Lift Components:	-airfoil lift -flapping lift
Drag Components:	-Parasite Drag (Body) -Induced Drag (Drag Caused by airfoil lift -Profile Drag (Drag from surface of wings)
Thrust:	-flapping -Gravity (In Gliding)

Optimization:

Minimize Drag (Streamlining) Minimize Weight (air Sacs, hollow bone, one gonad, feathers, etc.) Maximize Lift (Wing Shape) Maximize Thrust (Wing Musculature)

Schematic of the aerodynamic force induced on an aerofoil. This force is resolved into lift perpendicular to the direction of air flow (which is the result of the forward velocity of the animal and any flapping movements of the wing), and drag parallel to air flow. The aerodynamic force can also be resolved into a vertical component that counteracts the body weight and a forward thrust that counterbalances the backward retarding force, (alpha) is the angle of attack of the wing. (Modified from Nachtigall 1983.)