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3 - Hover

Published online by Cambridge University Press:  05 May 2013

Wayne Johnson
Wayne Johnson
Affiliation:
Aeromechanics Branch of NASA Ames Research Center
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Summary

Hover is the operating state in which the lifting rotor has no velocity relative to the air, either vertical or horizontal. General vertical flight involves axial flow with respect to the rotor. Vertical flight implies axial symmetry of the rotor flow field, so the velocities and loads on the rotor blades are independent of the azimuth position. Axial symmetry greatly simplifies the dynamics and aerodynamics of the helicopter rotor, as is evident when forward flight is considered. The basic analyses of a rotor in axial flow originated in the 19th century with the design of marine propellers and were later applied to airplane propellers. The principal objectives of the analysis of the hovering rotor are to predict the forces generated and power required by the rotating blades and to design the most efficient rotor.

Momentum Theory

Momentum theory applies the basic conservation laws of fluid mechanics (conservation of mass, momentum, and energy) to the rotor and flow as a whole to estimate the rotor performance. The theory is a global analysis, relating the overall flow velocities to the total rotor thrust and power. Momentum theory was developed for marine propellers by W.J.M. Rankine in 1865 and R.E. Froude in 1885, and extended in 1920 by A. Betz to include the rotation of the slipstream; see Glauert (1935) for the history.

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Chapter
Information
Rotorcraft Aeromechanics , pp. 39 - 91
Publisher: Cambridge University Press
Print publication year: 2013

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References

Bailey, F.J. Jr., “A Simplified Theoretical Method of Determining the Characteristics of a Lifting Rotor in Forward Flight.” NACA Report 716, 1941.Google Scholar
Glauert, H. “Airplane Propellers.” In Aerodynamic Theory, Durand, W.F. (Editor). New York: Julius Springer, 1935.Google Scholar
Goldstein, S. “On the Vortex Theory of Screw Propellers.” Proceedings of the Royal Society of London, Series A, 123:792 (April 1929).
Gray, R.B. “On the Motion of the Helical Vortex Shed from a Single-Bladed Hovering Model Helicopter Rotor and Its Application to the Calculation of the Spanwise Aerodynamic Loading.” Princeton University, Aeronautical Engineering Department Report No. 313, September 1955.Google Scholar
Gray, R.B. “An Aerodynamic Analysis of a Single-Bladed Rotor in Hovering and Low-Speed Forward Flight as Determined from Smoke Studies on the Vorticity Distribution in the Wake.” Princeton University, Aeronautical Engineering Department Report No. 356, September 1956.Google Scholar
Knight, M., and Hefner, R.A. “Static Thrust Analysis of the Lifting Airscrew.” NACA TN 626, December 1937.Google Scholar
Kocurek, J.D., and Tangler, J.L. “A Prescribed Wake Lifting Surface Hover Performance Analysis.” Journal of the American Helicopter Society, 22:1 (January 1977).CrossRefGoogle Scholar
Landgrebe, A.J. “An Analytical and Experimental Investigation of Helicopter Rotor Hover Performance and Wake Geometry Characteristics.” USAAMRDL TR 71–24, June 1971.Google Scholar
Landgrebe, A.J. “The Wake Geometry of a Hovering Helicopter Rotor and Its Influence on Rotor Performance.” Journal of the American Helicopter Society, 17:4 (October 1972).CrossRefGoogle Scholar
Sissingh, G. “Contribution to the Aerodynamics of Rotating-Wing Aircraft.” NACA TM 921, December 1939.Google Scholar
Theodorsen, T. “The Theory of Propellers.” NACA Reports 775, 776, 777, and 778, 1944.Google Scholar
Wheatley, J.B. “An Aerodynamic Analysis of the Autogiro Rotor with a Comparison Between Calculated and Experimental Results.” NACA Report 487, 1934.Google Scholar

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  • Hover
  • Wayne Johnson
  • Book: Rotorcraft Aeromechanics
  • Online publication: 05 May 2013
  • Chapter DOI: https://doi.org/10.1017/CBO9781139235655.004
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  • Hover
  • Wayne Johnson
  • Book: Rotorcraft Aeromechanics
  • Online publication: 05 May 2013
  • Chapter DOI: https://doi.org/10.1017/CBO9781139235655.004
Available formats
×

Save book to Google Drive

To save content items to your account, please confirm that you agree to abide by our usage policies. If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account. Find out more about saving content to Google Drive.

  • Hover
  • Wayne Johnson
  • Book: Rotorcraft Aeromechanics
  • Online publication: 05 May 2013
  • Chapter DOI: https://doi.org/10.1017/CBO9781139235655.004
Available formats
×