Back to modelling youth: Druine Turbulent

5 November 2024 (Overthinking?)

The curved slanted root

The next step is to make the pair of wing panels. The plan of the left and right wing panels show the root ribs are to be slanted (for dihedral) but are otherwise straight. The top view plan of the fuselage is clearly curve at the junction and the fuselage box structure has been completed. 

1. These curved root ribs are to be installed without extending the leading and trailing edges.
2. Two oversized piece of balsa are wetted and curved to match the fuselage curve.
3. Tape these curved root ribs to the fuselage.
4. Jig the fuselage and wing panel so that they have the correct dihedral angle relationship. The incidence is only tweaked when gluing the wing panels to the fuselage. I am probably overthinking if it is possible, to make a single re-usable jig that can be used for both panels for this temporary set up process and the final gluing process.  
5. Superglue the wing panel to the curved root rib, add gussets.
6. Remove the wing panel by unpeeling the tapes and sand the bottom of the curved root rib first, follow by the top of the curved root rib.

Point 4, a beam type of jig for dihedral and a cradle type for root incidence may be easiest.

I am probably overthinking about the curved root ribs. In order to get the oversized curved root ribs to have the airfoil shape in Step 6:

1. Superglue 2 pieces of balsa template that mimics the dihedral on the curved blanks.
2. Sand the bottom of the curved blanks until the base is flush with the balsa templates.
3. Measure the height of the normal straight ribs at the points where the balsa templates are and transfer this to the curved blanks.
4. Cut roughly to shape and proceed to Step 4, the markings will guide the final sanding to airfoil shape matching the normal rib airfoil in Step 6. 

Propeller shaft

The following instruction is when viewed downwards. For the simple hook, 1) use a vice and grip the short end of the wire across the shank of a vertically placed drill bit, the wire being near side 2) pull the free end around the shank clockwise beyond 180 degrees, 3) relax the vice and remove drill bit and the single coiled wire, 4) adjust the coiled wire so that the coiled wire appears to have a straight entry and straight exit, 5) grip with round nose plier and bend the longer end, adjust until it appears to bisect the loop, 6) cut off the other end of the wire leaving a gap for the rubber to pass through. 

Over thinking? This is almost as complicated as doing the reverse S hook.

Maybe a pair of round nose pliers bend in the air is enough.

For diamond hook, similarly, a pair of round nose plier to get the 2 critical points correct, the lowest point and the highest bend that is the shaft. Whether the other bends are perfectly right angled or round loop shouldn't matter.

I think I'll do the propeller shaft after the full model is trimmed as a glider. I'll have enough time to think if I should use a plastic tube as a bearing or I can use the aluminum from a beverage can to face the removable nose block as a bearing surface.

Modelling weight

I discovered that in the past, modelers used plasticene to balance the model. Plasticene has inherent disadvantage which I dislike. It appears oil is present in the product, I had to wash my hand with soap or it won't be cleaned. I noticed also that it stains balsa wood, and dropped off easily on my chuck gliders. Sand and small particles are attracted to plasticene. Therefore, it does not appeal to me.

Blu-Tack is a relatively modern product that is cleaner and stickier, although it is more expensive.

I'll use Blu-Tack when balancing my model. I can use it on tissued surfaces.

Balsa Cement

I read that balsa cement was a favorite with modelers when gluing on the horizontal stabilisers for free flight model. When more or less tail incidence is required, the modelers dissolved the joints with solvent and re-glue. So smart, I thought, I didn't know that.

Disappointingly, balsa cement is not readily available anymore. Superglue, a relatively new product, is readily available. I think I can use superglue in lieu of balsa cement and use acetone/alcohol/nail polish remover to dissolve the joints.  

 

Wheels

This is overthinking. To make 1" wheels from extruded foam.

Yes, I can make true spinning wheels using a drill and sandpaper, but this method does not appeal to me.

Method A

1. Make a 90 degrees perpendicular cut on the extruded foam sheet.
2. Using double side tape, stick two Singapore $1 coins to both sides of the foam sheet, the coins being directly on the 90 degrees perpendicular cut.
3. Cut or sand away the rest of the foam around the coin.
4. One advantage of using coins is that it is metallic and you can hot-wire cut perpendicularly the foam.
5. To save effort, you can stack 2 pieces of extruded foam sheet after step 1, aligning the foam sheet 90 degrees perpendicular edges.
6. Remove both coins and use a circle template to locate the centre of the foam discs.
7. Pierce the foam discs with thin wire, ream with drill bit, glue the axle bearing. 
8. Axle bearings may be short sections of plastic tubing or rolled paper tubing.
9. The coin's diameter is less than 25mm, glue paper strip around the discs until it is 1" in diameter.
10. Sand the wheels to shape.

Method B

1. Rough cut 1.5" square 6mm foam pieces. Make more, if you need 2 make 4.
2. Pierce the foam pieces with bamboo skewers.
3. Make a jig from corrugated cardboard, it has a 1" slot that is about 30mm wide.
4. Bend 2 spindle saddles to allow the bamboo spindle to rotate freely within.
5. Position the saddles so that they are 13mm from the edge of the jig slot. 
6. Place the hot wire bow cutter at the entrance of the slot and by rotating the skewer, the hot wire will cut the 4 discs of foam pieces.
7. Cut a pair of disc from thin aluminum or transparency sheet for each wheel.
8. Pierce each disc with a sharp pin for the axle.
9. Remove the foam discs from skewer and glue the thin axle bearing discs against each face.
10. Sand the wheels to shape.

I think I will choose method B because I have a small bow hot wire cutter and I can use the jig for many wheel diameters by adapting the jig. This method is also suitable for straight simple cones and an adaptation of this method can hot wire cut straight transitory cones using base and tip templates.  

Method C

This is the simplified method B and is without the jig board, steps 1, 2, 7-10 are identical.

1. Rough cut 1.5" square 6mm foam pieces. If you need 2, make 2.
2. Pierce the foam pieces with bamboo skewers.
3. Insert a circular cardboard template to each end of the foam. Simply draw the circles. pierce the centres and cut with a pair of scissors. 
4. Hold the skewer in non-master-hand and the hot-wire bow cutter with the master hand, slice against the templates.
5. Cut a pair of disc from thin aluminum or transparency sheet for each wheel.
6. Pierce each disc with a sharp pin for the axle.
7. Remove the foam discs from skewer and glue the thin axle bearing discs against each face.
8. Sand the wheels to shape.

I think I will choose method C now because I have a small bow hot wire cutter and everything is literary done by hand.  

4 November 2024 (12 hours?)

Decades later, the wizened youth rediscovered his creative spark. Now that I know what I know now and have what I did not then, it becomes easy.

I made a few photocopies of the plan  Oz : Druine Turbulent plan - free download and pasted them on some corrugated cardboard. Covered with transparent packing tape, these are my small, light, cheap and fast building boards. The packing tape and corrugated cardboard provides a surface where I can superglue balsa components and if necessary, to cut, for these reasons, I call them my jig boards.

Here, the fuselage side frames is superglued on the jig board and the spacers added, start with the longest and end at the tail and nose.

I deviated from the plan and tried laminated tips. Each tip is a single balsa strip with a few slits. The strip was wetted and superglued on the jig board. Nudging the strip with my fingers and a 10 cents coin (the 5 cents coin is a bit too thin), I spot glue the slitted slip to hold the curvature. Progress until the other end is reached.

The glass of water was not for drinking. It's for wetting balsa strips.

Here, the left handed wing tip will be discarded, it is not long enough.

This jig board is to build the right wing, I pasted the wing tip of the left wing over it. This way, the same jig board can be used for both wing panels.

The slightly rusty carbon steel guitar string is 0.38mm diameter (PL015).

A masking tape was laid on the cutting mat and drawn as shown. 

Lift one edge of the tape to slip in the guitar string, then fold over, and the small marks show where to bend. 

Here, the string is bent but not cut, and the masking tape has to be removed. 

Try to bend it symmetrically. It probably won't happen, but you can tweak it after the tape is removed.

Tweak the wire against the plan. The wire is so small that I can tweak it without pliers.

When satisfied, or in my case, when I gave up, I taped the wheel axles with masking tape onto the plan. The balsa piece below the wire has been test fitted to the fuselage. 

  

Later, I tissued over the wire and balsa and soaked it in superglue. I didn't feel like searching for cotton strings.

  

  

Jig for Curved laminated Balsa Strips

1 November 2024

This is for making 1/8" wide lamination from 1/16" balsa sheet.

1. Square up the 1/16" balsa sheet.
2. Slice thinly through but leave one end intact, repeat 1 more time.
3. Now slice the 1/8" strip. 

You now have a 1/8"x1/16" balsa strip that has 2 or 3 slits through most of the length.

Wet the slitted length.

Curl the slitted length with your fingers.

Superglue the intact end of the curled strip on to the packing tape protected jig board.

Nudge the curve over the plan and drop a bit of superglue intermittently on the slits to hold the curve.

16 April 2014

For a jig to form curved laminated balsa strips:

1. Prepare 2 rectangular pieces of compressed foam. Draw the inner curved line onto one piece cut along this line to separate it to form two pieces of formers, one being the inner former and the other, the outer former.  
2. Glue the smaller piece of inner former onto the second rectangular piece of compressed foam, this is the base board.
3. Select the thickness of the balsa strip. A thickness is suitable if it can be formed readily against the inner former without cracking and the finished product is functional, i.e., 1) not fragile, 2) sufficient strength for intended use, and 3) minimum of 3mm for overlapping of covering. If the strip shall crack while bending free hand, then it is too thick and the strip has to be made from thinner balsa. If the strip is too thin and fragile to be functional, additional strip to be added until the overall desired thickness is achieved.
4.  Prepare the balsa strip/s by soaking them for a good 15 minutes. Time depends on cross sectional area and hardness/water permeability of individual strip, even the temperature of water. 15 minutes would be sufficient for upto 1/8" balsa strips.
5. If using multiple plies of strip, wipe dry the strips, apply white glue to the mating areas and assemble into a single laminated strip.
6. Single strip only needs to be wiped dry.
7. Place strip/laminated strip flat on the base board and against the inner former. Starting at the end where the curvature is the least, temporary secure strip in position with tape.
8. Push the length of strip against the convex curve of the inner former starting at the taped end and lock in position with the outer former.
9. There will be a gap between the outer former and the balsa strip except at the two ends of the outer former. This is ok, because only the two ends are required to hold the strip against the inner former. Glue/pin/clamp the outer former to the base board. The force is at the two ends, these are where to put the pins/clamps.
10. Leave the strip in the jig for a day to dry out.
11. If using super glue for laminated strip, steps 4 and 5 may be omitted, thin super glue is used to tack the laminations after step 9 and the strip may be removed immediately after the super glue is set. After 15 minutes, more of the thin super glue is introduced to the laminating joints to complete the gluing.
12. Remove the curved laminated balsa strip (or formed single balsa strip) from jig and trim it to length.
13. White glue doesn't bond well to compressed foam, it is easy to prise the strip off, bending the jig slightly may help in stubborn areas. Super glue will bond or may erode compressed foam, but since they are used sparingly to tack glue the laminations, it is ok.
14. If jig is still usable, and is should be, repeat steps 4 to 12 for additional laminated balsa strips (or formed single balsa strip).  

Notes

Formed single strip will have spring back, laminated strips retain shape much better. The first choice, therefore, is to use laminated strips.

Curved line may be drawn tighter to accommodate the spring back of single strip but the amount of spring back, in the case of balsa, will not likely be consistent.

Laminations may be made from balsa, plywood, bamboo, paper, plastic, compressed foam, carbon fibre and other similar material.

White glue between compressed foam is not suitable, choose another adhesive that doesn't involve evaporation of solvent.

 

Cardboard Jigs

1 November 2024

Yesterday was Deepavali, a public holiday, and the family gathered at my place for lunch and mahjong. After lunch, I had a few hours free since I don't play mahjong. So I made a few photocopies of the plan  Oz : Druine Turbulent plan - free download and pasted them on some corrugated cardboard. The jig board is then taped with clear packing tape that was around the house. In less than 4 hours, I completed the horizontal stabiliser, the vertical fin and the two fuselage sides. It was actually quite easy, here are some key points that were different from when I was younger:

• Proper chair and table provides a comfortable work station. Compared to crouching on the floor or working on the coffee table, this is more comfortable. 
• The 1/16" balsa sheet was cut to a length that accommodates the longest member with one inch to spare, in this model, about 11". 
• With a Pilot G-2 07 pen, cross the balsa sheet on one side, and near both ends. This tells me which side I should rotate the 1/16" balsa strip to.
• Cut the required balsa strips of 1/8" and 1/16" width with an NT cutter against a ruler in smooth continuous strokes. The result is much better than making strips from 36" long balsa strip.
• Superglue was used for the joints. The capillary action works the glue into the joints. Balsa parts can be held over the jig board with your fingers before superglue is applied to the joints.
• Pressing an NT cutter onto the balsa strip, the balsa strip can be picked up and transferred to a cutting mat. This makes cutting the strips to exact length and angle easy.
• After one member is cut, align that member atop the balsa stick and cut the second member to exact length and angle by first cutting the angle of one end, and then using your thumbnail to align the ends of the member and balsa stick, before cutting the other end. 
• Fuselage spacers are duplicates. Make all the members in duplicates and set out accordingly at the top of your work space. 
• Dot the packing taped jig board with superglue to temporarily secure balsa pieces, away from the joints. No pins, weights, clamps are necessary. When frame glued, slip in the NT cutter between the balsa structure and jig board to pry off easily (#11 scalpel won't work as well as they are too short and stiff). I didn't need to bother cleaning up the jig board by swiping with solvent to remove the superglue, the jig board can still be re-used without this extra step. I did not use hot glue. If the frame was removed too early and there are still some superglue that is still wet, this will smear the NT cutter blade. The NT cutter blade is cheap and can be replaced, but it appears that it still works well for cutting, slicing and prying.
• If you press on 1/16" square balsa strip while it is on the jig board to transfer the balsa strip to the cutting mat, sometimes it will cut through and your task is done. The jig board seems to be tough enough and the cutter did not harm the jig board; I think this is because there is enough resistance from the packing tape and enough give from the corrugated board.
• Pre-curving of lower longerons was completed without template. Dip in hot water and bend by stroking the balsa strip. 

Next session, I'll have to do up the pair of wings, assemble the fuselage sides into a box structure, add formers to the top of the fuselage box, make the removable noseblock and undercarriage.

The fuselage sides will be temporarily glued upside down to the planform jig board with superglue. Start at the point of maximum curvature. Starting with the fore and aft spacer location, mark/cut the spacers in duplicates. Cut the next pair of narrower spacer and gradually bring in the fuselage sides. To handle the spacers that will be glued "in-air" (i.e. the bottom spacers) and also to help position the top spacers that is on the jig board, make a pair of tweezers or a pin prick. This is because there will not be enough space to put in your fingers. So you can start by making your tool. A pin prick is just a thin pin that is superglued to a 3" length of 1/16" square balsa, and it works by piercing it into the spacer. A tweezer is just 2 pieces of 3" lengths of 1/16"x1/8" balsa, spaced one end with a 1/4"x1/16"x1/8" balsa, assembled and glued with superglue.

30 October 2024

Added how to curve 1/16" square balsa strips using jig board and hot glue in posting of 25 October 2024.

25 October 2024

I often read of using a building board and from what I read, they are meant to be re-usable, needs maintenance and proper storage, relatively big and has a high initial cost outlay. 

The function of these yester-years building boards can be replicated cheaply. You can make it re-usable or disposable, very economically. The only requirement therefore is that it has to be flat. To differentiate from the traditional building boards, I refer them as jig boards.

• Make jig boards from flattish double walled cardboard, steel/plastic panels, wooden boards, glass/mirror by gluing on the section of plan.
• Pre curve the balsa strips over simple templates. Use tap water to wet the strips and hold in position until thoroughly dry.
• Use hot glue to temporary secure balsa strips, wet or dry.

On Hot Glue and Curving balsa strips.

1. On cardboard jig board (or those that are not meant to be used with pins), I think it is feasible to use dabs of hot glue to temporarily secure the longerons. Upon completion, it ought to be possible to pry the completed fuselage sides from the jig board, pieces of hot glue that are still on the jig board or balsa longerons can be peeled clean. Wet balsa can be hot glued to a dry jig board.
2. Spring back of balsa. Accept the fact that after removal from template, the pre-curved balsa strip will spring back a bit. You could make the template with tighter curvature to accomodate a bit of this spring back, but I wouldn't bother too much. How much spring back depends on the size and hardness of balsa, the tightness of curvature and whether we are using a single piece, double ply or triple ply. Held to the correct longeron curvature, wet the balsa again. When dried, the slight stress in the fuselage side will be present, but it has been reduced. This is the case also with tighter curved wing tips and stabilisers, the stress is inevitable and sufficient tension braces are needed to counter those stress and maintain the shape. 
3. Here's an idea for curving the 1/16" square balsa strips. Wet the over long balsa strip, position over the jig board and dab hot glue at the peak of curvature. When the hot glue has cooled, bend the wet balsa strip to conform to the curve line and dab another spot to secure. Alternating between the 2 ends of the first dab, work towards each end. Leave the balsa strip to dry thoroughly before removing from the jig board.

23 October 2024

I bought my wife a new ladies golf set, in came in a stout double walled cardboard box. We could keep the box and next time we want to travel (by air) with her golf bag, we could simply re-used the box. Just seal it up and it will be perfect golf case. She decided she does not want that, so the cardboard box has been cut up and I have a good supply of double walled cardboard pieces that I can use as jig boards, templates and carry boxes for my future builds.

Since it is 'free', my imagination will not be hindered. I can use pins, tapes or hot glue.

Building board = jig board = disposable jig board

Big heavy expensive = small light cheap = cheap and disposable

The jig board can be made of any material, so long as its function is served. 

We want the fuselage side frames be assembled squarely and symmetrically. I don't think assemblying in mid air will be suitable, we need another jig board.

On a piece of cardboard, corrugated cardboard works as well, paste the plan view of the fuselage, cut around leaving 1.5"-2" all round and I'll explain why later. This piece of cardboard will be the other "jig board".

Again, we will need jig pieces, but this time the jig pieces need to be tall enough to accommodate the fuselage sides. You could fabricate the bigger jig pieces, here's how to use the jig board to provide the jig pieces: you simply cut slits at the nose, the mid section and tail and then bend it up perpendicularly. The bent up tab pieces will serve as built in jig pieces for the fuselage sides. Offer the fuselage side frames to this jig board, usually, this means top side down because the top longerons are usually the straightest. Similar jig pieces that were used in the assembly of the fuselage sides can be re-used to 'lock' the position of the fuselage side frames.

Proceed then with cutting the horizontal spacers (in pairs if appropriate), using tweezers if necessary and place them between the 2 side frames. The tail of the fuselage ends as a tip, so proceed from the tail end and finish at the nose.

The assembled fuselage frame can now be removed, but there's an optional step you can take. This involves wetting the fuselage longerons while it is still in the jig, it may reduce the internal stress due to the planform shape. You can repeat this process but do allow a day or so before removing the fuselage frame.  

If your jig board is not destroyed by now, you can re-use it. Place the assembled fuselage frame, top side up, on the jig board. Use the jig board to hold the frame stable while you glue the top formers and stringers.

21 October 2024

Jigs may seem like a tedious step to undertake but it has obvious advantages.

Building equal fuselage sides

On a piece of cardboard, corrugated cardboard works as well, paste the side view of the fuselage, cut around leaving 1" all round for easy handling. This piece of cardboard will be the "jig board".

Jig pieces will be useful for positioning. They are just 1/16" or 1/8" scrap pieces of balsa, something like 1/2"x1/4" size. The jig pieces will be located at the nose, the tail and at each vertical spacer of the fuselage side. Some special jig pieces may be necessary, and these are usually just triangular pieces. It is very easy to make the special jig pieces because all you need to do is the extend the 2 lines, position a scrap piece over it, sight and cut along the lines.

Yes, you can just glue the perimeter's jig pieces onto the jig board. It is advantageous too, because you must not let these jig pieces move.

Once the jig pieces are in placed, the real construction starts. Longerons (the upper longerons are usually straight) are drop in position on the jig board, they can be longer than necessary, because they can be trimmed after the sides are complete. Do two sets of vertical spacers, because we are building a left and a right fuselage sides. These vertical spacers will be glued between the upper and lower longerons, so they have to be accurate. Lay all vertical spacers on to the jig board and glue to the top longeron. Soak the lower longeron pieces in water for 5 minutes, because they usually are curved and we need to soften the longeron. Drop the "softened" lower longeron on to the jib base, against the spacers. Using more jig pieces on the lower edge of the lower longerons to avoid crushing the lower longerons. Do not glue at this stage because the wet balsa has not set yet. Wait until the wet longeron is dried, about 2 hours, and then proceed with gluing it to the spacers.

Do not build the second fuselage side over the first, in case they bond together. Remove the first fuselage and start by placing the longeron, follow by the spacers you already cut, and finally the wet lower longeron on the jig board. Similarly, wait until the lower longeron is dry before gluing them together. 

Sand the 2 fuselage sides so they are identical.

Building the Wing

Similarly, on another piece of jig board, paste the planform of the wing and do up a jig board. This time, use 1/4"x1/2"x1/8" jig pieces for the perimeter. The reason why 1/8" balsa is preferred because the intended leading edge is 1/8"x1/16" on-edge. Start by positioning the leading edge and trailing edge on the jig board. The trailing edge may already be pre-sanded. If the model has tip pieces, these are also positioned and "protected" by the jig pieces. 

You can adapt the wing's plan for the jig board (most ribs are evenly spaced) so that you can use the same jig board for left-hand panel and right-hand panel. In tapered or curved planform, this would not be possible and it is faster just to make handed jig board.

With the perimeter wing frame more or less completed (less the base rib), the next step is to enable placing of the ribs vertically and accurately. Pre-cut ribs are offered first to the inside of the leading edge and then trim to fit the trailing edge The ribs' jig pieces can comprise of the same 1/4"x1/2"1/16" jig pieces previously used for the fuselage's spacers (but not glued on) with additional sticks glued on to the flat edge so that it can provide some kind of a wall to help with the vertical alignment of the ribs. When the ribs are all lined up with straight spar slot, insert the top spar and finally glue them together.

The wing panel is ready for follow up work.

Technology

Thank goodness for photocopier and printer!

Materials and Tools

30 October 2024

Added a bit about adding white glue to the finishing coat in 16 October 2024 posting.

24 October 2024

What kind of brush to apply the paint? Airbrush is not necessary for primer coating, base colour and washes, and I don't like cleanups, do you? 

16 October 2024

White glue and water based paint

White Glue

This material is hydrophilic and shrinks when dried, resulting in volume reduction so precise joints are needed for strength. It's flexible so it is better to absorb force and as a surface coating, it does not crack or craze. It can be re-softened, making it easy to clean; hands and tools can be washed in water and rubbing dried glue joints with a slightly-damp sponge/cloth, will remove excessive glue, make sanding less tedious. It is a good base for water-based paint, it can also become part of a barrier to protect polystyrene foam from foam-melting glue/paint. To prevent/reduce taut tissue from sagging too much in humid condition, a final fixative or lacquer can add stability and durability. Be aware that lacquer can craze.

Since white glue will dissolve in water, here's my idea for a rectangular wing.

Cut the rib template from plastic transparency sheet with a pair of scissors. The rib pattern will extend beyond the actual intended ribs, it extends to the entire chord of the wing. Yes, plastic transparency might not be suitable to be used as cutting template, but it can be used as a tracing template.

For flat bottomed airfoil, use a ruler and cut from 1/16" balsa sheet a strip of balsa, wider than the chord depth so that you get 2 straight edges and you can trace the top curvature of the rib template using the bottom of the template to align with each balsa edge, alternating the template and we minimise balsa waste.

Cut on the drawn curvature line, and stack the cut ribs and glue them together with white glue. When dried, this forms a block of balsa, roughly shaped, strong enough to handle as one but can be separated later with the magic of water.

Now sand the curved top, square the leading and trailing edges and slot for the wing spar.

Drop the entire perfectly shaped block into a bowl of water. Over time, the white glue will dissolve and the ribs will separate.

Water based paint

Water colour and poster paint are cheap, readily available and reversible. Acrylic is more expensive and while easily available, it is unreversible. All water based paint is easiest to clean up and are much safer to use. They work best on hydrophilic surfaces, only hydrophobic surfaces will require primer, so for tissue covered models, coated with white glue, no primer is required. 

Water colour is transparent and is best for washes, poster paint is opaque and is for accented lines and details. 

In planning the painting of tissued covered model, start with the basic tone, if it is coloured tissued, congratulations, as you already have a homogeneous coloured substrate, all it needs (if it is needed) is some washes to refine the basic tone. If it is plain tissue, it's not an issue, just apply washes with water colour to get the preferred tint. Tissue is translucent anyway, so a transparent colour will produce a striking dreamy effect. With water colour, progress from light to dark. The real plane is painted white? No problem, the tissue is white, apply slight tinted washes to homogenise and blur the tissue overlaps.

Poster paint is opaque and is great to cover up water colour mistakes or to make contrasting details. To ensure minimal paint, progress from light to dark because all else being equal, dark covers better than light.

If you spray coat (mist, not wet) the painted model with lacquer, the paint will be protected and will be durable. If you don't wish to apply lacquer, you can consider adding a tiny bit of white glue to the final paint coat/wash.

11 October 2024

Try as one might, if the former has to be precise, you can try to cut it carefully in one go but do not expect it to be perfect. Sanding down to an outline is an additional step and it will take quite a lot of time because one has to keep checking and make adjustment while sanding. 

How do you sand? Do you grip the former in one hand and use a sanding block or file in the other hand? Most would and I would, however it will still not be as precise then if you are able to guide the piece squarely across the sandpaper (not the tool across the work piece).

Grip the work piece against a square block, the forefinger is at the side of the work piece and the middle finger on the other side of the block. Rest the forefinger on the work piece to provide some stability and downward pressure. Slide the workpiece and block thus held, over sand paper and you can be assured of straight ninety degrees edges. Most importantly, you should grip it so that you can see the drawn outline on the work piece while sanding. 

8 November 2023

• 1mm: 1mm EPS: 20gsm
• 1mm: 1mm XPS: 30gsm
• 1mm: 1mm Depron: 40gsm
• 0.09mm: 1 pc Paper: 70gsm (A4 is 5g per piece)
• 1mm: 1mm Balsa: 160gsm (10lb/ft3, medium density)

Paper is 11 times thinner than any other 1mm material. Tissue is thinner. Weight of 1mm balsa is equivalent to 8mm EPS, 2.3mm XPS, 1.75mm Depron. 8mm EPS ought to be stronger than 1mm balsa. XPS (Extruded Polystryrene or Styrofoam) has its Compressive strength of 250 kPa, Tensile strength of 450 kPa and Shear strength of 250 kPa. Since I am taking 20gsm for 1mm EPS, while general EPS has compressive strength of between 40 and 72 kPa, the particular 1mm EPS ought to have compressive strength of 20/30*250kPa = 166 kPa.

Gms/m2:
Monokote 75
Doculam 42
Litespan 28
Cellophane 24
Reynolds 14

XPS (Extruded Polystyrene or Styrofoam) has its Compressive strength of 250 kPa, Tensile strength of 450 kPa and Shear strength of 250 kPa.

 Candidates for modelling use.

Covering:

• A4 paper, printer
• Store bought coloured paper and tissue

Structural:

• Expanded or extruded foam (EPS, XPS comes in various density)
• A4 paper, cardboard
• Incense sticks, disposable chopsticks, ice-cream sticks
• Stapler, paper clips
• glue, CA, tape, double sided tape
• Disposable plastic cups
• CF rods, bamboo
• thread

Tools:

• Pencil, pens, markers, paint, brushes, tape, masking tape, double side tapes
• Tracing paper, saranwrap, rubber bands
• NT cutter
• Files, sanding blocks, sandpaper, plane
• HWC
• Ruler, compass, divider
• Pins, thumbtacks
• foam board, corrugated cardboard, wood
• Soldering iron and solder
• Cutting mat
• 
  

Structure

Tension, Compression, Torsion

Triangle frame has torsion resistant.

Rectangle frame has no torsion resistant.

Thick end frame gives a bit of torsion strength, so does making similar triangular gussets.

Catastrophic failures are:

Wing fold, at dihedral joint and outwards. Wing twist. Wing break due to impact.

Fuselage folds. Fuselage cracks.

EPS, XPS, depron, compressed foam. XPS can be prepared in sheets and sanded

Unit weight (gsm) comparison of material

• 1mm EPS: 20gsm
• 1mm XPS: 30gsm
• 1mm Depron: 40gsm
• 1 pc Paper: 70gsm (A4 is 5g per piece)
• 1mm Balsa: 160gsm (10lb/ft3, medium density)

Balsa

Use of 1/16" balsa wood: 

Small sections unless made of firm wood are fragile and does not have insufficient strength, maybe to use larger section, for example if it calls for a 1/8"x1/16" 9lb/ft3 density and I don't have that heavy a wood, increase the size to 3/16"x1/8", this will require some structure changes to the layout to accommodate the larger section.

Use of 1/32" balsa wood:

Even though it is convenient and easy to cut out the entire shape from sheet wood, bear in mind that a frame structure of 1/16" will be stronger and more resilient. This thickness is especially useful for making laminations for curve parts. As 0.8mm is very thin, go with 3 laminates of 1/32".

Windex

I read that windex and other glass cleaner makes the balsa more pliable then with plain water. I don't think I'd use saliva and I have also read that soaking the balsa strips in windex for a few hours is good.

Gussets

This could be from balsa sheet or even bond paper. 

Tweezers

I think a pair of tweezers is a useful tool for handling balsa. However, I also think that using tweezers made from metal might crush the balsa. I have read that crushed balsa may be recovered by dipping a bit of water on the affected wood. Maybe a better pair of tweezers may be made from bamboo chopsticks or a folded piece of plastic card?

Other tools

The biggest tool may be the building board. For my case, I think a piece of 1" blue foam is ok. 

A tool that may surpass the building board in size would be a frame for stretching tissue. I think there's no easy way to get the tool made, so I think I could just buy a frame from Art Friend. Might as well buy 2 at least, because there's bound to be more than 1 coloured tissue needed. I think I should also get a smaller frame for doping trimmings, A4 sized. To attach the tissue on a wet day, have the frame coated with dope and use thinner to attach the tissue. Any leftovers on the frame may be sanded off and re-doped.

Dope replacement, I think I'll just use thinner and EPS. It is not for doping the completed model, it is only for the attachment of tissue. For final protection, I think I'd just buy a rattlecan of clear lacquer.

Coloured trims will need to be firm enough to handle and crisp enough to cut neatly. I think a doped piece of coloured tissue is good and it can be attached with thinner. I will try this, it may be better than white glue or glue stick. I'll experiment with the dope replacement and the rattlecan. I think the rattle can is also thinner solvent.

Intricate photos may be printed, treated, cutout and applied in a similar manner. Hence the need for a small frame of A4 size.

Kitchen plastic wrap would protect the plan from CA and the underlying building board is also protected.

Pins will be needed, I think the regular tailors' pins are good enough. Other pins and thumb tacks are also useful. Locations requiring temporary anchors may be pinned, against the transferring load or to both sides of the transferring load. 

Right angle braces can be made from blue foam and pinned to the board to hold the sides together or to hold the former perpendicular. Is 10 degrees a good dihedral for free flight?

Glue applicator. I normally used excessive glue, I used offcuts of sticks but they lumped easily and seems not to be able to carry sufficient glue. I think I could use the eye of a largish needle to be a glue applicator. Maybe the eye should be cut/grounded as I have read? Or maybe I can just use a soft wire and make the eyelet, seems less 'dangerous'. A 'O' sized nylon brush should also work very well for water solvent glue, it might be ruined and have to be replaced frequently if using superglue.

Air Brush!

24 October 2024

We decided that normal paint brushing meets with our needs. What kind of brush?

22 October 2024

Air Brush!

Painting aircraft models, flying or non-flying, do not require airbrushing. We are interested in applying an even coat of paint, or multiple thin coats, with the details, accents and lines so normal paint brushes are actually sufficient.

Airbrushing is the next level up, it promises thinner coats and therefore a lighter paint job, there is no brush marks and you don't get brush bristles stuck on the model. All sounds promising but the initial outlay is higher and it will be a new learning experience. You could just buy spray cans and leave it as that, but then you will convince yourself that you require a particular tone that you simply have to mix the paint yourself. Another reason to convince yourself is to be able to apply shading, not so much as to blending.

Having convinced yourself that you need to airbrush when you actually don't, you decided to invest in airbrushing equipment and paint. As mentioned, you need airbrushing equipment. The most expensive equipment is a steady supply of air, here you need to consider the capabilities of the air compressor. You want one that can provide enough PSI and volume of air to supply to your airbrush. You must also realise that air compressor are noisy, you can't just use it anytime you wish.

There are basically two types of airbrushes: gravity fed and syphon fed. On your internet trawling you will decide that gravity fed dual control is the way to go. Not only you get to control the amount of air but you get to control the amount of paint as well! And all those nice images off the internet confirms that this must be the choice. Well, not so fast, you should seriously consider the syphon fed type. Not only that it is cheaper, it is so much easier to clean and there are less parts to clean. Syphon fed airbrush, or spray guns, are easier to operate, you blast the air over the tiny paint nozzle and the air and paint mixes itself outside the airbrush. Remember that you are primarily interested in getting even coats? You can still achieve that with syphon fed airbrushes. The main down side of the syphon fed type is that the air supply needs to be of higher psi. I cannot over emphasized the clean up needs of airbrushes. You can only get satisfactory results if your airbrushes are cleaned and maintained.

Remember, airbrushing is a skill that takes time and practice to master. By starting with a syphon fed airbrush and focusing on basic techniques, you can achieve impressive results and enjoy the process. I still have an air compressor and dual control gravity fed airbrush that I have zero confidence in but reluctant to throw away. I am convincing myself that it is the equipment fault.

Rubber powered

6 September 2024

Winding stooge

The most direct and easiest way to wind up the propeller is to hold the model in one hand, normally the left hand for a right hander, and twirl the propeller with the other hand's forefinger. The correct way though is to stretch wind the rubber motor, and then hook on to the propeller. This manner requires a 2nd person to hold the model and then a rubber winder.

How do solo flyers do it? They have their rubber winder to create stretch and multiply winds and they have a winding stooge to hold the model. I have seen photographs that shows the motor peg to be aluminium tubing to allow the insertion of a small wire and I have also seen stick motors where the plastic propeller is held stationary and the wound rubber is attached to the rear motor hook. One modeller, and I think he must have been an experienced one, wrote all he needed is to place hooks in his shoe laces, which will then keep the plastic propeller stationary.  This method offers a simple and portable solution, as it doesn't require any additional equipment beyond the hooks and the model itself. It's a testament to the ingenuity and adaptability of modelers who often find creative ways to overcome challenges. Wear shoes, shoes with shoelaces.

16 August 2024

Hand cranked rubber winder

Use 2 crown gears (or spur gears), one will be the input and the second will be the output. Use 2 sleeves for the bearing and 2 short length of wire for the crank handle and output hook.

A wire will be passed through a sleeve inside the output gear and bent to hook onto the gear, drilling is required on the output gear to accept the anchor. The sleeve functions as an anchorpoint to the cover plates of the winder. The free end of the wire is then formed into a hook shape to accept the rubber band. 

The input gear is similarly treated, except that the free end of the wire is cranked so that the gear may be turned by hand.

Quad controlled nano plane

5 September 2024

I have not flown the ZY-320 (2 channel 2-motor plane of 210mm wingspan) but I toyed with it. After the model is initiated and is bounded to the transmitter, tilting one wing low causes a change in the spinning noise of the twin motors. This means it has a gyro to keep the wings level. The twin motors were 0714, driving 45mm pusher propellers and the cell is 150mah. The whole model is described as 25grammes. The cell is inserted from the rear, the motors are protected with skids in the motor mount and there are 2 very small wheels about 15mm diameter. ROG may be possible with this model.

If I were to use the airborne parts with minimum modifications and keeping the wheels and using the twin skids, I will need to make a beam mount for the twin motors, thus creating a sort of power pod and command centre. The easiest and laziest way to mount this pod is below the model. What are the effect of a low CG and low thrustline?

There will be inherent pendulum stability, doing away with dihedral at the model. The wheels and skids allow sliding landing on smooth ground. If model has no yaw stability, the pod can have fin or fins. The pod can have  horizontal stabiliser for pitching stability. The thrustline is below the centre of drag/lift, may need up thrust.

How about a parasail, an autogyro, a kite, a bird, a disc/square/oval or even a Doraemon?

23 August 2024

I just placed my order to AliExpress for a 2 channel 2-motor plane of 210mm wingspan. I think it'll fly indoors and it costs less than $20. Better to pay this then figuring out limitations and hacks to a CX-10.

I'll fly the model a few times to see if I like it.

If I do, I'll figure out how to get more 150mah batteries.

If I don't like it, it's $20.

If the model is all battered or I got bored flying it, I'll break out the parts and do my own model!

To convert a twin-counter-rotating-motor pusher plane to a twin-counter-rotating motor pulling plane, the motors will stay on the side they were, but remember to pull out and swap the propellers. 

The $20 model's board has some kind of stabilisation because the model does not have any dihedral. If it works out well, it can mean I am not restricted to modelling high wings. I am also not restricted to 2 engined planes, 3 or 4 engined would also work out well. And must it have propeller? Well, the <$20 model is supposedly a jet plane. 

I wonder what is the weight of the airborne pack. I have chosen the smaller model that flies with 150 mah cell. 

It is such a tiny model, but it is a SU or something so I would work out the entire model's horizontal area (fuselage, wing, tail) and not consider the 210mm wingspan. Just make the new model bigger for slower flight, bigger in terms of the aforesaid horizontal area.   

21 August 2024

Aliexpress still have Cheerson CX-10. CX-10 has the 1s mah battery inside the main body and exposes only the charging port. Extra batteries are available, with or without plugs and some are bundled with charger and charging adapter cables.

4 October 2016

This is the Eachine E010, only available as Mode 2.

I like the four bladed propellers in the protector rings and the rings are duct design with a good lip for better draw.

The vertical lift seems more powerful than the CX10A (and of course  more than the WD-TX which is heavier). It could be because of different motor speed control setting but perhaps not.

If I want, I can connect the ducted fans to WLToys receiver board and make an RC jet.: Boeing, Airbus or even the A-10? Many possibilities.

 

 

18 August 2016

Not a plane but I bought another CX10A and a CX-10WD-TX.
The latter is WiFi controlled, comes with a transmitter and it is a FPV drone that can take photos and videos. It also have height hold, one touch take off and one touch landing. I bought it from Rotor, listed price 69SGD.

7 June 2016

Ooh, a Blériot 115 or 155 is also possible and it seems they are easier to do than a HP42.

The 155 had the same 4 engine configuration but there's no 'inverted gull' kink to the lower wing and the engines were mounted clearly on top of the wings.

There's one door and it was at the nose!

The 155 was smooth skin, no corrugated steel sheets.
Easy radiators to do.

Both upper and lower wings were of equal span, so I don't have to measure the spans of the model.

It had interesting names, in this one, it was called 'Clement Ader'.

 Single tail, unlike the boxed tail of the HP42.

 This was the 115.

 It seems it had a front viewing windows for the passengers.

Don't know if the access for passengers were from the nose. But pity the pilots/navigator, sitting exposed.

Which motor should connect to which arm of the quad controller and which direction should that motor turn? This is what I came up with, but there's something wrong with it.



This configuration would work, but aileron input yaws the plane and rudder input rolls the plane. I haven't stumble on the correct configuration yet.

It's not just the inputs I am concerned about, it's how the quad controller will stabilise the model. When the quad controller detects a roll, translated, the low side speeds up when I'd rather have it speed up opposing motors that give a yaw, which is a roll...see? See? I can confuse easily by writing too much, no wonder I didn't get what I wanted.








So, here's the final configuration which I think is correct.

When I want to roll to the right, quad arms 1 and 3 gives more voltage, the opposing pair of motors at 1.30 and 7.30 speeds up and the torque rolls the model right.

When I want to yaw to the right, quad arms 2 and 3 (I have to verify this) gives more voltage to the motors at 1.30 and 4.30, which speeds up and yaws the model towards the right.

When I want to pitch up, quad arms 1 and 2 gives more voltage to motors at 4.30 and 7.30 and the model pitches up.

16 May 2016

This Eachine H8 mini was delivered last week. I bought it from Banggood because it is cheaper than the Cheerson CX10A, have bigger motors, propellers and the battery connection uses the white plugs.

I bought a Mode 1 type but the aileron and rudder are on the wrong sticks. It is actually a Mode 3 transmitter.

It flies ok, quieter than the CX10A, but it took conscious effort to adapt to Mode 3. So I could hover but not much more.

The propellers are bigger than CX10A's but smaller than the Hubsans which I had bought a few for experimentation. The motors spins free but that is probably because of the increased mass of the propellers?

The plastic frame is flexible and does not break. The guard rails looks ok but are not as useful as a cage because they are too small and do not form a protection ring.

28 April 2016

I am not sure if my visualising of movements is correct.

Question:
If the motors and propellers are forward facing but the board is mounted horizontally, the throttle, ailerons and elevator direction is the same, but what is the effect on the rudder, i.e. vertical axis?

There are two things to consider: the self-stabilising horizontal rotation about the vertical axis and the stick inputs.

Arguments:
When there is a deviation, for example, the quad board were to be displaced in a clockwise rotation (in a vertical axis, i.e. turning right), the two pairs of motors placed horizontally forward facing will react to compensate by rotating about the horizontal axis in an anticlockwise rotation (the model will bank right). This is contrary to the desired banking direction as what we want is for the model to bank left for left turn.
When the rudder stick is pushed to right, we want the model to bank right but the horizontally aligned motors will cause the board/model to bank left. This is also contrary to the desired banking direction because wheat we want is for the model to bank right for right turn.

Solution:
I think I can get the desired rudder stabilising and output by swapping the two pairs of motors, for example for the front-left motor, which translates to bottom-left, it shall be changed from clockwise rotation to one which has anticlockwise rotation.
Front view:
CA     to    AC
AC     to    CA

5 April 2016

Last night I decided to open up the CX10A. I didn't want to but I had to. It's either out with the soldering gun or out with the CX10A; there's no point keeping toys you can't play with. Forego the idea that one day it can be salvaged as parts for a new toy, life is too short.

First I pinched the 4 propellers out of the motor shafts. Then I took out the 4 screws and carefully plied open the latches which are molded to the white plastic bottom cover piece. Gingerly the top cover was removed and the PCB pried out.

Can't see really, but with the camera phone to the rescue, all becomes clear where the wire was disconnected. I tried to see if the solder will met the plastic sleeve, so I don't have to strip the wire: nope. I tried to strip the wire with a pair scissors and cut it instead. I tried again but was really gentle this time and managed to bare a fresh wire core. I tinned the bared wire, or at least I think I did. All this time I can't see what I was doing and it was by 'feel'. Whether the wire is tinned or not I do not know. All I know is that I tried. The soldering part was completed by 'feel' too. I tugged the wire and it seems to hold. The CX10A was re-assembled and it worked.  I then discovered there's this small square transparent plastic piece. I suppose that is to be inserted between the battery and the PCB. It worked for a couple of flights until I crashed it and the same motor stopped working.

I hadn't stored away my soldering gear yet, so I disassembled the CX10A, performed the soldering again (this time I didn't bare a new length or tinned the exposed end), assembled the CX10A and it is working. This time, it was much easier, experience equals familiarity? I didn't fit the small square transparent plastic piece, I wanted to but didn't find it (later on, I stored the plastic piece in the battery compartment of the transmitter.

I think that during a crash, the contact point broke off when that motor twisted. So I thought of hotgluing the motor to the bottom cover, knowing though, that that would mean that I will have some difficulties if I have to disassemble the CX10A again. I thought of superglue, UHU and then settled on a particular glue paste that came in a tube. This glue says it is all-purpose, it looks to be some form of paste compound which won't dissolve in water when dried. I remembered that the paste dried hard.
I applied a bit of it on the exposed sides of the motors after assembly. Then I decided to installed the cage (it has snapped in a few places, but should still be ok) and applied more glue to the bottom of the motors. Only time will tell, but I think this is a good move.

My CX10A flies only a bit longer than 3 minutes and the battery was hot to touch.

1 April 2016

It is the end! Banggood does not ship their lipos to Singapore, no matter how small!

I bought another CX10A and was having a good time until one motor stopped reacting. Perhaps it is a simple matter of opening up and re-soldering, but what shall I do if it is not. Meantime I bought another mini/nano Quad: Eachine H8 Mini Headless Mode 2.4G 4CH 6 Axis RC Quadcopter RTF, for $18.50. It looks to be larger and the lipo is 150mah with the white plug.

I also bought 10x of the male and female white plugs. They would come in useful one day.

30 September 2015

I printed this drawing on A3 for study. The Cheerson propeller fits inside the prop arc and the motor fits in the nacelles too.

A wing jig is required to have the wings assembled correctly because the top and bottom wings are polyhedral and the struts are numerous and requires careful alignment.

Prepare jig and slot in long strips of PVC to form the warren-truss for both front and back struts.
The struts between the top motors and the bottom motors to be made rigid. Glue CF rods to these four struts (front and back).
Prepare and finish the wings, checking dihedral breaks with jig.
Solder magnet wires to motors and glue motors onto wings.
Assemble and glue the jigged struts onto the lower wings and then the upper wings.
Remove jig and leave the glued in struts in placed. The jig would be destroyed in the process.
Cover motor with paper nacelles.
Glue on the diagonal struts.
Tidy up the motor wires. Solder motor wires to board.
Place and glue the biplane onto the finished fuselage.
Run the motor wires to the fuselage.
Cover fuselage and wing joints with paper.
Glue the board to nose.
Make hatch to access board. To switch on and to charge.
Glue the tail and landing gear to the fuselage.



The 4 arms (and SM LEDs) would protrude pass the fuselage's outline. The propeller fits in the propeller arc described.

Overview.

Comparison with 20" Kirby Cadet.

Perhaps 15" wingspan?

 

 

 

 

 

 

 

 

 

The motor would fit nicely in the nacelle's outline and the propeller is just about the right size. There seems to be no space for detailing the Bristol Jupiter engine.

 

 

 

 

 

28 September 2015

I took the Cheerson CX10A out yesterday and couldn't get it to bind. I charged the quad and the USB charging was lighted for a very long time. I picked it up and felt that the 1s cell is very hot.

I haven't been flying the Cheerson CX10A for a few months (maybe 6 months). I think the lipo was damaged by the deep discharge. I could buy a replacement cell from Banggood and replaced the damaged battery but I don't think it is worth my effort. I didn't enjoy flying it. I suppose the board and motors are ok from the last flight many months ago, so I thought how I could re-use and modify it to airplane use.









First to mind was a 4-propellers biplane. Preferably with 2 motors at the top pair of wings and 2 at the bottom. I scour the internet and found the Handley Page HP 42.

With this arrangement of 4 motors, I could place the board in a horizontal position. So long I make this model of HP 42 to be free flight capable, there should not be any reason that I can't control the flight direction when the board and motors are working. Infact, I would have auto-stabilisation which makes flying even easier.

When the model is banked, the 2 motors on the inside pair of wings would spin faster and the opposing twins slower. When diving, the 2 motors on the lower pair of wings would spin faster and the upper pair slower. This would keep the model in a level attitude and pushing the throttle up will have the model fly faster and higher.

The model could be built from simple foam and paper and I could extend the motors' leads by using magnetic wires instead since I have ordered some from Banggood.

The CX10A weighed 12.0gm. I suppose a Handley Page HP42 under 20gm is possible since there is no other airborne electronics to add.











I opened up my CX10A and noticed I don't have the antennae like in the CX10, maybe the antennae is printed on the board. As it works, I am not bothered.

Here's the top view. The charging socket is at the top and the switch is under the board.

A study of the connections of the batteries and motors. Positive: White, Red. Negative: Black, Blue






































































I like minimal intervention and work; I don't like wasting. So I thought of how I could make full use of the switch and charging socket. While it is a simple matter to solder battery connectors and use that as a switch and charging socket, just because I like to do minimal work, I think it might equally be easy if the battery and board are in one unit, like the way it came in, and provide recess instead to have access at the built-in switch and charging socket.

The placement of the board could simply be atop the upper wings of the HP 42 for easy access or I could do some other model with the board tucked in somewhere less conspicouous and even have the small LED shining bright. And this gave me this idea. A X-Wing Fighter.

Have the motors either in tractor or pusher mode.
Have the board glued underneath the fuselage.
Have thin transparent pvc foreplanes if necessary.

Maybe the foreplanes won't be necessary because of the mems gyro onboard.

Whatever it is, the most important thing for success is that the model must be able to glide.