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Overbanking tendency

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Overbanking tendency

Old 26th Oct 2021, 09:43
  #21 (permalink)  
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Hi Wiggy, I agree with you. Just to end the question, I would paraphrase freely Sikorsky's famous bumblebee quote: we, pilots, turn the aircraft without caring or knowing how lift behaves on the wings.
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Old 26th Oct 2021, 09:57
  #22 (permalink)  
 
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The difference in speed between the inner and outer wings will disappoint. In a 40' span aircraft at 80kts in a Rate 1 turn the outer is (averagely) going 0.62kts faster than the inner. Roughly 0.8% difference in lift.

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Old 26th Oct 2021, 10:20
  #23 (permalink)  
 
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It is actually a bit over 1.6% - lift is the speed squared, but it doesn't do much difference in your example. In a glider with 50' - 80' span and a speed of 35 - 40 kts it is however very real, but again, it isn't a problem, you see the bank increase and the yaw string go sideways, and correct with a bit of rudder and opposite stick.
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Old 26th Oct 2021, 11:12
  #24 (permalink)  
 
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Oops. Schoolboy error... and I knew there was something wrong as I looked at my scribble, but couldn't see it for looking.

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Old 26th Oct 2021, 11:27
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Another reason to have pilots begin on gliders before moving up the magenta line.
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Old 26th Oct 2021, 18:29
  #26 (permalink)  
 
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Called spiral instability which most aircraft suffer from except paragliders at relatively low bank angles..above roughly 40 degrees they go into a locked in spiral with nasty outcomes.
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Old 26th Oct 2021, 19:18
  #27 (permalink)  
 
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It's a curious mix of the original poster's "outer wing faster", vs. the dihedral which will tend to return things to wings level. Other things affecting it are the size of the fin and directional stability and even the wetted area above and below the CofG.

Last edited by Deskscribbler; 26th Oct 2021 at 21:11.
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Old 26th Oct 2021, 20:43
  #28 (permalink)  
 
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The difference in wing speeds, as a percentage of the turn radius becomes larger the more steeply you're banked (and the turn becomes smaller.) But this reverses past a certain point, where at very high banks, the wings are nearly on top of each other, and the relative difference shrinks again.

This is only one aerodynamic effect, and there are other minor ones that, as people above have said, there's no pressing need to understand, and can be simply counteracted by use of the controls while maintaining the desired bank, and essentially treated as turbulence or other aberrant minor upsets. For example, is the long-tail effect, where even though the CG of the plane (and the ball, or IRS) is perfectly balanced on the path of the turn circle, the vertical stabilizer is flying outside the circle and sees a relative wind coming from the outside, and therefore produces a yaw (and roll) toward the outside.

Dihedral, by itself, has nothing to do with this though. There is no physical process by which the projected wing area over the ground, effects the amount of lift. Dihedral effect is a response to sideslip and not bank, and will therefore only act on the plane if sideslip occurs.
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Old 26th Oct 2021, 21:21
  #29 (permalink)  
 
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Sideslip does build during a spiral dive though? The spiral tendency being partly a balance between directional stability reducing sideslip and the dihedral trying to use said sideslip to roll more wings level? So an aircraft with more directional stability will have a greater spiral divergence tendency (all others equal), and an aircraft with more dihedral less of a spiral divergence tendency (all others equal)? Worst being an aircraft with strong directional stability (big fin) and lesser dihedral?
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Old 26th Oct 2021, 21:46
  #30 (permalink)  
 
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Sideslip may or may not develop, that's a function of a host of external factors, as well as the rudder response (or non-response, or over-response) to them. Any effect that the dihedral has is a result of this sideslip, and not of the bank angle. If you're over-ruddering the turn (ball to the outside) then dihedral will tend to increase the bank, not return it to level.

Anyway, there's a common misconception of dihedral's function (It's looking now, that that's not what you meant, but the poster a few replies from the top certainly did with "The inner wing is flatter to the airflow") that says that the inner wing's bigger projected area over the ground, somehow translates to an aerodynamic significance. And this is not true: you can have a plane with (ridiculously exaggerated for effect) 45 degree dihedral at 45 degrees of bank, so the inner wing projects 100% of its area over the ground, while the outer wing projects 0%; and as long as there is no sideslip (ball is in the middle, airflow is straight down the fuselage) this fact has zero bearing on any force on the airplane.
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Old 27th Oct 2021, 02:11
  #31 (permalink)  
 
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All aircraft are different.

Fly the output (ie make it do what you want).

Some types need opposite aileron, others don’t. Except in a stall turn, then they all do.

(standing by for incoming………)
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Old 27th Oct 2021, 02:32
  #32 (permalink)  
 
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Incoming..symmetrical airfoil..if you get it right!
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Old 27th Oct 2021, 02:35
  #33 (permalink)  
 
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Using aileron in a stall turn can induce a spin very nicely and quite quickly . A cruel Method to introduce spins to newbies
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Old 27th Oct 2021, 04:12
  #34 (permalink)  
 
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All aircraft are different.

Fly the output (ie make it do what you want).
That's certainly been my experience.

Not to put a dampener on the discussion however - it's all been most interesting - and informative. May it continue please ...
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Old 27th Oct 2021, 05:37
  #35 (permalink)  
 
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I definitely have seen this tendency when doing a steep turn. I don’t want to say that all light aircraft have this characteristic, but I have seen it.

I happened to read the other day that had a description about this phenomenon.....

Proficiency: Take it to the bank - AOPA

"Overbanking tendency. In a coordinated turn, the aircraft moves along a cone so that, in any given amount of time, the outer wing moves faster through the air than the inside wing. The differential velocity means that the outer wing, with more lift than the inside wing, tends to roll the aircraft more deeply into the turn—so it is necessary to hold aileron against the turn. The wider the wingspan, the more noticeable the overbanking tendency becomes, so glider pilots know it well."

There is a bit of a diagram in the article for explanation.

Last edited by punkalouver; 27th Oct 2021 at 05:55.
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Old 27th Oct 2021, 06:47
  #36 (permalink)  
 
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fitliker

Must be another aircraft differences thing then because it was very much needed on the JP
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Old 29th Oct 2021, 00:53
  #37 (permalink)  
 
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Have we figured it out yet?
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Old 29th Oct 2021, 02:00
  #38 (permalink)  
 
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I don't think it can be figured out before an accurate sideslip angle for the noted symptoms is given.
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Old 29th Oct 2021, 11:16
  #39 (permalink)  
 
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I can hold a 45deg banked turn in my glider at ~55kts, and due to the span the outer tip is going some 33% faster than the inner one. It has always amazed me that there is very little, if any overbanking tendency; I suspect there are many other things at play, not limited to wing flex, fin/fuselage effects, rudder deflection, etc.

I agree with Locked Door about flying the output - apply control inputs to achieve your desired attitude...
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Old 29th Oct 2021, 12:55
  #40 (permalink)  
 
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One fairly important thing not mentioned so far is that the AoA of the inner wing is higher, and to an extent will restore the lift lost through lower speed.
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