3700. On Techniques for Correcting Entrained Air Errors during MOI Measurement of Aircraft Control Surfaces

Paper

Abstract

Knowing the true mass properties of aircraft control surfaces is critical to preventing aerodynamic flutter, a condition that can result in the loss of flight control or outright airframe failure. As the aircraft industry turns to a greater use of composites in airframe construction, layup variations in material density and manufacturing techniques result in as-built deviations from the mass distribution calculated in the CAD model. These moment of inertia (MOI) deviations can be up to 10%, thereby increasing the need to verify MOI of control surfaces through physical measurement.Control surface MOI measurements are subject to errors when the measurements are conducted in air. Errors in air measurements are principally caused by entrained air. This virtually-attached air adds apparent mass to the control surface and anomalously increases the control surface’s measured MOI. Typical MOI errors range from 5% to 25% of the control surface’s MOI.Concentrating on entrained air errors, this paper examines viable methods of error correction. Further refined by test article requirements, the methods are evaluated both experimentally and analytically. Application strategies are then developed, and expected outcomes are predicted. Lastly, a new gravity driven horizontal axis instrument, complete with its own novel error compensation, is introduced and compared to a variety of measurement and correction techniques.