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We know that UAVs that have appeared in various countries in the past, in order to have vertical take-off and landing performance, there are two mature solutions to choose from, one is to use the unmanned helicopter mode, and the other is to use the tilt-wing UAV mode, and the latest Flexrotor reconnaissance UAV launched by the American Aerovel company has the conventional shape of a fixed-wing aircraft from the appearance, but it can achieve vertical take-off and landing, so how does it achieve vertical take-off and landing?
The American Flexrotor reconnaissance UAV, which uses a conventional fixed-wing aerodynamic layout
The vertical take-off and landing method is similar to that of a helicopter
Flexrotor reconnaissance drone wingspan 3 meters, length 1.6 meters, empty weight 19 kg, maximum load 1 kg, maximum level flight speed 145 km/h, endurance 40 hours. The UAV adopts a conventional aerodynamic layout, a piston propeller engine is installed in the front of the fuselage, the middle part of the fuselage is cylindrical, the tail of the fuselage gradually shrinks into a conical shape, and the narrow straight middle wing is located on both sides of the fuselage, and the tail is V-shaped. The Flexrotor reconnaissance drone has a conventional aerodynamic layout, which seems to be a decent design, but in fact, there are two parts of this drone that are very special:
First, the piston propeller engine at the head of the drone has a large diameter of 1.8 meters, which is much larger than the proportion of propellers in the conventional layout (after all, the length of the aircraft is only 1.6 meters).
Second, the two ends of the wing of the drone are equipped with an electric small propeller engine, which has become the most special design on the appearance of the aircraft. In fact, the reason why the Flexrotor reconnaissance drone can achieve vertical take-off and landing despite the conventional fixed-wing aerodynamic layout is due to the above two special points. When taking off, first stand the Flexrotor drone vertically with the wings placed on a simple pair of launch brackets, or simply hold the drone smoothly in the air, maintaining a certain distance from the ground with the tail fin from the ground. After starting the engine, the two narrow propeller blades located in the front of the fuselage act like the main rotor of a helicopter, rotating at high speed to generate upward force.
Schematic diagram of the vertical take-off and landing status of the Flexrotor reconnaissance drone
We know that the helicopter needs both the main rotor and the tail rotor to balance the torque, otherwise the helicopter will keep turning in circles during take-off, in the same way, the nose propeller of the Flexrotor drone will also produce torque when it rotates at high speed during take-off and landing, so that the fuselage is subjected to the torque of reverse rotation, and if it is not stopped, the drone will not be able to take off like a helicopter without a tail rotor, or even damaged by rotation. To do this, Flexrotor drones use a pair of small electric propellers on the tips of the wings on both sides. This pair of small electric propellers, one positive and one negative, respectively located on the upper and lower sides of the wing, when working, its rotation plane perpendicular to the rotating wing surface of the main propeller, its effect is just like the tail rotor of the usual helicopter, when rotating at the same time, the force generated will drive the UAV to rotate, just can balance the reverse direction of the rotation moment generated by the main propeller, so as to maintain its own relative static state during the UAV take-off and landing.
After lifting off vertically and reaching a predetermined altitude, the Flexrotor drone uses its tail to steer the fuselage into level flight. After switching to normal level flight, the small propellers at the ends of the wings will automatically retract the blades to reduce drag during level flight.
The Flexrotor drone lands in the opposite direction of the take-off process, the drone first moves from a level flight state to a vertical state under the control of the tail, and then activates the wingtip small propeller, gradually reducing the throttle, and then slowly lands on the launch stand.
Flexrotor reconnaissance drones have the same VTOL as helicopters
Specially set up nose equipment compartment
As a reconnaissance drone, the Flexrotor drone also has a unique design in terms of the design of reconnaissance equipment.
We know that in the existing traditional UAVs with nose propeller propulsion in various countries, because the propeller thruster occupies the nose position, the equipment compartment can only be placed in the middle of the fuselage, and in order to improve the field of view of the camera equipment, it is necessary to protrude an optical turret, resulting in increased drag, which not only affects maneuverability, but also reduces endurance. In order to avoid this drawback, the Flexrotor VTOL UAV adopts a design that moves the propeller back and adopts a gear drive, which guarantees space in the nose equipment compartment, which not only has a good field of view, but also does not add additional air resistance, and since the equipment compartment is not mechanically connected to the propeller, there is no rotation problem that affects the operation of the equipment.
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epilogue
At present, the latest battlefield reconnaissance aircraft equipped by the United States is the "Scan Eagle", which needs a special launch device to fly, and needs to open a blocking net on the ground to recover, and the use of the Flexrotor reconnaissance UAV is similar to the "Scan Eagle" in terms of size and performance level, but it can take off and land vertically, without a special complex launch and recovery device, which ensures the requirements of using UAVs in a small field, and the scope of application has been greatly expanded compared with the "Scanning Eagle" UAV. In the future, it will undoubtedly become a competitor to the "Scanner" UAV. In addition, the Flexrotor reconnaissance drone can also be used in the commercial field for weather and environmental monitoring, as well as geological surveys.