Rudder Control Problems on Four-Engined Airplanes 400149
THREE ways to solve the problem of controlling a four-engined airplane after a failure of one or two engines at take-off are advanced: increasing vertical tail area; holding the airplane on the ground until control speed is reached; and coupling symmetrical engines together so that the failure of one engine reduces the power on the opposite one to less than take-off power.
Mr. Johnson shows that this problem becomes increasingly serious as the airplane power loading is reduced. He points out that the trend of normal design now existing is such that the wing loading is also increasing so that the difference between the take-off speed and the control speed with one engine inoperative does not change greatly. A serious problem is presented by the use of flaps on take-off from the point of view of rudder controllability of these four-engined planes with one or more engines inoperative, he avers.
It is impractical, Mr. Johnson believes, to provide enough vertical tail area to control the airplane by allowing a certain angle of yaw without depending upon the pilot's reaction to apply the proper amount of rudder. He shows that a fortunate condition exists in that, as the power loading decreases, automatic engine controls can be used to limit the power of the unsymmetrical operating engine to the point where ample controllability can be obtained.