Aerodynamics and Aircraft Performance
The four forces, and the one angle that matters
Lift, weight, thrust, and drag must balance, but the exam tests your understanding of how they trade. Induced drag decreases as airspeed increases; parasite drag increases with the square of airspeed. Total drag is minimum at L/D max, which is also best glide speed and the speed for maximum range; best endurance sits at minimum power required, a slower speed.
A wing stalls at a critical angle of attack, not at a specific airspeed, attitude, or weight. Anything raising load factor raises stall speed by the square root of that load factor: Vs(new) = Vs × √n. In a level turn, n = 1/cos(bank); 60° bank yields 2 G and a 41% increase in stall speed.
Vx and Vy are not constants. As altitude increases, Vx rises and Vy falls until they meet at the absolute ceiling. Vx is always lower than Vy in the same configuration. Adding weight raises every reference speed.
Density altitude is the great performance thief: high temperature, high elevation, high humidity, and low pressure all reduce both power output and lift, lengthening takeoff rolls and flattening climbs. Ground effect reduces induced drag and lets an aircraft lift off below normal flying speed - a trap that leads to premature climb and stall.
Trap: "The airplane stalls at 50 knots." False without qualifiers - it stalls at 1 G, gross weight, coordinated flight.
Worked example: Vs1 = 55 KCAS at gross weight. In a 60° banked level turn, Vs = 55 × √2 ≈ 78 KCAS.