An Experimental Investigation of the Longitudinal Dynamic Stability Characteristics of a Four-Propeller Tilt-Wing VTOL Model

摘要

The results of experiments conducted to evaluate the longitudinal stability characteristics of a 1/10 scale dynamic model of a four-propeller tilt-wing VTOL transport are presented and discussed. The Princeton Dynamic Model Track was used to measure the static stability and the transient response of the model at wing incidences from 90 degrees to 40 degrees. The results are interpreted in terms of full-scale aircraft characteristics. All data are presented for a C.G. position of 90% MAC (the most forward C.G. position of the aircraft is 15% MAC) and the horizontal tail and flap program differ from those presently used on the aircraft. The transient motions at wing incidences above 70 degrees were similar and dominated by high speed stability and low angular damping resulting in an unstable oscillation of approximately a 9-second period for the full-scale aircraft. The responses at wing incidences below 70 degrees were more complex due to a rapid decrease in the speed stability from a large positive value above 70 degrees to a negative value at 60 degrees. The values of the speed stability for the aircraft determined by a detailed analysis of the data in the neighborhood of 60 degrees wing incidence differ from those obtained from a preliminary analysis of the data by the LTV Aerospace Corporation. Typically, at wing incidences between 60 degrees and 40 degrees the linearized static stability derivatives M sub u and M sub alpha were small, nonlinearities were evident, and the small amplitude linearized motion was dominated by a divergence. At 40 degrees wing incidence, indications were that the dynamic motions were becoming stable. (Author)