Vertical Flight

Wayne Johnson

doi:10.1017/CBO9781139235655.005

4 - Vertical Flight

Published online by Cambridge University Press: 05 May 2013

Wayne Johnson

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

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Summary

Vertical flight of the helicopter rotor at speed V includes the operating states of hover (V = 0), climb (V > 0), and descent (V < 0) and the special case of vertical autorotation (power-off descent). Between the hover and autorotation states, the helicopter is descending at reduced power. Beyond autorotation, the rotor is producing power for the helicopter. The principal subject of this chapter is the induced power of the rotor in vertical flight, including descent. The key physics are associated with the flow states of the rotor in axial flight. Axial flight of a rotor also encompasses the propeller in cruise (V > 0) and static (V = 0) operation, and a horizontal axis wind turbine (V < 0).

Induced Power in Vertical Flight

In Chapter 3, momentum theory was used to estimate the rotor induced power Pi for hover and vertical climb. Momentum theory gives a good power estimate if an empirical factor is included to account for additional induced losses, particularly tip losses and losses due to nonuniform inflow. In the present chapter these results are extended to include vertical descent. Momentum theory is not applicable for a range of descent rates because the assumed wake model is not correct. Indeed, the rotor wake in that range is so complex that no simple model is adequate. In autorotation, the operating state for power-off descent, the rotor is producing thrust with no net power absorption. The energy to produce the thrust (the induced power Pi) and turn the rotor (the profile power Po) comes from the change in gravitational potential energy as the helicopter descends. The range of descent rates where momentum theory is not applicable includes autorotation.

Type: Chapter
Information: Rotorcraft Aeromechanics , pp. 92 - 122

DOI: https://doi.org/10.1017/CBO9781139235655.005 [Opens in a new window]

Publisher: Cambridge University Press

Print publication year: 2013

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References

Akimov, A.I., Butov, V.P., Bourtsev, B.N., and Selemenev, S.V. “Flight Investigation of Coaxial Rotor Tip Vortex Structure.” American Helicopter Society 50th Annual Forum, Washington, DC, May 1994.Google Scholar

Bergey, K.H. “The Lanchester-Betz Limit.” Journal of Energy, 3:6 (November-December 1979).Google Scholar

Betz, A. “Windmills in the Light of Modern Research.” NACA TM 474, August 1928.Google Scholar

Betz, A. “The Ground Effect on Lifting Propellers.” NACA TM 836, August 1937.Google Scholar

Betzina, M.D. “Tiltrotor Descent Aerodynamics: A Small-Scale Experimental Investigation of Vortex Ring State.” American Helicopter Society 57th Annual Forum, Washington, DC, May 2001.Google Scholar

Bourtsev, B.N., Kvokov, V.N., Vainstein, I.M., and Petrosian, E.A. “Phenomenon of a Coaxial Helicopter High Figure of Merit at Hover.” Twenty-Third European Rotorcraft Forum, Dresden, Germany, September 1997.Google Scholar

Brand, A., Dreier, M., Kisor, R., and Wood, T. “The Nature of Vortex Ring State.” American Helicopter Society 63th Annual Forum, Virginia Beach, VA, May 2007.Google Scholar

Castles, W. Jr., and Gray, R.B. “Empirical Relation Between Induced Velocity, Thrust, and Rate of Descent of a Helicopter rotor as Determined by Wind-Tunnel Tests on Four Model Rotors.” NACA TN 2474, October 1951.Google Scholar

Cerbe, T., Reichert, G., and Curtiss, H.C. Jr., “Influence of Ground Effect on Helicopter Takeoff and Landing Performance.” Fourteenth European Rotorcraft Forum, Milan, Italy, September 1988.Google Scholar

Cheeseman, I.C., and Bennett, W.E. “The Effect of the Ground on a Helicopter Rotor in Forward Flight.” ARC R&M 3021, September 1955.Google Scholar

Drees, J.M., and Hendal, W.P. “Airflow Patterns in the Neighbourhood of Helicopter Rotors.” Aircraft Engineering, 23:266 (April 1951).Google Scholar

Empey, R.W., and Ormiston, R.A. “Tail-Rotor Thrust on a 5.5-Foot Helicopter Model in Ground Effect.” American Helicopter Society 30th Annual National Forum, Washington, DC, May 1974.Google Scholar

Flemming, R.J., and Erickson, R.E. “An Evaluation of Vertical Drag and Ground Effect Using the RSRA Rotor Balance System.” Journal of the American Helicopter Society, 28:4 (October 1983).CrossRef Google Scholar

Glauert, H. “The Analysis of Experimental Results in the Windmill Brake and Vortex Ring States of an Airscrew.” ARC R&M 1026, February 1926.Google Scholar

Hafner, R. “Rotor Systems and Control Problems in the Helicopter.” Royal Aeronautical Society Anglo-American Aeronautical Conference, September 1947.Google Scholar

Harris, F.D. “Rotary Wing Aerodynamics – Historical Perspective and Important Issues.” American Helicopter Society National Specialists' Meeting on Aerodynamics and Aeroacoustics, Arlington, TX, February 1987.Google Scholar

Hayden, J.S. “The Effect of the Ground on Helicopter Hovering Power Required.” American Helicopter Society 32nd Annual National V/STOL Forum, Washington, DC, May 1976.Google Scholar

Johnson, W. “Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics.” NASA TP 2005-213477, December 2005.Google Scholar

Kisor, R., Blyth, R., Brand, A., and MacDonald, T. “V-22 Low-Speed/High Rate of Descent (HROD) Test Results.” American Helicopter Society 60th Annual Forum, Baltimore, MD, June 2004.Google Scholar

Knight, M., and Hefner, R.A. “Analysis of Ground Effect on the Lifting Airscrew.” NACA TN 835, December 1941.Google Scholar

Law, H.Y.H. “Two Methods of Prediction of Hovering Performance.” USAAVSCOM TR 72-4, February 1972.Google Scholar

Lock, C.N.H., Bateman, H., and Townend, H.C.H. “An Extension of the Vortex theory of Airscrews with Applications to Airscrews of Small Pitch, Including Experimental Results.” ARC R&M 1014, September 1925.Google Scholar

Lock, C.N.H. “Note on the Characteristic Curve for an Airscrew or Helicopter.” ARC R&M 2673, June 1947.Google Scholar

Makofski, R.A., and Menkick, G.F. “Investigation of Vertical Drag and Periodic Airloads Acting on Flat Panels in a Rotor Slipstream.” NACA TN 3900, December 1956.Google Scholar

Rabbott, J.P. Jr. “Model vs. Full Scale Rotor Testing.” CAL/AVLABS Symposium on Aerodynamics of Rotary Wing and V/STOL Aircraft, Buffalo, NY, June 1969.Google Scholar

Reeder, J.P., and Gustafson, F.B., “On the Flying Qualities of Helicopters,” NACA TN 1799, January 1949.Google Scholar

Schmaus, J., Berry, B., Gross, W., and Koliais, P. “Experimental Study of Rotor Performance in Deep Ground Effect with Application to a Human-Powered Helicopter.” American Helicopter Society 68th Annual Forum, Fort Worth, TX, May 2012.Google Scholar

Stepniewski, W.Z.Introduction to Helicopter Aerodynamics. Morton, PA: Rotorcraft Publishing Committee, 1955a.Google Scholar

Stepniewski, W.Z. “A Simplified Approach to the Aerodynamic Rotor Interference of Tandem Helicopters.” American Helicopter Society 11th Annual Forum, Washington, DC, April 1955b.Google Scholar

Taghizad, A., Jimenez, J., Binet, L., and Heuze, D. “Experimental and Theoretical Investigation to Develop a Model of Rotor Aerodynamics Adapted to Steep Descents.” American Helicopter Society 58th Annual Forum, Montreal, Canada, June 2002.Google Scholar

Washizu, K., Azuma, A., Koo, J., and Oka, T. “Experiments on a Model Helicopter Rotor Operating in the Vortex Ring State,” Journal of Aircraft, 3:3, May-June 1966.Google Scholar

Yaggy, P.F., and Mort, K.W. “Wind-Tunnel Tests of Two VTOL Propellers in Descent.” NASA TN D-1766, March 1963.Google Scholar

Yeates, J.E. “Flight Measurements of the Vibration Experienced by a Tandem Helicopter in Transition, Vortex-Ring State, Landing Approach, and Yawed Flight,” NACA TN 4409, September 1958.Google Scholar

Zbrozek, J. “Ground Effect on the Lifting Rotor.” ARC R&M 2347, July 1947.Google Scholar

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