Series 5 Tailplane stall

[t j]

I'v been wondering about this tumble since it was first posted. It seems to be the first, or first ever reported anyhow, so very rare. This airplane has balast in the tail to compensate for the extra weight in the nose. In other words, weight at the extreem ends of the longitudinal axis.

Weight at the extremes alters the moment of enertia. The moment for weight and balance purposes is calculated by multiplying arm times weight. Not readily apparant is that moment of enertia is arm squared times weight.

A small weight with a long arm can significantly alter the enertia.

When the flap handle is pulled up the nose pitches down which started the weights in the nose and the tail to swing around the center of gravity. Could the enertia been too much for the control surface...stab trim and elevator...to overcome?

The flap overspeed theory makes good sense to me. Maybe the extra weight at the extreme ends of the fuselage compounded the effect in this particular airplane???

[n85ae]

The IO-240B install already has the battery in the tail, I added 10 lb.s to
that. The plane did not pitch over when I applied the flaperons. It was
completely stable. It was shortly after I applied them (5+ seconds I'd
say).

So it wasn't that I applied flaperons and tumbled. I applied flaperons, and
was flying along stable and then wham it tumbled forward.

There was no warning, no wobbling, no twitchy stick, the nose just dropped
really suddenly.

Jeff

[SkyPirate]

Jeff,.. what took place ,..even if the plane is well balanced,..it would have still happened , flaperons,..ANY plane with flaperons,..kitfox..mini max..,, it doesnt matter,..( a full length control surface on the main wing)
because your pitch atitude and decent rate,..and I'll bet they were close to the same ,,..forward speed versus decent speed,..
you basically entered a downwind for a landing behind a larger plane ..the larger plane being your main wing the smaller plane the tail.
It's like I had said earlier if you fly back through an aerobatic manuevers wake ,..only you didnt fly through it,..your tail was flying in it,or not flying is a better example,.. until you cleaned up the disturbed air ,..which you did when you zero'd the flaperons,.. you had said you were worried about over stressing the plane when you pulled out ,.that indicated to me your decent speed was very close to your forward speed,..and when you lost the tail authority she actually went inverted ..( 2 G's inverted feels like a truck hit your butt pushing you up out of your seat)
As I mentioned before it's the same as doing a loop,..and you fly back through the wake,..with exception,.. with a loop you fly through the wake not with it,
with the flaperon at 22 degrees your main wing becomes the elevator if the tail is nulled,..you didnt stall the main wing ..you stalled the tail with your decent rate and disturbed air from the flaperons working together which hit the tail.
BUT ..you corrected it when you flattened the flaperons which cleaned up the disturbed air ,..which zeroed your elevator/main wing,..which gave control back to the tail,..so ..now ..what are we going to do for our next aerobatic manuever? ( and you said you didnt do aerobatics in your kitfox lol)

what was in your favor ,..altitude,..knowledge,.. and a spare pair of shorts ha ha

Chase

I'll add this ,..if you did the same thing in a conventional winged aircraft,..a cessna for example ,..and you gave any amount of aeleron during the tail stall,..the higher aeleron side will act like a brake,..the lowered aeleron side would give more authority to the flap on that side ,.the end result would be much worse,.

[BigJohn]

Jeff,

Excellent information on your part to possibly prevent someone else not coming out as fortunate as you. And the expert comments from others is very Valuable.

I don't believe that I read any where in the comments about your Elevator, i.e. the 5 which I fly and tail wheel has a smaller elevator than the 7 and by a significant amount, I early on noticed that I did not have what I thought was enough elevator authority is some situations expecially when I had possibly interupted or less air crossing the Horiz Stab. So Installed the Series 7 elevator on the 5 and it made a significant difference.

With you having more nose weight with your engine and your over all empty weight more than 150lbs heavier than my 5 and if you had the smaller elevator It is possible that with all the other factors just one more factor i.e. small elevator could have added to the issue. You may want to check on the larger elevator, like I said it made significant improvements on mine.

[n85ae]

I believe my Series 5 has the larger elevator, I think they switched over 1-2
years before mine was kitted.

However I'm not positive, I can measure it next time I go to the airport. What
are your dimensions?

[t j]

Okay, that makes my tail and nose weight enertia theory unlikely.

[SkyPirate]

thats a good find jlotty,. but with the cesnna's flaps being only part of the the control area,..not like the kitfox or any other flaperon plane. it being the complete control area,.. with the cessna,.. the flap vortices also make the nose pitch up due to the rotation of the vorticy,..right flap from the rear view counter clockwise ..left flap vorticy from the rear view clockwise,.. hitting the tail surface pushing it down,.. the larger vertical area helped with the adverse reaction of slipping/crossed controls at slower speeds ..at a higher speed the wash would engulf the whole tail nulling it out ,..hence the max speed for 30 degrees flap,..if exceeded which then makes the higher aeleron side work like a brake and the lower/down aeloron an added surface to the flap,.. what happens is now your plane will pull hard to the side the aeloron is up on until the tail swings out of the wash,..then it snaps back the other way violently,..the faster the forward speed the faster this reaction happens,..slower speeds can result in a flat spin
I'm no expert either ,..but aerodynamics are aerodynamics
it's a constant battle to have the favorable effect out weigh the negative even in life

Chase

[CDE2FLY]

Went flying tonight to explore the 22 degree flap dilemma:

Model 7, 914, CG middle of range, built in gap seals, fuel at 1/2 tank

Started at 10,000 feet and began a decent with 11 degrees of flaps. After I stabilized at 75 mph, pulled in 22 degrees and pushed the nose further down to build speed....80 mph....stabilized for 30 seconds....pushed nose further down....speed to 85 mph....stabilized for 30 seconds (1350 fpm decent) and recovered to level flight with 22 degrees of flaps still deployed. I had full control in pitch and roll although pitch forces through the stick were rather high.

I then tried forward slips in both directions with 22 degrees of flaps and 85 mph indicated. There was a slight buffeting through the stick but the slip was really extreme as was the rate of decent.

Although I wasn't sure what to expect, I do feel better knowing there doesn't appear to be any handling gremlins hiding in N725CE.

[n85ae]

I'm glad people are testing their planes, but be really carefull!

It might be related to my heavier motor, or the combination of that plus the
variable incidence tail. The 7 has the fixed tail I believe. Anyway I might just
have been lucky and hit the exact right combo.

My planes. getting a mechanical block for the 22 degree position this weekend
no matter what. I never needed the 22 degrees in 7-8 years flying the plane,
and one of the few times I ever used them this happened ...

Regards,
Jeff

[CDE2FLY]

Yes...I should have mentioned, mine is a fixed tail with manual trim. other Model 7s have the electronically adustible tail based on production date and/or selected options. As you indicate, the key will be to figure out what combination(s) result in what you experienced....I too would encourage a very careful approach to any flight testing. I stayed plenty high and had ahold of the flap handle the entire time just in case things started to go badly.