Kitfox abrupt departure sensitivity to low speed stalls

[jamesbdunn]

STOL Kit features & Kitfox low and slow sensitivities

I’ve been reading Kitfox accident reports. By far the leading cause of fatalities is low and slow abrupt departure of one wing stall and sometimes a related spin.

A tendency was to cite small wind dying out, or gusting, while flying at slow speeds; especially at high power. Also mentioned were small observed sudden control movements initiating stalling of one wing while in a turning moment. Slow flight turns frequently resulted in uncontrollable stalls of one wing.

The leading cause of aircraft damage is ground looping.

Does anyone have experience with the Sportsman STOL Kit?
It is NOT rated for a Kitfox, or at least not that I know of.

I’ve been reading about their performance on Cessna 170 aircraft; phenomenal. Even in slow and tight turns the wings will not stall. The approach angle of attack was more flat, providing greater visibility. Also, there were reports of the planes having a feeling of being more stable at touchdown.

Any PIREP’s to share here related to:
1) Sportsman STOL Kit actual performance
2) Retrofitting Sportsman STOL Kit features onto a Kitfox wing
3) Stuff I’m not considering in-general

The Sportsman STOL Kit is reported not to affect cruise speed.

[jonstark]

I operate three Cessna 180/182. The 64G has the standard wing, the 56 182 has MASA and WingX, and the 56 180 has Sportsman. The Sportsman equipped is my personal favorite. Slow flight is simply amazing! Stall horn blaring at 45mph indicated and still very controllable. If anything it increased my cruise speed. A Sportsman wing WILL stall though. Any wing will. Don't kid yourself!

Sportsman isn't available for any Kitfox aircraft. It is a certified modification. I'm sure Will Stene there can answer any questions you may have though.

You might contact Joa Harrison with landshorter.com about his Vortex Generators. I intend to install a set soon after flying my IV to compare before and after characteristics. They have worked wonders on another aircraft I fly.

Jon

[Av8r3400]

I think you'll find that the "stall spin" accident scenario is common across the board on all aircraft. There is nothing inherently wrong with the Kitfox wing or it's configuration that proper pilot training wouldn't solve.

These are STOL designed aircraft meant for these activities. The most important part is proper training and experience at altitude prior to doing these maneuvers near the ground.

A sportsman cuff is an attempt at fixing a non-problem with this plane.

[Esser]

Don't mean to be rude James but get some spin training. I can't recommend it enough. It still blows my mind that this isn't a basic requirement to get a pilot license in the US of A. I don't even consider myself checked out in an airplane unless I spin it and get a feel for how it feels behind the power curve. Of course some planes you can't safely do this. For sure this one thing won't save you completely but it's a good start. For example, after I spun an SZD-55 glider, I had a tonne of respect for getting it low and slow cause it will drop 800' in a blink of an eye. And after that. I never ever put it close to a wing drop situation because I knew the outcome.

I also think that most plans max accidents are low and slow. Kitfox has zero documented inflight structural failures. The rest comes down to pilot error or power issues.

If everyone wanted a plane that flew like a 170, we would all own 170s.

[av8rps]

I'll take a stab at this...

A bunch of years ago I had read a report that said the Piper Super Cub had the highest Stall-Spin fatality rate of any single engine aicraft. The reason for that was not that the Super Cub was a bad airplane, as everyone knows a Super Cub is one of the nicest flying, most docile airplanes you can own. So why so many bad accidents?

The answer as explained in the report was amazingly simple.... because of the exceptional capabilites of the Super Cub, it is being operated at its limits in challenginge operating environments. So in effect, if the design wasn't so much better than most others it probably wouldn't be subjected to those kind of situations, and then it wouldn't be having all those accidents.

The more I thought about that after reading it, the more that made sense to me. And now because STOL flying is becoming more popular than ever, that accident rate is likely to go up unless the pilot operators get better training to develop their skills, AND they improve their ability to use better judgement so as to avoid operating the aircraft too far at the outer limits of the envelope. It isn't the airplane...

I've been flying these planes since 1986 (Kitfoxes, Avids, Highlanders). And not that all the models operate exactly the same, but in my experienced opinion, the Kitfox is a docile, easy to fly airplane.

BUT like any airplane, if you fly it too slow and push it too hard you can get in trouble with it. So you need to be properly trained, being taught what you can do with it, and what you can't do with it. If you were to read all of my past years of posting you will stumble on my comments at least a few times that say I tend to carry a little extra speed in takeoff and landing modes than most, as I've tested my Kitfox enough to know at what point it will drop a wing in the stall. But again, every airplane I've ever flown has a limit that needs to be respected. And just for the record, my current Kitfox will drop a wing sooner than most, as it was built with less washout in the wingtips than what was recommended in the building manual. But even with less washout than suggested it is a really nice flying, predictable airplane.

I'm sure you could put some mods on the wing to make it even more docile than it already is. But I think to bring accident rates down it would be better to have new Kitfox owners get some Kitfox type specific traing from people like Paul L.at Stick and Rudder Aviation.

In a nutshell, I think it's likely the Kitfox is flying better than we are .

[PapuaPilot]

I think your questions have been answered.

I have flown both the Sportsman and Robertson equipped C-206. Both of them are much better in doing STOL then the with standard Cessna wing. The two fly different from each other. I don't recall any noticeable reduction in cruise speed.

The Sportsman is a drooped leading edge that is riveted on the existing Cessna wing, which makes a different airfoil that stalls at a lower airspeed. It is docile, but still stalls. Most often when a plane drops a wing in a stall it is because the plane is not coordinated. That is simply pilot error, whatever the reason.

Without a doubt modifications can be done to the standard KF to make it land slower. You could do things like adding vortex generators, gap seals, a different wing (Kitfox has the STi wing) or slotted leading edges (get the Just Aircraft Super STOL). It all depends on what performance you are looking for. If you want to land slower than don't expect a fast cruise speed.

I really like the balance that the Kitfox gives; good STOL ability and good cruise speed too. I found it funny that I passed a 180HP Super Cub in cruise (this past summer). Granted the Super Cub could land a little short, but not by much.

I enjoy doing STOL approaches at 1.1 Vso, but it has to be very calm to do so. Like others have said you have to get to know your aircraft. Every aircraft has it's capabilities, but it takes a pilot that has been trained, practices and has the skill to fly the plane. Not all of us are going to be a Bob Hoover. It is important to know our limitations and to stay within them.

[airlina]

I remember an old saying I once heard-" The Piper Cub is the safest airplane in the world, it can just barely kill you! "

[av8rps]

For what it's worth...

Steve Henry (the deadstick takeoff Highlander guy) has recently put a leading edge cuff on his Highlander and says it is the best mod he's done to it (and he's done a bunch). As I recall it dropped his already ridiculously low stall speed so much that he can land his modified Highlander within 10% the distance of his Super STOL. And he said it did nothing to his cruise speed. So he's pretty happy with his highly modified (now 145 hp Yamah Apex powered too) Highlander. However, the Highlander has the same airfoil the Model 1-3 Kitfox used, not the newer Riblett airfoil that is used on the newer Kitfoxes. So I don't know that it would do much on the newer airfoil, which ironically already uses a plastic leading edge extension, but for speed, not STOL reasons. I would've thought Mr. Riblett would have done that when he redesigned the wing as he certainly was a smart aerodynamicist. But who knows, maybe just drooping the leading edge on the Riblett wing would help to lower the stall without affecting the top speed?

With all that said, I have to say this: I really like the way my Kitfox flies, and performs. So I'm gonna leave it just the way it is. But who knows, maybe a sportsman type cuff could make it an even better airplane?

I told my buddy once who was insistent on streamlining his airplane but was overwhemed with all the details required to make fairings. "All it takes is some temporary plastic sheeting or cardboard and a bunch of duct tape to know if it works. Oh, and a test pilot"

[jamesbdunn]

Thank you ALL for your individual insights.

I'm taking them all in.

[Bud Davidson]

I am fascinated by the references to Harry Riblett's airfoils. Harry was, and may still be a member of EAA Chapter 240 in Wilmington, Del. When his book on airfoils came out I read it with intent of applying his work to the wings I was doing at the time. I happened to be President of the Chapter at that time.
What Harry indicated he had done was finish some work on airfoils done by his associates at what I think was NACA at the time. This was a lot of years ago so my memory may be faulty here. But, what I understood was he interpolated the original data thereby creating new light aircraft airfoils which work was abandoned when the industry suffered a downturn.
The point is, that I do not believe Harry ever conducted experiments with airfoils. The Avid/kit fox application is unique. Harry led the construction of a WAG Aero CUBY for our Chapter but did not incorporate a revised airfoil. He recommended I not redo my wing ribs suggesting the benefit would not outweigh the effort. So, that experimental application also never occurred. I have never heard of any other applications. But I left that Chapter 15 yrs ago.
Any of you who have read his book will observe his science and engineering without benefit of an editor. That does not detract from his remarkable work.
Bud