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

Аuthors

Kargaev M. V.^*, Savina D. B.^**

National Helicopter Center Mil & Kamov, 26/1, Garshina str., Tomilino, Moscow region, 140070, Russia

*e-mail: kargaev_mv@mail.ru
**e-mail: savina_db@mail.ru

Abstract

The task of ensuring an acceptable level of stress in all structural elements of the main rotor blade both in flight and in the parking lot of the helicopter is one of the paramount ones while its design. It is well-known that the stresses arising in the main rotor blade spar from the forces of the blade’s own weight and wind loading may reach significant values, and lead to the residual deformations appearance.

The blade tail sections are less strong than the spar elements. With the achieved spar strength level, ensuring an equal level of strength of the tail sections under the action of wind in the parking lot, especially for a blade with a large chord and width of the tail sections is necessary. Creating a light and durable tail sections design is a constituent part of the task on the main rotor blades designing.

In this regard, the strength computing method developing for the tail sections and, in the first place, its skin as the most loaded and significant by weight presents interest.

The problem on determining the stress-strain state of main rotor blade tail sections skins is being solved in the open press mainly for the cases of the in-flight loading.

The presented article proposes a method for stresses computing in the tail sections skin of non-rotating main rotor blades under the impact of wind in the helicopter parking lot, based on the numerical solution of the plane problem of elasticity theory, as well as computing stresses in the blade spar under the static impact of the wind. The obtained system of differential equations describing the skin stress-strain state by the grid method is reduced to a system of linear algebraic equations with respect to the sought displacements. The SVD-algorithm for the pseudo-solution construction was employed for this system numerical solution.

The article presents the results of computations performed for the main rotor blades skins of the Mi-38 type helicopter. The wind speed limit is determined by the condition of the tail sections skins strength of the blade being considered at the given blowing direction. Comparative calculations of longitudinal stresses in the tail section skin under the action of the blade’s own weight forces demonstrated close convergence with experimental data.

Keywords:

main rotor blade, tail section skin, wind loading, static strength, grid method, singular value decomposition

References

1. Kargaev M.V. Materialy XII Obshcherossiiskoi molodezhnoi nauchno-tekhnicheskoi konferentsii “Molodezh’” Tekhnika. Kosmos” (23–25 April 2020; St. Petersburg). V 4 tomakh. St. Petersburg, BGTU “Voenmekh”, 2020, vol. 1, pp. 150-154.

2. Kargaev M.V., Mironenko L.A. Bending stresses computation in a helicopter unmoored rotor blade blown about by the wind flow. Aerospace MAI Journal, 2018, vol. 25, no. 3, pp. 34-43.

3. Kargaev M.V. Stresses computing in the main rotor blade based on the nonlinear loading model under static wind impact. Aerospace MAI Journal, 2019, vol. 26, no. 2, pp. 34-42.

4. Kargaev M.V. Polet. Obshcherossiiskii nauchno-tekhnicheskii zhurnal, 2020, no. 4, pp. 52–60.

5. Ivanov A.N. Trudy opytno-konstruktorskogo byuro, 1971, vol. 8, pp. 120-137.

6. Johnson W. Rotorcraft Aeromechanics. NY, Cambridge University Press, 2013, 927 p.

7. Bielawa R.L. Rotary Wing Structural Dynamics and Aeroelasticity. 2nd edition. Washington, DC, AIAA, 2006, 584 p.

8. Surovtseva O.E. Prochnost’ khvostovykh otsekov lopasti nesushchego vinta vertoleta (Strength of the helicopter main rotor blade tail sections), Candidat of technical science, Kazan, A.N. Tupolev KSTU, 1994, 8 p.

9. Dudnik V.V. Konstruktsiya vertoletov (Helicopter design), Rostov-on-Don, Izdatel’skii dom IUI AP, 2005, 158 p.

10. Lekhnitskii S.G. Teoriya uprugosti anizotropnogo tela (Elasticity theory of anisotropic body). 2nd ed. Мoscow, Nauka, 1977, 416 p.

11. Ashkenazi E.K., Ganov E.V. Anizotropiya konstruktsionnykh materialov (Anisotropy of machine–building materials). 2nd ed. Leningrad, Mashinostroenie, 1980, 247 p.

12. Ryabinovich A.L. Ob uprugikh postoyannykh i prochnosti anizotropnykh materialov (On elastic constants and strength of anisotropic materials), Мoscow, Byuro novoi tekhniki, 1946, 55 p.

13. Varvak P.M., Varvak L.P. Metod setok v zadachakh rascheta stroitel’nykh konstruktsii (Method of grids in problems of building structures calculation), Мoscow, Stroiizdat, 1977, 154 p.

14. Horn R.A., Johnson C.R.. Matrix analysis. 2nd ed. NY, Cambridge University Press, 2013, 662 p.

15. Voskoboinikov Yu.E., Mitsel’ A.A. Sovremennye problemy prikladnoi matematiki. Chast’ 1. Lektsionnyi kurs (Modern problems of applied mathematics. Part 1. Lecture course), Tomsk, TUSUR, 2015, 136 p.

16. Ivanov V.K., Vasin V.V., Tanana V.P. Theory of Linear Ill- Posed Problems and its Applications. Utrecht, Boston, Koln, Tokyo, VSP, 2002, 281 p.

17. Tikhonov A.N., Arsenin V.Ya. Metody resheniya nekorrektnykh zadach (Methods of ill–posed problems solving), Moscow, Nauka, 1986, 285 p.

18. Tikhonov A.N., Goncharovskii A.V., Stepanov V.V., Yagola A.G. Chislennye metody resheniya nekorrektnykh zadach (Numerical methods for ill–posed problems solving), Moscow, Nauka, 1990, 229 p.

19. Brunton S.L., Kutz J.N. Data-Driven Science and Engineering: Machine Learning, Dynamical Systems, and Control. 2nd ed. NY, Cambridge University Press, 2022, 614 p.

20. Ushakov A.E. Metodologiya obespecheniya ekspluatatsionnoi zhivuchesti i bezopasnosti aviakonstruktsii iz PKM (Methodology for ensuring operational survivability and safety of aircraft structures from PCM), Moscow, Fizmatlit, 2012, 204 p.