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Dropping a wing during stall - causes?

Is the ball centered when you are doing slow flight? Is it possible your TKS installation affected your slow flight trim?

Also into wind keeps you easily inside the box but wind corrections for aeros goes beyond perfection (so I just leave that to judge/observer)

On centred ball/wing down, as long as ball is centred what the wing is doing wtr to horizon has no influence on wich wing drops first, tough a drop on the upper wing is “self corrected” by reduction in stall speed (even with wrong ailerons inputs it will catch in a stable fashion) while a drop on the lower wing is highly unstable when you touch ailerons by mistake.

I tend to slightly lift the nose toward the horizon using rudder while pulling/pushing stick forward this seems to make assymetric stall less surprising in terms of speed or at least predictible as where it goes but in practice few aircrafts will bite that hard on wing drops…

Last Edited by Ibra at 24 May 13:58
Paris/Essex, France/UK, United Kingdom

Is the ball centered when you are doing slow flight?

Yes, definitely.

Administrator
Shoreham EGKA, United Kingdom

I remind a similar report from here

I’ve not notice much impact on performance but can get a wing drop in the stall now which I didn’t before.

There definitely is a difference if you fly head on into the wind or if you fly with a crosswind in gusty conditions. It has to do with the rotational components of the gusts. It probably has no effect on that wing drop though.

Just speculating here. The leading edge on a wing is often a strong structural member. A highly curved aluminium leading edge sheet has a lot of rigidity. Together with the main and aft spar (and the skin), it is what constitutes the torsional stiffness. On many homebuilts you are not “allowed” to do anything to the leading edge, except at the very tip, where you can cut holes for lights typically. Those TKS panels are likely to change this torsional stiffness characteristic, in particular when the wing is loaded. This in turn could make the wing twist slightly different than before, one wing more than the other.

When the panels were mounted, were they mounted with simulated 1G, and/or with the wings fastened in a jig, or with the wings hanging freely?

The elephant is the circulation
ENVA ENOP ENMO, Norway

The TKS panels were mounted with the aircraft on the ground

I doubt the wing stiffness is changed much. The TB20 has big spars, and some of the panels are riveted while others (over the fuel tank areas) are just glued, with maybe 2 rivets holding one end.

I think with factory TKS installations they do it with the wings off the aircraft.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

The TB20 has big spars

That doesn’t necessarily mean anything regarding torsional stiffness. Main spars takes bending and shear due to lift. The torsional stiffness constitutes what’s in between the spars. The leading edge (the whole section from the main spar and fwd) is the main “torsion box” so to speak. Change this ever so slightly on each wing, and the wings will become asymmetrical when loaded. You have put on a slab of metal? along the leading edge where before it was thin skin.

The exact same principle is used on (well designed) fixed pitch propellers of wood or composite. They change pitch with fwd thrust, often as much as 4-5 inches.

IMO the wing drop is structural, it doesn’t take much (relatively speaking) to twist a wing enough to offset a wing drop. If it was my plane I would also test it at Vne to see of it is free of aileron flutter.

The elephant is the circulation
ENVA ENOP ENMO, Norway

It is possible.

However a left wing drop has been reported after other installations.

My reason for starting this topic was to find out general reasons for a wing drop, not specifically TKS related.

The PA38 was dreadful in this regard, although one could learn to keep the wings level with the rudder, during the stall.

Administrator
Shoreham EGKA, United Kingdom

Is there a particular reason for concern?

How predictable was the wing drop before, or was it very difficult to induce any wing drop?

In many ways a predictable wing drop could be argued to be a good thing.

Last Edited by Fuji_Abound at 25 May 10:39

I have only flown one particular SAAB Safir, but old pilots (really old ones) who have flown several of them can tell they are all different. Some fly straight, some requires a bit of rudder, some drop left wing, some right wing and so on.The Safir drops the wing rather violently, almost 180 degrees, but can be controlled with rudder nonetheless (and some practice). All due to minute differences when they were build. I don’t think it’s one particular reason, but a bit of anything, and it’s a normal thing. It’s just a matter of having the elevator authority to increase the AOA enough, and one wing will drop first. It’s just like two drops of water, one will go first, but which one is not an easy thing to say.

Also the Faeta we got, drops a wing. It starts buffeting (tons of warning), stretch it longer, and it violently drops the right wing. It’s always the right wing, so it must be something that is not entirely symmetric. Maybe another specimen drops the left wing? In the rain however, it does not drop the wing. It has a laminar profile, and the stall speed is increased by 50% at least. The drops may be so small you don’t even see them from the cockpit. Then it just mushes like a brick. It’s very much like a glider in the rain, and this must be observed when landing. Too many dead bugs may do the same thing, but haven’t tested that (and never will).

If an aircraft suddenly starts dropping a wing, when it mushed nicely before, then something more has happened IMO. Obviously it cannot handle the same AOA as before. The stall speed has effectively increased. It could be aerodynamic, it could be structural, could be both. Mounting a long slab of metal along the leading edge, effectively changing the foil as well as the torsional stiffness, is a major thing.

The elephant is the circulation
ENVA ENOP ENMO, Norway
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