We live in a time of great anticipation. There is so much pressure from politicians and industry leaders (and from competing entities like the EU) that it seems like we are now finally on a path where the FAA will make a set of rules and revise Part 108 to make BVLOS and flying over people a reality.
And it might be an understatement that a new Part 108 could revolutionize the drone industry by finally allowing drone operators to scale in a way never seen before. Yet even when the FAA releases a new Part 108 that makes BVLOS practical and scalable, there are components of Part 107 that will still be a big factor in your overall compliance.
Another way of thinking about this is: that even if you are allowed under the new Part 108 to fly BVLOS and/or over people, your drone will still need to be designed so that if it loses power and drops from the sky hitting a person, it doesn’t cause any harm.
Note that for the purposes of this article, we’re going to focus on Category 2 and 3 drones 1.
While there is a bit more to it, there are primarily two things to worry about (1) Kinetic Energy and (2) Lacerations.
Kinetic Energy
Category 2 cannot transfer more than “11 foot-pounds of kinetic energy upon impact from a rigid object” and Category 3 cannot transfer more than “25 foot-pounds of kinetic energy upon impact from a rigid object.”
So what does that mean? Good question. Get ready for some physics.
Kinetic Energy is calculated by multiplying the mass of the drone by its velocity squared and then dividing by 2 or KE = 1/2mV 2.
So you need to know the mass of the drone and its velocity. Well, how do you know its velocity? Another good question. You can try this out on this nifty calculator we found here.
But the regulations at the end of the day aren’t very clear.
Lacerations
Part 107 states that Category 2 and 3 drones cannot “contain any exposed rotating parts that could lacerate human skin upon impact with a human being, and does not contain any safety defects.”
So what is a laceration?
This is a bit more clear than Kinetic Energy. The short answer is that you have to draw blood.
The long answer is: “The FAA distinguishes between a laceration, meaning a cut that goes all the way through the skin and may require emergent medical attention, and an abrasion, meaning a superficial injury to the skin.”
So how do you know your drone complies? This is where the onus is on you as a drone operator. The FAA states: “The declaration of compliance establishes the applicant is declaring it has met the applicable injury severity limitations, the exposed rotating parts prohibition, or a combination of these requirements through an FAA-accepted means of compliance.”
OK, now that we’ve gotten the legal speak out of the way. What can you do about it?
Propeller Guards
Most drone manufacturers sell propeller guards as separate add-ons (and as a rule don’t include them as part of the original purchase).
The problem is that the majority of these are designed to stop horizontal impacts, not vertical ones. There are a few aftermarket companies that sell guards with far more protection, such as the Hextronics Hex Guard USA X1, which features a much more comprehensive design.
Will these be enough to comply? No one knows for sure.
By the way, in case you are wondering if the FAA cares about whether propeller guards will shorten flight time, the answer is: no.
“While the inclusion of propeller guards or full body cages could adversely affect the flight performance of the small unmanned aircraft, the safety benefits provided by the prohibition outweigh the potential loss of performance.”
Emergency Propeller Stopping Mechanisms
Skydio has developed emergency propeller-stopping mechanisms for its drones that may make it completely unnecessary to have propeller guards. Is this enough to comply?
The answer seems to be: maybe.
The FAA has stated, “Under this rule, blade guards or shrouds on exposed rotating parts are not required if applicants can demonstrate, by a means acceptable to the FAA, that unprotected exposed
rotating parts are incapable of lacerating human skin.
Implementing a rotor brake or similar approach to stop the exposed rotating part before it makes contact with a person may be effective. Similarly, folding propellers would be acceptable if the design is shown incapable of causing lacerations in accordance with an FAA-accepted means of compliance.”
Parachutes
Can parachutes solve the Kinetic Energy regulation?
To date, the FAA has yet to state whether or not they can but has provided about 100 waivers over the past few years for flights over people as long as there is a parachute.
So parachutes seem like a very valid approach, because how else could you slow down a large drone enough to meet the regulations? A few companies have some very exciting products in the works that look like they meet that challenge: AVSS and Indemnis.
Integrated Designs
What about drones that are designed from the ground up to incorporate blade protection? We’ve reviewed the Modovolo Lift before (here and here) but we never discussed the safety aspects of the design.
The primary purpose of the ducted rim design plus the spokes is to increase aerodynamic efficiency (a lot like a jet engine) but they serve another purpose.
Just like propeller guards, the rim and spokes could also act as protection from lacerations and the low weight of Lift will likely make complying with the Kinetic Energy regulations more achievable. But we don’t know for sure.
The overall thought here is that we don’t know what will work or not. We only see attempts and possible solutions – and these are incredibly important.
I think you’ll agree that the last thing we need is an accident where someone gets hurt. No one wants that and it will set back getting to more accessible BVLOS regulations.
Footnotes:
The FAA defines Category 2 and 3 drones as follows:
Category 2 eligible small unmanned aircraft must not cause injury to a human being that is equivalent to or greater than the severity of injury caused by a transfer of 11 foot-pounds of kinetic energy upon impact from a rigid object, does not contain any exposed rotating parts that could lacerate human skin upon impact with a human being and does not contain any safety defects. Requires FAA-accepted means of compliance and FAA-accepted declaration of compliance.
Category 3 eligible small unmanned aircraft must not cause injury to a human being that is equivalent to or greater than the severity of injury caused by a transfer of 25 foot-pounds of kinetic energy upon impact from a rigid object, does not contain any exposed rotating parts that could lacerate human skin upon impact with a human being, and does not contain any safety defects. Requires FAA-accepted means of compliance and FAA-accepted declaration of compliance.
