Spin Stabilization of an Air Ambulance Litter

This paper proposes a new approach to stabilize the spin of a suspended litter during air ambulance rescue hoist operations. Complex forces generated by the helicopter’s downwash may cause a patient suspended in a rescue litter to spin violently. In severe cases, the spin destabilizes the suspended load, risks injury to the patient, and jeopardizes the safety of the aircrew. The presented design employs an anti-torque device to arrest the spin that is safer and faster than a tagline and is without the tactical constraints of the tagline. The device follows tailored control laws to accelerate a flywheel attached to the litter, thereby generating sufficient angular momentum to counteract the spin and stabilize the suspended litter. An inertial measurement unit (IMU) measures the position, angular velocity, and angular acceleration of the litter and delivers this information to a microcontroller. The research and prototype design were developed under the support of the U.S. Army 160th Special Operations Aviation Regiment (SOAR).