wing length vs line tension

LAST EDITED ON Dec-13-04 AT 05:11 AM (CST)
 
So, am I understanding the TEOSAWKI wing length debate?

Longer outside wing = more line tension

BUT

Longer outside wing = too much lift needing extra tip weight

Thus

what is needed is equal lift distribution but un-equal drag distribution

so would a different wing section giving lower lift and increased drag on the outside wing be a possibility?

When I was building competition slope soaring machines we would generally have a different wing section at the root of the wing compared to the tip, in out case to have the tip of the wing continue flying when the root stalled.

so an ideal wing for a stunt model would have a wing section that blended from the inside tip to the outside tip with the section changing to give the same lift at the airspeed it is seeing. and having a greater drag as the lift/speed ratio decreased.

Just a bit of free thinking

Edit : one way of reducing lift would be to have some holes through the wing connecting the high pressure underside to the low pressure top side - probably only need to be small.

Regards

Mike

One thing is mass of the fuselage helping to put CG to proper place, and another thing is thrust line. Just make some angular offset to engine and you have what you needed.

Different airfoil in and out will change not only drag, but also max lift (or stall angle) so you can get what you did not want.

Doesn't make sense to me!!!

I believe in the OLD TYME RELIGION....

Inboard wing goes slower, needs more area.
Outboard wing goes faster, needs less area.

I will listen to reason, but I haven't heard any yet.

There are no reasons, we have only one wing - no inboard, no outboard, just that one

The only task is to put CG to it's AC.

The stall thing is cogent but I wonder if it would be better to make the outer wing stall before the inner? currently I would expect the inner wing to stall first as it is always flying slower and has the weight of the lines on it as well as the rotational reaction of the engine when flying upright.
We have approx 7% more airspeed at the outboard wingtip.
snf thats where I start to get confused. what is the difference between engine offset and leadout line rake?

Regards

Mike

speed does not change the stall point, so if you want to stall them together, you will need the same airfoil on both sides

But isn't the actual airspeed different inner to outer?

Regards

Mike

LAST EDITED ON Dec-13-04 AT 10:31 AM (CST)
 
>But isn't the actual airspeed different inner to outer?

What Igor is getting to is that stall is a function of angle of attack and airflow seperation on the skin as the angle increases. This is not speed dependent its' a function of airfoil design and geometry.

There is some great reading concerning pilots of spy planes like the SR-71 Blackbird and U2. They speak of flying right on the edge of stall at extreme altitudes where air density is low and yet they are zipping along at Mach 3 plus. In order to generate enough lift at altitude the angle of attack AOA was just below stall angle. Can you imagine a stall at 80,000 ft. The Blackbird is the most amazing plane ever built IMHO.

LAST EDITED ON Dec-13-04 AT 11:08 AM (CST)
 
>>But isn't the actual airspeed different inner to outer?
>
>
>What Igor is getting to is that stall is a function of angle
>of attack and airflow seperation on the skin as the angle
>increases. This is not speed dependent its' a function of
>airfoil design and geometry.
>

Darn! Man, I'm getting tired of engineering semantics! Yes, you and Igor are right, but Mike was trying to get to something else:

Airflow speed is dependent on airplane speed. For the same flow, geometry, and AOA, the stall will occur more quickly at a slower speed. Or, semantically, the changing AOA will have more of an affect.

If you have the same wing on the same airplane, but speeds differ from tip to tip, then the tip traveling slowest will stall first. A stall in a turn may result in a violent snap, because one tip stalls, but all of the lift is still producing force on the other side.

Stall happens easier at a slower speed. It may still be only airflow and geometry, but the speed dictates that airflow. Otherwise, the same geometry and AOA would result in a stall at any speed.

OK, everyone get out their keyboards and start shooting this one full of holes. Geeeeeez!!!

(I'm not energized, just frustrated - all this stuff depends on someone's definition (even convention), not just a simple observation and street-English description of the phenomenon.)

LAST EDITED ON Dec-13-04 AT 11:35 AM (CST)
 
You've got it right. The inboard tip will stall first, if the wing ever gets to a stall. Stunt planes almost never get anywhere near stall. Usually what happens is that part of the wing or tail stalls(airflow separates) first- the flaps or elevator or stab. The drag goes up tremendously when that happens, the plane staggers like a drunk, and you back off on the control and wait for the speed to come back and hope it doesn't crash.

Combat planes, esp. the F2D ships can often be driven to stall, esp. in windy weather. They are all using a number of tricks- slightly longer inboard chord(raise the Reynolds number to delay stalling) forward leadouts(makes the inboard tip drop slightly so it flies a longer path in maneuvers), less than max tip weight(makes the plane roll in slightly in maneuvers so the inboard tip flys a longer path), and engine offset, either angling the engine or moving the thrustline towards the geometric center of the wing. An angled elevator hinge line - helps smooth out quick changes in direction.

The reason I went to moving the engine to the left panel, putting the thrustline on the geometric centerline, was to get a constant outboard couple for line tension. It works. Works better than angling the engine, at least in combat. An angled engine tends to tear itself and the motor mount up in a crash. Offsetting the mount keeps the engine square to the wing so stuff doesn't get torn up as bad.

Most competition stunters are already close to this kind of setup already. The thrustline is generally very close to the geometric center, and ~ .5 inch to the left of the MAC(for equal panels). Everything has to be balanced very closely. It doesn't do to go haring off after huge engine offsets. Read some of Brett's posts on how a small change can make a big difference-IF it is the right change. Even when everything is trimmed just right, the plane still goes through all sorts of different air conditions just going around the circle, so the trim is never exactly right at every point in every maneuver. The pilot has to compensate all the time.

Yes. I caught your last post on the "Hinging" thread, and posted the link below.

>Darn! Man, I'm getting tired of engineering semantics! Yes,
>you and Igor are right, but Mike was trying to get to
>something else:

Tom... how long would you go to a doctor who, after you told him that you have a pain in your whatchamacallit, told you that the cure is to "cut off your thingie"? Gee,I hope it was a hang nail! Words have meanings and scientific words usually have specific and narrow meanings. Hard to talk concepts and get around it.

>>Darn! Man, I'm getting tired of engineering semantics! Yes,
>>you and Igor are right, but Mike was trying to get to
>>something else:
>
>Tom... how long would you go to a doctor who, after you told
>him that you have a pain in your whatchamacallit, told you
>that the cure is to "cut off your thingie"? Gee,I hope it
>was a hang nail! Words have meanings and scientific
>words usually have specific and narrow meanings. Hard to
>talk concepts and get around it.
>

Dick, I will try to keep from the hyperbola, but this is getting more frustrating still. My Doctor has the good sense not to deflect my concentration by arguing a point on a technical medical term. He also spent years learning how to communicate with a wide range of people's experiences and understanding.

I do the same thing in my career everyday. It does no good to argue the technical point when, with a little more effort, you can understand what was being said.

Quite frankly, it torques me off when someone starts arguing a point over a scientific principle that may only exist in definition or even convention, only. I see it happen a lot on this forum. Someone tries to ask a question or describe an observation. Then the first thing, someone pounces on them with a post that says they're all wrong, and they don't even know the definitions.

An example: Take the infamous force diagram. I push on a rock, and unless it moves, that means the rock pushed back, and we can draw up the force diagram to prove it. Yet, everyone knows a rock can't push. It serves little to correct someone on that point outside of a classroom.

The post just below about stall speeds vs. AOA is a perfect example. In one paragraph, it's stated that stall is not dependent on speed. Then the next paragraph states that stall in a bank may happen at a much slower speed. Does that mean that anyone said that stall speeds don't vary? That was never said. Yet the statement itself says stall happens at a certain speed one way, then a different speed another way. Yet, we're supposed to march on the order that speed has nothing to do with stall????!!!

You all are making me start to type like Jim ...

>Stall happens easier at a slower speed. It may still be
>only airflow and geometry, but the speed dictates that
>airflow. Otherwise, the same geometry and AOA would result
>in a stall at any speed.

Exactly what we're trying to say. Any wing stalls at some given AOA regardless of the speed. You're trying to have it both ways, and you can't. AOA drives stalls, not airspeed. This is why airplanes stick. In a 60 degree bank, stall speed may be more than double the straight ahead stall speed.

If CL wings stalled inboard tip first, then the things would roll into the circle every time they stall, as in landing approach stalls. But they don't. They stall straight ahead. Because the wing reaches critical AOA.

LAST EDITED ON Dec-13-04 AT 06:26 PM (CST)
 
>Exactly what we're trying to say. Any wing stalls at some
>given AOA regardless of the speed. You're trying to
>have it both ways, and you can't. AOA drives stalls, not
>airspeed. This is why airplanes stick. In a 60 degree bank,
>stall speed may be more than double the straight ahead stall
>speed.
>
>If CL wings stalled inboard tip first, then the things would
>roll into the circle every time they stall, as in landing
>approach stalls. But they don't. They stall straight ahead.
>Because the wing reaches critical AOA.

Good Grief! They only stall straight ahead if they're built straight and trimmed well - and they're a good design!?? Besides, I don't stall my planes when I land - if I can help it.

AOA and stall do depend on speed, it's just that that speed may vary depending on conditions (aka, the attitude of the wing, the forces trying to upset laminar flow on the wing surface, etc., etc.), and the AOA of flow separation changes under varying conditions - you just said it:

"This is why airplanes stick. In a 60 degree bank, stall speed may be more than double the straight ahead stall speed."

So it will stall at a different speed in a bank, but it's the bank that causes the wing to stall at a slower speed ... the egg then the chicken, then the chicken, and the egg. I give up.

Ah, Tom, dont want to be argumentative here but...

In a 60 degree bank, (perfectly coordinated, constant altitude, in equilibrium) the load factor experienced by the airplane is 2, in other words the airplane thinks it is twice as heavy as it really is.

The wing stalls at a constant angle of attack, but must generate twice as much lift as it does in straight & level flight. The only way the wing can generate the extra lift is to fly faster, before it stalls. How much faster?...Lift is dependent on the square of speed, so in a 60degree bank, the stall speed is 1.41 times the level flight 1G stall speed, in a perfect world, all things being equal & other disclaimers..

Apologies if this is an egg sucking/teaching issue...

No need to give up.

>The only way the wing can generate the extra lift is
>to fly faster, before it stalls. How much faster?...Lift is
>dependent on the square of speed, so in a 60degree bank, the
>stall speed is 1.41 times the level flight 1G stall speed,
>in a perfect world, all things being equal & other
>disclaimers..
>
>Apologies if this is an egg sucking/teaching issue...
>
>No need to give up.
>
>Cheers, Dave

Well, there you go again. Who said that stall speed wouldn't vary under different condtions? Just because someone makes the accurate statement that stall depends on speed, you and others make the assumption that we're saying, "this airplane will stall at 92.3 mph in every case." Ridiculous. You just said yourself - to prevent stall, the wing must "... generate the extra lift ..." and the way to do that is "... to fly faster, before it stalls."

But stall is not dependent on speed - right ... and the chicken doesn't depend on the egg, and there is no semantics.

Yes that my understanding too. What I was alluding too was that, by choosing an aerofoil for the inner wingtip that stalls at a slower speed for the same angle of attack as an aerofoil chosen for the outer wingtip, you could easily create a situation where the outer wing always stalled first or, assuming still air ( a rarity I know) both wings would stall at the same time despite the approx 7% difference in their relative airspeeds.

Regards

Mike

LAST EDITED ON Dec-13-04 AT 11:30 AM (CST)
 
Yep. Assymmetry in stalls (or lack of) is sometimes the difference between a bad plane and a really great one. DC-3's and C-130's come to mind.

Assymmetry in lift (or lack of) also causes something called Hinging, discussed ad nausea in this recent thread:

http://www.clstunt.com/htdocs/dcforum/DCForumID1/11536.html#2

>Yes that my understanding too. What I was alluding too was
>that, by choosing an aerofoil for the inner wingtip that
>stalls at a slower speed for the same angle of attack as an
>aerofoil chosen for the outer wingtip, you could easily
>create a situation where the outer wing always stalled first
>or, assuming still air ( a rarity I know) both wings would
>stall at the same time despite the approx 7% difference in
>their relative airspeeds.

The way I look at it, you don't want the plane to stall at all. If you're flying the plane anywhere close to a stall, you've set it up wrong. Set it up right, and you shouldn't need to insure that the outer wing stalls first.

(And if it does, you've got a problem if you reverse the turn suddenly!)

>>>What Igor is getting to is that stall is a function of angle of attack<<<

Exactly. Speed is not reason for stall. As you are slowing down, the angle of attack (AoA) necessary to keep it in air needs to be higher. When you exceed point where lift does not grow with AoA, but drag yes, and quickly, then happens stall. It is because as wing falls down at lack of lift, AoA grows more and more, lift is lower and lower and drag higher and higher. But still - primary reason is too high AoA and speed does not play role.

The truth about circular flow and lower speed at inner tip is hidden in dirty trick that ceter of pressure or aerodynamic center is little moved out of the circle (relative to geometric center). Therefore it enough to move CG to its place and all is OK. The AoA on inside tip is the same as at outer tip because they are just joined together. So stall really happens on both sides at the same time.

Yes, may be there are some minor differences like different RE numbers or induced AoA at different speeds, but that is very small effect to speak about.

LAST EDITED ON Dec-13-04 AT 12:22 PM (CST)
 
Quote Igor >>>>The truth about circular flow and lower speed at inner tip is hidden in dirty trick that ceter of pressure or aerodynamic center is little moved out of the circle (relative to geometric center). Therefore it enough to move CG to its place and all is OK. The AoA on inside tip is the same as at outer tip because they are just joined together. So stall really happens on both sides at the same time.<<<<<

I've thought about this and wouldn't a trim tab on top of the outboard wing be the fix to move the AC back towards the center of the fuselage? Making a nice clean situation of the CG, AC and axis of symmetry all nicely resting in the same place. Of course, in a wingover no lift is required so does it hinge at the top or would the nose yaw out (yawing out would be OK)?

>>>I've thought about this and wouldn't a trim tab on top of the outboard wing be the fix to move the AC back towards the center of the fuselage? Making a nice clean situation of the CG, AC and axis of symmetry all nicely resting in the same place. Of course, in a wingover no lift is required so does it hinge at the top or would the nose yaw out (yawing out would be OK)?<<<

Where is the problem with shifted AC? It is center of lift as well as center of drag, and if you put CG to the same place and thrust line appropriately, then all is OK. So why to make tabs?

BTW - you are right, such a tab will separate center of lift and center of drag - exactly like asymmetric airfoil will do. It could be nightmare at trimming.

>
>Exactly. Speed is not reason for stall. As you are slowing
>down, the angle of attack (AoA) necessary to keep it in air
>needs to be higher.

Sorry, Igor, try again.

>There are no reasons, we have only one wing - no inboard, no
>outboard, just that one
>
>The only task is to put CG to it's AC.

It's not the spoon that's bending ... you are THE ONE.

It's times like this that I wish I had gone ahead and studied aeronautical enginerring.

All of this is likened to an obese rodent's posterior to me.

Bill <><

>It's times like this that I wish I had gone ahead and
>studied aeronautical enginerring.
>
>All of this is likened to an obese rodent's posterior to me.
>
>
>Bill <><
>
>"It is better to remain silent and be thought a fool than to
>open your mouth and remove all doubt"
>Abraham Lincoln

Amen. Speaking of posteriors, Bill - check that post I made on tails in the Umland Cobra thread!

Bill, I guess that this is a sore spot for aeronautic types because many years of trying have failed to get the idea across that AOA is the issue, not speed. It has real implications because this is the misunderstanding that kills too many private pilots in stall/spin accidents. Please forgive the feverish tone. It's just an old, messy problem.
K

>Bill, I guess that this is a sore spot for aeronautic types
>because many years of trying have failed to get the idea
>across that AOA is the issue, not speed. It has real
>implications because this is the misunderstanding that kills
>too many private pilots in stall/spin accidents. Please
>forgive the feverish tone. It's just an old, messy problem.
>K

How many people have died at the end of the runway in overloaded small planes? Had plenty of air speed at rotation time.

Kelvin & Dick,

Oh, no problem. I try to read a lot of the technical stuff here with no real back ground in the field. It is my shortcoming. I have no problem when things are stated in "everyday" terms.
I'm glad y'all know all the "language" that goes with the technology and theories. Mine is a very limited vocabulary in the area.

Now if you want to get into football,baseball, or one of the subjects I teach, then I can help y'all out. (we're trying to decide on whether to run a 4-3, 3-5, or 4-4 combination on defense next year based on who we expect to have back)

We have been running a tuned pipe for over 10 years. HOW it "really" works, I don't know. How to "get it to work", I have somewhat of a handle on that, through having been told by guy who use them to the optimum levels. Maybe when I retire in a few years, I will burn up the "library" on aeronautical theory!

Bill <><

LAST EDITED ON Dec-13-04 AT 04:12 PM (CST)
 
SNIP
>Now if you want to get into football,baseball, or one of the
>subjects I teach, then I can help y'all out. (we're
>trying to decide on whether to run a 4-3, 3-5, or 4-4
>combination on defense next year based on who we expect to
>have back)

I like a 4-2-4, but I'd say it depends on how much oil ya put in the gatorade!

Of course it also depends on if ya got ABC AAC

ABC - A Big Corner

AAC - An Active Corner

I'd say it depends on who's better - the linebackers or the linemen? 3-5 if the linebackers are best, 5-3 if the linemen are better, 4-4 if they're about the same.

But you knew that.

Speed has nothing to do on the line of scrimmage, only angle of attack? But angle of attack depends on your speed for the tackle, doesn't it?

I'm sorry. You took the high road. That was smarter.

Hi Tom,
The 3-5 is "fairly" new and a take off of the 4-3, "shade 50", and old 5-3.
Caters to fast LBs and the need for only a couple good "down" people.
Personally, I like a multiple 4-4.
Bill <><

P.S. Dick, I think I would like to be able to put a bunch of castor oil in the other team's Gatorade sometimes! LOL!!

Thats why serious aircraft have AoA indicators - over rotation was the cause of the early DH Comet take off accidents - lots of alpha, not enough lift.

>Thats why serious aircraft have AoA indicators - over
>rotation was the cause of the early DH Comet take off
>accidents - lots of alpha, not enough lift.

An AOA of a certain value will cause a stall every time, regardless of speed, regardless of attitude, and regardless of thrust. It's the only thing that matters in causing stall, and speed is never a variable under any circumstances and never alters the AOA value required to cause a stall.

GOT IT.

AOA is the critical factor. But who's to say the angle of attack is constant across the wing, when it is zooming around a circle and around a tight loop. Also, if you've got big fabric bays, like on an F2D ship, the covering can sag and change the airfoil on you, depending on how tight the turn is. Or the trailind edge is slightly curved vertically. The plane can be trimmed to fly straight, until it gets into really hard maneuvers, then parts of the wing can stop flying unexpectedly.

As a practical matter, lightly loaded planes, 'ala combat, "fail" in maneuvers two ways- most common is as you feed in elevator, at some point the outboard wing drops, the plane yaws out, and starts to stagger around the loop very slowly. Painful in a match, but not fatal. Opening up the maneuvers will let it get around much better.

The other way, everything is fine until you give just a bit more control and/ or it hits the wind funny- the inboard wing drops and it cuts across the circle. This usually happens in one loop direction only, indicating a warp, but it can happen to a straight plane as it goes through the wind overhead.

Most of the F2D trimming tricks are to get the plane as neutral in roll as possible so it will go through changes of direction without going ape and still keep good line tension overhead and upwind. Many of the ARF planes are set up "safe"- they roll and pull strongly in tight maneuvers. This is fine for beginners and downwind flying. It doesn't work so great when you need to make a quick change of direction overhead, into the wind. If the plane rolls out 10 deg. in a loop, it has to roll the other way 20 deg. when you switch direction. You can move the controls much faster than the plane will roll during a direction change, so it comes right in, esp. if it's overhead. This can look a lot like it stalled and rolled.

eggs-actly.

>An AOA of a certain value will cause a stall every time,
>regardless of speed, regardless of attitude, and regardless
>of thrust. It's the only thing that matters in causing
>stall, and speed is never a variable under any circumstances
>and never alters the AOA value required to cause a stall.
>
>GOT IT.

I had this explained to me a long, long time ago on Usenet. Suddenly it made high speed stalls understandable, where a plane will suddenly drop out of a tight turn at high speed. You read about it a lot in accounts of turning fights in WWII fighters.

Tip stalls happen because things are rarely uniform across a wing - one side might have an imperfection in the wing, or the plane might be crabbing slightly, or there might be some local variation in the air (i.e. turbulence, etc.), so if the angle of attack is close to stall already, the angle may be exceeded at one tip before it is exceeded at the other. You reduce the tendency by making the root of the wing stall before the tip, by building in washout (the Spitfire had it, for instance).

LAST EDITED ON Dec-13-04 AT 11:21 PM (CST)
 
It still has to do with whether there's enough speed developed in the airflow over the airfoil. I guess in these semantic discussions, you can stick with the hard-nosed point that an airfoil will not lift at a 90 degree AOA regardless of the forward speed, but that's a ridiculous semantic point to make. It's the lack of speed that allows the unusual AOA to take place, and turns the wing into a leaf.

Even then, enough thrust in the right direction will overcome the stall, and also control the transition. Witness the F-22 specification requirement for full roll capability at 70 degree AOA.

Anyone who's twiddled sticks on an RC transmitter knows that too much pitch input at too low speed will produce a stall, and that speed and control input threshold decreases significantly in a turn. This is particularly important on a final approach turn into landing, and has happened to me on more than one occasion.

It's analagous to stating that a car skidding in a turn has nothing to do with speed - only the amount of turn input by the steering wheel. What's the usefulness in making that point? Anyone can turn the wheel much more beyond the point where control is lost, and that threshold decreases with speed. To demand an admission that it's only the steering wheel travel, and thus, the angle of the wheels that causes the skid, ignores the reality. It will also fail the driving exam. The multiple choice answer to what causes a skid is driving too fast.

The multiple choice answer to what causes a stall is flying too slow. Even if it happens at high "speed," it's still because of too much control input for that "speed."

I just get tired of the mental masturbation and complete submission some think necessary to contradict a rational observation.

The analogy with the skidding car is spot on - a graph of tyre slip angle v's adhesion (side force) looks remarkably like a alpha v's Cl graph.....

Dave, I do not think it is good analogy. If tyres are at some angle, they keep the track auntil side force exceeds adhesion. So the slippage depends on side force and not on angle. You can go slowly and follow tyres or quicly and skid.

Airfoil is different. Does not matter what is the force (lift) it depends on angle when wing loses lift. It clould be slow or quick, does not matter. The stall will come at the same angle. So I would say that tyre example is not analogy, it is just opposite.

Igor, my engineering friend, I respectfully disagree.
First, a tyre can only develop a lateral force with a slip angle - here I define slip angle as the angle between the direction of travel and the axis(disc)of the tyre, clearly a tyre can generate no side force if it is travelling straight ahead. - my apologies for not having a diagram - I am at a strange computer here.

Now, for a constant radius corner, at a constant speed, the tyre (lets consider only the front, for simplicity - Porsches have different rules!) has a certain slip angle to provide the side force necessary to restrain the car to the constant radius. If the car goes faster, the tyres must work at more slip angle to give more side force to again restrain the car to the constant radius. OK? This type of discussion can be found in texts on car suspension design.

The relationship between slip angle and lateral force is more or less linear up to a certain point, after that point, then the lateral force is no longer linear with slip angle - the curve goes "over the top", finally the lateral force decreases with slip angle (at a certain, higher slip angle) - this is the loss of adhesion that we feel in a skid. This is similar to the stall of an airfoil, the loss of adhesion(side force) is dependent on the slip angle of the tyre, not the speed. But however, it is the demand for side force caused by speed, that causes the "stall". I hope that my explanation is OK. This is what Tom is saying.

It is interesting that the behavior of a tyre at the point of non-linearity is much the same as the behavior of an airfoil. A tyre with a sudden change we consider to be tricky or dangerous. An airfoil with a sudden change at the stall is also difficult to fly and is considered to be not suitable for say, a private airplane flown by not-so-skilled pilots. Models are no different.

The analogy that Tom has provided is good - in a car we control the slip angle of the front tyres with the steering wheel, in an aircraft we control alpha with the stick(or our handle), it is much the same thing. Also interesting is that there are many, many, minor variables with tyre performance, as there is with airfoil performance - tyre pressure, material ( how soft is the rubber?), camber angle(very important) and tread stiffness.

I hope that this does not sound like a lecture, but I have spent many years training beginner race drivers and many hundreds of hours and thousands of laps testing and evaluating racing tyres!
Cheers, Dave.

Maybe next year I will be ably to fly F2b in Bratislava.

Dave, I like such lectures. I agree what you wrote, but it does not match what I understood from Toms post. He speaks about >>>steering wheel<<< or by other words tyre to vehicle angle and you speak about tyre to trajectory angle. And that completely change the situation.

Anyway - we are speaking about level flight. So direct analogy will be a wheel with side force and angle supporting that side force at straight path.

So if you compare that your analogy, then you have airfoil which at stronger and stronger force (load) making more and more lift at higher and higher AoA until stalling. On opposite side you have tyre, which does EXACTLY the same – stronger and stronger force needs higher and higher angle until the force exceeds the adhesion. So far I agree with your analogy. Evend drag will have similar analogy.

But now assume that the same happens at twice higher speed. The airfoil will make at its max 4x more lift, but the tyre will support still the same side force like before. It depends on adhesion.

This point of view (force) is easier to understand, and may be that my last note does not look too much important, but if you look to the problem from AoA point of view, you will get what I mean.

My example:
We have loop and wing, which is able to support mass of the model at some radius, which is very close to the stall. That will be analogy to your tyre example at curve.

You wrote that to support centrifugal force on the same radius and higher speed tyre needs bigger angle and the tyre will skid at speed, when centrifugal force exceeds adhesion.

But this is completely different on the wing. The wing AoA necessary to make enough lift at higher speed on the same radius is EXACTLY equivalent to that at lower speed, and more – the stall angle – means minimal possible radius of model is the same at all speeds – just because the stall AoA is speed invariant.

So it seems there is lot similar, but also lot different.

>>>Maybe next year I will be ably to fly F2b in Bratislava. <<<
You know you are welcome here. We can try tight loops to proof it

>It still has to do with whether there's enough speed
>developed in the airflow over the airfoil. I guess in these
>semantic discussions, you can stick with the hard-nosed
>point that an airfoil will not lift at a 90 degree AOA
>regardless of the forward speed, but that's a ridiculous
>semantic point to make. It's the lack of speed that allows
>the unusual AOA to take place, and turns the wing into a
>leaf.

No need to go to 90 degrees. Airfoils will stall at some point well short of that - and yes, it doesn't matter what speed it's going at, it'll still stall.

Remember how this all started - a comparison of the inboard vs. the outboard wing, and the statement that the inboard wing would stall first because it was flying slower. Will that happen because the inboard wing flies slower? NO. Because, assuming you're flying at a tangent to the circle (i.e. you plane isn't crabbing), and also barring such things as turbulence and crosswind, both wings will be at the same angle of attack, and therefore the inner wing won't stall first.

The only way the inboard wing will stall first is if it can adjust its AOA separately from the outboard wing and assume a higher AOA to compensate for the reduced airspeed. But since they're fixed with respect to each other, it won't happen.

LAST EDITED ON Dec-14-04 AT 07:27 AM (CST)
 
>>It still has to do with whether there's enough speed
>>developed in the airflow over the airfoil. I guess in these
>>semantic discussions, you can stick with the hard-nosed
>>point that an airfoil will not lift at a 90 degree AOA
>>regardless of the forward speed, but that's a ridiculous
>>semantic point to make. It's the lack of speed that allows
>>the unusual AOA to take place, and turns the wing into a
>>leaf.
>
>No need to go to 90 degrees. Airfoils will stall at some
>point well short of that - and yes, it doesn't matter what
>speed it's going at, it'll still stall.

That's a hyperbolic reference to make a point. The way you guys are, if I had picked 54.29 degrees, you all would argue what airfoil.

>
>Remember how this all started - a comparison of the inboard
>vs. the outboard wing, and the statement that the inboard
>wing would stall first because it was flying slower. Will
>that happen because the inboard wing flies slower? NO.
>Because, assuming you're flying at a tangent to the circle
>(i.e. you plane isn't crabbing), and also barring such
>things as turbulence and crosswind, both wings will be at
>the same angle of attack, and therefore the inner wing won't
>stall first.

Those are a lot of assumptions - and ones that can't be made.

>
>The only way the inboard wing will stall first is if it can
>adjust its AOA separately from the outboard wing and assume
>a higher AOA to compensate for the reduced airspeed. But
>since they're fixed with respect to each other, it won't
>happen.

There it is again. Check Serge's post. The supposition is that AOA is independent of airspeed, therefore, stall is independent of airspeed. So the absolute is stated - "stall is only dependent on AOA." It may be interesting to state that, but it's a theoretical exercise. The implications are that we have a bunch of ignorant full-size aircraft pilots flying around thinking that "stall speed" is an absolute lower limit that can't be undercut. Further, that as long as those said pilots are over that speed, then they think that nothing they do will cause a stall.

If they really thought that, I wouldn't step onto a plane.

As far as the inboard vs. outboard wing (yes, Igor - I know it's the same wing, but that statement made things even worse), stating that stall only occurs because of AOA was a complete distraction. Everyone is so quick to prove a point, that all sorts of real-world effects are ignored.

Given a certain airfoil and a certain weight, an aircraft must maintain a particular AOA with a particular speed (or it doesn't fly). No one is denying that too much AOA is the actual action that causes the stall, but it happens because the speed dropped. Therefore, to simply state "speed has no effect on stall" causes considerable consternation.

EDIT - deleted ramblings ...

Sorry - I should take a break.

>>>Therefore, to simply state "speed has no effect on stall" causes considerable consternation.<<<

You are right Tom, speed HAS effect to stall. The same as mass of airplane (wing load), as number of cylinders behind the prop (thrust unloads the wing at high AoA), as the CG position (CG more aft will cause more AoA) - even that bellcrank moved aft will have effect to the stall, but again - whatever the speed is, (or mass, CG number of blades on prop) if you keep AoA below stall AoA stall will not come. If you exceed stall AoA you will come to stall.

Better?

Igor,

I respect your brilliance (and Dick Fowler's, too). However, your analysis digression on the skidding tires analogy kind of makes a statement all by itself.

Somebody visualize this for me, I'm terrible at thinking in spherical geometry-

the inboard wing(in a loop) is flying slower due the point it is on the circle radius, and it is also flying slower due to the fact that it is looping in a smaller diameter. Wouldn't the angle of attack be lower on the inboard tip- not because the wing is twisting, but because the air is coming from a different angle than at the outboard tip?

:-) ... good question ... In loop you are right that there are differences, however if we say that AoA we measure at AC, then LE will have SMALLER AoA on inner tip compared on outer tip and AoA at TE will be higher at inner tip than at outer tip. Then I would say smaller loop will help (thanx stronger circular flow) to make more lift on inner side, not smaller.

It seems that some of the responses on this thread do not address the contrast between dependent and independent variables and how they are chosen. FWIW.

SK

>It seems that some of the responses on this thread do not
>address the contrast between dependent and independent
>variables and how they are chosen. FWIW.
>
>SK

Agreed.