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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  • 100KM

    I've read your 301km post yesterday, impressive stuff. Who'd think an electric foamy can stay up that long! Have you thought of solar? There might be gains on your already efficient Cyclops. Math didn't work out for my skywalkers. Definitely not the mugin.

  • 300km

    Congrats Hein. Yes I thought doing a post explaining the details was part of the requirement too. It is definitely encouraged.

    I'm working on another endurance attempt of course, with a new bigger plane. But I just can't find the time to make any progress so nothing to report yet.

    I was impressed by the ETH Zurich 81 hour solar powered flight.


    Don't know why they stopped.

  • 100KM

    Thanks moglos. lol Trung, yea I should. I'm planning on making another blog post, highlighting lessons learned with autolanding, but I don't get much time posting vids and blogs these days. Will make an effort.

  • 100KM

    Hein, you do so by posting a detailed blog about your plane and flight.  (advice designed to satisfy my own curiosity - wink wink)

    Sorry Moglos.  So are you working on a transcontinental flight now?

  • 300km

    Contact Gary Mortimer the admin.


  • 100KM

    Sorry for hijacking this post... but where does one claim one's 100km badge :D ?

  • Arrr. Ok Its hinged at the top. It looks good as it is on the top. You could put a strip of acetate running span-wise along the bottom to cover the gap. Acetate is the clear stuff you use on overhead projectors. (showing my age a little!) Its cheap and lightweight. Its also very flexible. The only problem is finding a way to secure it to the lower surface. It needs to be wide enough to cover the gap when the aileron / elevator is fully deflected up. EPO or what ever the stuff is is very hard to work with. Nothing sticks to it that well. 

    Adding gap  seals might be more trouble than its worth. I might be better to make a new wing the old fashioned way. Balsa ribs and stringers. Have a centre hinge and make the top and bottom surfaces extend to cover the control surface gaps. 

    I mentioned on my previous (blank) post about the possibility of using a small glow engine but that might be against your goals of pushing the limits of lipo endurance? I used a .15cu in glow with a 10oz (i think) tank and that lasted 40 mins. At least with fuel the total weight gets less and less as you fly. 

  • 100KM

    @moglos, Googling aileron gap seal (or similar) turns up a few hits. Some cut strips from acetate or mylar rolls. 0.005" thickness seems to be the most popular. I am not sure where you are located. You may be able to buy sheets intended for edf thrust tubes, or rolls of drafting mylar. You need something stiff enough to retain it's shape, but flexible enough not to resist aileron deflection. If you don't mind the high price, purpose-made rolls are sold here: http://www.icare-rc.com/tape.htm and perhaps at other high performance sailplane stores. I haven't tried this myself, but have some handy from an edf thrust tube so I will give it a go.

    ICARE, accessories, winglets
  • Moderator

    I think trying too squeeze any more aerodynamic advantage out of this platform risks weight and a tiny bit of complexity. Rather design from scratch a more glider type tractor airframe with provision for fat fingers! Yes there will be a 200 I know of at least one attempt. Who will be first!

  • 300km

    This is what I meant in case my description wasn't very clear

    3692937373?profile=originalI've just noticed your handwritten note on your image above about a thin strip of acetate glued to the wing only. I Googled "acetate strip" and found it is used for cakes. Is that what you're talking about?

This reply was deleted.