Join us a gain for another theory piece on drone flight. Today we’re full of hot air. Wait, that’s not it. Today we want to talk about air, hot and cold, as we discuss air density and your drone flight. More than anything, we’ll be talking altitude and temperatures.
Once again, this is mostly theoretical. The average high school senior in a physics class can probably school me, and I welcome them to do so in the comments below.
Science of Flight series
For more interesting tidbits on the science of flight, we invite you to check out our other articles on the topic. We’ve discussed propellers, rules, air speeds and more. See them all at the link below:
There is a good chance that you completely ignore air density when fly your drone. For the most part, that’s just fine, no harm done. What you may or may have not noticed is changes to flight performance and battery life as you fly in differing temperatures and altitudes.
Without diving into each and every factor that can change air density, we’ll focus on just temperature and altitude today.
Did you notice that your drone has a rated service ceiling? For example, the DJI Mavic Pro and new DJI Mavic Air are rated for 16,404 feet. This rating is based almost entirely on the drone’s ability to handle air density. Let me explain a little.
If you are flying for pay, or any other form of compensation, you must operate under a different set of rules and possess a commercial drone license. We call it the Part 107, it’s not too hard to get, but it will take some time to learn all the rules. We want to help you learn the rules and get your commercial license, check out our drone pilot training material.
You are likely aware of how air is more dense at sea level than it is up in the clouds. Things that fly rely on moving wings through the air, and the thicker the air, the easier it is to create lift. In simplicity, the thicker the air is, the less battery you need to consume to fly.
Also, as you turn, there is more air resistance to affect the change. That is, your drone will be more agile in thicker air. I am being quite vague on how this actually works, please read our coverage of propellers for some additional insight.
Bottom line, your drone has to work harder and harder the higher it flies. At least this is true of how fast it has to spin those propellers, there are other factors to altitude that both ease the strain and make things difficult – we’ll save that all for another day.
Your drone’s rated service ceiling is not how high you can get it off of the ground. First, the ceiling is based on sea level.
Second, and more important, proximity to ground has an affect on air density as well – mostly because of heat and wind deflecting up from the ground. If you plan to fly at the full 16,404 feet above sea level, you will likely have to launch from (at least 16,004 feet in the United States, that’s the law,) at least 12,000 feet realistically to get there. Hope you like hiking.
We can keep this one short. Take all you learned above about air density and your drone, now consider that cold air is thicker than hot air.
As you head out to soar around in the wonderful winter air, please take note of your manufacturer’s specifications for your drone. Most machines are not rated to fly in freezing temperatures.
A word of warning:
I can tell you from experience that the theory of longer battery life in cold weather needs further research to prove. Our point today is that your propellers will be at their most efficient in cold weather, which is great, but if your battery drains extra fast, frosts or even freezes, catastrophe. Please don’t push your luck.
Real world usage
There are many factors that make flight possible. As we continue to break down flight into the individual parts, I urge you to remember that they are just that, parts.
I wish I had taken more strict documentation of my flights to give you a better indication of real world results. I have flown at sea level in the heat and cold, I’ve flown in the mountains in both heat and cold, and I’ve flown several places in between. My maximum take-off elevation was approx 7,000 feet above sea level and my normal flights are at about 1,000 feet. The result: nearly identical battery life every time!
That’s right, with a few exceptions (flying in freezing temperatures and at over 112F,) my battery life on the DJI Mavic Pro has been consistent. My flights have all varied in strain on the craft, but the advantages and disadvantages of the situations all but balance out.
This article was written more for those of you pursuing the FAA Part 107 certificate. I had a number of questions on my test relating to air density as affected by temperature and altitude. Remember that cold air and low altitude are your friend, in terms of wing performance, and you should ace that part of the test.
We imagine that you can safely continue to ignore air density as you fly your craft. If you happen to do some of your own research, fly the same path in different temperatures, for example, please do share your results in the comments below.