Power system test
Testing responsiveness of power system. The electric propulsion system in this prototype demonstrated great performance at both low and high power settings. Later testing with ducted fans showed further improvement in efficiency compared to propellers. Larger versions can utilize electric or turbojet engines to generate the required thrust. Existing battery energy density only offers a fraction of the range that can be provided by jet or hydrogen fuels. In a hybrid configuration both electric and gas engines can be combined or substituted completely with hydrogen fuel for a completely zero-emissions helicopter. Another advantage is hydrogen’s energy density. Diesel fuel used in our turbine engine 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 really 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 the energy to weight ratio ten times greater than lithium-ion batteries. Consequently, it offers much greater range while being lighter and occupying smaller volumes.
High disk loading test
During this flight we were looking for any negative flight performance impact from adding additional weight to the aircraft including any noticeable vortex ring state issues which none were observed. 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
Temperature test of 4" thrust tube
Test run of the power system with 40 lbs thrust turbojet delivering 37 lbs of thrust at tube outlet. 37 lbs of thrust applied 10 feet out from the rotor shaft equates to 370 ft/lbs of shaft torque delivered per engine. This particular engine weighs only 3.2 lbs. Larger engines demonstrate even greater power to weight ratios.
Testing 3" thrust tube
Test run of smaller 3" diameter thrust tube with ambient temperatures of over 100 degrees Fahrenheit and 62% humidity! Raw engine power was down a couple pounds of thrust at just over 38 lbs due to the high ambient temperature but the engine was still able to deliver 34 lbs of thrust at 100% throttle and 33 lbs at 90% throttle from the tube outlet. This test also incorporated a different style velocity stack to compare its performance against the original funnel shaped design.
Indoor power testing
Electric power system test with propellers generating thrust. Propellers provide great static thrust and acceleration but are limited by the velocity they produce resulting and the need to position them closer to the rotor shaft which reduces their propulsive efficiency. In this test the rotation of the propellers were changed to cause the produced propeller vortex to spin counter to the rotor blade vortices which resulted in a slight reduction of power required to maintain hover. 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
First ducted fan test
First flight of ducted fan power system. Fans were eventually spaced even further from the rotor shaft due to their greater dynamic thrust compared to the propellers. It was observed that the power curves could be over 10% lower during hovering compared to the propellers most likely due to the improved propulsive efficiency of the fan units. Video cut short due to flying around the room out of camera frame.
Smoke testing / Vortex ring
An interesting observation made while balancing the power system with the blades removed showed that thrust from the motors created a 360 degree horizontal flow of air that could be felt up to 10 feet away. Based on this observation we decided to perform a smoke test to see how the thrust airflow would interact with the vortex produced by the rotor blades. The vortices from the rotor blades appear to be disrupted by the outflowing thrust from the motors and appear to be pushed further out from the rotor disk. Ideally thrust would be delivered further from the rotor shaft but in the case of the propellers there isn't sufficient dynamic thrust at those rotational speeds. 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