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Author Topic: Westland Whirlwind (fighter).  (Read 5098 times)
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« Reply #50 on: November 27, 2016, 02:55:25 PM »

The availability of trained pilots was very definitely considered, and remained a key strategic priority throughout the war with planning at the very highest levels of the Air Ministry, which is why we spent such a lot of money and time sending pilots to Canada for training in addition to maintaining full flying training in the UK throughout the war

But so was the  question of getting the best possible military effectiveness from the manpower and resources available to produce the weaponry of war.

In the case of the Whirlwind, in 1937 when the machine was selected for production it made sense to give it (if you'll pardon the pun) a whirl. When that decision was made no-one knew how history would play out in terms of the availability of other superior types. But by 1942, it was obviously both uncompetitive and uneconomically expensive - meaning wasteful in terms of the war effort - compared to machines which did the same job better. The Spitfire IX and P-51B were prime examples then becoming available in serious numbers. Making a smaller supercharged RR V12 costs much the same as making a large one of the same configuration: most of the cost is machine tooling and skilled labour, and when the large one is in genuine mass production (the Merlin) it costs less than a similar small one that's in small-scale production. So the skilled manpower of building and maintaining two complicated engines rather than one, for the same flying task, was unjustifiable. Same goes for other expensive components - a constant speed prop for a Peregrine doesn't really cost any less to make than one for a Merlin, and again doubles the maintenance burden for a single-seat fighter.

Combined with the high powertrain cost and maintenance burden was a high airframe cost. The large scale production of Spitfire at the Castle Bromwich plant, and the genuine mass-production of the P-51B/C, provided real economies of scale. It was a much better military decision to put your trained pilot in one of those machines than to put him into a Whirlwind.

All that said, it's a tremendously attractive and charismatic aeroplane, I wish we had a survivor, and this is shaping up to be a wonderful model which I'd much rather watch than another Spitfire or Mustang.
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« Reply #51 on: November 28, 2016, 07:48:21 AM »

Thismorning's work.

I see three approaches to cutting relief wedges out of flat sheet in the hope of coaxing it to form a double-curved shape. The first you might call the 'Perfect' method: by measuring the cicumference at several points of your desired final shape, you can plot the exact shape of the cutouts, which might look like a very thin trumpet shape or a very thin cigar shape. Then when you bind the wet wood to the mould the gaps will close exactly, but if you get it wrong the ultimate formed shape will be wrong too. Then there's cutting out deliberately oversized wedges, then there's cutting out deliberately undersized slits, which is what I tried in this case. Each method has pros and cons (surprise!) and this third style means that the panels of balsa, separated by the cutout slits, will overlap when bound to the mould. If these overlaps are accurately sliced off, the front few millimetres of each panel should butt-join with its neighbour (pic 1). The moulding wasn't quite as tight or curved as I wanted, so after CA'ing each panel to its neighbour at the nose, I wetted the front, rebound it and force-dried it. Pic 2 shows it at this stage and shows a shim of polythene sheet worked under the wood to act as a mould-release and protect the EPS from cyano. Getting wedges or fillets of balsa into the gaps can be a faff but I seemed to "have my eye in" this a.m. and it was quick work. Note: these wedges must not be forced into place (easily done) - this will push the whole effort out-of-round. The filling balsa must just sit in the slot without pushing the sides out. Each fillet is now fixed with CA and there's pic 3. Remaining pesky gaps - too thick to fill with CA but as thin as as a sheet of paper - are filled ad-hoc with bits of balsa sanded very thin (pic 4). This is a tricky time because the wedges glued with CA are now much harder than the surrounding wood but have to be sanded fair. I did this very gingerly using a rectangle of 1/16" balsa as sanding 'block'. A lot of angled light helps - thank you winter sun. That's pic 5.
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« Reply #52 on: November 28, 2016, 07:50:37 AM »

Now, pic 6 is why to use relief holes at the apex of each cutout. I mentioned that the initial binding involved some thinking and working on the hoof, and I cut this relief slit at the bottom of the nacelle half, without cutting a corresponding hole (lazy). These holes aren't strictly crack-stops as Marlin suggests - there's no tendency for the wood to split in these locations - they are to spread the compressive stress found at these points which otherwise rumple up as shown. I've just wetted, flattened, rebound and force dried this flaw but it's dried back in so I'll be cutting that out and patching it. I should have cut the slit longer and twizzled a hole at the top.

This may all seem involved but I swear it's taken nearly as long to write up as to do!

I then gave the same treatment to the overlapping panels in the rear portion of the nacelle (pic 7). I patched the flaw with a flat patch - risky because a hole that size has appreciable double-curvature and sticking a flat patch in can tug the surrounding area out of shape. I fixed the patch in bit by bit with dots of CA, bending it as I went and breathing hot breath on it. Pic 8 is the inside, showing that once again my attempt to get datum markings transferred from the EPS mould to the balsa shell has failed again.

This weighs 1.2g by the way. I may CA-coat it later but it's a beautiful day outdoors and chores need to be done.

Stephen.
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« Reply #53 on: November 28, 2016, 01:06:58 PM »

I got the major CA coating done. I used some fairly thick CA - probably the same as 'regular' viscosity but much thicker than the stuff I normally use for making things. Because the wood was thick too - say 0.5mm in this case - there was little risk of CA getting through to the EPS mould, but I slid a polythene sheet between wood and mould just in case. I apply CA with the pad of my middle finger - takes 5-10 minutes to cover the half-nacelle. It's not a method I can recommend, not because it's anything but effective and practical, but because some people might be revolted by it or worried their finger will drop off or something. One is left with a thick pad of dry CA on one's finger - the time taken for this to crack off in my experience varies from half an hour to a few hours depending on what's going on. Pic 1 shows the initial application (oh BTW I gave the shell a good sanding with medium-fine grit first). Pic 2 shows the shell after sanding the CA down (again, I don't know if CA dust is any more injurious than say, PVA dust or cellulose dope dust, but I strongly advise not breathing it anyway). The blobby look of the shell is due to having applied CA locally to fill pores in the wood (very deep in this individual piece). The CA is dotted on using a wire seen at centre right of the pic. I used to think this unviable - looked at the hundreds of tiny pores and thought "no way", but I don't think this application took more than ten minutes.

Thanks for the insights to Whirlwind history folks - very interesting stuff.

Stephen.
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« Reply #54 on: November 28, 2016, 04:27:02 PM »

As usual with your stuff this is a wonderful example of experimentation in constructional technique, and I am full of admiration. I wouldn't be disgusted by the fingerful of CA (wary of the fumes, though). But having on a few occasions inadvertently attached myself quite severely to the D-box sheeting of a 30" span Hurricane during construction with thin cyano, I am not in a hurry to repeat the experience. Keeping a large bottle of acetone and a helpful second party in the house is a safety combination I  recommend from personal experience.
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« Reply #55 on: November 28, 2016, 05:53:11 PM »

Interesting reading as usual Stephen. I like the way you use the round holes at the ends of the slits and then so easily fill them after moulding. Very neat.

John
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« Reply #56 on: November 28, 2016, 06:20:48 PM »

Good advice WIP. In my wish to be concise I missed a few points: my middle-finger pad is the CA spreader not applicator. I squeeze a few drops from the plastic bottle onto the workpiece then rapidly spread the drops out with said finger. This is repeated perhaps 8-10 times on a piece like this half-nacelle and so the CA 'rubs off on me'. The trick is to keep the finger moving; any halt can lead to embarassingly fond intimacy between pinkie and balsa. Finger pads are so exquisitely sensitive to what's going on that they tell you very accurately if a calamity is in train and if they tell me I'm about to be 'wedded to my work', I start twisting the finger rapidly and that releases it before needing acetone or scalpel. I attach a picture of the middle digit I used this a.m.; probably foolish because I may now be 'fingered' for the bank heist I pulled last week, but it shows that no damage accrues from spreading CA, given a bit of practice and sense.

Hi John, in theory those holes can be filled with the exact discs you've just twizzled out with your sharpened al. tube - but in practice I find the workplace so chaotic that it's easier to blow them and any other chaff onto the floor and then twizzle new discs from same-thickness balsa when the time comes. They're not always so neat when initially glued, but in this case because I'm using softer balsa I allowed the sheet to be thicker (closer to 0.5 than 0.4mm), so I could sand them down a bit more. Also CA, so long as it's not the thin or extra-thin stuff I normally use, is a good filler Smiley.

Stephen.
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« Reply #57 on: December 01, 2016, 01:22:31 PM »

Today I unwrapped the stbd shell of this nacelle and got it filled and coated in good time. There was a minor disaster when butt-joining it to its other half - I misaligned the join and had to resort to acetone to release the joint. The acetone distorted the balsa near the joint (by softening the CA coating) and the ultimate repair was a mess. I smoothed things out somewhat with a hot iron consisting of an extruded bar of aluminium which I heat in a flame and which is long enough to be cool to hold and yet store enough heat to give a decent working time. Then I trimmed the nose former (3mm balsa 3-ply) and got that in place. If only I could arrange to get markings from the EPS mould onto the inside of the shell the work would have been much faster and there'd have been no occasion for the misalignment foulup.

For this nacelle I opted for lighter but rather thicker sheet, and the result so far weighs 3.5g with little to add to bring it to the same state as t'other one. So not only does it look like ending up lighter than its partner, but a whole lot lighter than the mockup nacelles. One unhappy finding is that the joints between the different panels or petals of balsa which fold into the final curved shape, tend to distort over time. This means that, in cross-section, rather than a continuous curve there's a slight polyhedral kinda look. I observed this on the first nacelle but that was made from stiff balsa so I wasn't surprised that it didn't make a full curve. But this nacelle of softer balsa has developed the same look. It wasn't helped by my weilding of the hot iron.

Tomorrow I should be able to make the main former and internal reinforcement. The shells for the fuselage nose are nearly done too so things are moving on.

Stephen.
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« Reply #58 on: December 02, 2016, 07:30:12 AM »

I forgot to photo the laminated main former before installing it. I made a laminated former because I thought it would lend more resilience to the nacelle. I found that formers like this are so quick to make, that I may employ them more widely from now on. I used 4 strips of 0.4mm straight-grain balsa. There's no need to soak this to get it around the former. (That's a former former, so to speak. If you retired it from use it would be a former former former). The only problem with the laminating was to join the ends without sticking pins through the narrow strips. The -cough - former former has waxed edges, so I CA'd one end of the strip to it with just a smear of glue, then got the strip round snugly and butt-joined the ends. Once that was done the other three laminations were easily fixed likewise. Then I flooded one side with thin CA, released it from the waxed former (the strip-ends I'd deliberately CA'd to the former released easily), and flooded the other side. Result, one former approx 1/16"sq weighing 0.175g.

I've just re-read that and I can't understand a word of it - wish I'd taken a picture Sad. I think I've read of people using laminated formers in stick-and-tissue structures? Must look very elegant. I added a single cross-piece to the former; there will be a solid panel at the top when the nacelle mounting is made.

The other innards are two tearstraps and two buttresses. The tearstraps are glued about halfway between nose former and main former, and are meant to stop splits propagating - or, ideally, to stop them happening in the first place. . . Wood splitting in a crash is my main concern for this style of structure. The straps are approx 0.5mm straight grain and again could be curved to fit with no wetting - they're fixed with aliphatic, let dry until it was tacky, to avoid smearing it everywhere whilst muddling the straps into position. A temporary former was then jammed into place inside the straps, to ensure they made intimate contact with the shell while they dried.

The buttresses behind the nose former speak for themselves. Pic 2 shows the inside, including some of the (useless) blotchy markings transferred from the EPS mould to the shell. Pic 3 is an attempt to photo the installed laminated former - guess the lams are just about visible.

Then I joined the boat-tail and got the thing on the scales. 4.1 grams. Not too bad in my estimation.

Stephen. PS the former former former (I've finished with it now, you see) is visible at bottom of Pic 1.
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« Reply #59 on: December 15, 2016, 01:16:41 PM »

I've used up quite a bit of time experimenting with making better balsa/aliphatic sheet, and mucking up various attempts to make the nose section and rear fuselage.

I mentioned that there's a cost in time and effort to make the blank balsa/ali sheet I use so much. I haven't made any for a year or so and remembered it as quite a chore - but in fact it's quicker and less laborious than I recalled. However I'd lost the knack of producing the finish and light weight the stuff should have, and produced some very rough-surfaced, heavy sheets before getting things back on track.

I made a nose section from CA-coated balsa just as per the nacelles but didn't like it - despite care in building, the dreaded 'polyhedron effect' really showed up. Rather than an unbroken double curve there was a distinct flattening of each panel. I resoaked and I hot-ironed, got things just nice, but the flattening reappeared in a day or so. After telling strat-o that coating balsa with aliphatic after shaping the item in question wasn't reely possible, I thought I'd try again (been there done that yrs ago but my skills have changed since then). It still didn't work: as before, because the painted-on aliphatic needs to be sanded smooth, the surface becomes gouged by aliphatic dust coalescing into balls and rolls under the abrasive block or paper.

Then I made a tail section from half-shells of balsa/ali sheet. Didn't work out well either. Next was to try a tail section made from several panels, rather than two symmetrical halves. I've wanted to try this for a long time. Each panel should be able to adopt its allotted double-curve more readily than a large sheet - needing fewer relief cutouts, or perhaps none. A whole component could be made with panels the same as on the original (gear doors, hatches, cowlings etc).

This worked well, though it was a bit nerve-racking to join all the seams. Each successive seam is more difficult to glue, and more critical to the final shape, than its predecessor. The whole effort would have been much quicker if only I could transfer markings from the EPS mould to the inside of the balsa shell or panel. Still haven't solved that one, which means that rather than cutting a panel to exact size immediately, guided by exact markings, I have to remove a narrow slice off an edge then check it against the EPS mould then repeat and repeat until the edge matches the line drawn on the mould. Very slow job. However, the method required zero relief cutouts so time was saved because such cutouts need careful filling and fairing. Although these pictures don't show it, the Whirlwind's rear fus. has curvature directly comparable with, say, yer Spitfire or 109. The top is dead straight which suggests a simple tube - but not so, as I've found to my cost.

Pic 1 shows matching up two panels before gluing. The panels have previously been wetted and bound to the EPS mould to give them their shape. Pics 2 and 3 show the first glued seam (phew!). Pic 4 shows the second glued seam (pheeeuww. .!) and 5 the whole thing (phweeeeheuugh!). It weighs 2.4g without formers or other internal structure, and that's 1.3g less than the same component of my mockup Whirlwind made from plain 1/32 balsa sheet.

Pic 6 is of the nose section half-shells, and shows that preformed balsa/aliphatic sheet can be tortured into quite rounded shapes. Touch balsa, this should be the final, working nose section - so long as it doesn't go polygonal on me. . Shocked

Stephen.
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« Reply #60 on: December 15, 2016, 05:23:44 PM »

I've experimented with pure CyA resin parts by pressing a shape into modeling clay, removing it, pouring in CyA and letting it cure.  The end result was surprisingly flexible.  I was taken aback when I poured a flat sheet onto the modeling clay because not only was it flexible but it tore easily.  It could be the oil in the modeling clay was interfering with it's strength, but based on those experiments it kind of makes sense to me some of the things you are experiencing when your joints are under constant tension.

I guess what I was expecting from the CyA is something more along the lines of how a small puddle of cellulose-based glue hardens and becomes very tough, slightly flexible, resilient and difficult to tear.

Marlin
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« Reply #61 on: December 15, 2016, 06:58:08 PM »

Awesome stuff. In the true sense of the word!

Don't stop.

Dan.
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« Reply #62 on: December 16, 2016, 03:20:31 AM »

Agree with Dan Stephen. Very entertaining as well as informative.

John
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« Reply #63 on: December 16, 2016, 09:17:38 AM »

These builds of yours have been extremely informative, Stephen, and a number of the tips have been incorporated in my builds.

Quote
I've experimented with pure CyA resin parts by pressing a shape into modeling clay, removing it, pouring in CyA and letting it cure.  The end result was surprisingly flexible.

The face of my A-26 pilot was done using this technique.  The biggest problem was getting all the clay out of the crevices - toothbrush and toothpaste got most of the stuff removed, but still had to resort to acetone to clean it enough for the paint to (hopefully) stick.
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« Reply #64 on: December 19, 2016, 03:47:46 PM »

What happens if you use Ambroid or Duco? That's beautiful work.

BTW, for those who have undertaken a Whirlwind project but have found it a bit much, here's a way to salvage your work:
https://static.rcgroups.net/forums/attachments/6/8/2/8/a8616898-142-Westland_Whynotte_cover_reduced.JPG
See attached for more info.
Westland Whirlwind (fighter).
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« Reply #65 on: December 19, 2016, 06:16:31 PM »

Don't miss the even-more-elusive Westland Wynotte II.

Sorry, I couldn't resist.
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« Reply #66 on: December 19, 2016, 08:13:59 PM »

Beautiful Stephen!  Once again I am in awe of both your exceptionally talented building skills and your patience.
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« Reply #67 on: December 20, 2016, 03:44:21 AM »

Cheers fellas (Christmas cheer come to that). Lincoln and Mike, thanks for the info - the Whynotte I and II are definitely on my list now but only after the Sopwith So-so, the Hawker Homebuilt and the Fairey Fourflusher.

There are mysteries about CA - sometimes it will cure on an imporous surface perfectly clear with little or no loss of volume. It seems tough and flexible and seems a tempting material for small tansparencies and mouldings, but then sometimes it will shrink to a fraction of its original volume and become opaque and/or wrinkled, and be brittle and crumbly.  As for balsa-coating, I don't know if Duco or Ambroid are available in the UK - I'd give 'em a go if they come in small bottles - the main property I want in the coating formula is grain-filling ability.

I made the former that will join the fuselage tail section to the cockpit section. In side elevation the join is canted backward 10°. I decided to make it from laminations of 0.3mm balsa and because of the backward cant, the strips I cut were of a wavy outline (pic 1). I cut a balsa former to fit snugly into the rear fuselage, and then reduced it by 1.2mm all round. In theory by hooping 4x 0.3mm laminations round this former, the resulting laminated strips should also fit snugly in the fuselage.  Rahter than waxing the former to release the laminated hoop, I just glued the first strip onto it, thus making it a sacrificial former. Pic 2 shows a test fitting after two strips were fixed, and pic 3 shows the whole lot. The third strip was a bit wider than the inner two, and the outer one is about 12mm wide. In fact the former would no longer fit, so I sanded the wide outer strip off, sanded a bit further then added a new outer strip, which fitted nicely. Finally I cut the sacrificial former away leaving a rim, and fixed some hard 0.8mm crosspieces. Pic 4 is the final object pushed into place.

All this faff is because this is where I will grip the model for launching. Not only will the finished former have to resist crushing from my anxious grip, but it must spread the pressure over the balsa/aliphatic skin, because unsupported skin sags from repeated finger pressure, leaving dents either side of the former.  Again (thanks to cyanoacrylate) this is one of those things that hardly takes longer to make than to write up Smiley. It will be fixed permanently to the cockpit section and the tail section will be fixed to it with PVA, allowing removal after soaking if the tail needs repair or replacement. It weighs 0.35g which is very close to what a solid 1/16" bulkhead would weigh, but a 1/16 former doesn't answer the load-spreading requirement or provide much bonding surface for security of fixing.

That may have been quick to make but now I'm wrestling with the tailfin. This blends elegantly with the fuselage so you're trying to make one complex curve meet with a rotund single curve along a particular line (pic 5). It would be all too easy to shave too much of the fuselage skin away - it's easy to remove, very hard to put back. . .The way I'm going about this is to pick up the two parts, look at them from different angles, put them down, scratch my head, slot the fin into the fuselage, look at the result from different angles, put it down, scratch my head. . .This may take some time. . .

Stephen.
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« Reply #68 on: December 20, 2016, 10:06:33 AM »

the main property I want in the coating formula is grain-filling ability.

Thanks for these intriguing builds that really replicate fully skinned prototypes much better than stringers and tissue.  I appreciate that cyano rubbed in with your well smoothed finger gives a very fast result.  Large amounts of cyano would just about finish me off as even a quick dab of the stuff sets my eyes watering.  Many years ago I made large r/c gliders with balsa skinned wings.  Sometimes they would be glass over balsa and sometimes balsa alone.  The method of finishing was to coat the surfaces with epoxy resin thinned with methylated spirits. To get a nice smooth surface without a lot of rubbing down I would mop off the excess epoxy with paper towels and then overlay the resin coated surfaces with sheets of melinex rolled down to expel bubbles and get an even surface coating.  After curing overnight  the melinex would be peeled off to reveal a shiny, smooth and moisture proof surface that needed no finishing.  I don't know how much it could be bent and twisted after that because on my models it was always on finished structures.  Just a thought.
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« Reply #69 on: December 20, 2016, 05:38:09 PM »

Nice detail work there Stephen. Ah re the head scratching - that could be dangerous for the herbage that resides up there Smiley
Would a small fillet help the fin/fuselage blend ? This could be tissue or?
John
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« Reply #70 on: December 21, 2016, 12:25:04 PM »

Hi Ralph - epoxy's a possibility, but not for me - I'm with epoxy as you are with CA Smiley. I don't think I'm allergic to it but having used it in large quantities in the past I've had a life's worth of the stuff. The gloves and goggles, the precise mixing, the cleanup operation. . .however I suspect that it would be a good grain filler in a single application ( with a release film on top as you say) and as for flexibility and weight I would guess it would be in the same range as CA, aliphatic, dope and so on.

Hi John - I was very misleading by saying "blends elegantly"; on re-reading that does sound like it's faired nicely - whereas in fact the exact opposite applies. There's no fairing at all. I guess I meant that the two items, rear fuselage and fin, are both shaped with the other in mind, so no fairing is needed. Something like that. Come to think of it there's nothing remotely elegant about the Whirlwind tail - forget I ever said it Smiley

Anyway, I think I've just about got away with it - won't quite know 'til it's painted. It all started to go 'orribly wrong at the end and there's been some bodging involved, but to "take away some positives" as the England cricket team likes to say; 1) at least it looks vertical - not a given with my models Cheesy   2) it seems very tough and resilient, 3) the whole rear fus./fin assembly weighs 3.3g which isn't too tragic. Pic 3 looks down inside the fin - look Ma no ribs. This was a gamble that the fuselage would have enough stiffness to hold the fin to its correct section once glued in place. It seems to have paid off (thus saving weight). If it's gone all wonky by tomorrow morning I'll be very peeved.

Stephen.
Attached files Thumbnail(s):
Re: Westland Whirlwind (fighter).
Re: Westland Whirlwind (fighter).
Re: Westland Whirlwind (fighter).
Re: Westland Whirlwind (fighter).
Re: Westland Whirlwind (fighter).
Re: Westland Whirlwind (fighter).
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strat-o
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« Reply #71 on: December 21, 2016, 01:40:19 PM »

That's pretty neat.  Reminds me of a Constructive Solid Geometry computer model https://en.wikipedia.org/wiki/Constructive_solid_geometry where you have successfully achieved a union operation of two curved solids in real life.
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« Reply #72 on: December 21, 2016, 02:00:18 PM »

Quote from: strat-o
"a union operation of two curved solids"
There, y'see? That's what I was trying to express by saying the two components "blend elegantly" - only I didn't have sufficiently tekno-geek language to express myself Grin.  Thanks Marlin. Reminds me of when I tried 3D modelling to make flight simulator aircraft. I used an open-source thing called Blender. It was amazing but I realized it would take me about 5,000,000,000 years to learn it. I made a DC-3 cockpit and fuselage by sheer bloody-mindedness but there were holes in it so if you flew the flight sim you'd see the ground going past through various slits and gaps Cheesy.

Stephen.
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« Reply #73 on: December 21, 2016, 06:51:45 PM »

I think your fin / rear tail cone junction is an improvement on the original - hope that doesn't make it non scale Smiley Certainly more elegant Smiley

Westland's certainly didn't try too hard to achieve a smooth blend at that point.

I like the internal structure - neat and light.

John
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« Reply #74 on: December 22, 2016, 05:25:26 PM »

Stephen, as an aside, what are the possibilities of doing a polished aluminum finish using your moncoque techniques?  Seems everyone complains how difficult it is because it highlights every covering blemish.  I suppose your technique would highlight any surface blemishes.  Do you have any examples of polished or even unpolished aluminum finishes?  Thanks

Marlin
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