Today’s question from a reader is “Do drones work better without propeller protectors?”
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That’s a Loaded Question
There are two issues we have to deal with regarding propellers. One is safety and the other is performance.
On one hand, it really doesn’t matter if a drone propeller operates better, worse, or the same with protectors. Propellers can cause serious injury. As one pilot learned the hard way they can cut to the bone, including nerves.
To comply with the new rules regarding flight over people, drones will require protections for all moving parts. This can be accomplished with propeller guards or full-body cages.
There is one loophole and that is “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 in protecting from lacerations, but this requires the applicant to demonstrate their effectiveness in all likely small unmanned aircraft failure scenarios. Similarly, folding propellers would be acceptable if the design is shown incapable of causing lacerations in accordance with an FAA accepted means of compliance.”
According to the new rules:
Category 1 eligible small unmanned aircraft must weigh less than 0.55, including everything on board or otherwise attached, and contain no exposed rotating parts that would lacerate human skin. No FAA-accepted Means of Compliance (MOC) or Declaration of Compliance (DOC) required.
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. – Source
Unless your drone falls into one of the above categories it would have to have earned an Airworthiness Certificate issued under Part 21 of FAA regulations. Safety is a consideration of earning an Airworthiness Certification.
Fitting any propeller guard to a drone that has not been approved by the FAA leaves you with uncertainty if it impacts performance. It can harm performance if it is not properly engineered.
As part of the Final Rule for Flight Over People the following comment was made, “Commenters were also concerned about installing shrouds that would guard propellers. An individual wrote that propeller guards and full body cages can “adversely affect flight characteristics” and that propeller guards could increase the likelihood of loss of control for some quadcopters. In addition, DJI said shrouding an entire rotating part, if that part is involved in propulsion, can affect the aerodynamics and performance of the aircraft.”
I was part of an engineering project that designed public safety drones from scratch. Surprisingly, some of the teams designed a propeller guard that not only met the safety standards but actually demonstrably increased lift.
If a compliant propeller guard will or won’t increase lift will come down to competent engineering and testing by the manufacturer of the guard. You would need to request that data from the propeller guard manufacturer. If they claim it does without providing data on the performance I would take those claims as advertising puffery.
Pilot Final Authority
As the drone Pilot In Command (PIC) the final authority and compliance to the regulations must be verified by the pilot. You will need to determine and feel confident any propeller guards you may fit on the aircraft will meet the regulations and not harm performance in an unsatisfactory way.