3D Robotics

Congrats to the ETH Autonomous Systems Lab for this milestone with a Pixhawk-powered fixed wing drone. Next stop: crossing the Atlantic! From the team:

Two weeks after having demonstrated AtlantikSolar’s first 24-hour flight , the fixed-wing team of ETH Zurich’s Autonomous Systems Lab has reached another milestone: A continuous flight of its 6.8kg AtlantikSolar Unmanned Aerial Vehicle that spanned a total of 2316km and 81.5 hours (4 days and 3 nights) and has broken the flight endurance world record in its class. See the video below for an illustrative overview of that flight test.

More specifically, this fifth test flight of the AtlantikSolar 2 (AS-2) UAV

  • sets a new world record for the longest ever demonstrated continuous flight of all aircrafts below 50kg total mass, and is also the longest-ever continuous flight of a low-altitude long-endurance (LALE) aircraft (the previous record being a 48-hour flight by the 13kg SoLong UAV ).
  • is the second-longest flight ever demonstrated by an Unmanned Aerial Vehicle (behind Airbus Space’s 53kg Zephyr 7)
  • is the third-longest flight ever demonstrated by a solar airplane (behind Airbus Space’s 53kg Zephyr 7 and the 2300kg Solar Impulse 2)
  • is the fifth-longest flight ever demonstrated by any aircraft (both manned and unmanned).

In addition, the flight is a first important milestone to verify the UAV’s ability to stay airborne for multiple days while providing telecommunication services in large-scale disaster-scenarios or live-imagery during industrial sensing and inspection missions.

Flight Summary

The flight was performed at the Rafz, Switzerland, RC-model club airfield from July 14th-17th, of which the first three days provided very good sun conditions. Take-off was performed via hand-launch at 09:32 on July 14th, and after 2316km and 81.5 hours – 4 days and 3 nights – of flight, the aircraft landed safely and with fully charged batteries at 18:56 on July 17th. The fully charged batteries would in theory have enabled to continue the flight through the night again. With the exception of take off, the aircraft was in fully-autonomous operation 98% of the time, and less than 2% in autopilot-assisted mode via its Pixhawkautopilot.

The long-endurance flight provided very helpful insights on flight performance: The average level-flight power consumption in calm conditions (e.g. during night) was shown to lie in between 35-46W. Maximum power input throuh the 88 SunPower E60 cells during the day was around 260W. With this performance data, the aircraft managed to achieve fully-charged batteries (100% SoC) at around 13:05 local time, and thus even before the time of maximum solar radiation (solar noon, occuring around 13:30). After flying through each of the three nights, the aircraft on average reached a minimum state of charge of 35% at around 07:45 local time and thus still shows sufficient energetic safety margins for worse environmental conditions (such as longer nights, cloud cover or winds).

The flight also subjected the aircraft to a wide range of environmental conditions. Among them were thermal updrafts during the first evening/night (causing a remaining state of charge of 40% ), and downdrafts during the second night (remaining state of charge 32%). The last hours of the flight were marked by upcoming thunderstorm clouds and the strongest winds – up to 60 km/h – the aircraft was ever subjected to. Although the ground station was partially damaged by the winds, the airplane could be landed safely in autopilot assisted mode when the winds had calmed down a bit.

Future work

Having demonstrated the multi-day endurance capability of the bare UAV platform, the AtlantikSolar UAV project will now focus on extended endurance flights with payloads including optical and infrared cameras as well as atmospheric sensors. These payloads will also be carried during a long-endurance and long-distance mission of more than 12 hours and 400km that is planned for later this year in the Brazilian rain forest.

Further information

Detailed design and technical information on the UAV platform can be found in “Oettershagen P, Melzer A, Mantel T, Rudin K, Lotz R, Siebenmann D, Leutenegger S, Alexis K, Siegwart R (2015), A Solar-Powered Hand-Launchable UAV for Low-Altitude Multi-Day Continuous Flight. In: IEEE International Conference on Robotics and Automation (ICRA)”

Some more impressions from the flight were broadcasted live through our twitter account


This research was funded through ETH Zurich’s internal resources, private supporters, and the European Union FP7 Search-And-Rescue research projects ICARUS and SHERPA . In addition, multiple project partners and collaborators have contributed towards making this important milestone possible, and we’d like to thank all of them for their various and ongoing support. Finally, we are grateful towards the Rafz model aeroplane club for providing the airfield and the Aero Club Asas da Planície (Portugal) for providing the backup airfield!

Pilots: Rainer Lotz, Adrian Eggenberger, Philipp Oettershagen, Bartosz Wawrzacz. Development and Operations Team (Autonomous Systems Lab): Philipp Oettershagen, Rainer Lotz, Amir Melzer, Thomas Mantel, Bartosz Wawrzacz, Konrad Rudin, Thomas Stastny, Raphael Schranz, Jan Steger, Lukas Wirth, Dieter Siebenmann, Dr. Stefan Leutenegger, Dr. Kostas Alexis, Prof. Dr. Roland Siegwart.


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  • @Patrick:Tom was mostly right: For a low power consumption, the most important thing is that the aircraft flies at its optimal-power airspeed (ca. lowest sinkrate). You can read this paper to learn how we found this airspeed. In addition, autopilot-related aspects that guarantee proper stabilization of the aircraft are also important, i.e. you want an autopilot that properly stabilizes the aircraft roll and pitch (usually at low roll angles!) and you want rather smooth and slow throttle response. Being able to harvest energy from thermal updrafts (either passively by just "floating up" with them or actively by actively searching for them) is also a plus. Some of these things are also described in the pape rabove, and the active thermal tracking is part of the video at http://diydrones.com/profiles/blogs/ackling-the-european-refugee-cr... .

  • Developer

    they loitered for 3 days. So yeah, I imagine determining an optimum airspeed was important

  • So there isn't a prime tuning strategy for power optimization? Did they just find their optimal airspeed (cruise speed) and hold it?

  • Developer

    I don't think the efficiency has anything to do with the flight controller. Maybe a little here and there on motor use but the key to this article is the light aircraft and solar power generation.

  • How did they manage their power consumption so well with the Pixhawk? Any chance we could look at the power optimization code used?

  • Simply stunning! Any detailed information or pictures regarding solar cell mounting technique and mppt properties?  The scientific paper was a great read but I'm craving more info on this amazing project.  Is your power arrangement simply Solar Array>MPPT>3DR Power Module>ESC>Motor with the battery pack also connected to the MPPT?


  • Hi everyone, thanks for all your encouraging comments! It's great to have the DIYDrones/Pixhawk community here, we owe a lot to this!

    Note that to make access to detailed technical information about the plane easier, we have now added a link to the scientific paper to the original post. You can download it directly here. There is tons of information on the solar module & battery system, propulsion, actuation, the actual autopilot that we use (Yes, Pixhawk PX4 with some custom/modified state estimation and controllers) and aircraft performance. This paper also includes info about a 12h-flight that we did last summer (which is when the paper was written, so no info about the current flight is in there yet) Let us know if there are any other questions!

    @Rob_Lefebvre: Concerning your "increase the altitude question": Exactly, usually you will want to increase your altitude once the batteries are fully charged, to then use the potential energy by gliding down (motor ~ off) during the evening and night. This is how many large-scale solar-powered UAVs (mostly High altitude long endurance / HALE) do it, and this is what allows them to save a huge amount of battery mass. On our scale, this also brings some benefits (we use it in simulations), but due to the Line-of-sight constraint we're much more limited: We can't climb more than ~400m AGL. Usually, in the lower atmosphere, thermal up- and downdrafts are so strong that they can easily push you from 100<->400m altitude AGL within minutes, such that "constantly flying at the highest possible altitude to store potential energy" is actually not the most efficient thing to do in that case.

    Thanks again & great to share with you!

    Solar-powered 81-hours flight successful: A new endurance world record!
    Two weeks after having demonstrated AtlantikSolar's first 24-hour flight , the fixed-wing team of ETH Zurich's Autonomous Systems Lab has reached ano…
  • Rob that was gas powered so it would be in a different class. They did state in it's class.

  • Hmmm... I'm not sure how TAM gets off claiming the world record, when somebody else flew a model airplane across the Atlantic in the 90's.

  • Developer


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