Lift coefficient and drag coefficient

[Con-Trail]

Hello,

Is there anyone that can help me with the following questions?

What is the lift coefficient and what is the drag coefficient in relation to the lift to drag ratio?
Why is the relation lift coefficient/drag coefficient minimum and the lift/drag ratio maximum at Vmd?

Thanks!

C-T

[The African Dude]

I can answer the first question - Drag/Lift = Cd/Cl = a parameter Beta, the aerodynamic efficiency..

[Con-Trail]

I guess that a coefficent is proportional to the actual value (coefficient of lift is proportional to total lift in Newtons)

but I still don't understand why L/D is minimum at a high l/d ratio...

Thanks Dude!

C-T

[The African Dude]

Absolutely right - the total lift L = [(1/2)*(density)*(relative velocity squared)*(wing surfrace area projected on the chord line)] * lift coefficient.

Sorry I couldn't help with the other Q, but I'll have a look at my notes and get back to you if I can find something on it.

[1pudding1]

L/D is not a minimum when you have a high Cl/Cd. L/D and Cl/Cd will be the same at that flight condition, here Vmd.

[Mad (Flt) Scientist]

That second question sounds like a typo/SNAFU.

Lift = qS CL
Drag = qS CD

where q = kinetic pressure = 1/2*density*speed squared (as mentioned) and S = nominal wing area

So Lift/Drag = CL/CD

both are a minima at the same time, both are a maxima at the same time (unless you take the nonsense case of qS=0, which is physically pretty meaningless)

[Con-Trail]

That makes more sence, Scientist. The thing that threw me off was a question in an exam paper that suggested the opposite was true.

Thanks for your input guys!

C-T