Abstract
Unmanned aircraft used as high-altitude platform system has been studied in research and industry as alternative technologies to satellites. Regarding actual operation and flight performance of such systems, multibody aircraft seems to be a promising aircraft configuration. In terms of flight dynamics, this aircraft strongly differs from classical rigid-body and flexible aircraft, because a strong interference between flight mechanic and formation modes occurs. For unmanned operation in the stratosphere, flight control laws are required. While control theory generally provides a number of approaches, the specific flight physics characteristics can be only partially considered. This paper addresses a flight control law approach based on a physically exact target model of the multibody aircraft dynamics rather than conventionally considering the system dynamics only. In the target model, hypothetical spring and damping elements at the joints are included into the equations of motion to transfer the configuration of a highly flexible multibody aircraft into one similar to a classical rigid-body aircraft. The differences between both types of aircraft are reflected in the eigenvalues and eigenvectors. Using the eigenstructure assignment, the desired damping and stiffness are established by the inner-loop flight control law. In contrast to other methods, this procedure allows a straightforward control law design for a multibody aircraft based on a physical reference model.
Highlights
Aircraft operating as so-called High-Altitude Platform Systems (HAPS) have been considered as a complementary technology to satellites for several years
After selecting the desired eigenvalues and eigenvectors, the methodology of eigenstructure assignment is applied to the linearized state-space system of the multibody aircraft
This paper shows an approach for the inner-loop control laws of a multibody aircraft based on an artificial but physically exact target model
Summary
Aircraft operating as so-called High-Altitude Platform Systems (HAPS) have been considered as a complementary technology to satellites for several years. This article makes a contribution to an inner-loop control law based on a physically correct target model that modifies the flight dynamics of the unconventional multibody aircraft to become similar to the one of a rigid-body aircraft It is based on former research carried out in a PhD project on flight mechanics and flight control of multi-body aircraft [9]. The eigenvectors of the theoretical rigid-body aircraft are determined and later on used in an eigenstructure assignment to calculate the inner-loop control law for the very flexible aircraft without any spring and damping elements With this method, the classical, flight mechanical rigid-body modes and the formation modes are well separated from each other. The outer loop has to control the rigid-body motion of the aircraft only [10]
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