Eventos Anais de eventos
COBEM 2021
26th International Congress of Mechanical Engineering
Analysis and Modeling of an Aircraft Test Instrumentation for Airspeed Measuring Using Bond-Graphs
Submission Author:
Vinícius Leite de Morais Véras , SP
Co-Authors:
Vinícius Leite de Morais Véras, Luiz Carlos Góes
Presenter: Vinícius Leite de Morais Véras
doi://10.26678/ABCM.COBEM2021.COB2021-0047
Abstract
Aircraft tests require measurements of several parameters. As some of them are not provided by the aircraft itself, a prototype has to be equipped with test instrumentation. A typical test instrumentation for airspeed measurement is composed by a Pitot tube installed on a region of the aircraft nose, a pipeline and an electronic transducer. That a pipeline is subject to pressure dynamics, that may introduce some error due to lag. The lag of airspeed indication is a concern of regulation agencies. Two criteria for such lag is provided on AC 25-7D for an applicant to demonstrate compliance with CFR 14 §25.1323(g): (i) the lag may not lead to an error larger than 3kt and (ii) the impact on required takeoff distances due to such lag must not be an increase on distance larger than 100ft. No lag criteria for test instrumentation is provided on such regulatory documents, though. No study regarding installation requirements such as pipeline dimension could be found by the authors. A pipeline model composed by finite elements is herein proposed. Each element is a bond-graph sub-model composed by fluid resistance, capacitance and inductance: the resistance is calculated using laminar flow equations; capacitance is calculated based on Bulk modulus assuming adiabatic process, and inductance is calculated based on the inertia of the gas inside each line element. As, by premise, the transducer is installed far from the aircraft nose, the force of inertia acting on the air inside the pipeline is taken into account. The time response of the pressure sensed at the end of the line can then be obtained for a simulated acceleration of the aircraft representing a takeoff run. Time response of the airspeed error due to lag as provided by a test instrumentation is then evaluated for different installations and accelerations. Finally, guidelines for installation designs are suggested.
Keywords
Pitot tube, Flight Test, Bond Graph, airspeed, Lag
DOWNLOAD PDF VIEW PRESENTATION
