Computational modeling of aerodynamic interference of helicopter main and tail rotor at horizontal flight mode with a sideslip
Аuthors1*, 1**, 2***
2. Moscow helicopter plant named after M.L. MiL, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia
AbstractThe paper is focused on the problems of providing flight safety for a single-rotor helicopter at special flight modes. At these modes the tail rotor can be exposed to some conditions, under which its aerodynamic characteristics change drastically. Herewith in case of tail rotor thrust decay its effectiveness as a control unit decreases. This can lead to loss of directional trim of the helicopter, its uncontrolled rotation and crash.
The paper aims at carrying out the computational study of main and tail rotor interference during low-speed horizontal flight with sideslip.
The research was carried out by using the specially created software, which is based on the non-linear rotor vortical blade model developed at the “Helicopter Design” Department of MAI.
The research was carried out for a calculation model of a combination of main and tail rotor of Mi-2 helicopter. The case of horizontal flight with angle of attack of main rotor αн = 0º and flight speed V = 10 mps was modeled during the research.
The helicopter sideslip angles within the range of βн = -90…90º with pitch 10º were considered. The shape of the free vortical wake of main and tail rotors was built for the mentioned above modes with and without taking into account interference. Diagrams of induced velocities of the main rotor vortical wake in the area of tail rotor location were constructed. Reasons of interference effect emergence were analyzed and its influence on aerodynamic characteristics of the tail rotor was estimated.
As a result of the research it was established that main and tail rotor interference develops to a large degree at the considered flight modes. At that the interference is determined by the vortex wake structure of the main rotor, which forms two secondary vortex cores at horizontal flight modes, and the location of the mentioned vortex cores relative to the tail rotor. It was shown that the severity of exposure of the tail rotor to main rotor influence depends on the operation mode and rotation direction of the tail rotor. The research results show that the decrease of tail rotor thrust due to interference reaches its maximum of 26 % compared to the thrust of the isolated tail rotor at βн = -50. It was established that the counterclockwise direction of tail rotor rotation (upper blade moves backwards) is optimal in terms of influence of interference on its thrust.
The research results can be used for estimating and choosing the optimal direction of tail rotor rotation and determining directional control and stability margins during design and modernization of helicopters.
Keywords:main rotor, tail rotor, computational methods of rotor's aerodynamics, non-linear vortical model, horizontal flight mode with a sideslip, rotor interference, aerodynamic characteristics
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