In airplanes
LDmax (best lift to drag ratio) is the point where the wing's angle of attack is at a 'sweet spot' where it provides the most lift to drag. In an airplane that translates into the best glide speed (See FAA Airplane Flying Handbook pg3-16 for more details).
But in the helicopter, with the aerodynamic forces involved in an autorotation I'm not sure that things are the same. I have been told that LDmax for a helicopter is actually Vy speed - best rate of climb.
So I fly an R22, and I am sure most rotorheads know that helicopter, so lets take that as an example.
In the R22:
- Vy (best rate of climb) is 53 KIAS
- Vg (best glide in an autorotation) is 75 KIAS
So which (if any of those) is LDmax?
As a comparison, a Diamond 20 single engine airplane:
- Vy 75 KIAS
- Vg 73 KIAS (also identified as LDmax)
Many thanks for all contributions