Aerospace Science and Technology
Farid Shahmiri; Fatemeh Kiani
Abstract
The optimum rotor blade planform of helicopters required to minimize power, maximize rotor thrust, and maximize lift-to-drag ratio in forward flight, using a numerical optimization approach, is investigated. Here, the traditional approach is modified by Central Composite Design Data (CCD) and a flight ...
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The optimum rotor blade planform of helicopters required to minimize power, maximize rotor thrust, and maximize lift-to-drag ratio in forward flight, using a numerical optimization approach, is investigated. Here, the traditional approach is modified by Central Composite Design Data (CCD) and a flight dynamic simulation program coupled with a desirability optimization technique implemented in the process of blade optimization. The optimum blade planform parameters (i.e, root chord, taper ratio, taper offset, two-per revolution (2/rev) harmonic control, and 2/rev blade dynamic twist) for different gross weights and flight speeds are therefore obtained by this modified procedure. In addition, the main effects and the interaction of all parameters on helicopter performance are assessed. The results of optimization in case 1 confirm that the appropriate 2/rev harmonic control and twist of the partially tapered blades improve the helicopter power required by 2.6% and lift-to-drag ratio up to about 20% at a baseline gross weight. In case 2 of optimization, tapering the blade to 60% from 0.9R with an appropriately phased 1/rev and 2/ rev twist and 2/rev harmonic control increases the rotor thrust coefficient by 23%, and the lift-to-drag-ratio by about 15%. The helicopter gross weight is declared influence on the thrust increment achieved by the 2/rev twist and 2/rev harmonic control. Overall, 2/rev harmonic control can be incorporated into existing helicopters by a modification of the swashplate and control inputs can be transmitted to the rotor using a fixed outer member with a track linked to a conventional swashplate.
Aerospace Science and Technology
Hamidreza Jafari; Farid Shahmiri
Volume 12, Issue 1 , March 2019, , Pages 39-51
Abstract
In this paper, the particular solution technique for inverse simulation applied to the quadrotor maneuvering flight is investigated. The trust-region dogleg (DL) technique which is proposed alleviates the weakness of Newton’s method used for numerical differentiation of system states in the ...
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In this paper, the particular solution technique for inverse simulation applied to the quadrotor maneuvering flight is investigated. The trust-region dogleg (DL) technique which is proposed alleviates the weakness of Newton’s method used for numerical differentiation of system states in the solution process. The proposed technique emphasizes global convergence solution to the inverse simulation problem. This algorithm is evaluated by calculating the control inputs necessary to enable the quadrotor to follow a specified trajectory including climb-hover and cruise-hover maneuvers. The trajectory is generated by the direct simulation using a linear optimal control developed for the quadrotor. The model of rotors for the quadrotor is a nonlinear model developed based on blade element theory (BET), linear aerodynamics, and non uniform inflow over the rotor disc. The results show that the control inputs obtained from the inverse simulation are in good agreement with control inputs estimated by direct simulation. The results also confirm that the maximum difference between the prescribed trajectory and the trajectory generated by the direct simulation is less than 0.02%, and thus the potential application of the inverse simulation with the trust-region dogleg optimization is evident.
