Georges post is correct in the fact that any of these planes will fall out of the sky when put in the wrong position. It is also correct in the fact that just because one bites less, later, or not as severe does not make it OK to get all crossed up and fly through your own wake. However I think the point Coyote and others going back to cubs are trying to make is simply this. All aircraft are a compromise, and the fact is some will do better in areas than others. If you are going to be putting yourself in a position where a moment of inattention may place you in a bad way (daily), wouldn't you want to be in the aircraft that was the most forgiving for the given situation? And if an aircraft with the same exact wing profile did better at something than another wouldn't it be worth considering why rather than just dismiss the event since the pilot made an error as well?

FWIW while all cubs seem to be unique, one thing that doesn't change is the fact that a full rib from a cub, and a full rib from a husky are identical. The wings are greatly different, but certainly one could optimize on the characteristics that would help when you find yourself in this situation.
This is just my .02 cents and observation on a debate that will likely go on forever...

Take care, Rob

Rob,

Your point re: airfoils is well taken. That said, there are a LOT of differences in the two airplanes that are very different. Angle of incidence of the wing/tail, and other things.

There are also significant differences in performance characteristics. In some cases, endurance can be the selecting factor for an airplane, or speed, and sometimes takeoff or landing performance.

These are NOT virtually identical aircraft, in any case.

MTV

I know it's not an elliptical wing, but I think the tip is one large difference between the two aircraft. I don't think it's as simple as the wing tip, or a Maule would I believe be really bad in it's own wake.
Is removing some of the washout a "mod" that is often done to improve lift at slow speeds in a Super Cub?
I know in some types of aircraft that changing rigging in the search of better performance is common, usually you give up something if you do.

Coyote,

Something was left out of the quote you posted. Talk to that (actually THOSE, since there were two of them involved in the flight testing after the Border Patrol accidents) test pilot and he will tell you that they could NOT get the Husky to depart in this manner with only one airplane. To duplicate the hard pitch down, they had to use TWO airplanes, and maneuver the lead airplane dramatically, with full power to get the trail airplane to depart controlled flight. This was done to attempt to simulate the BP accident scenario, which did not appear to be a WINGTIP vortex precipitated upset, but rather the airplane flying into a burble of disturbed air left by the accident aircraft, which flew into its own PROPELLER generated turbulence, and apparently tripped the tail, causing a hard pitch over, which close to the ground was disastrous.

So, back to the SD coyote hunters, and the Utah APHIS folks: Two of these accidents do not appear to have the same characteristics as the Border Patrol accidents. In one of the SD accidents, the pilot simply flew it into rising terrain. If it stalled, it did so as he struck the ground. I'm sorry, but if you fly into a down draft, or place an airplane into an inescapable scenario involving terrain, it is simply not the airplane's fault. I didn't read the report on the other SD accident. The Utah accident was according to persons involved in the accident investigation, a stall/spin event, NOT a tail stall. THe airplane was rotating at impact.

The Border Patrol accidents appear to be unique in the Husky's accident record. The manner in which they were flying the airplane was also VERY unique, by the way.

Again, a lot of people have mixed their metaphors when discussing Husky accidents. Accidents like the BP experienced just haven't happened much in the accident database. The Husky, like the Cub, the Scout, the Cessnas, etc, has suffered some stall/spin accidents, one of which killed a friend of mine. Amazingly, the back seater in that accident wasn't beat up bad, though he had a pretty serious concussion, from his brain slapping the inside of his skull when they stopped.

Nevertheless, the Super Cub is undeniably the king of this type of accident, NOT BECAUSE its a BAD airplane, but rather, as someone mentioned here earlier, because it's very commonly used for low level reconnaisance flying. Sorry, but these are pilot error accidents.

Is the Husky slightly more aggressive in a loss of control? I don't think so. I've spent quite a bit of time TRYING to get a Husky and a Super Cub and a Top Cub to depart controlled flight. So far, I'm averaging about one departure for every 200 + attempts, for each of these planes. And, to get them to depart, they had to be cross controlled at least some, circling repeatedly, flaps deployed and partial power--just about where you'd be looking at something on the ground. I have only been able to get them to depart in this manner in absolutely calm, cool air. In each case I've experienced, the plane has gone over the top, on its back, and cleanly entered a spin. In each case, the plane has quickly recovered using normal spin recovery techniques.

I have tried really hard to duplicate the infamous "moose stall" and I believe I've been able to reproduce it, but definitely not predictably. I believe I also experienced the beginning of such an event at low level once in a Cub, but pitched out of the turn before it broke. I have a friend in Alaska who had this happen to him, and crashed on a mountainside. He and his gunner were badly injured, but he is firmly convinced that he ran into his own wake vortex assymetrically. They were circling in a canyon, cool calm weather, trying to push a wolf down canyon to gun it. The canyon wall probably saved their lives, since they impacted it inverted before the spin developed.

Think what you may of the Husky, don't fly them because they are immensely dangerous, or whatever legend you care to perpetuate, but whatever you do, don't for a moment believe that a Super Cub (or Scout, or Cessna, etc) won't kill you just as quick in this scenario.

I love ALL these airplanes, but as the man said, aviation is very unforgiving of mistakes. And we are all quite capable of making those.

MTV

Mike, you are correct in that the Utah plane was rotating, but not the in the sense of a spin. It was rolling hard to the right at impact. The right wing and right hor. stab were curled upward in an identical fashion. Most times in stall/spin impacts the outboard wing will break loose from fuselage from centrifugal force and swing in the direction of rotation. In Utah the aircraft hit very flat, rolling right with a lot of forward momentum. Strange stuff indeed. Joe

Joe,

The stall/spin accident I referenced that killed a friend of mine the airplane remained intact after the arrival, which was near vertical, but there was rotation at impact. Drove the leading edges of BOTH wings back to the spars, right wing was pushed up, but left wing was still attached, not as you suggest.

The Husky is a tough bird. As I noted, if you saw the picture of the airplane I'm talking about, you wouldn't believe anyone could survive that, but the back seater is alive and well. Rang his chimes really hard, but...

The BP accidents did not apparently involve any rotation, but they occurred from such low level (think agricultural application heights here) that there was probably no time to rotate in any case. In those accidents, the airplane's tail apparently quit flying, and the airplane nosed down dramatically. The Aviat test pilots who were able to duplicate this using two aircraft said it required 600 feet to recover enough air flow over the tail to fully recover.

But, the Husky accidents I've seen or heard of other than the BP all seem to involve rotation at impact. In fact, they look just like a lot of stall/spin accidents of various types of aircraft.

Fly the airplane, and give yourself lots of margin, is all I can suggest, no matter what you fly.

MTV

I'd be very interested to know if anyone out there has replicated the Border Patrol, Tail-Stall results with anything other than a Husky. Will a Cub, Champion, etc. experience Tail-Stall, and tuck it's nose under the same conditions? I'm kinda out of the loop here in central Nevada, and definitely not an expert on any of this, but the old stall-spin has been around as long as aircraft, and I hope I understand the dynamics. Tail-Stall however, is something I'd never even heard of until a couple years ago. Some of the posts seem to say that any airplane will tail-stall/tuck, but I'm wondering if we are lumping two completely different things together here. Isn't there a big difference between a wing stall with resulting spin, and a occasional tendecy for a plane to tail stall, tuck it's nose and head for the ground when it encounters vorticees? I agree, that this discussion will probably go on for many years to come, but just can't help throwing in my two cents worth in the interest of safety.

Joe,

The incident I described above in my PA-18-150 was of the, tuck the nose and head for the ground variety while in the vortex (of a Champ - which still blows my mind). The airplane didn't rotate, just skidded sideways and put it's nose down. Was at 200 feet, which was enough to recover, but glad I had that. (The airplane responded quickly despite the unusual attitude once free of the vortex.)

Brad

Well, the thread says “theory”, so here goes…

As an aero engineer I’ve been trying to visualize what’s common to these incidents. We have good, sometimes excellent, pilots in good, airworthy aircraft flying in what would be considered ideal conditions: smooth, calm, stable air, free from the nuisance of mechanical or thermal turbulence. Everybody seems to be looking at the wing tip vortex as a scapegoat, but really, the wingtip vortices of a cub or Husky are just not the evil tornadoes we might think. Sailplanes are towed aloft every day behind Supercubs, Pawnees (same wing as a Supercub, I believe), and maybe even Huskies. Part of every sailplane pilots training is to “box the wake” by flying above, below, and to either side of the propeller wake of the tow plane. I can guarantee that these sailplanes are encountering the wing tip vortices of the tow plane during their excursion around the box. They don’t fall out of the air.

Keep in mind, we are talking about light aircraft here. The wingtip vortices are part of a complete vortex sheet, shed by the wing as it moves through the air. The energy imparted to the air by the vortex sheet is what keeps the airplane aloft. Small plane, small energy. Big plane…lots of energy. The planform (shape) of the wing has some effect on the local strength of the vortex sheet. The cool thing about the elliptical wing is that it produces a pattern that matches the ideal spanwise elliptical lift distribution along its span. Hershey Bar wings are not pigs though and with a bit of washout, are almost equal to elliptical wings in efficiency. But, no matter what the shape of your wing, the total energy to keep it flying, along with the necessary fuselage, pilot and other sundries, is fixed and proportional to the lift being demanded from the wing. Circling will generate more influence on the air than straight and level flight, as will climbing.

Have you ever, as a kid or otherwise, stuck you hand into a bathub full of water and started moving it back and forth along the tub to eventually find the perfect forcing-function frequency to get all the fluid in the tub sloshing out onto the floor? OK. Back to the circling Husky. In dead calm, stable air the disturbance of the passing aircraft tends to persist. It is not broken up by local currents. The second common factor in many of these incidents is circling. As the aircraft completes each circle, the downwash from the trailing vortex sheet may be additive to the downwash from the previous pass. Also, in the circling case, the dynamics may be building the atmospheric equivalent of a whirlpool, like an inverted thermal, with a rapidly descending core. Fly one wing into the descending core and away she goes. No stall warning, no buffet, just one wing that stops flying while the other generates full lift and goes over the top.

A64: don’t helicopters exhibit a similar phenomenon while settling under power in a vortex ring? The aircraft is basically trying to gain lift in air that it has already sent downwards. If any of this is right (and that would be a stretch to prove) then MTV hit the nail on the head when he said “don’t circle”. You would be best to orbit your moose while alternating your circling direction with each pass. Better yet, be a sloppy pilot like me and perform irregular ground tracks at varying altitudes – anything to break up the perfect geometry that the perfect pilot makes in the perfect atmospheric conditions.

What about those cases where there was no circling? The one I read above had most of the same features(repetitive, possibly additive, atmospheric disturbance in calm, stable conditions), but in a linear environment. Three aircraft approaching the same point, one after the other, each adding to the previous sink. The third guy on the match got the bullet.

This is one way I could divorce the incidents from aircraft type. How long does the downwash persist in calm air? I was standing on the shore of Lake Hood when this C-130 made a low pass. The acoustic rush was cool enough, but if you watch the weeds against the blue fuselage of the floatplane, near the end of the video, you can see when the downwash arrived. It was strong enough to move my clothing and what’s left of my hair


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Yellowbelly, good points all.... i've often wondered about the flaps of a husky..... they are consideably larger than a cubs, make more lift and less drag than those of a cub. That with the fixed tail (no jack screw)... i've wondered if under exacting conditions it will loose air attachment and cause a pitch over... just wondering.... joe

Interesting thread.

My first airplane, and the one I flew to AK for my first flying job was a 1951 PA-18 with the O-235 in the nose. It was light, nimble and a very forgiving little airplane. It was my primary trainer (It was the first airplane I ever flew), and once north, the Old Timers took me under their wings and spent a lot of time and effort to show me how to fly. That little Cub did everything I ever asked her to do, and in all the time I had her, only once tried to kill me.

Icy Cape, Alaska... Along the Arctic coast between Point Lay and Wainwright. I was droning along at about 300 feet looking for dead walrus washed up on the beach so I could get the tusks. It was a nice day, no real wind to speak of, and just perfect for beachcombing. I spotted some brown color on the sand, and rolled the airplane into a left bank still at cruise power. As I came over the walrus I wanted to steepen my bank, and slow down for a better look, so I rolled the throttle forward for more power, and then reached down and pulled full flaps as I tightened my turn.

I was not in my own wake turbulence, as I hadn't completed a 360 turn yet. I was slow, but not uncomfortably slow, and as I pulled flaps the controls had been crisp and responding normally. The seat of my pants were very happy with where they were at the moment.

But, as those flaps hit the stop, all hell broke loose. That airplane pitched straight down instantly. No buffet, no rotation, nothing but windshield filled with beach. My hand was still on the flap handle, and as I pitched I dumped 'em, and recovered at what seemed like inches, but was in reality about 20 feet. The throttle was at high RPM when it all started, but I was surprised that I didn't bend anything because after pushing the flaps up I jammed that throttle full forward as hard as I could, and that little Lycoming was screaming as I pulled out of the dive.


Being young and dumb, I wasn't rattled enough to stop what I was doing, so after I pulled out and back up, I came back around set up, and landed next to my walrus. I flew back to Barrow and ran the incident by my gurus, and they told me that what I had done was "blank the tail" by pulling full flaps while slow and in a steep turn, with those big barn doors interfering with the airflow, and stalling the tail.

Is that really possible? I certainly don't have the answer. Was this just an aggressive stall that I didn't recognize? I don't think so, and I/we have tried to re-create that scenario time and time again, and none of us could ever get that Cub to do anything even close to that violent in all the subsequent attempts.

Gump

Hey Gump,

I'm far from an expert, nor do I have the level of experience that you and a lot of others have in cubs. I can say for a fact, though, that my PA-11, which has flaps, will blank the tail during a full power, full flap stall. Up elevator becomes ineffective, then shortly thereafter, the wing stalls. I have a -18 tail, too. Thankfully I've never tried it the way you mentioned, but from my limited experience I have a pretty good idea that your old timers knew what they were talking about.

Sometimes those things really scare the shit out of me.

gb

YB - I also thought about the glider thing as I've flown through the wake of a 170B towplane a number of times with an old Schweizer 2 seat glider and the only thing experienced was an airframe shudder. The first time I did it I expected to be flung out of control, break the tow line and head earthward but was assured that wouldn't be the case, and it wasn't. Why does a powered aircraft have such an issue while a glider / sailplane does not?

Brad

As I read the news bulletin, the trooper said that the wind was blowing to hard to land, my experience is thats not the kind of day to fly through your own turbulence. You can't get back around fast enough to catch it before the wind blows it away. But you can fly through another airplanes turbulence close enough to loose control. I about bought the farm one day flying close formation with another Alaska state super cub.

VF

BRD wrote:YB - I also thought about the glider thing as I've flown through the wake of a 170B towplane a number of times with an old Schweizer 2 seat glider and the only thing experienced was an airframe shudder. The first time I did it I expected to be flung out of control, break the tow line and head earthward but was assured that wouldn't be the case, and it wasn't. Why does a powered aircraft have such an issue while a glider / sailplane does not?

Brad

I am just guessing but the wing span on a glider is alot greater then the tow plane so the parts of the outer wing are still is clean air and help stabilize the towed plane... Make sense ??

Ben.

Yellowbelly,

Consider the relative stall speeds of the glider and towplane. Also, the glider isn't circling, nor is the towplane, at least not steeply. I've boxed the wake on another Cub with a Cub and Husky, and you can definitely feel the influence of the wake of the preceding airplane, but generally have the control authority to overcome it. In doing that, however, I've gotten to the point where it took virtually ALL the aileron authority I had to maintain wings level. THAT is what will get you, if you happen to encounter a wake--assymetrically, unexpected, maybe just a little crossed up, distracted, etc.

My point in all this is that I believe that these events that result in an upset are the result of a very specific convergence of conditions, which is why they are so difficult to replicate in training. If they were easy to replicate, we could simply built the training into our syllabus, and fix the problem, at least for the most part.

Point is, its' not that simple. I think the rest of your post is dead on.

Want proof of differences in wing tip vortices? Look at the Boeing 757 compared to the rest of the large aircraft. The 757 is now considered for wake turbulence purposes, to be a "heavy" aircraft, even though it doesn't meet the criteria vis a vis weight. That airplane generates a tremendous wake vortex, and its flight profile makes encounters with its wake more likely.

Now, when there's a wind and a maneuvering airplane involved in a loss of control accident, I seriously doubt that vortices were involved. In those cases, the infamous "downwind turn" is likely involved. And, of course, depending on your training/beliefs, there either is no such thing, or its' the worst culprit ever, aerodynamically. My belief is that is has nothing to do with aerodynamics, cause the plane doesn't care what the ground is doing relative to the plane. If it exists, it's psychological, induced by the pilot, trying to fly the airplane with reference to the surface, instead of the airmass.

Thankfully, or in some cases, regretably, there is still some magic involved in this aviation thing. Which is probably why many of us are enamored with it.

MTV

Well, definitely all this discussion is a good thing, thanks to everyone. Every bit of information is extremely interesting.

It just occurs to me that there are probably two professions, Border Patrol and Animal Damage Control, that fly almost daily in the same exact conditions that we are discussing, and they both, I think, have for the most part, kind of come around to a conclusion.... Does that mean it's absolutely right? I sure don't know, and I don't even know if they all completely agree, but I still think that these guys are probably the most proficient pilots out there at this particular type of flying. What they're saying should probably be at least considered just a little tiny bit.

Coyote,

Border Patrol, last I heard, was still using Huskys and Cubs. I don't know where APHIS is going at the moment. The US Fish and Wildlife Service and National Park Service are using a number of Huskys, and a number of Cubs, in Alaska and the Lower 48. Both those agencies do low level surveillance work every day as well.

What's your point?

MTV

Used to be a BP pilot here. He claims its the flaps on the Husky causing the problem. Hit your wake with the flaps down and it would blank out the tail and cause the nose to pitch down. Im sure these guys are flying more aggressive than some fish cop spotting game. Take it for what its worth. The same pilots never had that problem in thousands of hours of super cubs.

Yellowbelly,
What you describe helicopter wise is called settling with power when the main rotor starts injesting it's own vortex and your descending. Pulling power will aggravate it tremendously as your "feeding" the vortex, I have had rates of descent as high as 5,000 FPM when settling with power and full power applied. You can only stay in the ring state for a couple of seconds, aircraft movement in any direction and you will fly out of it.
It's called Vortex Ring state when it occurs to the tail rotor. Any of you guy's that have flown OH-58's know what I'm talking about.
I would also bet lunch on it being the primary cause of the V-22 accidents. Jet jocks were the pilots, and they don't know what settling with power is any more than they know what dynamic roll over is.
I would think that it would take a descending turn to stay in ones vortex as vortices descend.