Why do airplanes tend to turn left after takeoff?

Why do airplanes tend to turn left after takeoff and how to fix it?

If you’ve ever started the hobby of building and flying RC airplanes, there’s a good chance you’ve struggled during takeoff. I certainly did. In my early builds, I crashed more times than I can count because I couldn’t understand one simple thing — why the airplane kept turning left every time I applied throttle.

At first, it feels like a setup mistake, a bad wing, or poor piloting. But in reality, this behavior is a very common aerodynamic issue known as the turning left tendency. To counter it, RC airplanes use a small but critical design adjustment called right thrust, where the motor is intentionally tilted slightly to the right.

If your RC plane pulls left on takeoff, climbs unevenly at full throttle, or constantly needs rudder correction, this article is for you. We’ll break down why this happens, what forces cause it, and how right thrust fixes the problem — explained clearly for beginners, hobbyists, and advanced builders alike.

What Causes the Turning Left Tendency in RC Airplanes?

When power is applied, most single-propeller RC airplanes naturally tend to yaw or roll to the left. This behavior, commonly called the turning left tendency, is not caused by poor construction or pilot error. Instead, it results from several aerodynamic and mechanical forces produced by the spinning propeller — especially during takeoff and climb.

Right thrust exists specifically to counter these effects.

1. P-Factor (Asymmetric Thrust)

When an RC airplane pitches up during takeoff or climb, the propeller blades no longer meet the airflow evenly. The descending blade (typically on the right side) produces more thrust than the ascending blade.
This imbalance pushes the nose to the left, creating a strong yawing tendency at high angles of attack.

Right thrust compensates by slightly yawing the nose to the right, reducing the need for constant rudder correction.

2. Torque Effect

As the propeller spins clockwise (viewed from the cockpit), Newton’s third law applies an equal and opposite torque to the airframe.
This reactive force causes the aircraft to roll — and sometimes yaw — to the left, particularly at low airspeed and high throttle.

Right thrust helps offset this effect, making acceleration and climb smoother and more predictable.

3. Spiraling Slipstream (Prop Wash)

The airflow leaving the propeller doesn’t move straight back — it spirals around the fuselage.
This rotating airflow often strikes the left side of the vertical stabilizer, pushing the tail to the right and forcing the nose left.

By angling the motor slightly to the right, this yawing force is counterbalanced, helping the aircraft track straight during powered flight.

4. Gyroscopic Precession

A spinning propeller behaves like a gyroscope. When the aircraft pitches up or down, gyroscopic forces can create additional yaw moments — especially noticeable during abrupt throttle or pitch changes.

While this effect is usually smaller than torque or P-factor, right thrust helps reduce its overall influence on yaw behavior.

An illustration showing the slipstream effect, how the air flows spirally and eventually hits the rudder from left side causing the plane to Yaw to the left.

An illustration explaining the P-Factor effect on an ascending airplane (climbing with an angle) and how the rising blade (left one) has a smaller angle of attack compared to the down going blade (right one), the difference in thrust is causing the plane to Yaw to the left.

How Much Right Thrust Is Enough?

Most RC airplane designs incorporate 2 to 3 degrees of right thrust as a standard starting point. Some designs also include down thrust (a slight downward tilt) to counteract excessive nose-up tendencies during high-power flight.

Factors That Affect the Amount of Right Thrust

The ideal right thrust angle is not universal—it depends on several characteristics of the aircraft and flight conditions:

Position of the Vertical Stabilizer

The effectiveness of the spiraling slipstream depends on how much of it strikes the vertical stabilizer. A tail fin positioned directly in the path of the slipstream will be more affected, potentially requiring more right thrust to maintain balance.

Airspeed and Slipstream Strength

At low airspeeds and high throttle (such as during takeoff), the slipstream is stronger and more concentrated, leading to greater side forces. At higher speeds, the airflow straightens out, reducing its influence. As a result, more right thrust may be needed for low-speed, high-power phases of flight.

Aircraft Design Characteristics

Different aircraft designs respond differently to propeller forces:

• Biplanes, with their unique wing and fuselage configuration, may experience different aerodynamic loads than monoplanes.
• High-performance or aerobatic aircraft often require more precise thrust tuning due to their responsiveness and speed.
• Pusher aircraft (with rear-mounted propellers) behave differently and may not need right thrust in the same way.

Practical Tips for Adjusting Right Thrust

Whether you’re building from scratch or assembling a kit, here are some tips for adjusting right thrust effectively.

During Construction

• Check the Plans: Many RC kits or CAD designs specify the recommended motor angle.
• Use Washers or Spacers: A simple way to tilt the motor is by adding small washers behind the left side of the motor mount.
• Design with the Angle Built In: If you're fabricating your own parts (e.g., 3D printing or laser-cutting), you can build in the thrust angle from the start.
• Use Adjustable Mounts: Some motor mounts allow for small angular adjustments even after installation, which is helpful for fine-tuning.

In-Flight Testing

After the plane is ready to fly, you can use the following tests to evaluate your current right thrust setting:

Full-Throttle Takeoff Test

Take off at full power and observe if the plane veers to the left. If it does, more right thrust may be needed.

Hands-Off Climb Test

Fly straight and level at mid-throttle, then quickly apply full throttle and let go of the controls. If the plane yaws left during the climb, it’s a sign that additional right thrust may help.

Glide Test (Power-Off)

Reduce throttle to zero and let the plane glide. If it turns slightly right without input, you may have too much right thrust.

Making Adjustments

• To increase right thrust, add more washers behind the left side of the motor mount.
• To decrease right thrust, reduce or remove washers, or use a more neutral mount angle.

Avoid Overcompensation

Adding too much right thrust can cause the plane to pull to the right under power, especially during climbs or high-speed flight. Always make small changes and test the results before making further adjustments.

You can also start with a zero thrust angle—mount the motor straight—and observe how the aircraft responds in flight. If the plane reacts sharply when you increase throttle (for example, it pitches down or yaws aggressively to one side), that indicates the need for thrust angle adjustment. From there, begin introducing right or down thrust in small increments and retest.

Final Fine-Tuning

Even with the correct thrust angle, you may still need minor adjustments:

• Use rudder trim on your transmitter to correct small yaw tendencies.
• Ensure your propeller is balanced to avoid vibrations that can affect yaw.
• Slightly adjusting your aircraft’s center of gravity (CG) may also help with overall stability.

Conclusion

Right thrust is one of those subtle but critical elements of RC airplane design that can dramatically affect flight performance. Understanding the aerodynamic forces at play and knowing how to adjust your motor angle can help you achieve smoother, more predictable behavior in the air.

For more hands-on engineering guides, tutorials on aerodynamics, and tips on RC airplane building, be sure to explore more content here on Labdarna.

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