Kitfox abrupt departure sensitivity to low speed stalls

[av8rps]

I'm an advocate of everyone knowing what their airplane will do in a simulated power failure on takeoff.

I typically will go to 3,000 agl and use that as my imaginary runway along with the runway compass heading. I apply full power and start climbing at whatever airspeed I want to test, so I know what speeds and weights it will stall at with full power. Once I establish that I do simulated power failures so I know what to expect.

Once I know what to expect from an engine failure, at the same altitude I practice what altitude is needed to get back to the runway safely (aka "The impossible turn" made possible).

And if any of you think this is dangerous, think about the consequences when you have a real power failure on takeoff and you don't know what to expect. I've had 5 full engine failures in 4 decades of flying, 3 of them on takeoff. I'm here to tell you that you can't know your airplane well enough...

(and for anyone wondering, I landed successfully every time with no damage to me or the airplane. I always say "Even the space shuttle that weighs tons upon tons with short stubby wings glides. But you better know what speed it glides, and even more importantly what speed you need to flare and touchdown. )

Geez, I hope I'm not jinxing myself now???

[airlina]

Sound advice there Paul-as I was reading your post , I was thinking that guy does the exact same thing I do to practice. I have found that even with a"holy cow" what was that delay factor thrown in- 400'AGL is my number to make the 180 back. the actual manuever takes about 200 ' but I double it for mom and the kids. I have gone to a quiet grass strip and fooled around with the turn back for real with a pull to idle at 400' after takeoff and found that turn around wasn't the problem but having enough runway to land on was. I wouldn't try it from a short strip unless it was my only choice. The key is to have all this figured out BEFORE you add full power to takeoff-know what you are going to do before leaving the ground on every takeoff. Bruce N199CL

[av8rps]

I'm glad to know others practice for power outs and turns back to runway. It truly is one of the most important things to know when operating any aircraft imho.

If anyone thinks this is difficult or dangerous, the Kitfox, even on 230 lb amphib floats is a ***** cat compared to the same maneuver in my Lake Amphibian. But I practice it in that just the same. By comparison the Lake sinks like a stone with the gear down, flaps down and the prop at fine pitch. And because the engine is mounted high above the fuselage on a pylon, and because the super slow hydraulic trim tabs are 1/3 of the total elevator area and pitched way up for takeoff, when you lose power the drag of the prop along with those huge trim tabs forcing the nose up, will pull the nose pretty much straight up. So you instantly need to push full down on the elevator and get those trim tabs down as quickly as you can. But amazingly, with lots and lots of practice the Lake can actually do a turn back to the runway safely from only 500 agl. One more reason it pays to practice. However I'd double that number to 1,000+ feet agl if you are not well practiced.

The Kitfox and Avids have an amazing capability to do a safe 180+ degree turn in a very short time, which provides an amazing advatage to get back to a runway in the case of a power failure. I don't know of an airplane that could do that as well, and I've flown lots of aircraft. But unless you are well practiced, if you have an engine failure on takeoff and you aren't sure if you can make the turn back with a large margin of safety, plan to go straight ahead as even these super docile airplanes have their limits.

[HighWing]

Can you please describe for all of us what the Laker leading edge is, and what it does?

During the initial discussion of the vortex generators that some began putting on their wings, I seem to recall that most found a much more docile control feel nearing stall, but not much lowering of stall speed. Discussion then suggested the possibility that the shrink of the fabric between ribs and and false ribs gave some repeated variation of the original Riblett airfoil design across the span. Some buddies and I talked about it and since I was in the middle of a build, I became the Guiney Pig. I used aluminum and with some tweaks in the the installation hoped to eliminate the oil canning. One of the guys in our group flights had an early Rans S-7 and he got a lot of ribbing from the occasional appearance of his wings while on the ground and I knew what to try to avoid. He never had any issues in flight however. Being aluminum, what I did was heavier than the LLE, but it was not available yet.

[jiott]

I had heard a while back, maybe it was from John McB at the factory, that there was some thought that the standard wing (without LLE) with its leading edge "shrinkage between ribs & false ribs" gave a similar effect of vortex generators. It would sure be interesting to get some side-by-side testing to answer some of these questions.

[jamesbdunn]

Practicing power out return to runway.

What does experience show?

I'm not expressing an opinion here. I'm just trying to work the numbers a little.

When taking off on an asphalt strip, 2000 feet down the runway, the altitude is going to be between, what?

about 40 seconds down the runway

A medium pilot, full fuel: 700'/min or around 500' above the runway
At gross: 500'/min or 330' above the runway

Dumping the nose forward an air speed of what, 50 mph is needed to make a safe turn? Especially since you're going to be looking outside the cockpit more than inside.

If power out is before 2,000 feet it seems like a turn is not advised
just do your best to set it down before running off the end of the runway.

if power out is after 2,000 feet it seems like choices change a lot as altitude is increased before power out.

Is the runway long or short. Density altitude. Winds & Gusts. Grass strip next to runway as an alternate landing not requiring as much of a turn.
...


Then there is the bush.

Potentially no alternate landing zone other than runway without damage; but, perhaps safer than trying to get back to the rough strip.

Bush power out return to unimproved runway.

Are there seemingly acrobatic techniques when the choice is possible death regardless of which you choose? Choosing between extreme choices.

I'm guessing a full nose over well above stall, followed by full left rudder, full left aileron, while still nose over. then neutralize hard, wait a second, then enter stable glide. Just trying to get closer to being in the clear.

Obviously practiced at significant altitude to see if it would work before actually trying to use this, or something similar, in an actual situation.


This was just to frame the question.

What are bush strategies for power out return to runway?

[av8rps]

Wow, lots to talk about.

Regarding fabric shrink between ribs vs VG's, I think proving that will be very, very difficult as no two Kitfoxes are really alike. So I'm not sure exactly how we could prove that one way or another? Maybe if no one could catch a smooth leading edge Kitfox unless they put smooth leading edges on theirs, or no one could fly next to a VG equipped Kitfox unless they added VG's to theirs, how else would we ever know? Unfortunately (or, fortunately) for us, I think our Kitfoxes were so well designed that it is hard to see huge improvements with mods that may affect other aircraft designs very significantly. Or at least that's my take on it.

But I do want to comment on VG's: For anyone installing them you need to remember that VG's make the aircraft more controllable up to the point it stalls, but when it does stall it typically happens all at once as the wing is totally done flying then. Unfortunately, that means you don't have any real advance warning before finding yourself in a fully developed, deep stall. So for me, I'm admittedly not a real huge fan of VG's unless I can get a much lower stall speed benefit from the installation (and I've never experienced much VG benefit on a Kitfox).

Regarding the numbers for making a turn back to the runway; I don't know if anyone here can give you the numbers asked for as there are just too many variables in our Kitfoxes. The numbers can only accurately be determined in your own Kitfox by practicing with it at altitude as I suggested earlier in this thread, so you are prepared if you ever do have an engine failure. I suppose that might sound a little like I don't want to answer the questions directly, but I'm doing that intentionally because I wouldn't want anyone to hurt themselves in an engine failure situation they never practiced and only remember the discussion here where I was making reference to a very different Kitfox than what they own. I will however throw out one number I have used a few times that seems rather universal in the Kitfox and Avid / Highlander design - 60+ mph is a good general glide number, but be prepared to increase that as you get close to tbe ground so you have enough speed to flare. These are docile aircraft that glide exceptionally well, but if allowed to get too slow the high lift airfoil can develop a really high sink rate. So carry a few extra mph for the wife and kids

Engine failures in the bush flying environment? Well, that is a really huge, difficult subject. There is no good answer in my opinion as to what one should do unless we knew all the details of the situation. Best answer, train with Paul L. at Stick & Rudder. He'll stand the best chance of preparing you for a tough situation in the bush.

But I do have to say this, if I had to have an engine failure on takeoff in the bush, I'd prefer to be in an airplane like a Kitfox. Not only will it fly and land slower than many other aircraft, it also will out turn just about anything flying. A Kitfox is very nimble & agile, which is a huge advantage in a bad situation. And it has very little inertia compared to many other bush planes that typically weigh 2 or 3 times more. Plus the pilot and passenger are surrounded by cross triangulated chromoly steel, which is highly regarded for crash survivability not only for aircraft, but also race cars.

That's a lot of typing to be so vague, but I hope it helps to answer some of the questions asked.

[Ramos]

I know less than just about anyone here. I am just smart enough to know that the last post (#37) is not at all evasive. What it is, is chock full of wisdom that should be taken to heart!

[jamesbdunn]

...train with Paul L. at Stick & Rudder. He'll stand the best chance of preparing you for a tough situation in the bush.

Thanks, thought I'd drop in what I found about Paul L.

http://stick-rudder.com/index.php/ct...t-menu-item-13


So VG's remove the perceptible feel of impending stall? I had no idea they did that. So a stall indicator device becomes necessary if planning to operate near stall conditions, if using VG's?

Or, is there still sufficient indication of impending stall?

[av8rps]

James,

I like what the video below shows about the benefits of installing VG's on a Wheeler Express aircraft, as the Express benefits significantly from VG's. So in that case I am all for installing them. You will be able to land much slower, much safer than without VG's. A 200 knot aircraft that stalls at 40 knots is certainly impressive;

http://www.bing.com/videos/search?q=...8181&FORM=VIRE

And while I have not found a great benefit from VG's on any Kitfox I've ever flown, here's a really great video of an early Kitfox with VG's where the poster claims he lowered the stall by 5 mph with the addition of VG's. I've never seen that, but maybe the planes I flew didn't have the VG's in the most advantageous position? Take a look and decide for yourself. And make sure to read his comments;

https://www.youtube.com/watch?v=bIsWseMbDQU Wing without VG

https://www.youtube.com/watch?v=gor7LhsAILs Same wing with VG

Now I personally didn't see a lot of difference between with and without, as the pilot never let the stall fully develop in either video. And frankly, I don't believe we will ever see much improvements with our Kitfox wing as it uses flaperons and that makes a huge difference when talking about controllability and stalls. A good example is that the Highlander wing (same as early Kitfox airfoil basically) benefits greatly from VG's. Why is that?

Simple, because the flaps and ailerons are attached to the trailing edge of the Highlander wing, so they are affected immediately when the wing begins to stall.

So now compare it to the Kitfox wing with a flaperon that is flying in its own clean air under the trailing edge of the wing. Even with the wing stalled the flaperon isn't. And in fact, the flaperon is not only adding control authority when a normal aileron would be ineffective, but it also is providing some additional lift on the trailing edge of the wing where it tends to automatically reduce the angle of attack of the wing while also lowering the nose of the aircraft, which all helps to get the aircraft flying sooner. So in a nutshell, when the wing does finally stall on the Kitfox the recovery is going to be quick. And that's always been my experience in these airplanes. They typically will be flying again before the nose gets below the horizon. At least that's my take on it after flying these type of planes for decades, and owning both a Highlander and a Kitfox.

That tuft testing video of the Kitfox does a really good job to prove that the Kitfox has an extremely gentle and easy to recover from stall, whether VG'd or not. So again I'm not so sure we really need any VG's on our planes. I tend to think putting VG's on the bottom of the tail is the most beneficial thing to do with a Kitfox, as losing elevator authority is probably one of the more obvious areas we could help improve if we want to land slower. But maybe I'm wrong? Maybe others have learned how to better place the VG's on the wings and are seeing more benefit from them? If he really lowered stall by 5 mph as he claims, even though nowhere near as significant as the Express, 5 mph is still pretty good.

I'm admittedly pretty old fashioned and believe in flying by attitude and by the seat of my pants. I prefer flying a Kitfox that way as I think it is more fun. So I tend to like my Kitfox just the way it is. But for those that want to max out their Kitfoxes short field capabilities, maybe VG's are still worth it? But if I were to add VG's and planned to max out my Kitfoxes short field abilities (read as flying super slow close to the ground) I would for sure install a very accurately calibrated (to my specific Kitfox) angle of attack indicator so when I wanted to fly close to the stall I would know exactly when to expect it to happen. You do not want to learn unexpectedly that you just stalled when you are at tree top height above the runway.

With all that said, I'm never so proud to admit I might be wrong about any of this. So if others are seeing more benefits from the installation of VG's on their Kitfox than I know of, please chime in on this subject. There have been a lot of advances in aircraft design over the years from those willing to experiment. While I typically tend to fly my airplanes in a stock condition and work to better improve my abilities to operate it better, that doesn't mean we can't work better to improve the pilot and the plane.

Ramos,

Thank you for the kind words. Sometimes when trying to explain some of these things I feel like I might need to put on my flame-proof suit. It's nice the group here can have productive discussions without anyone feeling a need to defend themselves. That is not always the case when on many other forums...

We have a great group here

(note: Vg's on Kitfoxes have been discussed before here. Check it out at http://www.teamkitfox.com/Forums/showthread.php?p=49166 There is some really good additional info with testimonials and results there)