How Cold is Too Cold to Drone On?
By Rebekah Waters, FAA Safety Briefing Magazine
My New England-born parents taught me how to handle winter weather by prepping my vehicle (good tires, plenty of wiper fluid, full tank of gas, and clean all the snow off) and shoveling like a New Englander (early and often!). Thanks to them, you won’t find me rushing out for bread and toilet paper when the forecast predicts snow. There’s a similar amount of proactive preparation required for cold-weather drone operations. Weather is always a factor for aircraft, including drones — clouds, fog, or strong winds could leave you grounded. As the temperatures drop, there are even more factors to consider before takeoff.
Cold air can affect your drone’s battery. Starting a car with a cold-soaked battery can be hard. Drones are no different, as their lithium polymer batteries are greatly affected by cold weather. The colder the ambient air is, the slower the electrochemical reaction will be for any system. Slower movement equals more effort to create the same level of power required by the draw of the electronic speed controllers connected to the power distribution board. Think about cranking the engine of a cold car, especially with an older battery. It’s the same with drones and their batteries. Cold temperatures also increase the internal resistance of the battery, which can lower the battery’s capacity. The exact temperature ranges depend on the chemistry of the batteries, but basically, colder weather equals less power.
Cold weather can also impact the electric components in DC systems. The colder it is, the slower these systems will function. The effect may be minimal, but as the energy transfer from component to component slows, it degrades the overall flight duration.
Aircraft icing, another winter hazard, can affect multiple aspects of your operation. Icing can occur when the outside air temperature is near or below freezing and the dew point is less than 5 degrees from that point. Winter air can contain droplets of supercooled water. When conditions are right, they can form a layer of ice on any surface. This is most likely when the temperatures are at or slightly above freezing. The more ice that sticks to the wing or rotor blades, the less effective they will be at generating lift.
One upside to winter flying is the likelihood of colder, drier air. Cold air is more dense than warm air. This can improve takeoff and flight performance. Another benefit of winter flying is there is generally less turbulence which helps improve drone stability and makes for some beautiful smooth video shots!
Don’t want to wait for spring to fly? The risks posed by winter weather can be reduced by proper planning or using weather-resistant hardware. Be aware of weather conditions and changes during your flight. If you must fly in frigid conditions, consider using a hybrid-electric drone. In some models, the gas engine can warm and recharge the batteries. Some fixed-wing systems have pinholes in the wing surface that release a glycol solution during flight to prevent ice formation.
Sometimes low-tech solutions work just as well. The Alaska UAS Test Site Program is no stranger to extreme winter weather challenges. At the 2019 UAS Integration Pilot Program meeting, Cathy Cahill, director for the Alaska Center for UAS Integration (ACUASI) and professor of chemistry at the University of Alaska Fairbanks, shared an anecdote about how her team uses HotHands (small pouches that provide air-activated warmth when slipped inside gloves and socks) to keep their batteries warm until the time they need to use them.
While most drone operators won’t need to go to these lengths, it’s important to remember how weather might impact your operations. Expect reduced battery life, reduced flight time, and have a way to remove frost from rotor blades and keep a spare set handy! Always check the forecast, and make sure you are prepared both for your comfort and the performance of your drone.
Rebekah Waters is an FAA Safety Briefing associate editor. She is a technical writer-editor in the FAA’s Flight Standards Service.