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How The Tiger Moth Helped Revolutionize Ailerons

de Havilland DH.82 Airwolfhoud

Ailerons have come a long way since Orville and Wilber were twisting their wings to make airplanes turn in 1903. One of the biggest leaps in aileron technology came in 1931, thanks to the de Havilland aircraft company and their famous training aircraft: the DH.82 Tiger Moth.

An Adverse (Yaw) History

Differential ailerons came about because of something called adverse yaw, which causes airplanes to yaw in the opposite direction that they roll.

Early aircraft designers knew adverse yaw happened because downward deflecting ailerons produce more lift, and as a result, more induced drag. To make matters worse, adverse yaw was even more pronounced at slow speeds, because larger control inputs were needed to maneuver an airplane. This made aircraft hard to control, especially near the ground and in traffic patterns.

By the 1930s, designers starting coming up with ideas to combat adverse yaw. One of the best designs of the time was made by Geoffrey de Havilland: the differential aileron. De Havilland implemented one of the earliest designs of the differential aileron on the his infamous British military training airplane, and he had excellent results.

How Differential Ailerons Work

Differential ailerons work by moving the up and down ailerons different distances. The up aileron moves a greater distance upward, and the down aileron moves less distance downward. De Havilland accomplished this feat with a combination of mechanical linkages and bell cranks, which gave the ailerons the ability to be connected, yet move up and down at different rates. De Havilland's design accomplished two things:

  • The upward aileron pushed itself into the free air stream, creating increased parasite drag.
  • The downward aileron didn't produce as much lift, and in turn, didn't produce as much induced drag.
Differential Aileron - Up

By moving the ailerons at different distances, the parasite drag of the up aileron and the induced drag of the down aileron on the DH.82 were nearly equal. In a turn, adverse yaw was almost completely eliminated, even at slow speeds.

Differential Aileron - Up

Differential Ailerons Today

Differential ailerons are still used today on many training aircraft, and their principles remain the same. By equalizing drag on the down and up wings, turns are more coordinated with less input needed by the pilot.

Now that you know what differential ailerons are, check out this video of a DH-82 Tiger Moth taking advantage of its advanced ailerons in an aerobatic display. Enjoy!

Colin Cutler

Colin is a Boldmethod co-founder, pilot and graphic artist. He's been a flight instructor at the University of North Dakota, an airline pilot on the CRJ-200, and has directed development of numerous commercial and military training systems. You can reach him at colin@boldmethod.com.

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