Principles of Flight and Aircraft Systems
The Principles of Flight and Aircraft Systems domain asks why the airplane behaves as it does, and which mishandled system turns a normal flight into an accident.
Lift, angle of attack, and stalls
Lift depends on air density, wing area, airspeed squared, and angle of attack. A wing stalls at its critical angle of attack regardless of airspeed, attitude, or weight, so an accelerated stall in a steep turn occurs at a higher speed than a straight-ahead stall. Recovery: reduce the angle of attack, add power, keep the wings level, and use rudder to counter the left-turning tendency.
Load factor and speeds
Load factor rises with bank: 60° of bank produces 2 G, and stall speed rises with the square root of the load factor, about 41 percent. Maneuvering speed Va is the maximum speed at which full control deflection will not overstress the airframe. Vx is best angle for obstacle clearance, Vy is best rate of climb, Vfe is the flap limit, and Vne is never-exceed.
Systems
Carburetor icing is most likely between roughly −7 °C and 21 °C with high humidity, including clear, mild days, so apply carburetor heat before reducing power on descent. The magneto check should show no more than a 150-rpm drop and no more than a 50-rpm difference between magnetos. Lean the mixture for altitude, sump the tanks before each flight, and remember that the fuel gauge is the least reliable quantity indicator in the cockpit.
Worked example
An airplane stalls at 45 kt in level flight. In a 60° bank the load factor is 2, so the stall speed becomes 45 × √2, about 64 kt. Pulling harder in that turn at 60 kt accelerates the stall, and if the nose drops with the ball off center the result can be a spin rather than a simple stall.
Traps
Believing a stall requires low airspeed. Confusing Vx with Vy, or forgetting that Vx increases with altitude while Vy decreases. Skipping carburetor heat because the day is warm. Trusting a fuel gauge over a visual check of the tanks.