COMPUTATIONAL STUDY OF AERODYNAMIC CHARACTERISTICS OF SINGLE-ROTOR HELICOPTER TAIL ROTOR UNDER THE INFLUENCE OF VORTICAL WAKE OF MAIN ROTOR AT THE HOVER WITH CROSSWIND

For single-rotor helicopters there are special flight modes, when tail rotor (TR) is under significant inductive influence of vortical wake of main rotor (MR). Inductive influence of vortical wake of MR can provoke essential changes in flowing of TR and its aerodynamic characteristics comparing to isolated rotor. In this case increase of tail rotor pitch, necessary for helicopter controlling, is possible.The article contains computational modelling of TR work with vortical wake of MR at the example of MIL Mi-171 helicopter. The modelling has been made on the base of non-linear blade (free wake) vortical model of rotor, produced at Helicopter Design Department of MAI.Helicopter hovering modes with crosswind of various intensity Vz was considered. Thrust-time lationship forisolated TR and TR with vortical wake of MR for equal flight modes was obtained. Flow around the rotors was analyzed, its vortical wake was considered.The results make it possible to clarify the peculiarities of TR work on considered modes and MR influence on its work. It was found out that vortical wake of MR has a more significant impact on TR work with crosswind on the right, when TR falls into vortex ring state mode. Inductive influence of vortical wake of MR leads to vortexring state mode for TR on lower speeds (Vz :: 5 m/s) than in case of isolated work of TR (Vz :: 12,5 m/s). In that case,the required tail rotor pitch has increased by 13% for Vz = 5 m/s. The results of modelling and flight tests led to good agreement.

helicopter, main rotor, tail rotor, hover with crosswind, aerodynamic interference, aerodynamic characteristics

1. Shibaev V., Favorova T., Apollonov D. Trenirovki pilotov v rasshirennoj oblasti parametrov dvizhenija vozdushnogo sudna kak zalog bezopasnosti poletov [Training of pilots in the extended area of motion parameters of the aircraft as a guarantee of safety]. Ajerokosmicheskij kur'er [Aerospace courier], 2011, no. 5, pp. 48–49. (in Russian)

2. Butov V.P. Struktura, Geometrija i intensivnost' sputnogo vihrevogo sleda nesushhih vintov odnovin-tovyh i soosnyh vertoletov v real'nyh uslovijah poleta [Structure, geometry and intensity of wake vortex of helicopter rotor in real flight conditions]. Materialy 4-go foruma Rossijskogo vertoletnogo obshhestva. Moscow, 2000, issue 1, pp. 19–34. (in Russian)

3. Shajdakov V.I., Ignatkin Y.M. Metody rascheta induktivnykh skorostei za predelami diska nesushchego vinta vertoleta na baze priblizhennoi modeli vikhrevogo sleda [Methods for calculating the inductive velocities outside of helicopter rotor on the basis of an approximate model of wake vortex]. Ajerodinamika kryla i korpusa letatel'nogo apparata [Aerodynamic of aircrafts wing and fuselage]. Sbornik statei, MAI publ. 1980, 60 p. (in Russian)

4. Ignatkin Y.M., Makeev P.V., Shomov A.I. Nelineinaya lopastnaya vikhrevaya teoriya vinta i ee prilozheniya dlya rascheta aerodinamicheskikh kharakteristik nesushchikh i rulevykh vintov vertoleta [Nonlinear blade vortex theory of rotor and its applied for calculation of aerodynamic characteristics of helicopter rotor]. Vestnik Moskovskogo aviatsionnogo instituta, 2009, vol. 16, no. 5, pp. 24–31. (in Russian)

5. Ignatkin Y.M., Makeev P.V., Shomov A.I. Chislennoe modelirovanie prikladnyh zadach ajerodinamiki vertoleta na baze nelinejnoj lopastnoj vihrevoj modeli vinta [Computational modeling of applied tasks of helicopter aerodynamics based on non-linear vortex model of a rotor]. Trudy MAI, 2016, no. 87. Available at: http://www.mai.ru/science/trudy/published.php?ID=65636 (accessed 01.10.2016). (in Russian)

6. Zozulya V.B., Ivanov Y.P. Prakticheskaja ajerodinamika vertoleta Mi-8 [Practical aerodynamic of Mi-8 helicopter]. Moscow, Mashinostroenie publ., 1977, 152 p.

7. Ignatkin Y.M., Makeev P.V., Shomov A.I. Interferencija nesushhego i rulevogo vintov vertoleta pri polete so skol'zheniem [Aerodynamic interference of helicopters main and tail rotor at horizontal yawed flight]. Trudy MAI, 2015, no. 82. Available at: http://www.mai.ru/science/trudy/published.php?ID=58605 (accessed 01.10.2016). (in Russian)

8. Ignatkin Y.M., Makeev P.V., Shomov A.I. Chislennoe issledovanie aerodinamicheskoi interferentsii nesushchego i rulevogo vintov vertoleta na osobykh rezhimakh poleta [Computational modeling of aerodynamic interference of helicopter main and tail rotors at the special flight regimes]. Nauchnyj Vestnik MGTU GA [Scientific bulletin of MSTUCA]. Moscow. 2014. no. 200, pp. 47–54. (in Russian)

9. Ignatkin Y.M., Makeev P.V., Shomov A.I. Chislennoe modelirovanie interferentsii nesushchego i rulevogo vintov vertoleta na baze nelineinoi lopastnoi vikhrevoi modeli. [Computational modeling of interference of helicopter main and tail rotors on the base of non-linear blade vortex model]. Izvestija vysshih uchebnyh zavedenij. Aviacionnaja tehnika. [Russian Aeronautics], 2016, no. 1. pp. 41–47. (in Russian)

10. Volodko A.M. Bezopasnost' poleta vertoletov [Helicopter flight safety]. Moscow. Transport publ., 1981, 225 p. (in Russian)