Wind is one of the biggest concerns in aviation. The way wind is factored into manned aircraft automation is continuously studied and improved upon. In the field of professional mapping drones—where engineers push the edges of aerodynamics for the sake of retrieving useful data with dependable accuracy—wind remains a major determinant of whether or not a UAV is capable of carrying out its mission.
Why is wind such a complicated factor in flight?
The movement of air due to different pressure gradients, a.k.a. wind, can change and gust unpredictably near water or steep inclines. And its speed rises at higher altitudes. When wind changes abruptly over a short distance, windshear results, causing a strong gust. This is common around objects and buildings, but can also happen in open fields.
As it picks up, wind influences the environment. And at higher speeds, it demonstrates great force. No wonder professional mapping drones are limited to fly and capture data in specific wind speeds.
Different types of wind, and related drone behavior
|Wind speed||Environment||Drone behavior|
< 0.4 m/s
< 1 mph
Smoke rises in a straight line
Perfect conditions for cruise flight, hand-launched drones have difficulties taking off
Wind vanes move, leaves rustle
Perfect flying conditions
Small trees sway, crests form on water
Unpredictable landing accuracy for belly landing drones, tippings expected for tailsitters, possible data gaps for lighter drones
Branches sway, umbrellas malfunction
Not recommended to fly
Twigs break, hard to walk against it
Impossible to fly
Wind means different things to different UAVs. Clear wind guidelines exist around all types of drones to help pilots decide when and when not to fly. In most cases, wind at the high end of published limits means less predictable take-off and landing and challenges to gathering useful data. Knowing this will inform clearer decisions about what drones to purchase for mapping, and how to fly them safely and more reliably.
As we run through the following types of drones and some key points about their behavior in wind, it’s important to remember that the goal is to capture useful and accurate data while keeping the environment and equipment intact.
Multirotors in wind
Multirotors present a flexible and controllable option for small surveys, requiring medium accuracy in light wind. In heavier winds, these strengths can become compromised as follows:
During take-off and landing, Multirotors, like all other drones, can behave unpredictably in higher winds. The maximum wind tolerance for a popular multirotor, the DJI Phantom 4, is 10 m/s (22 mph). But is this tolerance absolute? And does it apply to every stage of flight? A bit of experience reveals that extra space must be provided for take-off and landing even within the high end of this range. This space accounts for possible wind turbulence due to the proximity of buildings, trees or even cars.
Once in the air, multirotors present some advantages. Their constant hover mode and ability to pitch forward while flying provide more control in response to the wind. However, if the wind is against them, their already-limited range is compromised as flight time becomes shorter.
Image capture in the wind by multirotors is limited by their design. As their payload weight increases, their already-limited flight time drops. This puts a cap on the quality of the payloads they can carry, because better sensors are usually heavier. However, multirotors are known to keep the image overlap well due to the gimbal compensating for the angular motion of the drone. This means well-reconstructed data, but only for a relatively small project.
Bottom line: multirotors withstand wind quite well regarding data collection; however, their flight time decreases significantly in higher levels.
What is turbulence?
Turbulence is a chaotic change in air flow that can happen next to vertical structures and in stormy weather. To reduce the chance of turbulence affecting drone operations, stay clear of structures that act as wind barriers near the ground.
Fixed-wings in wind
Fixed-wing take-off involves a catapult or hand launch technique. Although bulky, a catapult will stabilize the drone within a reasonable wind range. Hand launching is advised against the wind, with a clearance recommendation of 40 meters.
Flight in wind for fixed-wings is a familiar process to anyone who has flown in an airplane. It’s efficient due to air lift, which allows for longer flight times. Yet for a professional survey and mapping drone, sharp and well-timed image capture is the goal. So the design and material are important to consider in terms of how steady it flies as winds move around it from the side, front or rear.
Dos and don'ts of measuring wind pre-flight
Every drone has published wind limits. Operating outside of these limits introduces not only a risk to the data gathering, but also to the drone and surroundings. When measuring wind before flight, it’s key to measure it in an unobstructed way, by holding the measurement device above your head and standing in the open air.
Fixed-wing landing in wind at the top of their published wind-tolerance range can be especially unpredictable because it’s much more difficult to manually control the craft. Even in light winds, the landing area should be around 100 meters to ensure no damage to the drone or property. As it rapidly cruises down to land, gusts and shear winds can pull the drone off course or, in the worst cases, slam it into trees, objects or the ground.
Image capture in the wind for fixed-wing drones presents the same payload challenge as multirotors face, for different reasons. In fact, once in the air, a fixed-wing can carry a heavier payload. But when it’s time to come back from the sky, the weight of the drone must be light to prevent a harder impact on belly landing. The most popular fixed-wing for surveying features a range of payloads, but they are limited in their resolution and frame size to keep the weight down.
The lighter the drone for its size, the more likely it is to be unstable in wind. This can further compromise image quality due to an inability to keep the overlap. Incomplete data can then present as holes in the final map outputs.
Bottom line: fixed-wings perform relatively well in light winds. However, in stronger winds, collected data might have gaps due to instability in flight. Landing in strong winds can be unpredictable in all directions.
VTOL drones in wind
VTOL drones offer controlled take-off and landing combined with longer flight times and the ability to carry higher-quality payloads. However, when they are tailsitters, they present what people often mistake as a problem: their shape looks like a sail that is waiting to be blown by the wind during take-off and landing. Yet, when all things are considered, this overall design actually presents advantages.
VTOL take-off in wind requires extra space for the UAV to respond to the surroundings and reach its transition altitude, i.e., the height where it turns to fly like a fixed-wing. Still, it demonstrates control and adjusts itself in stronger winds. When placed parallel to the wind direction, a VTOL stays within a predictable area, avoiding obstacles (see illustrations below).
VTOL landing in wind. In the higher range of its wind limits, this drone can still place itself within five meters of its target. In winds higher than 10 m/s, the drone might tip over (experience a “tipping”); however, it’s important to note that a tipping is not a threat to a drone or its payload, as the most that might happen is a light damage to a middle stand or a scratched nose.
Image capture over large areas is where a tailsitter VTOL excels, even in some considerable wind. Because of the VTOL capabilities—which eliminate belly landings and hard impacts—the drone itself can be heavier. When the drone is a heavier composite frame, vs. lightweight foam, cruise flight will be steadier.
Because they present virtually no shock to the payload, VTOL touch-down landings also allow for heavier, higher-resolution payloads and more robust image capture with sensors that can support twice as much resolution and better light sensitivity through a full-frame lens. All of these combine to hold the image overlap and quality of data capture to the needed level, even in winds at the higher end of its limit.
Bottom line: VTOL composite frame drones are steadier and offer more reliable data collection, i.e., data without gaps resulting in complete mapping outputs. Their landing is still very accurate and the most that can happen is a tipping.
The right amount of take-off distance in wind
Which drone wins in the wind?
Weighing all the pros and cons, VTOL drones offer a more predictable and safe take-off and landing without the risk of drifting into obstacles. A composite frame with dependable overlap, thanks to high-quality payloads, offers high-accuracy data without gaps in mapping outputs, even in higher winds.