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Dropping a wing during stall - causes?

With the TKS installed, the TB20 drops the left wing during a stall.

It is quite a decisive break. Easy to recover from (in a few hundred feet) if you expect it… You have to be deep in the stall; yesterday the IAS was about 57-58kt which is close to book.

I can think of two reasons for dropping the left wing:

  • the TKS panels do not extend over the light cluster which is only on the left wing
  • there is a left-right imbalance due to the TKS fluid tank under the luggage compartment floor, on the LH side

I normally un-balance the fuel tanks deliberately to compensate for (a) me flying alone and (b) having the LH side heavier due to the TKS. This is easy, by watching the aileron positions when the ball is centred (if on autopilot) or feeling which way yoke L/R pressure is required (if flying manually).

I wonder if anyone might have specific ideas. I think perhaps e.g. @pilot_dar might have come across this during his certification testing.

Administrator
Shoreham EGKA, United Kingdom

Passing wind during a stall maybe stress related?

Tököl LHTL

Spelling error fixed.

Administrator
Shoreham EGKA, United Kingdom

Prop rotation slipstream effect: left wing often stalls first

United Kingdom

Slipstream and p-factor both result in left yaw.

LPFR, Poland

However, this happens only after the TKS installation. Before, there was no obvious wing drop. Also this is a power-off (engine idle) stall.

Administrator
Shoreham EGKA, United Kingdom

Use rudder to hint the direction of spin ;)

LPFR, Poland

That should depend on Prop rotation no? Coriolis effect maybe (if one believes it impacts toilet flush just a myth )? one hand/leg longer or stronger than the other?

Anyway you can fly on RHS and/or empty TKS and you will get a sensible answer !

Ps: the most scientific explanation I got as to why I was flying left wing down most the time on a tandem aircraft was due to my eye glasses not being aligned as they were tilted to the right (this was pointed to me by another pilot), seems to work when I changed them

Last Edited by Ibra at 23 May 21:49
Paris/Essex, France/UK, United Kingdom

Probably slightly changed the airfoil aerodynamics on the left one and it stalls a little earlier. I wouldn’t worry about it much, but good to keep in mind.

Peter wrote:

I can think of two reasons for dropping the left wing: the TKS panels do not extend over the light cluster which is only on the left wing there is a left-right imbalance due to the TKS fluid tank under the luggage compartment floor, on the LH side

A rectangular plan form wing should stall at the root before tip. Washout and using different cords is even more effective at this. My guess is not having the panel extend out onto the tips has changed this so that tip stalls closer to time the root stalls. Enough to make a difference to the flap up stall characteristics. I am guessing the flap down stall characteristics are unchanged with a definite wing drop as before? Have you tried stalling weight balanced slightly heaver on the right side?

Last Edited by Ted at 24 May 08:03
Ted
United Kingdom
30 Posts
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