1/24 scale DH Mosquito for rubber power.

[OZPAF]

made the other wingtip for practice, then repaired the faulty one with an almighty bodge, as ugly as they come. But it's under the skin, so who knows? I certainly don't .

I'm actually amazed that you can match preformed panels with the shaped LE, full stop.

Where is your English wheel to modify the curvature of the panels. ?

I remember reading an article quoting DeBolt stating that the Curtis P40 wings were built from the outside inwards. The Skin was laid up in jigs and the ribs attached to the skin. I wonder how many gaps there were between the ribs and the skin.

John

[dputt7]

Stunning!

[Prosper]

Thanks Australia .

John, shaping that billet of wood isn't so hard - after all the plan taper and curve are known and can be inked onto the initial blank; likewise the front elev. taper and curves. The cross-section of the inboard end of the piece is also known, coz it's the same as the nose-shape of the rib it butts against. That same shape is used to make the balsa tip mould that the skins are bound to for shaping. So with a bit of careful sanding the billet should have the same curves as the moulded skins. Close enough for this kind of a job anyway. That's why I ws so cross when I ruined the shape of the stbd billet by some brain-in-neutral last minute sanding.

Yesterday I just had time to make the tail surface skins/shells/prawn crackers. They're all from nominal 0.5mm soft C-grain. I find crossgrain generally better at adopting and holding moulded curves. Pic 2 shows the balsa moulds (foreground). The Mossie's tailplane had a symmetrical section so only one mould is needed for left and right surfaces. Note that the lines of the fin and tailplane are inked on the moulds. I dose the L.E.s of moulds like this with CA to strengthen them. Tissue binding needs to be firm, and sometimes can squash mould L.E.s, if of soft wood.

Pic 3 shows a freshly-bound stbd fin skin and a wet blank applied to the tailplane mould. The skin is glistening wet. This wet, there's the advantage of it sticking to the balsa mould - which helps placement while it's bound - but the disadvantage that such a wet article weakens the 'wet strength' tissue and it can easliy tear under the stress of binding. This is not precious Esaki of course but craft tissue used by lamp-makers: about twice the weight of Esaki.

After a sojourn in the hotbox, when the parts are unwrapped, I ink the correct finished outline of the skin on the skin, using the aforementioned markings on the mould, while the skin is still in intimate contact with the mould. It's hard to ink a freehand line along the leading edge, so I rub the side of a pencil lead gently along the L.E., which leaves a faint grey mark to guide the ink pen.

Stephen.

[Prosper]

Onto the control surfaces. The first picture is an X-ray image of the test model's fin and rudder. I took this because I have no drawings of the rudder, and needed to see it in order to 'reverse engineer' it for this model.

I do have a drawing of the tailplane/elevator, which is slightly modified because of the way the elevator meets the fairing on the Mosquito tailcone - more on that later. The series of photos is the best I can do - without a headcam - to illustrate the construction method.

Broadly speaking this involves cutting strips of wood (in this case quite hard, straight-grain 0.8mm (1/32"). A strip is laid on the drawing and sliced with a razor - used in the guillotine sense. The cut end is squared off with a brush or two of sanding block, the strip is pushed against another strip and CA'd. That's probably a poor explanation but I hope the piccies help. Note that the photos were taken scant minutes apart - this is a Supa-Kwik method. I anticipate that the rudder will follow as quickly.

[Prosper]

Really eagle-eyed viewers might just notice that the elevators somehow don't quite have the full streamlined, curved elegance that is the Mosquito's essence. Yes, I suppose they could do with a going-over with trimming knife and sanding block .

Stephen.

[Prosper]

I've added some thin balsa sheet to the 'balance horn' area of the rudder - this should hold the tissue to a nice convex curve. Also three hinges, made of baking-tray aluminium folded in two. The slits thru the spar, to hold these hinges, are made with a piece of razor stuck into the end of a bamboo stick. The fin spar is only 0.8mm thick so has doubler blocks stuck onto it to anchor the hinges.

The join of the two fin skins, along the leading edge, is just about visible.

[Prosper]

There are two additional little blocks of balsa glued inside the fin leading edge - one is to anchor the pitot probe, and one to anchor the aerial wire - if I ever fit one.

I had hoped to get further than this today, but there it is. The construction of the tailplane/elevators is so similar to what's shown here that I'll just crack on and not take photos.

Stephen.

[Prosper]

I glued the tailplane skins along the leading edges, but got no further because I decided that I really ought to have the fuselage - or at least the rear fuselage - ready before finishing the tailplane. This so that I can achieve the best fit between the two. So for the last couple of days I've been modifying the fuselage mould. I've split it into three main parts, for the same reason that I split the nacelle mould: exact joins between different skins are much easier to make. I hope to show this in photographs.

The fuselage mould was carved from many bits of odd block balsa stuck together. I used to make big moulds like this from expanded polystyrene, but never liked it - neither the hot-wire cutting nor the sanding. I found that packs of irregular block balsa offcuts were cheaply available, so took to balsa instead. But I looked at balsa block prices recently - blimey! Costs a fortune! I presume this is the wind turbine effect  https://eia.org/press-releases/ill-wind/ 

I made a separate mould for the bomb bay doors. That's because the subject I want to represent had the 'pregnant cat' bomb bay. From all my photos there's no really good indication of the curve of these doors. The pesky engine nacelles always obscure that area in photos. I think my first iteration might be a bit too curvy - but I'll see how it looks when matched up to the rest of the fuselage. What's seen in the photo is that first attempt, moulded in two halves and joined along the centreline. Note the red line - this comes from drawing a yellow Sharpie pen along the edge of the balsa skin before joining - whereupon it turns red when touched by cyano. This then gives a clear indication of the completeness of the joint. Mostly I use cyano in a sort of 'spot weld' fashion, but sometimes a totally glued joint is needed. The bomb bay skin is then loosely bound to the mould to encourage it to keep its shape until the time it's fixed to the rest of the fuselage.

This bomb bay has considerable double-curvature and I used reasonably stiff balsa, which led to three wrinkles in the skins from the initial wetting/binding/drying process. I cut these out and inserted balsa patches, circa 4x4mm. One of these is just visible (arrowed) in the picture.

Stephen.

[Prosper]

Today I reshaped the nose mould to make it suit a bomber Mosquito. I had to revert to holding the nose mould up against pictures on my PC screen to see how good (or bad) the match was. Hardly ideal but the best way available. It's not just about comparing the outline, but also comparing shape, by drawing lines on the mould (the little side windows are a good example) to see if they match the same lines on the photo. In the end the nose needed quite a bit of reshaping and is now about 6mm shorter than it was, which means a slab of balsa added to the back of the mould to restore the correct length. I then plunged a test of the Perspex nose. It looks like the side windows can be obtained from the same plunge as the nose bowl.

I then made a bomber canopy mould, and likewise tested a plunge of this. It clearly needs a good bit more shaping yet. It doesn't look right.

Stephen.

[OZPAF]

It takes a good eye to see those differences Stephen - and a fair bit of artistic capability.

It's a fascinating journey.

John

[Prosper]

. . .a fair bit of artistic capability.

S'funny you say that, John. About 18yrs back, I started to teach myself painting (aeroplanes of course ), and thought that the best way of seeing how light bounces off an object would be to make a model of said object and place it in the same relation re. sun, sky, clouds, whatever, as the subject I wanted to represent in oils. That's what went and gone an' got me into this daft hobby . I ended up dropping painting. Mainly due to eyesight troubles, but partly because this daft aeromodelling thing sucked up all my hobby time.

 Adding a plate at the rear of the nose mould means that it doesn't match the fuselage main section behind it - see the photo. Luckily I dodge a bullet here, because the sides are parallel, so they do meet each other properly, and the main discontinuity is at the top - where the cockpit is, so there won't be any wood there anyway. The discontinuity at the bottom is slight and I sanded it fair.

After reshaping the canopy mould somewhat I tried another plunge. Better but not quite there yet.

Meanwhile . . . what has the farmer done to my flyng field? It's been sprayed with pesticide, sprayed with slurry ('muckspreading'), and yet still has cattle on it, fed with hay. It's a churned-up, dead, smelly mess. Normally at this time of year it's lush green. I have a nasty feeling that it's going to be ploughed up - maybe soon - and planted with maize.

Stephen.

[OZPAF]

That doesn't bode well for your flying field Stephen! Whatever is planted there will just become a new challenge to miss  


John

[Prosper]

Moulding these nose skins was something. 3+ hands required to do the binding. It meant that the top and bottom skins had to be done individually - on less curvy moulds I would bind a left+right or top+bottom in pairs, to save time in the hotbox. That's approx 1hr for stuff like this, whether it's just one skin or two. I did manage to bind the left and right as a pair, so saved 1hr. Incidentally I measured the temp in the box - something I haven't done in years. 82°! That's going some. No wonder these parts are holding their curves nicely after unbinding.

The top and bottom skins had to have slim 'relief wedges' cut out at the front in order to bend to the curvature of the mould.

Today came the tricky job of shaping the edges so that they fit accurately. This is one of those 'sand a fraction off just here; check the fit; repeat' type ops that takes time. I stuck a thin strip of Sellotape to the mould to stop the skins from sticking to the mould, and commenced to join the skins until only one seam remained. I thought I had shaped the edge of this so that the skins fitted to the mould tightly at the front. I glued this seam 'in the air' - off the mould: easier to manipulate the join. But when I put the finished nose onto the mould it was loose at the front. I had to cut out additional relief wedges in each side panel and glue them closed, in order to get the right circumference at the nose. Those relief wedges have to have slightly curved sides.

[Prosper]

The balsa skins and the PETG nose transparency are formed on the same mould. But the balsa skins are much thicker than the plastic. Approx 0.4mm thicker. So there'll be a step between the two when the transparency is fixed in place. Hmmm. Heck, I don't even know how I'll fix it yet. One of the things i wanted to find out from the test model is the vulnerability of the nose with regard to landing. As I'd hoped, the nose turns out to be well protected by the nacelles and props. So I hope the light structure of the nose will suffice in this model too.

Stephen.

[OZPAF]

I had to cut out additional relief wedges in each side panel and glue them closed, in order to get the right circumference at the nose. Those relief wedges have to have slightly curved sides.

Good grief Charlie Brown!!   The final result result looks very neat!

The balsa skins and the PETG nose transparency are formed on the same mould. But the balsa skins are much thicker than the plastic. Approx 0.4mm thicker. So there'll be a step between the two when the transparency is fixed in place. Hmmm. Heck, I don't even know how I'll fix it yet.

A balsa hoop ring under the end of the fuse may allow it to be sanded gently down to the line of the transparency without it being too obvious?

John