METHODS TO EVALUATE THE MASS PROPERTIES OF A SCALE MODEL AIRCRAFT

摘要

Scale model ditching tests are sometimes conducted tornstudy the loads and dynamic behavior associated withrnan aircraft during water impact. To ensure scalabilityrnof the results, the model’s mass properties includingrnweight, center of gravity, and pitch moment of inertia inrnparticular must proportionally refl ect the characteristicsrnof the full-scale aircraft. This paper presents thernexperimental methods used to evaluate these massrncharacteristics for a 1/20th scale Gulfstream G550rnmodel prior to ditching tests conducted at the Universityrnof Georgia. These methods can be used for any similarlyrnsized model.rnTo determine the center of gravity the aircraftrnmodel is placed on a v-block assembly resting onrnthree force transducers arranged in an isoscelesrntriangle formation. The model’s center of gravity alongrnlongitudinal and lateral axes is found by summingrnmoments about a known reference axes system usingrnthe static forces measured at each transducer. To fi ndrnthe vertical center of gravity, the model is rotated aboutrnits longitudinal axis in a v-block fi xture, and the forcernreadings along the projection of the rotated plane arernthen manipulated.rnFor pitch inertia, a compound pendulum is used tornmeasure the aircraft’s period of oscillation which isrnrelated to the inertia about the axis of oscillation throughrnan analytical method [1]. The inertia of the pendulumrnapparatus by itself is then subtracted from the totalrnexperimental inertia, and the parallel axis theoremrnis used to determine the model’s pitch inertia aboutrnits center of gravity. To evaluate the accuracy of thernpendulum method, aluminum and steel brackets withrnknown mass properties are attached to the model’s tail,rnand the pitch inertia is measured again for each bracket.rnThe increase in inertia is then compared against thetheoretical increase.