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The Problem of Obtaining High Lift-Drag Ratios at Supersonic SpeedsThe importance of the lift to drag ratio is well known to all aircraft designers since it gives, to a great extent, the aerodynamic efficiency of the airplane. Aerodynamic efficiency, however, is only one component of the grand compromise that a completed airplane represents. At subsonic speeds, lift-drag ratios of well over 200 have been measured in wind tunnels on airfoil sections; but few powered aircraft have attained (L/D) value of 20. It is invariably true that the requirements of stability and control, structure, and flight operation all contribute to reducing the design (L/D) (sub max)) considerably below those exotic values which can be predicted from unrestricted aerodynamic theory. If, however, a certain range or operating efficiency is required, there is most certainly a minimum (L/D) (sub max)) value for which the goals are just attainable. If we examine the range equation we see that range is proportional to the lift-drag ratio, the thermopropulsive efficiency, and the logarithm of the initial to final weight ratio. The appearance of the lift-drag ratio as a linear factor in the range equation indicates that every attempt should be made to increase (L/D) (sub max)); however, the search for higher (L/D)max may lead to strange and unorthodox configurations. Most frequently, such configurations are ruled out by the adverse effects of their geometry on the weight ratios. In the present paper, we will deal with the maximum lift-drag ratio problem for conventional configurations having a wing and a body in close proximity to each other. No attempt will be made to select a particular configuration as being the best. However, the promising direction to go from the aerodynamic view will be stressed with the understanding that the other factors may outweight the aerodynamics
Document ID
20150018565
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Brown, Clinton E.
(NASA Langley Research Center Hampton, VA, United States)
McLean, Francis
(NASA Langley Research Center Hampton, VA, United States)
Date Acquired
September 30, 2015
Publication Date
May 1, 1959
Publication Information
Publication: Journal of the Aero/Space Sciences
Volume: 26
Issue: 5
Subject Category
Aerodynamics
Aircraft Stability And Control
Meeting Information
Meeting: Aerodynamics Session, National Summer Meeting, IAS
Location: Los Angeles, CA
Country: United States
Start Date: July 8, 1958
End Date: July 11, 1958
Sponsors: Institute of the Aerospace Sciences
Distribution Limits
Public
Copyright
Other

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