55 Pounds of Horizontal Rotors, Texas A&M’s Cyclocopter UAV

Texas A&M’s Advanced Vertical Flight Laboratory has spent years turning a century-old flying idea into something that can actually hold still in the air. Latest result is a 55-pound uncrewed aircraft whose four rotors spin like sideways paddle wheels instead of overhead discs. A recent flight-test video from lab director Moble Benedict shows the machine in controlled hover, using RPM and pitch-phase control on all four cycloidal rotors.

Ramsay Ramsey, a graduate student, tests his 25 kg quad cyclocopter as part of his Master’s thesis. In a 2022 article with David Coleman, Benedict, Saul Sanchez, and Atanu Halder, the design details are put out: this beauty is 1.8 meters long, 1.4 meters wide, and 0.8 meters tall, with four cantilevered cyclorotors and a smart five-bar system to pitch each blade once every revolution. Initial testing was done while connected. Later on, both the lab and Benedict’s own channel demonstrate the remote-controlled hover work on the same 55-pound airframe.

Cyclorotors behave quite differently from helicopter blades. Airfoils are supported by a horizontal axle, and their pitch changes with each turn, ensuring that each blade encounters the air at a suitable angle at both the top and bottom of their circle. Because the entire span moves at the same speed, the rotor can generate thrust at relatively low rpm. Changing the phase of such pitching results in a thrust vector that jumps almost immediately. Benedict claims that rapid vectoring is why the layout can manage gusts faster than a traditional rotor and why the airframe can hover at weird pitch angles, which is highly helpful if you want a camera to stare sideways without using a hefty gimbal.

The 55-pound ship’s four rotors are each six-blade units with a 0.67 chord-to-radius ratio, a symmetric NACA 0015 section, and a pitch amplitude of 45°. In-house 2D CFD tests determined that the mix provided a punchy combination of strong thrust and excellent power loading at around 700 rpm. The frame tubes are carbon fiber, as light as the vibratory loads allow, and include a carbon cowling and mounts for batteries and electronics. Plus, blades and supports on this type of machine have been claimed to account for only a fifth of the empty mass, a figure that they take as a real budget rather than a slogan.

Control is complicated on purpose because the four rotors may change speed and thrust direction separately, giving you eight control knobs and an overactuated hover. To maintain the aircraft upright, a bespoke autopilot uses a cascaded PID loop. That software is handling the behind-the-scenes work in the new hover footage; cage-like rotors continue to whirl, the body remains level, and nothing in the video appears to be an accident.