Nomenclature f i = lift of ith rotor, N g = acceleration of gravity, kg · m∕s 2 h = altitude of helicopter, m J x , J y , J z = moment of inertia around roll, pitch, and yaw axes of helicopter frame, kg · m 2 K i = maximum lift of ith rotor, N k μ = ratio between reactive torque and lift of rotors L, M, N = airframe roll, pitch, and yaw torque of helicopter, N · m m = number of rotors m a = mass of helicopter, kg p, q, r = roll, pitch, and yaw angular velocities of helicopter, rad∕s r i = distance from center of ith rotor to center of mass, m T = total thrust of helicopter, N v h = vertical velocity of helicopter, m∕s η i = efficiency parameter of ith rotor ϕ, θ, ψ = roll, pitch, and yaw angles of helicopter, rad