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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  • Will be interesting to know why you went for the Panasonic cells instead of the GEB batteries.

  • Giovanni, I don't suspect the servos will actually benefit that much.  If it was pure manual control it might.  But since this is a gyro controlled machine, the hysteresis of the Analog servos will result in them actuating back and forth constantly, so they'll be burning power anyway.

  • Awesome ramp takeoff.
  • I second what Rob said! Have you tested another esc to compare data? Probably a much lighter Esc32 (for example) will do so much better in terms of efficiency (it's also a lot more tuneable) and save a lot of weight. Motor and prop too don't look like very optimised for this type of task, as Rob suggest, you will do better with a smaller prop, that will also produce less drag.

    Also the digital servos you are using are very power hungry, because the idle current is for sure much more than an equivalent analog one. And again you will save some ma and some weight using simple plastic analog servos.

  • Curious if you did actual power system performance testing? Did you compare, for example, a HobbyWing Platinum Pro ESC to the ZTW?  If now, you should.  In independent testing, the typically are head and shoulders above others in efficiency.

    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.

    If attempting to set records, I'd used a very marginal propulsion system, augmented with a high power system for launch, that is jettisoned at altitude.

  • I answer to myself on flying in circle. from the picture of your flying site I see that the radius is about 600m, which means that at that speed it is about 2N centrifugal force. the average banking is then 2 degree which result in a difference in lift needed of 0.5% so also around 0.5% increase in drag. most likely neglictable...congrats again!

  • impressive, congratulations!! I wonder if you have compared flying in circle with a rectangular path. in theory flying in circle is a little bit less efficient as to generate the lift to offset the weight you have to either fly faster or with a higher lift coefficient, which in both cases increases the drag hence the energy needed to fly. now may be the radius is so large that it is difficult to see the difference...

  • That's really impressive, well done!

  • Really incredible, if somebody would have told me I would not believe it.....

  • MR60

    Wow, just Wow !

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