This post is also available in: עברית (Hebrew)
The US Federal Aviation Administration (FAA) currently doesn’t allow small (less than 55 pounds) commercial unmanned aircraft flights over people for fear the craft could injure or kill someone if it fails without a safety net of its own.
There are three paths to commercial drone flights over people, the same avenues the FAA offers for most safety issues that arise. In this case they are: build an unmanned aircraft with provable reliability on-par with a Boeing airliner; build one from light, soft or frangible materials that will break apart or otherwise not harm on impact; or add a risk mitigation system that meets the requirements another way. The entrepreneurs in Indemnis (Latin for “without harm”) have chosen the third way, developing an innovative parachute for getting drones back on the ground safely.
The unpredictability of how the quad-rotor drones would fall meant the lines fixed to the frame of the small crafts would reliably entangle. If the lines made it out as intended then the parachute was likely to snag on the control surface; it was hopeless if the drone was in a spin, which is almost an inevitability of physics. The concept of a rigid parachute evolved into the Nexus small unmanned aircraft recovery system, which uses an inflated fabric deployment tube to move the parachute line attachment point out of harm’s way.
“We looked at that problem and kind of just ran with it. We knew that we had a technology problem that we needed to overcome and we knew that we had a regulatory problem that we needed to overcome and those are really the two things that Indemnis focuses on — making regulated commercial flight over people possible,” said CEO Amber McDonald.
The key to the Nexus is the Dyneema polyethylene fabric the deployment tube is made of. It is a product of DSM Co., a Netherlands-based scientific product development firm. And the key to the Dyneema is its remarkable strength.
“Upon deployment (the Dyneema tube) will inflate, throw that parachute — guard the parachute lines as it rises up — and throw that parachute at 90 miles per hour in 30 milliseconds away from drone and all potential control surfaces or areas of entanglement and it stays inflated, like a piece of steel, to 30 psi, like the same as your car tire,” McDonald described.
Dyneema is more commonly used for large ship anchor lines and medical supplies but it’s most widespread application is for ballistic armor, as it is twice as strong as Kevlar and 15 times stronger than steel.
The biggest challenge the Dyneema presents is its low melting point, which makes bonding it problematic. Ultrasonic and high heat welding will destroy the fibers of the material. The team developed a radio frequency welding process — now patented — that allows the fabric to be joined to itself and form the inflatable tube without sacrificing strength.
The Nexus parachute is also made of Dyneema, but more for its light weight than its remarkable strength; it’s about half the weight of the lightest comparable nylon.
When FAA officials became familiar with the Nexus they asked Indemnis to allow them to use some of the company’s internal testing standards to help write risk mitigation regulation.