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Urban prepares to let AirMule UAV off the tether

Urban Aeronautics is planning untethered hover flights in March for its vertical take-off and landing AirMule unmanned air vehicle, having achieved more than 30 tethered tests of 1min duration.

Designed for cargo and medical evacuation missions, and formerly called the Mule, the UAV completed the tethered tests in calm to moderate winds. It was hovered autonomously at an altitude of 2ft (60cm) using its fly-by-wire control system, which employs inertial measurements augmented by GPS navigation.

"We've achieved an important milestone in the development of our AirMule, having successfully completed the first phase of flight tests," says Urban president Rafi Yoeli.

"The next phase will involve free hovers at various heights above ground and low-speed flight manoeuvres. It is expected to last a few months. Once completed, we will follow this second phase with full flight envelope testing of the vehicle."

AirMule Urban Aeronautics
© Urban Aeronautics

Above: Urban Aeronautics' AirMule hovers for about 1min during one of its thirty tethered filght tests

The untethered hover tests will see gradually increasing altitudes, monitored with two on-board laser altimeters and vehicle stability tests in the x and y planes.

An initial assessment has shown that the AirMule's vane control system is generating more than 2.0 Radians/sec² of roll acceleration for roll and yaw control. Urban says that roll acceleration will double with planned improvements, enabling "very high precise hovering in gusty wind conditions". Following testing the company is confident AirMule could cope with wind speeds of up to 50kt (92.5km/h).

Urban's ground control team monitors the performance of the AirMule's Turbomeca Arriel 1 730hp (544kW) turboshaft engine, two main lift rotors and their hydraulic pitch change mechanisms, three proprietary gearboxes and other subsystems using three datalinks. These provide 460 channels of real-time telemetry.

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