Date Released: July 10th 2020
Subject: Alta X Motor Stall on Fast Vertical Descents
Effectivity: All Alta X
Require Action: Modify flight envelope (reduce vertical velocities)
This service bulletin is being issued to alert all Alta X pilots of an in-flight failure that a Freefly test pilot experienced on July 9th 2020.
During flight testing a Freefly test pilot executed an aggressive maneuver in manual mode that involved climbing to ~400ft while initiating a zero throttle zero horizontal speed descent. The pilot let the Alta X fall at zero commanded throttle for 4 seconds. At the end of the 4 second fall the Alta X was traveling vertically at ~ 16m/s (35mph). At this point Motor 1 (front right) stalled and shut down and the Alta X crashed. The Alta X was equipped with a 20lb payload for this test.
Freefly replicated the issue by testing on our ground test setup (truck with Alta X motor and prop mounted) and was able to replicate the issue at speeds of 20m/s to 22.5 m/s (45 to 50mph)
Some key points to convey regarding this issue:
Freefly will be issuing additional updates as our investigation continues
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