Have you ever felt as if you’re drifting towards the left side of the runway during takeoff? Don’t worry; it doesn’t mean you’re a lousy pilot. There are specific reasons why your plane tends to veer to the left. In fact, there are four of them, and they are known as left-turning tendencies. Let’s explore how these tendencies work and why you need to use right rudder during takeoff to correct them.
Torque
Torque, the very first left-turning tendency we’ll discuss, stems from a renowned figure named Sir Isaac Newton. Newton’s third law states that “for every action, there is an equal and opposite reaction”.
Most western aircraft have engines that rotate clockwise when viewed from the cockpit. This is where torque comes into play. When you increase the engine power for takeoff, the rightward rotation of the engine and propeller forces the left side of the airplane down onto the runway. As the left side is pressed onto the runway, the left tire has more friction with the ground compared to the right tire, causing the aircraft to desire to turn left.
P-Factor
P-Factor, also known as “asymmetric propeller loading”, occurs when the downward-moving propeller blade takes a larger “bite” of air than the upward-moving blade. This happens in two scenarios:
1) Your plane is flying at a high angle of attack (takeoff and slow flight are good examples), and
2) You’re taking off in a tailwheel airplane.
In both of these situations, the downward-sweeping blade has a higher angle of attack than the upward-sweeping blade. With a higher AOA, the downward-sweeping blade generates more thrust (or lift), making the airplane lean to the left.
Gyroscopic Precession
A spinning propeller is essentially a gyroscope, which has the two characteristics of a gyroscope: rigidity in space and precession. We won’t delve into a detailed physics lesson here, but we’ll briefly explain precession. Precession occurs when you apply force to a spinning disc.
Here’s how it works: when you apply a force to a point on the disc, the resultant force is felt 90 degrees in the direction of the disc’s rotation. For the most part, this applies to tailwheel airplanes when the tail lifts off the runway during takeoff. As the tail rises, a force is applied to the top of the propeller. Since the propeller rotates clockwise, the force is felt 90 degrees to the right. This forward-moving force on the right side of the propeller causes a leftward yawing motion.
Spiraling Slipstream
Spiraling slipstream is the fourth and final left-turning tendency. It occurs when the propeller is moving at a high speed and the plane is moving at a slower speed. And there’s no better example of this than during takeoff.
During takeoff, the air accelerated behind the prop (known as the slipstream) follows a corkscrew pattern. As it wraps around the fuselage of the plane, it hits the left side of the aircraft’s tail, creating a yawing motion and causing the aircraft to turn left. Spiraling slipstream is influenced by the aircraft’s design and the phase of flight, so it’s difficult to quantify its exact effect on the plane. Here are some pictures to help you visualize it.
Why You Need So Much Right Rudder
The four left-turning tendencies create the forces that make the airplane veer left during takeoff. Applying right rudder helps to counteract these forces and maintain a perfect centerline throughout the takeoff roll.
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