In the Second World War, the Americans and British built large aircraft driven b
ID: 2075902 • Letter: I
Question
In the Second World War, the Americans and British built large aircraft driven by four engines turning propellers mounted along the wings. Two inner engines were located closer to the fuselage, and two outer engines were mounted further out along the wings. (a) One such aircraft, the Flying Fortress, was known for its ability to still fly de- spite extensive damage In particular, they were able to fly with three engines destroyed. Would it be easier to fly such an aircraft with (1) only an outer engine remaining, or (2) only an inner engine remaining? Why? (b) There is another report of an aircraft of this sort losing hydraulic control, eliminating its ability to steer using normal means. However, the pilot was able to steer by altering the power supplied to the engines, and landed safely. How was he able to do this? Explain using concepts from our Phys211 class.Explanation / Answer
The center of mass of a working aircraft is located at the central part of the plane where wings meet the fuselage. Four propellers provide enough thrust to fly the plane, but when one engine is active then that engine produces thrust, which produces significant torque around the center of mass of the aircraft.
As we know:
Torque about a point = (distance of applied force from that point) X (applied force) = r X F
This torque increases as the r increases, i.e. outer engine produces a greater torque than the inner ones about the center of mass.
As torque increases the plane starts to turn without any steering, the pilot has to balance the plane by steering it in the opposite direction. One active outer engine, thus, makes it more difficult for the pilot to control the plane.
B)
As the engines can produce torque about the center of mass when working solo, those could be used as a method of steering the plane in a horizontal plane.
An only active left engine produces a torque that turns the plane to the right and an only active right engine produces a torque that turns the plane to the left. The choice of inner and outer engines provides slower or steeper turn of the aircraft. Combination of the number of active engines from either side provides various amount of torques. The pilots made this kind of choices to turn the plane when the hydraulic system failed.