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Author Topic: 1/18th scale Spitfire for rubber power  (Read 16204 times)
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kaintuck
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« Reply #350 on: August 08, 2021, 02:40:22 PM »

Looks as if the Spit ran into a 109 Shocked

Rebuilt please.....
Marc
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Don McLellan
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« Reply #351 on: August 08, 2021, 02:47:36 PM »

Agree with Kaintuck, rebuild if possible.  To me, the tree strike didn't look all that significant, but the damage certainly was.  When you do the damage investigation, please post some pics of you findings.

Cheers,
Don
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OZPAF
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« Reply #352 on: August 08, 2021, 09:34:14 PM »

I know it's easy for us to say - but I also hope you repair/rebuild it Stephen.

John
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Indoorflyer
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« Reply #353 on: August 08, 2021, 11:18:55 PM »

Sorry to see the damage.

In post #345, viewing the last image in the series (wingtip damage)-- it looks like your hitchhiking fly is still on board!
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Prosper
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« Reply #354 on: August 09, 2021, 04:16:48 AM »

Hullo chaps - rotten show, what?

Indoor - well spotted! (or should I say fly-spotted?Cheesy) You should be in the NTSB! I didn't mention the wingtip fly in case the 'running gag' was too frail to register. Doesn't it look like exactly the same one? It would definitely account for the right wing dropping.

Now seriously, yes of course I'll be rebuilding the model. The tail section broke off raggedly, and broke the light former there in half - half attached to the ripped-up tail section and half still attached to the rear fuselage. I haven't soaked the wing off yet - there's definite damage exactly where you'd expect it - namely where the big underwing radiator disrupts the wing spars and so weakens the wing structure. Other damage - for example as in the photo where the wing skin has burst at the leading edge -  should be fixable with glue. Appearance-wise, the wing was a mess from the outset of the build, so I'm not too worried about how it will look. The nose section ahead of the firewall - esp. that large area of the top cowling torn out - may just be gluable-backable, otherwise a new top cowling will be needed. I will post some pictures as I go. I don't know how audible it is in the Youtube upload but there was a horrid sharp 'crack' when the model hit the treetrunk and then a perceptible pause (I thought for sure the model was stuck in the tree), before it dropped down with another harsh smack onto the stones. Those were two major decelerations, and I'm pleased the model survived at all.

Stephen.
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Prosper
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« Reply #355 on: October 20, 2021, 09:53:26 AM »

Hullo everyone - it's only me. I made a start on the second fuselage. Finally. . .

Lack of time has been the main problem here. I haven't done any aeromodelling for weeks. After a hiatus like this I always doubt the ability of my hands, eyes and general motor skills to cope with these scale models, but I re-started three days ago and have done OK so far.

Anyway what pic 1 shows is the game of arranging paper patterns on the sheet material in such a way as to minimise waste. As you doubtless guess, there are many many possible combinations, and it's easy to abandon all pretence of productive work and simply spend all day playing this game. The rules are: to make a left and a right where needed - not two lefts or two rights. . . to have the grain running in the needed direction for a given panel. . . and not to cut a tail panel from a heavy thick sheet of material, or conversely a cowling panel from a light sheet. . .I can't recall if I've committed that last folly, but I've certainly managed the other two over the years. I cut the individual parts out with sharp scissors, or a scalpel where there's much curvature.

Pic 2: This is a blank panel which became the top cowling. For panels with lots of double-curvature I cut relief holes and then slit the sheet from the hole to the edge. I used to cut out oversize wedges (rather than slits) so that there would be no overlapping when the sheet was bound to the mould with tissue. Cutting out the wedges was easy - but filling the gap after the part was moulded was tiresome - analogous with 'infill' in stringer/former construction. In theory you can cut out a perfect wedge which closes up exactly as the sheet is bound onto the mould, but that's unrealistic in practice (I've found. . .).

Anyway, now I just cut slits, accept overlapping when the sheet is bound to the mould, and sort it out afterwards. Quicker and easier, if less craftsmanlike.

I cut the relief holes with an al. tube that has its tip shaved out with a scalpel. Unsurprisingly, the cutting edge of the tip is very delicate and needs resharpening often. The holes are not made by punching into the wood, but by spinning the tube back and forth 'tween finger and thumb while exerting little downward pressure. The little discs normally jam into the tube and have to be prodded out with a length of wire. The discs are retained for re-fitting later on.

One of the main reasons for making a fuselage out of so many individual panels is that this time-consuming business of relief wedges is not necessary. In the case of the Spitfire only the top engine cowling and the oil tank under the nose need this treatment. The ultra-curvy under-cowling immediately behind the propeller is plunge-moulded plastic.
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Prosper
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« Reply #356 on: October 20, 2021, 09:56:20 AM »

Individual panels are put under the water tap momentarily, allowed to soak for a few minutes, then are bound to the mould with tissue paper and/or sticky-tape, and confined to the hotbox for about an hour. The first picture shows a typical cargo fresh out of the hotbox. Some panels, like the nose cowling cheek panels, centre-right, take so much binding to get them pressed to the mould that everything disappears under tissue and sticky tape.

Back to the top cowling. After dealing with the overlapping bits (I tried to describe how I do this but it reads like gobbldegook), Pic 2 shows two joins glued, the discs replaced and just visible is one end of a plastic sheet slid up between mould and balsa, to prevent sticking.

I use a length of tube, heated over a flame, to smooth joins down. This works a treat. Pic 3 shows the cowling after plying the 'tube iron', and pic 4 shows the final result after any necessary filling, general sanding, and removal from the mould. I'll probably revisit this in a week or so because joins can 'un-fair' themselves over time - I guess maybe that the filler is still shrinking, and the balsa is still reabsorbing water to match the ambient humidity, after the hot dry moulding process.

Stephen.
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OZPAF
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« Reply #357 on: October 20, 2021, 08:01:03 PM »

The hole and slitting systen works well with the compound curvature Stephen. The final sanded result with the replaced discs of balsa, is quite impressive.

Good to see you back on your moulded masterpieces.

John

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Prosper
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« Reply #358 on: October 22, 2021, 04:55:41 AM »

Hi John, Thanks!

Yesterday I moulded more panels and spent time dealing with the main fuselage side panels. It's better to glue these together before moulding, and it's some job. Most of the 'panel lines' evident on a Spitfire fuselage are overlapping, so one appears higher than the other by the thickness of the Dural. This is evident in many photos, so I wanted to try emulating it. I've found it difficult to bring off. First, if one can arrange a lighting situation that illuminates the work adequately, as soon as one's paws or tools get where they need to be, the work is in shadow. Second is the flexibility of the thin sheet material. It wants to be wavy all the time. I thought that simply putting a thin sheet of something under the panel that is meant to be higher. . .well, obviously I could just put a sheet of paper or something under the higher panel, run glue along the join and kazaam! a join with a neat raised edge! It doesn't really come out like that - again because of the softness and un-cooperativeness of the material.

Thirdly, the long join along the main fuselage has a kink in it. Cutting and sanding two straight edges to butt together is a negotiable task - but when there's a kink. . .grrrrrrrrh: I think it took me as long to get those panels joined as four times as many straight-line joins.

The photo is lit to show the result on the left side of the fuselage. The nose is on the left. To get bearings, note the cockpit hatch, the access hatch behind the cockpit and the curved lower edge where the wing fillet panels will go.

As you can see, the raised join isn't very even (see the arrow), but it's done now. Also it's probably exaggerated somewhat: 1mm is approx 0.06mm at this scale - but here's a case in which I'll accept a degree of exaggeration to achieve an effect.

BTW, the very annoying kink is seen near the rear end of the panel join.

Stephen.
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Prosper
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« Reply #359 on: October 22, 2021, 12:19:58 PM »

Another lot out of the oven.

Some panels are difficult to press to the mould - one solution is to make negative moulds, as seen here. These are simply two thicknesses of the pulp card I use for cutting mats and other jobs. the card is wetted, the two layers stuck together with lavish amounts of glue, and the whole lot pressed against the mould using - well - loads of binding tissue and sticky tape probably, perhaps with a few rubber bands for luck. When all that's dried thoroughly the negative mould holds its shape.

Note that the Spitfire's wing fillets have very little compound curvature despite their luscious appearance. The only significant double curvature is right at the front, and these sections are in the hotbox as I write this. They went in okay, but there's just a chance that they'll split as they dry.
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Prosper
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« Reply #360 on: October 22, 2021, 12:23:58 PM »

Quote from: Prosper
After dealing with the overlapping bits (I tried to describe how I do this but it reads like gobbldegook)

My description of how to deal with the overlapping parts of curvy panels may have been too incomprehensible to post, but here's another go, with photos doing most of the explanatory work:

1) here's the overlap, when the binding is removed. 2) see how the overlap causes the edge to curl up like a British Rail sandwich. This is why I fought shy of permitting overlapped moulding for so long. Never mind - just use the edge of the higher lap as a guide to very delicately slice along with a sharp razor. Once you've sliced through the lower layer [underlap??], the wedge that's now trapped underneath can be teased out; the two edges pressed together, and CA run along the join. After sliding in a plastic sheet to stop the part sticking to the mould that is. In the photo the join looks like a deep groove but that's just an ink line I drew before slicing the wedge out. Now, the curling-up of the overlap can lead to a wavy result (tho' not in this case), and that's where the ironing with a hot tube (or somesuch) comes in, to make all fair. Plus the obligatory sanding and filling of any gaps, of course.

Stephen.
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Invader3
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« Reply #361 on: October 22, 2021, 04:12:20 PM »

Fascinating techniques, Stephen - and your patience astounds me!

John
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kaintuck
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« Reply #362 on: October 23, 2021, 02:57:48 PM »

Thank you for posting....riveting work yours is!!!
Marc
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Prosper
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« Reply #363 on: October 24, 2021, 10:54:34 AM »

Hi Marc - I wish I could figure out a way to represent rivets Grin.

Thanks John - I wish I could claim to be patient. People will tell you I quite often mislay my duster. Isn't that the phrase? Or is it 'lose my rag'?

Picture 1 is from yesterday and shows where the whole 'exploding mould' business comes into play. This is the rear fuselage. Each panel of balsa/aliphatic sheet can now be cut and sanded exactly to shape, by pressing the panel against its relevant segment of mould and sanding the panel's edges flush with the edge of the segment. The idea is really simple and the execution is simple too, mostly. . .

Pic 2 (taken thismorning) shows what I mean. The last strokes of the sanding block are done gingerly, because the balsa from which the mould is made is softer than the balsa/aliphatic sheet. As soon as a stroke contacts the mould itself, red ink comes off on the sanding block. Also, the red edge of the mould segment takes on a pinkish, dusty tinge. I think this is clear in the photo.

Simple, except for the top and bottom skin panels. Where these are concerned, pressure on the panel's edge from the sanding block lifts the edge away from the mould. The skin must be pressed firmly against the mould close to where the edge is being sanded, but the small size and the curved surface of the mould make this really awkward - "all fingers and thumbs" type stuff.

Pic 3 shows the first join being prepared. To avoid the skin panels sticking to the mould, a strip of adhesive-backed plastic film (AKA covering film) is stuck along the join line - and then to raise the edge of one panel another strip is added, to one side of the join line. Pic 4 shows the joint. I've used bits of sticky tape to keep things where they need to be. I used to avoid using sticky tape stuck directly to the skins, in case it broke up the aliphatic coating of the skin when being peeled off - or even caused the skin to split. It's such a useful aid though that in recent times I've been resorting to it, and peeling it off slowly and gently (dare I say patiently ?Cheesy). Pic 5 is the join in a glancing light, to emphasise the raised edge of the lower panel. It looks over-raised where I've marked the arrow, however this is not shadow but the red ink line running along the panel.

The join on the stbd side is broken by an access panel. This is a poor fit around the top, forward corner. I hope this doesn't look too bad on the finished model. I now think I should have made another attempt. The narrow slot along the bottom edge is to accommodate the dummy hinge. I seem to recall from my research that this is a battery access panel.

Stephen.
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Pete Fardell
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« Reply #364 on: October 24, 2021, 11:41:31 AM »

Inspirational work as always, Stephen. The things you persuade balsa that it can do never ceases to amaze me. You must be like some kind of inspirational god to the poor stuff. "But we're just balsa wood! We can't possibly do that!" say the stiff flat sheets. "Yes you CAN!" commands mighty Prosper!
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TheLurker
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« Reply #365 on: October 24, 2021, 12:11:16 PM »

So, not Prosper, but Prospero?
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Prosper
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« Reply #366 on: October 24, 2021, 12:38:28 PM »

Well I can't remember The Tempest, except that a character (Miranda?) says "what brave new world is this?", thus giving Aldous Huxley the title for a great work of prophesy; and - I think Miranda again - says "surely no ill could dwell in such a temple", which describes a delusion that has been very important throughout history. So I don't recall what Prospero was like in his domain, but I don't persuade balsa so much as harass and bully it. I must admit I feel bad about that [evil snigger - exits stage left] Cheesy.

Stephen.
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TheLurker
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« Reply #367 on: October 24, 2021, 12:52:30 PM »

Quote from: Prosper
....People will tell you I quite often mislay my duster....

...I don't recall what Prospero was like in his domain...

Autodidact wizard.  Bit grumpy too. Smiley
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Pete Fardell
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« Reply #368 on: October 24, 2021, 01:04:15 PM »

So, not Prosper, but Prospero?
Yes, Prospero is about right, although Prosper's magic is possibly a bit more powerful?

(At school I played Stephano in The Tempest once. Stephano is of course a drunk who stumbles around, falls in a swamp and contributes nothing useful to the sum knowledge of the island. Oh well.)
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Prosper
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« Reply #369 on: October 25, 2021, 03:08:53 AM »

Well never mind Shakespeare, here's a modern 'kitchen sink' drama. . .

I only have a couple of panel-mouldings left to do and just now had carefully peeled the tape off and released one side of the tailfin ready to do the other side. I saw that at the forward base of the fin panel, where it blends with the fuselage, the skin hadn't quite taken the curve of the mould so I decided to apply a tiny drop of water and use my 'tube iron' to stroke it into shape.

SCENE: KITCHEN SINK. IDIOT DROPS FLIMSY PANEL INTO SAUCEPAN OF OILY WATER.

I'm sure I remember my mum or grandma or someone saying "always do the washing up". . .now I know the reason. . .

The real concern was that I thought I had no sheet material left from which to cut a replacement panel. This would have entailed quite a delay while a new sheet was coated, cured, and thinned down. Luckily I found I could just squeeze a replacement from this off-cut.

Quelle palaver.

Stephano.
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Pete Fardell
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« Reply #370 on: October 25, 2021, 04:42:09 AM »

But don't forget that if Alexander Fleming had done the washing up he'd never have found penecillin. That could so easily have been a similarly ground-breaking moment where you discovered some unforeseeen and miraculous effect of oily water on balsa!
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Prosper
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« Reply #371 on: October 25, 2021, 04:05:51 PM »

Quote from: Pete Fardell
But don't forget that if Alexander Fleming had done the washing up he'd never have found penecillin
That's all the excuse I need. . .sorry grandma Cheesy

Pic 1 shows where I finished earlier today. Pic 2 - I made two laminated-card shells for holding the difficult top and bottom skin panels to the mould. They came too late to make any difference to this build, but will save more time (and entirely more vexation) than they took to make, where any future Spitfire builds are concerned.

Then I moulded the replacement fin panel and its opposite number. Next I joined up the lower part of the tail section, and the rear fuselage section - and lastly attached the leading edge to the fin skins. Arguably this could better be described as attaching the fin skins to the leading edge. . . .I'll ponder that and report back.

Stephen.
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Prosper
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« Reply #372 on: October 26, 2021, 12:59:10 PM »

Not a huge amount of progress today, but I got the fin more or less finished.
Quote from: Prosper
Arguably this could better be described as attaching the fin skins to the leading edge. . . .I'll ponder that and report back.
Well, I tried to explain what I meant here, but again it reads back like nonsense. I'll take step-by-step photos next time, perhaps.

Also the top decking panel behind the cockpit is now in place - I found this panel very difficult to attach to the side panels in the last model, but it went better this time. I'd hoped to get on to the wing fillet panels but ran out of time.

Stephen.
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Prosper
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« Reply #373 on: October 27, 2021, 01:36:53 PM »

Now the wing fillet panels are fixed to the fuselage, with an attempt to have them raised fractionally above the fuselage panels to represent the overlap of the original.

In side-elevation, the top line of the rear fuselage lifts slightly where it joins the fin. For me, this peaky bit at the back means that once the rear fuselage skins are glued together on the mould, the mould cannot be freed from the fuselage shell. The taper of the rear fuselage dictates that the mould must be tapped out from the back, but the peaky bit will rip open the top decking. Thus a loose component at the back of the mould, which drops away when the mould is tapped out. To accommodate this peaky bit, the top decking panel has to be slit at the back, and so it splays out when the skin is bound to the mould. One little task today was to glue a wedge of balsa aliphatic sheet into the gap. It still needs a quick bit of sanding to fair it with the tailfin.

The mould also appears to be trapped in the tail section once the skin panels are all joined together, but the tail section and fin are separate components, so the lower part can be tapped free from behind, whereupon the fin part drops free.

Stephen.
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kaintuck
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« Reply #374 on: October 27, 2021, 02:17:05 PM »

Just a neat way to build model!...REAL panel lines, not inked on Shocked
I have a few more years of stick n tissue to build, but I DO want to try your method of molded panels...
marc
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