Tito wrote: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.

For some, even empirical evidence will not sway their positions, let alone the wisdom of blue collar bush pilot.

I have learned a ton from all of these posts above. I appreciate people sharing their beliefs for some of us not-so-experienced pilots. The Husky and Cub are both on my short list when I manage to scrape the schillings together. I won't be flying anything, circling low and slow, ever. Too much to lose.

For me, when I hear that numerous pilots, flying low and slow for a living, for many years and thousands of hours, say that the Husky has a more pronounced "tuck" in certain wake conditions, than the "other" planes they have flown for thousands of hours, I will file that in the memory bank!
I cannot consider these hightimers the enemies of logic. How could I?

Experience is the world's greatest teacher......it gives the Test first........then the lesson. It would be easier to call "bu!!sh!t" than to heed, except that the benefits are greater for me when in their position.

A64 wrote:

I would think that it would take a descending turn to stay in ones vortex as vortices descend.

I totally agree that it's a long stretch of the settling with power of helo aerodynamics to the present discussion of circling fixed wingers... but...as a thought exercise, the circling Husky starts to look like a 35 foot, single-bladed propeller rotating at one RPM (if he's flying a double standard rate turn). If he's the perfect pilot, he's maintaining altitude to the precision of a gnats eyelash. Yes, the vortex sheet descends, and in perfectly calm air will persist, but what happens to the air above the sheet? For some distance ABOVE the wing, the air also HAS to descend, so, by the time our perfect pilot starts his second orbit, he IS in descending air, similar to, but without the ferocity of, the thrashing helicopter rotor system which is, by comparison, living an aeronautical life on amphetamines. Our perfect pilot's seat of the pants prompts him to compensate, by adding AoA or power or both to maintain his perfect altitude, resulting in him sending even more air down the elevator shaft. I'm just wondering if the geometry sometimes acts like the water in the bathtub analogy whereby, a seemingly small force gets a disproportionate amount of fluid moving. If this is starting to sound like the spinning, perforated discs where the holes have to line up perfectly for the bullet of an accident to pass through, well, I agree. That's why it's so hard to duplicate, and why it doesn't happen that often. It's also why I don't lose much sleep over it.

BTW: I believe the V-22 was particularly vicous in this arena as it's huge prop-rotors were seldom in the same vortex ring state when settling with power, leading to asymmetrical lift and an even bigger nightmare than "merely" plummeting earthwards with full power.

YB

MTV:

Good points, all.
Yes, the sailplanes have long, high aspect ratio wings that probably stick out beyond the area influenced by the tow plane, especially considering you are following him only a few wingspans behind. Also, sailplanes require a lot of coaxing to roll at all and are not known for high roll rates.

However, what student solo pilot hasn't been thrilled the first time he managed to finish a 360 with enough precision to intersect his own wake and feel the burble that proved someone has been here before. At 16, I guess my protection lay in my attention span which was too short to ever entertain the thought of a 720.

Point is, its' not that simple.

Yep, every time we fly, we are skating along on thin ice over a sea of complexity. We can't even agree on the basics like "how does an airplane fly?" Nothing about it is simple. If it were, a peach fuzz of frost on your leading edge wouldn't kill you. So, if we don't want to drown in Greek letters, we have to approach it empirically: yes, that frost will kill you - don't know exactly how or why, but just know it will. I think all those excellent pilots we were talking about above were ultra well-honed empirical aviators who, by convergence of circumstance, crossed over into a region of complexity, an area that all their experience didn't or couldn't predict. Their misfortune prompts discussions like this and we add to the empirical knowledge of the community.

Our discussions on circling flight have reinforced my committment to my personal flying style. From now on, when my turns around a point become eggs around a point and I finish the circuit 40 feet lower than I started, I can turn to my instructor and say "I meant to do that - for the sake of safety."

On wing tip vortices: I've heard that the XB-70 had the mother of all vortices. It sure made mincemeat of an F-104 that got too close, and made a bad day for a lot of folks, including everyone on board the XB-70. How could anything that beautiful have something so ugly under her skirt?

YB

I find it amusing that, as in person to person communication, the stories of
"I met a guy once who said" almost always hold more sway with folks who are already inclined to believe something than someone who actually seeks the truth.

I've spent a few thousand hours in both Huskys and Cubs, much of that at or below 200 feet, doing all kinds of tasks, but generally locating things on the surface and tracking them.

I've never experienced any negative aerodynamic effects in either airplane that suggests to me that there's a problem unique to that aircraft type.

On the other hand, I've never crashed one of the things either. I have looked pretty hard at this "moose stall" phenomenon, however, and tried really hard to duplicate it, with very limited success.

If you fly an airplane as the Border Patrol was flying its Huskys (and at least three BP pilots told me in the late 80's that they were flying the Husky more aggressively than they were the Cubs, mostly due to its much greater power) I think you may be dancing with the devil. That's what they concluded as well, I think.

The guys shooting coyotes run into the ground occasionally, largely because its' a VERY demanding flight environment and task. So is trying to determine if each of 30 adult cow moose, mostly standing in deep cover, has a day old calf or not. I've spent 50 minutes of intense flying at very low heights doing that task, continuously flying over the same spot, which is where I concluded that flying circles is a bad idea generally.

Again, the key is to fly whatever you are flying well, and always with a margin. Note in the accident report of the SD aircraft posted above that he was circling (I assume pretty tightly) at (by the pilots statement) 60 mph. Stall speed in a 45 degree banked turn at their weight would be higher than 60 mph in that airplane at operational weight. That's a formula for disaster in many airplanes. Airplanes running into their own wakes at or very near critical AOA?? Why wouldn't one expect the airplane to do something untoward? People who fly ANY of these airplanes around a lot in maneuvering flight this slow are closer than I care to be to the edge.

The bottom line once again is this: Find someone who has direct experience with some really unique flight characteristic of one of these planes, and WHO has actually flown one. I'd like to hear from them. I know a lot of people who've flown both types extensively and while some of them don't like the control feedback characteristics of the Husky, they don't complain about any of these types of catastrophic events.

One thing that I heard from Border Patrol pilots in the late 80's, when I was looking at the Husky as a Cub replacement, was the advice to put a placard on the instrument panel of the Husky which simply says "This is not a Cub". The airplanes offer very different control feedback, particularly at high AOA and slow speeds. They fly differently, and feel different, and a lot of what one does in the low level environment involves flying the airplane largely by feel. If you're very familiar with the feel of one plane, and get in another..... Some in BP felt that the performance of the Husky encouraged some pilots to get in deeper than they should have. All the BP pilots I talked to, and they were all in the units where the accidents occurred, told me not to worry about the Husky--they thought it was a great airplane. This was NOT information shared for public information, but rather information shared between law enforcement agencies. They had been told not to talk about the accidents either way publicly.

For what it's worth, believe whatever you like. My suggestion is get in one of the airplanes yourself and give em a try.

And understand that working an airplane close to the ground, in maneuvering flight has risks. Learn to minimize those risks.

MTV

From the NTSB report of the Utah Husky crash:


Flight Testing

During the course of this investigation, the retired/contract test pilot for Aviat Aircraft was contacted regarding the flight characteristics of the accident airplane during low-level, orbiting flights, and testing that was accomplished in the early 1990s. He reported that as a result of two Border Patrol accidents, Aviat was requested to flight test the Husky A-1 airplane for its flight characteristics when encountering its own wingtip vortices. During calm wind conditions, in a full flap configuration, approximately one out of seven attempts to fly through the airplane's wingtip and flap vortices would result in a pitch down. At altitude, the airplane would fly out of the pitch down, but the test pilot warned at a low altitude the pilot may not have time to recover the airplane prior to ground impact. The test pilot advised that the best way to avoid this condition was to alter the flight path when performing low-level, orbiting flights to prevent encountering the airplane's wake.


MTV, no need to feel that you are alone in truth-seeking. I think it is fair enough for each of us to say that our experiences with certain aircraft may be different than others.

I rely on the experience of others in this realm because I haven't flown any bushplanes, but I'd love to when I get the chance. Thank you for your input as well. You have contributed a great deal to my understanding of low level flying. May we all be more safe going forward.

I certainly DO NOT feel that I['m the only one "truth seeking" in this realm. I guarantee you that there are a lot of people in Alaska who've lost good friends, some who've lost several good friends, to loss of control accidents.

I can show you an NTSB report which clearly states that the cause of the accident was a stall/spin. I was at the scene with the pilot's spouse when the NTSB was "investigating" the accident. There was absolutely NO evidence of a stall/spin. In fact, there were long skid marks down the hillside, indicating a fast arrival, followed by an endo. The proximate cause of that accident was contaminated fuel, but the NTSB blew that off, even though the pilot's spouse proved it unequivicolly to me.

Point is, I have discussed the BP accident flight test program with BOTH of the test pilots involved. Both have told me a very different story than what is portrayed in that report. Challenge it to NTSB, as my friend did, and you'll be blown off.

Unfortunately, since that experience with NTSB, I don't trust much of what they publish on general aviation aircraft. I parked an airplane on a mountainside when a crankshaft failed. NTSB demanded that the engine be recovered and torn down. I witnessed the teardown. Crank was sent off for metallurgy. No reports were ever filed, and the final report said the crank failed at the #2 rod journal, for unknown reasons. They didn't even READ the dang lab reports, fer cryin out loud. Why? Cause it didn't say Boeing on the side, and it didn't kill 150 people so some NTSB geek would get his "air time" on network TV.

Don't believe everything you hear from the NTSB, in other words.

MTV

mtv wrote:I don't trust much of what they publish on general aviation aircraft.

Your comment reminds me of a report on one particular mountain accident that drove that point home for me. The most likely explanation was the pilot's failure to handle a combination of high DA and high winds. Probable Cause, according to NTSB, was "The flightcrew's failure to maintain clearance from trees. A factor was trees north of the departure end of the airstrip." No $hit $herlock.

CAVU

As I noted earlier, this phenomenon isn't exclusive to Husky aircraft....

http://www2.tbo.com/content/2008/jun/20 ... d-lakes-a/

Working airplanes low, in maneuvering flight can be hazardous to your health, no matter what you fly.

Be careful out there, and think about what you're doing FIRST.

MTV

When I first got my cub I would take it high and do different manuevers to learn the airplane.
One day I was doing steep turns with 60 degree and up bank angles.It was calm air and I did a 720 and decided it was fun and kept going.About 2 turns later it pitched hard out of the turn all by itself.Scared the hell out of me.
I don't turn circles down low after that one.

Bill

Keep the speed up, I say...

Aussie,

Precisely. It is easy to get comfortable in an operation you've done for many hours and years. Get comfortable at the wrong time, and let the speed bleed just a bit too much, then encounter your own wake, perhaps with the ball maybe a half ball out of center, and there you go.

It won't happen every time, or we'd be able to effectively train people to avoid it. In fact, it happens so infrequently that it's nearly impossible to reproduce.

Unfortunately, in little airplanes that people use to look at things on the ground, it happens with some regularity. Note that the Border Patrol's latest ugly one was in a Cessna 182. Similar scenario.

MTV

When I was doing sailplane training in Australia, they taught the concept of "safe speed near ground". Sailplanes spend a lot of their time sniffing out thermals and when they find one, they slow right down and start circling in a steep bank, sometimes in the company of a lot of other aircraft- precisely the kind of activity we recommend avoiding in power planes. With one big difference: The safe speed near ground concept dictates that below a certain altitude, say 1000 ft, you must exercise discipline to ignore the temptation of a flight-saving thermal and commit to a landing. You should speed up and focus only on completing the approach and landing.

Quite a different mission profile to power planes. Gliders go slow up high and speed up near the ground. We seem to do the opposite in power planes. However, at pattern altitude or less, I now find myself thinking if I were in a sailplane right now, I'd want to be sure I had that safe speed near ground. Makes me do a double check on ASI.

YB

something about low and slow rings pretty loud here...

add to it small motor's and no turbo's...

'ya gotta fly her 'till it quits moving...qouted bob hoover....

my first flight instructor was tops on this, and showed me many

times just how people get killed in small airplanes...

most by not continuing to fly the airplane from about 50 ft

off the ground, fly it in, no matter how bad it looks...!