where Rwb is the rotation matrix between world and body
coordinate axis, FiD
= FiD
(θi,vx,vz) and FiL
= FiL
(θi,vx,vz) are
the lift and drag forces produced at the wings.
We should remark that above model boils down to a
quadrotor model when (θ1,2,3,4 = π/2).