TABLE OF CONTENTS "The balancing of a gliding or flying machine is very simple in theory. It merely consists in causing the center of pressure to coincide with the center of gravity. But in actual practice there seems to be an almost boundless incompatibility of temper which prevents their remaining peaceably together for a single instant, so that the operator, who in this case acts as peacemaker, often suffers injury to himself while attempting to bring them together."
Wilbur Wright
Simply stated, stability and control is the science behind keeping the aircraft pointed in a desired direction. Whereas performance analysis sums the forces on an aircraft, stability and control analysis requires summing the moments acting on it as a result of surface pressure and shear-stress distributions, engine thrust, etc., and ensuring those moments sum to zero when the aircraft is oriented as desired. Stability analysis also deals with the changes in moments on the aircraft when it is disturbed from equilibrium, or in other words from the condition when all forces and moments on it sum to zero. An aircraft that tends to drift away from its desired equilibrium condition, or that oscillates wildly about the equilibrium condition, is said to lack sufficient stability. The Wright brothers intentionally built their aircraft to be unstable because this made them more maneuverable. As the preceding quotation from Wilbur Wright suggests, such an aircraft can be very difficult and dangerous to fly.
Control analysis determines how the aircraft should be designed so that...
