Pistachio Scale

18 April 2024

Summary of how to mark and prepare all the parts to build the fuselage of a 10" wing span U.S. Army Douglas Observation YIO-43 from a reduced print of a 22" wing span plan from Outerzone.

Drawing the profile of the fuselage

1. Trace the profile of the fuselage from the reduced print. We're re-designing the construction method, much details will be ignored, but some would remain.
2. Transfer the datum line to the tracing.
3. Draw a parallel line to the datum, at the cockpit line. Draw another parallel line to the bottom of the datum line. These 2 lines indicate the rubber housing sides.
4. Draw perpendicular lines to these 3 lines. They indicate the chosen formers' position and where the profile outline intersects, indicate the depth of these formers.
5. Measure the formers' width from the planform of the fuselage and indicate them on the tracing at each former's location. 

Fabricating the formers by drawing onto a 1/16" balsa wood sheet.

1. Draw a centre line along the grain.
2. Draw perpendicular lines to the centre line to indicate the datum of the formers.
3. Draw parallel lines and perpendicular lines; fuselage's depths and widths at each former, the constant side housing.
4. Use a circle template and draw circles in the datum line of the formers to clear the rubber motor.
5. Use circle template and draw half circles to the top and bottom of the formers so that they become radiused rectangles.
6. Trace the radiused rectangles on the inside with a thick pen if the side housing and plankings are from 1/32" balsa. If any is from 1/16" or thicker, then you have to trace an inner outline with the same width, free hand would do. 
7. Cut rough and sand until the pen marking dissappeared. Cut and sand the central hole that clears the intended rubber motor.
8. Reinforce the formers if their edges are lesser than 1/8".

Rubber Housing Sides, draw on 1/32" balsa wood sheet

1. Draw 3 parallel lines with equal spacing to indicate the width of 2 housing sides.
2. Draw perpendicular lines across to indicate the formers' positions.
3. Optional: glue in 1/16" reinforcement or former stoppers at intermediate former positions.
4. Cut the whole housing sides but don't split the sides yet. Make it 1/8" longer at the nose.
5. Chamfer the tail end of the 2 housing sides so that they can meet together when the tail is brought together according to the planform.
6. Split the 2 housing sides to left and right pieces.
7. Optional: curl/bend the nose ends of the separated housing sides so they can approximate the planform at the nose and can wrap the nose former.

Notes on the removable nosepiece

1. Cut the removable nosepiece from 1/16" thick balsa sheet or the very thick cardboard (about 1.2 mm thick). It is a disc because the real aeroplane example has a spinner. 
2. The nose end of the housing sides are capped with 1/4"x1/16" thick balsa strips, the grain runs perpendicular to the grain of housing sides. If the removable nosepiece shall be much larger than the nose end of the housing sides, add additional 1/4"x1/16" thick balsa strips to the top and bottom capping.
3. Sand the cap-reinforced nose end of the housing sides to match the removable nosepiece.
4. Add 1/4" strips of the very thick cardboard to a 1/16" x 1/16" balsa strips, equal length. These are tongues that are glued to the removable nosepiece and fit inside the top and bottom capping strips of the nose end. The tongues prevent the removable nosepiece from spinning with the propeller and allows fine adjustment to the thrust line by adding shims between the removable nosepiece and the nose end of the housing.
5. Add in the plastic thrust button (re-purposed from the end cap of Pilot G7 ink tube) to the removable nosepiece, a snug-fit is good enough.
6. Fabricate the shaft from a straightened paper clip. One end is bent 90 degrees, it is bound to the underside of the propeller with thread and superglue. This avoids making a hole through the propeller. The other end is then fed through a glass bead and then the plastic thrust button on the removable nosepiece and finally a rubber hook of either a round or diamond shape is bent and the excess wire is snipped off.  I am thinking that a diamond hook is better for the house-hold/office rubber bands.

Since the removable nose piece is simply a disc, you can make many removable nose pieces with different propellers, e.g. different diameter, pitch, shape, 3 blades, with hook for winder, with engaging ramp for free-wheeling or when the original piece is broken beyond repair.  

Assembly

1. Choose the widest intermediate fuselage former and use white glue to glue it to the rubber housing sides. Before the glue sets, glue the tail end. Place the housing sides on edge, over a table edge so that the former cannot interrupt the placement This is important to make sure the positioning of the housing sides is as accurate as possible. Set to dry before proceeding with next step. If superglue is at hand, use any combination of tape, clip/peg, or rubber band to hold the 3 pieces in position, and then use superglue to set in position.
2. Glue in the nose former (or frame), allow for thrustline angles.
3. Glue the remaining formers.
4. Cap/plank the formers with 1/4"x1/32" balsa strips. The strips may be curled or bent if necessary.

Covering

1. Finely sand to prepare the fuselage for covering.
2. Cover with overlapping tissue to the housing sides, caps/planks etc. Covering makes the individual components act as one. 

17 April 2024

Laminated formers is possible but is more work and due to spring back, not that accurate. Remember that simplicity is less or easy work, and we wish to have that for our pistachio/grapenut scale model airplanes. Formers cut from sheet material are accurate and stable, they do not have springback.

Sheet formers may be cut or sanded from balsa, EPS, XPS or depron-like sheets.

Yes, you will have to make a 1/2" hole for the rubber motor to pass through and perhaps reinforce those formers where the material is less than 1/8" width.

For ease and accuracy of assembling the fuselage, glue to the 1/32"x1/2" motor housing sides pieces of 1/16" square strips at the formers' back/front positions. This forms the backstop (or front stop as the case may be) to the formers and eliminate the alignment mistakes.

  

16 April 2024

Fuselage formers

Where the fuselage's bottom profile has a significant compound curve, use 2 ply lamination for the bottom formers. Ideally, a 3 ply lamination of 1/32" balsa is stronger and more stable. A 2-ply lamination will also work to some capacity which will be sufficient for a pistachio scale plane. Glue them to the motor housing and they add to the strength and integrity of the motor housing. Cap the bottom with a curled 1/32" balsa strip to lock it all in place. If there is a main undercarriage, use two of such former to achieve stability and put in extra strip across these 2 formers to provide a base for the main undercarriage. A matrix of the housing sides, the formers, the bottom cap piece and the side pieces confers much structural strength. It is simpler to have laminated formers. However, if there is no internal clearance requirement in the fuselage, EPS foam block could be used (but consider the difficulty in sanding). You could use hollowed out XPS foam block and that will sand easily and because if it is weighty, it is useful weight because it is at the nose end, all considered though it is still a lot of work for little to no strength if it is glued to the motor housing. Where the members are non structural and only need to be supporting the tissue covering, then simple formers cut from 1/32", 1/16" or 1/8" balsa sheet is ok, you could also use formers made from foam. 

Making a laminated curved balsa piece (single curved surface, relying on the induced stress of the balsa wood)

1. Pull and tape wet 1/32" balsa strips to a pre-shaped former until dry. The former can be made from Depron type of foam sheet.

2. Pin wet 1/32" balsa strips along the plan until dry. Do not pin directly against the wet balsa strip as it will cause kinks rendering it useless, use scrap balsa pieces to spread the force on the balsa strips.

3. Make an adjustable jig so that the wet balsa strips can be clamped together. Ideas : on a sturdy base, fit discs, rollers, flat strips. 

15 April 2024

Simplify the fuselage construction for a Pistachio Scale Plane

Earlier, I mentioned shortening the motor housing, today, I think the motor housing should be the length of the fuselage because the rear end of the fuselage needs to be supported and it is easier to obtain the correct fuselage planform. 

The idea of the motor housing does not change, it is just integrated fully into the fuselage and minimise the effort to make a correct planform. The additional weight is small, especially when 1/32" thick balsa was used as the motor housing sides.

Anyway, the main difficulty is maintaining the space between the housing sides. You cannot place any balsa members in the centre to space out the housing because that's where the rubber motor runs. You could glue pair/pairs of balsa members to the top and bottom edges of the housing, but this is only possible if the depth is 3/4" to minimise the interruption when the rubber motor rotates.

And so, to simplify the housing, use depth of 1", it will be more durable.

The fuselage planform as identified from the nose to tail: The nose former, a pair of 1/4"x1/32" spacers, the motor peg former and finally when the two housing sides are brought together.

Form a slight curl by wet bending the nose end of the housing sides and V-cut or >-fold the housing edges if necessary to blend to shape, Glue the peg former, bring the tail end to close, bring the nose end to wrap around the nose former and glue to the top and bottom of the housing sides, the pair of 1/4"x1/32" spacer. 

Ultra-Simplified Pistachio Scale Fuselage with Integrated Motor Housing

Here's an even simpler approach to your Pistachio scale fuselage with the motor housing built directly into the structure:

Materials:

• Two balsa sheets (1/32" thickness recommended) - slightly larger than your desired fuselage size
• Wood glue suitable for balsa
• Sandpaper
• Razor blade or balsa cutter
• Water (for wet bending)

Steps:

1. Fuselage Sides:

   • Cut the two balsa sheets into rough rectangles, with a width slightly exceeding the desired fuselage width and a length a little longer than the planned fuselage length (including the motor housing).

2. Motor Housing and Fuselage Shape:

   • Wet the balsa sheet near the nose end (about 1/3 of the length) to make it more pliable.
   • Carefully bend this section upwards on both sides to create a gentle curve, forming the basic fuselage shape and motor housing pocket. You can use a dowel or rounded object as a guide for shaping.

3. Motor Peg Former (Optional):

   • If your motor requires a separate peg former for alignment, cut a small balsa piece to fit inside the motor housing pocket at the designated location and glue it in place.

4. V-cut or Folded Tail Closure (Optional):

   • To create a pointed tail shape, you can make a small V-cut at the rear end of the balsa sheets (before bending) and glue the cut edges together to form a point. Alternatively, make a slight fold inwards (like a > shape) at the tail end to create a tapered look.

5. Joining the Fuselage Sides:

   • Apply wood glue to the top and bottom edges (along the length) of one balsa sheet.
   • Carefully place the other balsa sheet on top, aligning the edges and ensuring the motor housing pocket is formed correctly. The bent nose sections should meet at the front.
   • Clamp or hold the sheets together firmly until the glue dries.

6. Tail and Nose Closure:

   • Once the main body is glued, trim any excess balsa at the tail end to achieve the desired shape.
   • You can add a small, thin balsa piece to close the tail opening completely (optional).

7. Shaping and Finishing:

   • Sand down any uneven edges or imperfections after the glue dries.
   • Use a balsa stripper or file for more precise shaping if needed.

8. Motor Installation:

   • Create a small slot at the rear end of the motor housing to allow the propeller shaft to exit.
   • The motor can be glued directly to the inside of the motor housing pocket.

Benefits:

• Extremely simple construction with minimal parts.
• Integrates motor housing for rear support and easier planform shaping.

Considerations:

• This method relies on shaping the balsa sheet during the wet bend, so practice on scrap balsa first to get the desired curve.
• The 1/32" balsa might be delicate, so handle it carefully during shaping and construction.
• You might need to add a small reinforcement strip (like a landing gear mount) later if the fuselage feels too weak.

Additional Tips:

• Use a light but strong wood glue specifically formulated for balsa models.
• A light coat of clear dope after sanding can improve the finish and add strength (optional).
• Ensure the motor housing allows smooth rotation of the rubber motor without any rubbing.

This approach offers a very basic and quick fuselage construction. Remember to customize the shaping technique and add reinforcements if needed based on your specific design and motor size.

   

12 April 2024

Tiny Timbers, Big Fun: Building a Pistachio Scale Plane

Building a model airplane at pistachio scale is like creating a miniature masterpiece! But with such a small size (think 8-9" fuselage!), achieving complex details can be tricky. Here's how to keep things simple and hopefully, it'll fly:

• Think Big Blocks, Not Tiny Tweaks: Forget fiddly formers and delicate stringers. Instead, use solid foam blocks to build the fuselage. This simplifies construction and keeps your workload manageable. If you are doing the 'sticks and tissue' way, change it to "blocks, slabs, sticks and tissue". You only need to create a strong enough motor housing of 6" or less to handle the pull of the rubber bands (read on for my suggestion). Everything else is more for aesthetics, you can still add a few formers to pretty things up.

• Simple is Spectacular: At this scale, focus on clean and well-assembled construction design and techniques rather than chasing ultimate precision. Neatness will go a long way in making your plane look fantastic! Do less, don't do more and don't add too much detail to chase fidelity.

• Strength in Simplicity: Remember, even a tiny plane needs some muscle. The motor housing area within the fuselage is key. Make sure it's strong enough to handle the tension of the rubber bands. 2 slabs from 1/32" thick balsa sheet with cross-grained formers at the front and back is strong enough to handle the tension of the household rubber bands. Don't over-engineer and complicate, it's only 6" long!

Basic Fuselage Design

If the aeroplane subject is near flat-sided, you can use 1/32" balsa sheets to build up the fuselage. There won't be much weight savings if you switch to a frame construction. This is because longerons and spacers that uses strips thinner than 1/16" square will result in a lot of breakages during handling and the glue, even when applied sparingly, adds to the weight. 

If you must choose a subject that has large elliptical or curvaceous cross sections, you can use thin slabs of expanded foam suitably hollowed out and strengthened for motor housing. It will be very light, but the amount of fine sanding is going to get you.

For a subject that has moderate or even small elliptical/curvaceous cross sections, you can build a motor housing to the planform and then add bits of balsa or foam to make up the rest of the fuselage.

Motor Housing

This is the core of the fuselage. It is the structural component that handles the stress of the rubber motor and impacts, everything else is attached to it. 

Identify on the side profile where the rubber motor will run and how long the housing is going to be. You do not want to answer that it is from head to tail. Think of the final CG and the space limitation, and you'll find that the motor housing is only about 60% of the length of the fuselage. There are 3 main components: 2 lengths of 1/32" thick balsa (no less than 3/8" wide), 1 nose and 1 tail former of 1/16" thick balsa.  The nose former is set to the thrust line. If the nose former has straight sides, you can pre-bend the nose end of the housing sides to form a curved planform. If the nose former has to be small and round, remove a V wedge out of the nose end of the housing sides, close the V and you have an approximation that gives it both a bit of curve planform and because it is a slight V, it fits better over the nose former. At the tail end of the housing is the tail former where the tail end of the fuselage is framed up. 3/8" ahead of the tail former glue 1/32" short pieces to the 2 housing sides to provide bearing surface to the 3/32" bamboo motor peg. All junctures may be reinforced by gluing balsa and/or tissue pieces.

Fixed Noseblock with Motor Access - Pistachio Power!

Since the removable noseblock concept is a bit more work and weight, here's an idea for your fixed noseblock and yet with motor access: simply allow an opening at the bottom of the fuselage. When not flying, we rarely look upwards at the model, so the bottom slot is visually hidden. Optionally, cover with painted light weight tissue connection, just make sure it peels off cleanly without damaging the fuselage.

Remember, at this scale, functionality takes priority! The slight visual difference from the bottom is a small price to pay for the ease of motor changes. If you need further convincing, consider that the No-Cal version has the entire starboard side exposed!

9 April 2024

Construction ideas for 10" wing span U.S. Army Douglas Observation YIO-43, reduced print of a 22" wing span plan from Outerzone.

Removable noseblock

The whole propeller and spinner should come with a removable noseblock so that rubber band can be fed to the fuselage and hooked to the propeller.

The concept: To receive the removable noseblock, former 1 ("F1") shall be cut from 1/32" thick cardboard glued to the fuselage sides and the square hole reinforced with 1/16" balsa strip. The square hole is to receive the 1/8" thick square balsa/foam block that is glued to the removable noseblock. The removable noseblock is made from 1/8" thick balsa/foam sheet, and it is shaped when it is positioned to F1 and an oversized spinner disc ("SD1") in placed. Fit the thrust bearing on the removable noseblock, i.e. SD1. 

Propeller

1. Cut 2 pieces of spinner discs ("SD2", "SD3" which is a smaller version of SD2) from 1/32" thick cardboard.
2. Cut 3 pieces of blades from thin plastic cup, cut 3 pieces of blade support, 1.5"x1/8"x1/8" balsa strips with one end sanded to 45degrees, assemble and glue. 
3. Make a ramp from a short section of ink tube.
4. Fit spinner thrust button to SD2, insert ramp tube, glue the square ends of blades to the flat side of SD2, glue SD3 over all.
5. Straighten a paper clip, bend one end to a hook, insert straight end through the inner tube of the nose thrust button, through the spinner thrust button, bend to a loop so that it can engage the ramp.     

Fuselage

The key feature of fuselage construction is an integral horizontal crutch, everything else is built up from the basic key feature. There are two main members of the horizontal crutch, curved by putting spacers between 2 slabs of 1/32" balsa sheet. At the nose it is glued to a 1/16" cross member to receive the removable noseblock. Another feature is that the formers may be a combination of the traditional flat type and a simple wet/heat bent balsa strip 1/8"wide by 1/32" thick that is anchored to the key horizontal crutch.

Cabane and rigging

Use small diameter bamboo dowels to make up the wing cabane structure, the top rigging post and horizontal stabiliser support. Bamboo is used because they don't break as easily as balsa. Rigging is fine cotton thread superglued at rigging points, purely for show. Rigging points may be reinforced with paper discs cut from photocopier paper. Only the wing cabane is structural, it secures the wing's CS with the horizontal crutch, drill holes accurately in the CS with a template and let the dowel fit in small slotted cardboard pieces at the horizontal crutch for better gluing surfaces. 

Wing

This wing design prioritizes minimal weight and drag, similar to a sail. Here are the key features:

• Strong Leading Edge: A sturdy leading edge (1/16" x 1/8" strip) forms the front of the wing and provides stability.
• Optional Spars: For additional support, one or two spars can be incorporated:
  • Single spar: 1/16" x 1/8" strip
  • Double spars: 1/16" x 1/16" strip (each)
• Thin Trailing Edge: To minimize drag, the trailing edge is made from thin paper, avoiding the drag created by sanding balsa to a taper.
• Minimal Ribs: A small number of ribs (e.g., 4) made from 1/16" thick material maintain the wing's shape while keeping weight low.

This design concentrates drag on the leading edge and spars, keeping the trailing edge sharp and efficient. This approach offers a lightweight and efficient wing suitable for various applications.The key concept is a strong (1/16"x1/8" strip) leading edge, if single spar, 1/16"x1/8", if double spars, 1/16"x1/16", thin trailing edge of paper (avoid sanding balsa to taper and being less drag), all spaced out with minimal numbers of 1/16" thick ribs. Most drag will come from the leading edge and spar/s, the trailing edge is razor sharp. It is like making a wing sail. 

1. Cut a pair of the curved outline from thin photocopy paper ("outline").
2. Tape a silver tissue piece on a flat surface, decorate with lines of ribs and ailerons.
3. Flip over the silver tissue and glue the outline.
4. Prepare ribs ("R1", "R2"), dihedral template, spars and leading edges from 1/16" balsa sheet. Leading edge being 1/8" wide, spars being 2 pieces of 1/16" wide.
5. Prepare centre section ("CS") from 1/32" balsa sheet, wet to pre-curl.
6. Glue CS to angled R1, glue leading edges and spars to angled R1 and straight R2, prepare for covering.
7. Glue the prepared tissue to top of the wing frame. Complete the finishing with EZE dope.
8. Remove wing from board, cut and sand the dihedral joints through the CS.     

Stabiliser

Use the same method as the wing. The horizontal is first glued to the fin and then the fin is glued to the fuselage.

Canopy

The concept: Creating a canopy for your miniature aircraft is crucial, but keeping it lightweight is equally important. This method tackles that challenge by transforming clear parcel tape into a realistic greenhouse canopy. The beauty lies in its simplicity. Since the model is so small, the tape itself provides enough rigidity to act as the frame. By adding thin black lines directly onto the tape, we can mimic the intricate frame structure of a real greenhouse canopy, achieving a detailed look without adding weight.

Simplified Construction but it'll smudge: 

1. Draw a developed plan of your canopy's individual panes on a separate piece of paper. Tape this blueprint down to a flat surface. Secure a sheet of clear parcel tape over the blueprint, sticky side facing up.
2. Cover with another layer of clear tape, sticky side down. Gently press to remove any air bubbles.
3. Draw with a sharpie or permanent marker the frame structure.
4. Cut out the entire canopy shape from the double layered tape. Fold it along the creases to form the 3D structure.
5. Wait until your model's fuselage (body) is finished and painted. Trim the canopy for a snug fit with minimal gaps on the fuselage. Secure it with spot glue and camouflage any remaining gaps using small pieces of silver tissue paper. You can also re-trace with sharpie/permanent marker.

Experiment: Try using sharpie, permanent marker, paint pens to shade a piece of transparent parcel tape to determine which pen works satisfactorily. 

• The ideal pen will leave a visible, well-defined mark without smudging or significantly reducing the transparency of the tape.
• Based on your experiment, choose the pen that offers the best balance of these factors for your project.

Construction:

1. Canopy Frame Creation:

   1. Draw a developed plan of your canopy's individual panes on a separate piece of paper. Tape this blueprint down to a flat surface. Secure a sheet of clear parcel tape over the blueprint, sticky side facing up.
   2. Take a small piece of paper, color one side silver and the other gunmetal. Cut this into thin strips and color the exposed edges with a black marker. Carefully lay these strips onto the sticky tape, mimicking the frame structure you see on your blueprint.

   Canopy Shaping and Attachment:

   1. Once the frame with the strips is complete, cover everything with another layer of clear parcel tape, sticky side down. Gently press to remove any air bubbles. Now you can carefully cut out the entire canopy shape from the layered tape and paper. Fold it along the creases to form the 3D structure.
   2. Wait until your model's fuselage (body) is finished and painted. Trim the canopy for a snug fit with minimal gaps on the fuselage. Secure it with glue and camouflage any remaining gaps using small pieces of silver tissue paper. You can even add a touch of paint for a flawless finish.

Undercarriage

Making a functional and stiff undercarriage complete with wheels that spin would either require a lot of work and increased weight. The anchor points have to be reinforced and thin wires or steel pins have to be used.

An alternative is to make up a simple main landing gear from balsa. The wheels are made from depron foam and cannot be spun. If it is necessary to reduce friction, glue small fishing line to the contact points. so that they can slide on hard floor easily. At the fuselage juncture, the attachment is thin rubbery foam glued to the fuselage reinforcement rails of 1/16" sq balsa. It would be durable because the soft mounting will give way on impact and spring back to its position.

The tail gear is just a piece of 1/32" cardboard cut to shape and coloured accordingly, because it measures less than 1 cm in dimensions. 

Air scoop, radiator, exhaust, machine gun and rail, venturi, pitot tube, step plate, spreader bar

These are non-functional and can be modelled from paper, card, foam and balsa.  

8 April 2024

The fuselage will house 2 looped pieces of house-hold rubber bands. Bear in mind that if it is a motor stick, a 1/8"x1/4" balsa is stiff and strong enough. Make up the fuselage sides of 1/32" balsa sheet. Each side has a doubler of 3/8"x1/32" balsa strip. This long rectangular doubler piece is glued to the inside of the fuselage sides, once at the nose end, once in the middle with a 3/8"x1/4"x1/16"thick spacer and finally at 1/8" pass the motor peg. Note that only the middle of the doubler has the spacer piece, this is to create a gap between the fuselage side and the inner doubler, and by tensioning over a form, the fuselage has a curved planform. For the motor peg location 1/16" combined thickness is sufficient, there is no need for a cross-piece of 3/8"x3/8"x1/32"thick reinforcement plate.

Trim the nose ends for thrustline. Glued top and bottom cross pieces 1/4"x1/16"thick to the doublers. Then it is a simpler matter for a removable noseblock with 1/8"x1/8" cross piece to house over the reinforced fuselage sides. What remains is to glue the tail end of the fuselage sides together before adding top and bottom formers to the fuselage doubler. This horizontal crutch construction is then readied for stringers and reinforcement pieces. 

In the photograph are 2 pieces of plastic salvaged from the ink cap of "Pilot G-2 07" pens. I think this will have multiple uses, first things that come to mind are nose buttons and wheel hub as is. As can be seen in the photograph, it fits a paper clip. It is light, the wobble is slight and the surfaces glide over each other easily. The outer ridged tube can be pared off if necessary. The top lip's diameter is 1/4", the inner tube's OD is about 1/16", the overall height is 3/16" and the 1/4" lip is about 1/32" thick.

A removable nose-block and propeller is essential for my model, without it, I cannot change the rubber bands. The nose-block can be made from sheet balsa, minimum of 1/16" thick, but 1/8" overall thickness would be preferable for easy handling. I could make one from the very thick cardboard of 1/32" thick because unlike balsa, cardboard's strength is all-round. An idea is to have a 1/16" balsa base topped with the 1/32" cardboard. To locate the removable nose-block means I have to provide sufficient depth for at least a single dowel peg, preferably two. So when constructing the nose end of the fuselage, add 1/8" balsa to the rear of the nose end. I can cut 2 identical pieces of 1/16" cardboard formers, one will be fixed to the fuselage and the other to the rear of the removable nose-block.  I would just make 2 spinner back discs from the 1/32" thick cardboard, one will be fixed to the front of the removable nose-block and the other spinner disc accepts another end cap and propeller. Making 1/16" diameter holes through balsa and cardboard would be easily done by using pins to insert through follow by a drill bit to widen. The Douglas aircraft has a spinner, but at pistachio scale this is too fiddly to do well. After the propeller is secured and working properly, then think about beautifying it. At pistachio scale, 1/8" square balsa shaft seems huge, but anything smaller is not suited for propeller turning.

Douglas is a 3 bladed propeller, for ease though, a 2 bladed propeller can be substituted. The paper clip would weaken the 1/8" balsa strip too much. Instead, slip in endcap and spinner disc, bend 90degrees and tie and cyano'd to underside of a thin bamboo dowel. Only then glue the propeller blades and a flat rubber piece to represent the spinner cone.

To make a 3 bladed propeller, rely on 2 spinner disc to capture the 3 blades, and in this case, the 90degrees bend is over the top disc. Similarly, a triangular flexible foam piece can be glued to the top disc to represent the spinner. At pistachio scale, it would be acceptable, only with larger scale type will the spinner be focused upon.  

5 April 2024

Pistachio scale refers to a rubber-powered miniature replicas of real aircraft and have a wingspan of no more than 8 inches (20cm).

Are they suitable for me? No, while they use simpler construction techniques and require few parts, they demand precision and care when working with small parts and lightweight materials, and flying is tricky as they are sensitive to wind and air currents. They are not a good option for beginners. However, if anyone is interested in a challenge, this is one. Once you manage to build one, you will bream with pride and confidence especially when your modelling friends are surprised by your handicraft. Getting the miniature craft to fly requires dedication and practice, so be forewarned and be mentally prepared. If you like tinkering and problem solving at minimal costs and space, this may be for you. Looking for something easier, try Walnut scale. 

According to Gemini:

• Pistachio Scale: Up to 8 inches (20 cm) wingspan. These are the smallest type of free flight model, known for their extreme miniature size and delicate construction.
• Peanut Scale: Up to 13 inches (33 cm) wingspan. These are also quite small and simple to build, making them a popular choice for beginners.
• Walnut Scale: Up to 19 inches (48 cm) wingspan. These models offer a bit more complexity than Peanut scale while remaining relatively manageable.
• Sport Scale: Typically larger than 24 inches (61 cm) wingspan. These models are more detailed and require more experience to build and fly.
• Coconut Scale: Greater than 36 inches (91 cm) wingspan. These are the largest and most complex free flight models.

OK, I printed out a a 22" span model on A3 paper and it turn out to be 9" wingspan, close enough for my pistachio scale. The aircraft chosen was a Douglas YO-43, a complex aircraft. I could have chosen a simpler cabin civil airplane. Douglas YO-43 challenges: Parasol with cabane and rigging, 3 bladed propeller, free-wheeling, horizontal tail in middle of fin, oval cross sectioned fuselage.

1/32" balsa sheet, bit of 1/16" balsa sheet and card, depron foam, guitar wire, rubber bands, photocopy paper, tissue, bamboo/wood, plastic tubes from used pens, aluminium from soft drink can.

Sopwith Camel

3 April 2024

From my memory of the 16" wingspan KeilKraft Sopwith Camel kit. I built one (did I?) almost half a century ago. See Outerzone's Sopwith Camel (oz1391)

Content of the kit

I remember that it was a comprehensive but basic kit (contradiction?). You get a nice big plan, I felt I transformed into an Engineer or Scientist who is about to embark on a great journey. I was a teenager, the plan was easy to understand, there are lots of references and diagrams and a stage-by-stage construction write up.

KK assumed you enjoy finding bits and pieces of stuff and saves their time by actually requiring you to know foreign words like 'bond paper', 'radio wire', 'thin card' and 'postcard' (ok, I do know what is a postcard) and have them at hand. You do get a piece of wire to bend and cut, a plastic/nylon cowling, thrust button, a set of wheels, a propeller and almost everything else to complete a basic model. I think tissue was provided. If you are interested to make the twin machine guns though, you have to provide straws and needles, the plan explains how. If you want to have rigging (and which WWI biplane does not have rigging!) you are on your own, there is no instruction on the plan and you have to source something suitable yourself.

The kit provided a few short length printed balsa sheet. You are expected to cut out and sand accordingly to ensure they fit reasonably well. Thankfully, I remembered that it fitted okay, but what did I know as a teenager? I don't remember if my kit came with a decal sheet, it probably did, as shown in Outerzone's scan. The kit also had a rubber strip and a bundle of balsa strip wood.

You have to ready your own set of tools, sandpaper, glue, dope, paint etc.

Building

It was easy to build, but tedious to cut out from the sheet balsa. I don't think I cut out the ribs perfectly, I didn't pin them all together to sand them to final shape, that was an advance concept and it was not spelled out in the instructions on the plan. The leading and trailing edges were from strip wood, they were easy to assemble and glue together to make up the centre sections and wing panels. The fin, stabiliser and fuselage sides were easy to cut out. I didn't manage to bend the wire undercarriage accurately and didn't know how to adjust.

Covering and Painting

I don't remember that I had problem covering the model and I used poster paint to colour the model.

I was proud of my handiwork. 

Flying

Didn't happen.

I must have forgotten to re-read the instructions, I don't remember adjusting the centre of gravity. I only remember that the plastic propeller whirled for only a short time. 

Looking back, this kit is not suitable for flying: 

• Sopwith Camel has a very short nose, even if you put in a lot of nose weight and balanced the model correctly, I think it will not reach the required flying speed. It will only be a powered shallow dive.
• Radial engined biplanes have a lot of drag, the glide will be non-existent especially if it is overweight.
• The kit build is very heavy. The plastic cowling, generous sections of balsa may make it slightly more durable for crashing, but I can't think there can be any chance of a graceful flight.
• I don't think that increasing the rubber motor will help because the provided propellor is too small. 

Was it fun? Yes, it was a form of tedious fun, after you convinced yourself that it's the journey that matters and not the destination.

As re-told by Gemini:

The Kit: A Blueprint to Adventure

The KeilKraft Sopwith Camel wasn't fancy, but it sparked your imagination. The big, clear plan felt like a treasure map, and the instructions were like a guide for a young engineer. It came with basic materials – balsa sheets, wood strips, plastic bits – and expected you to be resourceful. Thread, paper, even needles and straws – these were your tools for extra details. It was a kit that challenged you to think outside the box.

Building: A Journey with Balsa

Building the plane was easy in theory, but cutting the balsa pieces perfectly? That was a whole other story. Sanding them smooth? Even trickier. But you persevered, slowly transforming the raw materials into the iconic biplane. The wings, tail, and fuselage took shape, and the little propeller seemed ready to spin dreams into flight.

Taking Flight (Almost)

Covering the model and painting it with poster paints – that was the fun part! You saw your creation come alive, a source of immense pride. But then came the moment of truth – launch day. Sadly, the flight was short-lived. Perhaps the weight, maybe the center of gravity – whatever the reason, the Sopwith Camel took a nosedive instead of a graceful soar.

The Importance of the Journey

Looking back, you realize the kit might not have been perfect for flight. The design and weight might have stacked the odds against it. But that doesn't diminish the experience. Building the Sopwith Camel was a journey, a test of patience and resourcefulness. It was a reminder that sometimes, the fun is in the process, not just the destination.

Ready for Take Two?

So, the Sopwith Camel never quite reached for the skies. But maybe that sparked a passion for flight. These days, there are tons of resources to help you build a model airplane that can take off. Interested in giving it another shot?

27 March 2024

When I was in my early teen, something clicked, maybe it was a lack of girls in my all-boys secondary school, maybe it was my lack of interest in the barbaric sport of football, maybe it was something else, I went crazy over aeroplanes. I was an aerophile, an aero-fanatic (I checked the dictionary, yup, I was clearly a fanatic). I saved my meagre allowance and bought myself a KeilKraft Sopwith Camel rubber powered model kit.

The KeilKraft Sopwith Camel is a 16" wingspan balsa model kit. I thought that it is an appropriate kit for a budding aeromodeller (yup, from the past issues of a magazine aptly named Aeromodeller, available at the Junior Flying Club, I qualified myself as an aeromodeller). I thought to myself that I ought to follow the history of aeroplanes. I would start with propeller planes and end with jet planes. It wouldn't be right to jump into modelling the Hawker Hunter, I ought to start with early planes. And so, after a few visits to the local hobby shop and the library of the Junior Flying Club, I splurged on the balsa kit which came in a nice colourful box depicting an artist impression of the Sopwith Camel.

I spent hours to complete the model to the best of my ability and did everything I could. Not surprising though, I did not get a single flight.

As re-written by Gemini:

Ah, the teenage years. A glorious time of raging hormones, questionable fashion choices, and in my case, an all-consuming obsession with aeroplanes. Let's just say the ladies weren't exactly lining up for a chat about the finer points of ailerons and rudders at St. Brute's School for Boys (football was more their thing, bless their little hearts).

So, fuelled by a potent cocktail of aeroplane obsession and zero sporting talent, I decided to become an aeromodeller. Yes, I looked it up in the dictionary – full-blown fanatic, me. Now, a sensible person might've started with a glider made of paper and a dream. Not yours truly. No, I went straight for the historical jugular with a KeilKraft Sopwith Camel kit.

Let me tell you, that box promised a majestic bird of war, a miniature terror of the skies! Reality, however, was a bit more…balsa-y. I spent what felt like weeks meticulously gluing and pinning, convinced I was practically building the real thing (minus the machine guns, thank goodness for concerned parents). The finished product was…well, let's just say it looked like a Sopwith Camel that had spent a rough night after one too many celebratory loops.

The big day arrived. Heart pounding like a piston engine, I wound up the rubber band motor, a terrifyingly powerful contraption that threatened to launch the plane straight into the stratosphere (or at least Mrs. Henderson's prize begonias). I tossed that not-so-graceful bird into the air, and…nothing. Zilch. It just sort of…flopped. Like a particularly enthusiastic but untalented bird trying to impress its mate.

Turns out, balsa wood and teenage enthusiasm aren't quite enough to defy gravity. But hey, that's the beauty (and occasional frustration) of model airplanes! Maybe the Sopwith Camel never graced the skies, but the memory of that spectacularly ungraceful launch? Pure comedy gold. Who needs girls when you've got the thrill of a balsa wood near-disaster, right?

 

Crutch Construction

4 April 2024

Building a Simple Scale Model Fuselage: Prioritizing Ease and Visual Appeal

This guide outlines a method for constructing a scale model airplane fuselage that prioritizes ease of construction and visual impact. Here's the breakdown of the steps, keeping the most important aspects (side profile and planform) visually accurate while simplifying the least noticeable (cross-section):

Materials:

• 5mm Depron sheet
• Balsa wood (strips and sheet)
• Glue suitable for Depron and balsa
• Sandpaper (various grits)
• Hobby knife
• Flexible strip (like thin wire)
• Drill (optional)

Steps:

1. Side Profile:

   • Cut the desired side profile of the airplane from 5mm Depron.
   • Mark and cut out a hole for the rubber motor to pass through.

2. Formers (Cross-Sections):

   • Cut rectangular blanks from 5mm Depron for each former location (except for areas needing extra strength like the nose block and motor mount).
   • Ensure the height and width of each blank correspond to the dimensions from the side profile and planform (minus 2.5mm for the central keel piece).
   • On each former blank, sketch an approximation of the actual cross-section.
   • Cut out the center of each former to accommodate the rubber motor.

3. Attaching Formers:

   • Glue the Depron and balsa formers (made from the blanks) onto the side profile cutout.
   • Carefully sand the glued assembly to create a streamlined and symmetrical fuselage shape.

4. Longerons and Stringers:

   • Use a flexible strip (like thin wire) to sight from the nose to the tail of the fuselage. This helps visualize and mark the positions for longerons (vertical supports) and stringers (horizontal supports).

5. Reinforcement:

   • Use a sanding tool (slot tool) to create grooves along the marked positions for longerons and stringers.
   • Glue the balsa longerons and stringers into the grooves.
   • Add additional balsa pieces for reinforcement as needed.

6. Finishing Touches:

   • Drill holes for control linkages or other features if required.
   • Sand the entire fuselage for a smooth finish.

Benefits of this method:

• Simpler Construction: This approach focuses on replicating the most visually impactful aspects (side profile and planform) with simpler methods for the formers.
• Reduced Complexity: By using rectangular blanks for formers and approximating the cross-section, you save time and effort compared to creating detailed formers.
• Visually Appealing: The finished fuselage will maintain a realistic side profile and planform, which are the most noticeable aspects of a model airplane.

Instead of using 4 longerons of 1/16" sq balsa strips to withstand the compression and torque of the rubber motor, it is possible to substitute with 2 strips of 1/2" wide by 1/32" thick balsa. It will also provide support to holding the model plane in your hands. Remember, the rubber motor does not extend throughout the length of the fuselage, neither need the wider balsa sheet. The rest of the stringers can be thinner or lesser. Using 1/8" wide x 1/32" thick balsa for seatings and other strong points.

Modular Power Pod for Easy Swapping

This design incorporates a detachable power pod that screws onto the nose of the fuselage or the inside of one. This pod houses the rubber motor, the primary source of weight and force for your propeller. By making it modular, you can quickly swap between different power pods with varying rubber motor configurations to experiment with different flight characteristics (more power, longer flight times).

Simple Construction:

The pod itself can be built using a lightweight 1/8" x 1/4" balsa motor stick. This stick can be outfitted with a propeller, bearing, and any other necessary components like a hook for launching with elastic. To attach the pod to the fuselage, glue small plastic tabs to the front and rear of the motor stick. These tabs can then be screwed or secured with double-sided tape to the underside of the fuselage.

Benefits of the Modular Pod:

• Fast Motor Changes: The modular design allows for easy swapping of rubber motors, letting you experiment with different flight performances.
• Weight Distribution: The pod concentrates weight in the nose, potentially eliminating the need for additional weight to achieve proper balance.
• Lighter Fuselage: The fuselage itself can be built lighter or even use a simple curled paper skin (like rolling paper) since the pod takes care of the weight and strength requirements. Leaving the bottom of the fuselage uncovered allows for easy pod attachment.

This modular power pod system offers a flexible and customizable solution for your model airplane, letting you experiment with different power configurations and optimize your plane's performance.

26 March 2024

For small rubber powered model aircraft fuselages, it is common to use 2 fuselage sides, whether cut from sheet balsa or constructed into a frame made of 1/16" square balsa longerons and spacers either vertically, diagonally, or horizontally. This method is especially useful for slab sided fuselages. 4 pieces of 1/16" square balsa longerons is strong enough for the rubber strain, and the cavity is generous. An example is the cabin type of  It can also be used for fuselages with non-flat cross sections, by adding on side formers and stringers. If not careful, the fuselage sides are glued skewed and it is not symmetrical on the planform.

A common method for non-flat cross sectioned fuselage is to use crutches, formers and stringers. If the crutch is the vertical keel type, the formers are split into left and right halves, these are more commonly used in WWII fighters and it ensures the side view is correct. Mind, the cockpit discontinues the keel and create stress points. Less common is the horizontal crutch system which ensure that the planform is correct, i.e., no banana fuselage. If the crutch coincides with the passage of the rubber motor, that would be great because then you get a structure to withstand the compression and torque more directly. Now, I have not seen it before, but it ought to be possible to use a double crutch system, one vertical and one horizontal in one fuselage, perhaps because it is double the work!

Drawing formers and ribs for a model airplane with Excel

26 March 2024

How to easily draw formers and ribs for a model airplane that looks about right?

MS Excel, Insert, Illustrations, Shapes: Lines, Curve; Basic shapes, Oval.

Curve can create rib shapes, planform of fuselage.

Oval can create elliptical formers, planform of wings

Ask Gemini for more info.

200mm/8" Flyers

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.

Rogallo Sail?

22 March 2024

Rogallo Wing Advantages:

• Simplicity: Easy to build and lightweight, perfect for low wing loading models.
• Inherent Stability: The curved profile creates lift and some inherent pitch stability without separate horizontal stabilizers (in low wind conditions).
• Low Stall Speed: Works well with low wing loading models that need low airspeed to stay aloft.

Rogallo Wing Disadvantages (Reduced Washout):

• Decreased Stability: Reducing washout (wing twist) improves lift but decreases inherent pitch and directional stability.

Adding Stabilizers:

• Improves Control: Vertical and horizontal stabilizers (fin and rudder) compensate for the reduced stability from washout reduction.
• Enhanced Maneuverability: Allows for better control over the model's pitch and yaw (turning).

Considerations:

• Size and Weight: Keep stabilizers lightweight to maintain the low wing loading advantage.
• Balance: Carefully balance the model with the added stabilizers to ensure proper flight characteristics.
• Wind Conditions: In higher winds, additional stabilizers become even more important for maintaining control.

Overall, using a Rogallo wing with added stabilizers for a low wing loading model is a viable option. It offers a good balance between simplicity, lift, and control.

Here are some additional points to consider:

• Experiment with Washout: You can experiment with different levels of washout to find the optimal balance between lift and stability for your specific model.
• Control System Design: The control system for the rudder and elevator needs to be lightweight and efficient to minimize drag.
• Flying Practice: Models with Rogallo wings and additional stabilizers can still be tricky to fly at first. Be prepared to practice and adjust the control throws for smooth flight.

You could probably do up a model this way but it would need much convincing if I were to do a scale subject. For one, if CF rods were used as the leading edge (and only spar) of the rogallo wing, for lightness, it would bend under the strain of the sail and the trailing edge of the sail would also be ballooning. It wouldn't look right.  

_________________________________________________________

Rogallo rc, need find geared motor, WLToys, other mini receiver

FF with stick or foam, solder capacitor

Sniffi glider, 2mm depron glider

Late 280: seaplane, plank/delta

Twin motors: from KF606, E010, E009; for parachute, twin planes, biplane, extended wing

1/2 gram receiver: solder thin lacquered wires?

Rogallo using drinking straws for spars?

Obviously only suited to AUW of only about 10g?

And is it acceptable to have less sweepback? I think so, let's say we only want sweepback of 20degrees. 180degrees -2 times 20degrees is 140 degrees. Give maybe 10% for the rogallo sail, so that makes it 150 degrees for the sail foil. Maybe it is better to cut out some at the keel and leave some at the tips.

Over A3 sheet of paper, draw the sail's dimensions. Draw parallel lines so that keel and spars can be wrapped by sail.

Flatten a piece of drinking straw, make a strip of cardboard which has the width slightly wider than the flattened width of drinking straw. The centre keel may alternately be inserted through alternating slits in the sail. To make the pockets for the spars, place the cardboard strip along a leading edge and then fold the outside and stick the sail foil together with double sided tape. Withdraw the cardboard strip and a pocket is formed neatly.

Paper Rogallo?

Again, targeted for AUW of only about 10g.

A4 paper can make a mini rogallo sail. The leading edge will not exceeding the breadth of the paper. The maximum wingspan is around the length of the paper and area around 3/4 of the paper's area. A paper airplane's or dart's wing's strength relies on single folded paper. Maybe a paper rogallo of single layer but with strengthening on lines and edges by folding once and with the curving foil is strong and rigid enough.

 Cut a square from A4 with a diagonal crease. The leading edges have 5mm overlap glued. Mark centre of leading edge for strut support. Extend a line between the 2 strut support locations. Where the line intersects with the keel (that's the diagonal crease mark in the beginning), is the central column support location, 5mm either side are the central strut support location and this gives additional dihedral to the rogallo.

Pierce the 4 holes, insert a thin bamboo stick and bring in the leading edges slightly so that the paper is curled. The rogallo is now basically done except for CG adjustment and the addition of central strut structure for the RC stuff.

A 3 ply foam gondola can be constructed to house the RC gear and the 1s cell. The center laminate is cut from 5mm foam to hold the RC gear and 1s cell. The outer laminates closes the RC gear and 1s cell and can be thinner foam.

2 pieces of 2mm foam strips can be the hanging central struts, placed at a Vee to each side of the gondola. At the top of each end is a hole where the thin bamboo stick passes through. The 2 motors are glued to the struts. At this point, the whole gondola and V struts will pivot around the thin bamboo stick. A 3rd strut is needed to set the gondola at the correct angle to the keel of the rogallo.

If the paper rogallo crumples too easily at the nose, additional thin bamboo stick can be inserted in the keel.

I experimented with making a simplified rogallo from an A4 sheet of paper:

• too flimsy with paper alone, the folded leading edges are too weak to maintain form.
• it is easier to fold than to curl, When I thought about it, two cones can be represented by 2 folded cones, isn't that the Dart280 idea?

So the conclusion is, without the supporting frame, paper itself is too flimsy, CG was definitely wrong and the flying speed required for a glide was apparently fast which isn't what I'm after. If supporting frame is required, then might as well use lighter sail material?

AutoGyro

21 March 2024

I watched on Youtube a video of indoor autogyro. They are hard to set right and even when they are trimmed, the performance is mediocre at best. When some of them tripped against the wall or ceiling, most does not recover. Of those that flew without accidents, their ascent is steep with the propeller thrust and their glide descent is also steep, looks like they are using relatively torquey rubber motors.  They mostly have 3 to 4 blades of narrow chord on a rotor that is balanced and spins well with just a wave of the model. In comparison, normal airplane models seem so much easier.

Here's an idea for the design of a 4 bladed autogyro rotor for rubber-powered indoor flights.

It appears that the autogyro can be trimmed by increasing or decreasing the angle of attack.

On a clock-wise spinning autogyro, when viewed from top, twisting the blades to increase or decrease will result in variation to the unequal lift, thus changing the direction of the flight like a flat wing's ailerons. Most autogyros have the rotor at an angle of attack to the flight path, some dihedral also for slight stability, largish horizontal stabiliser and fins but the overall length of the fuselage is short, thus it isn't too effective, especially for directional stability, thus requiring fine adjustment of the CG. The 'roll' though can depend on the previously mentioned blade adjustment, but if the model has horizontal stub wings, that can increase the adjustment ease and aid in roll and pitch stability.

To get a rotor that I can adjust the angle of the blades, the fixation to the hub need to be adjustable, here's how:

The hub can be a piece of firm foam, either a circular disc or a square disc. Cut slots to the disc, dissecting at 90degrees for a 4-bladed rotor or at 120 degrees for a 3-bladed rotor.

The slots will accept the blades bamboo rods and by friction alone, allow adjustability. Glue the rods to the hub only when satisfied with the dihedral and blade's angle of attack.

The top and bottom hub surfaces can be reinforced with 1/32" ply pieces or just plastic pieces. Insert a plastic tubing through the centre of the hub.

As re-written by Gemini:

Adjustable Rotor Design for Indoor Rubber-Powered Autogyro

This design proposes a simple and adjustable rotor system for a lightweight, indoor rubber-powered autogyro. The key feature is the ability to fine-tune the angle of attack for each rotor blade, allowing for precise trimming of the aircraft.

Core Components:

• Hub: Constructed from lightweight but firm foam (disc shape - circular or square). Slots are cut into the disc at 90-degree intervals for a four-bladed rotor (or 120 degrees for three blades).
• Blades: Bamboo rods are inserted into the slots, allowing for adjustments in blade angle. Friction holds the blades in place initially.
• Reinforcement: Thin ply or plastic pieces are glued to the top and bottom of the hub for added strength.
• Drive Mechanism: A plastic tube is inserted through the center of the hub to accommodate the rubber band drive mechanism (not described here).

Adjustability and Trimming:

• The friction-based slot system allows for easy rotation of each blade, enabling adjustments to the angle of attack. This directly affects the lift generated by each blade and is crucial for trimming the autogyro for stable flight.
• Once the desired blade angles and dihedral (optional) are achieved, a small screw or locking pin can be added at the base of each slot to secure the blades in place.

Considerations:

• Balancing: Adding or removing material from individual blades for angle adjustments can disrupt the rotor's balance. To maintain balance, consider marking or numbering the blades for re-installation in their original positions.
• Dihedral Angle: While 90-degree slots allow individual adjustments, achieving a true dihedral effect (where opposing blades have a slight upward angle) might be challenging. Pre-cutting the bamboo blades with a slight dihedral angle before insertion could be an option.

This design offers a simple and effective method for achieving adjustable blade pitch in a lightweight indoor autogyro. With some refinements for securing the blades and potentially achieving a dihedral angle, this concept has the potential to improve the flight stability and controllability of your rubber-powered aircraft.

5 March 2024

Designing an Autogyro Rotor

Here's an outline for the design of a simple autogyro rotor for a rubber-powered model plane.

Balancing Lift and Area:

• The autogyro needs less wing area compared to a fixed-wing aircraft for similar lift due to its spinning rotor.
• While the target wing area for the model plane is 24 square inches (12" span, AR 6), the rotor blades can have a combined area of around 16 square inches.

Rotor Design:

• The rotor will have two 8" x 1" balsa wood blades, totaling 16 square inches, which is 2/3 the wing area and has a span of 167%. The rotor disc area is however, much larger.
• A 4" "zero lift" hub will connect the blades, resulting in a total rotor span of 20 inches.

Hub Construction:

• The 1/2" wide hub will be made of three parts: a 4" horizontal balsa beam, a flexible plastic strip 6" long, and a short 1" length of plastic tube.
• The plastic tube will be glued perpendicularly to the horizontal beam to serve as the central pivot point.
• Stoppers, which can be strips of 1/16" balsa, will be attached to the plastic strip to create a slight upward angle for the blades (static coning) and enhance stability.

Blade Construction:

• Two airfoil blades will be made from 1/16" balsa wood.
• The trailing edge of the blades will be thinned to 1/32" to 1/64" for the rear half to improve airflow.
• The leading edge will be sanded to a slight taper for the front quarter with a slight radius underside.

Assembly:

• Chamfer the ends of the horizontal beam and glue the plastic tube perpendicularly.
• Glue stoppers to the flexible plastic strip at a slight angle.
• Punch a hole in the center of the plastic strip and insert it through the bottom of the horizontal beam.
• Apply glue and secure the stoppers against the chamfered edges, then let dry.

Building the Rest of the Autogyro:

Tail Assembly:

1. Motor Stick: Cut a 10" x 1/4" x 1/8" balsa motorstick.
2. Motor Bearing: From an aluminum can, cut a strip and bend one end to form a bracket, use a pin so that the propeller shaft can pass through. Bind and glue this to the motorstick as a motor bearing.
3. Tail Hook: Bend a Z-shape from a paperclip and glue it to the motorstick.
4. Tail Feathers:
   • Fabricate the horizontal stabilizer and vertical fin from 1/16" balsa square strip.
   • Cover one side of each with tissue paper.
   • Glue them to a 4" long, 1/16" balsa square tail boom.

Rotor Mount:

1. Mast and Support: Cut a mast and overlapping angle support from 1/8" balsa square strip.
2. Shaft: Straighten a paperclip and cut a 1.75" length.
3. Attaching the Shaft: Glue 1/2" of the shaft to the top of the mast, leaving 1.25" protruding.

Final Assembly:

1. Glue the tail boom to the motorstick's rear end.
2. Assemble the propeller and rubber band on the motorstick.
3. Find the balance point of the motorstick.
4. Glue the rotor mount to the motorstick, aligning the mast top with the previously identified balance point.
5. Insert the rotor onto the protruding wire shaft, add a glass bead, and glue another bead on top to secure it.

19 February 2024

Teetering Offset Hinge for 2-bladed Indoor Autogyro

Have the 2 bladed rotor prepared.

They are two identical airfoil blades connected to a rectangular strip of plastic. 

Mark out the centre of the rotor and draw a slanted line at 30-45degrees on the plastic strip.

Crease on the slanted line and bend up 5-10degrees on each blade, this will the 2 blades to form a cone angle, works like dihedral and decalage and each blade will have a negative incidence of 5-10 degrees.

Fold a rectangular strip of aluminum (from aluminum can) into a 'M' shape.

The spin shaft pass through the 'V' in 'M' and close the 'V' until it is back to back, glue the shaft in position.

Bend the two 'I' in the outerflaps so that it flares upwards.

Glue the outer flaps to the centre of the rotor along the slanted line.

Now we have a rotor with a perpendicular shaft that will spin freely in the autogyro model plane.

5 February 2024

This is an idea of construction for a small hub for 2 bladed rotors that may be suitable for small and very light autogyros. The rotor is teetered and hinged so that there is some form of correction for asymmetrical lift.

Material list:

• Paper cut to hub-shape
• Right angle balsa/foam spacer pieces 
• small plastic/paper tube
• thin pvc sheet that is flexible and springy for 
• shaft either of CF or paper clip
• bearing made from beads and or thin plastic/metal washer 
• Disc stoppers made with paper/paper card/plastic/wire/rubber etc.

Draw a big T on the plan. Cut 2 pieces of paper to the shape of the hub. Lay 1 piece of hub-shaped paper on the plan. Cut a piece of tube to the horizontal hinge length. Insert a temporary shaft into the tube and lay it over the hub-shaped paper. Cut a piece of tube to the vertical tube length. Insert another temporary shaft into the tube and lay it over the hub-shaped paper. Cut 2 spacer pieces to shape and glue to 1)hub-shaped paper, 2)horizontal and vertical tubes. Sand spacers flush to top of the 2 tubes and glue another hub-shaped paper over it all. Remove the temporary shafts. Cut the horizontal tube and remove the centre portion which will be the pivot tube. Cut the thin pvc shape and glue the pivot tube at the offset angle in the centre of the thin pvc shape. Glue the blades on the thin pvc strip. 

On the actual shaft, glue a stopper, insert the vertical tube, bearing and stopper. Glue the blades to the thin pvc strip. thread short shaft through the horizontal tube and secure the ends from falling out.

Now, this is building up the rotor hub, if we used paper clip as the shaft, we could bend to shape and if it retains under stress, it would be simplified.

Material list:

• small plastic/paper tube
• thin pvc sheet that is flexible and springy for 
• shaft from paper clip
• bearing made from beads and or thin plastic/metal washer 
• Disc stoppers made with paper/paper card/plastic/wire/rubber etc.

Cut the thin pvc shape and glue the pivot tube at the offset angle in the centre of the thin pvc shape. Glue the blades on the thin pvc strip. This is the rotor.

Bend the paper clip; first a 90 degrees bend, another 90 degrees bend so that it runs parallel, and another 90 degrees bend so that it is perpendicular. Maybe the bent shape will open up, maybe it will remain. Insert stopper, bearing, horizontal pivot tube, bearing and another stopper. Then the assembly is inserted to the vertical pivot of the model and add bearing and stopper. 

Another method

Material list:

• Balsa block/laminate
• Aluminum brackets from aluminum can
• small plastic/paper tube
• thin pvc sheet that is flexible and springy for 
• shaft from paper clip
• bearing made from beads and or thin plastic/metal washer 
• Disc stoppers made with paper/paper card/plastic/wire/rubber etc.

Make a rectangular hub base from balsa block or laminates of thinner balsa. Insert and glue a straight length of paper clip, perpendicular to the hub. Fabricate 2 identical brackets from aluminum can or pivot tube from plastic tube with spacer, glue to ends of hub. Measure the distance between the brackets and cut the pivot tube. Cut the thin pvc shape and glue the pivot tube at the offset angle in the centre of the thin pvc shape. Glue the blades on the thin pvc strip. This is the rotor. Offer the rotor to the brackets and insert a paperclip shaft.

Insert vertical shaft to the vertical pivot of the model and add bearing and stopper.

Another method, using paper

Material list:

• Paper
• small plastic/paper tube
• thin pvc sheet that is flexible and springy for 
• shaft from bamboo/toothpick/carbon-fibre rod
• bearing made from beads and or thin plastic/metal washer 
• Disc stoppers made with paper/paper card/plastic/wire/rubber etc.

Cut the paper to hub template. Fold in half. Glue the shaft and pivot tube. Cut to release the central pivot tube. Cut the thin pvc shape, glue the blades. Glue the central pivot tube at the offset angle in the centre of the thin pvc shape. This is the rotor. Offer the rotor to the pivot tubes in the paper hub and insert another shaft.

Insert vertical shaft to the vertical pivot of the model and add bearing and stopper.

29 December 2023

Spinning propeller. spinning rotor

Keep the disc of propeller or rotor spin true, or just less wobbly. That means the bearing holes must have some play but not too much and be spaced a good distance apart.

Bearing structures could be made from thin aluminium sheet with the holes pierced then folded to the hub.

The hub may be 2 identical sheet balsa pieces to anchor and spaced apart the folded bearing structures.

Since the hub is sheet balsa, it will provide good gluing surfaces to the 2 blades.

Distance between bearings, the "height" or "depth" of sheet hub, may be 1/4" for 3-7" prop and 1/2" for 20" rotor. 

Propeller shaft is perpendicular to sheet hub. Rotor shaft can be angled to create a conical disc.

Propeller and rotor shafts may be flat to glue directly onto the sheet hub or they may be thin carbon fibre rods so that the angle of attack may be adjusted. If adjustable rods are used, the holding structure may be tissue/paper, pressed over the rod and glued with superglue on to the sheet hub.

To fold the bearing structure, a former can be used. A former can be 2 pieces of hardwood (ice cream stick), with one edge square and a pin perpendicular to the edge to locate the hole in the bearing structure. Then a plier to fold the aluminium over the same edge.

The blades may be like a paddle where there is no twist between root and tip. Or, the blades may be twisted to form something of a helical pitch.

There is no perceivable benefit to have tip weight to the propeller blades but it may be beneficial to have tip weight to the rotor blades to introduce some momentum stability while the rotor spins.

Rotor constructed above does not have flapping hinge.

Thin rotor blades may bend under flying load and cause something like flapping hinge but there's hardly any control of the hinge axis.

Flapping hinge is beneficial to rotor blades to avoid roll-over.

The flapping hinge may be set at an angle to introduce negative angle as the blade hinges up.

The limit of hinge may be a pair of simple thin aluminium bracket at the flapping point.

6 July 2023

Foam blades with CF rod as spars

1. Blades from foam dinner plates. 
2. Glue CF rod to blade.
3. Balance.

Cardboard hub

1. Draw and mark hub strip on cardboard. 
2. Punch holes according to mark.
3. Fold ends to form isoceles triangle.
4. Make aluminium bearings from drink cans. 
5. Cap the top of the isoceles triangle cardboard hub with the top folded aluminium bearing and add the bottom bearing to the base of the isoceles triangle.

Assembly

1. Insert CF ends of the blades through the isoceles triangle hub.
2. Insert Shaft through the bearings.
3. Adjust and balance.

If the isoceles triangle is used with the base as the top, we have a flat top bearing surface which is better since the lifting/dragging force pushes against the top stop of the shaft. The sides are used as tensile members. The ends of the sides can be lapped to the counterpart side.  

3 July 2023

Paper blades

1. Rectangle blanks, equal lengths, width at 150% of chord. 
2. On underside, mark at 50% chord along span.
3. Crease fold the longer 100% of chord width, the crease line will be 50% and the long edge meets the marked 50% chordline.
4. Slit along marked chordline, glue paper tabs to secure, top of chord and bottom of chord. 
5. Cut 1/32" balsa spars to width of 40% chord.
6. Insert balsa spars to paper blades' pockets, ensure they are identically placed in each blade.
7. Spot glue the balsa spars to the tip and root of the paper blades.
8. Join the balsa spars to the hub and a rotor disc is formed. Could use the balsa spars itself to make the bottom hub.

22 March 2023

Today I am thinking about leverages for pitch roll and yaw stability.

If the rotor is flat, it can't provide any leverage.

Pitch stability

It could be an elevator at the back or a lifting plane at the front. Which is more effective? In the front lifting plane, it would be at the verge of stalling. Front fin would destroy yaw stability, so my choice would be a rear elevator.

A wing can be pitch stable itself, this involves having lifting portion and stabilising portion of the wing front and rear respectively.

A rotor with a dihedral angle will have this form of pitch stability as well.

Yaw stability

It would be a fin at the back. 

Roll stability

It could be by the center of gravity, but more likely some dihedral is required so that together with the fin, there will be less slip.

A dihedral rotor ought to have roll stability too, but I am thinking it is not constant and need supplementation.

To supplement, I think the pitch and roll stability can be enhanced with a lifting plane just in front of the rotor.

So actually, the rotor could be flat without any dihedral if the pitch and roll stability are mainly by a lifting plane. Using the spinning rotor as a additional lifting/dragging device. 

In a beautiful world, a conical rotor only need a fin (for yaw stability).

Differential thrusts changes the pitch, the yaw and affects the roll slightly.  

3 March 2023

Paper blades and ribs.

Ribs: Glue halved paper ribbons to spar.

Blade area: Cut blanks, do a fold, glue to spar and ribs.

That way the ribs can be adjusted for incidence and curled for airfoil.

1 March 2023

Conventional: Tube bearing, bent up tabs, strings and disc

As many rotor blades as needed is made identical with longish spars. 

At root end of each spar is secured an aluminum tab from aluminum can.

Have the central plastic tube surrounded by the aluminum tabs and secured the exposed aluminum tabs against the tube and open up the spars like petals around the pistil. Then glue the blades on each spar, secure with a central disc and adjust.

If the blades are already on the spars, just arrange them with a jig on the tip of the blades.

A disc of card, foam or anything like that with a central hole, is used to lock the tube's perpendicular position, the position of each blade around the tube, and the dihedral angle.

Spars can be made from balsa strips, or carbon rods.

Tabs or joiners to the tube, can be aluminum sheet as mentioned above, or cotton thread.

28 February 2023

How about a cone as the rotor?  It wouldn't spin. What makes it spin? Oblique airflow pushing the blades forward. So what is needed? Some openings in the cone for the air to rush by obliquely? Or just some negative incidence? But there appears to be zero incidence blades and why not?

Try a paper cone with 50% cutouts, the root and the tip will be solid rings. At the top is paper cross pattern to locate the central hub which is a paper tube. Acting like flat blades and adding area to rotor surfaces.

An inverted cone = some camber, more chord = more camber. Very draggy.  But autogyro is draggy and drag contributes lift?

Will location of opening affects anything? It's a 360 conical disc, why should it? Shape of openings? Is circular holes, oval holes, triangular holes, half circles one way or the other way or root or tip? 

27 February 2023

Hub for 3 or 4 bladed rotors, with a different assembly

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. If it is to be a 3 bladed rotor, then there is 3 spokes.
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue the arms over the hub piece (don't need chamfering, think of it as adjustability).
5. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
6. Remove the arms and bottom hub.
7. Lay the top hub upside down through the spindle, over the plan and line it up to the work plan.
8. Bend up each spoke of the top hub to a jig, fold down the tab and remove.
9. Re-insert the arms and bottom hub to the spindle.
10. Drop the top hub to the spindle and glue the tabs to the arms.
11. Strip identical spacer strips (same height as the jig) and glue to top of the arms and the bottom of the top hub. Alternatively, a tube can be used but it shall be inserted between steps 9 and 10.
12. If the top spokes are too weak, glue balsa strips to reinforce the top diagonal spokes.
13. Remove assembled hub from work base.

Hub for 3 or 4 bladed rotors, with a round tube as upright

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. If it is to be a 3 bladed rotor, then there is 3 spokes.
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue the plastic hollow tube to the hub piece, vertically.
5. Glue the arms over the hub piece (don't need chamfering, think of it as adjustability).
6. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
7. Chamfer a piece of balsa sheet to meet the vertical tube and the arm, strip to make the corresponding number of diagonal struts.
8. Glue the diagonals to the work piece.
9. Lay the top hub piece through the spindle, over the tube and bend to meet the diagonals and glue in place, 
10. Remove assembled hub from work base.

Hub for 3 or 4 bladed rotors, built up 

1. Cut out the top and bottom aluminium shape, punch hole in the centre. In case it is a 4 bladed rotor, the hub piece is a cross-shaped sheet. 
2. Make a work base that will support the spindle, glue the work plan over the work base.
3. Lay the bottom hub piece through the spindle, over the plan and line it up to the work plan.
4. Glue uprights to the hub piece.
5. Lay the top hub piece through the spindle and over the uprights. Bend to meet the uprights and glue in place, 
6. Glue the arms over the hub piece (chamfered for dihedral).
7. Bend up the arms to dihedral height over the work base, use a dihedral jig. Start with one arm, then turn and do the bend on the next arm until all arms are bent to the dihedral jig.
8. Chamfer a piece of balsa sheet to meet the upright and the arm, strip to make the corresponding number of diagonal struts.
9. Glue the diagonals to the work piece.
10. Remove assembled hub from work base.

10 January 2023

hmm.... just a criss and have the blades as the cross. Reinforce with aluminium strips for the bearing points.

6 January 2023

Foam blank with 45degrees bent to provide negative incidence and dihedral

Tin can aluminium strips with double 45 degrees bend to support the blades at top and bottom.

The bottom strip may be bent at the axle hole or bent into a curve.

The axle passes through the bottom strip, foam blank, and top strip, anchored at the bottom, guided by a wire loop, through the rotor assembly, a single bead and secured at the top with a 90degrees bent or stopper.

Foam blank may be extended with paper sails supported by strips which are glued to foam blank, treat the foam blank as a spar.

6 December 2022

No suitable nozzles? How about carbon rods, paper clips and some ready at hand stuff? 

• A short piece of carbon for the blade shaft and at both ends, tie a Z bent paper clip
• Glue blades on the Z bent wire flat over the table
• Bend for dihedral and twist for incidence
• Glue the spindle rod perpendicular to the center of rotor, reinforce with thin card patch or other means.

5 December 2022

Re-using Covid ART nozzles for spinning Hub and dihedral blades. 2 blades rotor.

If the chosen carbon fibre rod fits tightly in the nozzle hole:

• ice cream stick with hole in middle
• thin aluminum strips to ends of ice cream stick and blades
• Bend the aluminum strips to give equal dihedral and angle of attack 
• Covid ART nozzle hotglued to ice cream stick, over the hole, I prefer bottom.
• insert carbon fibre rod through the nozzle and the ice cream stick

If the rod spins freely (but not too wobbly) in the hole in the Covid ART nozzle kit, insert the rod through one nozzle, sandwich the icecream stick and then another nozzle. Once satisfied, glue the nozzles to the ice cream stick.

11 November 2022

Spinning Hub

• A piece of round or square cardboard with a centre pivot hole. Or a pyramid formed from 4 triangles or ring of 4 triangles, so that this pivot hole is set above the cross-piece pivot hole. (can also have a square cardboard supported by 4 perimeter cardboard spacers or a central single piece spacer with a larger hole in the centre) 
• A piece of cardboard cut to a cross shape with a centre pivot hole.
• The 4 arms are bent to 15 degrees angle, superglue applied to lock the 15 degrees dihedral and decalage.
• The ends of the 4 arms are cut to 15 degrees angle.
• The pivot holes are cored to fit the shaft and reinforced with superglue, since they are made from cardboard.

Flapping Blades

• Root of each blade (4 in total) is a small triangle with a 15 degrees cut to match cross piece.
• Leading edge is a piece of balsa or foam, glued to the root piece.
• Root chord and tip chord is balsa or bamboo.
• Covered on top with 70 g/sm photocopier paper
• Flapping hinge is a trapezoidal piece of flexible foam.

Assembly:

1. Pin the hub in the centre pivot hole, use the same 15 degrees jig to raise and superglue the 4 arms so that the arms is raised to 15 degrees. When one arm is set, rotate the hub and do the next arm.
2. Remove pin, place scrap pieces of flexible foam under the cross piece and re-pin. This raises the entire cross piece, letting the blade to slid under,  
3. Glue flapping hinge to underside of each blade, slip and glue the flapping hinge under the cross piece, make sure a gap of 3mm is between the cross piece and blade root.
4. The 15 degrees jig will support the blade while the glue set.

23 September 2021

Sure Fire Autogiro

Rake: 3/8" over 6"

Slant: nil

Dihedral (each blade): 2.3/4" over 13"

Angle of Attack: 0

Blade x2 clockwise: 11" x 2.3/8" paper

Downthrust: similar to Rake

With horizontal stabiliser

Cierva Autogiro

Rake: nil

Slant: nil

Dihedral (each blade): nil

Angle of Attack: negative 1/8" over chord

Blade x4 anti-clockwise: built up

Downthrust: nil

With roll paddle and elevator

Can't find more.

If blades can be set zero, one less to get wrong.

Rotor hub can be made from a piece of flat wood, paper clip bent to give dihedral where blades are patched.

Blades can be balsa built up with paper

22 September 2021

How about plastic tubes for the hub? If doing a very light version, bent plastic tubes from cotton bud may be enough. 

Bend 2 lengths of plastic tubes in their centre by crimping. (the dihedral effect)

Glue bent plastic tubes at right angle to each other. (4 rotor blades)

Prepare jig to hold the crossed plastic tubes evenly.

Example of a jig: one centre pin, 4 spacers to support the crossed tubes.

Pierce centre, enlarge for shaft.

Use a temporary shaft, tie the crossed tubes with thread and glue.

Prepare 4 rotor blades.

Using previous example of jig: add a triangle to one of the spacer. The triangle set the angle of attack of each blade. Can add blocks so that each blade will be located at the same place.

Glue each blade in turn.

Or, to make the angle of attack adjustable by gluing a bamboo stick to each blade and insert the bamboo into the tubes. Doesn't fit? Sand down before gluing to blade or split the tubes' ends.

A 2 blade rotor with doweled blades would be:

1. Pierce a hole in the centre of a plastic tube, enlarge hole to shaft diameter.

2. Bend up for dihedral, not in the centre of the tube, just a short distance away to avoid skewed hole.

3. Insert blade, adjust to angle. Just eyeball and spin the rotor.

Shaft shall be from a paper clip? It is easy to bend.

9 April 2018

On Sunday, I tried Version 2. Version 1 had a bamboo boom and vertical tail. Version 2 had foam fuselage, horizontal stabilizer and 2 tip fins and  affixed to the other components of Version 1.

I tried running start to spin the main rotor fast at full throttle. The initial launches rolled right and crashed within a foot away. I finally got a left arc about 2 m away after having adjusted the model to have left rudder, left weight, and left rotor. The 8.5mm motor and 56mm propeller seems incapable of overcoming the drag.

The fooling around stopped after I noticed my sewing pin is bent. Maybe next time, I can try rotors with flapping tips. From the anticlockwise prop (from front), anticlockwise rotor (from top), I can have left thrust, left weight, left rudder and left rotor. Or I am also thinking of normal elevator and rudder and if one rotor does not balance, twin rotors. I need also better pushrods then the soft wire can afford.



Version 2

These did not grip the thin soft wires I am using and the nuts get loose easily.



Version 1, as the motor stick is screwed, thrust direction is adjustable. The hotglued boom came loose easily and the bamboo size lacks torsion strength.




While making Version 1, I originally thought of making it a pusher.

5 October 2017

Previous was using plastic tubing, how about just beads?

This will limit the contact of the axle to the two points on the hub.







The ice cream stick option has the blades at 0 degrees. Pack with beveled pieces at the blade holding area, or instead of beveled pieces with balsa blocks that has angled saw cuts (similar to sketch on right), the blades will be held at an angle. Or, maybe we can leave it at 0 degrees, and use flat blades that have toe-in/toe-out near the tips by angling it upwards, which ought to propel the blades.

Or how about a spinning disc, spun by peripheral winglets? The centre area is slow anyway and can't possibly have much difference whether it is spinning slow, fast or not at all. When the disc stop spinning, it's still a larger flying surface than is possible with the normal blades' area.

Change the kite to an autogyro? I think a tractor propeller and a large tail is good.

1 February 2016

Even-Bladed Hubs

Too much theory only ends in theory and I get confused. Maybe just try the following. If I set the blades carefully, I could have some coning too.

2mm dowels from Daiso (Basswood?) for hub and blades leading edges.
2mm foam blades (from Daiso) are glued to the 2mm dowel leading edges and wrapped in "Scotch" tape.
Large heat-shrink sleeves to set the angles and dose of superglue when set is as desired.

How about a Cootie but with this blade hub?

16 September 2015

On the following chain of thought, of which all hypotheses are without any substantiation or even personal experience:

1. Negative angle of attack is necessary to get the rotor spinning in the correct direction against the model's direction.
2. Lift or drag of the rotor amounts to the same thing, it lifts the model so long as there is some element of vertical vector.
3. Negative angle of the rotor blades is not too critical, even if it is at -45 degrees, there would still be 'lift' (point 2 above), except that we shan't go there because everyone will tell you it's wrong and I won't be needing that! (And also for point 12 below.)
4. The angle the entire rotor is presented to the wind has to be positive. I think this is the most important aspect. If it were negative, the model sinks instead of rising.
5. Combining point 3 and point 4, if there is not enough negative angle of the blades, at some point it could become a positive blade angle to the wind if the positive rotor angle is excessive. If a blade angle is positive to the wind, then it would retard the spinning rotor because it would attempt to spin in the opposite direction. The rotor would then stall, and hence a faster spinning rotor is safer than a slower one.
6. Carrying on from point 5, this mean that the negative angle of blade must be greater than the positive angle of rotor.
7. The torque of a free spinning rotor is unlike a motorised rotor. The torque is in the same direction as the rotor direction. Hence, if a tractor propeller has left torque, the rotor should spin clockwise when viewed from top because the blade going against the direction of the wind will create more lift, in this case, the left half of the rotor has more lift then the receding right half of the rotor.
8. Since the rotor is functioning as a wing, dihedral would be desirable if we are using rudder to turn the model. Air flowing through the rotor will tend to cone the rotor in the correct direction, yet the faster it spins, the more centrifugal force of the blades will flatten the cone.
9. Should the blades be like a normal flatbottomed airfoil or should it be mounted inverted instead? If it is mounted like a normal airfoil then the rotor would have more lift because of the downwash. If it is mounted inverted, we are having air directed upwards and therefore there would be less lift and more drag.
10. Carrying on from point 9, the main objective should be to have the blades advancing with the least drag and therefore, a thin non-cambered foil is desirable. Something that has a smooth entry and exit.
11. When the model flies faster, the rotor spins faster and the model rises, so downthrust is required to 'lift' the tail.
12. If there is no elevator to lift the tail, the flyable CG range is very limited and the downthrust has to do the 'lifting' of the tail. There is no lift when downthrust equals negative angle of blade and hence the tractor propeller should be set at a greater negative angle.
13. For a simple rotor, the negative angle of the blades shall be fixed. If the positive rotor angle is 8 degrees and we desire a negative effective angle of 3 degrees, this means the blades are set at 11 degrees and the effective downthrust angle is 3 degrees.
14. When the propeller is lower than the rotor, and assuming it is not a very long way infront of the rotor, there is a upwards turning moment. Therefore the downthrust angle has to be set greater than 3 degrees. However, if we have a stabiliser set at a positive angle leewards of the propeller, the stabiliser would have some downthrust to pitch the model down when forward speed is increased.
15. A simple autogyro with the following parameters: A coned rotor with blades set at 11 degrees negative is set 8 degrees positive (round disc don't really stall) to the datum line. Motor is set at 3 degrees negative and stabiliser at zero degrees.