When an aircraft is descending is left reduced and drag increased, please can some check my figures. :)? this1

Question

When an aircraft is descending is left reduced and drag increased, please can some check my figures. :)?
a340 at -2degrees angle of attack
wing area 5825ft squared
density ratio= 0.5328
speed 435knots
altitude; 20,000ft
I worked lift out to be
Lift = -559,819.26 pounds
and drag to be
Drag = 43,797.82 pounds

do these sound right, if not can you tell me how to do the coefficient for descening of an aircraft for the values of lift and drag??

Answer 1

On descent, the lift and drag increase by use of the flaps. Yur figures for airspeed ar every high though.

Answer 2

The angle of attack won't give you any of the numbers you have listed here--it varies along the span of the wing. What can be determined is the lift coefficient, Cl = L/(qS), where L = lift, q = dynamic pressure and S = wing area. You sem to have 2 of the numbers already. q = .5V^2*p = .5*(1.15*435*44/30)^2*.00238*.5328 = 682.619 lb/ft^2

Therefore, Cl = 559819.26/(682.619*5825) = .14079

Since L/D is 12.78, Cd = Cl/12.78 = .011

This is a reasonable Cl for a plane going 435 knots with the flaps and landing gear retracted. Likewise for the L/D of 12.78. The descent rate will be entirely dependent on how much thrust is coming from the engines. If zero, then the glide ratio will be 12.78:1 and the rate of descent = 3434 ft/min

Answer 3

I'm not even going to bother with your numbers, but descent is typically initiated by reducing thrust.
Drag is increased by use of leading edge slats, flaps, speed brakes. Lift is increased, and thus stall speed reduced, by use of the slats and flaps.
This is why on final approach, there will always be a thrust increase. To compensate for the increased drag of the lift devices