Multirotor UAV Safety Considerations
There are many considerations to be made when considering an Unmanned Aircraft System (UAS). An evaluation of the company that is producing the UAS would seem prudent, right?!?! Are they viable? How long have they been in business? Do they have a philosophy? These are good questions to consider.
What type of Unmanned Aerial Vehicle (UAV) do you need? Are you into photography? Videography? Photogrammetry? Are you covering large areas? Small areas? Linear stretches? What industry are you serving? Agriculture? Earth moving? Civil design? As-built construction? Land development?
So you think that you have the hardware figured out and you have decided you need a multi-rotor UAV…what about the software? Does your UAS have a process? Has the process been vetted? Will they demo the process for you? Does it include Pre-flight, In-flight and Post-flight reflection?
Support. What about support? Do they have a plan for answering the myriad of questions you may have? 24/7 phone support? Is their software proprietary? How will you learn it? Training? Is it included in the cost of the UAS? Webinars? YouTube?
There are SO many concerns that a conscientious pilot must consider when weighing the purchase of a UAS. But there is an important consideration that is too often overlooked by not only pilots but also UAS providers…SAFETY. What safety considerations are made when building a UAS? What safety considerations should be made when considering the purchase of a UAS?
Does your UAS manufacturer have a philosophy? What did they set out to do when the picked the component pieces of the UAS? Did they want to be the lightest UAS? The most rugged? The cheapest? I would want to see some language in their mission statement that clearly states that they set out to be safe. Recall that the FAA in its definition of what it regulates as a “drone” considers a drones weight limitations as over a ½ lb and less that 55 lbs. 55 POUNDS! You are going to want a 55 lb anything to be under control when it is zipping through the air. Considering a company that logically states its chosen philosophy is to build a safe UAS seems obviously prudent. Being primarily focused on the safety of people and property also serves the secondary function of protecting the aircraft system and ensuring continuing operation. BONUS!
Safety has to start with the frame, the basic structure with which all the motors and sensors and electronic componentry will be fastened. A safety minded manufacturer will pick materials and components that exceed the torsional and moment strength requirements of the calculated flight forces. Composite materials like e-glass, carbon fiber and Kevlar are perfect for UAS, as they have characteristic strength with light weight. Look for aluminum at points of connection, again, a material that has high rigidity and strength along with light weight. Check to see if the UAS manufacturer has documented the stress calculations on the components of the frame and can articulate why they chose which material and component. Did they adhere to their philosophy when choosing materials and components?
When considering safety as it relates to your UAS Electrical system, one word comes to mind…RELIABILITY! My UAS Electrical system has to be realiable if it is going to be safe…and a safety minded UAS manufacturer should be able show that their UAS Electrical system:
- Can handle more that the maximum draw the motors can provide.
- Has connectors that are stronger than required and are secured to prevent accidental or incidental release.
- Has power regulators that exceed the required current.
- Has duplicitous parallel power supply to the core systems, most importantly,the autopilots and the radio control link.
- Has a critical power loop that is separated from any fluctuating current supplies, such as any gimbal or servo motors to remove the risk of any failure to the critical power loop.
- Has a power system that is split into core functions and live motor supply, separated by an electronic switch to provide safety to the system and has a failure mode of this electronic switch that defaults to ON, so that any failure in flight will not affect the operation of the aircraft.
- Has some form of a “remove before flight” pull tag, located on top of the power unit to provide
- maximum safety to the operators any time the aircraft is powered: in the setup phase, during
- operation and post flight.
- Has a fused non-critical power loop system to prevent damage to the critical power loop in
- case of failure of any non-critical component, such as the gimbal.
- Has a power distribution control to the electronic speed controllers (ESCs) supported with a capacitor bank in the main power line to provide consistent voltage to the motors and prevent surges.
- Has capacitors and connectors in the power supply lines that are specified at greater levels than required.
- Has a peer reviewed and tested wiring loom.
- Has a intuitive main battery tray system for easy insertion of the battery, ensuring no chance of wrong insertion, short circuiting or risk of damage to the aircraft power supply system.
- Has selected batteries produced by a reputable battery manufacturer.
Much like the Electrical system, in order for the Propulsion system to be safe it must be reliable. Can your UAS manufacturer communicate to you why they chose all of the component parts of the propulsion system? Were they light? Inexpensive? Were they tested? What is the history of the motors engineering, bearing performance and overall durability? How was the Electronic Speed Control paired with the motor? Does the ESC exceed the throughput of the motor? Does the ESC have a cooling strategy? Is the ESC positioned to eliminate the possibility of electromagnetic interference with the Auto pilot system? Propellers…yes, propellers! An integral part of the propulsion system. Can the UAS manufacturer communicate how their choice of propeller aligns with their safety philosophy? Does the UAS have documentation on the historical performance and durability of the propellers? What is their plan for the care and storage of the propellers? Do they have a pre and post flight condition for propeller inspection?
It is probably better to describe the Autopilot as the Flight Control System (FCS). What has your chosen UAS provider done to ensure safety in their Flight Control System? Once your UAV is in the air, it is the reliability of the FCS that will make certain your UAV stays on course. When considering the reliability of a FCS a UAS manufacturer should be building in some redundancy in how the UAS will collect and consider GPS data. Many of the recorded problems encountered by UAS pilots involve faulty calibration. By inserting redundant FCS measures into a UAS increases the likelihood of a proper calibration. Does the FCS work to help eliminate pilot error? Does the UAS supply operational procedures and training designed to work in coordination with the FCS to eliminate potential flight error?
Inherent in an “unmanned” vehicle is the need to control the UAV remotely. As such, the UAS will have some kind of a Control Station (CS). Because of the distance the UAV will have the ability to travel away from the pilot, the Control Station and the UAV will have a means of communicating. There are many different styles of Control Stations, some as simple as a hobbyist remote control unit all the way to a sophisticated telemetry displaying, data collecting, high end computing tablet. In most instances, the Control Station will communicate with the UAV via some form of radio signal. Whatever the style of the UAS Control Station, from a safety perspective, you want it to have redundancy in its operation and some security in its radio connection. As mentioned in the Electrical section, redundant and over spec’d components help to ensure the constant operation of the Control Station. Secured radio link with the UAV can be achieved a number of ways…frequency hopping systems have been found to be difficult to hack and reliably connectable. If a UAS system is delivering telemetry to the Control Station, this valuable information is also an added safety feature, as it can alert the pilot to unusual or potential dangerous conditions on board the UAV. There should also be fail safes on board the UAV, like auto landing sequences, in the event radio connection is lost.
No one expects the worst case scenario to happen. But if…or when it does, wouldn’t it be a relief if your UAV has one or more failsafe systems? As previously mentioned, some UAS have auto landing failsafe systems. They are designed to automatically abandon the prescribed or programmed flight plan should the Control Station and the UAV lose radio link. In some more sophisticated systems, the pilot is able to identify safe landing zones and program them into the flight plan. Should there be a problem in-flight, the pilot can quickly direct the UAV to the safe landing position. One very simple but effective failsafe that has been introduced is the use of a parachute. UAV’s with parachute capability have telemetry that controls the deployment of the device. If the UAV were to be out of level by a predetermined degree, the operating system on board of the UAV would deploy the chute and shut down all electrical activity. Careful thought and consideration must go into the decision to be involved in the UAV / UAS industry. While this discussion was certainly not comprehensive, it is hoped that it created some possible features to look for in a safely constructed and engineered Unmanned Aircraft System.