Why Do Most Drones Have Four Rotors When Helicopters Don't?

The Ziyan “blowfish” designed for delivery of goods. (Image courtesy of Ziyan UAV.)

Drones could turn the logistics industry upside down, using unmanned aerial vehicles (UAVs) in home deliveries and for transporting goods. Amazon has been pushing for this since 2013.

Drones are entering a number of different industries, being used as tools in construction, handling surveying and mapping and even in farming. One thing stands out, however: Why are these drone designs using the quadcopter propeller layout, rather than that of a helicopter?

Jiangping Wang, founder and CEO of Ziyan UAV, believes it has to do with the simplicity of the design, which dates back to the early 1900s. The design was rejected by the U.S. military in the 1960s in favor of the helicopter, using a single rotor for movement and another smaller propeller for stability.

Wang notes that the low technical barriers and existing open-source platform of quadcopters are what make them so appealing to hobbyists. Complexities in wing configuration, rotor design and autonomous flight control have led many UAV designers to focus on quadcopters rather than unmanned helicopters.

This doesn’t make quadcopters the best commercial option, however. A quadcopter with more propellers lacks the aerodynamic lift brought by the wings and body in a fixed-wing aircraft. Quadcopters are also inefficient due to their numerous propellers and the blade tip vortices they generate—in addition to their limited size.

Quadcopters, do you even lift? (Image courtesy of Wikimedia Commons.)

There is a reason the military uses the helicopter configuration we’ve all become so accustomed to. Quadcopters simply lack the aerodynamic efficiency of the single-rotor helicopter.

Wang believes that the logistics industry will never have the breakthrough it needs to bring UAVs into regular commercial use so long as we’re fixated on the multiple-propeller design.

Ziyan UAV is developing several different unmanned helicopters, each distinct in size and power, for different applications.

“This is a true unmanned aircraft that we are developing, not some kind of toy that you play with for a day or two and leave it behind, or a something that will create safety concerns. It is a safe, high-speed unmanned helicopter that could be applied to the logistics industry perfectly,” said Wang.

Quadcopters have their place in the consumer market as toys and tools for hobbyists and budding engineers. For commercial and industrial applications though, it may be time to go with what we know works.

Just be ready to defend yourself when the skies are taken over.