Significance of 1 Wing higher than the other just before reaching stall speed

11 Answers

1. 
   

   
   

   Nathan Parker on Aug 09, 2012

   “Please explain, aerodynamically: Why, when entering a stall with a banked angle (1 Wing higher than the other), the higher wing will drop once the airplane reaches its stall speed?”

   It doesn’t. As long as the airplane is coordinated, it will usually stall straight ahead. The only times during a turning stall that I’ve seen the airplane roll towards the high wing is when the airplane was in a slip.

   “one of course has to use the rudder instead of ailerons to maintain wings level during stall.”

   Actually, one does not. Quite confusing for the student and unnecessary. Fly the airplane just like normal when setting up for the stall: Maintain heading with coordinated use of aileron and rudder. If one wing starts to drop off, you’re stalled, so lower the nose and apply full power. Dirt simple.

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2. Best Answer
   
   

   
   

   Lucas on Aug 11, 2012

   First of all there is really no aerodynamical stall speed but only a “stall angle of attack” = Critical Angle of Attack. now if one wing is raised it is because that wing has the aileron lowered increasing its angle of attack and thus its lift. so lets say that the critical angle of attack of this airplane is 17 degrees. while banking to the left the right wing would be, lets say at 13 degrees AoA and the left wing at 12. Now if you pitch up the right wing would reach the critical AoA 1 degree sooner than the left, causing it to stall first.

   Lucas
   http://passfaaexams.com/

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3. 
   

   
   

   Nathan Parker on Aug 11, 2012

   During a turning stall, you’re fighting the overbanking tendency, so the wing with the downward deflected aileron is the *low* wing, not the high wing. If the above reasoning were correct, then the airplane would always roll off in the direction of the bank. It doesn’t. I have never seen a turning stall roll in either direction unless the pilot was significantly uncoordinated.

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4. 
   

   
   

   Lucas on Aug 11, 2012

   First lets say I am turning at an angle of 10 degrees and induce a stall what kind of over banking tendency are we talking about here? Are you flying an airplane with neutral or negative static stability?

   Second if my reasoning was correct the high wing would stall, by the way if you are wondering which one is the high wing it is the one opposite the direction of the bank, so the airplane will actually roll off in the opposite direction of the bank.

   Third I have given over 200 spin endorsements during my carear and I can tell you that I have seen airplanes entering spins with the ball nearly centered.

   Fourth I always try my best to help the students with their questions rather than try and find something wrong with the answers that someone else provided.

   That said, no worries. Aviation is full of opinions and 50% of what you learn is from something called “hangar talk”.

   Happy flying to all

   Lucas

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5. 
   

   
   

   Nathan Parker on Aug 12, 2012

   “Are you flying an airplane with neutral or negative static stability?”

   Doesn’t matter. Lateral stability (“dihedral effect”) only kicks in when a sideslip exists. Without a sideslip, the airplane has no ability to right itself from a bank. A ball-centered turn will have no sideslip, so there is no inherent tendency for the airplane to level the wings, so the only rolling tendency in effect is the overbanking tendency. This tendency increases as rate of turn increases, and the rate of turn near the stall is very high, since the airspeed is so slow.

   But none of that really matters. My point about the low wing having the downward deflected aileron is an empirical observation, not merely a theoretical one. A student pilot is capable of verifying it.

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6. 
   

   
   

   JB on Aug 13, 2012

   Side note: Ailerons/spoilers/flaperons, etc. do not remain deflected DURING a coordinated, level flight turn. They are deflected to initiate the turn and again to exit the turn; but they are NEUTRAL during the turn (assuming no aileron trim is used as well). Thats why the control wheel/stick is centered after entering a turn. Otherwise, you would be doing aileron rolls, which not many guys can do during a 360 degree turn 🙂

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7. 
   

   
   

   Brian on Aug 14, 2012

   “During a turning stall, you’re fighting the overbanking tendency”

   Which is the case because each wing is flying at the same AOA in a coordinated turn. Except the high side wing is moving more quickly, generating more lift, and thus requiring what Nathan’s already explained.

   Lucas, unfortunately your boastful retaliation doesn’t make incorrect information become correct. Your opening sentence was the only accurate piece of information in your reply. I know it’s tough to be wrong, trust me I’m a professional at it, but sometimes its worth taking that step back to relearn something we thought we knew.

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8. 
   

   
   

   Steve Pomroy on Aug 15, 2012

   QT: “First lets say I am turning at an angle of 10 degrees and induce a stall what kind of over banking tendency are we talking about here?”

   That depends on your airspeed. Lower airspeed implies a tighter turning radius, and therefore a bigger difference between the speeds of the two wings. This is why overbanking is more pronounced during slow flight.

   —–
   QT: “Are you flying an airplane with neutral or negative static stability?”

   Doesn’t matter. Stability concerns the aircraft’s response to a displacement from a trimmed position (either AOA or slip angle). Overbanking doesn’t require an initial displacement, and if there is an initial displacement overbanking is not affected by it. Overbanking always tends to roll the aircraft into the turn. There is in fact no such thing as a trimmed roll angle (as noted above by Nathan).

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   QT: “while banking to the left the right wing would be, lets say at 13 degrees AoA and the left wing at 12.”

   Where are these numbers coming from?? Why is there a difference between left and right?? If we assume a level coordinaterd turn, there is no difference. In an aircraft with positive lateral stability (i.e. – dihedral effect), a climbing turn will induce a higher AOA on the high wing, and a descending turn will induce a higher AOA on the lower wing. These differences result from the up/down-going airflow and the fact that the two wings are at different bank angles (due to dihedral). Sorry, not sure I can explain it better with words only. This needs a diagram.

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   QT: “Third I have given over 200 spin endorsements during my carear and I can tell you that I have seen airplanes entering spins with the ball nearly centered.”

   The ball doesn’t indicate coordination. It indicates lateral acceleration of the instrument. In unstalled flight with low rotation rates, that is a pretty good (but not perfect) approximation of coordination. We use the ball as a proxy for coordination just as we use the ASI as a proxy for AOA. If you want to see an actual coordination instrument, fly gliders and check out the yaw string. Unfortunately, a yaw string won’t work on a single engine due to slipstream.

   The indication of the ball is worthless during a spin, spin entry, and spin recovery. This is why, if you are disoriented, you don’t look at the ball to determine spin direction, you look at the needle. The aircraft I fly these days has a turn and slip on both sides of the cockpit – one for the instructor and one for the student. They usually indicate opposite one another during spins (the right one indicates ball right, the left one indicates ball left, regardless of the spin direction).

   —–
   QT: “Aviation is full of opinions and 50% of what you learn is from something called ‘hangar talk’.”

   True. And this probably goes a long way toward explaining why there are so many misconceptions in this industry. Hangar talk is only useful if you know to take it with a grain if salt.

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9. 
   

   
   

   Nathan Parker on Sep 01, 2012

   “Unfortunately, a yaw string won’t work on a single engine due to slipstream.”

   Actually, it works fairly well mounted right behind the propeller. The propeller slipstream changes direction with sideslip.

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10. 
    

    
    

    nine on Sep 02, 2012

    Hello,
    Just to have everybody in the right frame of mind, there are many videos on youtube showing wing drop during stalls, especially significant with flaps deployed.

    @ 28 Seconds: http://www.youtube.com/watch?v=rjbcz74XEac

    So base on Nathan Parker’s answer, in that video, the pilot failed to maintain coordinated during establishing of stall correct? Theres just too many answers and i’m just focusing on flying straight then stall, not turning stalls.

    I understand that airplane’s such as Cessna 172 or DA 40 have a slight tendency to wing drop, and its most significant with the Light Sports aircraft (Shorter wingspan).

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11. 
    

    
    

    Nathan Parker on Sep 02, 2012

    “the pilot failed to maintain coordinated during establishing of stall correct? ”

    There’s theory, and then there’s reality. In theory, if you have a perfectly symmetrical airplane and zero sideslip, both wings should stall at the same time. In reality, no airplane is ever perfectly symmetrical and it may well be that one wing will stall before another.

    To flesh out what Steve said above, the ball isn’t a perfect measure of whether or not the airplane is in a sideslip. The ball measures lateral acceleration (acceleration left or right), and a sideslip will accelerate the airplane laterally due to the lift generated on the fuselage. One time it doesn’t work perfectly is when setting up for a power on stall. In this scenario, with a perfectly centered ball, the airplane will accelerate to the left because you have the rudder deflected to the right to keep the nose straight, and the rudder lift will “lift” the airplane to the left. You can see this with a yaw string. Most often, the airplane will roll off to the right. Interestingly, this tendency can be eliminated if you relax the rudder a bit and be slightly uncoordinated. If you had a yaw string, it would be straight, and the airplane will stall straight forward.

    In turning stalls, I’ve never noticed any rolling tendency at all, but I think that this is largely due to the fact it’s hard to get a good stall in a turn. The reason is that you have a reduction in elevator authority in a turn because the airplane is pitching about the lateral axis, meaning the nose is going up and the tail is going down. The tail going down reduces the tail down force, which you have to fix by using up some of your elevator authority.

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