At 12:24 15 January 2011, Big Wings wrote:
Doesn't air density affect it as well (altitude, temperature,
humidity)?
Are you talking TAS, IAS or CAS?


At 03:07 15 January 2011, Bruce Hoult wrote:
A given aircraft at a given weight and in similarly clean condition
will always perform at a fixed L/D (lift/drag) at any particular speed
and G loading. It is an aerodynamic property.




In principle, no ... (L/D)max is a non-dimensional ratio, so air density
effects and IAS/CAS/TAS effects cancel out*. It's a constant and is
determined by the product of the zero-lift (profile) drag coefficient and
the induced drag factor.

Changes to the profile drag coefficient (dirty wing, flaps, airbrakes,
undercarriage etc) or the induced drag coefficient (flaps, winglets etc)
will affect the max L/D, but as Bruce says, for a given aircraft at a
given weight in a similarly clean condition at a given speed and g-loading
it will be a constant - as long as by 'speed' you mean IAS.