Cold Weather Operations

We are to used the wonderful photographic opportunities that winter offers in Scotland – snow, ice and crisp sunshine. In addition to the pilot wrapping up warm against the cold, operating a Unmanned Aerial Vehicle (UAV) or Drone in these conditions requires special consideration particularly of the batteries. Failure to do so can lead to poor performance and catastrophic loss of power.

River Findhorn
Iced covering the full width of the River Findhorn at Relugas south of Forres in Moray, Scotland

The high power Lithium Polymer (LiPo) batteries used with most UAVs are complex chemical devices able to store and deliver significant power. The chemistry has distinctive characteristics that have to be carefully managed for safe flight operations. The batteries do not perform well below 15C and very poorly below 5C. Ideally, batteries should be warmed to around 20C before use. Another issue is that the battery power falls off a cliff at the end of its power output cycle. If this happens the drone motors will cut and the drone will fall out of the sky. This can prove very expensive and present a risk of harm to people and property.

The DJI Inspire 1, as operated by MoraySky, uses an Intelligent Flight Battery that employs software to track usage and charging and for monitoring battery inflight usage and performance. The batteries comprise 6 cells which are individually monitored and the voltage displayed to the pilot. Recent firmware updates to the batteries and aircraft offer improved support for cold weather operations. I have noticed that the new firmware has improved the Inspire 1 performance and increased available flight times.

First, the aircraft motors can not now be started with an internal battery temperature below 15C. The battery must be kept warm in a car or thermally insulated box or be pre-warmed using pocket hand warmers or the DJI Battery Heater. The heater takes 10-15 minutes to warm the battery to 20C or more with the consumption of 3-4% of available battery power. During flight the chemical reaction within the battery quickly heats the battery up to 30-40C. I have found the best technique is to put the next battery in the heater on removing the first. It is then ready and warmed ready of the next flight.

Secondly, the Inspire 1 flight control software has been changed to reduce the maximum power that can be drawn from the batteries before they come up to temperature. This affects initial aircraft performance but helps prevent excess stress and possible damage to the battery. Once the battery is up to temperature these restrictions are removed.

Battery Monitor
Display showing battery usage with available power at 32%

Finally, the pilot needs to regularly monitor the battery voltages and warnings during flight and ensure that the aircraft is safely on the ground before the battery power reaches critical levels. The DJI GO app continuously displays battery charge as a percentage and the average battery cell voltage. Tapping this display brings up detailed information of voltage, power, temperature and individual cell health. By default the pilot gets a Low Battery Power warning at 30% and a Critical Battery Condition warning at 10%. Ideally, the pilot should be already returning to land and be on the ground by 20%.

By knowing how the batteries will perform and taking the sensible actions described above will ensure safe drone operations.

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