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Author Topic: 1/18th scale Spitfire for rubber power  (Read 4780 times)
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Prosper
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« Reply #100 on: January 06, 2021, 11:51:50 AM »

Here's the wing jig. The tips have just been added and the central support extended. The test model had wingtips built separately and fixed to the wing off the jig. Also each wing was built separately, then joined off the jig, after which the belly panel was added. I hope to make the whole wing in one piece this time. The tips added to the jig are of two layers of thick card, moulded and glued as described up the thread. The card is soft, pulpy stuff - I hope the tips'll be adequate to the task.

Next I have to perform the last two jobs on the wing skins, namely cutting out the uncovered part of the wheel well and various other little cutouts - and then embossing the aileron rib tapes and stitching as I did for the rudders and elevators. Once that's done I can sit the bottom skins in the jig and perhaps commence some actual assembly at last!

Stephen.
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packardpursuit
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« Reply #101 on: January 06, 2021, 01:41:00 PM »

Ah, a "British bird" . The very suggestion takes me back to when  American youth culture became enthralled with many things  influenced greatly by our own limited understanding  of popular English youth culture.

Now, I could never decide if I was supposed to be a "rocker" or a "mod"? For a time, I was fairly  convinced I was probably "Gear"( one of the stages of teen angst/conceit?) .  

IIRC, the activation of dried white/alephatic glues ( for dry bonding heat activation bonding situations)  is called "polymerization" and first read about the procedure in Model Aviation magazine, about 1967 or '68( post-Carnaby St, but definitely pre -Zeppelin).   I believe  it was presented as a method of attaching sheet balsa, wrapped over ribs/spars to make something called ( also new to me) , a " D tube" wing structure. Years later, this particular adhesive knowledge  proved quite instrumental in advancing my worth as a custom fixture fabricator,  which in turn, led  back into paying aircraft woodwork.  

BTW- heat activation of dried white/ alaphatic glues is usually only good for one heat process. Once polymerized. said adhesives will not re-activate with the the same level of initial bond strength, if at all. It is my understanding that the heat activation causes the glue to change molecular structure.

Spitfires, models of same, and neat model building techniques are still pretty  "Fab"!

Anyone ever consider "beer can" sheet aluminum might provide viable skins for a flying model? I've used it for decking around  open cockpits and it works quite well with simple shapes.  Hope to report results of HLG experiment, using the material for airfoiled wings in lieu of 1/4" sheet balsa.  My gut tells me it will prove a bit too heavy for rubber, as it comes from the can, but might prove quite adequate for wing/fuselage skins for 24"-30" outdoor IC scale? So far I think learning cheap effective annealing would be beneficial. Etching could prove important to reducing material/thus model  weight?

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billdennis747
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« Reply #102 on: January 06, 2021, 01:49:08 PM »

Anyone ever consider "beer can" sheet aluminum might provide viable skins for a flying model? I've used it for decking around  open cockpits and it works quite well with simple shapes.  Hope to report results of HLG experiment, using the material for airfoiled wings in lieu of 1/4" sheet balsa.  My gut tells me it will prove a bit too heavy for rubber, as it comes from the can, but might prove quite adequate for wing/fuselage skins for 24"-30" outdoor IC scale? So far I think learning cheap effective annealing would be beneficial. Etching could prove important to reducing material/thus model  weight?


Litho plate can be etched to paper thickness with sodium hydroxide solution and is great for detail. The trouble with using it structurally is you only get one crash!
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dosco
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« Reply #103 on: January 06, 2021, 04:34:49 PM »

BTW- heat activation of dried white/ alaphatic glues is usually only good for one heat process. Once polymerized. said adhesives will not re-activate with the the same level of initial bond strength, if at all. It is my understanding that the heat activation causes the glue to change molecular structure.

Perhaps that is the answer to Prosper's problem. Make the skin (with the aliphatic), hit it with heat.

Fiddle with the skin to fit it to the substructure, apply white glue, let dry, hit with heat ... voila! Wing!

-Dave
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strat-o
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« Reply #104 on: January 06, 2021, 04:38:44 PM »

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Litho plate can be etched to paper thickness with sodium hydroxide solution and is great for detail. The trouble with using it structurally is you only get one crash!

Well that would certainly add to the realism  Cheesy
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Prosper
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« Reply #105 on: January 07, 2021, 04:55:24 AM »

Quote from: Packard
BTW- heat activation of dried white/ alaphatic glues is usually only good for one heat process. Once polymerized. said adhesives will not re-activate with the the same level of initial bond strength, if at all. It is my understanding that the heat activation causes the glue to change molecular structure.
I think I've noticed that with CA. For thrust bearings I use brass tube fixed in the noseblock with copious amounts of CA. This can easily be reset to a different thrustline by stuffing a hot wire into the tube, whereupon the CA melts, the wire is used as a lever to set the new angle, and as it cools the CA hardens again. I've wondered if the CA is as good after two or three goes, and as a precaution give the area another dose.

Dave, if I understand you right you're nearly there regarding "Prosper's problem". I wouldn't use the re-melting idea to stick wing skins to spars from the outside except in an emergency - but it's nice to know the technique if indeed there is that emergency Smiley. The only alternative I can think of is to cut holes in the skin to get gluing access and then try to 'make good' the holes. Very time-consuming, and quite possibly disastrous cosmetically.

My workplace is chilly this morning. I lose some sensation in my fingers after a while. I mightn't get anything done today.

I thought 'Mods and Rockers' was a peculiarly British bit of silliness. I didn't realise anyone else was aware of it. Da yoof is awys up to somefink innit bro.

Stephen.
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dosco
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« Reply #106 on: January 07, 2021, 09:38:07 AM »

Dave, if I understand you right you're nearly there regarding "Prosper's problem". I wouldn't use the re-melting idea to stick wing skins to spars from the outside except in an emergency - but it's nice to know the technique if indeed there is that emergency Smiley.
Stephen:
So I will say this (admittedly out of complete ignorance of your fabrication technique):

Seems that you could possibly use the "aliphatic remelt" process with some relative ease. Put some indexing features on the jig and skins (could be marks, could be tabs, etc.) so as to register the alignment of the pre-glued areas (spars and matching locations on the skin).

Since the initial aliphatic (used in your skin fabrication process, per your previousl descriptions) can be "remelted" only once, and prior to the wing assembly process, there shouldn't be any worries about gumming up the iron, or having other problems.

Anyhow, don't let my rambling affect your plans. Am watching with interest!


Quote
My workplace is chilly this morning. I lose some sensation in my fingers after a while. I mightn't get anything done today.

Perhaps another reason to use a warm iron to affix the wing skins? (I'm kidding)

Quote
I thought 'Mods and Rockers' was a peculiarly British bit of silliness. I didn't realise anyone else was aware of it. Da yoof is awys up to somefink innit bro.

Oh, there is quite the following of "British motorcycle culture" here in the colonies. I have some friends that are very much into British motorcycles.

-Dave
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Prosper
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« Reply #107 on: January 07, 2021, 11:09:04 AM »

Quote from: Dave
Put some indexing features on the jig and skins (could be marks, could be tabs, etc.) so as to register the alignment
That's zackly what I will be doing, as I hope to show over coming days. It's the re-melt bit I'm doubtful about. I might experiment in a small way in another build, because if it did work straightforwardly it would be most useful. Anyway, we'll see, and as I said there is one way in which I've already used the technique to good advantage, which I'll get to when I make the fuselage.

Yes I believe we made some classy motorbikes, tho' much too noisy for my taste - 'Bonnies' and Norton Commandos were names thrown around in my youth. . .but there's some irony in a present-day U.S. admiration for the cultural aspects, surely: surely the culture came here from the U.S. in the first place - Brando 'The Wild One'; Hell's Angels and so on? And isn't Bonneville something American, a luxury car or something? I bet the canny Triumph marketing department were very purposefully trying to suggest 'Americana'! Secondly I bet half those Brit rockers would have wanted a Harley D more than anything on Earth! But the 'Mods and Rockers' thing was a specific phenomenon, where at various times the two tribes squared off and laid into each other. I think it was 90% media hype to 10% reality, but it got the establishment in a tizzy about 'moral collapse'.

Stephen.
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packardpursuit
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« Reply #108 on: January 07, 2021, 02:14:05 PM »

Wow! I was only thinking of the musical "British Invasion". I had totally blanked on earlier exposure to B.S.A's., Triumph's, Nortons, JAP's, and Matchless! Which I was quite aware of at age 10, or so. Most of the hill climbers here seemed to favor B.S.A.'s but had friends that rode them all. 1st day, after school , freshman year 1964-65, my good friend and fellow FF modeler, did a wheelie across the entire student parkin lot on his barely street legal Matchless. Instant school fame! His dad and mine, used to hill climb and race flat track together, before WWII.  I liked motorcycles, rode quite a few, had a blast!  However,  I could barely afford modeling, at the time.

I still like Spitfires, and the occasional Kinks tune, on Youtube.

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Prosper
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« Reply #109 on: January 11, 2021, 10:33:36 AM »

I've done nothing for two or three days but this morning managed one small task, the cutting-out of various bits of the wing skins - mostly bits too small to see here - and trimming off excess material round the edges. This bottom skin, all trimmed except for a slight excess at the L.E., now weighs 2.1g.

Stephen.
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packardpursuit
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« Reply #110 on: January 11, 2021, 01:22:17 PM »

Wow.  "rough" line work is quite artsy  and convincing.
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Prosper
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« Reply #111 on: January 11, 2021, 02:53:10 PM »

I meant to say - but senility got the better of me - that the photo shows the inside of the wing. The lines are drawn to facilitate matters generally. Note the redundant line delineating the outboard edge of the u/c door - I got my measurements wrong and spotted it in time.

There are black-line markings on the outside too - to facilitate the scribing of panel lines . . .but here's a problem: it takes several tons of spray paint to obliterate these lines (I've found). To remove the lines before painting requires a solvent: a solvent which will attack the surface coating as well as the black ink. I'll have to do my best there.

Stephen.
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DavidJP
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« Reply #112 on: January 13, 2021, 10:08:03 AM »

Hmm like the fact that the bottom wing skin weighs 2.1gm.  About the same as the tailplane on peanuts I have built. 

I was divided on mods and rockers because I liked motorbikes but also I liked the smart clothes of the mods.  So I posed as both.  I don’t think a motorbike was essential though because of cost.  Vespas and Lambrettas were more so. Yes there were “bundles” as we called them but they were a lot of dust and noise mainly. Some I believe may have carried a bicycle chain but I never saw one actually used - possibly swung about maybe - but l in the main we were too scared of the consequences of being caught with one.  Same with drugs - apart from the rich only being able to afford them they were known to do terrible things to you.  And most parents would have dished out terrible punishment if you had them.

A ‘bike I coveted was the Aeriel Square Four - 1000cc and we thought it must be capable of breaking the sound barrier as it was almost twice the capacity of anything else. 

Once again Stephen you are delighting us with your fascinating build - you are multi- talented indeed.  Thank you. 
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Prosper
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« Reply #113 on: January 13, 2021, 01:46:57 PM »

Quote from: DavidJP
So I posed as both.
Did that mean you had to beat yourself up on Bank Holidays?

Sorry David - couldn't resist.

Today I scribed various lines on the belly panel, and also stamped the little flap-actuator doors on the wing top surfaces - something I'd forgotten during the previous scribing session. I also finished the ribs to their final shape.

All reasonably painless, but . . .I knew that getting the belly panel to join neatly with the wing panels would be a job. The area at the rear is all curves, and the line between belly panel and wing panel - although a straight line seen in plan view - cuts across the curves obliquely. What I did was to place the wing panels on the jig then slide the as-yet untrimmed belly panel underneath one wing panel. Then I moved it about until its centreline and fore-and-aft position were correct; then, pressing all down snugly against the jig, ran a fine pen along the edge of the wing panel, so marking the exactly required line on the belly panel. Repeated for the other side.

Easy and quick! Trim the panel to those pen lines, and glue the panels together!

Well, not really. The whole gluing effort was a size ten mess. There are ugly gaps between the panels and I'm not confident of the three-dimensional shape that's resulted, which could impair the proper blending of wing and fuselage. I'm not entirely sure what went wrong. No doubt lack of light and poor eyesight didn't help (I had three electric lights plus whatever daylight there was, and still couldn't see well). I think everything was too shifty. Although I used sticky tape and weights to keep the wing panels in place on the jig, there was a lot of aligning to key marks on the jig, then rechecking the other wing panel was true, then noticing that the belly panel had budged meanwhile, and re-setting it disturbed the wing panels . . .

I'm really glad I opted to make the two pairs of wings one at a time instead of concurrently. At least this gives me a chance to work harder on the problem when I come to make the next pair. This pair is for the PR.IV model.

The last pic shows the PR.IV fuselage on the now-irrevocably-glued lower wing surface. The real test comes when I fix the ribs and spars in place, at which point the wing, now minus only the top skins, should integrate tightly and accurately with the fuselage. Should.

Stephen.
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Pete Fardell
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« Reply #114 on: January 13, 2021, 02:41:46 PM »

You've been working this kind of magic for so long now, Stephen, that I don't know why I'm still amazed. But I am. That last photo photo for instance: essentially you seem to be able to create beautiful things in balsa exactly as if balsa were sheet metal and had all the same necessary properties! How much did the devil pay you for your soul?
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Prosper
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« Reply #115 on: January 13, 2021, 05:25:24 PM »


Quote from: Pete Fardell
exactly as if balsa were sheet metal and had all the same necessary properties!
Ah. well, you've put your finger on it there Pete. Except for the fact that I haven't yet made a model which satisfactorily exhibits the basic notion - and I may well never do - it's this: have you ever seen, real or video, the alloy sheets which make up a Cessna or Piper? (Or before milled panels became common, any aeroplane - a bomber or pressurised airliner?) They're so floppy it's ridiculous. They belong in an orchestra as the wobbly sheet which simulates thunder.

So, without meaning in any way to sound pleased with myself, I'm still amazed too, because every single build using this coated sheet style, the same thing happens: I make the basic material, typically 0.3mm thick, and think; yeeks! this is way too weak! Then, when I've assembled it into a tailplane or rear fuselage or whatever, I think - wow, that's too strong for this application. Must make it lighter next time Smiley. You'd think that I'd have got over it by now but nope: happens every time. The same with the wing spars which are raw balsa thinned to 0.3 or 0.4mm. Yeeks! Way too flimsy! The chances are they're not.

Stephen. PS the devil paid me £36 4/6d. I was young at the time and thought it was a fortune. Only years later, grown-up, did I realise I'd been rooked. But it's okay - he's not a bad bloke. We have a laugh.
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OZPAF
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« Reply #116 on: January 13, 2021, 07:42:33 PM »

The whole monocoque structural approach is really amazing when as you mention the individual skins are so flimsy yet require little in the way of reinforcing to become an efficient load bearing structure.

Man learned from nature in this regard.

Regardless of any gaps Stephen - that is inspiring work. Pete is spot on regarding the representation of the flowing curves of the metal original.
The panel approach on the fuselage has worked well!

john

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dosco
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« Reply #117 on: January 13, 2021, 08:24:45 PM »

The whole monocoque structural approach is really amazing when as you mention the individual skins are so flimsy yet require little in the way of reinforcing to become an efficient load bearing structure.

Man learned from nature in this regard.

Regardless of any gaps Stephen - that is inspiring work. Pete is spot on regarding the representation of the flowing curves of the metal original.
The panel approach on the fuselage has worked well!

john



Concur. Looks stunning ... I particularly enjoy the grain pattern on the "exact replica" ... just so awesome.

-Dave
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DavidJP
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« Reply #118 on: January 14, 2021, 03:33:13 AM »

Yes Stephen as a matter of fact I did beat myself up on Bank holidays as it was one way of ensuring I did not get hurt!

 Now this Devil fellow - could you put in word for me perhaps?

For once I am lost for words on your progress thus far on the Spitfire. 
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Prosper
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« Reply #119 on: January 15, 2021, 12:46:47 PM »

Thanks chaps.

This building method does lend itself to monocoques; as John says, even a little bracing stiffens the shell up remarkably. I hope to show this when building the second fuselage, which I probably won't get to until the second wing is complete. I've often thought that a hybrid of stick and tissue flying surfaces plus monocoque fuselage might produce the best in terms of speed of building and weight. But only where the original's flying surfaces are fabric covered, that is. I've had the Norseman and the Fairey Albacore on my list for years . . .

I didn't have much time today but got the mainspars just about finished. I just wrote a detailed description of how this assembly goes together but it means nothing, so I deleted it. Suffice to say that the bits in pic 1 are the mainspars - the nearer one with its caps or flanges added - and the rest is what joins the spars across the fuselage, plus the root ribs. This is an exact copy of what I did with the test model and it proved very strong. Pic 2 shows how with minimal fiddling the assembly wedded with the fuselage - none of it's glued up, but it just held in place by friction long enough to take a snap before the spar fell off. I hope to get this all fixed onto the bottom of the wing tomorrow, and the other spars too.

Stephen.
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TheLurker
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« Reply #120 on: January 15, 2021, 01:15:18 PM »

That's looking rather special.

Quote from: Prosper
... a hybrid of stick and tissue flying surfaces plus monocoque fuselage might produce the best in terms of speed of building and weight. But only where the original's flying surfaces are fabric covered, ...
Hmmm.  Early MK I Hurricane?  You'd only have to do the front half of the fuselage as a monocoque and not half so many complex curves.  Smiley
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Prosper
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« Reply #121 on: January 16, 2021, 04:36:15 AM »

Quote from: TheLurker
You'd only have to do the front half of the fuselage as a monocoque
Well this is where it gets interesting Lurker - I don't see any "have to", as in feel compelled to take a less desirable option. The rear fuselage with those innumerable stringers would I suspect be heavier than a monocoque, and embossed stringers might look better than balsa ones at the scales I build to. The greater the curvature the less internal support the monocoque needs. Then, the Hurricane wing with its excessive thickness and great number of ribs might end up as heavy as an all-sheet wing and take longer to build. And you'd be stuck with an early Hurricane; I prefer the idea of a 20mm or 40mm or CAM or AFDS Hurricane. As a very rough guide I think that all-sheet wings come out 1.5 to 2 times as heavy as S&T wings with normal rib-counts - but fuselages are the same or lighter, esp. at the back where it counts.

Stephen.
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« Reply #122 on: January 16, 2021, 02:55:57 PM »

Hurricane.  Another legendary aircraft that largely lives in the collective consciousness of modeler's and enthusiast, as being more complex than it actually was/is.

I'm probably going to get some heat on this, but I contend all stringers on Hurricane are true straight lines (no curve evident when viewed from any angle).   IF true, stringered portions of Hurri fuselage could be done with scribed/embossed sheet balsa of simple curvature panels. Fitting in quite well, as per Prosper's usual practice? AFAICT, the odd curved/faired  bump in the stringer lines of spine, just aft of cockpit, is where fabric bridges a  gap (natural forming  fabric fillet?) from top of heavy external ply gusset bracing the wooden radio mast, to fair back into the stringer lines.

At present, I really  like A.L. Bentley's Hurricane drawings. I feel his only SLIGHT correction of the fuselage side stingers, as he shows them in Top/Bottom views.

https://www.rcgroups.com/forums/showthread.php?2676971-Hawker-Hurricanes

 I included the whole thread (still relativeley short, at this time), because I feel some of straight v. curved observations/discussions  relevant there ,  also have application to what we are dealing with in understanding observable Spitfire shapes.
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