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.

Views: 9609


Moderator
Comment by Gary Mortimer on December 12, 2013 at 6:04am

Brilliant I shall watch with interest and be ready to issue the badge ;-) As to the bobble effect of EPP some say it improves efficiency, golf ball style others disagree. I bet getting the weight down to the lowest possible and flying on a flat calm cold day will help. 


Developer
Comment by davidbuzz on December 12, 2013 at 6:13am

there's no closeup of the tip of the nose, but it looks kinda flat in the first photo...   at the very least make the nose smooth and slick, at best, make it so it comes to a point at the front and the rear..... especially the rear.... , and never exceeds 15degrees from the axis of the plane ( typically breakdown of laminar flow occurs in air at ground level at between 12-15degrees ).       remember what you're doing here is often called in the car world "hyper miling"... eeking effeciency through reduced friction.         Also, get rid of all those rough and/or sharp edges.     that big one undet the bottom where the tail boom starts to taper from the main fuselage is a killer!    think smooth and sleek everywhere, w, and you'll be fine, and try not to add any weight while doing it, actually, that's the next thing to do, remove all the extra stuff you don't 100% need... like the plastic housings around your receiver and autopilot, and I'm sure there's some non-structural foam elements you can cut away...
http://ecomodder.com/forum/2110-post1.html


Moderator
Comment by Gary Mortimer on December 12, 2013 at 6:17am

I was thinking that pitot could go if you were flying on a calm enough day it ought to handle the speed ok. I might make a wire dipole and embed it in the wing rather than anything protruding. Its certainly a challenge with that airframe ;-)

As they say the only thing to add is lightness.


Admin
Comment by Thomas J Coyle III on December 12, 2013 at 6:20am

@moglos,

I have an early version of the Maja and had to make numerous improvements to get it to fly well. The fuse will begin to droop over time so I added some carbon fiber rods to help stiffen it longitudinally. Also it took a .25 brushless motor to get it off the ground and to fly smoothly due to the battery weight required to get any reasonable flying time out of it.

Regards,

TCIII ArduRover2 Developer


Developer
Comment by davidbuzz on December 12, 2013 at 6:23am

yea, gary's right,  ditch the pitot entirely,  the only time a pitot is adding value with an APM is when the aircraft's speed relative is small relative to the wind speed. ( such as lightly loaded floaty aircraft travelling slowly.    you'll be putting substantial battery weight onto the airframe, so the wingloading is "at the upper end of normal", and you're aiming to go substantial actual distance, so "slow flying" is not a target.  :-)


100KM
Comment by Trung Nguyen on December 12, 2013 at 7:03am

@moglos,

Were you manually incrementing airspeed between laps, or did you find an automated method to do so?  I am interested using a similar parametric methodology to optimize my plane for endurance and/or distance.

Comment by Mark on December 12, 2013 at 7:49am

The easiest way is to improve your hardware - get a glider-like airframe. You have chosen one of the most inefficient airframe.

Glider needs the least amount of power to fly while getting the best penetration with clean wing surfaces.

Nothing personal, just trying to post my personal opinion.

Cheers,

Mark

Comment by AKRCGUY on December 12, 2013 at 9:14am

Do you have PID's you can share?

Comment by Christiaan van Vollenstee on December 12, 2013 at 9:17am

I will be following this, there isn't a lot of people that go thru that amount of effort to get the best effiency out of their equipment.


Admin
Comment by Morli on December 12, 2013 at 9:36am

Maglos,

First of all good luck with your attempt with badge. Pls remember 100k.m exceeds the standard regulation in many places ( not trying to pour cold water but I had to say it). I intend to try atleast half the distance when I am ready some day. BTW what RC are you going to use? I assume your are going for lap distance and so the RC range won't be issue.

I agree with Mark regarding choice of airframe.  But most of the gliders are too sleek to accommodate the required hardware decently. I am trying to figure how to put two 5000 batt and keep autopilot  accessible yet maintain the CG of glider( ASK21). I did not get the courage to modify the sleek beauty. So for now the experimentation is on skywalker which had a test walk yesterday after major contact with mother earth few months back.

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