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How it works

The thrust drive system converts thrust generated utilizing a jet engine, ducted fan, or propeller into useful rotor shaft torque needed to power helicopter rotor blades. In the thrust drive system, the required torque is delivered to the rotor shaft when thrust is applied tangentially at a distance from the rotor shaft. The thrust generated by the engines is introduced into thrust tubes near the rotor shaft and at an optimum distance from the rotor shaft, the thrust is expelled from a nozzle at the outer extremity of the thrust tubes. The resultant thrust causes the thrust tubes to rotate around the axis of the rotor shaft. Since each thrust tube is connected to the rotor shaft, the rotor shaft and its connected rotor blades rotate. For example, the torque delivered to the rotor shaft attach to the 10' rotating thrust tube assembly would be approximately equivalent to 10 times the amount of thrust delivered from the thrust tube outlet.  In the event of a power loss, a one-way clutch disconnects the thrust support hub allowing the rotor blades to rotate uninhibited for autorotation.  The thrust drive system usually has two or more thrust tube assemblies that are directly connected to the rotor shaft and cause its rotation. Additional thrust can be delivered by adding more thrust tubes and more powerful engines allowing this system to provide an incredible amount of shaft torque delivery while utilizing very powerful yet compact jet engines. In the thrust drive system, the rotor shaft is isolated from the fuselage eliminating the need for gearboxes, tail rotor, and related drivetrain.

Methods of powering a helicopter
Engines that can be used to produce thrust to fly the helicopter

There is a wide variety of engines available to produce the required thrust.  The best propulsive efficiency and range are provided by jet engines which are the preferred method of thrust production at this time. Electric brushless motors have demonstrated proven performance but are still seriously limited by the low energy density of today's battery technology.  Furthermore, serious heat and internal battery resistance issues have arisen when power levels are run at the sustained high power output needed by proposed eVTOL aircraft during taking off. These battery capacity and cooling issues have limited the few flying examples of actual maned eVTOL aircraft to less than 30 minutes of flight time. However, a hybrid approach of using jet-fueled or hydrogen-powered turbojets for takeoff and landing along with the option of electric power for forward flight propulsion allows for an ultra low emissions aircraft without sacrificing range. Additionally, standard turbojet engines can run interchangeably on diesel, kerosene, Jet-A or hydrogen and can even get a sizable boost in thrust from water injection.  When considering low emissions fuel sources another advantage of hydrogen is its energy density. Diesel has an energy density of 45.5 megajoules per kilogram (MJ/kg), slightly lower than gasoline, which has an energy density of 45.8 MJ/kg. By contrast, hydrogen has an energy density of approximately 120 MJ/kg, almost three times more than diesel or gasoline. In electrical terms, the energy density of hydrogen is equal to 33.6 kWh of usable energy per kg, versus diesel which only holds about 12–14 kWh per kg. What this means is that 1 kg of hydrogen, used in a fuel cell to power an electric motor, contains approximately the same energy as a gallon of diesel.  Hydrogen used in fuel cells has an energy-to-weight ratio ten times greater than lithium-ion batteries. Consequently, it offers much greater range compared to batteries while being lighter and occupying smaller volumes.

Thrust Support Structure
  • 7075 aluminum alloy extrusion

  • Carbon fiber / Kevlar 

  • Single or double walled construction

  • Contains complete power system including engines and ducting or ducting only when engine thrust is delivered through the rotor shaft

  • Electrical and fuel connections provided by slip rings

  • Aerodynamic low drag airfoil skin


Torque generated from nozzle outlet transferred through structure to the rotor shaft.

One way bearing functions and benefits for helicopter use
Types of clutches that can be used on a helicopter

Disconnects thrust support hub in the event of power loss to allow the rotor blades to rotate uninhibited for autorotation.

Bearings used in helicopter shafts and transmissions
Types of bearings that can be used in a helicopter

Provides connection of the rotor shaft to the fuselage.

Yaw Control Options
  • Electromagnetic 

  • Aerodynamic rudder

  • Direct drive electric

  • Or combination of above 

Exploded diagram of axial flux yaw control device
Images of axial flux motors and components

Since there is no longer a need for anti-torque a simple vertical stabilizer and rudder can provide yaw control. Also, yaw control can be provided without a rudder by utilizing a magnetic rotor affixed to the rotor shaft and then by energizing copper coils that are attached to the fuselage structure which would allow the aircraft to be actively controlled by a simple change in electrical polarity and controlled current output. This system is essentially just an electric motor with the rotor shaft acting as the motor axle and the fuselage acting as the motor case.   

Slip ring applications
Types of slip rings

Supplies fuel and electrical connections to engines through the rotor shaft.

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