Flight test results of automatic tilt control for small scaled tilt rotor aircraft

A small scaled flight model of the tilt rotor aircraft for the Smart UAV Program at KARI(Korea Aerospace Research Institute) has been developed and tested. Since the flight characteristics of a tilt rotor aircraft are new to KARI, the scaled model was used as a test bed to evaluate the flight control algorithm for the full scale smart UAV. The flight test of the small scaled model was performed after various ground tests including tethered hover test. The control laws in initial phase consist of rate SAS feedbacks, control surface mixers, a rotor governor and a manual tilt command path. A rate feedback SCAS control law was used in order to evaluate the flight characteristics of the tilt rotor aircraft. As the flight test proceeds, an attitude SCAS was added because the attitude of aircraft was not clearly recognized due to the small size and fast speed of the aircraft. The first full conversion to a fixed wing mode was made through the manual tilt command by the external pilot. And then the automatic conversion was successfully performed by speed hold command in compliance with a pre-defined conversion corridor. Several problems unexpected were found during flight tests including oscillation of long period mode near helicopter mode, a delayed response to the altitude command and etc. The flight test results of the small scaled tilt rotor aircraft using an automatic tilt control is described in this paper and the solutions of the problems noticed in the flight test are presented.