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3 Answers

Aerodynamics on Slowflight.

Asked by: 845 views Aerodynamics, Commercial Pilot, General Aviation, Private Pilot

I first would like to say thanks to Skyfox, and Brian for their help and assistance with my previous post on Spin Aerodynamics.

They were all helpful in understanding and greatly detailed.

I just wanted to verify the ideas on slow flight when we use more of rudder than aileron. So,  "in a slow flight turn, for a given amount of rudder the aircraft needs much less aileron to put in the needed amount of roll, possibly even requiring opposite aileron to prevent excessive roll."

Is this because the airplane might enter into cross controlled stall and spin?

I read somewhere in the book saying that cross controlled stall involves aerodynamics of sweepback design.

Connor.

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3 Answers

  1. Best Answer


    Brian on Nov 11, 2016

    It’s not that more rudder is needed, but that rudder needs to be used more presicely. Often times, especially when a turn to the left is initiated, pilots use too much rudder and then fail to establish the correct amount of rudder to keep coordinated. Where ever you had the rudder when you were straight and level is where it needs to be when in a level turn. Now if you slow down even a little more and don’t increase your rudder you’ll be uncoordinated again. Try flying extremely slow, stall horn blaring, and use only your feet.

    This same concept can be seen on a typical Vy climb. If you need ailerons to keep the wings level you are uncoordinated. Try trimming for a perfect Vy and then, with hands off the controls on a smooth day, keep the wings level with the rudders. After a few moments, when you think you have the correct pressure and all is stable, check the ball; bet you it’ll be perfect.

    The same goes for slow flight. There isn’t an over banking tendency, there is a piss poor rudder use tendency.

    —-

    Yes a side slip acts just like a forward or aft swept wing. This is due to the chord length being increased when striking the wind at an angle. For the forward wing (low wing in a slip) the wing tends to stall at the root before the tip. Vice verse for the wing on top that is aft swept. To understand it better check out Aerodynamics for Naval Aviators and look for information on wing sweep.

    For a better visual try taking a piece of paper and folding it in half once so that it looks like a typical Hershey bar wing. Trace some lines for the ailerons, flaps, and fuselage. Next, with a different color pen, draw lines about a half inch apart straight from leading to trailing edge. Now flip it over and repeat, but this time rotate the paper clockwise so the left wing is at the 10 o’clock position and the right wing is at the 4 o’clock position. Now trace lines diagonally from leading to trailing edge, parallel to each other and a half inch apart. Look at the difference between the forward swept wing (left) and aft swept wing (right).

    Compare the two sides and refer to the first paragraph.

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  2. connor on Nov 12, 2016

    Thank you very much Brian, I read the page 307~ 311 and it was a lot more helpful.
    Now I understand the concepts of sideslip and sweepback design and their principles.

    Let us say that I am turning left with my left rudder input(plus engine torque effect + slipstream etc..) and maintain coordination, with aileron and rudder both.
    By mistake, the plane enters stall with up right aileron and down left aileron.
    As a result, right wing swings down and left wing rises, increasing AOA between relative wind and alieron.?
    I know, from the previous discussion that we put the dynamics on this matter and talked about the other factors, which I am able to analyse and understand, could you give me ideas on above matter including ‘blanket effect’ caused by the fuselage?

    In a meanwhile, I will go through the Naval aviator’s aerodynamics book again to see if I missed anything out.

    Thank you ,

    Connor.

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  3. Brian on Nov 14, 2016

    You’re confusing yourself with the aileron. You started with a coordinated left turn (left aileron up) and somehow turned that into a right aileron up stall with the left wing rising (right roll). I’m not sure what you’re trying to ask there.

    Blanket effect only exists when a side slip exists. All it means is that the fuselage disrupts, or blocks, the air passing over a portion of the wing. It’s no different than when you shield your cell phone mic from the wind. In this case your hand would be creating a blanket effect on the cell phone mic.

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