  We propose a new position control strategy for VTOL-UAVs using IMU and GPS
measurements. Since there is no sensor that measures the attitude, our approach
does not rely on the knowledge (or reconstruction) of the system orientation as
usually done in the existing literature. Instead, IMU and GPS measurements are
directly incorporated in the control law. An important feature of the proposed
strategy, is that the accelerometer is used to measure the apparent
acceleration of the vehicle, as opposed to only measuring the gravity vector,
which would otherwise lead to unexpected performance when the vehicle is
accelerating (i.e. not in a hover configuration). Simulation results are
provided to demonstrate the performance of the proposed position control
strategy in the presence of noise and disturbances.
