weather permitting.. otherwise the Ultimate goes again.