Aerodynamics and Aircraft Operation
Aerodynamics and Aircraft Operation tests how an ultra-light generates lift, why it stalls, how load factor and density altitude change performance, and how to handle takeoff, landing, and emergencies. Questions often ask for a calculation or a cause-and-effect explanation rather than a definition.
Lift, drag, and stall
Lift depends on air density, wing area, airspeed squared, and angle of attack. The critical angle of attack is fixed; a stall can occur at any speed, attitude, or weight if that angle is exceeded. Indicated stall speed rises with weight and load factor, and performance falls with high density altitude. Parasite drag rises with the square of speed; induced drag falls as speed increases.
Load factor and turns
In a level turn, load factor n = 1 / cos(bank). At 30° n = 1.15, at 45° n = 1.41, at 60° n = 2.0. Stall speed increases by the square root of n: new stall speed = normal stall speed × sqrt(n). Limit load factor and maneuvering speed set the boundary for gust and control inputs.
Takeoff, landing, and stability
Takeoff and landing distances increase with density altitude, tailwind, uphill slope, soft or tall grass, and a forward CG (higher stall speed). Ground effect reduces induced drag near the surface. Crosswind technique uses aileron into wind and rudder to track the centreline. An aft CG reduces pitch stability; a forward CG increases stall speed and reduces elevator authority.
Worked example
An ultra-light stalls at 40 kt in level flight. In a 60° bank, n = 1 / cos 60° = 2.0. Stall speed = 40 × sqrt(2) = 56.6 kt. If the pilot pulls to the buffet at 60° bank, the aircraft stalls about 17 kt faster than in level flight, with less margin above the accelerated stall. At 75° bank, n = 3.86 and stall speed = 78.6 kt - a steep turn can put you near the stall without any warning.
Traps that cost marks
Believing a stall needs a low airspeed; ignoring load factor in turns; using sea-level takeoff figures at a high-density-altitude strip; mistaking ground effect for extra lift; and loading aft of the limit.