An alternative to our tip jet design involves a platform that employs a separate thrust support structure, featuring a direct-drive motor coupled to either a propeller or ducted fan. This configuration has demonstrated excellent flight characteristics and endurance compared to other small electric rotorcraft. However, scaling up to larger drones may necessitate the use of gas engines or our alternative design, which incorporates turbojet engines in a more compact tip jet configuration. A recent short flight test of the control system included a low-altitude autorotation, focusing on evaluating the one-way bearing that allows the rotor blades to spin independently of the rotor shaft.

Testing the responsiveness of the power system. The primary goal of this build was to evaluate a one-way bearing that allows the rotor blades to spin independently of the rotor shaft as a safety feature. In case the motors stop mid-flight or if something causes the shaft to stop rotating, autorotation would still be possible and potentially improved without the friction from other components. The electric propulsion system in this prototype performed exceptionally well at both low and high power settings. Later tests with ducted fans showed further efficiency improvements compared to propellers. Larger versions of the system can utilize either electric or turbojet engines to generate the necessary thrust. However, current battery energy density only provides a fraction of the range that can be achieved with traditional jet fuel or alternative fuels such as hydrogen.

A prototype test flight was conducted with more aggressive power curve settings and high-altitude autorotation. The V2 iteration of this design will incorporate slip rings, allowing the batteries to be housed within the fuselage, along with an airfoil-shaped "thrust support structure" to significantly enhance aerodynamics and overall efficiency. The ultimate goal of this design is to enable both propellers or ducted fans to transition forward in flight while the rotor remains effectively isolated by a one-way bearing at the rotor hub. This will allow the drone aircraft to operate in a gyrodyne configuration, achieving higher speeds and extended range compared to traditional helicopter-only flight.

During this flight, we monitored for any negative impact on flight performance from the added weight, including potential vortex ring state (VRS) issues, none of which were observed. This was a preliminary test of a gyrodyne design that differs from previous approaches, which relied on the same thrust for both takeoff and forward flight. Earlier attempts, such as the X-50 Dragonfly, tried to rotate one of the blades during this transition, making the aerodynamic shift extremely complex and ultimately leading to the loss of prototypes. In this design, we avoid disrupting the rotors by incorporating a separate support structure that allows the thrusters to be positioned and pivoted independently.

Test run of the power system using a 40 lb thrust turbojet, delivering 37 lbs of thrust at the tube outlet. This test was conducted to evaluate the temperature drop from the engine to the thrust tube after cooler air is drawn in by the augmentor. Notably, this engine weighs just 3.2 lbs, and larger engines demonstrate even more impressive power-to-weight ratios.

A thrust tube test run was conducted in ambient conditions exceeding 100°F with 62% humidity. The high temperature caused a slight reduction in raw engine power, generating just over 38 lbs of thrust. However, the engine sustained 34 lbs of thrust at 100% throttle and 33 lbs at 90% throttle at the tube outlet. This test also introduced a new velocity stack design for comparison with the original funnel-shaped model. Further testing is planned with redesigned thrust tubes featuring various profiles and thermal coatings to reduce temperature and pressure loss. This power system serves as the core of our "Thrust Drive" reaction-powered helicopter design and will ultimately be integrated into a thrust-powered tilt-rotor aircraft. Its design even enables the possibility of a mono-tilt rotor helicopter, as it eliminates counter-torque requirements.

Electric power system test using propellers to generate thrust. While propellers provide excellent static thrust and acceleration, their efficiency is limited by the velocity they produce, which necessitates positioning them closer to the rotor shaft, reducing their overall propulsive efficiency. In this test, the direction of the propeller rotation was reversed, causing the propeller vortex to spin counter to the rotor blade vortices. This adjustment resulted in a slight reduction in the power required to maintain hover. The Thrust Drive System converts the thrust generated by a jet engine, ducted fan, or propeller into usable rotor shaft torque to power the helicopter’s rotor blades.

First flight test of the ducted fan power system. The fans were later positioned further from the rotor shaft due to their superior dynamic thrust compared to the propellers. It was observed that power curves could be reduced by over 10% during hovering compared to the propeller configuration, likely due to the improved propulsive efficiency of the fan units. The video was cut short when the aircraft flew out of the camera frame and collided with a nearby table—whoops!

An interesting observation was made while balancing the power system with the blades removed: the thrust from the motors created a 360-degree horizontal airflow that could be felt several feet away. Based on this, we decided to conduct a smoke test to examine how the thrust airflow interacted with the vortices produced by the rotor blades. The rotor blade vortices appeared to be disrupted by the outward thrust from the motors and were pushed further out from the rotor disk. Ideally, thrust would be delivered farther from the rotor shaft, but with propellers, there isn't sufficient dynamic thrust at those rotational speeds. This power system configuration differs from the thrust drive system and is instead an experimental gyrodyn design. The ultimate goal is to enable the aircraft to function as a compound helicopter by incorporating two or more thrusters mounted on a sprag clutch-separated thrust support structure. This setup allows the thrusters to remain stationary and forward-facing once the aircraft transitions from hover to forward flight.