Overview of drone landing methods

Controlling a drone can be nerve-wracking. No matter how careful you are, if you are not careful, thousands or tens of thousands of dollars of drones may lack arms and legs, run out of electricity, or start flying around and then hit the ground heavily. So, how can we make our drone flight landings safer? First, let's take a look at the main ways drones are recycled.

The development of UAV aerial recovery has gone through three periods: the first period was due to the use of circular parachute systems without glide capability, which is typically used on the American Firebee AQM-34N reconnaissance UAV. The second period began on the basis of the widespread use of ram-winged parafoels with high glide capability, typical of which was the mid-range UAV recovery project developed by the American Vertigo company. The third period was marked by the emergence of intelligent hooks. When the tow parachute rope is in the mouth of one or more intelligent hooks, the hook claw will automatically close after sensing the combination rope (tow parachute rope), completing the hook hook work, greatly improving the application of recovery.

Uav recovery methods can be summarized into parachute recovery, air recovery, landing gear skid landing, arrester net recovery, air cushion landing and vertical two main landing recovery. Some UAVs use non-aircraft recovery, which is usually the recovery of the mission equipment bay, and the rest of the aircraft is not recovered.

For example, the U.S. D-21/GTD-21B had its mission equipment bay ejected from the aircraft and retrieved by C-130 aircraft. Some small UAVs do not use recycling tools when recycling, but rely on a part of the body to directly contact the recycling basking machine, using this simple recycling method of UAVs is usually less than 10kg, and the maximum feature size is below 3.5m. For example, the United Kingdom's UMACII flying wing UAV, after the completion of the mission to land on the belly of the aircraft recovery.

1. Parachute recovery

This is a more common form of recycling. The parachute consists of a main parachute and a secondary parachute (also known as a drag parachute). When the UAV completes the task, the ground station sends a remote control command to the UAV to slow down the engine, slow down the aircraft, and lower the height. When the appropriate flight height and speed are reached, the decelerating parachute is opened to sharply slow down the aircraft and reduce its height, at which time the engine has stopped; When the UAV drops to a certain flight altitude and speed, the recovery control system sends a signal to make the main umbrella open, first in a tight and inflated state, after a certain period of time, the main umbrella is completely inflated; The drone hangs under the main umbrella and lands slowly. The ground touch switch under the aircraft is switched on, so that the main umbrella is separated from the drone.

This is the simplest description of the parachute recovery process, omitting the intermediate steps and processes. In order to minimize the damage after the recovery of the drone, especially to protect the airborne mission equipment, some drones are also installed in the body of the ground part of the shock absorber, inflatable bag is a commonly used shock absorber. Also consider landing as far away from the mission equipment bay as possible.

For example, when Canada's CL-89 is recovered, the drone turns 180° up and down, so that the belly is on the top, the back is on the bottom, and the landing air bag before and after the back is on the ground, absorbing the impact energy and protecting the mission equipment in the belly. Some drone body landing parts are designed to be more fragile parts, as a shock absorber for the aircraft landing. For example, the British "not dead bird" flips 180° after recovering the parachute, the belly of the aircraft is up, the back of the aircraft is down, and the back fairing is fragile, allowing it to be flattened when landing, absorbing the landing impact force, and protecting the mission equipment nacle of the belly of the aircraft.

2. Aerial recovery

Retrieving drones in the air with humans is currently only available in the United States. In this way of recovery, there must be an air recovery system on the manned aircraft, and in addition to the drag umbrella and the main umbrella on the UAV, there must be a hooked laurel umbrella, a sling and a rotatable shedding mechanism.

The simple recovery process is as follows: the ground station sends out a remote control command, the Yang force umbrella opens the umbrella, and the engine stops at the same time. When the UAV drops to a certain height and a certain speed under the resistance umbrella, the recovery control system sends out a control signal to open the main umbrella, open the hook umbrella and the main umbrella, and the main umbrella is first tightly inflated, and soon it is completely inflated. At this time, the hook umbrella is higher than the main umbrella, and the sling under the hook umbrella is guaranteed to point to the direction of the main umbrella, and the wind flag indicating the direction is installed on the sling, so that the man-machine can easily identify and hook the hook umbrella.

At this time, there are man-machine into the upwind, hook the drone hook umbrella and sling, when the drone is hooked, the main umbrella automatically out of the drone, a man-machine winch the drone, hanging away in the air. This method of recovery does not damage the drone. But in order to recover the drone need to dispatch a man-machine, the cost is high; The man-machine driver is required to have higher driving skills during recovery. Affected by the weather and customs, coupled with the performance of the umbrella can not be estimated in advance, its recycling reliability is low. As recycling technology improves, the reliability of recycling will improve. For example, the "Firebee" II of the United States uses the air recovery method, in the recovery, the helicopter hooks the hook parachute 24.08m higher than the main umbrella.

3. Landing gear run

This method of recycling is similar to that of human machine, but the difference is:
 

① Runway requirements are not as harsh as human-machine requirements.

The landing gear of some UAVs is partially designed with a more fragile structure, allowing damage to the ground during landing and absorbing energy. For example, the British "Big Duck" I is a small UAV weighing 15kg, with a wingspan of 2.70m and a captain of 2.10m, with landing skis under the fuselage and wingtip skis, which are fragile and allowed to break off when recovered to absorb the impact force.

③ In order to shorten the landing distance, some drones such as Israel's "pioneer", "Dog", "Scout" and so on in the tail of the tail hook, in the landing slide, the tail hook hooked the ground interception rope, greatly shortening the landing distance.

4. Catch net or "skyhook" recovery
 

It is one of the most common recycling methods of small UAVs in the world to recover UAVs with arrester net system. The arresting net system is usually composed of arresting net, energy absorption device and automatic guidance equipment. The energy absorption device is connected with the arresting net, and its role is to absorb the energy of the UAV hitting the net, so that the UAV will not bounce on the net after touching the net, resulting in damage. The automatic guidance device is usually a television camera placed behind the net, or an infrared receiver mounted on the interceptor grid, which reports the deviation of the drone's return route to the ground station in time.

When the UAV returns, the ground control station requires the UAV to slide at a small Angle and the maximum speed shall not exceed 120km/h. The operator monitors the UAV flight through the TV monitor, determines the deviation of the return route according to the images captured by the ground TV camera or the signals received by the infrared receiver, and then controls the UAV semi-automatically. Correct the flight path, align it with the line of sight of the ground camera, and fly towards the arrest net. The overload of the UAV when touching the net is usually not greater than 6g, so as to avoid greater damage to the arresting net. For example, the Israeli "Scout", the United States "goshawk" and so on are recovered with interceptor nets.

The "skyhook" recovery function is similar to that of the arrester net, when the UAV is controlled to fly to the rope, the hook of the unmanned wing tip is used to hook the rope for recovery. The Scanning Eagle UAV in the United States uses this method of recycling.
 

5. Air cushion landing
 

In the 1970s, there were hovercraft and hovercraft, which used the air cushion effect to leave the ground or water. The drone's air cushion landing works the same way. Attach a "rubber skirt" around the belly of the drone. In the middle, there is a bag with a hole, the engine presses the air into the air bag, the compressed air is ejected from the bag hole, and the high-pressure air zone - air cushion is formed under the belly of the aircraft, and the air cushion can support the drone close to the ground without violently impacting the ground. In the mid-1970s, the United States used Australia's "Jindavik" UAV as a research aircraft for air cushion landing to conduct experimental research on air cushion landing projects and achieved great achievements.

The biggest advantage of air cushion landing is that the drone can land on unpaved ground, mud, snow or water, regardless of terrain conditions. In addition, it is not limited by the size and weight of the drone, and the recovery rate is high, it is said that it can reach 1 sortie in 1 minute, and the air recovery is 1 sortie in 1 hour.

6. Vertical landing recovery

Vertical landing UAV is flexible, rapid response, suitable for low-speed, low-altitude close-in flight, can take off and land vertically and hover in the air, does not need a specific landing site, can perform tasks in narrow space, so it is widely used. According to the number and layout of rotors, vertical landing UAVs can be divided into single rotor UAVs, double rotor Uavs, four-rotor UAVs, ornithopters, rolling wing aircraft and flying butterfly UAVs.

What you need to pay attention to is:

1, why with a full bar floor oil straight drop? Anyone with a little discretion wouldn't fly like that, would they?

A: We wanted to show you most clearly the problems that occur when you go straight down at high speed, under more extreme conditions. In fact, as long as the sinking rate exceeds the more safe range, these hidden dangers will objectively exist, especially stall. The factors that lead to the instability of the aircraft are too fast and straight landing, and we would like to emphasize the importance of landing on a course.

2, then I stop in the air, down to a certain height and then break the pole to start the electric machine how?

A: Previous members of the team have tried this on their own, and the result is that they are sent home. Don't play with thousands of devices and lives. Stall is needless to say, after the propeller stops, the flight control can not stabilize the attitude of the aircraft through the adjustment of the speed, we can estimate how many degrees the aircraft will roll in the air.

3, in our test, our spirit 1 withstood the test, the ambient wind speed was not large, the flight control made compensation for the attitude stability, and did not roll over in the air. With the upgrading of UAV products, manufacturers have also made more and more safe limits on the maximum sinking rate, but the route landing still helps to improve the stability and safety of the aircraft.

4. After consuming part of the electricity, because the maximum power was not as high as at the beginning, we could not change the stall state in each high-speed linear descent, and the aircraft fell to the ground repeatedly and could hardly control the direction after bouncing. What was shown in the video was only the most serious loss of control.

5, if the aircraft is mounted on the head camera, the shake during high-speed descent is difficult to eliminate the head, which will affect the quality of the shooting picture. It is also easy to cause damage to the head and camera after falling to the ground.