Hoverflie turns Crazyflie drone into hovercraft with 3x ground-effect lift

Small rotorcraft used indoors face severe flight time limitations, and ground-effect hover is notoriously inefficient due to the suckdown effect. Researchers Mrinmoy Modak and Daniel S. Drew from (presumably UC Davis) tackled this by designing Hoverflie, a custom rotor shroud system for the off-the-shelf Crazyflie 2.1 micro air vehicle. Their shrouds redirect airflow to exploit beneficial ground effects while suppressing the suction that reduces lift at intermediate heights. Using a custom test platform with precise height and duty-cycle control, they parametrically tested duct, intake, and nozzle geometries, then built an empirical model that accurately captures the suckdown effect—something standard rotorcraft models miss.

The optimized configuration achieved nearly three times higher in-ground-effect force while maintaining comparable out-of-ground-effect thrust, though the added mass reduced free-flight control authority. Manufactured via thin-film thermoforming, the lightweight shrouds boosted total single-charge flight time by 60% in ground effect (i.e., hovering close to the ground) but reduced free-flight time by 30% versus a stock drone. The team also demonstrated controlled flight, near-ground hovering, and smooth hover-to-flight transitions using a simple mode-switching controller with quantified tracking errors. This work provides an experimentally validated, easily adoptable foundation for hybrid drone-hovercraft systems, opening possibilities for longer-duration indoor inspection, surveillance, and warehouse logistics where ground-effect operation is viable.