Skip to main content Accessibility help

We use cookies to distinguish you from other users and to provide you with a better experience on our websites. Close this message to accept cookies or find out how to manage your cookie settings.

Close cookie message
×
Hostname: page-component-745bb68f8f-b6zl4 Total loading time: 0 Render date: 2025-01-13T20:47:31.424Z Has data issue: false hasContentIssue false

5 - Forward Flight Wake

Published online by Cambridge University Press:  05 May 2013

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

Summary

During translational motion of the helicopter, when the rotor is nearly horizontal, the rotor blades see a component of the forward velocity as well as the velocity due to their own rotation (Figure 5.1). In forward flight the rotor does not have axisymmetry as in hover and vertical flight; rather, the aerodynamic environment varies periodically as the blade rotates with respect to the direction of flight. The advancing blade has a velocity relative to the air higher than the rotational velocity, whereas the retreating blade has a lower velocity relative to the air. This lateral asymmetry has a major influence on the rotor and its analysis in forward flight. Thus the rotor blade loading and motion are periodic with a fundamental frequency equal to the rotor speed Ω. The analysis is more complicated than for hover because of the dependence of the loads and motion on the azimuth angle.

As a consequence of the axisymmetry, the analysis of the hovering rotor primarily involves a consideration of the aerodynamics. In forward flight, however, the lateral asymmetry in the basic aerodynamic environment produces a periodicmotion of the blade, which in turn influences the aerodynamic forces. The analysis in forward flight must therefore consider the blade dynamics as well as the aerodynamics. This chapter covers a number of aerodynamic topics that are familiar from the analysis of the rotor in vertical flight. In particular, we are concerned with the momentum theory treatment of the induced velocity and power in forward flight. Then the rotor blade motion and its behavior in forward flight are considered in Chapter 6.

Type
Chapter
Information
Rotorcraft Aeromechanics , pp. 123 - 151
Publisher: Cambridge University Press
Print publication year: 2013

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Ashley, H., and Landahl, M.Aerodynamics of Wings and Bodies. Reading, MA: Addison-Wesley Publishing Company, Inc., 1965.Google Scholar
Cassier, A., Weneckers, R., and Pouradier, J.-M. “Aerodynamic Development of the Tiger Helicopter.” American Helicopter Society 50th Annual Forum, Washington, DC, May 1994.Google Scholar
Castles, W. Jr., and De Leeuw, J.H. “The Normal Component of the Induced Velocity in the Vicinity of a Lifting Rotor and Some Examples of Its Application.” NACA Report 1184, 1954.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
Coleman, R.P., Feingold, A.M., and Stempin, C.W. “Evaluation of the Induced-Velocity Field of an Idealized Helicopter Rotor.” NACA ARR L5E10, June 1945.Google Scholar
Cook, C.V. “A Review of Tail Rotor Design and Performance.” Vertica, 2:3/4 (1978).Google Scholar
Curtiss, H.C. Jr., Erdman, W., and Sun, M. “Ground Effect Aerodynamics.” Vertica, 11:1/2 (1987).Google Scholar
Curtiss, H.C. Jr., Sun, M., Putman, W.F., and Hanker, E.J. Jr. “Rotor Aerodynamics in Ground Effect at Low Advance Ratios.” Journal of the American Helicopter Society, 29:1 (January 1984).CrossRefGoogle Scholar
Drees, J.M. “A Theory of Airflow Through Rotors and Its Application to Some Helicopter Problems.” Journal of the Helicopter Association of Great Britain, 3:2 (July-August-September 1949).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
Glauert, H. “A General Theory of the Autogyro.” ARC R&M 1111, November 1926.Google Scholar
Glauert, H.Elements of Aerofoil and Airscrew Theory. Cambridge: Cambridge University Press, 1947.Google Scholar
Hamel, D., and Humpert, A. “Eurocopter EC135 Initial Flight Test Results.” Twentieth European Rotorcraft Forum, Amsterdam, Netherlands, October 1994.Google Scholar
Hansen, K.C. “Handling Qualities Design and Development of the CH-53E, UH-60A, and S-76.” Royal Aeronautical Society International Conference on Helicopter Handling Qualities and Control, London, UK, November 1988.Google Scholar
Heyson, H.H. “A Note on the Mean Value of Induced Velocity for a Helicopter Rotor.” NASA TN D-240, May 1960.Google Scholar
Huber, H., and Masue, T. “Flight Characteristics Design and Development of the MBB/KHI BK 117 Helicopter.” Seventh European Rotorcraft and Powered Lift Aircraft Forum, Garmisch-Partenkirchen, Germany, 1981.Google Scholar
Johnson, W. “Model for Vortex Ring State Influence on Rotorcraft Flight Dynamics.” NASA TP 2005-213477, December 2005.Google Scholar
Leverton, J.W. “Reduction of Helicopter Noise by Use of a Quiet Tail Rotor.” Vertica, 6:1 (1982).Google Scholar
Lynn, R.R., Robinson, F.D., Batra, N.N., and Duhon, J.M. “Tail Rotor Design. Part I: Aerodynamics.” Journal of the American Helicopter Society, 15:4 (October 1970).CrossRefGoogle Scholar
Mazzucchelli, C., and Wilson, F.T. “The Achievement of Aerodynamic Goals on the EH101 Project Through the “Single Site” Concept.” Seventeenth European Rotorcraft Forum, Berlin, Germany, September 1991.Google Scholar
Nathan, N.D., and Green, R.B. “Wind Tunnel Investigation of Flow around a Rotor in Ground Effect.” American Helicopter Society Specialists' Conference on Aeromechanics, San Francisco, CA, January 2010.Google Scholar
Prouty, R.W. “A Second Approximation to the Induced Drag of a Rotor in Forward Flight.” Journal of the American Helicopter Society, 21:3 (July 1976).CrossRefGoogle Scholar
Roesch, P., and Vuillet, A. “New Designs for Improved Aerodynamic Stability on Recent Aerospatiale Helicopters.” Vertica, 6:3 (1982).Google Scholar
Sheridan, P.F. “Interactional Aerodynamics of the Single Rotor Helicopter Configuration.” USARTL TR 78-23A, September 1978.Google Scholar
Sheridan, P.F., and Wiesner, W. “Aerodynamics of Helicopter Flight Near the Ground.” American Helicopter Society 33rd Annual National Forum, Washington, DC, May 1977.Google Scholar
Stepniewski, W.Z.Introduction to Helicopter Aerodynamics. Morton, PA: Rotorcraft Publishing Committee, 1955.Google Scholar
White, F., and Blake, B.B. “Improved Method of Predicting Helicopter Control Response and Gust Sensitivity.” American Helicopter Society 35th Annual Forum, Washington, DC., May 1979.Google Scholar

Save book to Kindle

To save this book to your Kindle, first ensure [email protected] is added to your Approved Personal Document E-mail List under your Personal Document Settings on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part of your Kindle email address below. Find out more about saving to your Kindle.

Note you can select to save to either the @free.kindle.com or @kindle.com variations. ‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi. ‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.

Find out more about the Kindle Personal Document Service.

Available formats
×

Save book to Dropbox

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 Dropbox.

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.

Available formats
×