JM
Joost Meulenbeld
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1
The DelftaCopter is a tilt-body tailsitter unmanned air vehicle which combines a large swashplate controlled helicopter rotor with a biplane delta-wing. Previous research has shown that the large moment of inertia of the wing and fuselage significantly interacts with the dynamics of the rotor. While this rigid rotor cylinder dynamics model has allowed initial flight testing, part of the dynamics remains unexplained. In particular, higher frequency dynamics and the forward flight dynamics were not modeled. In this work, the cylinder dynamics model is compared with the tip-path plane model, which includes the steady-state flapping dynamics of the blades. The model is then extended to include the wing and elevon dynamics during forward flight. Flight test data consisting of excitations with a large frequency content are used to identify the model parameters using grey-box modeling. Since the DelftaCopter is unstable, flight tests can only be performed while at least a rate feedback controller is active. To reduce the influence of this active controller on the identification of the dynamics, one axis is identified at a time while white noise is introduced on all other axes. The tip-path plane model is shown to be much more accurate in reproducing the high-frequency attitude dynamics of the DelftaCopter. The significant rotor–wing interaction is shown to differ greatly from what is seen in traditional helicopter models. Finally, an Linear-Quadratic Regulator (LQR) controller based on the tip-path plane model is derived and tested to validate its applicability. Modeling the attitude dynamics of the unstable DelftaCopter from flight test data has been shown to be possible even in the presence of the unavoidable baseline controller.
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The DelftaCopter is a tilt-body tailsitter unmanned air vehicle which combines a large swashplate controlled helicopter rotor with a biplane delta-wing. Previous research has shown that the large moment of inertia of the wing and fuselage significantly interacts with the dynamics of the rotor. While this rigid rotor cylinder dynamics model has allowed initial flight testing, part of the dynamics remains unexplained. In particular, higher frequency dynamics and the forward flight dynamics were not modeled. In this work, the cylinder dynamics model is compared with the tip-path plane model, which includes the steady-state flapping dynamics of the blades. The model is then extended to include the wing and elevon dynamics during forward flight. Flight test data consisting of excitations with a large frequency content are used to identify the model parameters using grey-box modeling. Since the DelftaCopter is unstable, flight tests can only be performed while at least a rate feedback controller is active. To reduce the influence of this active controller on the identification of the dynamics, one axis is identified at a time while white noise is introduced on all other axes. The tip-path plane model is shown to be much more accurate in reproducing the high-frequency attitude dynamics of the DelftaCopter. The significant rotor–wing interaction is shown to differ greatly from what is seen in traditional helicopter models. Finally, an Linear-Quadratic Regulator (LQR) controller based on the tip-path plane model is derived and tested to validate its applicability. Modeling the attitude dynamics of the unstable DelftaCopter from flight test data has been shown to be possible even in the presence of the unavoidable baseline controller.
The DelftaCopter, a tilt-body tailsitter UAV, endures large gyroscopic moments due to the single helicopter rotor providing its thrust. In previous research by de Wagter et al.[1] the DelftaCopter’s attitude dynamics were modeled using a rigid rotor, as is customary for small helicopter modeling. A controller based on this model was unable to compensate coupling between pitch and roll rate caused by gyroscopic moments. In this paper, two models are compared for reproducing the attitude dynamics of the Delfta- Copter in hover. The Cylinder Dynamics (CD) model, used in the previous research, assumes a rigid rotor. The Tip-Path Plane (TPP) model incorporates flapping motion of the blades and was developed by Mettler[2]. The two models are compared by fitting each model’s parameters on flight data using chirps, sine waves with increasing frequency, as system identification maneuvers. The TPP model is shown to be much more accurate in reproducing the high-frequency attitude dynamics. An LQR controller directly based on the TPP model is shown to yield adequate tracking performance. This validates the applicability of this model to the DelftaCopter. For forward flight, an extension to the TPP hover model is proposed incorporating the aerodynamics of the wings and elevons. It is shown that with the extension, chirps in forward flight can be simulated with reasonable accuracy. This paves the way for a model-based controller in this flight state.
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The DelftaCopter, a tilt-body tailsitter UAV, endures large gyroscopic moments due to the single helicopter rotor providing its thrust. In previous research by de Wagter et al.[1] the DelftaCopter’s attitude dynamics were modeled using a rigid rotor, as is customary for small helicopter modeling. A controller based on this model was unable to compensate coupling between pitch and roll rate caused by gyroscopic moments. In this paper, two models are compared for reproducing the attitude dynamics of the Delfta- Copter in hover. The Cylinder Dynamics (CD) model, used in the previous research, assumes a rigid rotor. The Tip-Path Plane (TPP) model incorporates flapping motion of the blades and was developed by Mettler[2]. The two models are compared by fitting each model’s parameters on flight data using chirps, sine waves with increasing frequency, as system identification maneuvers. The TPP model is shown to be much more accurate in reproducing the high-frequency attitude dynamics. An LQR controller directly based on the TPP model is shown to yield adequate tracking performance. This validates the applicability of this model to the DelftaCopter. For forward flight, an extension to the TPP hover model is proposed incorporating the aerodynamics of the wings and elevons. It is shown that with the extension, chirps in forward flight can be simulated with reasonable accuracy. This paves the way for a model-based controller in this flight state.
Conference paper
(2018)
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Christophe de Wagter, Bart Remes, Rick Ruijsink, Erik van der Horst, Freek van Tienen, Dennis van Wijngaarden, Joost Meulenbeld, Kevin van Hecke
Enlarging the flight envelope of aircraft has been a goal since the beginning of aviation. But requirements to fly very fast and to hover are conflicting. During the design of the DelftaCopter, a tail-sitter hybrid UAV with a single large rotor for lift in hover and propulsion in forward flight, the design of the rotor needs to properly balance hovering requirements and fast forward flight requirements. The initial design with a one meter rotor placed too much emphasis on efficiency in hover, while most flights consist of very short periods of hover and very long phases of forward flight. Two new rotor designs and corresponding motors were tested an open jet wind tunnel. The propulsion system was tested from hover conditions to very fast forward flight in search of the most optimal operating point for each condition. The resulting system requires merely more power than the initial rotor in hover while it is capable of much faster forward speeds. The power requirements are shown to be compatible with modern power sources like Lithium-Ion batteries, which form the next step in improving the efficiency of hover-capable fast UAV.
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Enlarging the flight envelope of aircraft has been a goal since the beginning of aviation. But requirements to fly very fast and to hover are conflicting. During the design of the DelftaCopter, a tail-sitter hybrid UAV with a single large rotor for lift in hover and propulsion in forward flight, the design of the rotor needs to properly balance hovering requirements and fast forward flight requirements. The initial design with a one meter rotor placed too much emphasis on efficiency in hover, while most flights consist of very short periods of hover and very long phases of forward flight. Two new rotor designs and corresponding motors were tested an open jet wind tunnel. The propulsion system was tested from hover conditions to very fast forward flight in search of the most optimal operating point for each condition. The resulting system requires merely more power than the initial rotor in hover while it is capable of much faster forward speeds. The power requirements are shown to be compatible with modern power sources like Lithium-Ion batteries, which form the next step in improving the efficiency of hover-capable fast UAV.