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Theoretical study of the effect of ground proximity on the induced efficiency of helicopter rotorsA study of rotors in forward flight within ground effect showed that the ground-induced interference is an upwash and a decrease in forward velocity. The interference velocities are large, oppose the normal flow through the rotor, and have large effects on the induced efficiency. Hovering with small ground clearances may result in significant blade stall. As speed is increased from hover in ground effect, power initially increases rather than decreases. At very low heights above the ground, the power requirements become nonlinear with speed as a result of the streamwise interference. The streamwise interference becomes greater as the wake approaches the ground and eventually distorts the wake to form the ground vortex which contributes to certain observed directional stability problems.
Document ID
19770017115
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Heyson, H. H.
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 3, 2013
Publication Date
May 3, 1977
Subject Category
Aerodynamics
Report/Patent Number
NASA-TM-X-71951
Accession Number
77N24059
Funding Number(s)
PROJECT: RTOP 791-40-08-01
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.
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