Are Drones a Legitimate part of “Aviation”? (A: We’d better treat them that way, for our own good.)

I wrote the following email last month to the host of an aviation podcast I listen to, when he asked for feedback from listeners about whether airshows should have drone sections, which some have started to do. A few weeks later, AOPA, which I joined last year when I started flight training, made news in aviation circles with their decision to invite drone operators to be members. With the status of drones in aviation a hot topic right now, I decided to post the letter I’d written here. I’m relatively new to both worlds, so that’s the perspective that I come to this with: I’m not so entrenched in one or the other as to have a tribe to root for, but I’m not so much an outsider as to have no concept of the issues involved.

IMG_7926

I’m also a systems analyst by training and my habit when it comes to a transitional period like the one we’re in currently is to try to figure out what the core economics imply for final state of the system. In this case, that sure seems to imply an eventual inevitable end of most commercial manned aviation, though it will take to while to happen. Given that future, my concern then becomes what can be done to either postpone the end of manned aviation, or to leave a space for it in the airspace at least for recreational purposes.

Here’s the email.

As preface, I have a foot in both worlds. I have been flying a drone recreationally for about a year now and I earned my FAA commercial drone rating on the second day it was available last year, but I also just did my first solo toward my Private Pilot on Friday. (In a Grumman Cheetah). I’m in my late thirties and in my case, flying the drone rekindled something I had forgotten about and not seriously considered in my earlier youth. Drone flights in the park led to flight simulators, led to a discovery flight.

It will take a while, but it seems inevitable that drones or drone-like things scale up and become manned. The three worlds of little toy and mission-specific drones, autonomous flying vehicles like the ones that Uber and Google are working on, and traditional GA will cross-pollinate and converge and it will become harder and harder to draw lines that cleanly separate this from that. Nobody is going to need a pilot certificate to take a flying Uber and most people don’t need a pilot cert to fly a drone (but even if you do, and I speak from experience, it’s much cheaper and easier to get than Private or even Sport pilot, and I don’t see that changing). So these things do and will have a much lower barrier to entry once they are developed. That means there will be a lot more people using and piloting drones and taking a flying Uber than people getting a traditional GA rating. The difference in scale will just be staggering.

Maybe that means fixed-wing GA goes away eventually, but I hope it doesn’t. There is an opportunity here for the GA community to welcome drone operators and operations, build relationships and participate in extending and updating rules and norms so that everyone can coexist. I think having all three communicating and sharing space and experiences with each other, like at an air show, is going to be important to that. If GA as a community tries to ignore drones as “something else”, I don’t think that’s going to end well for GA, because there will be a lot more of them than us, and the tables could easily turn: we’re concerned about drones in the airspace, but there will come a time when the general public starts to become concerned that these non-automated, human-piloted aircraft are a danger to their safe airborne Uber. I think we’d better do what we can to be a “we” instead of an “us and them” before that happens. We have an opportunity to forge great relationships across the gap here and help create some kind of future for GA, or to ignore the coming changes and let GA become something people used to do.

But don’t even get me started on whether there should be a car show at an air show. Or what a flying car means for that question…

Phantom 4 – Max Motor Speed Reached

You’d never know it from the high of 85deg today, but the leaves have finally started to change for the season here in North Alabama, so I took my Phantom 4 up this afternoon to get a few shots of the Fall colors.

South Hartselle Fall Afternoon

South Hartselle Fall Afternoon

I’ve been getting more comfortable flying the Phantom, so after I got a few shots I decided to go a little higher than I’ve ever gone before. The legal limit is 400ft AGL, but I’ve never been much higher than 200. Starting from about 120ft, I climbed gently for a few seconds, then gave it max throttle to see what she could do. The drone shot straight up into the air, crossing 200ft in seconds. After a few seconds, my flight display showed a warning “Max Motor Speed Reached”, so I let off the throttle and the warning went away quickly…but immediately my heart started to sink, as the video feed from the drone showed that it was falling from the sky.

I could still see it above me (this was a more or less straight up and down flight), and I could hear the motors changing speeds up and down rapidly. I experimentally gave it some throttle and could hear the motors speed up and see the fall slow down on the video feed, so I could tell I still had some control. Over the next several seconds, I continued to feather the throttle, giving it just enough to keep the sink rate slow but not daring to hold constant throttle against the fall. Somewhere above 100ft, it stopped losing altitude and hovered in place. I landed gently and found no damage upon inspection; neither the motors nor the battery were even particularly hot.

A propellor is just a wing that gets its lift from moving fast in a circle instead of fast in a straight line. Just like any other wing, a propellor can stall. When a wing stalls, there isn’t enough lift being developed to keep it in the air anymore. I am not an aeronautical engineer, so my analysis could be wrong here, but I assume a quadcopter can stall because I do know that helicopter blades can stall: see https://www.aopa.org/news-and-media/all-news/2014/may/08/rotorocraft-rookie-helicopter-stalls and https://en.wikipedia.org/wiki/Retreating_blade_stall.

Just as an intellectual exercise, I decided to perform a little investigation. According to Wikipedia, a helicopter blade stall can be caused by any of the following factors:

  • High gross weight
  • High airspeed
  • Low rotor RPM
  • High density altitude
  • Steep or abrupt turns
  • Turbulent ambient air

We can rule out some causes easily. High gross weight: I haven’t added anything to the craft, it is as it came from the factory. Low rotor RPM: according to the warning message, I was in the opposite case. Steep or abrupt turns: I was climbing straight up.

Density altitude had actually been my first thought when I realized the propeller may have stalled. Today was a pretty hot day after all, I figured. It’s not actually the most likely cause, but let’s work it out anyway. Because the air gets thinner as you climb, a wing has to go faster to develop the same lift at higher altitudes than at lower ones. Temperature and pressure affect this too (as in high and low pressure systems, from the weather report), since air expands (gets less dense) as it gets hotter, and a low pressure system literally means less dense air. Density altitude is a formula that tells you how high the aircraft “feels” that it is, taking into account temperature and pressure.

I live pretty close to an airport and have an app that gives weather and altimeter for other nearby airports as well, so I gathered or interpolated the following information, based on the available information for the closest airports:

Altitude: 692ft MSL
Altimeter: 30.14 inHg
Temp: 81deg F
Dewpoint: 50deg F

MSL means “mean sea level”, so the measurement above means that ground level where I am is 692ft above sea level. AGL means “above ground level”, meaning the actual distance above the ground. The numbers above are all approximate, b/c 1. I’m not the NTSB, and 2. the stakes are pretty low here. For instance, I used the reported altitude of the nearby airport even though I was actually launching from higher ground, maybe 20 feet higher.

According to the flight log kept by the DJI app, the highest altitude I reached was 282ft AGL, so that puts me at 692ft + 282ft = 974ft MSL. Plug all those numbers into a density altitude formula and I get 2515ft, so at the point where the drone started falling, it’s as if I was flying at 2515 feet above sea level, though I was actually only 280 feet above the ground.

(I want to point out here, for those who may have missed it, that density altitude is a measure of performance of an aircraft, not an actual height above the ground. My max height above the ground on this flight was 280 feet. Flying a remote aircraft at 2515 feet anywhere, much less near an airport, would have been both dangerous and illegal in my circumstances.)

I couldn’t find any official numbers on this, but I found one reference online that the service ceiling of a Phantom 4 is 19,685 ft. More importantly, I found many people in online forums reporting that they use their Phantom 4 in places like Colorado, at density altitudes around 8000 to 12000 feet. So it should be safe to say that I didn’t exceed the capabilities of the drone flying at a density altitude of 2515.

Wind this afternoon was calm. I was going straight up and down so I should have been in the same air column the whole time. That doesn’t necessarily rule out turbulence, but I think it makes it less probable.

That leaves high airspeed, and that is my best guess: I accelerated so quickly that I reached a vertical climb speed that stalled the propellors. The motors tried to compensate by running all the way up to full speed. Stalled, the craft lost altitude until the combination of the craft’s flight controller and my own feathered inputs got it back under control. That’s my theory at least.

Edit: After a good night’s sleep, one other possible cause occurred to me: altimeter error. Every time you take off, the Phantom 4 counts your current position as altitude zero and displays your altitude then as an offset from that. One thing I failed to mention above is that the log for this flight showed an altimeter reading of -26ft at landing, though it started at zero and I launched and landed from the same spot. I originally chalked that up to the device failing to track altitude change during the time that it was falling, but I didn’t look into a mechanism for how that could happen. I researched it this morning and it turns out that the Phantom 4 uses a barometric pressure altimeter. I did do something just before the flight that may have affected the accuracy of an altimeter: I took the Phantom from inside (about 72deg F) to outside (about 81deg F). Air density decreases as temperature increases, so if the device was just hovering in mid-air, not actually moving, but warmed up to ambient outside air temperature, it may have “thought” it was gaining altitude and tried to compensate.

I’m not sure if that really tells me anything, though. Presumably the unit had done some warming to ambient temperature before it self-calibrated upon being turned on, so I could cherry-pick any intermediate temperature that worked and say that accounts for a 26ft drop. Further, though I was paying more attention to keeping the drone out of free fall than I was the altimeter, I am fairly certain that the actual drop was greater than 26 ft. Regardless, reading the DJI forums, it sounds like the general consensus is that the barometer in a Phantom 4 does experience temperature-driven inaccuracy in its height readout, but the effect is small, and it’s common for the height to drift by several feet during a flight. I still have a feeling that the -26ft landing height is telling me something about what happened to the drone at the apogee of its flight, but I don’t know what.

Hartselle Depot Days at Dawn 2016 – Drone Video

I helped my wife set up a crafts booth to benefit my daughter’s dance class at the yearly Depot Days festival in Hartselle, AL this morning. Just after sunrise I snuck up the hill for a minute to get this video of the vendors starting to set up for the festival day to come.

We also got over to the annual fly-in at Moontown in the afternoon. I have a little video from there too, which will be part of a Moontown-specific video I’m going to do later, but today was mostly a bust there: cloudy and drizzling with a ceiling touching the tops of the surrounding mountains all day, and nobody flew in or out while we were there. Pretty though.

Screen Shot 2016-09-17 at 6.26.14 PM

First Flight as Remote Pilot in Command

I flew my first official drone flight under my new Remote Pilot certificate today, to get some footage for a video.

Hartselle from the Air 2016

I only got my drone, Geary, a few months before the text of FAA Part 107 was released. The rule for hobby flight under Part 107 and for the rules that preceded it is that you must notify any airport within a 5 mile radius of your flight. However, all my flights prior to getting my certificate were no higher than treetop level, so I interpreted that rule to have something like this appended: “unless you’re flying so low that nobody wants to hear from you about your piddly drone flight and the only possible traffic conflict with a manned aircraft is from one that is already in the process of crashing into you.”

Today, I planned on going up to about 100 or 150 feet above ground level (AGL) to get some nice shots of the town, which is above the treetops around here. As a remote pilot certificate holder, that 5-mile notification rule is relaxed for me: I don’t have to notify anybody, so long as I’m not in controlled airspace (meaning, not near a larger airport) and am staying out of airport traffic patterns. I planned to fly at my parent’s house, which is near the middle of town and about 2mi NNW of the local small airport. Though I never saw a plane fly as low as 100ft over that house the entire time I was growing up there, I do occasionally see them pass over at maybe 1000 feet, possibly on their way to join the left downwind for runway 36. Two miles out is too far to be only 150 feet off the ground on landing, and I’d only be up for about 5 minutes, but it only takes moments to cause a problem in the wrong place at the wrong time, and it seemed the neighborly (and safe) thing to do to stop by the FBO at the airport and let them know I’d be flying a drone a few miles north later in the day. There is a phone number for them in the chart supplement, but I live nearby, so I just drove over.

This is a tiny FBO, the kind of place that only has one person on duty at a time, so the lady I talked to at the front desk was also the management on duty and manning the Unicom, and I’m pretty sure I’ve seen her out there mowing the lawn before too. She was very nice and had no objection to my flight, but she also had a deer-in-the-headlights look that told me receiving a notification of an upcoming drone flight was a new experience for her. Though I know there have been other drones operating within 5 miles of that airport (I’ve seen the footage), it is entirely possible that I’m the first person to try to notify them.

One example of how new these rules are, and how airport operators definitely should not be relied upon to know them yet, is that when I told her that I had a handheld radio I could use to monitor for incoming traffic (for those manned aircraft that bother to call their approaches), she suggested that I respond to anyone who calls to let them know there’s a drone up. This is definitely not the FAA policy — they are pretty clear that you’re to monitor, not transmit, if you’re monitoring CTAF on the ground during remote flight operations. She did also offer to warn anybody on approach to watch out for the drone herself, and per my understanding that would be the correct procedure since the FBO is licensed to transmit, while I am not. My plan for the foreseeable future is not to communicate with manned aircraft, but rather to get the heck on the ground if I see a plane coming my way, or hear a transmission that implies one will be soon.

By the way, the flight went off without a hitch and I got some nice panoramic shots of town for my video.