Four Left Turning Tendencies

1. P-factor:
   • Also referred to as asymmetric loading
   • P-factor is a complex interaction between aircraft relative wind and rotational relative wind
   • The descending blade has a higher AoA and therefore increased thrust
2. Gyroscopic Precession: the force applied (which moves a propeller out of its plane of rotation) is felt 90° from that location, in the direction of rotation
   • Gyroscopic Precession is more prevalent in tailwheel airplanes at lower airspeeds with high power settings
   • In a tail-wheel plane on the take-off run when the tail comes up it will produce a left turning tendency, as the top of the propeller is "pushed" forward and the bottom is "pulled" aft
   • When the nose is raised for climb it will produce a force to the right
   • When the nose is lowered for a descent, it will produce a force to the left
   • In the helicopter community, gyroscopic precession is also called Phase Lag
3. Torque: with a clockwise rotation of the blade the aircraft rotates counter clockwise
4. Slipstream: the corkscrew wind strikes the tail (rudder) on the left side

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​Controllability

• Aircraft ability to respond to control inputs w/ regard to attitude and flight path

Controllability and Maneuverability are conflicting ideas and the two
must be balanced by the designers for the purpose of the aircraft
Nothing in aviation is free and the price for higher lift is always higher drag

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Adverse Yaw

• Adverse yaw is caused by imbalanced drag between the wings which causes a yaw moment on the aircraft, opposite the direction of turn
  • Any time the ailerons are used, adverse yaw is produced
• When the outboard aileron is deflected down, lift on the outboard wing increases and lift on the inboard wing decreases, which causes the airplane to roll
• However, as a downward-deflected aileron is increasing the airfoil's lift, it is also increasing the drag
  • In a turn to the right: the right aileron is up and the left aileron is down
  • In a turn to the left: the left aileron is up and the right aileron is down
• When the aileron is deflected down, lift and drag are increasing (more-so on the outboard wing)
  • This slows the outboard wing and the rudder must be used in the direction of the turn to overcome the outboard wing's increased drag to keep that drag from holding the wing back
• With no rudder input, the nose will yaw outboard (to the outside of the turn) while rolling into the turn
• The ball indicates this yaw by sliding to the inside of the turn
• The rudder is used to offset the unequal drag of the wings that is created only when the ailerons are deflected
• Unbalanced drag only exists while the ailerons are deflected and the airplane is in the act of rolling
• What that also says is that when the airplane is in a steady bank, as when established in a turn, the ailerons are neutral so the lift on the two wings is balanced
• The drag is also balanced
• That being the case, the rudder isn't needed while actually in the turn
• Also, since the airplane is in a steady-state condition (banked), no aileron deflection is needed to maintain that condition
• The farther out the wings are (ailerons) the more of a moment this drag will have

• Why Adverse Yaw Matters:
  • When you turn, stall speed increases
  • If you're experiencing adverse yaw without having the correct amount of rudder in to counter, then you are uncoordinated
  • If you get slow, uncoordinated with a higher stall speed, then you can find yourself in a spin

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