Living Room Rubber Band planes

23 November 2022

Bearing

tube bearings

pig tail bearings

plastic tubes like used pens, wire passing through the diameter. Hot wire can pass through the plastic.

thin aluminium strips from discarded drinking cans. They are thin, can punch through with thumbtack.

rolled up thin aluminium strips from discarded drinking cans. No need to punch through.

same aluminium but in U channel

thin aluminium strips wrapped around balsa structure, use beads.

washers

can be thin aluminium strips from discarded drinking cans, maybe of any shape not necessarily must be round

Spars

sq/rect balsa

round sticks, wood/bamboo

Blades

balsa

card

plastic

aluminium

28 February 2022

Wobbly propellers? I thought this out over the weekend.

2 balsa spar strips are placed side by side on the cutting mat. A perpendicular line is scored across the 2 strips to give a shallow groove. Flip 1 spar over to the other spar and glue the strips together, with a pin at the scored location. When the pin is removed, there is a pilot hole for drilling out.

Much like sanding a balsa trailing edge, sand the ends of the propeller spar to the angle required for gluing on the propeller blades.

Some variations:

• The 2 spars overlapped throughout. (strongest/heaviest)
• The overlapped joints are kept short. (lightest with the spar offset to one side of the blades)
• The spars may be deeper. (strongest/heaviest/accurate/U-turn hook/rotor if the spars are later sanded to the rotor dihedral)
• Taper the spars. (lighten)
• Propeller blade ontop, middle, or bottom of spar, fixed, folding or hinged.
• The 2 spars may be overlapped at an angle (rotor dihedral). 

I just thought of this:

If the spars are deep enough, cut an angle template with a slot to slip in the spar. The angle presented by the template will give some guidance to the amount of tilt the blades are to be glued on the spar. A variation of a removable template is to make 2 permanent oversized templates, which are glued to the spar and can be sanded down.

Maybe I can do a free-spinning rotor for an auto-gyro if the groove is enlarged and thin aluminum bearing is glued top and bottom of the hub.

24 February 2022

pig tail wire thrust bearing

The front bearing will not be flat and continuous because the wire overlaps itself. Grinding is too much work and the actual bearing surface is the washer/bead. So I think an incomplete loop is enough and a larger tolerance wire bearing is easier to get right at slight efficiency loss.

1. Cross the wire and mandrel perpendicularly and grip both with a pair of plier.
2. Loop the wire once around the mandrel.
3. Remove the mandrel and slide a side cutter along the wire to snip off the overlapping end.
4. Flatten the twisted loop so they are now on a single plane.
5. Grip the flattened loop and bend the wire 45 degrees perpendicular to the axis of the loop.
6. Make another 45 degrees bend so the free end of the wire is now parallel to the flattened loop.
7. Insert mandrel through the loop and cross the wire.
8. Grip juncture with a pair of plier and spiral loop the wire once around the mandrel.
9. Trim the wire to length.

motor hook

If I am using paperclip, the diameter of the wire is large, so I don't think I want to pierce the propeller spar, instead I think I can tie it below the spar. 

1. Form loop
2. Grip loop straighten shaft end, trim hook end
3. Twist loop to line the loop with the shaft
4. Insert 2 beads
5. Bend 90deg 

propeller

1. bamboo spar dowel
2. propeller blades
3. Make jig to assemble propeller

22 February 2022

The most difficult to get right: propeller, mount and shaft.

I have tried the plastic tube from cotton bud for the spar, it didn't twirl true. I must have 'drilled' and glued inaccurately. 

Got a few ideas from the internet:

• 3/8"-1/4" square balsa with saw cut
• Glue 90degrees bend to one half of spar before butt gluing the other half
• Tie 90 degrees to one side of the spar
• pig tail wire thrust bearing
• tube thrust bearing

My ideas:

• Using used gel pen: works like the internet idea for propeller hub, another short length can be drilled so that it can be a propeller hanger for stick fuselage, if holes are oversized, wedges can be used to adjust thrustline
• Prop hub: Tie 90 degrees bend to bottom side of the spar. Or make something like a hook?
• Prop hub: Use aluminum strip from drink can, pierce a hole, bend into a channel, thread the bend through the hole, UHU balsa/bamboo spar over the bend and rub close the channel.
• Prop hanger: Use aluminum strip from drink can, pierce 2 holes, bend one edge to a channel and the other edge at 90 deg, snip away so that it can be UHU glued to motor stick. The rear hole can be snipped, bent open to receive the motor shaft and bend back to secure the motor shaft.
• Use plastic coated paper clip for shaft. They are thinner and came with plastic coating at the hook portion so it will protect the rubber?
• An alternative to forming a hook in the shaft for a winder is to form an intermediary double hooks that hook on to the spar.

Plastic coated paper clip for shaft. They are thinner, more malleable to bend accurately and come with plastic coating that'll protect the rubber from burrs. After the hook end is formed, strip the coating away from the remainder. It might be knocked off-true, but since it is malleable, it is easier to bend straight. It is easier to bend the shaft until it spins true and the propeller also spins true. I suspect it is only usable for small living room rubber band planes where the rubber motor does not pull too hard. So it can be paired with the drink can prop hanger because that is also usable in weak pull.

Just tried the plastic coated paper clip. I used the inner bend as the rubber hook, straighten by hand, tweaked the inner bend to a rubber hook shape, used a side cutter to snip off the bigger bend and the excess at the motor hook, seems that the pull point is inline with the straightened shaft, used a side cutter to bite into the plastic coating against the hook, pulled the plastic off. Tried to straightened further by pulling (didn't work, got a lot of grip marks instead). Rolled on wooden block shows it is not straight, but maybe it is good enough. The exposed wire looks thick, definitely thicker than a clothesmaking pin, close to 1/32". Because my motor hook has a long free end, it is heavier on that end so I think the 90degrees bend can be bent away from the hook leg to balance a bit. I stopped at one, but maybe I should do several to see if they can be improved upon, for example, not using the plier to try to straighten? And I can try them with all the different ideas for hub and hanger.

The double hook is simply a large paper clip, straightened then folded against itself and the ends are then bent to hook with the opening in the direction of winding. 

 

29 November 2021

The aim of this exercise is to use 2 pieces of regular rubber bands looped to form a 6" 2 strands motor. I have not tried it before, but I think that when compared to slipped looped rubber bands, the one slip loop should be lighter than the square and 8 knots commonly used. Besides, if it is meant to inspire people to trying it themselves, the rubber source should be easily available. I will always have conveniently at hand regular rubber bands 'fresh'. 

This link is great!

scraps (indoorfreeflight.com)

Plastic tube from cotton bud. Use for hub? Difficulty is drilling the 2 holes in the 1/2" long, 1/8" plastic tube. How? Take a 1" tube, tape from one end, 1/4" of masking tape around the circumference. Then lay it on flat, tape on bare end, mark 1/2 thickness on both sides of the tube. Use a pin the punch/melt the 2 holes. Remove remnant of tape. Enlarge the 2 holes so a wire from a paper clip can pass through, don't need to be free wheeling if not making a free wheeling hub. Trim the tube so that both ends are at 1/4" away from the holes.

Propeller and tail hooks are from paper clip. Hand winding from the propeller with a fat finger is probably harmful. Make a loop on the propeller hook to allow use of a winder.

Winder: A Z crank with no gearing. Take the largest paper clip and straighten the wire. Make a hook at one end. Insert a full plastic tube. Bend 90degrees, leave a 1" arm and bend another 90degrees so that the remaining wire is parallel to the hook end. A winding stooge is needed.

Winding stooge: maybe a screw eyelet on a wooden block long enough to step on and with a S hook.

Procedure: After winding rubber bands on the stooge, unhook the winder and hook the rubber end on to propeller. Pinch the hub to stop propeller from spinning. Unhook rubber from stooge's S hook and hook onto tail hook.

How to simplify it so that the rubber can be winded by a finger? A longer propeller hub. How long? 2" overall allows 3/4" for the finger and 1/4" for the propeller blade. Seems iffy and will destroy the blade setting or even pull out the blade.

Motor stick:  Seperate motor stick from plane so that Attach motor stick with tape to model? This allows thrustline and even CG to be adjustable. Use bamboo dowel like that of the propeller spars. Use 2 split plastic tube lengths to be intermediary between motor stick and model. Glue the 2 plastic tubes to model plane and 'clip' on motor stick. Motor stick will twist but the tail hook will stop the motor stick from spinning freely. Space the motor stick with a stopper so that the rubber won't bind or slap against the model plane. Or a stopper can be a short length of balsa stick glued to the motor stick.  A thought,  longer or shorter motor sticks can be used, not limited to the length of the fuselage.

Simplify model plane construction. Use hot wire cut thin polystyrene foam sheet for wings and tails and slightly thicker for the fuselage because the compression and torsion from the rubber band is freed from the model plane.