SB003 Alta X – Motor Stall on Fast Vertical Descent (7/10/20)
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:
- This issue has only been observed in a zero throttle straight down descent
- We will be characterizing this failure further in the upcoming weeks to issue better guidance
- Altitude / Position modes are limited to 4m/s descent speed and will have no issue
- Do not execute zero throttle descents in manual mode
- If you need to execute zero throttle descents in manual mode, do not execute zero throttle straight down descents that achieve velocities faster than 13m/s (30mph)
Freefly will be issuing additional updates as our investigation continues
Still need help? Get in touch with our support team.Contact Us