Aircraft Flight Dynamics: Takeoff, Landing, Stability and Spin Recovery

Takeoff

Takeoff speed: 120% to 130% of stall speed (V_S0).

Conventional gear: raise the tail to reduce drag and angle of attack.

Wind: headwind shortens the takeoff distance.

Ideal conditions: low altitude and temperature, runway slope, dry air, and headwind.

Landing

Three-point landing (conventional gear): idle power, stall.

Tennis-style landing: conventional gear, low RPM, touch the main wheels first, then keep the velocity on the track.

Conditions: rest on a slope (uphill or downhill) is the same.

Longitudinal Stability

Static stability: stable, dynamically stable, unstable, or neutral (preferred: unstable or indifferent).

The center of gravity (CG) must be in front of the center of pressure.

Lateral Stability

Lateral stability requires minimal effort. Static stability may be stable, dynamically stable, unstable, or indifferent (preferred: unstable or indifferent).

Lateral Factors: Dihedral

A wing that is laterally unbalanced causes the aircraft to sideslip toward the lower wing. Increasing dihedral increases stability; decreasing it reduces stability.

Sweepback

Sweepback affects sideslip and skidding: one wing receives the relative wind more directly than the other. Sweepback increases stability.

Keel Effect

When the lateral area above the CG is larger than the area below it, stability increases. When the lateral area below the CG is larger than the area above it, stability decreases.

Fuselage Effect

The fuselage can shield the wing from lateral airflow, reducing stability and impairing dihedral.

Weight Distribution

A high fuselage-mounted wing acts like a pendulum, increasing stability. A low wing tends to increase weight and lack of balance, reducing stability.

Directional Stability

Directional stability is less important and requires little effort without risk. Static stability may be stable, dynamically stable, unstable, or indifferent (preferred: unstable or indifferent).

Directional Factors: Sweepback

Deviation to either side causes skidding, exposing the fin to the wind and causing yawing. Increasing sweepback increases directional stability; decreasing it reduces stability.

Keel Effect

The greater the lateral area behind the CG, the greater the directional stability.

Spins

A spin occurs when the pilot reduces power to idle, stalls the wing, or lifts the nose. When airspeed is lost, one wing stalls first. If the pilot pushes the rudder pedal fully to one side, the aircraft will skid.

Accidental Spin: Asymmetric Stall

• Motor torque: the critical angle of attack on one wing may cause the aircraft to rotate counterclockwise.
• Different wing incidence: one wing stalls before the other due to incidence differences or motor thrust.
• Stall ailerons: do not use ailerons at the critical angle of attack.
• Turns: a steeply banked turn with insufficient lift, combined with sideslip and dihedral effects, can lead to a spin.

Recovery: interrupt the rotation by moving the rudder opposite to the rotation, then pull the stick progressively to exit the dive.

Flat Spin

Flat spins occur in tail-heavy aircraft when the nose rises and the spin becomes flat. Recovery is nearly impossible at this stage. Shifting the center of gravity forward can help; moving it toward the nose lowers the spin and returns the aircraft to normal. In a flat spin, strong turbulence may make the elevator and rudder ineffective, and strong drag reduces the descent speed.

Physics Fundamentals

• Distance traveled over speed-time units.
• Mass: the quantity of matter in a body.
• Force: anything capable of producing or changing movement.
• Speed units: km/h, mph, kt. Mass units: kg, lb. Force units: kgf, lbf.
• Acceleration: change in velocity over time. Acceleration = force / mass.
• Inertia: the natural tendency of a body to remain at rest or in uniform, rectilinear motion.