RE: Tip Stall--a misnomer?
 

Tip stall might be regulated in full-scale aviation, but it exists known as 'aileron reversal"... and is mentioned as a genuine problem..
One site which looks at stall characteristics:
http://flighttest.navair.navy.mil/un.../FTM108/c3.pdf
For model airplanes, tip stall IS a major problem, it occurs in many different types of planes, and from what I've observed, and flown, its cause is as I described, a wing close to stall with an aileron deflected down, rolls to the down-aileron side. It doesn't yaw, it rolls.
I've seen one full-scale tip stall, and been in Tristars which demonstrated the "nose-slice" at stall..

RE: Tip Stall--a misnomer?
 

Yep, saw that with my aileron glider. There was some yaw but it was definetly more roll than yaw. It was like the air under that wing just dissapearred.

RE: Tip Stall--a misnomer?
 

That sounds too familiar........

How many times do we hear "The wind got under one wing and flipped it over" at the flying field after a plane crashed at the flying field while attempting to land? It happens mostly on windy days and the pilot thinks he has more airspeed (sees ground speed) on his downwind leg and then attempts to turn into the wind to land with the plane too slow. Lower wind velocity near the ground helps too I would imagine.

RE: Tip Stall--a misnomer?
 

Some very good explanations here. Tip stalls are blamed on anything that the pilot cannot really understand/explain when the plane goes out-of-attitude. Dick explains this well when he refers to other surfaces possibly stalling first. If any flight surface stalls it not only stops creating the desired force but suddenly is a drag inducing parasite. This drag has other consequences which will often cause a sudden out of control situation. The pilot usually only observes when the wings suddely go where they should not - bad, bad, crunch! Ouch! Aerodynamics is fascinating yet few pilots ever bother to even learn the basics of what really makes their planes fly.

The original post is accurate in that the tip is not all that stalls - it is where it will start - the stalled condition of the wing will progress quite rapidly until the whole wing is stalled, unless the pilot takes corrective action.

Maintain thy airspeed less the ground rise up and smite thee mightly!

RE: Tip Stall--a misnomer?
 

Tall Paul & Bmathews: You both have some good points. I don’t deny that actual tip stall does occur, and we could go on forever debating what percentage of actual upsets is due to it. My reply to onewasp’s original question is still that “tip stall” is in fact a catchall phrase that sometimes is and sometimes isn’t an accurate description of what is actually taking place.

Regardless of the actual phenomenon, the solution is always simply to avoid operating near the stall angle when near the ground.

Q500 brings up a factor that is probably more significant than any aspect of a model’s design. In flying full-scale aircraft, the pilot always has an instrument that tells him his margin above stall. The airspeed indicator (and the AOA indicator when available) provides enough information for the pilot to avoid operating close to the stall, and give a good indication of the margin when such operation is desired.

On the other hand, the R/C pilot has to depend on visual indications alone to infer airspeed. Even with experience, such inferences may be well off the mark, and when turning or flying downwind, can be quite deceiving. “Tip stall” isn’t a problem except when operating near the stall margin, and an awareness of the effect of the wind on the perception of speed would go a long way toward eliminating the problem.

RE: Tip Stall--a misnomer?
 

For the RC airplane to have a sudden uncommanded roll - there can't be too much other than something that has caused one wing to have more lift than the other. The wing section stalling at the inboard location will make a pretty small rolling moment compared to the outer wing section so a rapid roll is probably tip related.

If we look at the things that will cause a tip stall in our models (and they are noted in detail in the many posts above) they will all be related to flight conditions such as tight turning, high wing loading and control deflections - all initiate or add to a tip stall condition.

Then if you see a heavy scale ship on a too slow landing approach suddenly drop one wing and fall out of the sky - there is a tendency to call it correctly a tip stalling condition. You might not know for sure since you can't observe the flow characteristics of the wing but based on the airplane and it's flight characteristics it can be pretty correctly called by an observer.

If it isn't a tip stall but instead is a full wing stall the airplane won't do the roll motion, such as Dick's small foam airplanes in a full stall mode. If the airplane is going straight and pulled up into a stall on purpose in general the stall be straight ahead, very few airplanes will seriously drop a tip unless the high turning, etc. conditions are met.

RE: Tip Stall--a misnomer?
 

One of the "observe this" tests we have done was really simple -
we were working on getting best possible stabilized flight in a very high AOA -aprox 45 degrees to 75 degrees.
One model had a tendency to dart off quickly to one side -or the other-sorta like the wing quit on that side.
This was the first time we tried simply adding about 30% to the elevator and rudder area ( just some 3mm foam plate and CA and back in business.)
this fixed the problem -instantly.
Another new model - same thing - the fix again the same setup -except in this case the model pitched over when holding at this critical angle - adding more elevator area fixed it.
The CG can be shifted aft ,which will lessen the condition -- but the fix brings in a bad pitch couple in knife edge and when rolled to inverted - the elevator trim produces a instant -"hands off " outside looping.
None of this was likely ever seen on full scale machines but in that this is a model forum - I thought the info could help.

RE: Tip Stall--a misnomer?
 

It’s been said that, “One test is worth a thousand expert opinions”. A number of years ago, for a school science project, a young friend and myself tuffed the wing of my Cherokee with yarn. We flew to a safe altitude and I put the airplane through a series of planned maneuvers while he videotaped the tuffs through the window. The pattern of stall development was quite obvious. The tuffs would begin to lift and flutter as the flow begun to separate and as the stall deepened, some of them would actually reverse.

A coordinated stall straight ahead would result in a symmetrical pattern like the first sketch below, progressing from the root outward. When the airplane pitched downward (by definition a complete stall) the stalled area covered less than three quarters of the wing and the tips were always in an unstalled condition. A stall from coordinated turning flight (even steep turns) was similarly symmetrical with no tendency to progress to the tips.

When rudder was applied at the instant of stall to produce an incipient spin. The stalled area quickly increased on the side toward which the rudder was deflected (as shown on the second sketch) and the wing abruptly dropped, characteristic of what is often described as a tip stall. However as revealed by the tuffs, at no time did the stall progress as far as the tips.

Of course, this is only one test point with a rectangular wing and no twist. I suspect if it had been a Mooney, because of its stall characteristics, the stall would have been more abrupt, but in coordinated turning flight there is still no tendency to fall off on one wing at the stall.

I repeat, I have no doubt there are instances of actual tip stall. However the use of that term to describe every case of upset where a wing suddenly drops, is sort of a catchall, that is sometimes accurate and sometimes not. Perhaps a better term would be “asymmetrical stall”

RE: Tip Stall--a misnomer?
 

Some of the most spectacular and almost synchronized tipstalls occur in the SAE competitions, right after takeoff when the turn to the downwind leg is begun.
As the pilots for the most part are semi-skilled at best, the rudder isn't a part of the airplane's control system once it leaves the ground. (They don't use it for turning.)
Af the Tailwinds field this turn is to the right.
The crashers all roll to the left.
That's the down-aileron side.

RE: Tip Stall--a misnomer?
 

Very interesting stuff Lou, I agree with the coordinated flight, if done right the airplane never knows it is banked. I wonder if in your flight testing if the inner wing stall was due to the fuselage interference effect. It could mess up the inner section a lot at high angle of attack. A similar wing on a glider/high wing airplane might not have the same effect.

That kind of testing is a blast, one of the fun times I had doing a wind tunnel test was in our low speed wind tunnel and the F-15. We were looking for patterns of flow separation to try to study why the verticals weren't being as effective as they should have been in the first design goaround. We tufted everything and took movies (film type - real movies) and tried to figure out what happened. Of course with that wing and fuselage nothing applies here but watching the tufts go backward is something most guys haven't seen, especially the managers who weren't aero types. They were usually surprised. Lots of fun.

Dick you need to try those effects one at a time. Do the vertical tail first and check effects, then do the horizontal tail. It is a very interesting study. Foam has been the play thing of a lot of us serious aero types. It is so quick to make changes.

Another old tale - We were trying to approximate a SuperCritical airfoil on a variable sweep fighter in our supersonic wind tunnel. The guys in the project sent me a set of templates and said test them. We did a lot of initial changes with red wax and tape, it was easy to see where it was and treated nicely it would stay put if taped over. The tunnel guys formed a top layer on the leading edge of the wing (about 40% chord from LE and back) and I (as the resident genius aero type - well the only aero type there) had to scrap and mangle the wax into a suitable shape. Keep in mind that supercritical airfoils in real sizes are extremely critical (pun) as to shape and roughness factors and you can see it was a hopeless task. Anyway I ended up with a great set of aluminum and wax wings and test them we did. They actually worked a little.

It is hard to beat making and testing and seeing what the effect is. With a little thought you can usually come up with reasons (after all the air and things that go through it are subject to the same laws of the universe that the rest of us are) for what you see. Do that enough, Dick, and you soon will be faced with becoming an aero engineer yourself!

RE: Tip Stall--a misnomer?
 

Paul, I forgot to comment, the carnage at one of those competitions must be hard to watch. Someone without much flying experience or not knowing what lies in store for the unwary is almost a sure bet for a crash under those conditions. You can probably tell what is going to happen just a few seconds after the wheels lift from the ground. I can visualize the almost slow motion effect one of the planes must have.

RE: Tip Stall--a misnomer?
 

Ben, the carnage is typical of a scale contest, with labors of love attempting their first (and frequently last) flight.
There was one plane which went perfectly vertical on lift off.. the pilot (a guest pilot provided by SAE) managed to save it... barely..
When the designer was asked "where is the c.g.?", he said "what is this c.g. you speak of?"
With zero nose ahead of the wing, the c.g. was back by the trailing edge.
Many pounds of lead later, it was moved forward to a barely acceptable position.. The plane got off the ground, but ISTR it failed downwind.. :(
I remarked to the pilot, "This makes you an ace this weekend, John... that's the fifth plane you've been flying that crashed.".. :)
In reality, if he couldn't fly it, no one could.
We gots world-class "guest pilots" here.. :)

RE: Tip Stall--a misnomer?
 

Truly boggles the mind!

RE: Tip Stall--a misnomer?
 

On the Tristar, we prepared the wing on the #1 by locking the leading edge slats up, and bondo-ing all the joints where the slats fit onto the wing itself.
Used all the bondo available in the Antelope Valley.
On the first takeoff, about Vr, as the wings began to take the load off the wheels, they flexed up.... The bondo vanished in a white snowstorm..
End of test.
Removing what bondo that didn't leave ruined a lot of the wing leading edge sub-fairings.
In flight testing, we tufted, and got those things going every way, including forward at cruise Machs..
We tried fairing in the motor pylons to the wing leading edge, with a common-sense fairing everyone agreed would work...
The puddle of air 1/2 way back was a complete surprise...
We didn't use these fairings..
On the first flight with these, BTW, it was noticed the one on the right wing lifted..
"Enough to throw a small dog thru the hole", according to our Director of Flight Test, Sam Wyrick.
We found these things hadn't been screwed on to the structure.. the holes for the fasteners had been filled in with sealant, and the point of the (unique) Tri-head screwdriver pressed in the wet sealant, which was then painted.. The work had been signed off by one of our "never leave the flight shack inspectors, a continuous problem we had.

RE: Tip Stall--a misnomer?
 

Ya know, I've often said that the SAE copetition should let in a team of modelers as a control group. But I doubt if Acedemia could withstand the shame that would occur. I think the idea of developing a plane is great but I suspect that if you look at all the successful teams they have at least one long time modeler on the design team who's done there own designs successfully in the past.

I know that I'd love to have a go at a project like that. But to heck with the molded carbon whozzits. Some carbon for sure but other than that it would be all modelling. I'd tell the students what the design was going to be in shape size and structure and then get them to analyse the snot out of it just so they feel useful.... :D

OK, OK, I know it's not THAT bad but I suspect a modeling only group would embarass a lot of the students and teachers both.

RE: Tip Stall--a misnomer?
 

an arrow engineer ?
I guess I could add that to the list -tho who would want a recent engineer graduate who was in his seventies --
No wait - eighties -I was never good at staying awake in class--and it has only gotten worse -
The other day I fell asleep while gumming a mouthful of tapioca .
seriously

RE: Tip Stall--a misnomer?
 

SAE confession time.....

The only teams I thought did well had a serious modeler on them or being advised by one. There was one school that brought nearly the same design every year until the rules changed.

We decided to throw together a prototype as soon as possible. It was one of the best things we did. My part of the project was the wing. I did a foam core sheeted with balsa that came out heavy. The wing needed a little washout and the fuselage just did not work. It was weak and hard to work on. The fuselage broke multiple times on hard landings. We lifted 15 pounds of steel with that plane. That was the max we could get off the ground in 200 feet at a DA of about 7000 feet with no wind. It wasn't too bad considering the plane weighed 24 pounds and was powered by a 61.

The problem with the fuselage was that they were getting on a 3D CAD program and making theses nice tear-drop swoopy shapes. They had never built anything like it before so it was never built right. The shapes also compounded the construction problem. The second fuselage was even harder to get in to access and it broke in the first flight. It only flew once. Again it was not built strong enough for what it was going to do.

I built the second wing. The new wing had a sheeted foam core D-tube and the rest was built up with glass on the D-tube at a 45 degree bias. It was bigger, but much lighter than the original. It had 3 degrees of washout, was tapered, had nearly a 10 foot span, and had a lot of camber. That was the most difficult wing I had ever built and don't think it would have been possible if I hadn't scratch built planes in the past.

I finally sat down with a piece of graph paper and designed a new fuselage. I made it strong, light, and accessible. I built it from light ply, carbon fiber, foam, and fiberglass. It was lighter and stronger that the two other fuses. After it flew very successfully we reverse engineered it for the report creating the 3D model and CAD drawings.

So, I built the wing, the fuselage, helped with the tail boom, tail feathers, and landing gear, did the final assembly, flew the plane, and helped with a good deal of the report. I didn't mind it too much because it was more of a labor of love.

I also did static thrust testing on a bunch of props and found our secret weapon. We were asked if our engine had been modified the way it was running. I also made 3" aluminum wheels with O-ring tires and double ball bearing on the axles. I couldn't believe some of the landing gear set-ups I saw. We had very little rolling resistance which made takeoff easier, but landing was interesting because it would roll out a good distance.

Our final plane was very difficult to fly. It was very unstable in the yaw axis, but was flyable if you stayed on top of it. There is no way that an unexperienced pilot could have flown it. We flew it multiple times and lifted 20 pounds well before the competition at a higher altitude than where the competition was to take place. After the first day of flying we were in first place. We ended up lifting over 25 pounds and taking third place overall. I was suprised to see how many teams made the journey without having ever flown their plane.

For us, we were all mechanical engineers and not aero engineers. The project was more about teamwork, crunching numbers, designing a product, and documenting everything. Now that I look back, I almost wish I would have chosen a different project.

It was fun and I would do it again if I had the chance, perhaps we should start the RCU Heavy Lift Competition.............that would be exciting. Anybody interested????

RE: Tip Stall--a misnomer?
 

Lou you mention that, "......... the most common cause of so called “tip stall” is inadequate compensation for adverse yaw when operating near the stall angle."

Indeed that is probably the most common cause but the final result of that is that the tip stalls and over you go. Regardless of what is happening to the rest of the airplane whether other control surfaces or stalled or not the only thing that is going to cause a rapid roll from level flight with no aileron commanded is that one wing stop lifting. Most common causes result in the tips separating into a stall. Call it tip stall.

RE: Tip Stall--a misnomer?
 

Well buckos --
I tried yet another goofy test -
I rigged my lil 3D MiniX with four wing tension wires - --by twisting the panels - the wires would hold a new washin/washout - better yet - twist one panel - the wires caused opposite twist in other panel - anyway ---
holding the model at high AOA - the assymetry really did----nothing to cause a
tip stall - however
dropping into forward flight - the twisted wings required lots of opposite aileon just to hold position.
So far - under these conditions - (stalled out in a hover at about 45 degrees)
the twist in the panels meant absolutely nothing .
Once forward motion begins - it's another story.
I know - this is not real world flying to many.
but to me -controlled flight is flight -no matter how it is accomplished.

RE: Tip Stall--a misnomer?
 

Ben, go back and read the tuff stuff. I was on board and I can assure you that the wing drop was abrupt and sudden. And at no time was the tip area stalled as indicated by the tuffs. It is only necessary for any significant area of wing on one side to stall before the other to produce an abrupt wing drop, not necessarily at the tip. As a matter of fact, in a perfectly symmetrical stall (coordinated), if the tips stall, they stall at the same time resulting in a pitch down, not a roll. Only if there is something producing an asymmetrical stall distribution will one wing drop. And the most common factor by far is yaw at the moment of stall.

By the way, in response to your previous comment, on the Cherokee, the fuselage interference may have affected the particular pattern of stall that began near the root. However even remote from any fuselage, with a rectangular wing and no twist, the stall always begins near the root and proceeds outward.

Tip stall is a fact. However it is sometimes an accurate description of what is taking place, and sometimes not.

RE: Tip Stall--a misnomer?
 

Lou I agree with you totally althought when I first read your comment I thought to myself, "I thought I had read the tuff stuff already." :-) Joke

But I guess it is a matter of talking about our models only, the sequence and where you put the emphasis. You emphasize the yaw leading to the tip stall and resulting roll. I don't go that far back in time, regardless of what causes the tip to stall, at the point where it stalls and there after it will have a characteristic motion we can recognize and call it a tip stall.

If we see that characteristic motion during certain points of the flight envelope of the model (again I am talking about a model which is where we hear the phrase most often) then the tip stalled. It was no doubt at all times brought on by uncompensated yaw and lots of it.

I doubt we get too many fully perfect approaches to the stall so that both wings stall at the same time in model work.

Again I agree with what you have done and your observations.

RE: Tip Stall--a misnomer?
 

So the twisted wing test is meaningless---
I only twisted em about 6-8 degrees (each panel )
I thought all the stuff about wash in /wash out would apply to any size any condition.;)
looks like I am washed up.

RE: Tip Stall--a misnomer?
 

To agree with you would be wishy-washy wouldn't it?

RE: Tip Stall--a misnomer?
 

Yes you are washed up Dick, actually we didn't want to tell you the twisted wing test is meaningless....... interesting but explainable I think.

Washin, washout and the like is finesse wing shaping stuff that matters when you are doing the fine tuning of a wing for a given application.

It is only prestall and lower that twist shows up big time. At the stall and slightly after maybe medium. When you fully stall out both wings big time at very high angle of attack then twist doesn't matter a lot.

RE: Tip Stall--a misnomer?
 

When flying this thing, a 2003 rules SAE plane.. rudder, elevator, NO ailerons, I got a tip-stall on a takeoff.. The plane self-recovered.
This occured at least twice.