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Commercial Drone Article
- 1. On The Commercial Drone By Terry Drinkard The US, Europe, and other large markets are exploring new regulations to allow the commercial use of drones for small package delivery. Currently, there are no commercial quality package delivery drones in service. There are undoubtedly a dozen different groups working to enter this market. Amazon, I believe, is developing one in house. The potential payoff is huge. Even setting aside Amazon, the US market alone will likely top 100,000 units, globally, the number is likely to grow to millions. Think about it. Walgreens alone has over 8,000 stores. Eight thousand. Every one of which would like to deliver your prescription to your door for a small fee. And you will gladly pay it because you don’t have to get dressed and drive down to the store. It’s a bargain for everyone. The big customers for such an aircraft, aside from Amazon, are UPS, DHL, various other drug store chains, sandwich shops, coffee shops, and even auto parts stores. It’ll be a big deal to those people, but I think the really huge impact will be in home delivery of pizzas. No more waiting for some kid in a rusted-out hoopty to finally deliver your pie. While it isn’t a flying car, it’s something. There are state of the art hobbyist drones currently available for prices up to $3,000. Professional photography drones for the film industry (to replace helicopters for aerial shots) are currently available for approximately $10,000. A commercial quality delivery drone could easily retail in the US for $15,000 or more, depending on a number of variables. Call the average package delivery drone price around $20,000 over the next ten years and say the industry hits the million drone mark at the end of that decade. That’s twenty billion dollars. Billion. With a “B”, like Bill Gates. That’s not counting a lot of fairly obvious add on items like maintenance, spare parts, mission controllers, and not least, drone boxes. The humble cardboard box It seems obvious to me, an airplane designer, that a custom designed box is the way to go. It needs to have enough structural rigidity to be clamped securely to the airframe. It has to be just waterproof enough that it can spend twenty minutes in the rain at thirty knots or so and deliver your prescription without any water damage. The pizza guys, of course, will need their own variation, as will the coffee guys, the taco guys, etc. Whoever gets the box right will win big without ever having to solder a wire or solve an equation for the power required to hover. Design challenges The box isn’t the only challenge, of course. There are a number of what I think are pretty critical issues that have to be resolved effectively before we can declare victory and begin shipping product. The airframe is an obvious place to start. First, I have to say that what I’ve seen in the hobby market makes me despair of the current generation of designers. Fortunately for them, the loads are so tiny that even major mistakes aren’t likely to cause serious problems. However, write this
- 2. down: If you don’t understand how an I-beam works, you can’t design airplanes. That’s a rule in engineering. Much like the one that goes, “If you can’t correctly pronounce ‘nuclear engineer’, you can’t be one.” I support these rules. The current knee-jerk response is to demand a high cost carbon fiber airframe. I’m not convinced that is actually required in this application. Granted, if you were doing rockets, the fuel mass fraction problem is always going to drive you toward saving ounces wherever possible. But, this is a piece of durable commercial machinery. I think an ounce or two of additional weight can be tolerated pretty well. Especially if that ounce or two saves us several thousand dollars per unit in production and gave us a more durability in service. I’d do a trade study on an aluminum airframe. As fun and as normal as those challenges are, they are not what I think is the real core challenge. Nevertheless, I fully intend to write about my impressions of the fun parts first before I have to drill down into the unpleasantness ahead of us. Configurations Package delivery from a drug store or a pizza store to a home or local business or the local park is a VTOL type of mission. I.e., straight up to clear houses and powerlines and straight down to drop off the package at walking speed or less. A fixed wing CTOL drone can’t really do that mission well. I’ve got concerns even about helicopter drones. At this point in the technology development cycle, I’m favoring a multi-copter configuration with six rotors. Let me make the argument. First, a rotor gives us that VTOL capability that we need for the mission. Multiple rotors give us some redundancy if we lose a motor. Obviously, I’m not favoring a single motor with a complex gearbox powering multiple rotors. Or maybe that isn’t obvious. A single motor with a single complex gearbox would make our drone highly susceptible to single point of failure crashes. There is no reason to accept that level of risk if we don’t have to and we don’t. We always want to balance single component failure rates and configuration failures. With a single motor, if we lose the motor, we lose the drone. That’s not acceptable. I prefer a multi- motor design where we lose performanc—but not the entire aircraft—if we lose a single motor. Given what I know at the moment, the best way to do that is not the common quad-copter configuration. A loss of a single motor still loses the entire aircraft. Same same tri-copter and bi- copter. My back of the envelope calculations tell me that a five rotor design is the absolute minimum we can stand, and a six rotor design would be better. The reason may not be obvious. When we are flying a quad-copter (or a multi-copter), for example, we generally have the rotors evenly distributed around the Center of Gravity. The loss of a single engine will require us to shut down (or feather) the opposite engine instantly to avoid flipping the aircraft over because of the asymmetrical lift. Even with the opposite engine shut down, we are now trying to fly a bi- copter which will require twice the lift from its motor/rotor assembly as before. This is a heavy
- 3. performance penalty. To carry that additional capability around all day every day, the drone will have to have significantly bigger rotors and heavier, more powerful engines. Not the best trade ever. Instead, look at a six-rotor configuration. If we lose one motor (or rotor), we can shut down the opposite side and have four motor/rotor assemblies operating at 50% greater performance. We can add an additional 50% capability for a much lower weight penalty than we can add a 100% additional capability. Not a bad trade. I firmly believe that there are some really sweet electronics that can help immensely when the drone requires a reconfiguration of the power and lift distribution. But, I also believe in giving the configuration as much natural help as I can. Engines or motors Let me start out with a categorical statement. The first generation and probably every other generation of commercial package delivery drone is going to be battery powered. We have zero need for supersonic, or even high transonic performance, so jets are out. Nor do we have a need for available power in the tens of horsepower, so reciprocating engines are out. No, we are unlikely to need even as much as a quarter horsepower at this point, which is handily provided by battery powered electric motors. The best motors at this time are rare earth element permanent magnet motors. Probably the brushed motors are slightly more efficient than the brushless ones, but they come with a maintenance burden we would probably want to avoid if we can. This isn’t my field, but I see no reason why we can’t make powerful, highly efficient electric motors with high reliability right here in the Western world. I suspect whoever can solve this little problem will make a lot of money. One key design feature is being able to rapidly and easily swap out motors (mechanical design) and integrate them into the drone system (software design). That is, if we needed to change out a motor for some reason, the new motor’s response in terms of lag and power produced—assuming these are significant parameters—can be automatically compensated for by the flight management system. Since experience in commercial aviation tells me that engine changes are rare, but significant, and since software doesn’t actually weigh anything, I think we should plan for it. Rotors Rotors are an interesting item. Currently, they seem to be mostly a molded thermoplastic item with understandably poor aerodynamic performance. I do see the occasional carbon fiber rotor, but again, I wonder what we are buying with that kind of expense. The key here is high fidelity reproduction of a high performance rotor designed for the Reynolds number and Mach regime in which we expect to operate. I have no idea how much CFD time people have put into their rotors, but that seems like an area ripe for exploitation.
- 4. Let us talk safety for a moment, since that should inform our rotor design. A commercial drone should never crash. However, that’s not the reality of the situation. Eventually, a commercial drone is going to run into someone’s dog or toddler or grandmother sitting on the porch. Guaranteed. Can grandma survive an encounter with a razor sharp carbon blade that might splinter on contact with her skull? Something to think about. How much rotational energy is held in the rotor during normal operations? What can we do to make impact with the rotors less likely (a configuration choice) or more survivable (a rotor design choice). We should give these questions some deliberate thought. The Last Hundred Feet Time for the really ugly questions. How are we doing to monitor this thing? How is it going to navigate? How is it going to see, recognize, and avoid traffic? How will it find your front door? These are non-trivial questions, but there are a couple of fairly obvious answers. Navigation is the pretty straightforward GPS. It’s everywhere, in everything, and globally available. Not a bad start. That said, I’m not certain that GPS has the unlimited availability and can penetrate everywhere we will need to fly. Maybe it does, but I haven’t seen that data. Still, it’s an excellent beginning. On the bad side, there’s nothing in GPS that tells me where your front door is. Can I merge this with Google Maps? Is there a different product that will provide that information to me? Is this product available now? Or does someone need to build it? While I’m navigating to your front door, how do I get my drone to autonomously navigate that last hundred feet? Under the oak tree limb, past the trellis, and onto the front porch, wait, that’s a screen door! Can it be done autonomously? Or will I need to have a drone operator for that critical last hundred feet? And once my drone operator flies it to the front door, can my drone remember that route and repeat as necessary? How will it know if something changed? I think there are things that can be done to make it easier at first. Like setting out a table or mat with a visual target on it that the drone can use. I’d like to be able to buy that mat at Home Depot or order it off Amazon. I think there is room for a good bit of creative work here. With a discrete target set up by the home or business owner, I’m pretty sure we can automate it all the way to the front door and back (except for the minority of folks who screw up placement of the target). While I’m thinking about it, there’s likely some privacy issues surrounding the video stream from the drone and the home owner’s property. No idea what, but it’s probably worth asking the question. Traffic Avoidance Assuming the market grows as I believe it will, we can expect quite a few drones running down Maple Street during the day, delivering prescriptions, novels, and a gasket kit plus a sushi lunch special. There have to be rules of the road and we need some way for other drones to see us and for us to see them. An on board radio beacon of some sort seems a reasonable solution. One with
- 5. very low power so they don’t blanket everything everywhere, but powerful enough to give the oncoming traffic a chance to “see and avoid.” Radio is available during times of darkness and bad weather, unlike visual recognition. Moreover, I’m pretty sure it’s a very well understood technology with low weight requirements, so, cheap and light. I’d really like it if the traffic beacon tells me the orientation and bearing of the other drone. This is another problem for which I don’t really have a rock solid answer, but I have an idea. Anyone remember the old VOR system? Of course, you do! It had a master signal and a “spinner” signal that changed phase with the master signal depending on your orientation to the station. Not that different from a radio altimeter, really. A traffic beacon that worked in the same way would automatically tell each receiving drone their bearing from the transmitting drone. Maybe each drone’s traffic beacon can encode a short burst of useful data such as identification, altitude, and speed. I think that kind of system could be adapted to drones, assuming it can be made small enough. The key is being able to do a quick computation on the range and bearing of the other drone so as to be able to compute an avoiding course. Kind of a mini-TCAS. A lightweight and inexpensive but highly reliable mini-TCAS. It’s sort of like a highly localized ADS-B in that it allows the surrounding traffic to know where everyone else is. The beacon itself gives the receiver an orientation, though I’m not certain it’s sufficient for our needs. The Cellular Data System Getting data from the drone to the mission control box and back, telemetry, is going to be a challenge. We need to be able to communicate back and forth with the drone pretty close to real time, if we have to pilot it the last hundred feet, and in any case, we will want to know the status of the drone at all times, particularly if there has been an accident or crash of some kind. Moreover, the traditional aviation reporting systems are tied directly to radar coverage, and we aren’t going to have any radar coverage on Maple Street. Given the number of drones I expect to be operating here in the US, to say nothing of the rest of the world, it’s clear to me that the traditional aviation reporting infrastructure is gloriously inadequate. The only infrastructure on the planet (or in low earth orbit, for that matter) that can handle the level of usage I foresee is the cellular data network. This is completely outside of my understanding, but I rather imagine that each drone would have to assigned some kind of MAC address possibly even a phone number, which may seriously impact system at some point. That said, I see no serious alternative to utilizing the best available infrastructure for the next ten years or so. Impersonal Historical Forces Or economic forces.
- 6. It seems clear to me that the time is ripe for an explosion in the number of drones working our skies. We have huge economic pressure on companies to innovate and reduce costs while providing additional value to us, the customers. The drone technology is close to the point where they can be put safely in the air to drop off my copy of the most recent William Gibson novel without killing anyone. I don’t think there is any way that opposition to the drone movement can stop it or even seriously slow it down. The only questions remaining ask how we are going to do it, not if.
- 7. It seems clear to me that the time is ripe for an explosion in the number of drones working our skies. We have huge economic pressure on companies to innovate and reduce costs while providing additional value to us, the customers. The drone technology is close to the point where they can be put safely in the air to drop off my copy of the most recent William Gibson novel without killing anyone. I don’t think there is any way that opposition to the drone movement can stop it or even seriously slow it down. The only questions remaining ask how we are going to do it, not if.