Blade Coupled Bending-and-Torsional Oscillations Computing While the Helicopter Main Rotor Spin-Up and Deceleration under Wind Conditions

Аuthors

Kargaev M. V.^{1, 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: kargaev_mv@mail.ru

Abstract

In accordance with the requirements of the helicopters airworthiness standards, besides the critical flight loads the main rotor (MR) design should as well withstand the loads originating in the ground cases, such as blade hitting the hinges arrester (limiter) while the rotor spin-up or deceleration, sharp rotor deceleration, as well as “any other critical loading, expected during normal operation”. The blades hitting the hinges arrester while the MR spin-up or deceleration are probable at the strong enough wind presence at the helicopter parking lot. Likewise, significant blades deflection occur in this case, which, at certain wind speeds, may lead to the blade hitting the helicopter tailbeam or its other structural elements. The similar problem occurs while the rotor rotation absence as well.
As far as the blades parameters are being selected mainly based on ensuring strength,  aeroelastic stability, as well as acceptable level of stresses and vibrations in flight, the task for special cases consists in determining restrictions and/or setting the operation regulations, ensuring acceptable levels of at these restrictions of critical (maximum) loads and/or displacements. In the case of rotor spin-up and deceleration under wind conditions, the task consists in determining the maximum wind speeds, at which sufficient clearance is ensured between the rotor blades and the other parts of the structure to prevent the blades from hitting any part of the structure in any expected operating conditions.
The author of the article obtained the equations of coupled bending-and-torsional oscillations of the main rotor blade rotating at variable speed under non-stationary wind conditions for the case of large displacements. The approach to the numerical integration of these equations is proposed as well, which allows to quantifying the maximum wind speeds during the spin-up and deceleration of the main rotor, computing the strength of the blade in ground loading cases, and in particular, during the MR sudden deceleration and when hitting the stops of the MR hinges. The results of the maximum wind speed computing during spin-up of the main rotor of the Mi-171A3 helicopter are presented.

Keywords:

main rotor blade, wind loading, main rotor spin-up and deceleration, Galerkin method, Newmark method, SVD-algorithm, stress-strain state

References

1.  Normy letnoi godnosti grazhdanskikh vertoletov SSSR (Airworthiness standards of civil helicopters of the USSR). 2nd ed. Moscow: Mezhduvedomstvennaya komissiya po normam letnoi godnosti grazhdanskikh samoletov i vertoletov SSSR; 1987. 411 p. (In Russ.).
2.  Mezhgosudarstvennyi aviatsionnyi komitet. Aviatsionnye pravila. Ch. 29. Normy letnoi godnosti vintokrylykh apparatov transportnoi kategorii (Interstate Aviation Committee. Civil Aviation Safety Regulations. Part 29. Airworthiness standards for rotorcraft in the transport category). Moscow: Aviaizdat; 2018. 185 p. (In Russ.).
3.  Normy letnoi godnosti vintokrylykh apparatov transportnoi kategorii NLG-29 (Airworthiness standards of rotorcraft NLG-29 transport category). Moscow: TSENTRMAG; 2024. 252 p. (In Russ.).
4.  Kargaev MV., Mironenko LA. Bending stresses computation in a helicopter unmoored rotor blade blown about by the wind flow. Aerospace MAI Journal. 2018;25(3):34-43. (In Russ.).
5.  Kargaev MV. Stresses computing in the main rotor blade based on the nonlinear loading model under static wind impact. Aerospace MAI Journal. 2019;26(2):34-42. (In Russ.).
6.  Kargaev MV. Dynamic stresses computing in the main rotor blade based on the non-linear loading model under unsteady wind impact. Polet. Obshcherossiiskii nauchno-tekhnicheskii zhurnal. 2020;(4):52–60. (In Russ.).
7.  Mil' ML, Nekrasov AV, Braverman AS. et al. Vertolety, raschet i proektirovanie: v 2 tomakh (Helicopters, calculation and design: in 2 vls). Moscow: Mashinostroenie; 1966/1967. (457+424) p. (In Russ.).
8.  Johnson W. Rotorcraft Aeromechanics. NY: Cambridge University Press; 2013. 949 p.
9.  Bielawa RL. Rotary Wing Structural Dynamics and Aeroelasticity. 2nd ed. Washington: DC, AIAA; 2006. 584 p.
10.  Ivchin VA, Aver'yanov IO. Development of a method for calculating deformations of the elastic rotor blade of a helicopter in the planes of thrust rotation and torsion by direct integration. Nauchnyi Vestnik MGTU GA. 2011;(172):80–87. (In Russ.).
11.  Grishanina TV, Russkikh SV. Kolebaniya vrashchayushcheisya lopasti nesushchego vinta vertoleta (Oscilations of the rotating main rotor blade of the helicopter), Moscow: MAI; 2016. 54 p. (In Russ.).
12.  Kargaev MV.  Dynamic stability of the helicopter main rotor blade under the harmonic influence of wind. Polet. Obshcherossiiskii nauchno-tekhnicheskii zhurnal.  2020(11):21–31. (In Russ.).
13.  Yudakov AA, Boikov VG. Numerical methods of multibody mechanical system’s dynamic equations integration, based on methods of direct integration of finite element method’s dynamic equations. Vestnik Udmurtskogo universiteta. Matematika. Mekhanika. Komp'yuternye nauki. 2013;(1):131-144. (In Russ.).
14.  Horn RA, Johnson CR. Matrix analysis. 2nd ed. NY: Cambridge University Press; 2012. 662 p.
15.  Voskoboinikov YuE, Mitsel' AA. Sovremennye problemy prikladnoi matematiki. Chast' 1. Lektsionnyi kurs (Modern problems of applied mathematics. Part 1. Lecture course). Tomsk: TUSUR; 2015. 136 p. (In Russ.).
16.  Ivanov VK, Vasin VV, Tanana VP. Theory of Linear Ill-Posed Problems and its Applications. Utrecht, Boston, Koln, Tokyo: VSP; 2002. 281 p. (In Russ.).
17.  Kargaev MV, Savina DB. Stresses computation method in the skin of non-rotating main rotor blades tail sections under the impact of the wind at the helicopter parking lot. Aerospace MAI Journal. 2023;30(3):17-25. (In Russ.).
18.  Tikhonov AN, Goncharovskii AV, Stepanov VV, Yagola AG. Chislennye metody resheniya nekorrektnykh zadach (Regularizing algorithms and a priori information). Moscow: Nauka; 1990. 229 p. (In Russ.).
19.  Brunton SL., Kutz JN. Data-Driven  Science and Engineering. 2nd ed. Cambridge University Press; 2022. 614 p.
20.  Osipov KA. Computational mesh generation in computational aero-hydrodynamics probllems. Trudy TsAGI. 2019;(2791):1-27. (In Russ.).