Anatomy of a 100km attempt

I'd like to fly my plane 100km. Partly to earn the cool badge, but mostly to see if I can.

The airframe is a Bormatec Maja airframe which is made from EPP, has a wingspan of 2.2m and an empty weight of 2kg.


I've been tuning it over the last several months to get the best efficiency I can. I've tested dozens of different setups such as props, motors, PID settings, C of G positions etc by flying a circuit in auto mode. By post-analyzing the telemetry data in Excel I can look at the wattage (and speed, pitch etc) for each lap to see what effect the particular setup had on efficiency. I found the AVERAGEIFS function invaluable to pull data from the telemetry csv file and calculate the average values per lap.


The two biggest breakthroughs were finding the best C of G (20% improvement) and best motor and prop combo (50% improvement in several steps, thanks to Reto Buettner and his expertise for helping achieve the last 20%).


Some of the smaller details I've been working on include:

  • Fairings (seen below in front and behind the wing mount).
  • Swapping the protruding telemetry antenna for a smaller monopole one (rfdesign.com.au ).
  • Filling gaps, like the hole left by removing the antenna, the flaps hinge gap, around the aileron servos etc.


To calculate the maximum range I used a formula that calculates how adding weight affects speed, drag and power consumption. The manufacturer says the Maja can carry a payload of 1.5kg which allows me 4 x 5000 mAh (1.6kg of batteries, AUW of 3.6kg). I calculated a maximum range of 85 km if I run the batteries down to 20% reserve. (I don't want to wreck my batteries but the range becomes 102km if I run them down to 10%.)

I've done one round of flight testing with 4 x 5000 mAh on board and the results were slightly better than my calculations. At an airspeed of 13 m/s it consumed 89 W (8.2 A @ 10.9 V). Extrapolating that out gives a maximum range of 89km. Just short of the ton, but still worth a crack.

Both the manufacturer and another experienced Maja pilot expressed concern about making it any heavier, but I'm tempted because my calculation for 5 batteries (AUW 4.0kg) is a range of 103km. My experience with 4 batteries was good so 5 doesn't seem out of the question. I’m still undecided whether I should go for 5 or look for further improvements with 4.

I've got three more small things to try.

  • The EPP surface isn't very smooth so I want to cover the wings (I've got some CP Laminating Film - 1.7 Mil on the way).
  • Doing something about the white plastic rods used to hold the wings on. They're very convenient, but I'll find something that doesn't stick up like that. I'm not sure that I'm brave enough to trim the coroplast trim to the wing.
  • Moving the Pitot tube to the wing so the tubes and brackets don't cause drag.

I think I’ll make an attempt with 4 batteries anyway. I'll happily land with 20% reserve if it looks like my 89km calculation is correct. But if conditions are very good I might get lucky.

Any other suggestions for how to improve the range appreciated.


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  • I also had problems with my first order from Fasttech! I don't order from them anymore. Now i got from ebay fast and cheap :)


  • Moderator

    Eish that's a blow I know folks are working up 5 hour flight times with this battery tech. To my mind 6 hours will become the new 40 minutes within 2 years. (Everyone used to push for 40 minute flight times)

  • Moderator

    Just a heads up with Fasttech.com. The first order I placed for 36 Panasonic NCR 18650b cells was shipped in 48hrs and arrived in 12 days, the second order was ONLY shipped after 20 days and after another 30 days had still not arrived!

    After much correspondence with Fasttech who insisted the parcel had shipped, the tracking number showed up as 'returned to sender', turns out it had never left Hong Kong because of the clamp-down by Hong Kong Post due to restrictions applying to the shipping of Lithium batteries. I filed a PayPal dispute as responses from Fasttech took at least 24-36 hours.

    Eventually a week ago Fasttech admitted they could not ship any Lithium batteries and refunded me my money two months after placing the order!

    So anyone looking to order from them, just check with them before placing an order to avoid the same frustration I had

  • Admin

    John Rambo,

    Nice batts.Price are little high.

    So we can build our own sets. Charging them would be a problem I guess. Thanks for the link.

  • I would definitely replace 5000mAh Lithium batteries with these wonders: http://www.fasttech.com/product/1141100-panasonic-ncr18650b-recharg... to reduce the battery weight by some 20%-30% (buy non-protected ones to go couple % further).
    Depending on 5000mAh battery manufacturer, inside you'll fine cheaper cells, like 2400mAh or 2700mAh.

  • Admin

    I feel skywalker better airframe than maja for looks, edges and space.

  • Maja is just not a nice clean airframe, reminds of a C-130 cargo plane. On the positive side it should have lots of room for batteries. You might even to be able to strap one under each wing next to the fuselage, I've seen this done on EZ stars for long range flight. I think with the right motor/prop it can do it.

  • 100KM

    My X8 broke the 100km barrier with 5x5000mAh 3S batteries on a 900kv motor and 12x8 prop which gave it an AUW of about 4kg.  It flew at about 70km/h average speed.

    My Tlog file is on droneshare : http://www.droneshare.com/view/bi47v7s

  • Moderator

    ...and you can spin that very important big efficient prop.

    There are quite a few 300-400kv multicopter motors around now. T-motor have a few and even Hobbyking has a couple (http://www.hobbyking.com/hobbyking/store/__26963__Turnigy_Multistar...)

  • Moglos, that is correct.
    However the higher voltage reduces current losses in wiring and motor (less heat generated), thus making the overall setup more efficient.
    The challenging part is finding a 6S brushless motor with half the kV (or less) that is the same weight and size as the 3S motor.

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