Angle of bank and stall speed

4 Answers

1. Best Answer
   
   

   
   

   EAD on Feb 24, 2017

   I think there is a fundamental misunderstanding about what a stall actually is. A stall only occurs when the wing exceeds its critical angle-of-attack. This can occur at any indicated airspeed and at any pitch attitude.

   Since most aircraft do not have Angle-of-Attack (AoA) indicators we have to use our airspeed indicator as our “substitute”. What we know as “stall speed” is therefore just the indicated airspeed the wing will exceed the critical angle-of-attack, but only in straight-and-level flight.

   When you bank the aircraft to turn, you are converting some of the vertical component-of-lift into a horizontal component-of-lift to pull you around. Since there is less “upward” lift than when you started the turn, you will start descending and will need to pull back on the yoke/stick to increase the AoA and generate more lift to keep from descending.

   Your indicated “stall speed” will be higher than normal since you already have a higher AoA to maintain altitude in the turn (vs straight-and-level). For proof of this, ask your instructor to demonstrate an accelerated stall and watch the airspeed indicator.

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   Tailwheel on Mar 03, 2017

   I agree with EAD, and would further comment that we do in fact have a better AoA indicator substitute than the airspeed: I submit the position of the yoke (or stick, if you\’re fortunate enough to be flying an aircraft so equipped) is an excellent indication of AoA.

   The yoke/stick controls the elevator, and the elevator controls AoA

   Hold the yoke in the mid point of its fore and aft travel, aka \”neutral\”, and AoA will be neutral. You will have zero induced drag.

   Hold the yoke part of the way aft, and your AoA will be positve, but usually not in excess of the critical AoA. This positive AoA will result in some induced drag.

   Hold the yoke ALL the way aft, and – unless you\’re out of CG – you will be stalled. This is largely independent of pitch attitude or angle of bank.

   The further aft your yoke is, the closer you are to the positive critical AoA. The further forward the yoke is, the closer you are to exceeding the negative critical AoA (eg: when pushing from inverted to enter an outside loop).

   When banked, in a level turn, you will notice the yoke has to be held further back to hold the nose up. Provided you added a little power, or just got lucky with the air currents, your speed may not be any different from when you were straight and level, but the position of the yoke is telling you that you are closer to the critical angle of attack.

   ALWAYS be mindful of the position of the yoke. In the middle of fore/aft travel, you\’re safe. The further you diverge from the middle, the more induced drag you have and, eventually, if you pull or push the yoke too far, you will not only be experiencing a lot of drag, but you will also be stalled.

   Matt Crane
   ATP (E145, BE300)
   CFI/CFII/MEI/AGI
   etc…

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   Lemontree on Mar 04, 2017

   Thanks Tailwheel. I think your answer is very practical. But I’ll have to disagree with you on one point. You said that when the yoke is in the neutral position, the induced drag is zero, but that isn’t true because there’s always induced drag as long as the wings generate lift.

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   Brian on Mar 14, 2017

   I love these discussions. There isn’t a false statement by the posters question or the two replies. Somehow, however, the connection was lost.

   Three important factors stand out:

   1) Stall happens at critical AOA
   2) A turn does not mean doesn’t result in stall speed increasing if you’re willing to sacrafice altitude.
   3) Most important: Stick position directly correlates to your main wing AOA.

   Tailwheel did a great job explaining this, but I think you may have misunderstood him when he said “neutral point.” The neutral point is what an aerodynamicist would call the zero lift AOA. Aerobatic pilots use the term to describe the point where you place the stick to hold a vertical up or down line. Since, in this case, you intend on flying a vertical path any lift will cause you to fall off your perfect vertical line. In other words, you place the stick in the neutral (zero lift) position and you can hold your line. You might know this as the point where you experience zero gravity in a push over or parabolic flight.

   Long story short – neutral point = no lift AOA = no lift = no induced drag. 😉

   Now that we have cleared that up you should go back and put more focus on tailwheel’s discussion of stick position. This is the key to understanding your risk to stalling an airplane. And he explains how to do it with stick position very well.

   To give an extreme example – If there is no requirement to hold altitude then you can pull a plane to 60 degrees nose up, bank it to 90 degrees, push the stick to the zero lift (neutral point) and it will fall off the top into a dive without ever stalling. In fact, the maneuver the hammer head is done in much this way from a 90 degree up line.

   What you need to know is bank as steep as you want, but don’t pull more than 1G in that turn and you’ll still be subject to the same 1G stall speed you always were. Or, in the case of a Cessna, never let your knuckles pass the door hinge and you won’t stall. Learning to feel your G-load, namely its relative position to 1, and how to understand stick position is a far too often overlooked item in a pilots training. It’s why every pilot should train aerobatics after private. 😉

   If you want a demo and live near NJ feel free to email me and we can go show you.

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