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Old Feb 09, 2013, 02:28 PM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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One thing is that even with turbulators or other tricks is to avoid using larger amounts of aileron when flying low and slow. Instead use just a whisp of stick and be patient as the model slowly rolls into the desired turn. And a little rudder as suggested above used along with the aileron can't hurt either. This way you'll avoid the tip stall issue in a more effective manner. Turbulators or washout is simply a little added insurance.
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Old Feb 11, 2013, 06:01 PM
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Portland oregon
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Lots of good thoughts here.
I suspect a few of you may have some full scale stick time.
So what are your thoughts on differantial ailerons and tip stalls?
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Old Feb 11, 2013, 10:14 PM
Really?!?
ChrisS's Avatar
Lost ...on the 3rd rock out
Joined Sep 2001
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Differential aileron may help a little, anything to keep the wing tips from stalling before the roots. In my experience, differential is commonly used to correct for adverse yaw, the idea being that the more lift a wing is making, the draggier it becomes...so you use more up aileron than down. Which in turn keeps the plane from wanting to yaw into the direction of the downward deflected aileron.

In one of the earlier posts it was mentioned to add a little "up" to both ailerons. This is in effect the same thing, just done collectively and not a bad idea either.

Again, all this supposes you already have a starting place, and you don't. Fly the plane before you do anything, then go from there. Just remember to keep the speed up. Airspeed and altitude are your best friends.

Chris
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Old Feb 12, 2013, 01:56 AM
B for Bruce
BMatthews's Avatar
The 'Wack, BC, Canada
Joined Oct 2002
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Differential can help but typically if you need it you're still trying to use too much aileron control without coordinated rudder for the speed you're flying. The adverse yaw it counters is caused by the down traveling aileron moving the camber and angle of attack into the higher drag region of the airfoil lift/drag charactaristics. On the other hand if you fly a little faster or use less aileron input and wait for the model to more slowly roll into the turn you can avoid the adverse yaw.

The tip stalling is just an extreme example of what starts out as some adverse yaw.
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Old Feb 12, 2013, 10:16 AM
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BMatthews's point re keeping up speed and coordinating rudder is well-taken. I have a semi-scale Rumpler Taube with wings sort of shaped like maple tree seeds. Because the ailerons trailing behind the wing trailing edge, it's easy to rig the ailerons for some washout. I also built in some mechanically-rigged differential.

Even with these methods, the Taube exhibits adverse yaw when climbing away and turning -- if I don't apply rudder. I am still trying to get into the habit of leading with rudder, then applying aileron for a nice, smooth turn. Why should it matter? Why not let the Taube yaw a little, as long as it turns in the direction I want? I suppose it's because yawing in a turn is considered "bad form," the sign of a poor pilot.

Also, this Taube has no wing dihedral, so it may wander into an uncommanded turn if a small gust lifts a wing tip. Applying opposite rudder, then aileron, brings it back onto a straight heading.

Jim R....
...who yaws upon awakening more than he used to...
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Old Feb 12, 2013, 12:08 PM
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Palmdale, CA
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My Eindecker had a flat wing and ailerons. And a flying rudder.
It would do very amusing flat turns with the rudder, with the nose yawing to the outside of the turn and the inboard wing dropping, so it would crab more and more as the turn progressed. The use of ailerons only, or with the rudder was the fix.
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Old Feb 12, 2013, 02:01 PM
agnotology
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Joined Jan 2007
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This is completely off topic, but the beautiful Rumpler reminded me of Igo Etrich from Bohemia, part of Austria then. He designed the Taube, and the Germans "borrowed" the design at the beginning of WW1.

He designed some very cool airplanes. How is this airplane (attached) for 1913? Aluminum panels and celluloid windows; three passengers and a pilot. The first enclosed passenger airplane. The family resemblance to the Taube is pretty obvious.

He did some interesting flying wing stuff just after Lilienthal as well

http://www.ctie.monash.edu.au/hargrave/etrich.html

Kevin
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Old Feb 15, 2013, 05:21 PM
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Portland oregon
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OK guys, what would be the effect fo flaperons to a tip stall prone wing. Ailerons are not full span, but only on outer portion of wing.

Flaps allow slower flight but this is contrary to reflexing by lifting aileron a bit.

Yes I have confused myself ....so.... ..your thoughts?
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Old Feb 15, 2013, 07:49 PM
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If you were to drop the ailerons to act as flaps you would be adding aerodynamic washin to the wing, and make it more prone to tip stalls. You definitely don't want that. Flaperons work best when they are tapered and use the full span of the wing, or in addition to conventional flaps, or with larger inboard flaperons that act mostly as flaps like in the Fiesler Storch.
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Old Feb 18, 2013, 02:04 PM
The Prez....... again
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United States, IA, Rockwell
Joined Jul 2011
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Quote:
Originally Posted by BMatthews View Post

There's another way to make the center stall first. A stall strip or shaping the leading edge so the inner area has a sharp small radius shape and the tips set up with a relatively generous radius will work to some extent similarly to washout in the tips.
I've done this on several planes. It does a wonderful job of controlling unwanted stalls.

Ken
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Old Feb 18, 2013, 06:57 PM
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HMNNN
I have considered a stall strip near the root but I never thought about blunting the leading edge out toward the tip. Or as Ken stated "generous radius "

Anyone elst think a leading edge mod might work???
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Old Feb 18, 2013, 10:12 PM
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Portland oregon
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My reason for all the questions is that when the model arrived it had damage to the wing.
Airborne models was quick to replace the wing for me, Great guys.
But when I removed the covering I found I could repair the wing . So I decided to add split flaps and look into the tip stall problem. Since it has no covering now it would be a great time to make any mods that might help.

I have the flaps about done..a three flap setup crossing under the fuselodge and I also have the wing jiged in a twist for washout with a light spray of water on the balsa to help it set.

So now if I do a bit of sanding on the leading edge before recovering, I should have a very interesting spare wing to play with. The weather has been lousey so what else can a guy do!

I guess I missed that part of BMatthews earler comments but reworking the leading edge makes a lot of sense to me.
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Old Feb 19, 2013, 09:22 AM
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United States, UT, Salt Lake City
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Quote:
Originally Posted by Oldog View Post
HMNNN
I have considered a stall strip near the root but I never thought about blunting the leading edge out toward the tip. Or as Ken stated "generous radius "

Anyone elst think a leading edge mod might work???
I don't hold much hope for this type mod- on a model- the size simply cancels the effects seen on much large craft.
On models with high aspect ratio wings - the real issue is speed difference on panels (tips) as the model turns- this can occur very easily at lower airspeeds no amount of reshaping will affect this problem
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Old Feb 24, 2013, 08:08 PM
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Portland oregon
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OK with a high aspect wing the "root speed" could be quite faster than the"Tip speed" while in a turn. So it seems that with a short low aspect wing the difference in speed would be much less as "root" vs "tip". This being the case a short constent chord wing must be less likely to "tip stall".
My wing being tapered is also thinner as it gets out toward the tip. So the shape of the airfiol
remains constent, just smaller.
Would this then tend to act like a constent chord?
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Old Feb 26, 2013, 10:28 AM
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United States, UT, Salt Lake City
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Quote:
Originally Posted by Oldog View Post
OK with a high aspect wing the "root speed" could be quite faster than the"Tip speed" while in a turn. So it seems that with a short low aspect wing the difference in speed would be much less as "root" vs "tip". This being the case a short constent chord wing must be less likely to "tip stall".
My wing being tapered is also thinner as it gets out toward the tip. So the shape of the airfiol
remains constent, just smaller.
Would this then tend to act like a constent chord?
No but it is essentially a lower aspect ratio setup
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