ASN Wikibase Occurrence # 264902
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| Date: | Wednesday 18 September 2019 |
| Time: | 14:35 UTC |
| Type: | Velos Single Rotor UAS |
| Owner/operator: | Private |
| Registration: | Unregistered |
| MSN: | VUAV10417006 |
| Fatalities: | Fatalities: 0 / Occupants: 0 |
| Aircraft damage: | Destroyed |
| Location: | Hangingstone Hill, Dartmoor, Devon -
 United Kingdom
|
| Phase: | En route |
| Nature: | Survey |
| Departure airport: | Hangingstone Hill, Dartmoor, Devon |
| Hangingstone Hill, Dartmoor, Devon | |
| Confidence Rating: |  Information verified through data from accident investigation authorities |
AAIB investigation to Velos Single Rotor, (UAS, registration n/a): ESC failure, Hangingstone Hill, Dartmoor, Devon, 18 September 2019. The AAIB Final report was published on 9 April 2020, and the following is the summary from it...
"The single rotor UAS had completed a 13-14 minute automated survey flight in an area of the Dartmoor national park. Once the survey had been completed the pilot took control of the UAS and flew it back towards the Take Off and Landing Site (TOLS). During the return flight the pilot noticed that the aircraft was slowly descending, so he increased the collective input in an attempt to climb back to the original height. This did not have an effect, so he gently reduced the collective input and pulled back on the cyclic control to reduce forward speed. As he did so the UAS pitched up violently and then fell to the ground from approximately 30 ft agl.
=Recorded data=
Recorded data from the accident flight was downloaded and interpreted by the UAS manufacturer. The manufacturer determined that the UAS was returning to the TOLS after completing its desired activity when the accident occurred. It was toward the end of the flight and the batteries were in a low energy state.
The data showed that three minutes prior to the end of the flight the left ECS malfunctioned. This resulted in it and the left motor shutting down, for the remainder of the flight. As the malfunction occurred, a short circuit was recorded across the batteries. This lasted for approximately one second and reduced the battery voltage to below their minimum operational level.
After the loss of the left motor, the right motor was commanded to increase its output. This increased the right motor current load, which in turn reduced the battery voltage further. To maintain the main rotor speed the governor started to compensate for the lowering voltage by increasing the current demand.
Approximately one minute before the loss of control, the right governor was demanding 100% power to maintain the required rotor speed, however the available voltage diminished to a level where the batteries no longer had sufficient charge to maintain it. The rotor speed then dropped below that able to sustain flight, resulting in the aircraft pitching up.
It was not possible to determine the cause of the ESC failure; however, it should have been possible for the UAS to land away from the TOLS in the event of a single ESC failure. The pilot flying the UAS was operating alone in visual line of sight, supplemented by using FPV and was not monitoring the telemetry which was shown on a separate screen positioned behind him as he flew the aircraft. Had he been monitoring the telemetry screen he may have noticed cautions regarding the ESC failure and the rapidly diminishing battery charge which should have prompted the pilot to land the UAS immediately. The position of the screens had been optimised for the planned mission but did not allow easy viewing of vital information which could have prevented the accident.
=Damage Sustained to Airframe=
Per the above AAIB Report, the UAS was "damaged beyond ecnomical repair"
Hangingstone Hill, is a hill in North Dartmoor in the southwest English county of Devon. At 603 metres high, it is the joint third highest peak in Devon and Dartmoor, together with Cut Hill, which lies around 4 kilometres to the southwest. The hill lies within the military training area on Dartmoor and is not accessible to the public except at certain times
Sources:
1. AAIB Final Report: https://assets.publishing.service.gov.uk/media/5f4519d1d3bf7f69a60dc90a/Velos_Single_Rotor__UAS_registration_na__04-20.pdf
2. https://en.wikipedia.org/wiki/Hangingstone_Hill
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 29-Jun-2021 20:21 | Dr. John Smith | Added |
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