Herr Engineering's Piper Tri-Pacer

 23 February 2022

1. Cover tail surfaces. Use pins to pierce through for the rigging holes.
2. Cover bottom and top of wings, do not cover the centre section. The wing tips may not require separate pieces of tissue.
3. Cover bottom of fuselage in 2 pieces: rear piece is until the former for the main landing gear wires; then the front piece with a small hole to pass the nose gear's wire, trim and glue down to the main landing gear former, the nose former and then all round.
4. Cover the top of the fuselage from the nose former to the cockpit.
5. Cover the nose block. Remove the air-inlets, drill for propeller mount. For simplicity, it will be fixed 3 deg right and 3 deg down thrustline as per instruction. Not the best solution, but it is simple and I'll take the risk. Or don't cover the nose block because it will be time consuming. To cover such a compound curved nose piece will mean thin strips of tissue around the nose piece, sanded, then a flat (ish) tissue piece that has been cut to shape for the front end. If tissue covering is intended, do it before drilling and mounting the supplied brass pieces. For the reason that I doubt the supplied rubber will be so long as to climb the motor hook, I shall use the supplied motor hook.
6. Cover lifting struts
7. Cover the main landing gear fairings. Or substitute the balsa fairing with 2mm foam. The supplied balsa pieces are hard (heavy) and the design does not depend on them for any load bearing. Paper is not used because it distorts too easily.
8. Cover the cockpit from the inside, trim the window openings, cover the short columns.
9. Cover the sides of the fuselage.
10. Apply decals to tail.
11. Apply decals to fuselage.
12. Apply decals to wings.
13. Before the wing is glued to the fuselage, do I want the cockpit to be occupied? Tri-Pacer is a 4 seater, I don't know which is the pilot in front so just place 2? The rear bench can seat 2, but I think 1 is enough. Paper pilots/passengers can be cut from paper and glued to a stem between the middle longerons. Alternatively, the paper cutouts can be pasted on the side windows. Doing this will mean the side windows are to be glued on before the wing and front windshield are glued on.
14. Glue wing to fuselage (4 dots). At this point, the centre section  is bare, and the reason for not covering the bottom of the centre section is because we don't need tissue between 2 balsa surfaces.
15.  Mark CG on fuselage/wings juncture
16. Glue lifting struts: 1) chamfer both ends of each strut, 2) insert 1/2 staples (straight) to wing ends, full staples (V) to fuselage ends, 3) poke holes in wing for staples, 4) bend wing ends' staples to holes, 5) bend V staples to bottom of fuselage, 6) dots of UHU together. Really, why bother? Just chamfer and dot them together, any load bearing advantage is minimal when it is just glued to the lower longeron. The V-wire gives a good surface area for gluing though, but maybe a trapezoidal piece of tissue is a great alternative to cover and glue the lower ends of the pair of struts to the longeron, one on each side.
17. Glue horizontal tail to fuselage (2 dots on leading edge, one dot at trailing edge). As the tail is covered, before gluing, sand away the tissue from the bottom where the glue spots to the fuselage will be, this include the centre top spot where the vertical fin will be glued later.
18. Glue rear top stringer to fuselage. A support is needed on the bay infront of the tailplane because the vertical tail starts ahead of the horizontal tail.
19. Cover top of rear fuselage, over the horizontal tail.
20. Cover top of cockpit and wing centre section
21. Glue vertical tail to fuselage (dots at leading edge, trailing edge and bottom of rudder). Slit the top cover of rear fuselage. However, if the horizontal tail's trailing edge is to be capable of re-setting, then the vertical fin may have to be raised to allow clearance and so it can only be glued by the last fuselage post.
22. Glue cockpit struts (CA thread to V then UHU 3 dots)
23. Glue wind shield (UHU to wing, 2 bottom edge). The supplied plastic seems a bit too stiff, consider replacing if it does not form properly.
24. Glue side windows (dots to corners and rear). Can use thinner plastic bag material. This step can be done after the fuselage side is covered and probably before gluing on the wings.
25. Glue landing gear fairings to wire (3 dots), or preferably with a strip of tissue where it joins the longeron and a tiny dot on the wire (or an even smaller piece of tissue) so it can move independently when the landing gear wire flexes.
26. Install wheels (bend and cut)
27. rubber loop
28. Balance to marked CG. See below about solder wire.
29. Test glide
30. Trim horizontal tail (UHU can be softened with alcohol) 
31. Trim CG (stability)
32. Trim wing and vertical tail.
33. Mark new CG location out on the rib doubler for struts.
34. Test flight with partial rubber.
35. Trim thrustline (torque, add card stock to shim)
36. Trim wing (roll, gurney flap to left wing)
37. Trim vertical tail (yaw, gurney flap to direction of glide circle)
38. Mark final CG.
39. Add tail rigging, wheel rigging.
40. Use solder for weight adjustment. Plasticine is oily, will stain balsa and tissue and will dislodge, it can only be a temporary field adjustment. A piece of solder UHU glued to a tissue piece and coated in glue stick can be glued over a slit in the tissue of the model. Glue stick can be de-bonded with alcohol and it will allow correction.
41. Weights can be attached to nose wheel, inside nose piece (dig and glue), against the stringers (slit the tissue), tail post, wing tips.  
42. Masking tape can be used to mark the CG because it can be peeled away. The designed CG location is marked on the fuselage/wing juncture so that the wing can be glued back with them as the alignment marks. The final CG location can be marked with permanent marker and at the rib doubler at wing struts because the landing gear will obstruct direct balancing.  

1/16" balsa strips

18 February 2022

1/16" round strips

Start with 1/16" square strips. Even if they are not true squares, they should be fine. Here's an idea for a sanding jig for making 1/16" round strips simple. 

1. 2 ice cream sticks are placed side by side with a 1/8" gap.
2. A strip of sandpaper is glued across the ice cream sticks.
3. 1 piece of 1/16" square strip is glued to the outer edge of one ice cream stick (on the sandpaper).
4. 1 piece of 1/16" square strip is glued to the inner edge of the other ice cream stick (on the sandpaper).
5. The ice cream stick backed sandpaper strip is folded along the length to face each other with the square strip forming a 1/16" space.

The sanding action is by pulling and rotating slightly the 1/16" square strip to chamfer and round the corners of the strip. Since the sanding action is by the same grit of sandpaper, the sanding will be on 2 edges at a time and will stop sanding once it is reduced to the diameter of the 2 strip spacers.

1/20" balsa sheet

1/16" is 1/4 thicker than 1/20" (1.5mm vs 1.2mm). The difference is about 0.3mm. It shouldn't matter but if I really want to, for example, to make laminated wing tips, here's an idea for sanding 1/16" balsa sheet to 1/20", short lengths and widths only.

1. Glue lower grit (coarser) sandpaper to worksurface, higher grit sandpaper to sanding block.
2. The other option is not to use sandpaper on worksurface because its only purpose is to help hold the balsa in place without moving. 
3. Glue spacers to lower grit sandpaper (or worksurface).
4. Place 1/16" balsa sheet and sand lightly in one direction, pulling action. When starting on one side, it is ok to hold the balsa at one end and sand away from that end. Then the balsa is turned around so that the unsanded end can also be sanded. Then the other side of the balsa can be similarly sanded.

 

8 February 2022

Razor blades

Double edged razor blades are relatively cheap, thin (0.1mm?), sharp and has 2 cutting blades per piece.

On the minus side are the lack of a pointy tip, relatively flexible (if you need a stiff blade) and has to be handled very carefully to prevent injury.

This makes it suitable for chopping 1/16" square balsa sticks but not for cutting 1/16" thick balsa sheet.

Each blade comes wrapped in a folded piece of tissue and is inserted in a small paper envelope. I snapped the blade without removing the tissue or envelope, one end at a time with a small half round plier. I didn't find any bends at the snapped ends.

The other side of the cutting edge looks ragged but can be handled with a bit of care. The snapped blade can also be gripped with a cross-handle. The handle method is a bit better for sighting a vertical chop (and some rocking). I changed to this method for general chopping even though I almost completed most of the kit.

1/16" square strips

One thing I discovered about 1/16" square balsa strips supplied in the kit is that they may be cut from 1/16" sheet and some widths are slightly wider than 1/16". This is a problem and should be sanded down, preferably before using. In my case, it was used and it may be the reason for the slightly skewed fuselage.

Curve bends

Some curve bends were required in some strips. All I did is to wet with water and pressed between thumb, forefinger and middlefinger. Bend a bit more than the required curve to allow for some spring back when released.

Solvent: UHU and white glue

Water will soften and dissolve dried white glue, so will white glue itself. Alcohol appears to do it to a certain extent, but it wasn't conclusive. Alcohol is a great solvent to soften UHU All Purpose glue. 

UHU is more 'gap-filling' and appears much stronger than white glue.

Applying solvent allows glued pieces to be repositioned and once held in position, holds it new position without additional glue.

A dressmaker pin is a good white glue applicator. I squeezed a small blob of white glue on a sauce plate and used the pointy end of the pin to pick up some white glue to apply to the ends of balsa sticks. The sauce plate I use is also good for placing pieces of balsa which has their ends applied with glue to soak in and thicken. White glue washes off the sauce plate easily. I used a bit of transparent tape if I use UHU. 

24 January 2022

I started building Herr Engineering's Piper Tri-Pacer yesterday and here are what seems to work. The model is an 18" wing span flying scale model, stick and tissue type without preformed plastic and all the balsa pieces laser cut. 1/16" has to be precise but not to worry, it is not precision engineering as a little film of white glue will fill nicely. Making jigs, templates and specialised tools sounds great but is not an absolute. 

I started with this laser cut kit because I have no confidence of cutting balsa parts accurately. After I complete this model, I will have learned something from the process and gained some confidence to truly scratch build. My ultimate goal is to build a flyable peanut scale model airplane.

Building board

I didn't start the kit because I was looking for a suitable board.

• Essential for locking the pieces in the right places.
• I didn't build the model earlier because I couldn't decide on the material and size of the building board.
• I used an scrap piece from a 1" blue foam board, approximately 400mm long and 100mm wide. It is not big enough for the whole 18" wing which I prefer, but it covers more than the centre-section and one wing panel, and the whole fuselage also fit inside the board.

Blue foam is good with pins, there is no rubbery feel that I get with poking polystyrene. Blue foam is also structurally flat, firm and stiff and has no grain direction as it is relatively (to balsa) homogenous. 1" is light and I can grip it easily. The size is easy to handle. Normal transparent tape will tape nicely and it won't damage the blue foam surface when it is time to pull it off. The pin marks will remain but it does not interfere with future uses. Both sides are equally usable, although we only do one side at a time when building the structures, I can pin my structures on both sides when shrinking the tissue (haven't try yet). 

Taping the plan

• Make and cut photocopies of the plan. Use a pair of scissors to cut around the structure.
• Using 15mm plastic transparent tape, with handle (double back on itself), tape on the blue foam board across the joint areas of the structure plan. I have my tape handles either left of the structure or top of the structure.
• Continue with taping over all joints and end at the board beyond the structure. 
• On completion, pull the tape handles to peel away the cut plans from the blue foam building board.

The plastic transparent tape I used is normally for stationery purposes, it is smooth and thin, glue will not bond well to it and the structure can be easily prised off. It doesn't have gluey residue and provides a firm surface (supported by the firm blue foam) for chopping with razor blade. It is not loose like shrink wrap. 

Pinning and trimming sequence

• Cross pin the main parts. Choose pins for clothes making, not the notice board type, we want thin and long pins. 
• Straight pin the other laser cut parts to form the outline. This allows the pieces to be lifted vertically. 
• Identify the main balsa strips that runs straight and longest and trim to length before gluing and straight pin against the main parts. Check to ensure the outline fits snugly.
• Remove outline pieces and glue back in place.
• Let the glued outlined pieces dry thoroughly.
• Work on the biggest cross piece before the smaller ones.
• Do the cross piece against the main balsa strip, cut the free end to size, glue in place and then do the opposing cross piece.
• Complete the remainder cross pieces.

Straight pinning means pinning down vertically. It provides a lateral restraint, it locks the lateral position so if force is applied against it, thin balsa strip will not be displaced. It is also useful because balsa pieces can be lifted. If it is not feasible to have the pin directly oppose lateral forces, it is ok to pin on either or both sides of the force.

Diagonal or cross pinning means to pin diagonally or at a cross. It locks the piece in all direction.

against a butting force.

2 fuselage sides

• Remove all pins from the completed fuselage side.
• Lay a sheet of kitchen transparent shrink wrap over the fuselage side.
• Straight pin around the fuselage side.
• Cross pin the main pieces over the completed fuselage.
• Complete the rest of the pieces and balsa strips.
• It is easy to use the razor blade to chop the new strips.
• When dry, remove pin, peel off kitchen shrink wrap and prise away the original completed side from the plan.

The strips I have in the kit is not exactly 1/16" square. For the most part they are but inspect it closely and decide which is the 'up' side that gives 1/16" thickness. Sometimes I built with the sides, so the second fuselage side will have this strips thicker than 1/16". I intend to sand both sides after it is assembled into a box structure. On hindsight, I could sand the first completed side before building the second fuselage side. Never mind, it may not be precise but it is accurate enough that a bit of sanding will take care of it. I marked the inside of the second side so that I know which side is to be inside.

Double-edged razor blades

Advantages: very thin and sharp.

Disadvantages: flexible

• Each razor blades comes wrapped in a small piece of tissue inside a paper envelope.
• Grip at one end in the middle with a plier and snap against a flat surface.
• Do the same at the other end.
• Take one snapped piece out of the tissue and leave the other in the tissue and envelope. 
• Do only straight down chops. 1/16" balsa strips require only straight chops anyway. 

I didn't use NT cutter (utility cutter) or #11 scalpel. I didn't tape the razor blade or made any form of handle. Finger nails over the razor blade works.

Chopping 1/16" balsa strips

• Position the cutting edge over the 1/16" balsa strip to cut, somewhere in the middle third of the cutting edge, hold one end down and apply pressure on the other end follow by equal pressure on both ends to complete the chop.
• If it is a cross piece, lift the outer balsa strip to insert the cross piece balsa strip under and butt to the other side. If the outer balsa strip is a straight line, and it usually is, perform the chopping motion as before described using the inner side of the outer balsa strip as a guide. The razor is so thin that it is acceptable. The pin board will only be slightly damaged but it still function well.
• If a cross piece is towards laser cut outer pieces, mark with pencil and chop the cross piece at the chopping board. Sometimes the cut piece is too short, then it is relegated to the next length down.

White glue

• Squeeze a small blob of white glue in the middle of a small plate.
• A pin works as a glue applicator.
• A pin also works as a pick up tool for laser cut pieces because you can pierce the pieces. You leave them around the small plate if you are waiting for the glue to soak in a bit before using the pieces.
• As the white glue blob evaporates, it gets thicker. When it is too thick, wash and peel the glue blob off the plate. 
• White glue dries transparent.

Bending 1/16" balsa strip

• A cranked continuous strip is stronger, lighter and more accurate than with segment pieces.
• Use a small dish with a bit of tap water, and twirl the balsa strip between wet forefinger and thumb around the crank part.
• Hold one end against a wooden block and use the edge of the block to crank the strip slowly. Go slightly beyond the required angle.
• The cranked piece is then glued to the balsa structure with straight pins.
• Leave the 2 free ends long for trimming.
• For gentle curves (I didn't encounter this), wet the curved portion and a bit beyond, grip with the non-master forefinger, middle finger and thumb, pull slowly with the master hand at a slight angle, control the non-master hand's pressure.
• For tighter curves (I didn't encounter this), grip the curve portion between a hot solder tip and a surface, pull with master hand. Re-wet frequently.  

Mumbo Jumbo (Pre-Start)

 Sure, any cutting tool can do that, how accurate though? Yes, can be sanded off, again, we have to be careful or it is not accurate even though we took more time to sand it off. The end that was cut or sanded may not fit in exactly as the adjoining surfaces. It could be crooked, not straight; at the wrong angle, or tore off a bit. Why sand if it can be cut precisely?

Cutting precisely is not just using the utility cutter against a straight edge. Yes, it looks straight, but is the cut perpendicular? To cut with a slicing cutter we need the cutting edge to be at an angle towards the direction of cut and yet the cutter need to be held perpendicular when viewed from the side.

1/16" strips can be chopped off but utility cutter may crush the wood and still it may be chopped skewed or slanted.

A tool for chopping

A base is needed to rest the stick. A pivot is needed at the right height, depending on the chopping tool for chopping action, the force will be out to in. I think double razor blade snapped in half is the cheapest and most easily available chopping tool. Maybe a slicing action is better instead? A pair of guides will be needed to chop or slice with the cutting tool.

If all's required is to have the blade slide along a guide, then maybe:

• 2 pieces of 2"Lx1"Wx1/2"T square cut blocks. Daiso
• 1/16" scrap balsa piece, grain running parallel to block.
• Sandwich stick and scrap piece between 2 blocks.
• Use edges of blocks to guide slicing cut.

Or just hold the cutting tool vertically lor.

One ice cream stick, scrap balsa spacers. Lay stick in the slots, Place on cutting mat. Press with left forefinger over the stick and spacer. Cut using edge of ice cream stick as straight edge. Helps to hold the stick accurately. Or use Daiso blocks? If has a pivot for cutting arm? Arm can be ice cream stick with half blade superglued.

Don't snap the double edge razor blade?

A ply handle pivot to the base block with razor blade screwed on. Bring lever down and use it like a guillotine against the base block. 

Andrew Moorhouse

 16 February 2022

I found this designer of model airplanes on Outerzone.

His designs uses, in particular, his Luton Minor:

• laminated curved parts are from 1/32" thick strips, wetted and formed around cardboard templates and pinned to a plastic film covered building board to dry.
• 2 layers of 1/32" balsa sheet propeller blades, formed around a can, sanded while on can. When completed, they are glued to the 1/4"x1/4" propeller hub.
• 1/4"x1/4" balsa propeller hub and shaft, cross cut at ends, and uses tin plates with holes in the centre glued to the hub/shaft for bearing surfaces. Brass or alloy tube is also mentioned as an alternative.
• Uses nylon button nose. 
• His motor shaft has a square loop at the front so it can be winded with a winder. A small piece of wire acts as the catch that locks onto the loop while it is pivoted with a pin on the lighter side of the propeller. This pivoting catch disengages when the rubber tension is released and allows the propeller to become free-wheeling.

His plans are handwritten and complete patterns (including colour scheme) and printed parts are also pdf for printing. His kit consists of 1/16" and 1/32" sheets for strip wood, formers and ribs. Makes me want to find some 1/32" sheets. Very inspiring.

Brass or alloy tubes are mentioned as an alternative to tin plates. I think I will not because I may have to buy various tubing to get the appropriate size and I can't cut the ends squarely without lots of sanding. Even if I managed to find one that fits, I wouldn't use tubing as a button bearing replacement because it seems I will be relying on the fit and glue on the noseblock. A button bearing has a flange support to spread the compressive load to the fuselage frame. 

Tin plates are not so common now, I can still find them but aluminum cans are so easily at hand. I think it will be a good idea to substitute with small pieces of aluminum sheets cut from aluminum cans. I don't have his nylon thrust button, again, maybe I can substitute it with aluminum pieces as well. After all, while they may be thin and light, they will experience only minimal side forces and ought to be stiff enough to spread the compressive load from tensioned rubber to the fuselage structure. If 4 pcs of 1/16" can withstand the compressive load, I don't see why aluminum pieces can't when they are glued to a much thicker balsa base (nose block).

To make the 4 pieces (2 pairs) of aluminum bearing plates:

1. cut a strip off the side of an aluminum can with a pair of scissors/shears;
2. uncurl and flatten strip;
3. use a thumb tack to pierce the aluminum material against a wooden block; and
4. trim to shape and size with a pair of scissors/shears.
5. glue the 2 pairs to the solid balsa hub and noseblock, the burrs from the piercing faces each other so that no cleaning up on the outside is needed.  

Flight paths of rubber powered models

 15 February 2022

Initial torque of rubber is large and decreases rapidly, except for those very lightweight indoor see-through type of models which has a very long run. 

On power drive, the model flies in left circles. It is possible to fly in right circle during the power phase but that would mean lots of right thrust to overcome the torque.

I think I will have left circling powered flights.

When the power lessens or ceased, should the transition be continuing with left circles? I'd like that but I think my glide will be right circles. This presents a problem. If I trimmed the model to glide right, that also means that anything other than a right glide will be draggy, it will stall when it is flying straight for a short portion. There's always a straight portion in a S-flight path.

So, should I aim for a C flight or a S flight? 

After thinking it through, a S flight for torquey model to minimise power dives and a C flight for longer runs indoor type.

Features of C flight models, flights that yaws to fly left:

• long motor runs, low torque, big propellers
• longer left wing
• more wing incidence
• more right thrust
• Yawing flight: left rudder for left glide, wash-in at left wing, wash-out at right wing to keep wings level.

For my Herr Engineering's Tri Pacer, the instructions call for a S flight. I may have to re-read that. A modeller replied my query and said he had the same model and did left/left, i.e. a C-flight, with minimal adjustments.