The Flying Black Thing.
AKA The Black Flying Thing.

April 2007 – The Son of Black Rainbow.

I wasn't planning on building another flying machine so soon. I was thinking about making a tube I could cut several propeller shrouds from but I got carried away. Sometimes I just can't help myself. Sometimes an idea grabs you and demands to be given flesh.

Black rainbow started with a shopping trip to buy wax. I still had enough wax (just). This project started with a shopping trip to buy a 26 cm cooking pot. Inside this pot was placed a cut-off plastic bucket full of water and the remaining gap was filled with molten wax. This formed a tube for moulding the propeller shroud.
The battery tube plug was cast in a component box and shaped mainly using a clothes iron (which I only use for wax). Originally I had in mind a smaller tube just big enough for a battery. Not knowing what batteries I might need in future I made it bigger. When I measured the plug I found it was almost wide enough for my camera so two pieces of waxed spruce were pinned to the sides to enlarge it.

This model was intended just to be tough – camera carrying is a bonus.

Vacuum resin infusion is my standard way to make composites these days. To make things interesting I infused the shroud and battery tube in one operation so the bounding between the two is as good as possible. The carbon was laid up dry and held in place with sewing cotton and dressmakers pins. The resin diffusion medium is cheap thin shade cloth. The resin was infused through the port in the lower left of the photo and vacuum applied to the inner part of the wax tube (port visible upper right). The infusion port was pointing up during infusion.
Things did not go smoothly. The plastic bag was too small and didn't conform properly and formed resin paths where I didn't want them. I had to intervene and create ad-hoc infusion ports to save it.

There were also some wrinkles where the carbon was too loose. With care I might have been able to massage them out but I was under time pressure and missed it. I ground these off later and patched them. These photos are after the initial trim. The holes along the inside are where wooden pins held the two wax plugs in alignment during infusion and curing.
The reddish thing is my camera. This has been left showing for the photo – normally it slides completely inside.

Here it is ready for it's test flight. It has been trimmed some more. I expect it will be trimmed more after I get the bugs out. The battery tube has holes added for lightness, ventilation and access. The large hole it for the camera to see out when mounted for side view.
This time I used a larger box-like motor tube. This means I have flat surfaces to attach the fins and I can twist the tube off axis to try to compensate for the motor torque. Here it is tacked in place with CA so I can break the join and reposition it till I'm happy with the angle. Unlike the rainbow, the tube shape also let me run wires around the motor inside the tube so I didn't need to route them through the main fin. The motor tube and main fin were both infused carbon moulded around a wax former. The motor is the dual stator CDROM motor I stole from the rainbow. It is kit built 18 turn delta wound. The blue thing inside the fin is an 18 amp ewatts brushless ESC – quite cheap at $24aus. It is heavier than the phoenix I used previously but a fraction the cost. Power comes from a 1800mah 11.1V LiPo. Deans connectors are used for the battery connection. Foam holds the battery in place and provides crash protection.

The steering is above deck this time. The rainbow's steering works fine but gets in the way when trying to position things to adjust COG. This one uses a bluebird metal geared mini servo with a cyberchute servo arm. The cyberchute servo arm extenders are too short so I made my own. They are made from some clips I found in the tackle section of a cheap shop (crazy clarke), some antenna tubes and golden cable. Golden cable is brass plated steel wire. The cable is passed through the tube – the ends looped back and soldered. Two layers of heat-shrink stiffen the clip attachment.
The radio receiver (RX) is a six channel JR. The width of the RX sets the internal fin width which is just under 15mm. The hole were the RX sits now is large enough for the ESC to be inserted there and manoeuvred into place. I am not using a separate BEC this time.

Up Up and away!
I'd like to report it flew brilliantly but I can't. It has the same problems as the rainbow. The offset motor doesn't seem to help much. The prop is probably too close to the canopy attachment points for it to have much effect. With the plastic chute fitted - it took three or four launches to get it to stay in the air without twisting up the bridle lines and crashing. Once I got it up and cruising it wasn't too bad. The gondola shimmied like both the rainbow and cyber-chute do. I'm pretty sure this is gyroscopic precession problem. A lighter prop should help reduce this.
I thought I was going to it crash into a tree but I didn't. I pulled the power, did a U-turn, restored power at it came back like it was on rails. I landed it at my feet.

I'd also like to report it successfully flew the rainbow kite but again I can't. It did fly a little better than on “the black rainbow” but ultimately the gondola would become unstable the twist the lines.

This aerobatic manoeuvre was unintended.

I'm pretty sure increasing the weigh would help but I'd like the solve this while keeping the weight down and speed low.

Just adding the camera weigh may be enough.

I'm also fairly sure these problems are worse for small, light, high power models with pusher props. These issues don't need to be eliminated – they just need to be reduced to the point where the launch and flight are stable.

The propeller causes several problems. It causes a roll in the opposite direction to the direction in which the prop rotates. It also has gyroscopic effects so when the model wants the pitch nose up the forces cause a sideways twist (ie yaw). The same it true when turning – the nose will want to pitch up or down depending on the direction of the turn.

One obvious answer is the use co-axial props. Unlike co-axial helicopters where both props are driven from below and concentric shafts are needed – a paraplane can use two independently mounted and driven props. This would be relatively easy to do.

I'm not ready to build another one but unless I can get this one working easily a co-axial design might be appear here one day.

I'm experimenting with fixed rudder like fins stay tuned.

Thanks go to Len Martin for taking the action photos for me.

Cheers Eddie.M.

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