Series 5 Tailplane stall

[n85ae]

I landed it without any flaperons on a long straight in landing like the wings
were just about to fall off. This weekend will be a very thorough exam.

I'm also removing the trim assist spring, and putting a mechanical block
on the flaperon lever. Some may argue this, but I suspect that without the
spring, or having 22 degrees available it would never have happened.

[jrevens]

I am based at KBJC... been there for 21 years with the first airplane I built. I also learned to fly there in the early 1970's. It's a small world.

A further comment about my experience... my elevator was not just partially ineffective - it was, as I said, as if there was a total disconnect. The stick was floppy-loose fore & aft. The strange thing was that the condition continued, going straight down & close to exceeding red-line, until the flaps were retracted. No other control inputs nor throttle changes had any effect. It evidently stabilized in an attitude/AOA where the tail remained in a stalled condition.

Again, I apologize, as this is not Kitfox specific, but I hope it might be useful in some way.

Hi -

That sounds very similar to what I had happen. Not the kind of thing you
expect. Just one second your flying along, and the next it's "Whoa, what
heck ..."

Where do you fly from? I learned to fly out at KBJC and get out there a
couple times a year.

Regards,
Jeff

[Dorsal]

Not sure how the spring assist could have effected this though I can definitely appreciate preventing full flaps after that experience.

[n85ae]

In my opinion the Spring assist, tricks you into holding more pressure than
you should. That stick force when you pull in the flaperons is telling you
something, which maybe just pulling harder isn't the best solution to. The
spring mechanically pulls for you.

It did not cause what happened, but I think it helped assist me to get in a
place that caused what happened. If that make sense.

Jeff

[n85ae]

I have the variable incidence tail. It works well enough, but is a bit sensitive.
I'll give the plane a solid look over this weekend make some minor changes
as I mentioned and take it out and do some flying. It's always been a very
easy flying airplane with no bad habits until I used that 22 degrees flaperons.

I really never needed them before, so if not using them is all it take to prevent
another upset like that then that's my solution.

I will have to do some thinking about baggage stowage. Just tossing stuff in
the back is not good enough I can say now.

Regards,
Jeff

[rogerh12]

If going too fast with too much flaps is a issue, is there a kitfox "known safe" maximum flap position where one does not need to worry about going too fast with flaps extended? That is to say, the plane would reach Vne anyway before the flap down angle would present any additional elevator control issues due to speed. Sort of a , no-wories-mate flap angle.

Or maybe you have personal flight experience where you were technically going too fast for flaps, but had them deployed to some degree anyway, with any adverse flight effects.

Roger

[Dave Holl]

Hi all
A very scary moment
Here in the uk we have to limit the flap to the first position.
I would have a good look at the flaperon hangers to ensure no cracks or distortion.
I had an loss of pitch stability event a few years back in my Jodel aircraft where by missmanagement of the fuel, quater in front tank and full in rear with one rear seat pax on slowing up to join the circuit(patten) the stick went very slack in my hand and for a moment I thought the elevator control had become disconnected the aircraft slowley pitched down and eveything became normal! After on the ground I checked the weight and balance and it was right on the aft limit.
I must say I was glad to be on the ground
Dave

[av8rps]

After flying a multitude of Kitfoxes and Avids for over 25 years, and doing just about anything you can imagine with one, I believe that this situation was likely caused by a tail stall, and not the flaperons.

Unlike many that think our flaperons are useless, I use flaperons for every takeoff and landing (I've adjusted my flaps so I get nearly 30 degrees of throw). And yet, I've never experienced anything that I would say is unusual or scary.

Here's just one example of the extent I've tested my flaperons; I recently blew out (!) both back quarter windows on my Kitfox amphib while practicing SEVERE full flap slips in both directions in an effort to figure out how to land my speedy little amphib shorter. (I began the testing at high altitude to be safe. I didn't want to learn at low altitude that my severe fuselage angle combined with a slow airspeed, a huge sink rate, and totally uncoordinated flight would result in something like a snap roll). But even in that situation, the Kitfox was solid and stable.

Oh yeah, I have also mistakenly had my flaps on as high as 100 mph and never had an issue. Once the flaps actually took themselves off from the air pressure caused by the speed.

So I think you hit the nail on the head when talking about the tail stall.

Thank you for sharing this information Jeff. It is very good for all of to know. And if it happened to you, it can happen to others.

[CDE2FLY]

Jeff - really glad you were able to share your experiance....I'm sure we'll all be on heightened alert with regards to the use of high angle flap settings....especially at higher speeds!

Ironically, the night you posted, I had been out flying my Model 7 and although I rarely use the 22 degree flap setting, I had been experimenting by pulling 22 degrees on final (65-70 mph) to determine under what conditions the higher flap settings might be helpful. In the 7, the higher flap setting definitely adds drag allowing for a steeper approach without an increase in speed....helpful if the approach is a bit higher than optimal. What really stands out is how much higher the elevator stick force becomes to maintain the targeted rate of decent (no spring assist in my airplane).

It seems that your experiance is a rare occurance in the Kitfox (thankfully!) which make me wonder if there were several factors contributing in a rare combination such as:

1. Flap setting at 22 degrees above 80 mph...not recommended but if this were the only factor, I'm sure there would be many more similar reportings.

2. Forward CG...the IO 240 adds 100+ pounds to the nose of the airplane as compaired to the 900 series Rotax. Not sure where your CG is but if it's forward, it's not going to help the situation as the horizontal tail has to work that much harder to keep the nose up.

3. Forward wing sweep...the construction manual for the Series 7 (and I assume the 5) calls for a forward wing sweep with the heavier engines to move the center of lift slightly forward to help offset the extra weight in the nose. When I pull in 22 degrees of flaps, there is a pronounced shifting of the center of lift rearward requiring a significant increase in stick back pressure. Can you confirm if your airplane has the forward sweep?

Not sure if what you experianced was a tailplane stall or flap overspeed but based on the infrequent reporting of similar experiances in the Kitfox, I suspect yours may be the result of several combining factors including those listed above.

Thanks again for sharing your experiance with the rest of us and really glad it had a happy ending!

[n85ae]

A couple things:

I don't mind any comments that I exceeded the flap speed, I did BUT not
by a lot.

I have a fairly forward CG, but I also have a ballast box in the tail. I have
for an IO-240B Kitfox a decent CG, because I took the step to add ballast
in addition to the battery. Empty weight is 967

I have the forward wing sweep

My plane is a taildragger.

I almost always three point the plane, and have no issues with elevator
authority with 0-11 degrees flaperons. I don't have a gap seal on my tail
and I don't need it.

I never use 22 degrees for landing. I've only used 22 degree's when test
flying the plane, and normally do not like the feeling. Too much stick
force required, and the variable incidence tail is all the way at the end of
it's range which just makes me not comfortable.

This was the first time I ever used 22 degrees in a fairly steep fast descent

Just want to say one thing, so nobody gets the wrong idea. I was NOT
screaming down like a Stuka and pulling the dive Brake lever. I was just in
a "normal" steep descent. Which normally I'd pull the nose up and slip to
keep the speed from building too high. In this case I was "probably" just
past 80 mph indicated, and pulled in 22 degrees. I wasn't watching it that
closely.

I'm not a timid pilot, but I'm also not somebody who takes chances. I don't
do aerobatics in my Kitfox, or live on the edge trying to see just what I can
get away with in the plane. I've had spin training, but don't spin my plane,
etc. Just want to emphasize this was not during a Chuck Yeager moment
that it happened.

Even IF Chuck Yeager were in the plane, I seriously doubt he could have
reacted any faster than I did. He'd probably just have a lower heart rate
after recovery.

I feel that it's not likely what happened to me to reoccur with somebody
else, but IF it did and you were in the pattern. You would NOT recover
before you hit the ground. I would suggest that 22 degrees flaperon
position "might" be dangerous, and an unrecoverable upset may occur
with no warning.

So I'd say take this as a caution from me, as it did happen, AND in a
flight mode that could EASILY be recreated in the pattern. Like high
on final and a tad fast.

Regards,
Jeff