Expert: Paul Soderman - 4/18/2006

Question
hi paul,
i'm a little confused as to how to calculate the coefficents of lift and drag during take off and landing for a dc-10. i was wondering if you could tell me what formulas i need to use and what data i need to find.
thanks,
susan  

Answer
Hi Susan

The lift coefficient is:  Cl = L/qS
where L = lift , q = dynamic pressure = rho*V^2/2, S = wing area

In level flight, which is almost true for takeoff and landing, lift = weight.
V is airspeed in appropriate units
and rho is air density in appropriate units

So, you need to find the aircraft weight, airspeed, wing area, and air density and you have it.  A similar equation holds for drag coefficient by substituting drag for lift.  In steady flight, drag = thrust.

Paul