Combateer (oz14688)

 

Combateer (oz14688) by Jan Odeyn 1997 - plan thumbnail

About this Plan

Combateer (aka So Watt). Control line combat model, for electric power with Graupner 500 direct drive motor, or similar.

Direct submission to Outerzone.

Update 18/7/2023: Added article, thanks to RFJ.

Quote: "Electric powered control line models, with power through the control lines, or onboard batteries, is not entirely new, but few aeromodellers have attempted this form of aeromodelling. In a world where noise pollution, real or imagined, is becoming increasingly noticed and acted upon, control line modellers have to face up to the same restrictions as other aeromodelling participants. One advantage of control line flying is that it can be operated in small areas which are more likely to be found close to cities, towns and villages; where free flight and R/C modellers would have no chance of flying. But, and it is a very big but, this is only an advantage if there are no complaints from nearby residents.

Control line enthusiasts have not been the fastest to respond to the inevitably noise level limits and one has to admit that the noise to a layman, or laywoman, of a model circulating for minutes on end, often with no silencer fitted, is hardly going to be acceptable. Obviously the noise levels can be reduced by using smaller engines, larger propellers and engine mufflers (silencers) but why not electric power? Is it practical? Will it give a satisfying performance? We know that it is suitable for certain types of scale models but what about aerobatic control line designs, will the power/weight ratio be suitable?

Jan Odeyn, from Belgium, is an experienced and successful control line modeller and he too had thoughts of electrifying control line stunt designs. Rather than sit back and wonder he decided to carry out some tests and the Combateer is the end result of his practical application.

ELECTRIC PIPE DREAMS: After looking through a modelling catalogue (there wasn't anything worth looking at on TV) I noticed the existence of electric motors and , yes, these were also used for planes. The publicity did the job and some days later I found myself at the model shop, buying these electric products. To my surprise all this (Graupner 500, Robbe 7 cells 1700 mAh battery pack and a delta peak charger) was cheaper than one ordinary I.C. stunt engine.

DESIGN: TRIPLE WEIGHT, HALF THE POWER: After weighing everything it looked as though I'd spent my money too fast. With an alarming 350g for the battery and around 200g for the complete engine (mounting, prop and switch) I already had a lot of weight and no aeroplane! However, to make the 550g fly I had to design something. I needed a light plane with a lot of surface and a combat-like flying wing seemed a logical solution. The outline of the new model was already fixed, more difficult was how to keep that heavy battery pack in place in a light structure.

I combined the strength of the wing and the engine bearers, so it found its way into the wing. I put the battery 3cm out of the centre and saved some 30g of tip-weight, the thickness of the airfoil was determined by the space of the engine (36mm) - no complicated calculations needed for this design.

CONSTRUCTION: There is little wood needed, but select light wood for all ribs and wing sheeting. For spars, trailing edge and elevator I selected slightly heavier wood.

You only have to make a template of the tip rib and this one is used to cut all other ribs. I cut 3/32 balsa strips of 36 mm height and of the length required (measured on plan); drew a centre-line and as the spars are on the thickest section of the wing just put a straight intersection to the tip rib. Ribs that are sheeted are made thinner afterwards also use the tip rib template as a guide.

Construction is done with the lower spar on the building board and the trailing edge lifted by aluminium curtain rails of 'I' form, to the correct height. No need to leave spaces!

As much of the building is done this way to be sure to have a straight wing. I connected the upper and lower spars with 1/16in. balsa to make the wing stiffer. During the construction of the battery compartment be sure of a snug fit for the specific pack. Covering is doped tissue paper to make it as stiff as possible. I use the same aluminium supports while the covering is drying and to prevent the wing sticking to the building board I put a extra rail flat underneath the lower spar.

After covering glue the bearers in place, using epoxy but after removing covering on that area. To fix the engine I used a steel collar keeping the holes in the engine free for cooling (and saving 10g). Don't let the halves of the steel collar touch each other. The use of the steel collar is also improving the magnetic field of the engine and the efficiency. Cut cooling holes for the battery in the upper and lower covering on both sides of the engine as shown on the drawing.

All electric wires are 2.5mm and car type connections are used, the switch is from the same source and simply glued in place. Don't forget a fuse of 20Amp.

FLYING: Total flying weight was 710g with an airframe weight of 115g, it's a strange feeling building as light as possible and then putting all that weight into the airframe. The first flight lasted about one minute and proved that some redesign was needed. Trying to loop it there wasn't enough space around (especially downwards) and the plane slid through the grass, but got airborne again. The next loop I met the same problem but by now the engine had broken away and there was damage to the covering and some front ribs. It was too stable due to its forwards balance point.

After the repairs I decided to move the centre of gravity backwards but this took 45g of lead. To keep it the same weight I removed one cell off the pack and to maintain power I put a speed 500 Race, 7.2V and 15Amp motor in front (also a low priced motor).

To make the wing as efficient as possible I added 0.8mm plywood raised tip ribs and balsa ones for the elevator, I feel they are retaining the air on the wing.

The next flight the plane proved capable of big round manoeuvres, even a round wingover is possible, as is the lazy eight. When careful placed a traditional eight is possible. Oh yes, line length is 13m 20cm (43 feet) and the tension is low, but without giving problems. The plane needs about one lap to build up speed and I advise you to keep up the speed. Don't turn too tight or it will start shaking and lose speed (a real stall).

Flying time is around four minutes and then almost all battery power is gone. Power is declining for about 30 seconds, so keep the plane in the air as long as possible to lower the airspeed. Due to the weight it's travelling several meters through short grass before it stops, but until now no damage was done to the propeller or plane. The battery is so low that even the fuse is saved. Immediately switch off the power and do not discharge any further to avoid damage to the cells (by changing polarity).

On the first flights I use a kind of cut-off simply by connecting the elevator and switch. On full down the power would be cut, although it worked it was not too reliable. Before recharging allow the battery to cool down, I keep the battery in the plane but out in the sun.

IMPROVEMENTS: To avoid 45g of lead I will move the engine rearwards, cutting the leading edge. I also noticed that my battery can't furnish the full 15 Amp for the engine and it isn't working on its full potential. The Sanyo NSCRC/SP can do so, but are heavier (350g for 6 cells, 1300mAh).

I had a lot of fun working on this project and even put aside the construction of my urgently required F2B plane. Others will follow and I hope to share my joy with other people. Perhaps it will become a new C/L event."

Supplementary file notes

Article.

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Combateer (oz14688) by Jan Odeyn 1997 - model pic

Datafile:
  • (oz14688)
    Combateer
    by Jan Odeyn
    from Aviation Modeller International
    May 1997 
    31in span
    Electric C/L
    clean :)
    all formers complete :)
    got article :)
  • Submitted: 30/06/2023
    Filesize: 465KB
    Format: • PDFbitmap
    Credit*: theshadow
    Downloads: 284

Combateer (oz14688) by Jan Odeyn 1997 - pic 003.jpg
003.jpg

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