Fan Wheel

20 December 2024

I thought I could make a 1" wheel just by folding and gluing a strip of paper, so I did an experiment. The strip was cut from a grided piece of paper, each grid is 4mm. So I thought perhaps 18 folds is sufficient and proceeded to do just that. I chose 12mm as the radius. Here's the result. 

As you can see, the number of folds (19) is insufficient, next time work out the circumference and add some buffer, especially when the strip of paper has to be glued by 1 fold and this fold has to be the correct direction. I guess 21 folds is needed and so if a tube is to be glued to be the wheel hub, may 23, 25 or 27, i.e. some odd number.

Yes it is light, no it is not ideal. It is not 'realistic' and I don't know about its functionality. 

6"x3/16"X1/16" Motor Stick

17 December 2024

It appears that a 6"x3/16"x1/16" motor stick is sufficiently sturdy for a single loop of 160mm x 1/16" rubber band. This motor stick could also serve as a spine for a small model plane's fuselage. Here's the steps involved:

1. Make the motor stick, install the nose bearing, tail hook, propeller shaft, propeller and rubber band.
2. Cut from polystyrene 2 pieces of the profile of the fuselage.
3. Lay the profile flat on the table and mark where the motor stick and rubber channel will be inside the profile.
4. Hot wire cut the channel in both profiles and bring them together, sandwiching the motor stick.
5. Cut and sand the polystyrene to the cross sections.
6. Cover with tissue, paint and the fuselage is done.  

For short nosed planes, for example the rotary engined biplanes in WW1, the nose moment is too short and requires much nose weight, which makes it difficult to fly as a free flight rubber powered model airplane. Let the motor stick protrude out of the stub-nosed model. Yes, it is un-scale like, but it is a trade off to lessen the nose weight. 

Further simplification can often make model planes easier and be great for their flying ability, example, making it a NoCal or making it Slab-Sided. Either set out the motor stick in the case of a NoCal, or set in the motor stick in the case of Slab-Sided. NoCal design is often used to maximise flying, but it is more work than SlabSided which also has the advantage of being aesthetically slightly better.

1. As before, make the motor stick etc, the rubber power unit.
2. Draw on a 1cm thick polystyrene sheet, the profile of the fuselage.
3. Strengthen those areas where necessary. You can make anchor points for undercarriage, hard points for wings/tails, dihedral braces etc.
4. Round off the polystyrene profile, on the starboard side, slit the thrustline, insert and glue the motor stick of the rubber power unit, only the rubber band and bearings are exposed to the starboard side.
5. Cover with tissue, paint and the fuselage is done.   

Experimentation is the way to discover them. I wonder, if it is possible to power a 6" plastic rubber powered propeller with a single loop of 1/16" rubber band. the main advantage is that it is ready made and the propeller's airfoil should be great. It is also more durable.

Scraps (building a dream)

16-17 December 2024

If it has not been realised, it is still a dream.

Oz : Scraps plan - free download

I tried to build 'Scraps' over the weekend. The motor stick (fuselage), wings, tails are all from 1/16" balsa sheet. The only exception on the plan is the propeller hub and blades, calling for 1/8"x1/8" and 1/32" balsa sheet. The longest wood is only 8" (200mm).

Some things I've discovered: 1) my smallest plier is too big, 2) I don't have a fine-toothed saw, 3) the motor stick is only 1/16"x3/16" cross-section, 4) annealing paper clip helps to make it softer and it can be easily work hardened, no need quenching, 5) 1/16" balsa appears to be a limit, any thinner and it is too flexible. 

Wing Rib

The 7 wing ribs are identical. The wing will only be covered on the top side, the ribs are curved for better airflow.

1. Cut 2x1"x1/8"x1/16" balsa pieces (guide rail).
2. Superglue one guide rail on packing taped jig board.
3. Cut a balsa sheet to the exact length, place it against the first guide rail.
4. Superglue the second guide rail against the opposing edge of the balsa sheet. Be careful not to glue the balsa sheet. Remove the balsa sheet. 
5. Cut a strip of card, about 1" deep, longer than the combined rails and balsa sheet.
6. Superglue the card on the guide rails, this will become the rib template.
7. Remove from jig board the rib template, reinsert the balsa sheet between the guide rails. Remember to stripe the balsa sheet beforehand so we will know which edge is against the leading/trailing.
8. Cut and sand rib template and balsa sheet to curvature.
9. Slice off the 7 required pieces of curved ribs by pulling down the rib template from the top edge of the balsa sheet 1/16" at a time. I didn't measure, I think my ribs are only slightly deeper than 1/16". I will sand the whole wing to finish it up, but I can't add depth. A cross section of 1/16" square appears to be a limit.

Nose Bearing

My thinnest paper clip is still too thick, I annealed it to close the nose bearing as much as possible, it has much free play.

On the next iteration, I will try to make a nose bearing from aluminum can. The aluminum wall is very thin, it is very easily pierced with a pin. I will cut strips with a pair of scissors, pierce them one at a time, assemble 2 or more of this together, bend to shape and drip superglue into the joints. This ought to result in a light easy nose bearing with perfect play.  

And yet another design which I think will be lighter is to cut a right angled triangular piece with rounded corners from the same aluminum wall. Pierce near the apex, then with the temporary shaft in placed fold the triangle over the 1/16" thick balsa motor stick. While it is only a single skin, the fold, the short moment, and the ample gluing area makes it strong and rigid for the pull of 1/16" rubber loop.

All these designs do not allow thrustline by itself, the model is too compact, but if the motor stick can be longer and we have a longer propeller shaft, then it is possible to by making a second pivot point on the propeller shaft, such as a small looped wire or strip. Get the propeller shaft into the loop and then superglue the end/s of the wire or strip.

Propeller Hub and Propeller blades

The plan calls for a 1/8" square balsa hub with diagonal cuts to receive 1/32" balsa blades. I don't think I can make small saw cuts on 1/8"x1/8" and thought out an alternative.

The Hub

My propeller hub is a 3cm length of lollypop stick (the plastic stick, not paper). Start by using a hot needle to pierce the plastic tube 1.5cm from a squared end. The plastic tube is small, so eye-ball the entry as near centre as possible. Re-heat and re-enter the pierced hole to heat pierce the other side of the tubular wall. Hopefully, the exit point is accurate, usually it is off, but sometimes it is still usable as is by enlarging he hole slightly. The propeller shaft is supposed to enter and exit the tube hub perfectly (perpendicularly and in the centre), but if it does not, make the offending hole that bit bigger until it does. The propeller shaft at the final stage will be binded with thread and held in placed with superglue, so it is still usable.

Now temporary insert the propeller shaft and use the grids on the cutting mat to help with scoring the plastic tubular hub at 1.5cm from the propeller shaft. Score both sides and snap off. Sand the tubular hub square, scrap the inner edges with a NT cutter to remove burrs.

This hub accepts blades with cylindrical blade spars, the spar will be held by friction with the hub, so the angle of attack of each blade can be adjusted. 

The Blades (adjustable angle of incidence)

I have a 6" plastic propeller for rubber power. I think I will make the propeller blades this way:

1. Trace and cut out multiple copies of the propeller blade's shape from 70gsm photocopy paper. 
2. Apply glue stick to the first paper blank, place it over the plastic propeller (either the top side or the under side), glue side up. Place the second paper blank over it.
3. Apply glue stick to the third paper blank, place it over the second paper blank, glue side down.
4. 3 ply of 70gsm paper ought to be sufficient, if it is later discovered to be insufficient, repeat the 3rd step for each layer. 
5. Cut out identical lengths of the blade spars, they have to fit the hub snugly later. It is ok to have loose fitting spars because they can be tissued over later.
6. With the paper blade still on the plastic propeller (serves as a jig/alignment tool in order that subsequent blades are made identical), superglue on a blade spar. 
7. Remove from plastic propeller, soak in superglue (strategically along the leading edge) to lock in the twisted curvature of the propeller blades. If the glue stick came undone later, wet it and bring it back to the plastic propeller jig to dry. You can also consider soaking in a bit of superglue along the delaminated area.

Gluing the Propeller Spars to Blades

This section is on how to do up the previous step 6, gluing spar to blade.

Obviously, a flat spar offers a larger contact area to the blade, however, for simplicity, I'd use round sectioned spars. How to hold the blades securely and accurately is the focus of this section.

• With the laminated paper blade still on the plastic propeller, draw a straight line, tip to tip on the single paper blade. Mark where the line intersects the hub. On the blade, the line marks the spar's position.
• Glue the spar with an end against the hub and following the marked line on the blade.
• Prepare a few tissue patches and glue it on the blade, round it over the spar. This should add sufficient strength and security.

 

200mm/8" Flyers

12 December 2024

Using only 160mm rubber bands, 1/16" and 1/8" balsa sheets, 0.7mm diameter stiff stainless steel wire, pen tubing. I think the motor sticks shall be kept n.e. 8", wingspan n.e. 8".

Build sequence for 8"x3" wings:

1. Make a cardboard airfoil template, slice from 3" (along grain) piece of 1/16" balsa sheet, moving 1/8" each time. This creates identical ribs of 3" length, 1/8" deep and 1/16" thick.
2. Superglue ribs perpendicularly to packing-taped building board. At the dihedral joint, use 2 ribs, set to the dihedral angle to avoid sanding later. 
3. Glue on top of the ribs, 8"x1/8"x1/16" leading and trailing edges.
4. Cover the top with tissue while still at the building board. Slit at the dihedral joint and remove from building board.
5. Crack and glue at the dihedral angle.

The wings will be glued on 1"x1/8"x1/16" wing posts and the wing posts will be friction fitted to rolled tissue tubes which are later glued to the motor stick.  

22 March 2024

A simplified method for building a lightweight model for beginners or for models that prioritize weight savings.

The Wing

Consideration: Need a slightly strong leading edge to withstand knocks but a very thin trailing edge to affix the covering. 

• Most wings have straight leading edge so you can use a 1/8" balsa strip that can be sanded to shape later. 
• Most wings are double covered spaced by ribs, and you need ribs also to maintain the planform of the wings. Instead of drawing up all the ribs and cutting them meticulously, you can substitute with right angle triangular profiles that can be sanded to rib shape later.
• All wings have a sharp trailing edge and it is too much work to sand sharp balsa trailing edge only to have them buckle at the last moment or when knocked. Substitute them with a single fold paper strip so it will cover the sharp ends of the previously mentioned right angle triangular profiles.
• Over a drawing of the wing planform, lay down the creased paper strip so that the crease or fold is to the trailing edge.
• On the drawing of the wing planform, draw a parallel line from the leading edge to show where the rear of the balsa leading edge shall be. Use this to mark the length of each triangular rib profile by first placing the sharp end on the line of crease. Cut and number each rib.
• Pin the 1/8" square balsa strip over the drawing and glue the ribs in place.
• Glue the other flap of the paper strip to the top of the ribs.
• Remove and sand the curvature of the ribs.
• Lay it back on the drawing and use a straight sanding tool to sand 1/16" square slots onto each shaped rib.
• Glue the 1/16" top spars onto the wing.
• Reinforce those areas that will be stressed with some balsa.
• Remove wing and sand thoroughly before covering with tissue.  

The Empennage 

Consideration: Need this to be very light because it is at the tail where there isn't much chance of it being knocked. Deformation can be easy to set right by just running the edge between thumb and forefinger.

• Cut an outline of each empennage from paper. 5mm wide should be sufficient.
• Glue a 1/16" spar to the outline.
• If some area is too far from the spar, put in some balsa strengthener.
• Sand the empennage before covering both sides. 

The Fuselage

Consideration: It is there to separate the wing from the empennage. It could be built with balsa, then you have to consider if it is to be rubber powered. If so, some strengthening is necessary, 4 pieces of 1/16" square longerons is enough. Start with building a basic balsa frame of 1/16" square sticks to house the rubber. Add formers, strengtheners, stringers. Sand and cover. Foam construction is to cut to shape, sand, and cover, if rubber powered, hollow the foam, sand in slots to receive 1/16" square longerons, recess for balsa strengtheners at places that will be stressed.  

19 January 2024

All righty! Let's make a mini class of free flying models for living rooms. Hand tossed, catapult, rubber powered propeller. There's pistachio scale, but that's too difficult. So let's just make small things that can fly, adopting the 8" wingspan rule. 

Material and tools shall be commonly available, for beginners, carbon fibre, balsa and nichrome cutter are permissible.

Models may be tossed, catapulted or uses rubber band to power the propeller. Rubber powered propeller models are to use the rubber bands used by hawkers/office, beginner can use 'speciality' indoor rubber. 

Material MUST be cheap, so the first rule is:

Rule 1: Material cost for each model shall be less than 1 SGD, 5 SGD for beginner.

Adopting the 8" or 200mm format, which can be drawn on a single A4 sheet of paper, comes the second rule. 

Rule 2: Rubber powered: either the span or the length does not exceed 8" or 200mm. If it is a glider, up to A4 length.

In general 8" span is chosen so it will turn tightly in the living room and also for economical reasons, to maximise the use of a 36" length of 3" wide balsa sheet:

• 4x8"x3" + 1x4"x3"
• 3x8"x3" + 1x12"x3"
• 3x12"x3", etc...

It is possible to make 16" span from 8" sheet balsa.

Start with a catapult glider, perhaps a tow glider, then a rubber powered flyer and then maybe a scale flyer, start with no-cal before progressing.