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Author Topic: 1/18th scale D.H. 85 Leopard Moth  (Read 8524 times)
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fred
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« Reply #75 on: July 25, 2018, 06:14:49 PM »

Possibility that the Styrene sheet used was of Poor Quality ?
Been Lots of Chinese sourced plastics that are proving to be of Very Low  (excreable?) quality.
They look /act well for about a year then turn to be glass brittle... often shattering in use.
 All this in complete absence of UV exposure.
Moderne times  Wink
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OZPAF
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« Reply #76 on: July 25, 2018, 08:39:47 PM »

That's interesting Stephen - I'm very curious now as George K is using a lot of this in his S39 build. Fred may be on to something there.

Trials and tribulations! How are the kestrel chicks handling your current UK heatwave/

John
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Prosper
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« Reply #77 on: July 26, 2018, 01:44:56 AM »

Ah! That could well be the explanation, Fred. Thanks.

John, the kestrel chicks are now self-sufficient and dispersed. I think the dry warm conditions might suit them well - it's the coming winter that they'll have trouble with.

Stephen.
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g_kandylakis
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« Reply #78 on: July 26, 2018, 02:48:24 AM »

Good morning from me too.

I have been following this thread from the very start with great interest, as I did with the previous ones, with a lot of innovative construction methods and ideas. Thanks Prosper !

On the matter of styrene, I cannot provide any input yet. It is my first use of this material. I did become a little worried when I first read about brittleness. However, I also have a lot of material from old plastic kits and it looks normal after many years. Quality might be an issue. Luckily I am using what appears to be rather good quality material (evergreen), but only time will tell...

George

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Prosper
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« Reply #79 on: July 26, 2018, 03:15:50 AM »

Hullo George, thanks for stopping by. The stuff I've used in recent years is Evergreen. Very expensive for what it is. I've been wondering if the styrene has more plasticiser nowadays to make it seem supple and workable - this evaporates over time and the styrene crumbles like goat's cheese. OTOH the styrene can be heated for vac-forming or plunge moulding (which would presumably evaporate plasticiser rapidly) with no short-term ill effects. I don't have any old plastic models but do have some 50 thou plasticard from 40+ yrs ago. I shall dig it out and see how it behaves today or soon.

Stephen.
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Prosper
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« Reply #80 on: July 29, 2018, 04:03:25 AM »

I'm now nearly ready to join the fuselage halves. I just have to 'dry brush' a bit more paint onto interior faces then I can give it a shot - today maybe since it's set to rain all day.

Quote
. . .I could choose to make a fancy, detailed interior which would be rendered daft by having a dirty great rubber motor running right through the middle of it - or make a crude and sketchy interior which would be sore-thumb visible from every angle because of all the glazing. . .
Now this issue is right upon me. I can see that the rubber motor will completely dominate the cabin, running as it will just below the windows and right through the centre of the instrument panel. I was going to attempt a basic throttle-box, trim wheel and a few other bits and bobs just to make it look homely , but now I don't know. I'll still have limited access to the interior until the undercarriage is made and installed, so I'll leave this matter for now.

The B&W photo is of sister ship, G-ACHB, taken in 1933. The interior looks light in colour to me - my eye says it's lighter than the rich green or red upholstery often seen in lightplanes of the era (or at least in their restorations). Nancy Bird talks of the "french grey" interior of her early Leopard Moth VH-UUG, and here's VH-UUL still extant with what looks like an original cabin, though I don't know that for sure. [in fact after another dekko - does that look more like PVC upholstery than old leather?]

Anyway I've gone for french grey. I consulted the internet to find out what colour french grey is, and according to one website it's a cool blue-grey, another website has it as a warm creamy grey, and so on. It seems that french grey is whatever you like. It's just light rather than dark.

It just happens that the shade I definitely wanted is identical to a bottle of RAF Sea Grey Medium I mixed a year or so back and of which I still have a goodly amount sloshing around. Isn't that lucky?

Stephen.  P.S. I couldn't find the ancient 50 thou plastic card. I know I've seen it in the last couple of yrs but. . . Either I consumed it in some non-modelling job, or - I did have a major modelling-related purge earlier in the year. . .maybe chucked it out as no longer fit for purpose. . .
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Prosper
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« Reply #81 on: July 29, 2018, 07:29:26 AM »

Joining the fuselage halves is not straightforward in this build. I didn't think it would be, but there's more accuracy required than I can easily deal with. I've got away with it so far, but it all gets more difficulterer from now on. I may carry on this p.m. but for now I'm a bit 'noivis in da Soivis', and what's more it's nearly lunchtime.

1. Strips cut from brass sheet with scissors. The brass measured 0.12mm on my vernier calipers.

2. Marked and holes twizzled with the relevant-diameter twizzler. It went through this brass knife/butter style, despite never having been sharpened. Sharpening just means cutting a new edge with a wire cutter.

3. The hinge tabs are lined up and filed to about the same shape.

4. Slits are cut in the bottom fuselage cross-member (these tabs will be the wingstrut hinges)

5. The tabs are fixed thus with liberal doses of the thinnest CA after checking alignment.
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Prosper
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« Reply #82 on: July 29, 2018, 07:32:42 AM »

6. A companion tool to a twizzler is this stabber, made from a snapped-off width of razor blade with the end filed, stoned, honed and stropped to razor sharpness. This is one of several I have; this one cuts 2mm wide slits.

7. With slits cut thru the longeron and fuselage skin the brass tabs can be pushed through. The pictures show inside and outside. I wanted the holes to be 1mm from the fuselage side and lo! they are. Now I have to repeat that three more times. The bottom cross-member isn't glued in place yet.

Stephen.
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Prosper
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« Reply #83 on: July 29, 2018, 11:50:58 AM »

I didn't quite get it finished, but it wasn't nearly so hairy as I thought it might be, and the pics show the final dry-run test of pushing piano wire through the hinges and seeing if they're aligned. Yes! Not only is there no binding in either pair of hinges but port and stbd hinges are lined up, meaning that if I can be as accurate with the corresponding wing and strut hinges, the wings should fold symmetrically. Having the wings fold so that one wingtip ended up higher than the other wouldn't be a good look. . .

None of this is glued up yet - I'll be fixing and gusseting and doubler-ing this next. Now where was I - ah yes. "Go G! Go G" Smiley

Stephen.
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OZPAF
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« Reply #84 on: July 29, 2018, 09:42:10 PM »

Precision and all by hand. Good one Stephen - like your twirlers and slitters Smiley

John
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Prosper
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« Reply #85 on: August 04, 2018, 04:41:17 PM »

I've spent a while of my spare time fiddling with this model - picking bits up, scratching my head, and putting them down again - that sort of thing. I had to make a new 'windscreen top tube' for want of a better term - the old one (seen perched behind the new one in the photo) didn't project from the fuselage sides quite enough, so I wouldn't have been able to pin the wings in place. Just how I'm going to pin the wings in place is still a bit of a mystery, but I know roughly how it ought to be done. I'm also making new skins for the top and bottom of the rear fuselage. After painting the original ones I could see that the grain wasn't well filled in places.

Stephen.
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Prosper
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« Reply #86 on: August 06, 2018, 04:01:25 AM »

A bit more done thismorning. . .first I CA'd the external strip, strake or spine to the top rear fuselage skin. The strip was made last evening, and is aliphatic-coated balsa, but when cut to width this exposed the sides - uncoated - so I sealed these with CA.  The second pic shows how painting revealed roughness in the strip (excess CA), and sanding this smooth obviously took off the paint in places. The silver paint I'm using shows little interest in sticking to hard outside edges - it retreats from them. Lots of touching-up required to cover these areas.

The next four pics are of the pins which  hold the "windscreen top tube" in place. First I hammered some 0.41mm piano wire flat on an anvil (remarkably small taps needed to do this), then bent the flat over, clipped the end off and filed it all to shape then cut the pointy-end so that the pin is about 5mm long. This was then pushed through the top tube into a pre-twizzled hole in the cabin vertical member and then fed several drops of thinnest CA, which finds its way rapidly into every gap. The head of the pin is arrowed in the last pic.

I hope to get some more done today.

Stephen.
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Prosper
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« Reply #87 on: August 06, 2018, 02:04:22 PM »

Quote
I hope to get some more done today.
Well, not much, but I did most of the work needed to close up the rear fuselage, and then got all the cabin tubing done. This latter effort has increased the rigidity of the body enormously given that the 'tubes' are 1mm dia bamboo. However I'm doubtful that they're the 'right kind' of strong: once faced with the job I saw that the only way to fix most of 'em was to butt-joint them with CA. They may well ping apart under the sudden wrenches of landing/crashing, esp. as the joints are not very good. The windscreen tubes going into the cowling former are pushed right through the former so should have some strength. The side tubes that go from the top of the windscreen into the top longeron were simply sharpened and stabbed a short way into the longeron, Dracula-style, before CA'ing. I thought this shouldn't impact the strength of the longeron much. All this fuss is important because these bamboo sticks are doing nearly all of the work of holding the cabin square, and much of the work of holding the front of the wings.

I need to slap a bit more Sea Grey Medium* around the cabin, and I've just spotted a structural omission in one of the photos, then I'll get the rear fuselage further on, then comes the undercarriage.

*Oops, I mean "Deluxe Interiors French Grey"

Stephen.
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DHnut
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« Reply #88 on: August 06, 2018, 02:28:56 PM »

Stephen,
            I know itis a bit late now but I have used carbon tube and joined them using short wire pins with little weight penalty on my AOP9. This has taken a lot of punishment. The glue of choice was epoxy that seemed have a little resilience. The Leopard looks very tidy and I like the wing fold and your twizzling.
Ricky   
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« Reply #89 on: August 06, 2018, 04:17:04 PM »

Quote
I hope to get some more done today.
the 'tubes' are 1mm dia bamboo

Where do you source your bamboo ?

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Prosper
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« Reply #90 on: August 09, 2018, 07:18:16 AM »

Ricky, I'm hoping to use carbon tube for the fuselage - or cabin area anyway - of an Auster V/J.1 one day. I didn't think it worth buying tube for the few members in this build - and anyway I didn't know what diameters they would need to be until you sent me those excellent close-up photos!

Hi Mefot, the bamboo is sourced from Tesco, or Co-Op or the like (cocktail sticks) and the 1mm bit happens here - "somewhere in England". You can turn the sticks down between folded sandpaper, with the stick being spun by a power drill, or I used a brass tube as in reply #67.

I haven't had the chance for an involved session on the model, so I've used bits of time to get the u/c strut blanks made. The core is balsa between carbon. The unidirectional carbon was unpicked from some cloth; I'm guessing it may be 3k but that really is a shot in the dark. One strip covers both sides of the balsa core. Pic 2 shows the cores and the folded outers which are balsa/aliphatic sheet. The picture shows where I've sanded the carbon very thin in a few spots, but it's still stiff enough I think. The next pic shows the cross-section of a strut, 3.8mm chord and 1.3mm wide, which are the scale dimensions I derived from photos.

A lush coat of silver paint leads to a nice shine and I tried to capture the gleam in hazy sunshine but this was the best pic I could get.

Stephen.
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OZPAF
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« Reply #91 on: August 09, 2018, 07:39:47 PM »

They should be strong enough Stephen and I guess pretty light as well.

The cabin area looks very convincing with your bamboo dowels simulating tubes.

John
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« Reply #92 on: August 13, 2018, 03:03:45 PM »

Thanks John - the painted  u/c strut blanks together weigh 0.65g. They'll lose some weight because they'll be cut back to size, but they'll gain some from the piano-wire joints.

I did some more work on this at the w/end but it was along the lines of 'one step back, two fwd': previously I'd replaced the rear top fuselage skin, but I found I was still unhappy with this second one - the fit and the quality. However, only after a good hour or two trying to "make it good" with various fudges, did I concede that it still didn't look "good" to me. Making a brand new piece was quicker than the time I'd spent tryin' to fix the old one. False economy. The new(est) version makes me happy.

Then today I made a nose cowling. Plunge-moulded, 40 thou (≈1mm) styrene sheet. I knew that the shape of the plug which would yield an accurate result was critical and that plunge-moulding is hardly an exact process, but as much by luck as judgement I got the plug right 1st time. It was third time lucky with the plunging though (pic 1), and just as well because I'm nearly out of 1mm plastic card. . .another two failures and I'd have been drumming my fingers waiting for a delivery.

Pic 2 shows the shaped item - it still needs work but is accurate to < 0.25mm in the critical dimensions.

Pic 3 shows the result of mucking around with the cowling trim and the main intake. The typical Gypsy engine nose cowling is more hole than cowling, which is why I opted for plastic. The picture reminds me of some childrens' cartoon character but I can't think what or why.

Stephen.
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billdennis747
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« Reply #93 on: August 13, 2018, 03:37:16 PM »

The picture reminds me of some childrens' cartoon character but I can't think what or why.
A Minion
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« Reply #94 on: August 13, 2018, 03:59:25 PM »

Ta Bill, I searched minion and got: "Evolving from single-celled yellow organisms at the dawn of time, Minions live to serve, but find themselves working for a continual series of unsuccessful masters, from T. Rex to Napoleon. Without a master to grovel for, the Minions fall into a deep depression. But one minion, Kevin, has a plan; ac… MORE"

How I've lived approx six decades and been keen on biology, history, paleontology (or is it pop music) and warfare without ever having having learned about this, beats me. Could these minions explain why the world is in such a godawful state at present?

Stephen.
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« Reply #95 on: August 13, 2018, 04:08:54 PM »

https://www.google.co.uk/search?q=minion&source=lnms&tbm=isch&sa=X&ved=0ahUKEwiX-8Ca6urcAhVMI1AKHe-9D2oQ_AUICigB&biw=1517&bih=735#imgrc=tdNPXItM05ijWM:
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« Reply #96 on: August 13, 2018, 05:20:08 PM »

Belatedly - for what it is worth I have some styrene sheet of varying thicknesses and it is all of fifty years old  - I bought it in a local model railway shop where the owner was retiring which is how I can date it!  Seems very useable still.
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« Reply #97 on: August 14, 2018, 06:39:43 AM »

My stock is about 20 years old and seems okay. I think it can suffer loss of strength from exposure to UV so is probably best kept in a dark cupboard or drawer if stored for long periods.
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Prosper
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« Reply #98 on: August 14, 2018, 10:45:08 AM »

Warning: don't open the link that Bill posted! It's okay - it's not malware - it just links to a page full of hundreds and hundreds of pictures of these minion toys. It will leave you feeling very ill.

Thanks for the styrene info fellers. Another thing that happens to plastics is the slow evaporation of the plasticisers that make them ductile, so perhaps keeping the material cool helps too.

Today I've spent some time puzzling how to make the plastic nose cowling fit into the model's nose former whilst adequately supporting the propshaft and accommodating six or so grams of lead. . .whilst still being hollow enough not to block the apertures cut into it, and to allow some rudimentary engine details. I want the disc behind the propeller recessed too, to look lifelike: in the original it's just a great big 'ole.

I put a coat of silver on the cowling to show any flaws; there are two or three, which I'll fill with CA.

Stephen.
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« Reply #99 on: August 15, 2018, 03:59:25 AM »

Quote
Today I've spent some time puzzling how to make the plastic nose cowling fit into the model's nose former whilst adequately supporting the propshaft and accommodating six or so grams of lead. . .whilst still being hollow enough not to block the apertures cut into it, and to allow some rudimentary engine details

My suggestion would be to have to have a flange on the inside of the cowl(styrene?) mating with a closely fitting hoop former( also styrene) in the nose.

You could put some of Bill's minions to work on this problem Smiley

John
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