Aerodynamic interference of helicopters main and tail rotor at horizontal yawed flight

Аuthors

Ignatkin Y. M.^1*, Makeev P. V.^**, Shomov A. I.^2***

1. Moscow Aviation Institute (National Research University), 4, Volokolamskoe shosse, Moscow, А-80, GSP-3, 125993, Russia
2. National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia

*e-mail: k102@mai.ru; ignatkinym@mai.ru
**e-mail: vaultcity13@gmail.com
***e-mail: shomov_aleksandr@mail.ru; a.shomov@nhc.aero

Abstract

It is known that on horizontal flights with low velocities vortex wake of main rotor rolls up, making two secondary vortex cores on the periphery of each wake. Top intensity of these cores is observed on the flight velocity V ≈ 10 m/s. There can be episodes when tail rotor of a helicopter is nearby one of these vortex cores. In this situation tail rotor happens to be in powerful unsteady field of induced velocities produced by vortex core and this may lead to sharp change in its aerodynamic characteristics, including significant rotor’s thrust drop. This fact can provoke flight accident, connected with tail rotor’s loss of efficiency and uncontrolled rotation of a helicopter.

The aim of the paper is computational modeling of main and tail rotors’ interference horizontal flight regime on low velocities with sliding.

The research has been conducted on the basis of non-linear blade vortical model of a rotor created at the department «Helicopter Design» of MAI and software package based on it.

For main and tail rotor’s of MIL MI-2 helicopter there was been modeled horizontal flight with angle of attack of main rotor α_H = 0° and flight velocity V = 10 mps and slide (yawing) angles β_H = −90...90°. As a newest of computation there were obtained dependencies of tail rotor’s thrust change (due to interference for two variants of its rotational direction) on slide (yawing) angle in relation with isolated tail rotor’s thrust at the same regimes. There is observed change of relative thrust due to interference from 68% to 174% (where thrust of isolated rotor is taken as 100% in each computational point) depending on tail rotor’s rotational direction’s, flight velocity V and slide (yawing) angle β_H.

For the most typical regimes there is demonstrated a form of free vortical wake of main and tail rotor’s. There are analyzed reasons of interference and its influence on aerodynamic characteristics of tail rotor.

The results of research can be used in the process of rational directions of tail rotor’s estimation and evaluation resources of handling in yaw (directional controllability) in flight at different regimes with yawed low velocities flight.

Keywords:

main rotor, tail rotor, computational methods of rotor's aerodynamics, non-linear vortical model, horizontal flight regime with a helicopter slip, rotors’ interference, aerodynamic characteristics

References

1. Ignatkin Y.M., Makeev P.V, Shomov A.I. Elektronnyj zhurnal «Trudy MAI», 2013, no. 69, available at: http://www.mai.ru/science/trudy/eng/published.php?ID=43135 (accessed 10.10.2013).

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7. Ignatkin Y.M., Makeev P.V, Shomov A.I. Elektronnyj zhurnal «Trudy MAI», 2010, no. 38, available at: http://www.mai.ru/science/trudy/eng/published.php?ID=14148 (accessed 23.06.2010).

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