The process of rotor speed variation under tiltrotor cruise state has been studied, and the integrated variable speed control method of tiltrotor based on two-speed gearbox is proposed. Firstly, a nonlinear model predictive controller (NMPC) based on state variable model of the component-level model of the turboshaft engine is designed. Then based on the integrated engine model, the two-speed dual path tiltrotor driveline comprehensive simulation model was developed by utilizing gear kinematics theory, blade element analysis and the theory of classical mechanics. Finally, both a Parallel Shift Control (PSC) strategy and a Sequential Shift Control (SSC) strategy in tiltrotor cruise state were analyzed and compared with conventional PID controller. It is shown that the rotors’ speed can synchronously vary by 50 percent under the PSC strategy in tiltrotor cruise state. Meanwhile, disengaging the engine in turn by freewheel clutches can reduce the rotors’ speed from 190 rpm to 102.5 rpm along the specified path under the SSC strategy. The overshoot and droop amount of the power turbine speed can be reduced to less than 1.5 % with the steady error no more than 0.2 % through NMPC, which realizes the fast response control of the turboshaft engine.

A novel control method combining nonlinear model predictive control (NMPC) with linear kalman filter (LKF) and adaptive notch filter (ANF) for an integrated helicopter/engine system with variable rotor speed is proposed to enhance the response ability of turboshaft engine. Firstly, based on the integrated helicopter/engine model with variable rotor speed, an ANF combined with frequency estimation is introduced. Then, in order to estimate the significant and unmeasurable performance parameters utilized in model predictive control, such as temperature before turbine, a nonlinear model predictive controller based on LKF is presented. The simulation verifications demonstrate that the fundamental frequency of torsional vibration changes from 1.30 Hz to 2.70 Hz when the rotor speed varies continuously by 50 %. In this case, compared with the notch filter, all torsional vibration amplitudes are damped below 0.1 % by ANF. Meanwhile, in comparison with the PID controller, the NMPC can reduce the overshoot and droop of the power turbine speed to less than 1 % with steady-state error no more than 0.5 % at the off-design point of NMPC based on adaptive torsional vibration suppression. The applications of LKF and similar transformation improve the control accuracy and robustness performance of the NMPC designed at a single operating point.

A real-time optimization control method is proposed to extend turbo-fan engine service life. This real-time optimization control is based on an on-board engine mode, which is devised by a MRR-LSSVR (multi-input multi-output recursive reduced least squares support vector regression method). To solve the optimization problem, a FSQP (feasible sequential quadratic programming) algorithm is utilized. The thermal mechanical fatigue is taken into account during the optimization process. Furthermore, to describe the engine life decaying, a thermal mechanical fatigue model of engine acceleration process is established. The optimization objective function not only contains the sub-item which can get fast response of the engine, but also concludes the sub-item of the total mechanical strain range which has positive relationship to engine fatigue life. Finally, the simulations of the conventional optimization control which just consider engine acceleration performance or the proposed optimization method have been conducted. The simulations demonstrate that the time of the two control methods from idle to 99.5 % of the maximum power are equal. However, the engine life using the proposed optimization method could be surprisingly increased by 36.17 % compared with that using conventional optimization control.

In order to solve the problem of torsional vibration instability of control unit in helicopter/engine system during maneuver flight, this paper has conducted the research on the integrated torsional vibration suppression of helicopter/engine system. Firstly, an integrated helicopter/engine model combined with torsional vibration is established based on the UH-60 helicopter model. Then the torsional vibration filter that is composed of a notch filter and a low-pass filter is applied to speed control loop of the engine to suppress the torsional vibration of power turbine speed. It is shown that the integrated helicopter/engine model combined with torsional vibration can simulate the torsional vibration characteristics under variable rotor speed, and both the low-order and high-order amplitudes of torsional vibration can be effectively eliminated below 0.04 % at constant rotor speed through utilizing the torsional vibration filter. Meanwhile, when the helicopter operates under variable rotor speed, the fundamental frequency of torsional vibration varies from 1.30 Hz to 2.30 Hz. However, all torsional vibration amplitudes within this frequency range can be damped less than 0.05 % through the notch filter whose bandwidth is 2.3 Hz, which proves the remarkable effect of torsional vibration suppression.

In order to describe how the variant BPR affects the flow performance, a qusi-2D fan model was proposed. In the model, the stage cumulative method was applied to compute axial flow and the simplified radial equilibrium equation was applied to compute radial flow, then a dual-level iteration program was proposed for the nominal performance calculation. To compute the non-nominal flow characteristics on non-nominal BPR, a triple-level iteration program with the compensation factor was proposed to obtain the radial profiles. On that basis, Blade angles were designed for this model on the design point. With the inflow deflection factor designed as 0.8 and the loss factor along blade as 0.95, the pressure ratio error is only 0.21 % and the isentropic efficiency error is 0.06 %. Simulation showed that the variant-BPR profiles and the overall characteristics of flow at fan exit or for bypass & core ducts could be well computed with much less time-consuming.