As the first snow has started to fall in Ukraine, writing something about drone operations in cold weather seems fitting. This article will highlight some challenges of operating class I[1] unmanned aerial systems (UAS) in cold weather, predominantly civilian drones. Some of these issues are known and described in the Swedish handbook for winter warfare[2], while others are less known outside the drone community. However, with drones becoming more common within all branches, there is a need for a common understanding of the limitations of operating remotely piloted airframes during winter. I hope this article raises questions by commanders and staff about their specific systems’ limitations and that they turn to their UAS personnel to answer those questions.
Moving into a third winter period in the Russo-Ukrainian war, we are likely to see periods of low or no drone activity, just like the previous winter of 2023, which may affect ground operations along the front. During 2023, one could note a distinct drop in published drone videos released by Ukrainian and Russian channels on social media. The unpredictable weather with snow, low cloud ceilings, lower temperatures, and fewer daylight hours[3] are factors attributed to the drop in drone activity.[4] For countries like Sweden, finding solutions to the most common issues that arise during winter is vital.
To conduct cold weather drone operations, actions must be taken to ensure that the operations can be carried out according to planning, especially in Ukraine, where the drones, especially the First Person View (FPV) platforms, are built with civilian-grade components and minimal or no protection from the elements. While a military-grade system is usually rated to operate around minus 30 degrees Celsius, a civilian platform for hobby use is limited to around minus 10 degrees Celsius. Although we see quadcopters operating in colder temperatures in Ukraine, it must be accounted for when planning. As of now, we don’t know how many drones are lost due to cold weather, although there are indicators that the losses are at least not insignificant.
One reason for the lower temperature threshold for quadcopters (especially FPV) is that the batteries are smaller and generally more exposed to the chilling effect of wind. Lithium polymer (LiPo) batteries used in FPV platforms are robust, low-weight, and highly capable of delivering power. However, their weakness is that even mildly cold weather will negatively affect the performance, which means shorter flight time and slower speed—also, charging these batteries when cold may damage the batteries.[5] This, of course, affects not only the batteries in the drone but also the batteries in the controller, as well as tablets and smartphones (which all usually use Lithium-ion batteries) used to coordinate and watch ongoing missions. The civilian fix is to fly while sitting inside a car or by bringing other gear like hand warmers or dedicated battery warmer bags to keep the batteries warm. In a trench, the operator likely needs to use body heat or keep batteries near a running heat source if there is one. Operators in Ukraine are running several missions during a shift, which means that one operator can’t keep all equipment warm with only body heat. This would undoubtedly become a team effort, which means we must develop solutions that can be applied with minimum effort in the trenches during winter. Operating UAS reliably requires power sources to power batteries, equipment and heaters. Solutions like portable power stations[6] are becoming more common in Ukraine to secure the power supply during power outages.
Using LCD screens in a cold environment can become challenging because their refresh rate becomes slow and sluggish. They could also break if used in sub-zero temperatures. In Ukraine, FPV-specific LCD monitors are often built into smaller DIY ground control stations (GCS), where one GCS can monitor up to four aerial vehicles at any time. It becomes essential to have an external heat source that keeps the GCS above 10 degrees Celsius. When building your own GCS, make sure that you either use generated heat from other components to keep the LCD monitor warm or apply specific heaters to the screens.[7] This may also affect the displays on RC transmitters commonly used for FPV.
However, not only batteries or screens are affected by the cold. Most platforms available on the market and used in Ukraine are made of plastic (although carbon fibre frames are also common), and various types of plastic are more or less vulnerable to cold weather. Changes on a molecular level make the plastic less flexible, more brittle, and thus more prone to cracking. This can become problematic when a platform is exposed to accelerating forces when turning or diving towards a target. In a war where more and more parts are printed in 3D printers or modifications of platforms are typical, there is an added risk that those modifications will add vulnerabilities to the platform. Nevertheless, there are ways to work around the limitations of plastic. Operating in a cold environment may increase drone expenditure, which becomes a logistical issue in the long term.
Flying in cold weather has always been associated with icing on propellers, wings, and fuselage. Unmanned platforms are no different, regardless of size. When flying in cold and humid weather or through fog and clouds, ice may build up on the wings and propellers, affecting the airflow and lifting power, making the platform more challenging to control, and increasing the risk of the drone dropping from the sky. Although there may not be any snow- or rainfall on the ground, there might be higher up. While large unmanned aircraft may use various de-icing chemicals or built-in technologies to stop icing on the wings[8], drone operators operating smaller aerial systems today must understand how icing occurs and use that knowledge to think of creative solutions, such as applying silicone-based lubricants or water repellents on propellers that prohibit water from “sticking” to the surface.[9] Icing occurs not only on propellers or the aircraft’s body; the sensor, specifically the glass protecting the sensor, may also be affected, thus hindering the operator from observing the surrounding environment and potential targets. This is especially true for sensors not sealed correctly, where moisture can enter the housing.[10] This can also happen to FPV drones, where the electronics are unprotected. However, since they are usually used as “one-way drones”, the need to protect the boards is usually not as significant as it may be for other platforms. It should be noted that research is being done to prevent icing on smaller UAS.[11] However, it is unlikely to be realised in the short term on the systems most common on the battlefield of today.
Bringing drones and other equipment indoors from the cold risk creates moisture from condensation on the equipment, risking damaging the electronics or, if brought out again, forming ice on the equipment. Since the equipment probably needs to be brought in to recharge or for maintenance, it is seldom an option to leave it outside. Instead, one possible way of handling the problem is to use the old photographer trick, putting the sensitive equipment in a closed plastic bag before taking it inside. The moisture will then gather outside the bag, keeping the drone, goggles and transmitter dry. This can be used on various electronic equipment, not only drones.
Autumn, winter and early spring usually mean more windy days. With small unmanned systems, even minor winds result in significantly more power being drawn from the battery to keep the platform level or fly in a straight line. The tricky part is that the wind on the ground is probably less potent than the wind 30, 100, or 1000 meters up. It is not always easy to tell how fast the wind blows at altitude or in the target area. A strong headwind en route to the target area of interest will shorten the playtime while gusting winds from the side will complicate striking the target. A GNSS-denied area could result in a platform drifting off course without the operator noticing. Suppose we can’t get support from a weather function with a forecast. In that case, the planning must account for the probability of winds cutting a mission short, complicating navigation or a high risk of vehicle losses during specific periods of the year. It is essential that not only the UAS operators know the system’s weather limitations but also the staff that may rely on systems like loitering munitions to shape an upcoming operation.
While this article has focused mainly on the equipment and how the different parts react to cold weather, we must not forget how exposure to the elements affects the operator. Flying an FPV requires fine motor skills in the fingers when using a typical RC transmitter[12], which the operator will lose when exposed to the cold for too long. Although drone teams in Ukraine have moved indoors or underground away from chilling winds, some teams are still forced to operate in an environment which lacks heating or proper shelter. Some drone teams have used specific “controller mittens”[13], while others utilise thermal ponchos for added warmth and protection of both operator and equipment. Flying without GNSS in a snow-covered landscape could become complicated when landmarks are hidden underneath the snow, which may affect automatic navigation that uses data from Google Maps (or something similar).[14] This would require additional navigational support from a technician or team leader. Being able to launch and recover platforms quickly is mainly related to survivability. Still, it is also required to protect sensitive electronics from snow or rain, and this boils down to the operator’s training in preparing, launching and recovering a vehicle in snowy conditions day and night.
Finally, even though military-grade systems can operate in lower temperatures than civilian-grade systems, that capability comes with a higher price tag. As we have seen in Ukraine, operating UAS in a peer conflict will undoubtedly result in many lost systems. Using military systems in such an environment comes with the risk of running out of spare parts faster than the supplier can deliver. Using civilian systems or building platforms from parts available on sites like Amazon makes the systems less dependent on specific spare parts since a frame from one manufacturer can be replaced with another. Every system has its place within the military operation and should be used where it best serves the purpose, just like the various branches. This article should not be viewed as an argument for either military- or civilian-grade platforms but rather both.
The combination of cold weather and the ever-growing focus on electronic warfare and counter-UAS (CUAS) capabilities could significantly limit the ability to operate smaller unmanned systems during winter; solutions that enhance resistance to the cold while maintaining low cost are needed. Although we see drones today equipped with optical fibre control systems as a counter to jamming efforts, sub-zero temperatures will likely affect the optic cable. This will be the first winter where we may witness how drones with optic fibre perform during cold weather, and if so, they are something to be used to a greater extent during winter.
This article concludes by saying that man still competes against nature, whether in physics or the weather; whichever actor can “tame” nature this winter and, with that, minimise downtime, for UAS may gain the upper hand until spring arrives. For countries in the high north like Sweden, where the winters are long, there is a need to study in great detail how Ukrainian and Russian units conduct drone operations in cold weather. This author would recommend that the Nordic UAS schools conduct joint studies of the subject to prepare for a conflict in the Arctic, especially on a lower tactical level.
