METHODS TO EVALUATE THE MASS PROPERTIES OF A SCALE MODEL AIRCRAFT

摘要

Scale model ditching tests are sometimes conducted to study the loads and dynamic behavior associated with an aircraft during water impact. To ensure scalability of the results, the model's mass properties including weight, center of gravity, and pitch moment of inertia in particular must proportionally reflect the characteristics of the full-scale aircraft. This paper presents the experimental methods used to evaluate these mass characteristics for a 1/20~(th) scale Gulfstream G550 model prior to ditching tests conducted at the University of Georgia. These methods can be used for any similarly sized model. To determine the center of gravity the aircraft model is placed on a v-block assembly resting on three force transducers arranged in an isosceles triangle formation. The model's center of gravity along longitudinal and lateral axes is found by summing moments about a known reference axes system using the static forces measured at each transducer. To find the vertical center of gravity, the model is rotated about its longitudinal axis in a v-block fixture, and the force readings along the projection of the rotated plane are then manipulated. For pitch inertia, a compound pendulum is used to measure the aircraft's period of oscillation which is related to the inertia about the axis of oscillation through an analytical method [1]. The inertia of the pendulum apparatus by itself is then subtracted from the total experimental inertia, and the parallel axis theorem is used to determine the model's pitch inertia about its center of gravity. To evaluate the accuracy of the pendulum method, aluminum and steel brackets with known mass properties are attached to the model's tail, and the pitch inertia is measured again for each bracket. The increase in inertia is then compared against the theoretical increase.