Springer Nature is making SARS-CoV-2 and COVID-19 research free. View research | View latest news | Sign up for updates

Operational Modal Analysis of a Helicopter Rotor Blade Using Digital Image Correlation


A novel procedure to perform operational modal analysis on a reduced-scale, 2 m diameter helicopter rotor blade is described. Images of the rotor blade rotating at 900 RPM are captured by a pair of high-speed digital cameras at a sampling rate of 1000 frames per second. From these images, the out-of-plane bending deformation of the rotor blade is measured using Digital Image Correlation, with a spatial resolution of 7.2 mm and an accuracy of 60 μm, or 0.006 % of the rotor radius. Modal parameters including natural frequencies and mode shapes are determined from the bending deformation through application of the Ibrahim Time Domain method. The first three out-of-plane bending modes were identified at each rotational speed and compared to an analytical finite element model of the rotor blade. The experimental and analytical natural frequencies agreed to within 0.2 % in the best case and 10.0 % in the worst case. The experimental mode shapes were also found to closely match the analytical predictions. The results of this study demonstrate the ability of this procedure to accurately determine the modal parameters of rotating helicopter rotor blades.

This is a preview of subscription content, log in to check access.

Fig. 1
Fig. 2
Fig. 3
Fig. 4
Fig. 5
Fig. 6
Fig. 7
Fig. 8
Fig. 9


  1. 1.

    Bucher I, Ewins DJ (2001) Modal analysis and testing of rotating structures. Philos Trans R Soc London, Ser A Math Phys Eng Sci 359(1778):61–96

  2. 2.

    Wilkie WK, Mirick PH, Langston CW (1997) Rotating shake test and modal analysis of a model helicopter rotor blade. Technical Report NASA TM 4760, National Aeronautics and Space Administration, Langley Research Center, Hampton, Virginia 23681

  3. 3.

    Schroeder K, Ecke W, Apitz J, Lembke E, Lenschow G (2006) A fibre bragg grating sensor system monitors operational load in a wind turbine rotor blade. Meas Sci Technol 17(5):1167

  4. 4.

    Molenaar DP (2003) Experimental modal analysis of a 750 kw wind turbine for structural model validation. In: ASME Wind Energy Symposium, pages 332–339. American Society of Mechanical Engineers, p 2003

  5. 5.

    Abrego AI, Olson LE, Romander EA, Barrows DA, Burner AW (2012) Blade displacement measurement technique applied to a full-scale rotor test. In: American Helicopter Society 68th Annual Forum, Fort Worth, Texas, May 1 3

  6. 6.

    Ozbek M, Rixen DJ, Erne O, Sanow G (2010) Feasibility of monitoring large wind turbines using photogrammetry. Energy 35(12):4802–4811

  7. 7.

    Baqersad J, Poozesh P, Niezrecki C, Avitabile P (2016) Photogrammetry and optical methods in structural dynamics - a review. Mech Syst Signal Process:–

  8. 8.

    Lundstrom T, Baqersad J, Niezrecki C (2013) Special Topics in Structural Dynamics. In: Proceedings of the 31st IMAC, A Conference on Structural Dynamics, 2013, chapter Using High-Speed Stereophotogrammetry to Collect Operating Data on a Robinson R44 Helicopter, pages 401–410. Springer New York, New York, NY, vol 6

  9. 9.

    Kahn-Jetter ZL, Chu TC (1990) Three-dimensional displacement measurements using digital image correlation and photogrammic analysis. Exp Mech 30(1):10–16

  10. 10.

    Wu P, Ifju P, Stanford B (2010) Flapping Wing Structural Deformation and Thrust Correlation Study with Flexible Membrane Wings. AIAA J 48(9):2111–2122

  11. 11.

    Tran J, Sirohi J, Gao H, Wei M (2015) Reduced-order modeling of loads and deformation of a flexible flapping wing. In: AIAA 2015-0177, 56th AIAA/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference, Kissimmee, Florida, Jan. 5–9

  12. 12.

    Ha NS, Vang HM, Goo NS (2015) Modal analysis using digital image correlation technique: An application to artificial wing mimicking beetle’s hind wing. Exp Mech 55(5):989–998

  13. 13.

    Sirohi J, Lawson MS (2012) Measurement of helicopter rotor blade deformation using digital image correlation. Opt Eng 51(4):043603–1

  14. 14.

    Sicard J, Sirohi J (2013) Measurement of the deformation of an extremely flexible rotor blade using digital image correlation. Meas Sci Technol 24(6):065203

  15. 15.

    Ibrahim SR, Mikulcik EC (1977) A method for the direct identification of vibration parameters from the free response, Shock and Vibration Bulletin. Bulletin:47

  16. 16.

    Ibrahim SR (1986) Double least squares approach for use in structural modal identification. AIAA J 24 (3):499–503

  17. 17.

    Ibrahim SR, Pappa RS (1982) Large modal survey testing using the ibrahim time domain identification technique. J Spacecr Rocket 19(5):459–465

  18. 18.

    Cameron CG, Karpatne A, Sirohi J (2016) Performance of a mach-scale coaxial counter-rotating rotor in hover. J Aircr:1–10

  19. 19.

    Schmaus J, Chopra I (2015) Performance and loads prediction for a high advance ratio coaxial rotor

  20. 20.

    Allemang RJ (2003) The Modal Assurance Criterion – Twenty Years of Use and Abuse. Sound Vib 37(8):14–23

Download references


This material is based upon work supported by, or in part by, the U. S. Army Research Laboratory and the U. S. Army Research Office under contract/grant number W911NF-13-1-0463, with Dr. Matthew Munson as Program Manager.

Author information

Correspondence to J. Sirohi.

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Rizo-Patron, S., Sirohi, J. Operational Modal Analysis of a Helicopter Rotor Blade Using Digital Image Correlation. Exp Mech 57, 367–375 (2017).

Download citation


  • Digital image correlation
  • Helicopter blade deformation
  • Modal analysis
  • Rotating natural frequency
  • Rotating mode shape