At the rear of the 1903 Wright Flyer one finds a pair of rudders. The rudders are movable surfaces which are controlled by the pilot. This slide shows what happens when the pilot deflects the trailing edge of the rudders. How does changing the rudder angle affect the aircraft?
As described on the inclination effects slide, changing the angle of attack of a wing or airfoil changes the amount of lift generated by the foil. With increased downward deflection of the trailing edge, lift increases. The rudders are mounted so that they will produce forces from side to side, not up and down. With greater rudder deflection to the right as viewed from the back of the aircraft, the force increases to the left (as shown in this slide). The force (lift) of the rudder is applied some distance from the aircraft center of gravity. This creates a torque on the aircraft and the aircraft rotates about its center of gravity. If the pilot reverses the rudder deflection to the left, the aircraft will yaw in the opposite direction. We have chosen to base the deflections on a view from the back of the aircraft towards the nose, because that is the direction in which the pilot is looking
Let’s investigate how the rudder works by using a Java simulator. You can change the rudder setting by using the slider at the bottom.
Please note: the simulation below is best viewed on a desktop computer. It may take a few minutes for the simulation to load.
The Wright’s initially did not think that they would need a rudder on their aircraft since birds don’t need rudders. The 1900 and 1901 aircraft were designed without rudders. But during the glider flights of 1901, the brothers encountered flight conditions when the aircraft would suddenly spin out of control during maneuvers. They included dual fixed rudders in the design of the 1902 aircraft to overcome this problem. The test flights of 1902 initially went better than in 1901, but in about one glide in 50 the glider would again spin out of control on recovering from a turn at low speed. Laying awake one night, Orville concluded that the rudders were acting as vertical wings in which turning generated an angle of attack and thus an unwanted force in the wrong direction. His solution was to replace the twin fixed rudders with a single movable rudder. The next morning Wilbur agreed and offered the idea to tie the rudder deflection into the wing warping system. Once done, the glider worked beautifully, keeping the nose of the aircraft pointed into the curved flight path. All subsequent Wright aircraft included dual, movable rudders.
The Wright’s used flat plate airfoils for their rudders and deflected the entire surface from side to side. On modern aircraft, the rudder is a separate piece attached to the vertical stabilizer. The combination creates a symmetric airfoil and produces no lift when the rudder is aligned with the stabilizer. Forces to the left or right then depend on the deflection of the rudder. Modern fighter planes sometimes have two vertical stabilizers and rudders because of the need to control the plane with multiple, very powerful engines.
You can view a short movie of “Orville and Wilbur Wright” explaining how the rudder was used to control the yaw of their aircraft. The movie file can be saved to your computer and viewed as a Podcast on your podcast player.