Ben, Bruce, Dick, John, Lou, Paul, (alphabetical order)

Isn't "Tip Stall" really a misnomer?

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I don't think so.
One tip stalls, the plane rolls over towards it..

Paul,

First thanks for the input:

"I don't think so.
One tip stalls, the plane rolls over towards it.. "

Perhaps the 'guts' of my question really are didn't the whole panel stall? Isn't the immediate and violent reaction due to that rather than a portion (the tip)?

Part of a wing can be flying while another part of the wing can be stalled. A simple example would be a wing having wash-in where the tip is at a higher angle of attack and the airfoil is the same across the panel.

Another example would be the airfoil at the root having a higher stall angle than the airfoil at the tip. The tip will stall before the root.

My error for not being more definitive.

Let's assume we are dealing with a single airfoil section from root to tip. Also let's assume that it is one of the NACA 00 series like a 0012. It also has no wash out/in but is a tapered planform (moderate taper medium aspect ratio).

Now, if you would re-consider the question----???

many times -the tail has stalled out and the plane looses sense of direction - so it yaws -then the wing craps out.
If you make a plane with very low aspect ratio wing and a Veeeeeery long arm to the tail group - it is all but impossible to get a "tip stall"
the thing will simply mush .

In that case I think it's still possible. This is getting beyond my scope of knowledge but I believe that even if an airfoil is the same the chord of the wing at any given location affects the stall due Reynolds numbers and who knows what else.

For example, if the root chord is 20" and has a 1" LE radius and the tip chord is 5" having a 1/4" LE radius I would think that even though the airfoils are the same that the air could more easily break away from the smaller radius LE at the tip. Maybe it doesn't work that way. I'm not sure.

I see what you're asking in your original question though. I've seen several heavy scale models roll over and die at low speed. Everyone calls it a tip stall, but it could just be that the whole wing stalled and it randomly fell one way or the other.

Just because a plane rolls over doesn't mean it was a tip stall.

Constant chord wings can still tip stall because the tip is "open" and leaks air around in a vortex formation. However with most of the good ones the angle and speed difference between the tip stalling and the rest of the wing following is very narrow.

To me the question is: Is the term tip-stall misused regularly?


Carl

Trying to summarize the answers to this point:

I think 'Tip Stall' is misunderstood and mis-applied by most modelers. Certainly by me -----which is the reason for the question.

To the experts, it is a set of circumstances leading to the stall of a wing panel (or one wing) beginning at the tip. This 'local stall' is very closely followed by the stall of the full panel resulting in the rather violent snap. The whole panel stalls but since it was induced by the tip we have the 'Tip Stall' label.

Is that a fair summation?

I may be wrong but I think it's possible for a circumstance where the tip stalls, parts of the wing are still flying even as the plane is rolling over. The flying part of the wing simply isn't creating enough lift to prevent it.

Perhaps but even constant chord etc can tip stall in a turn. In a turn, even onto final, any turn. the inside wing and therefore the inside tip is traveling slower than the outside wing or the wing section closer to the fuse. So it may start as a tip stall and become a complete stall on the one side.

Here is a quote from a more learned aero-engineer which gives pause for reconsideration----no authorship is posted as I do not have permission (or authority) to do so. He is speaking of forces in a coordinated turn---

"This also brings up the subject of tip stall. We're using a lot of small increases in angle of attack here to keep things in balance, and of course there's a limit on how much of that you can do before the airfoil says "ENOUGH!" and quits flying. Because of this, the stall speed increases as you increase the bank angle. It also means that, because it is flying slower in a turn, the inside wing tip is the most likely candidate for a stall in a turn, unless the designer has used airfoil selections, planform changes, etc., to make the center of the wing stall first. The lower speed at the inside wingtip actually exacts a double penalty, because in addition to the lower airspeed, you also get a lower Reynolds number, which increases the drag and reduces the maximum lift coefficient.

Virtually any model can be made to tip stall if the weight is low enough to allow a small enough turning radius. Because of this, contrary to what you might expect, airplanes with very low wing loadings are actually the most at risk for tip stall."

I would have received a zero had I attempted to answer the last paragraph---(had it been posed as a question). In fact I would have guessed that light wing loading was one 'cure' for 'Tip Stall' tendencies-----shows how little I grasp of the aerodynamics involved and I'm not too happy to acknowledge that incidentally. But "them are the facts"!

Can't remember who said that, but it's usually true.

Now we are getting back to where I feel comfortable ;-)

I said that because I haven't found light planes to be more wicked than heavy ones. On the other hand, I don't build heavy planes. I think the heaviest I've ever flown was a 96" Sukhoi weighing about 26 lbs. As I recall the wing loading was about 35 oz/sq. ft. That's not heavy for that size plane.

I think if you go to the scale forum and ask about some of those planes and their stall characteristics you might get better info about how heavy planes behave.

Sport models like most of us fly even at their heaviest aren't really that heavy. We call them heavy when they weigh more than they could.

That bit about light models stalling easier is an interesting one. I suppose it's true but most of us don't fly models that light at the extreme where it's an issue. Also most such models have a low aspect ratio so the speed differential from inside to outside wing isn't that high. Adding dihedral also confuses the issue if the model is side slipping at all in the turn. Not sure how but I'm sure it would all have an effect.

Tip stallling the inside wing in a turn is a common thing to do on gliders with their higher aspect ratio wings that tend to be flown slowly. The higher span ratio increases the speed difference from the inside to outside wing and you set the stage for a tip stall. If just flying slowly isn't enough to do it then cranking in a whack of aileron with the low wing aileron going down and thus increasing the local angle of attack suddenly will certainly do the trick. The flat winged aileron birds are particularly suceptible to this where the poly ships don't seem to get it as badly. See my coments in the first paragraph for this bit.

Oddly enough we don't see that much about constant chord wings tip stalling. Without being able to test a model it's hard to say if they do tip stall consistently or if our choice of airfoils prevents it. Certainly it's possible to induce a tip stall with various control inputs but for a simple straight forward stall it may be that the constant chord wing lets go all at once. Certaily it's very close to all at once. Oddly enough this is one area where a person can do their own testing. Some thread tufts taped onto a wing and that wing attached to a boom that extends out from a car or truck far enough to avoid the bow wave could be remote controlled by the passenger to up the angle at various speeds until you see the heavy thread tufts start dancing about, lifting from the surface and even pulling forward. That's your stall. Doing such testing with existing wings on a stub fuselage at speeds of around 8 tp 20 mph depending on the model design would simulate the model landing and flaring to a stall. The 8 would be for a glider wing and the 20 for a sport power model. No damage would be done to the wing at that angle and speed but a lot of data on the stall progression could be had. The boom should probably extend out about 10 feet from the front bumper and hold the wing about 5 to 6 feet up to avoid, or at least minimize, any ground effect or bow wave off the vehicle. The angle of attack control could be a cable rig up or a control rod or whatever as long as it can move the model through a 10 to 15 degree angle and hold the settings at speed.

Tapered wings are another story. There's been lots of horror stories about highly tapered wings on scale models. P38's, DeHavilland Comets and a few others with high taper ratios are well known to require lots of washout or a fancy airfoil transition to avoid nasty tip stalling and rekitting.

Bruce,

Thanks to you (and all who have participated here---I hope it goes on).

My problem in understanding has been a natural affinity for relatively high----well let's call it moderately high aspect ratio (vs. sailplanes)---- designs (that preference also identifies my age group). These designs are used in fully aerobatic models which are capable of the complete pattern schedule though they are NOT currently competitive--nor intended to be--with the two meter planes. (they sure fly prettier though)

I just don't feel that I had an understanding---certainly not a good understanding--- of the adverse affects of the higher aspect ratio designs. I have a limited understanding of the effects of the lower Reynolds numbers as chord is a multiplier but I hadn't put it all together properly . This exercise has certainly helped.

I do not feel we are at the bottom or end of the useful information to be gleaned here so I sincerely (perhaps selfishly) hope that the thread will continue for a period.

The usual tip-stall occurs when a plane is flying close to the stall angle... and a turn is commanded with the ailerons...
The down-going surface -increases- the angle of attack for the wing section ahead of the aileron.
As the wind is already close to the stall angle, the effect of the downward deflection -lowers- the angle of attack for stall.
The wing portion then stalls.
This effect is seen almost every day with weight lifters, which commonly tip-stall and roll over after takeoff when beginning the turn to downwind.
With a right turn, the plane rolls left... and the pilot is usually caught by surprise, and keeps the right roll command in, which prevents the left wing from recovering.
The cure for these planes is to not use down aileron! 100% differential, so the aileron only goes up.
For these planes that's all the roll control needed.
For the usual plane, typically a scale model which also is typically overweight for the wing area, tip-stalls occur because the airplane is turned too tightly, or slowed too much. Correcting the flight path with aileron creates the tip-stall.. Caution in steep banks and keeping the speed up is the best cure.

If you're looking to help avoid tip stalling then look into the idea of ending the ailerons well before the tip. Having a segment of wing with no aileron that is about 1/2 to 3/4 of the tip chord is often seen and is used normally to help avoid increased tip turbulence. But decreased tip turbulence goes with a lesser chance of a tip stall. I've got nothing else to base this theory on but perhaps some others can comment.

Often a hack ship modifed to test such things can tell you a lot.

To add to Dennis' comment, you can also use a quad flap arrangment if you have a good computer radio. You can program the ailerons to both move slightly up to give washout for low-speed flying. They can still work as ailerons, but will be farther from stalling, if that makes sense.

Just read all the stuff on light wing loading stalling easily- (?)

All of the models we are now flying/testing etc., have extremely low loadings and the wing planforms go all over the place from tapered to rectangular
BUT all are very small (30" span) flat foam models
the rectangular wings are 3.3-1 aspect ratio
the tapered are typically 10"- 12" root and 5"-6" tips
We fly the crap out of these at high /low speed and the one thing noted is that the rectangular 3.3 planform -when dived at full bore -the snapped instantly to level -and power cut - will simply settle evenly - no tendency to snap out.
But at high AOA flight , holding power -it gets a bit wishy washy from side to side .
The models all will rudder turn (180 or 360)in just a few span lengths - at any speed and there is no "tip stall"
The tendency to get wishy washy in high AOA has been cured -every time --by simply adding MORE elevator area - not changing cg -just adding more elevator area.
My observation is that this has increased TRIM DRAG -resulting in better yaw control -If that makes sense. The elevators may be at 45 degrees deflection in holding these very high AOA attitudes-whilst maintaining altitude
We change the tail group area by simply instant glueing on more piecesof flat foam-OR slicing away some of it
results are sometimes surprising .
the ability to change all this and re fly/test in a matter of minutes -really has helped me eliminate a lot of ideas -which simply were not applicable.
You guys who have not taken advantage of the cheap quick flying setups currently available - are missing out on a revolution in model flying.
I have never had as much fun - and put as many "whys" and "ifs" to rest as I have since I started playing with these.
The info learned -thru direct observation -may not impress some who have not tried this approach -but it sure seems to work

onewasp – The term “tip stall” is used as a catchall phrase to describe an effect in which one wing suddenly drops causing a rapid rolling motion.

As such it is sometimes correct and sometimes not. Actual stall at the tip is not necessary for the sudden uncontrolled roll to take place. It is only required that there is a sudden loss of lift on one side anywhere along the wing. What is often blamed on tip stall is due to a sideslip resulting from inadequate use of the rudder to overcome adverse yaw. Many flyers are in the habit of using the ailerons only to command roll, which causes no problem unless the airplane is operating near the stall angle. If the angle is near the stall on both wings, a little added yaw is enough to cause one side to stall before the other.

Having said that there is no doubt that stalling at the tip is sometimes the actual cause. The planform and washout give some clue as to whether actual tip stall is the culprit. A sharply tapered planform with no twist is surely prone to stalling at the tip first, whereas a rectangular planform especially with a little twist almost never stalls at the tip first.

To sum up, tip-stall is not always a misnomer but it is not always an accurate description of the phenomenon either.

Tall Paul – Just a comment regarding your reply:

As you can see from the attached data, deflection of the aileron (flap) actually increases the angle of attack for stall to a higher lift coefficient delaying the stall. The problem of aileron deflection causing a stall and dropping the wing on which the downgoing aileron is deflected (called aileron reversal) was in fact a problem with some of the very early designs of the last century. I'm sure that it could show up in models that depart from conventional parameters, but I doubt if it is a factor in most cases.

Lou, from a slightly newer, but still really old NACA report (good old 824, available online, as is 664) with the information presented better..
lowering a flap raises the flyable Cl, but that occurs at a lower alpha.
When all the wing is at the no-flap alpha close to stall, and part of it is deflected down, that part of the wing is stalled.

I certainly agree that that is possible. However airplanes designed in compliance with FAR part 23 (all full-scale general aviation aircraft) must meet the stall characteristics quoted below. None that I have flown, nor any that I can bring to mind have gone to a configuration other than plain flap type ailerons in order to avoid aileron reversal at the stall. In other words, though what you describe is possible, it isn’t a very common phenomenon. I stand by my opinion that though there are certainly other causes, the most common cause of so called “tip stall” is inadequate compensation for adverse yaw when operating near the stall angle.