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Uses, Advantages & Benefits

The vastly simplified thrust drive system reduces drive system components and their associated points of failure.  The engines are located far enough from the fuselage structure to not only greatly reduce cabin noise and vibration but also reduce the proximity of the largest potential ignition source in the event of an accident.  Safety is improved by the ability to operate the aircraft with a lower risk of vortex ring state and much greater inertia helping to prevent the rapid loss of rotor rpm. 

Autorotation benefits

Due to the high rotational kinetic energy of the thrust drive system, more time is available for the pilot to react in the event of complete loss of power before autorotation is initiated. Also, the thrust drive system is automatically decoupled from the rotor shaft by a sprag clutch at the hub eliminating any drag or power loss from failed drive components during autorotation. This is in contrast to a conventional helicopter that encounters transmission friction even when engine power is lost and may also require negative anti-torque thrust to overcome transmission friction losses during autorotation. Additional friction preventing safe autorotation can also occur if there is a failure of any critical conventional drive component.

Description of VRS vortex ring state
Airflow in VRS vortex ring state compared to normal airflow
Thrust drive LLC thrust from nozzles interfering with VRS vortex ring state

There are several factors that affect the way vortices are disrupted by the thrust drive system.  The thrust tube's airfoil angle of attack can be pre-set or actively controlled to aid in reducing the disk loading of the main rotor blades.  Jet thrust exits the Thrust Drive System just above the rotor blades which interferes with vortex formation and continuously supplies a large volume of air from the outlet nozzle at the ends of each thrust tube which then flows outward radially above the portion of the rotor disk that is producing the greatest lift for the aircraft. The observed effect of this during smoke testing with a prototype thrust drive system and rotor was that any vortex formations were pushed out radially increasingly as thrust output was increased with rotor blade pitch only increasing the amplitude of the vortex further out radially to the rotor disk. The 1/6 scale model also demonstrated the ability to quickly and abruptly take off and land completely vertically even while fully loaded without any noticeable VRS effects as opposed to a conventional model of the same scale that showed noticeable settling under the same conditions.  Another area of research being explored is that in the power system configuration there is an additional airfoil co-rotating and stacked above the main rotor that is able to adjust its angle of attack by naturally "weathervaning" into the prevailing airflow. By essentially placing a wing (airfoil) inside the main rotor upwash just outside the rotor span, that effectively increases the rotor span -- in this case, more blade area could produce more lift, but the vortex would not get stronger. The vortices can't fully be eliminated but relocating them to boost efficiency is a worthy objective. 
See also:

Counter torque/Tail rotor
  • Elimination of constant opposing force requirement and mechanisms

  • Yaw control using a simple rudder

  • Tail boom is optional 

  • Tail rotor and boom strike eliminated

  • Tail rotor failure not an issue

  • Tail can be completely eliminated with electric yaw control

  • Elimination of conventional drive components reduces noise and vibration

  • Eliminate cost and weight of components

  • Engine power is only used to generate lift, not to drive counter torque components 

  • Increased payload for available shaft power or same payload with a lower shaft power requirement

  • Reduced cost and complexity of manufacturer and maintenance

Diagram showing one example of the Thrust Drive System

In this thrust drive system configuration engines directly supply thrust through a separate isolated structure.  As in the case with most of the thrust drive system configurations when four or more engines are utilized two or more engines can be shutdown to improve fuel efficiency when the aircraft is not fully loaded during forward flight.

Integrated drive components into rotor airfoil

This is the standard configuration with the thrust tubes integrated into the rotor blades.

Standard Compound Configuration of thrust drive llc propulsion system

A basic compound configuration where the microturbine engines provide reaction power for takeoff, landing, and helicopter maneuvering only. Once the aircraft has achieved sufficient forward speed the microturbines are turned off allowing engines and propellers located on the ends of stub wings to provide thrust for forward flight with greater fuel economy while rotor blades and thrust tubes continue to rotate and provide partial lift in a gyrodyne configuration. The gyrodyne can also be configured with only thrust tubes providing lift as rotor blades. An alternative configuration incorporates an indexing clutch that stops the thrust tubes in a position perpendicular to the fuselage and uses a servo to rotate one of the thrust tubes 180 degrees to allow the thrust tube airfoils to both point forward to provide lift along with the engines providing forward propulsion. The turbine engines are fully compatible with hydrogen fuel and electric or turbine engines can be used interchangeably for zero-emissions rotor power and or forward propulsion. A great past example of a gyrodyne design was the Faraday rotodyne. The aircraft flew exceptionally well and was able to achieve 200 mph in the 1950s while carrying up to 40 passengers without the benefit of computers or software.  If not for the extremely loud air fed rockets at the ends of the rotors that produced a nauseating 120 db of sound even at 600 feet away there's no doubt it would have entered full production. In the Thrust Drive System, sound emissions are similar to a conventional helicopter but can be even lower due to the enclosure around the engine and thrust tubing.  The long tubing that entrains the thrust coming out of the engines is similar to an exhaust pipe on a car further reducing sound emissions.  The gyrodyne configuration is not only achievable using the Thrust Drive System but practical to fly from existing helipads and city centers due to lower sound emissions.

High speed dual rotor VTOL thrust drive system using turbofan engine

The above configuration reflects an approach to achieve a fast compound helicopter with minimal moving parts and points of failure along with simplified maintenance. In its take-off configuration, a valve diverts the majority of "warm cycle" pressure through the rotor shaft which is then distributed to a series of short counter-rotating airfoil-shaped thrust tubes (rotor blades) to produce thrust for takeoff and hover. As the aircraft transitions to fast forward flight the valve re-positions to allow the majority of engine pressure to provide forward propulsion while reducing pressure provided to the counter-rotating thrust tubes as induced power requirements become lower in forward flight.  Fly by wire servo flaps are incorporated into the rotor blades to provide flight control without the use of complex and difficult to maintain rotor head control systems.  As common with Thrust Drive System designs heavy transmissions and other conventional drive system components are not required. Compressor bleed air is used for yaw control and auxiliary reaction controls.

Retrofit Thrust Drive System on simple rotor mast with additional mass and gyroscopic forces to dampen mast bumping effect

This simplified drawing depicts the thrust drive system integrated into a teetering rotor head.  The added spinning mass dampens rapid head movement to eliminate mast bumping and causes the rotor to behave more like a semi-rigid rotor system.

Additional Safety and Serviceability Enhancements

  • In certain configurations engines no longer directly embedded above or next to fuel tanks improving safety in case of a crash 

  • Flexible aircraft shape and footprint

  • Operate from same landing pads and facilities as conventional helicopters 

  • Existing pilot skills and training are fully compatible

  • Major aircraft components are the same or similar in construction 

  • Reduction or elimination of unloaded rotor mast bumping by incorporating gyroscopic damping of power system onto the rotor head and side thrust produced by the tail rotor

  • Improved safety has the potential to lower insurance cost 

Improved efficiency for drone aircraft
Thrust Drive Standard with extended tail

A variety of thrust drive configurations are in the drawings below. Depending on the application, the thrust drive system can be optimized to achieve specific performance requirements.

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