“More Right Rudder” | The Left Turning Tendencies

You smoothly apply full power for takeoff on your Piper Cherokee 140. You’re pressed back into your seat as you quickly begin accelerating down the runway of Boeing Field in Seattle, Washington. A quick glance at your engine gauges verifies that everything is working as it should. Committed to take off, you approach rotation speed, but notice a strange pulling to the left. “Is this normal?” you ask your flight instructor. “We’ll talk about it on the ground” he dismissively responds. So what’s happening? Why does the plane have a left turning tendency?

It comes down to four basic physics principles which affect propeller driven aircraft. You’re flight instructor will likely discuss these during your first few flight lessons! 

The Four Left Turning Tendencies are:

Gyroscopic Precession

One of the more difficult forces to remember and understand is Gyroscopic Precession. This phenomenon occurs on any object that is spinning—such as the aircraft’s propeller. This physics principle states that if a force is applied to a spinning object, the resultant force will affect the spinning disk 90 degrees later in the direction of motion. Consider when a single-engine tailwheel aircraft is taking off. As the aircraft builds speed, the tail raises off the ground. That change creates a force on the top of the spinning prop and is experienced

90 degree later to the props rotation. This results in a forward-force acting on the right side of the propeller creating an asymmetry causing the aircraft to yaw to the left. The pilot will need right rudder to correct this action.

Torque

Everyone has likely heard of torque at some point. Typically in reference  to automobiles or maybe during a high school physics class, torque is simple to understand. Newton’s third law of motions states that “every action has an equal and opposite reaction”. Apply that to the aircraft’s engine. 

Spiraling Slipstream

The spinning motion of the prop creates an, almost like, tornado swirling around the aircraft. This circulation of air wraps around the plane, starting from the prop and ending at the tail.

The left-turning tendency, here, occurs when the air flowing around the plane impacts the vertical stabilizer at the tail of the aircraft. The rightward rotating air impacts the left side of the tail, pushing the nose to the left. Right rudder, once again, can correct this force.

Asymmetric Propeller Loading (P-Factor)

Remember that the propeller of an aircraft is an airfoil. In the same way that the aircraft’s wings generate lift, the propeller does the same! Think of the propeller as a spinning wing, pulling the aircraft through the air. So how does that relate to a left turning tendency? It all has to do with angle of attack. As the right side of the propeller descends, it actually takes a bigger “bite” out of the air. This means the descending right blade has a greater angel of attack, creating greater lift. 

Significance to Pilots

So why are the left turning tendencies so important for pilot to know? Moreover, why do FAA examiners ask this on every Private Pilot checkride? The answer is simple: maintaining positive aircraft control and coordinated flight is critical to flight safety.

While in flight training, you may have heard your flight instructor annoyingly reminding you to add “more right rudder” or to “step on the ball”, in reference to the inclinometer. He or she is giving you this reminder to foster the good pilot habit of maintaining coordinated flight. This is important, because in the event of an inadvertent stall, the aircraft is less likely to enter a deadly spin so long as it is in correct coordination.

Always remember, the left turning tendencies of the aircraft are worst when the aircraft is simultaneously; slow, in a high angle of attack, and when the engine is operating at high settings. The aircraft is especially vulnerable to this type of situation in take-offs and go-around maneuvers. It’s actually the same reason power-on stalls are more likely to result in an inadvertent spin entry! The last thing a pilot ever wants to do is aggravate a stall resulting in a spin. Just remember to always anticipate the need for right rudder during takeoff and climbs, reference your inclinometer, and develop good rudder use habits. It will keep you and your passengers safe!