WZ-G - Coaxial Gyrodyne

An aerospace show in May 2021 at an unreported location in China showcased three models of new vertical aviation concepts, including a helicopters with coaxial rotors and a six-blade pusher propeller. The designation and institutional sources of the Chinese design were not reported [the WZ-G designator is an arbitrary placeholder]. A Gyrodyne is a type of VTOL aircraft with a helicopter-like rotor system for takeoff and landing that also includes one or more conventional propellers to provide forward thrust during cruising flight. The concept is generally similar to the Sikorsky X2, S-97 Raider and SB>1 Defiant series. There are two striking things about the design. The first is its set of two rotors, mounted one on top of the other and turning in opposite directions around a central shaft. The second is the absence of a tail rotor. In its place sits a backwards-facing “pusher” propeller. In China, the coaxial conficguration has been seen in a few small Vertical Takeoff UAVs, and of course in many consumer toyes, bu thte pusher prop is new to China. It cannot immediately be determined from the single photograph of the display model whether the vehicle is piloted or a UAV.

This compound helicopters, or gyrodyne, design is a vertical takeoff and landing (VTOL) aircraft with both a helicopter rotor-like system for hover, takeoff and landing and also a conventional propeller, such as a pusher propeller, to provide forward thrust during cruising flight. With a central fuselage housing avionics and a pusher propeller for forward propulsion, the aircraft's unique hybrid power system saves weight over conventional power schemes, increasing the aircraft's range and efficiency. Conventional helicopters have a limited top speed due to the problem of retreating blade stall, in which the rotor blade with the smaller resultant relative wind exceeds the critical angle of attack.

The concept of an aircraft with both VTOL and cruise modes promises a “best of both worlds” possibility. Traditional airplane designs use wings as primary lift surfaces. This is efficient and allows them to fly long distances while maximizing their use of stored energy. A limitation of traditional airplanes is that they require a runway for takeoff and landing. This ground infrastructure requirement limits the locations where airplanes can take off and land. On the other hand, rotorcraft such as helicopters and multi-copters do not require runway infrastructure since they feature Vertical TakeOff and Landing (VTOL). With the advantage of VTOL capability comes a cost: traditional rotorcraft are less energy efficient than similarly sized airplanes, they require more costly maintenance, and they typically fly more slowly—factors that limit their effective range and increase operating costs.

Coaxial helicopter essential characteristic is: two secondary identical rotors are mounted on same root one on the other at regular intervals between two rotors in rotor shaft. The direction of rotation of two secondary rotors is on the contrary, their reaction torque can offset each other. In this way, just not needing to refill tail-rotor. The directional control of helicopter by upper and lower two rotor always away from differential change complete.

Compared with a single-rotor helicopter, the coaxial counter-rotating rotor helicopter has the advantages of short rotor arm, low power consumption, no need of mounting a tail rotor to balance counter moment generated by rotation of the rotor, more flexible structural design and the like. Coaxial helicopter major advantage be it is compact-sized, outer dimension is small. This helicopter has no rail rotor. There are two secondary rotors to generate lift, every pair rotor Diameter can also shorten. Airframe components can compactly be arranged in helicopter center of gravity, so flight stability is good, be also convenient for grasping It is vertical. Compared with single rotor tail-rotor helicopter, driving efficiency obviously increases. Furthermore. co-axial helicopter aerodynamic hovering efficiency is also relatively high.

The Kamov 50 coaxial contra-rotating helicopter designed and manufactured by the Russian Kamov design office is a typical representation of this type of helicopter. The coaxial helicopter with a relatively simple structure in the prior art usually has the defects that the upper rotor wing and the lower rotor wing cannot unify the differential pitch variation and the synchronous torque variation of the single propeller, the helicopter needs to be regulated by the rotating speed of the rotor wing besides the pitch regulation when realizing the maneuvering such as lifting, rolling, pitching, yawing, back flying and the like, and the maneuvering cannot be carried out by directly changing the pitch. Such solutions can result in slow and inefficient aircraft maneuvers due to the effects of rotor system inertia.

The Ka-35D rotorcraft is a combined helicopter (rotorcraft) having combined carrier and propulsion systems. The combined carrier system consists of a wing and rotor screws transversely located at its ends. The combined propulsion system includes gas turbine engines that drive rotors, and turbojet engines mounted on the wing to create propulsive force. The combined carrier and propulsion systems provide the rotorcraft with the possibility of vertical take-off and landing, hovering and the ability to switch to airplane flight modes at high speeds. The main part of the lifting force in airplane modes is created by the wing, and propulsion (propulsive) forces are created by jet engines. Using the wing to unload the rotors with increasing rotor speed allows increasing the speed of horizontal flight up to 550 km / h, increase aerodynamic quality and reduce the load in the carrier system. The disadvantage of the technical solution adopted on the Ka-35D rotorcraft is the use of separate power plants (lift and propulsion), and the propeller autorotation mode in airplane flight modes, which limits the possibility of increasing the flight speed over 500 ... 550 km / h.

The Sikorsky high-speed coaxial helicopter provides for the use of so-called “rigid” coaxial rotors, which, according to the company, ensure the full use of the advancing blades in a symmetrical coaxial pattern, the ability to move the stall boundary on the retreating blades, reduce the flywheel movement of the blades and increase the bearing capacity and aerodynamic quality of the rotor. In this concept, a reduction in rotor speed is also contemplated. This concept ensures the achievement of a maximum flight speed of up to 450 km / h.

The S-97 high-speed coaxial helicopter has a streamlined fuselage on which two three-bladed rigid rotors are located coaxially (on the same axis) to create lift; cockpit for two pilots located in the bow of the fuselage; tail unit, consisting of a horizontal stabilizer with deviated (controlled) surfaces, two vertical keels (washers) at its ends with rudders and a ventral vertical keel fairing; three-post flight retractable landing gear with two front main and one tail support; six-bladed pushing propeller of an adjustable pitch located in the rear of the fuselage and serving to create horizontal (propulsive) force. The power plant of the helicopter consists of gearboxes, shafts and one gas turbine engine, from which all the propellers are driven - both bearing and pushing propeller. The rotor bushings and the upper rotor shaft are covered with fairings.

Placing the pushing screw directly in front of the rear of the fuselage, i.e. significantly closer to the center of mass of the high-speed combined helicopter significantly reduces its moment of inertia, which increases maneuverability and reduces the strength requirements of the transmission and the rear of the fuselage, which leads to a decrease in the mass of the high-speed rotorcraft.