Bell’s New, Self-Flying Cargo Drone Hauls a Heavy LoadSeptember 4, 2019
They say things are bigger in Texas, and it seems that goes for drones as well as pickup trucks and cowboy hats. At least, if Fort Worth-based Bell’s new, autonomous cargo carrier is any indicator.
The four-motor, vertical-lift electric UAV is one of the largest commercial cargo drone projects to reach the skies. It stands nearly 6 feet tall and 9 feet wide on the ground (it rests on its tail before transitioning to horizontal flight after liftoff). It weighs 300 pounds and can carry an additional 70 pounds of cargo, slung in an aerodynamic pod between its two wings. That all-important stat gives it the name APT 70, the letters standing for “autonomous pod transport.” It first started flying in December via remote control, and in the past three weeks began fully autonomous flight, Bell announced this week.
The helicopter manufacturer developed the APT 70 for NASA’s drone integration program, formally known as the Systems Integration and Operationalization demonstration activity. In that effort, it’s primarily intended to demonstrate commercial drone missions in public airspace, as well as their autonomous behavior beyond an operator’s line of sight.
But Bell thinks it has found a sweet spot with this configuration in terms of payload, range, and usability that will appeal to a wide array of customers. “When most people think of cargo drones they imagine these small and cute little things,” says Scott Drennan, Bell’s vice president in charge of engineering innovation, which includes drone drone development as well as its larger air taxi initiative. “But when you get the payloads that most companies actually find useful, it gets to be a much larger aircraft.”
Each of the APT 70’s four motors sits on a pylon attached to its own narrow fuselage, with horizontal and vertical stabilizers at the rear. These act as the legs and feet for the aircraft while on the ground. They power four blades, which provide vertical thrust at takeoff. The aircraft then pitches forward for horizontal flight, with a pair of stacked wings (a bit like a biplane) generating lift and enabling higher speeds. It can fly at 100 mph, though will typically cruise at 75, and cover up to 35 miles on a single charge while carrying its maximum payload. Altering the relative speeds of the rotors allows maneuverability comparable to that of a nimble quadcopter drone.
The large drone is a successor to a smaller demonstrator, the APT 20, that Bell has been flying for several years. Though both aircraft first flew as remotely piloted systems, their operation was always augmented with autonomous functionality, including the ability for the aircraft to remain stable and in its current flight mode should the pilot release the controls. Now the APT 70 can take off, transition to horizontal flight, fly to a string of waypoints, return to its starting point, and land entirely on its own.
Getting the drone to convert itself from vertical to horizontal flight and back proved the greatest challenge. “The general autonomous flight features are pretty well understood at this point,” Drennan says. “But during the transition, you have to be careful about power management and speed, and particularly how much altitude you might gain or lose in that process—what we call the conversion corridor.”
The APT 70 has also proven itself competent in a variety of conditions. On Monday, it flew amid 15-knot winds with 19-knot gusts. When the wind is a factor, the aircraft automatically orients itself at liftoff so the wind flows along the length of the wings rather then directly into a broad, flat, sail-like surface, reducing buffeting and drift. It then rotates into the wind for the transition to horizontal flight, enabling more airflow around the wings. It reverses that process for landing. Though it has basic proximity sensors to detect obstacles and determine its distance from the ground, it doesn’t yet carry the see-and-avoid technology that will be required for UAVs to operate in public airspace. That, along with developing commercially-approved backup systems, is next for the program. Bell aims to begin beyond-visual-line-of sight tests next year, on the road to starting commercial service in the early 2020s.
To that end, Bell is working with Japanese logistics provider Yamato to develop a system that will get packages into and out of that pod between the wings. The current prototype has a wheeled cargo container that can be maneuvered by ground crews before being raised into position onto the aircraft itself. “It’s a very human-centric design that makes sure the operators aren’t straining or exposing themselves to injury,” Drennan notes. “It’s also a great separation of responsibility—we handle airworthiness, they handle ground-worthiness.”
As for future cargo variants, the company says the system is scalable well beyond the 70-pound capacity currently flying, and it thus has even bigger things in mind. APT 70 will be followed eventually by the APT 880 that will haul 880 pounds of cargo around the skies, for some truly Texas-sized package delivery.