24 Hours Of Le Airplanes

There’s no more famous road endurance race than the 24 Hours of Le Mans, where teams compete to see how far they can drive in a single 24-hour window. The race presents unique challenges not found in other types of racing. While RC airplanes may not have a similar race, [Daniel] a.k.a. [rctestflight] created a similar challenge for himself by attempting to fly an RC airplane non-stop for as long as he could, and a whole host of interesting situations cropped up before and during flight.

In order for an RC plane to fly for an entire day, it essentially needs to be solar powered. A large amount of strategy goes into a design of this sort. For one, the wing shape needs to be efficient in flight but not reduce the amount of area available for solar panels. For another, the start time of the flight needs to be balanced against the position of the sun in the sky. With these variables more or less fixed, [Daniel] began his flight.

It started off well enough, with the plane in an autonomous “return to home” mode which allowed it to continually circle overhead without direct human control. But after taking a break to fly it in FPV mode, [Daniel] noticed that the voltage on his battery was extremely high. It turned out that the solar charge controller wasn’t operating as expected and was shunting a large amount of solar energy directly into the battery. He landed and immediately removed the “spicy pillow” to avoid any sort of nonlinear event. With a new battery in the plane he began the flight again.

Even after all of that, [Daniel] still had some issues stemming from the aerodynamic nature of this plane specifically. There were some issues with wind, and with the flight controller not recognizing the correct “home” position, but all in all it seems like a fun day of flying a plane. If your idea of “fun” is sitting around and occasionally looking up for eight and a half hours. For more of [Daniel]’s long-term autonomous piloting, be sure to take a look at his solar tugboat as well.

Thanks to [timrb] for the tip!

22 thoughts on “24 Hours Of Le Airplanes

  1. His “solar tugboat” ran on pre-charged batteries with a small solar cell array that wouldn’t have come even close to providing the power levels required to run the propulsion system. It was about as “solar” as putting a small solar cell array on the roof of a Telsa.

    1. That’s a little unfair. Yeah, he had about 720wH of batteries, but also 200W of solar panels on his 8 hour 20 mile kayak tow mission. And, there is a period of hours of the trip where the battery voltage doesn’t drop much or even goes up a little. And that’s a chain of 2 boats. It just doesn’t take that much power to move a small boat at a few mph.

    1. By that argument any serious attempt would be using those extra thin printed cells – they are basically a crisp packet of flexible solar cell tech – so so much lighter, and flexible to the wing form with pretty decent efficiency (while new they are damn close to silicon cells however last I check degradation was still rather high).

      The fact that such tech while existent is likely not going to be easy/affordable to get in the specs you need…

      You design around what you can easily get, and understand, and sometimes it is just a free design choice – in this case a bit of extra weight really isn’t going to be a bad thing to something that is supposed to fly all day – you need some inertia to deal with the changing winds on even a calm day and the potential to fly deliberately with any wing angle you like to the sun – tacking like a sail boat if needed means the higher output potential of crystalline with good orientation is still a very valid choice.

      If you want to make a rival, with presumably unlimited budget and go head to head with a different set of design choices I’d love to see it! But otherwise…

    2. You pop up on every single solar related video and say this. Why don’t you build a plane that does this? Either you’ll discover there are engineering tradeoffs or you’ll discover the next big thing.

  2. Having built and flown FAI record setting pure solar (no battery) model planes, I appreciate and congratulate this effort. I went the long thin wing route fully packed with cells and had a 6 hour flight. It took several winters to converge on my final record setting design.l in about 2001. (Plane name solar solitude) This design is a lot simpler and has a further big advantage over the long wing approach. When you add solar panels to long , high aspect ratio wings, you add mass which lowers the torsion resonant frequency and can lead to wing flutter. I ran into this problem and almost lost my plane. Lower aspect wings like this are not as prone to this problem. To solve wing flutter you need to torsionally stiffen the wing which adds weight. Another problem for high aspect ratio wings is that they are prone to wind shear which has destroyed several commercial day/night flyers.

    After seeing this foamy fly, and have an energy excess, I agree this this is good way to go for hobby use and for FAI record setting. I suggest checking out the FAI sporting code to see what the current requirements are for record attempts and then going after a few records. The Europeans hold solar powered model records last I checked (mainly Wolfgang Schaeper – Germany). You’ll have to join NAA (US aero club to set the US record) and FAI (now part of the Olympic records group) as well as get an official observer (join AMA the US model group). You’ll have to declare your goal ( no random flights allowed) and after you obtain it, write it up. Its a bunch of work but you’ll get a record document like the astronauts do and maybe invited to the annual records ceremony at the Smithsonian.

      1. I solved my wing flutter issue by beefing up the D box structure extending forward from the main spar. I ironed on heat shrink wing covering to the balsa which helped a lot. I also built individual boxes which were glued to the back of the main spar between each rib. These were also covered with heat shrink. The D box and the boxed formed 2 torsionally stiff tubes that worked well to resist wing flutter and didn’t add a lot of weight. Before adding this the flutter led to the d box balsa splitting and I almost lost the plane. In a later wing variant I wrapped the tubular main spar with aluminum to stiffen it and to act as a power return for the solar cells.

        I read your link and wonder if your plane loss could have occurred due to solar power induced oscillation. With the sun to the back of the plane, a climb will induce more power which increases the climb. But the increased angle of attack can’t be maintained so the plane noses down which decreases power output and causing increased nose down. This can lead to wild swings. I almost lost a plane this way when flying it from an ultra light. As I flew, I lost sight of the plane and with hands off control it went into oscillation and a steep dive. When we finally located it again it was headed toward the ground. I pulled out of the dive but the resulting wing bend cracked the cells so I lost power from wings. Fortunately there was enough power from the un damaged fuse and tail cells. To control the plane. I landed the plane while flying above it in the ultralight. This wasn’t as hard as you’d think since I flew it until the plane and it’s shadow met. The solution to this was to add an autopilot that used the horizon in front and behind the plane to maintain a constant angle of attack in the most efficient area of the wing polars. This prevents stall and saved a lot of broken cells. If there’s not enough power to fly the plane gently lands.

  3. Might be worth looking into wings with bell spanloads rather than elliptical. More length for a given lift (= more area = more solar cells), lower mass for a given lift (lighter overall), and proverse yaw and induce tip thrust aids controllability and lowers overall drag (lower motor power needed, wing remains flatter during turns so less self0occlusion of cells).

    1. There are two practical factors that may affect the use of bell or elliptical plan forms for wings. While these plan forms are very efficient they get this efficiency by maximizing lift across the wing. That is the entire wing is lifting uniformly and because of this the entire wing will also stall when stall occurs. When this happens, lift is dramatically lost and the stalling wing will drop leading to dramatic loss of control. A simple maneuver such as a low speed turn during landing could drive the inside wing into stall causing it to drop and lead to a crash A more graceful stall is very helpful so ideally you’d like stall to occur first near the root of the wing and occur last at the tip since the wing is a big lever and loss of lift at the tip applies higher roll torque.

      Rectangle wings stall first at the root and last at the tip so they are a natural, simple choice for making solar wings. However this also means they are not as aerodynamically efficient as other wings.

      Another factor is that solar cells perform at their max potential when they are put in series with other cells that have similar performance. To have similar performance they should be the same size and see the same illumination. This is easiest to do with rectangular wings where rectangular cells, all the same size can be mounted on the wing .

      1. On my rectangular wing I have 3 rows of solar cells, on each wing.
        this fed a 6 channel mppt of my own design. So each of the six cell sets had the same illumination on all the cells. All six mppt ran as a boost converter(s) into a common rail.
        There was also a 24V common cutoff signal, so that if you pulled the throttle back it would not boot to inifinity.

  4. Not solar but MIT built a gasoline powered (5 HP) drone that flew for 5 days. It was intended to function as a communications tower in disaster situations so the design requirements were pretty steep– up to 15,000 feet and capable of withstanding high winds– even if they had an assisted launch. Their GPkit analysis was as interesting as the plane. Sorry, Bman but the article is 5 years old.


    1. If your interested in amazing flights, check out Maynard Hill and specifically his ‘Spirit of Butts farm ‘ record setting planes. https://en.m.wikipedia.org/wiki/The_Spirit_of_Butts%27_Farm
      This plane flew across the Atlantic at a total weight of 11 lbs using about gallon of gas. Maynard was legally blind when he worked on this project. During the winter he would build a few planes and in late summer/fall when conditions were right he and a small team would travel to Canada to launch them. They were GPS guided and satellite tracked. After a few years one finally made it. You can see it and a bunch of other cool and record setting planes at the AMA museum in Muncie Indiana. He was a great guy and inspired my solar flight record setting attempts. Many of his records were set in the 60s.

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