3 cylinder model

17 October 2022

Over the weekend, I played around with the model and did this:

Mounting the Electric Motor (not the capacitor yet)

1. Cut one tooth pick into 2, about 2/3 long and 1/3 long
2. Glue the 2 pieces at opposing sides of the electric motor. I choose to have the wiring away from either picks.
3. Tape the picks and motor together.
4. Poke into the nose of the fuselage.

I didn't cut the reinforcing hard card base for the 2 picks. I think the base of the electric motor will not enter into the soft nose and also since it is 2 picks the lateral load should spread sufficiently.

The Engine

With the electric motor in-placed at what seems to be right, I proceed with the engine modelling:

1. Hot wire cut 3 pieces from drinking straw. I made a cube jig for this, the result is straightish but not really square, good enough.
2. Cover the tubes with silver tissue: 
1. Cap tissue: tissue over one end, gum it to the sides.
2. Cylinder tissue: tissue around sides, capturing the cap tissue ends.
3. Fin tissue: Draw black parallel lines, cut 3 strips, roll around the cap end.
3. Cylinder base:
1. Cut 3 strips
2. Cover with tissue on one side
4.  Assemble cylinder to base:
1. Glue 2 cylinders to one end
2. Glue last cylinder to middle
5. Glue the base onto the electric motor.

The Capacitor

This was left to the last because it can help to trim the model. I only did the casing for the capacitor to slide in. It is a section of a very large diameter straw with the piercing end, cut with hot wire cutter using the cube jig. The piercing/sloping end allows the slightly protrucing capacitor charging jack to rest and not to twist around. This tube was covered with silver tissue. The intention is to mount the tube like an underslung canister at the nose of the fuselage. It is not a scale feature but it is a fake feature and is convenient and easy. I don't have to cut slots in the fuselage for the capacitor. With the canister mounted, perhaps by a wire hook or just glued to the underside of the fuselage, the capacitor can be inserted or withdrawn, thus allowing the trimming of the CG.

Choice of having the capacitor below the fuselage is for pendulum effect and also thrustline.

Thrustline above CG will have a down thrust moment, thereby less angular thrustline will be required. The centre of drag should be nearer to the wing as that is the largest drag producer. Who knows, maybe the blocky undercarriage may also bring the drag centre closer to the thrustline and that would be ideal.

12 October 2022

Variation of yesterday's idea.

The engine will be the point of interest. Every pair of eyes will be drawn to it when they look for details. A bit more detail is needed.

Each cylinder is not a single cylinder but 2 cylinders, I can fit a bigger straw over a smaller straw. Or if I can't find 2 appropriately sized straws, split one to fit over the unsplit straw or maybe I should just wrap some paper/tissue on one end of the straw so that outwardly, it appears to be of 2 diameters. 

1. cut three identical length straw
2. cover with black tissue
3. strip of silver tissue with parallel black lines
4. wrap with strip of paper to bulk up
5. wrap with striped silver tissue over the paper rolled open end
6. roll the pre-striped tissue over the paper tube end, covering the tissue tabs of step 5 if any.  

The task now is to think how to make a mount that incorporates 3 tongues at the right positions (to glue on the above made cylinders), allowing electric motor to be centrally located fit and generally look like a crankcase. For durability, I want it to be made from flexible "EVA" foam.

3 prongs (120 degrees apart), hexagon (crankcase), rectangular (fuselage nose), motor pass through or insert through...

Ah ha! 

The electric motor with its two toothpick legs is to be inserted to the nose of the fuselage. As the fuselage is only white styrofoam, it would simply tear on each crash. I need to strengthen it.

The nose presented is a small rectangle. An idea is to cut a piece of rectangle from thick card and have  2 holes drilled/punched through to prevent the 2 picks from tearing away. This card has sufficient area as it covers the entire nose and does not interfere with the re-inserting of the picks (for down and side thrust adjustments).

The engine can basically be a piece of flat EVA foam with 3 tongues to which the 3 straw cylinders are attached. The foam piece is slotted at the bottom to clear the electric motor. This 3 cylinder engine is glued to a strip of EVA foam which is in turn glued to the hard card base. This strip need not be fashioned, it could be a 'U' shaped piece as its purpose is only to hold the engine to the nose. Yes, the crankcase is missing, but it's only a little bit. But if the visual bothers me too much, I can add thin card to slot over the EVA tongues before putting in the cylinders. The thin card is to cover the 5 sides out of the hexagon shaped crankcase.

Slightly more work is to cut and fold to make a hexagonal front cover, leaving the bottom and rear uncovered. The bottom is missing to clear the electric motor and the rear is missing to glue on the EVA mounting support.

1. Card nose
2. Insert electric motor, solder and mount capacitor
3. Test flight
4. Adjust CG and thrustline
5. no need to remove propeller and I can glue the engine and crankcase unit.

Oh!

Why bother with 3 tongued EVA piece? Just make the card crankcase and have enough gluing area to the base of each cylinder! No slots, no EVA piece and the cylinders can be glued staggered slightly! Just make the engine mouting EVA strip longer to support on the inside of the crankcase.

Hmmm...

Toothpick bound to the electric motor would be light and strong, but wooden toothpick is not bendable. How about something that can bend so that the thrustline can be adjusted?

Bind two wires (paper clip) to the electric motor? Or cut from stainless steel wire?

Another thought is matching the engine to the electric motor. The crank case would not fit snugly to the nose and the rear end of the electric motor would be offsetted from the centre of the fuselage.

Something to think about.

So, I will have to think how the engine can be glued to the nose (not the electric motor). Previous thought was a single looped strip glued to the rear of the crankcase cover, maybe I have to think how it can be glued to the rear of the engine (on the crankcase). The difficulty is how to fit foam mount to a hexagonal crankcase. Small short strips? Maybe inside of the top side of the hexagon behind the top cylinder and 2 stubs behind the lower 2 cylinders?

Oh! What if I glue a hexagon piece of EVA foam to the thick card motor mount? Then it is possible to locate the crankcase like a cap over this hexagon piece. 5 short straight strips can be glued to the hexagon piece to provide adjusting area as well as gluing area to the engine. 2 or 3 degrees off should not affect the fit since it is cardboard crankcase over EVA foam anyway.

11 October 2022

OK, I tried for an RC model but it was quite a lot of work for an untidy piece that I can not be proud of and I left it at that last year.

Now, for a 15" wingspan capacitor powered model, I think I will simplify a bit more so that it looks neater. The purpose is only to have something that suggests a motor from at least 2 metres away, and to consider that at the nose end, there will be knocks and bumps. Hey! My pilot is just an outline anyway.

At first I thought about doing up a single mould to make the cylinders by shrinking plastic tube. Then I drop this idea because any fins I put in the mould would unlikely be visible, much, since the shrinking will bridge over gaps and I am not going to try vacuum moulding. Paper tubes will look like paper tubes, so idea is dropped as well. Winding around with 3D pen was dropped because my experience was negative.

After much simplifying:

• mount is flexible foam to tack glue on fuselage's nose
• each base cylinder is strip of flexible foam with a slot to receive the cylinder top
• each cylinder top is just a piece of card paper glued at ninety degrees to the base cylinder

Frontal view is just 3 narrow rectangular strips equally spaced around, less disruption to the head-on airflow. Side and plan view will show some idea of cylinder tops. It should look the part from many angles when viewed 2 metres away, squint if necessary. 

1. Cut a card/paper strip and silver tissue both sides and draw in parallel black lines over the tissued sides. Cut 3 pieces for the 3 cylinder tops.
2. Cut 3 strips which has a slit/slot to receive cylinder top. If I don't want to cut a slit/slot, I could also leave it as that and glue the cylinder tops to its edge.
3. Cut a rectangular strip for the mount. Hot bend or glue strips to two opposing edge (for mounting to fuselage's nose). Hollow out for pass through or fit over of electric motor.
4. Assemble by gluing the 3 strips on the mounting piece, glue the cylinder tops to the 3 strips. 

After a while, I searched for Anzani engines and found photographs of actual engines. The cylinders is fairly uniform, the fins protruded only a bit. They were either black or silver. So instead of doing flat strips like steps 1 and 2 above, to improve the look, I revert to drinking straws:

• Draw parallel lines with black marker on silver tissue
• Cut a rectangular strip, the lined portion represents the fins, yes it is reversed, i.e. not silver lines on black tissue, but black oil based markers are cheaper and easily available.
• Glue tissue strip around a drinking straw and cut to length, repeat 3 times for 3 cylinders.
• Insert and glue the straw tubes to the 3 prongs of the flexible rectangular strips, with the strips at the back end of the straw for step 4.

8 June 2021

It depends what skill, tools, material and what size and weight of the model. In case of a peanut scale, my hexagonal crankcase is about 12mm OD and 10mm deep, and each cylinder is about 6mm OD and 10mm long.

The actual steps taken for the peanut model were:

1. Cut a strip of paper with tabs all-round, bend and glue together. Immediately place inside a circle template to adjust the hexagon shape.
2. Mark and cut from transparent drinking straw 10mm long segments with two slots, something like a 'E'. Two rings are next to each other on one end to simulate the finned cylinder, the last ring is at the other end and is the base of the entire cylinder to allow gluing.
3. Glue the cylinders to the hexagon.

Tips:

• Use circle template to hold the hexagon shape until the glue dries.
• Flatten the drinking straw to mark out the fins and base of the cylinder.
• Use scissors to cut the drinking straw to "E" shape.
• Open up the 3 loops and pass a small dowel through the 3 loops and finger roll to round the straw.
• Glue with UHU All-Purpose or POR, the near translucent cylinders and paper hexagon.

28 May 2021

To make something like the Anzani 3 cylinders in Y configuration for small aircraft models using bendy drinking straws in a fast and easy manner:

1. Crankcase is 6 sided. Cut strip of paper from photo-copy paper, mark 6 segments, crease on the lines, glue together and loop the strip around so that it is at least 2 ply thick to get a open ended hexagon. No need to make back or front to close because the motor will be there anyway and it is a very small engine model.
2. Glue small foam squares to 3 sides. Offset the squares so that when the assembled cylinders are glued on, the cylinders will also be offset in fore-mid-aft positions.
3. Extend the bendy portion of the drinking straw. Cut 3 equal length sections. Slit lengthwise if the bendy portion can not fit over the straight drinking straw.
4. Cut 3 lengths of the straight sections of the drinking straw. Slip the bending portions through one end, this allow 'exact' length of cylinders to be adjusted.
5. Glue the 3 cylinders to the foam squares on the hexagon crankcase.
6. Spray black, rub-in or dry-brush silver highlights.

Self-stabilised cylinders in case of crash?

1. As before.
2. Skip this step.
3. As before.
4. Where the cylinder shall meet the crankcase, leave a short 'tongue'.
5. Poke a slit through the crankcase to receive the tongues. When the tongues are at the rear, the cylinders can snap back and recover should they be knocked rearwards.
6.  As before.