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Bell XV-15.

Bell XV-15.

Source publication
Conference Paper
Full-text available
This paper describes the development, implementation, and validation of a generic tilt-rotor simulation model with coupled flight dynamics, state-variable aeromechanics, and aeroacoustic. A major novelty of this work lies in the integration of the flight dynamics with a state-space free-vortex wake code that adopts a near-wake vortex-lattice model....

Contexts in source publication

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... general tilt-rotor (GenTR) simulation model is representative of a Bell XV-15 ( Fig. 1) and loosely based on GTR-SIM (Ref. 8) while introducing a number of significant improvements. More specifically, the model includes the rigidbody dynamics, a blade element rotor model coupled with flapping dynamics adapted from GenHel (Ref. 1) and Ref. 9, and a 3-state Pitt-Peters (Ref. 10). The model also includes nonlinear lookup ...
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... rotorcraft is trimmed at hover in helicopter mode (i.e., with the nacelles at β m = 0 deg according to the definition in Ref. 8) and at 170 kts in aircraft mode (i.e., with the nacelles at β m = 90 deg) for validation. Figure 9 shows a comparison of the lateral dynamics eigenvalues for each of these conditions with those from US Army/NASA flight test data and from Ref. 9. Figure 10 shows some sample frequency responses at hover as compared to US Army/NASA XV-15 flight data and simulation data from Ref. 9. While the general agreement is good, it is worth noting that the available flight-test data does not provide the exact information on CG location, moments of inertia, weight, and flap setting. As such, it is difficult to draw definitive conclusions. ...
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... such, it is difficult to draw definitive conclusions. Figure 10 shows the GenTR time response to lateraldirectional pilot inputs at hover as compared with US Army/NASA XV-15 flight test data. This figure shows a generally good match between the GenTR and flight test data time histories. ...
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... x x x 0 is the zeroth-harmonic state vector without the position and yaw angle states included. Figure 12 shows the periodic angular rates obtained with the modified harmonic balance algorithm (solid line) using an error tolerance of 1e−7. As expected, since the tiltrotor in consideration has three rotor blades with equal mass and since the state harmonics retained in the solution are three, the higher-harmonic content of the periodic solution is limited to the third sine and cosine harmonics. ...
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... three-dimensional visualizations of the state-space freevortex wake with a near-wake vortex-lattice model are shown in Fig. 13 for different flight conditions. These results correspond to the tightly coupled flight and free-wake dynamics trimmed at hover (Fig. 13a), at 120 kts during conversion between helicopter and airplane mode (Fig. 13b), and at 170 kts in airplane mode (Fig. 13c). Figure 13a shows the contraction of the wake below the rotor, indicative of ...
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... three-dimensional visualizations of the state-space freevortex wake with a near-wake vortex-lattice model are shown in Fig. 13 for different flight conditions. These results correspond to the tightly coupled flight and free-wake dynamics trimmed at hover (Fig. 13a), at 120 kts during conversion between helicopter and airplane mode (Fig. 13b), and at 170 kts in airplane mode (Fig. 13c). Figure 13a shows the contraction of the wake below the rotor, indicative of the effectiveness of the implementation. The interested reader is invited to consult Ref. 11 for more detailed results on the validation ...
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... three-dimensional visualizations of the state-space freevortex wake with a near-wake vortex-lattice model are shown in Fig. 13 for different flight conditions. These results correspond to the tightly coupled flight and free-wake dynamics trimmed at hover (Fig. 13a), at 120 kts during conversion between helicopter and airplane mode (Fig. 13b), and at 170 kts in airplane mode (Fig. 13c). Figure 13a shows the contraction of the wake below the rotor, indicative of the effectiveness of the implementation. The interested reader is invited to consult Ref. 11 for more detailed results on the validation of the vortex wake ...
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... of the state-space freevortex wake with a near-wake vortex-lattice model are shown in Fig. 13 for different flight conditions. These results correspond to the tightly coupled flight and free-wake dynamics trimmed at hover (Fig. 13a), at 120 kts during conversion between helicopter and airplane mode (Fig. 13b), and at 170 kts in airplane mode (Fig. 13c). Figure 13a shows the contraction of the wake below the rotor, indicative of the effectiveness of the implementation. The interested reader is invited to consult Ref. 11 for more detailed results on the validation of the vortex wake ...
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... results correspond to the tightly coupled flight and free-wake dynamics trimmed at hover (Fig. 13a), at 120 kts during conversion between helicopter and airplane mode (Fig. 13b), and at 170 kts in airplane mode (Fig. 13c). Figure 13a shows the contraction of the wake below the rotor, indicative of the effectiveness of the implementation. The interested reader is invited to consult Ref. 11 for more detailed results on the validation of the vortex wake model. ...
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... helicopter. The observer is fixed in the aircraft body frame. In this condition, the nacelles are tilted vertically at β m = 0 deg. The observer is located three rotor radii in front on the main rotor and lies in the plane of rotation of the rotor (i.e., approximately 6.92 ft along the water line). The observer position is shown qualitatively in Fig. 14. The chosen flight condition is hover. The azimuthal resolution used for the simulation is ∆ψ = 1 deg, such that the number of time steps per revolution is n ψ = 360. The spatial resolution used to discretize each rotor blade surface is 10 chordwise panels and 10 spanwise panels, as suggested in Ref. 45. Note that the blade upper and ...
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... such, a total 1200 panels are used to characterize the surface of all rotor blades. Figure 15 shows the total acoustic pressure generated by the rotors, as well as the acoustic pressure components, i.e., thickness, near-field loading, and far-field loading for a hovering condition. ...
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... closed-loop performance of the flight control law discussed above is demonstrated for a transition from hover to 10 kts forward flight. Figure 16 shows the closed-loop response to a 10 kts step input at hover. Figure 16a shows that the velocity command is tracked by the closed-loop dynamics while off-axis velocity responses are contained and stable. Figure 16b shows how the tilrotor initially pitches forward to accelerate and slowly settles to a small, positive pitch attitude once the target velocity is reached. ...
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... 16 shows the closed-loop response to a 10 kts step input at hover. Figure 16a shows that the velocity command is tracked by the closed-loop dynamics while off-axis velocity responses are contained and stable. Figure 16b shows how the tilrotor initially pitches forward to accelerate and slowly settles to a small, positive pitch attitude once the target velocity is reached. ...
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... 16 shows the closed-loop response to a 10 kts step input at hover. Figure 16a shows that the velocity command is tracked by the closed-loop dynamics while off-axis velocity responses are contained and stable. Figure 16b shows how the tilrotor initially pitches forward to accelerate and slowly settles to a small, positive pitch attitude once the target velocity is reached. Like for the velocity response, the off-axis responses in the roll and yaw angles are minimal and stable. ...
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... for the velocity response, the off-axis responses in the roll and yaw angles are minimal and stable. Figure 16c shows the closed-loop controls corresponding to the maneuver in consideration. The control system applies forward stick to achieve the desired nose-down pitch rate to tilt the rotor thrust forward and subsequently eases off the longitudinal stick once the target longitudinal speed is achieved. ...

Citations

... As in similar works [6,4,14], to ensure the validity of the control system a robust mathematical model was developed. The resolution of the model affects the validity of the control system and thus we must ensure the model considers all parameters within the scope of the chosen configuration. ...
... Given the derived safe operating area, we can select several points, within the region, as design points for our control simulation [14]. At each point, we will tune the PID gains to achieve the best result and then use gain scheduling to tie the design points together, as the aircraft transitions. ...
Preprint
Full-text available
Tiltrotors are an aircraft concept with the ability to rotate their rotors freely, achieving vertical take-off and fast forward flight. The combination of helicopter and fixed-wing flight into one aircraft provides versatility in mission selection, yet challenges persist in their construction and control. Tiltrotor aircraft can operate in three primary modes: helicopter, fixed-wing, and transition, with the transition mode facilitating the shift between helicopter and fixed-wing flight. However, control within this transition region is inherently challenging due to its non-linear nature, hence tiltrotors have been predominantly limited to military applications. Thus, this paper aims to explore transition mode control for a large-size tiltrotor aircraft, tailored to civil applications. A novel, large-sized, tiltrotor concept is presented, accompanied by a derived mathematical model describing the aircrafts behaviours. A PID control method has been used to control the height, pitch, and velocity variations within the transition mode with secondary control loop developed to control the tilt angle during transition. The derived model and control are then implemented within a MATLAB simulation, where the control method was iterated to improve performance. The results show a full transition was achieved in under 14 seconds, where altitude variations were kept below 10 metres. Though the transition mode control was successful, a collective look at the data showcases issues with assumptions as well as thrust discontinuities. The implications of these results are discussed, with suggested improvements proposed for future work.