View Full Version : On drag
September 24th 06, 11:13 AM
Is it a fair assumption that at best L/D speed the drag will be the
least?
Thanks in advance,
Ramapriya
Jim Macklin
September 24th 06, 12:48 PM
No, because it is a ratio of lift over drag.  You could 
reduce lift and also reduce drag.
L/D Ratio Because lift and drag are both aerodynamic forces, 
the ratio of lift to drag is ... Aerodynamicists call the 
lift to drag ratio the L/D ratio, pronounced "L ...
      www.grc.nasa.gov/WWW/K-12/airplane/ldrat.html - 13k - 
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aero This phenomenon is called (aerodynamic) ground effect. 
.... values could be reached, his X-112 achieved an L/D value 
as high as 23 in ground effect flight. ...
      www.se-technology.com/wig/html/main.php?open=aero - 
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High-Lift Aerodynamics, Tables of Lift-to-Drag Ratios On 
Table 1 we have a summary of aerodynamic efficiency L/D (for 
high speed flows, transonic as well as supersonic, the 
efficiency is ML/D, ...
      www.aerodyn.org/HighLift/ld-tables.html - 6k - 
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[PDF] Efficient Aerodynamic Shape Optimization File Format: 
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      Efficient Aerodynamic Shape Optimization. Antony 
Jameson ... Wing L/D. Wing L/D vs. Mach at fixed CL. 
Baseline. Redesign. - - - : Baseline. -- : Redesign ...
      aero-comlab.stanford.edu/Papers/jameson.iowa.add.2005.pdf 
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Aerospaceweb.org | Hypersonic Waveriders - Vehicle 
Characteristics Hypersonic vehicle design issues, 
configuration, aerodynamic behavior, compression lift ... 
Maximum lift-to-drag ratios for hypersonic vehicles and the 
"L/D ...
      www.aerospaceweb.org/design/waverider/design.shtml - 
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  Aerospaceweb.org | Ask Us - Ground Effect and WIG Vehicles 
The aerodynamic efficiency of an aircraft is expressed 
through a quantity called the lift-to-drag ratio, or L/D. In 
steady, level, non-accelerating flight, ...
        www.aerospaceweb.org/question/aerodynamics/q0130.shtml 
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> wrote in message 
 ps.com...
| Is it a fair assumption that at best L/D speed the drag 
will be the
| least?
|
| Thanks in advance,
|
| Ramapriya
|
Marc J. Zeitlin
September 24th 06, 06:55 PM
Jim Macklin wrote:
 >> > wrote in message
 >>  ps.com...
 >> | Is it a fair assumption that at best L/D speed the drag
 >> will be the least?
> No, because it is a ratio of lift over drag.  You could 
> reduce lift and also reduce drag.
For a given aircraft flying straight and level, lift=weight.  Unless 
the weight's changing (or you accelerate the aircraft by turning), the 
lift doesn't change as you change speed - it still has to equal the 
weight to keep the plane in the air.
Given that, then yes - maximizing L/D minimizes drag.
Obviously there are many cases where this won't be true, but for the 
most part, it is.
-- 
Marc J. Zeitlin         
                         http://www.cozybuilders.org/
Copyright (c) 2006
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