300km

### 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.

• 300km

@ ben, you posted a blank post. Should there have been an attachment? Please post again, whatever you did didn't work.

• 300km

@ben: Aha, I see what you mean, something to stop the air from moving up through the hinge space. My wing is EPO (or whatever foam) and the hinge is just a cutout/narrowing to allow the foam to flex. No air can pass through there.

I was thinking of something to cover the cutout so that wouldn't be a source of turbulence. But if I was going to apply tape as in your drawing it would need to have enough flex that it didn't make the joint rigid. Also I have real trouble with tape. It just doesn't stick to the EPO foam.

I did wonder about a length of silicone fuel tubing to fill the cutout space. It would crush down nicely to allow movement, but I guess it would add a fair amount of resistance (to the servo trying to crush it) when you consider the 60cm length of the aileron.

• Hi,

If you google wing fairings (images) you will see lots of examples of different fairings for different components. Designers go to great lengths in order to reduce drag and increase speed. Some older aircraft have kits you can add to reduce the drag.

Although not applicable to your craft, wheel fairings reduce drag enough to gain 5-10 knots on light aircraft! A blunt object in free-stream airflow will have the same overall drag as an aerodynamic shape up to 10 times its thickness! So you can see the importance of reducing blunt objects on aircraft. Also avoid putting anything on the tops of the wings. I see lots of things like antenna, batteries, even cameras fixed to the critical wing surfaces. Anything on the top of a wing will destroy lift in that cord-wise area and create turbulance (drag.)

A flight control seal is nothing more than a length of flexible material on the hinge line. Paper would work but it needs to be damp proof. As long as you dont have large gaps you will probably be fine.

The biggest way to improve performance is to make the wings and body as smooth as possible. Somebody commented on the golf ball dimples but they serve to create eddies and turbulence and are not conducive to lift production. The golf ball dimples drastically reduce skin friction which is the main form of drag on a ball.

Hope that answered some questions.

• 300km

@ ben I looked (quickly) into filling the aileron space but couldn't find a way to do. Do you know how to do it?

Do you have a picture of an example of the wing/fuse fairings you mentioned.

The Maja already has small downward winglets, they extend maybe 1 inch downward.

• 300km

I've posted a full blog post on the successful flight at

http://diydrones.com/profiles/blogs/anatomy-of-a-126-km-flight

• Nice project!

Try reducing interferance drag between the fuselage and wing by using fairings.  Very little weight gain if you use foam. Aileron, flap, elevator and rudder seals will also reduce drag. It seems like it has a fairly short span vs Cord length. Winglets greatly reduce 'lift induced drag' whilst increase lift.

Aft cg will also increase range.

• 300km

Magic, thanks. Wow doesn't it look good. Is there one for 200km?

• Moderator

Congratulations, welcome to the 100 club!!! Badge awarded ;-)

• Congratulations on your success!

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