Health and usage monitoring of Spanish National Institute for Aerospace Technology unmanned air vehicles

Abstract

Structural health and usage monitoring of unmanned air vehicles is of increasing interest not only for the evaluation of flight loads and the use of data in order to estimate the remaining lifetime of the structure but also for a fast and reliable assessment of structural impacts due to unexpected events that can produce significant loads on the structure, such as hard landings and gusts. This is especially important with composite material structures where damage is quite often barely visible. In-flight load and usage monitoring enables fast turnaround times and increases the availability of the unmanned air vehicle. The Spanish National Institute for Aerospace Technology has been developing, for over two decades now, unmanned air vehicles for surveillance, reconnaissance, and aerial targets. At the moment, a health and usage monitoring system for the Spanish National Institute for Aerospace Technology’s medium altitude and long endurance unmanned air vehicle called MILANO, based on fiber Bragg grating sensors that measure strain and temperature, is being developed. The sensors are integrated in the outer and central wing box and the central and rear fuselage. The health and usage monitoring system is based on the experience gained during flight test activities of the tactical unmanned air vehicle SIVA, an all-composite material unmanned air vehicle developed and assembled by Spanish National Institute for Aerospace Technology. One SIVA is instrumented with 15 fiber Bragg grating sensors that measure both strain and temperature in different structural points of interest, such as the outer wing, the wing attachment, the front and rear fuselage, a stabilizer, and the landing gear. The use of optical sensors instead of electrical sensors has the advantages of lower weight penalty, longer durability, and total immunity to electromagnetic interferences. Structural deformations of the unmanned air vehicle have been measured during flight and used to calculate structural flight loads. Temperature-induced thermal strains have been compensated for. This article explains the results and data evaluation of the performed flight tests, describes the equipment used and the sensor applications, and presents the health and usage monitoring of Spanish National Institute for Aerospace Technology’s tactical and medium altitude and long endurance unmanned air vehicles.