Puddleduck Manual

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This expanded instruction manual is intended to complement the printed manual supplied with the plan. The expanded manual contains a wealth of photographs to help clear up any uncertainty in the written instructions, but if all else fails do get in touch with us and we will help out however we can.

Puddleduck is based on an earlier design – Jemima – which was first published as a free plan in RCM&E magazine in 2013. A substantial redesign of Jemima took place in 2016, making various improvements in terms of flying performance and ease of construction. As a result, this model can confidently be tackled by first time builders and flyers. Total time for construction of the prototype was around twenty hours – including time lost in stopping to take the photographs which accompany this manual.

If this is your first foray into the world of traditional modelling, you should find nothing difficult here, although you would be well advised to read up on traditional construction methods – there is an enormous amount of information available online as well as in numerous books on the subject. The most important piece of information I can give is to say that, if at any stage you are unsure of how best to proceed, STOP and don’t continue until you are happy that all is clear.

Before opening the glue bottle, take time to look through the sheets of pre-cut parts and familiarise yourself thoroughly with the drawings – it should be clear which pieces fit where.

The model is built in a series of sub-assemblies – tailplane, wings, fuselage etc., which are then brought together towards the end of the build. For each sub-assembly, begin by identifying all the laser cut parts on the laser cut sheets. Each part is retained in its sheet by short “bridges” which are gaps in the laser cut lines. These bridges will need carefully cutting through with a scalpel or Stanley knife to free the parts from the sheet. An inevitable side effect of using a laser to cut out balsa and ply parts is that a certain amount of scorching of the wood occurs – this leaves a sooty black residue around the cut lines. The soot will not affect the ability of the glue to stick the parts together, so there is no need to remove the residue before assembly, however, in handling the parts, you will inevitably get some soot on your hands which will then transfer itself to the wood (and anything else you touch) giving it a “grubby” look. While this may look unsightly during the building process, any surface grubbiness will disappear during the sanding process after construction. Assemble the parts over the plan (after first covering the plan with non-stick clear plastic sheet) using aliphatic resin.

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The picture above shows all the component parts of the model laid out ready for work to commence – a set of laser cut parts, a selection of strip and sheet wood and the printed plan.

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The first thing to do is to stick the plan to a building board and then cover it with clear plastic sheet to prevent the glue adhering to the plan. I always cut my plans into manageable sections but if you do this, just make sure that you don’t cut off a crucial piece of information in the process!

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The laser cutting process involves feeding sheets of balsa wood into a flat bed laser and the head moves across the sheet, controlled by a computer. As it cuts the material, it leaves scorch marks behind. This scorching does not need to be removed from the edges of the wood as it does not affect the strength of the glue joint. To prevent the newly cut pieces from falling out of their host sheets of wood, “bridges” are left in place. These are short sections which are not cut by the laser. To remove the parts from the sheet, cut through the bridges with a scalpel. As the picture above shows, this can leave a small bump of material which will need to be sanded back flush with the edge of the part to ensure a good fit.

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Begin by pinning down the three laser cut pieces of the first fuselage side.

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The balsa strips are added, along with two triangular gussets front and rear. These add strength to what would otherwise be unsupported joints. I have used Super Phatic for this stage as it dries quickly but gives a very strong and flexible joint.

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While waiting for the glue to dry on the fuselage side, the elevators have been assembled following the same process as for the fuselage. While the glue is drying on those I have moved on to the rudder. The outline of this part is made up initially from strips of 1/2″ x 1/4″ (6x9mm) balsa. Once it is complete, the curve will be cut by hand. By this point, the glue on the fuselage side has dried, this part can be removed from the board and sanded smooth on both sides.

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Although not essential, I chose to mark the positions of the balsa strips on the rudder outline before removing this from the board and filing small notches with a 6mm spar slotter. This will have the effect of increasing the strength of the glue joints later, although it is definitely an optional step rather than a necessity. If you are not going to add the notches, there is no need to remove the rudder from the plan, just go ahead and add the strips as soon as the outline is in place.

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The rudder has been returned to the board and the balsa strips have been added. You can see that I have not positioned the rudder back exactly on its outline as drawn on the plan – this was deliberate as it allowed me to build the fin at the same time without worrying about sticking the two components together. In any case, having cut the slots for the strips, there was little chance of getting them in the wrong place, regardless of whether or not the rudder was over the plan.

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With the fin and rudder out of the way, the first fuselage side is returned to the board but this time underneath the plastic sheeting. Building the second side over the first ensures the two sides are identical.

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This is my favourite method of making formers. Strips of 1/8″ x 1/12″ (3x12mm) balsa are cut slightly over length and pinned in place over the plan with a healthy dollop of Aliphatic Resin at each corner. Here I have used pieces of graph paper to keep everything square – the plan used to build the prototype was very much a sketch and didn’t have former shapes drawn on it. Making formers in this way is a classic example of taking advantage of the strength of material being used – balsa is incredibly strong when compressed along its grain and formers made in this way ensure that the grain effectively forms a continuous loop around the part. If I were to make the same shapes out of rectangles of flat sheet they could easily distort when compressed across the grain. To overcome this, they would have to be made of a lot more material than necessary with this method.

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Once the formers have dried, they can be removed from the board and trimmed along their edges to get rid of the overhanging ends of the strips. Make sure that each former is square and that F3-F6 are all the same width. The two fuselage sides can be separated and sanded smooth on both sides but also around the edges, holding the two sides together to ensure they are identical. One fuselage side can be placed flat on the building board and F3-F6 can be glued in place along one edge, using a set square to keep them perpendicular to the fuselage. I used Roket Max for this stage as it provides a more or less instant bond. The inside faces of the two rear fuselage ends can be chamfered slightly to increase the gluing area once these are brought together. The fuselage can now be rotated upright and the other side added. For this stage I used Aliphatic Resin to give myself a chance to reposition parts before the glue dried. You can see from the picture above that I am using a fuselage building jig and I highly recommend this, although it is possible to get the same result by using weights and building the fuselage over a known straight line on the board.

With the forward fuselage held in the jig, the rear ends can be brought together and held with spring clamps. Do a trial run first, without applying any glue. At this stage, no force is applied to the fuselage behind F6 – simply bringing the rear ends together will allow the fuselage to adopt a natural curve. Make certain that the point where the rear ends meet is exactly on the centreline of the fuselage and also ensure that the tailplane seat that you have just formed is level – balance a long ruler across the top of the seat and check that it sits level when viewed from the rear. When you are happy that all is as it should be, release the clamps, apply glue to the mating faces and reassemble. At this stage, slide the rear fuselage jig supports into place to secure the rear sides, but don’t try to apply so much inward force that the fuselage gets distorted – all we are trying to do here is ensure the curve is even on both sides. The ply reinforcement pieces are added behind F3 and F6, ensuring that the holes in these align accurately with the holes in the fuselage sides.

This brings us to the stage shown in the picture above. Note that some camera distortion has crept into the photograph – it appears that the forward fuselage jig is angled outwards when in fact it is perpendicular to the building board.

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Triangular pieces of Lite ply are added to the rear section of the fuselage, top and bottom. On the upper surface this will provide a firm gluing area for the tailplane while on the lower surface it will provide an anchor point for the tailskid. F9 is not a complete former but rather two strips of 1/8″ x 1/2″ (3x12mm) balsa added horizontally in front of the ply.

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Here you can see the ply triangles in place, upper and lower sections of F9, plus the doubler for the upper section as well as F7 and F8. A couple of points to note here –

1. Extra balsa has been added across the tops of F7 and F8. This subsequently proved unnecessary but was done at the time because I had intended a finish on the top of the fuselage that would have required it. There is no need to add the strips as shown in the photograph.

2. On the right hand edge of the picture, just behind F6, a reinforcement strip can be seen. This IS essential, and it will also be necessary to add a strip of 1/8″ balsa between it and the rear edge of F6. The reason for this strip is to prevent the upper edge of F6 bowing to the rear under the load imposed by the wing bands once completed.

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The undercarriage mounting plates, made up from two lamination of 3mm poplar ply, have been added to the forward fuselage, along with the triangular section reinforcement strips.

The internal doublers can be added, along with the firewall (F2). The plan makes the position quite clear but note that F2 must be added the correct way around to give right thrust – the holes in this part are intentionally offset to the left slightly to ensure that the centre of the propellor is on the centreline of the model. The two balsa doublers are slightly different lengths to correctly position F2 – make sure the longer doubler is on the right hand side of the model! The picture below should make matters obvious, although it was taken after covering was complete.

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As can be seen from the picture above, it is easier to fit the motor before adding F1. It is just about possible to access the screw heads with a small Allen key once F1 is in place, but this is quite fiddly and so I highly recommend fitting the motor first.

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The hatch is made from four pieces – a base and three formers – strip planked with 1/8″ balsa. As you can see from the first picture, the initial result of strip planking is always a little disappointing but a bit of perseverance with increasingly fine grades of sandpaper soon gets things looking better. If you have never tried strip planking before, it is one of those jobs that seems daunting at first but is actually far easier than it looks. Start at the lower edge and work on alternate sides using 1/8″ balsa strips. As the radius is smaller at the front than the rear, you will need to taper the strips slightly. The final, central strip will need to be cut to shape by trial and error.

With the hatch in place, final sanding and shaping of the forward fuselage can be done. At this stage, while access is still straightforward, make up and fit the battery tray. A simple wooden box will suffice, of suitable proportions to accept your chosen battery, and with a strip of hook and loop tape to hold the battery in place. It can be supported on rails fixed across the inside of the fuselage. Once this is in place, the floor piece can be added between the forward undercarriage plate and F1, along with the coaming which can be made from a piece of soft block sanded to match the shape of the rear of the hatch.

These picture show how the hatch is retained – tiny neodymium magnets have been added to the base along with balsa blocks along the edges which help to locate the hatch within the fuselage sides. A pair of screws (steel, not brass) are fitted inside the fuselage sides and adjusted so that they just meet the magnets when the hatch is in place. Now the hatch drops neatly into place with a satisfying click. You can see that the front of the hatch has been relieved with a small drum sander to clear the rotating outer casing of the motor.

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The first job to tackle on the wing is making up the sheet skins. You might think that this is something that could be done over the wing structure but that way leads to trouble. You must make the skins up on a flat board before the rest of the wing is constructed. Make them slightly oversize so that they can be trimmed to fit later. My method is to pin the pieces of sheet balsa down flat and then run a line of thin cyano such as Roket Hot along the joins. after a few seconds the glue will be dry and the sheets can be sanded smooth. Take care as the sheets will be fragile at this stage. Once done, move them safely out of the way.

While the glue on the wing skins is curing, cut the ribs free from their balsa sheets. A quick clean up with a sanding block, just to remove the lumps left by the balsa bridges, and a set of identical ribs are all ready to go.

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The right hand lower skin has been pinned to the board, along with the lower cap strips and trailing edge strip. The rear of the skin will need to be trimmed to ensure that it just touches the trailing edge strip with the skin in place. The balsa main spar has also been stuck down with Aliphatic Resin and pinned in place. This has been positioned such that the rear edge of the spar slightly overhangs the rear edge of the forward sheeting, thereby ensuring that the capping strips are firmly attached not only to the forward sheeting but also to the spar itself. Next take a few ribs and position them over the mainspar so that they can be used to accurately locate the 1/8″ balsa sub spars. The position of the sub spars as shown on the plan is reasonably accurate but there is no substitute for using the ribs to determine their precise location. Note that in the picture above, the ribs are not glued in place – nor are they in their final positions, they have just been slid into place temporarily. A dot of cyano on each sub spar where it crosses the capping strips keeps everything in place and the ribs can be removed.

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The ribs can now be glued into their final positions. At this stage, only the rear two thirds of each rib is glued down – from the mainspar back. This is because the forward portion of each rib curves upwards slightly and with the tail of the rib in contact with the sheet, the nose will be slightly away from the forward sheeting. Each rib is held perpendicular to the board while the glue sets – with the exception of the innermost rib (left hand side of the picture) which has been set at an angle to accommodate the dihedral once this panel is joined to the centre panel. The required angle is shown on the plan and a laser cut template can be found in the parts set. Upper spars have also been added and shear webs will follow.

The shear webs have been added forward of the mainspar. Note that the grain of the webs must run vertically and not horizontally. The reason for this is that the function of the webs is to resist the tendency of the wing to flex in the vertical plane. The webs do this by preventing the upper and lower spars from effectively sliding against each other – in order for the spars to move like this they would have to tear the webs along their length. If the grain was oriented horizontally, it would not be difficult for this force to shear the webs, but with the grain vertical the webs are far better able to resist this force. The innermost web must be trimmed to match the angle at which the innermost rib was set in the previous step.

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The dihedral braces will sit behind the mainspar and to accommodate them, a 3mm spar slotter is used to cut notches in the three innermost wing ribs. This task could just as easily be performed with a small hacksaw, a file or even a scalpel. It could also have been done prior to gluing the ribs in place, however leaving it until this stage ensures that the mainspar does not obstruct the notch during construction.

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The lower forward skin has been raised slightly off the building board until it just touches the lower edge of the ribs – a length of 1/8″ balsa can be slid underneath the skin to support it in place while a small amount of thin cyanoacrylate is run along the edges of the ribs (but be careful that no glue soaks through the skin to glue the length of balsa permanently to the underside of the skin – a length of tape along the top of the strip will help avoid this).

Next, the 1/8″ balsa false leading edge can be glued in place. Note from the picture above that it is oversize and protrudes some way above the upper edges of the ribs. Incidentally, you can see that there are notches in the ribs which appear to be ready to accept subspars in the region of the sheeted D box – these are present because the original design had no D box and therefore required forward spars, however when I redesigned this area the spars became redundant but I left the notches anyway to give myself the option to change my mind and revert to the original design later. These notches have been removed from ribs supplied in the laser cut parts sets.

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Two minutes’ work with a razor plane and sanding block sees the false leading edge trimmed back in line with the tops of the ribs. A handy tip here is to put small strips of masking tape across each rib so that, as the false leading edge approaches its desired shape, the razor plane scuffs the masking tape warning you to slow down before you cut into the rib.

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Time to add the top sheeting. Begin by fitting the trailing edge sheeting strip and then take the upper skin (which you made earlier) and hold it in place so that the rear edge sits just forward of the main spar, as shown above. Trim the back of the skin so that it just touches the trailing edge strip. As for attaching the sheeting itself, this is one of those jobs where you wish you had more hands but there is a way to make life easier. I apply a line of Aliphatic Resin along the upper edges of the ribs where they will meet the forward sheeting, then I run a line of thick cyano’ along the forward edge of the rear spar, where the rear of the upper sheeting will sit. I then position the rear edge of the sheeting on the line of cyano and press it down for a few seconds until the cyano has taken. Now gently lift the forward edge of the sheeting just enough to allow the nozzle of the cyano bottle to run a bead of glue along the top of the false leading edge. Smooth down the sheeting, working forward from the spar and apply even pressure along the forward edge until it has stuck firmly down. The sheeting is now held securely in place by the two lines of cyano while the bead of slower setting Aliphatic Resin dries. The process is identical for the sheeting over the two innermost ribs rear of the mainspar.

You can see in the picture above that the rear edge of the sheeting is not in line with the rear edge of the mainspar – as I mentioned above when doing the lower sheeting, this is deliberate as it allows the capping strips to attach to the spar at their forward extremity.

Treatment of the trailing edge is very straightforward and although I don’t have a photograph to illustrate the process, the plan makes the situation very clear. The upper and lower strips are trimmed back until the pointed ends of the ribs just begin to show. A single strip of 1/4″ balsa is then glued to the trailing edge and planed to shape.

The centre section has been completed, with full width sheeting top and bottom. The balsa leading edge has been glued in place ahead of the 1/8″ false leading edge and the first passes have been made with the razor plane. Note the masking tape behind the leading edge, just as described above when trimming the false leading edge.

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While the glue dries on the second wing panel, the wing tips have been pinned down and the tip ribs glued in place. Note that the ribs overhang the outer edges of the tips. This is intentional as they will be sanded back to shape in situ.

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Back to the centre section now – the three panels have been joined with aliphatic resin, the centre section being held flat on the board while the wing tips were propped up to give the correct dihedral. A small strip of the upper sheeting had to be removed to allow the dihedral braces to be slid into position from above. The sheeting was replaced after the dihedral brace was fitted, and gently sanded back to meet the rest of the sheeting. You will recall my comments earlier about not sanding sheeting in situ, well on this occasion we can get away with it because the small piece of sheeting that we are sanding here is supported from below by the main spar. You can also see a tiny gap along the top of the join – ideally, the panels would have come together perfectly with no gap here at all but life rarely works out like that! The gap is inconsequential as it can be hidden with a tiny amount of filler if desired, and anyway the glassfibre bandage we add at the next stage will negate any compromise in the strength of the joint.

Strips of 50mm wide glass fibre bandage have been added to bridge the wing joins on both sides. This is most easily achieved with the wing standing on its trailing edge, as if it were flying vertically upwards. Pencil lines are drawn on the balsa skins to show the approximate edges of the bandage, then slow setting epoxy is painted within the lines, the bandage is pressed into the epoxy and more resin is added over the top, flatting the bandage down as it is applied. This is a messy job, definitely not one to be undertaken indoors, and not in your best clothes as a few stray drops of resin are inevitable and they don’t wash out! After the whole thing has cured thoroughly – at least 24 hours – the bandages can be sanded smooth and trimmed in line with the trailing edge. The wing is now complete and ready for covering.

The prototype was covered in Solartex although any iron on covering would work just as well. When covering the tailplane, be sure to leave an area of bare balsa where it will glue to the fuselage – this ensures that the glue joint here is sticking wood to wood and not wood to covering material.

The undercarriage can be made by bending piano wire to the shapes shown on the plan, or a ready made undercarriage can be used.

I used mini servos operating the control surfaces via snakes although there is plenty of room for fitting standard servos if required. The control movements shown on the plan work well and should not need increasing – my philosophy as far as control movement is concerned is that I set the model up with lots of control deflection but then use exponential on the transmitter to reduce the movement around the centre. If you are not going to use exponential then you may want to reduce the movement to around 60% of that shown.

If you are new to flying model aircraft, the first flight should be undertaken by an experienced flyer. That said, Puddleduck is a very easy model to fly and will happily potter around serenely on half throttle.

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