Anatomy of a 425km Flight


On the weekend I did a 425km flight with my Vigilant C1.

Setting a new distance record is something I’ve been slowly working towards ever since flying 301km with the Cyclops EPO plane in 2014 

John Smith and Gene Robinson of RP Flight Systems supported me by providing the Vigilant C1 airframe. It has a 3m high aspect wing and loads fuselage space making it ideal for long endurance missions.

In terms of flight testing the biggest performance gain was from tuning the powertrain setup. I tested two options, a 4S battery vs a 6S battery with the stock 300kVa motor. The 6S with stock motor won hands down with a performance difference of around 25%.

I also tested half a dozen different propellers, a couple of APM parameter settings, three different flying patterns and different battery payload capacities.

I tested each parameter by flying repeated circuits of an octagonal test lap and analysing the telemetry log files to work out the power consumption. I could calculate the watts used and the distance covered to work out the best settings. I could extrapolate those figures to see how far I could fly if I used the full battery load.

One dilemma I faced was concerning the flaps. With such an efficient airframe heavily loaded I wanted flaps to control the airspeed and glideslope for landing. But I didn’t want to power the flap servos and carry the weight for the whole flight when I only needed them for 30 seconds at the very start and end of the flight. In testing I gradually reduced the flaps each landing and was relieved that I could land easily with a long low approach. I did however have trouble taking off. I used a bungee that dragged the plane along the ground. Even though I achieve plenty of speed, the fact it was on the ground meant I couldn’t rotate to pitch up. With flaps I had enough lift to take off every time but without them I couldn’t.  It took three attempts without flaps the first time to get airborne and even then it only happened because I hit a bump that bounced me up off the ground. I decided to remove the flap servos and glued the flaps in place and I made a ramp out of some plywood sheets and used that for the first time for the record attempt. 

With the 6S setup I used a HobbyKing power module and the figures it gave in testing seemed too good to be true. I calibrated it against the amount of energy the charger put back in and that showed the power module had been underreporting the current used by about 25%.

I watched the weather and picked the best day I could have hoped for. It was very calm for the first half of the flight with only a light wind later in the day. I flew a large loiter circle (guided mode) with a 600m radius giving almost 2km per lap.

I tracked distance covered vs battery voltage and vs battery percentage remaining and found gave very consistent results that sat just above the 400km projection line all day.


I trusted the voltage reading more than the battery percentage remaining. I knew the Li Ion batteries would be 95% depleted when they reached 3V per cell so I planned to terminate the flight at that point.

All in all it was a big day, 425km of flying taking 7 hours, 48 minutes.

What I’m most excited about is the possibilities this milestone opens up. With an airframe like this the range limitations for tasks such as pipeline monitoring, mapping and search and rescue have just been moved to another dimension altogether.

Setup Details:

  • Plane Vigilant C1 V tail – fibreglass and carbon fibre construction with 3m wingspan.
  • Stock Vigilant C1 motor – 300kVa
  • Pixhawk autopilot
  • Panasonic 18650B Li Ion batteries. 6S 9P = 30600mAh.
  • Aeronaut CAM Power Prop 13x12
  • HobbyKing telemetry module
  • HobbyKing power module
  • Distance covered: 425km (264miles)
  • Flight duration: 7hr 48 min.
  • Average groundspeed 15.3m/s (55km/hr)
  • AUW = 5.7kg (12.5lbs)
  • Goteck DA2311T Servo
  • ZTW 65A Gecko ESC


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  • 300km

    Hi Rogerio

    Is BMS battery management system? No nothing like that. I did see the charge of each cell when charging them and they were very consistent.  The balance plug system was quite fiddly so I would only do a balance charge every other time.

    I don't remember the weight. I think the cells are around 45g each plus the weight of the tabs, leads and heatshrink. 

  • moglos

    Thank you, now it's a little clearer for me. Did you use any BMS system 
    integrated with the battery pack? Besides, could you tell me the final
    weight of this montage?
  • 300km

    Hi Rogerio

    I used Panasonic 18650B Li Ion batteries. 6S 9P = 30600mAh total. I built them myself into 6S packs, it was a very DIY approach. I bought a cheap welder to weld them together, and heatshrink to hold them together. I used some JST leads that I bought from HobbyKing as the connection from each one, and I built a 9 JST to 1 XT60 lead to connect them all together. 

    I made small cuts in the heat shrink so I could insert balance charging leads. I pulled a 6S balance charge extension lead apart and just pushed the pins in between the heatshrink and battery terminals.

    See photo of three of the 6S packs in the fuselage.


  • moglos

    Very interesting his work, although doing a certain time still remains
    differentiated. I was left with one question, the battery pack, did you
    do it? How was their connection? And the resulting weight, could
    you tell me?

    Thanks in advance
  • 300km

    Hi Rob_Lefebvre

    I didn't read, or recognise the significance of the no-load current comment you wrote (on September 14, 2016 at 2:52pm)

    Seems like you were averaging about 4A, while using a power system designed for 65A.  The no-load current of that motor is probably 1-2A by itself.

    Are you saying a much smaller motor could save me 1-2A? Or would a smaller motor still have a significant no-load current. 

    The maximums on take off were 20A x 22v = 440W. They stayed there for 5-10 seconds then dropped to about half for the remainder of the climb. I think I could take off at 15A easily, and probably 10A with a bit of practice/planning.

    Hi Andrew Rabbitt

    I've googled Active Freewheeling and found two ESCs, (ESC32 V3 and Ultra ESC) but they both seem to be kitsets that you need to solder yourself. I could handle that I guess, but it makes me think they are a pretty fringe product. Does anyone know of a ready built one (in the 10-20A range)?

  • Read your previous posts and was excited to read your new record, 
    congrats and thanks for sharing your detailed work. 

  • Supper achievement for battery powered flight !

    Pls post your .tlog and .bin files

  • Sneak preview for you guys.  This is my modelling based on a Skyfun-sized airframe (circa 8:1 L/D, I think) and a nominal motor sized for the prop chosen.  All theoretical and considers motor, propeller and airframe efficiency but not ESC or battery discharge.


    I'll elaborate in my post over the weekend. 

  • 300km

    JB, no I don't, not as such. Do you know how to calculate prop efficiency from the telemetry data?

    Can anyone confirm my understanding of the physics is correct?

    Whole power train energy cost in level flight is simple, power=drag (or I guess, battery power * prop/motor efficiency = power out = drag.)

    But in a climb you'd need to subtract the energy converted into gravitational potential to see if the power spent on overcoming drag has reduced. 

    Gravitational Potential Energy (in Joules) = mass * g *  height. 

    Watts * seconds = Joules

    I have telemetry data from one flight where I tuned the TECS parameters by changing the altitude setting in loiter mode. That will have a climb of 60m, and then level flight, and then a descent of 60m. I'll see what the data says later tonight or on the weekend. 

  • moglos

    Do you have any rough figures on prop efficiency in climb vs cruise I could use to compare? If my above statement is true regarding using gravity as propulsion, then I would have thought that there would have to be a sweet spot between aircraft climb rate aerodynamics and prop efficiency. I will need to do some googling tonight when I have more time.

    on FC: It might be possible to re-purpose geofence to do this without assigning altitudes for WP's and regardless of aircraft orientation. One could set the lower geofence altitude to trigger climb and the higher one to glide. You would probably have to get it to "fly level" if you are doing sharp turns (maybe by using the WP radius) for efficiency reasons, but otherwise it should work. I can ask Tridge to maybe look at it when we meet for the OBC in 10 days. I'm sure he will be interested to help after the comp.

    It seems one of the first challenges to overcome in long range flight is getting the bird airborne (and landing with lots of weight). A quadplane is actually quite useful for this, although it in itself adds extra weight, it also allows for a "unlimited runway in the sky" and very high stall speed/low drag aircraft design, including optimising the whole forward propulsion design only for cruise and not climb/launch as required.

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