What are the five ways to improve in-flight stability?

• A. Nose down attitude; Increase weight of sling load; redistribute weight of sling load; install a drag chute; reduce airspeed
• B. Nose up attitude; Decrease weight of sling load; move weight forward; remove drag chute; increase airspeed
• C. Maintain level attitude; Increase airspeed; reduce sling load weight; deploy parachute; accelerate
• D. Use autopilot; adjust rotor speed; modify sling load geometry; use landing gear

Answer: (A)

In-flight stability for a sling-loaded helicopter comes from damping the load’s swinging motion and reducing the forces that drive that swing. The best way to achieve this is to increase the load’s damping and align the flight conditions to minimize pendulum action. A nose-down attitude helps keep the load line closer to the helicopter’s velocity vector, which reduces swing energy. Increasing the sling load weight adds inertia to the load, making it resist rapid swings and settle more quickly. Redistributing the weight of the sling load so the load’s center of gravity is better aligned with the helicopter’s centerline reduces the pendulum effect and helps keep the load from swaying as much. Installing a drag chute provides an aerodynamic brake on the swinging load, directly dampening oscillations. Finally, reducing airspeed lowers the excitation and energy available to swing the load, giving the damping effects a chance to take hold.

Options that suggest nose-up attitude, removing the drag device, lightening the load, or speeding up tend to worsen stability by increasing the pendulum energy or reducing damping, so they’re not as effective in improving in-flight stability.