The longitudinal handling characteristics of the Skysurfer X8

Abstract

For decades the physical appearance of aircraft remained more or less unchanged. The increase in efficiency which still can be made by improving this design, is limited. More researchers have started to investigate new design options that represent a departure from established concepts. The main drivers behind these endeavors are the tightening regulations on emissions and noise as well as the expected profitability for the customer. With the use of scale models for flight testing, it is possible to validate novel aircraft concepts while minimizing investments in terms of costs and time. Novel aircraft often have unproved handling characteristics which is why a quick method to verify these new models would be beneficial. The objective of this research is to investigate the longitudinal handling characteristics of the Skysurfer X8 by assessing whether the criteria for the short period damping, phugoid damping, bandwidth and Control Anticipation Parameter are in accordance with the military standards. Mathematical models for the aircraft's behavior are extracted from the aircraft by performing system identification in the frequency domain. This is done by measuring the aircraft's input and output signals while performing frequency sweeps on one of the control inputs during a flight test. These measurements are used to derive the input-output system. This procedure is followed for every longitudinal control variable of the aircraft. The models derived from the flight test are validated by comparing the handling characteristics (short period damping, phugoid damping and Control Anticipation) to a simulation performed in XFLR5. The frequency identification method described there is validated with frequency sweep data generated from an aircraft’s known state space system and the flight tests are performed with a modified Skysurfer X8 which is equipped with two wing mounted engines. Based on the validation the method proves to be reliable. The experiment shows that the handling characteristics of the Skysurfer X8 are at least at level 2 of the military standards. This level is satisfactory, given the small size of the test aircraft. The method is capable of capturing a model of the pitch angle and pitch speed response relative to elevator deflection, which is used to estimate all handling characteristics. Improvements can be made in the frequency sweep maneuvers for the throttle and the measurement error and resolution should be further investigated.