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Frazer Nash FN5 gun-turrets


Fidd88
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4 hours ago, Jeff said:

I have no words in my vocabulary for this.....................when I first joined this forum, I 'thought' I was a model 'builder'........... then it became painfully obvious, after seeing the talent here, I reduced my rank to "model assembler"........................ now, I must reduce my rank even further, to just 'model gazer'................... this, and what Peter does is the epitome of VERY FINE Scale Modeling.................... this project is so MUCH more than model making or 'scratch building', it is everything, EXACTLY like the Barnes Wallis went through in making the first design, it ALL has to be engineered and done mathematically , this is so many light years ahead of my skills, and is absolutely mesmerizing, the attention to the finest detail is stunning, and like the others watching this come together, I will be watching with much interest and intrigue for as long as it takes, this is absolutely mind blowingly good...............  "Press On" Fidd................. out-bloody-standing !

Blimey. Well I'm glad you chaps are enjoying the builds as much as I have been. Seeming as you are still, here's a picture or two of making the ribbed hoses with O-rings and heat-shrink tape. I think for anything smaller than 5mm OD, I'd strongly recommend shrinking the tape over 3d printed ribbed hose, instead of threading o-rings, as the effect is really a bit too subtle. You'd laugh if you knew the lengths I go to to avoid having to do mathematics! There was some simple geometry involved in getting the elevation and depression, and getting the sight-bar to remain parallel to the guns via the swinging arms and pushrods. But that's about as nasty as the mathematics got.

In the pictures below, the finished hose is approximately 5.2mm max OD. The "Ballooning" was caused by the O-rings or insulation getting too hot and generating gas in a localised pocket. On the next attempts I did not try to shrink all the tape in one session, but let it cool between passes with the soldering-torch, which prevented further gas pockets forming.

o23.jpg

o22.jpg

o21.jpg

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Re-reading my post above, I forgot to mention that in picture #2 (middle of 3) you can see the 2-3mm spigot of wire+insulation+shrunken tape that I left before the start of the O-rings. Having the tape longer than the rings obviously helps stop them from moving. It wasn't possible to achieve the hoses without the tape, as the O-rings attract dust and stray hairs like you wouldn't believe.

This was more or less essential to be able to glue on metal tubes without the latter appearing over-size. Although the K and S metal tubes were nominally the correct ID (internal diameter) to take the "spigot" I found it necessary to drill out the tubes a little from 3.69mm (or thereabouts) to 3.8mm iirc, which as you'll appreciate is pushing it a bit as the wall-thickness is only .14mm. However it can be done on the pillar-drill, but a machine-vice is most necessary. Proxxon do some really great little machine-vices for about £60, which I use all the time. The tubes were drilled to a half depth, so that the small brass tubes would fit nicely into the undrilled portion.

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  • 4 weeks later...

Not much been happening lately, beyond getting a modeling mate over who had a good selection of oil-paints, pastels and pigments, and more importantly the knowledge to apply them. I'd used quite a lot of Alclad "dirt and grime" around areas of the internal turret area which would have been very hard to clean and which probably had some hydraulic-fluid attracting every bit of dust going! We found that methylated spirit, with a drop of washing-up liquid in it, brushed onto the Alclad-painted SLS nylon proved the perfect thing to cause the subsequently applied mixture of water and black/grey pigments to spread well over the area, and then dabbed it back with a little absorbent paper. In concert with the previously applied 'dirt and grime' I think this worked well.

A week or so #1 daughter and I exhibited the turrets at the LMA's Gaydon show, and were very busy from circa 10:30am  until 4pm when it stopped. The highlight for me was a young Polish lad of about 5, who operated the syringes powering the elevation of the guns grinning all the while. He then asked about the Polish language 'cautions' on the turret doors, and his father explained about Poles flying these aircraft in the wartime RAF, and the lad was completely 'made-up' on digesting this. It was fun to see this education and enthusiasm!

As my CNC router still has some as yet undiagnosed fault, I've been trying to find someone local who can cut out the 610mm by 610mm MDF panels to make the initial plug for the mould to vacuum-form the front windows. Things should proceed apace on making the moulds and thence the windows once this occurs.

The dirtied webbing straps

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Chordal brace stiffener with a little muck

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Front right side, hard to clean for "erks".

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Central console and supporting metal structure now much toned down with dirt and grime

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Left-hand ram, ditto

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general view

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Front left baffle

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  • 4 weeks later...

Stunning modelling congrats, just a quick question, where do you source your drawings from, prior to drawing the up in an appropriate package. I have access at work to all the Autodesk products via the company license, just have to install them. Would be good to know where to find measured plans.......

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Many thanks, to answer your question:

Simple: There aren't any. :secret: No technical drawings of Frazer-Nash turrets survived to this day, so I got there by brute repetition of drawing the shapes, fitting them together in an assembly drawing, and continuously revising the designs over the best part of 4 years correcting things by reference to photographs and examination of the turrets at Brooklands. I had some help from Cosford and the BBMF who kindly photographed their turrets from angles not usually photographed, eg from underneath to figure out the hydraulic lines routing. The only two drawings I had to work from were book illustration line-drawings from the LH side and top, which proved quite incorrect, particularly on the geometry involved in keeping the sight-bar parallel to the guns whilst missing all the gubbins within the turret as the bar and sight moved, and much else besides. I did have help from Mark Evans who has drawn some components from recovered wreckage, and these CAD drawings, reworked to some degree, helped enormously in getting everything to scale.

I'm currently working on the master-assembly drawing to incorporate all the dimensional corrections that were too impractical or expensive to fix on the current models. Once this drawing is complete, the intention is to rework the two turret drawings to the most common RC scale for aircraft carrying FN5's, and reducing the weight still further, and simplifying some aspects of the build. It can then be made available as a kit, or I may build turrets on a  commission basis if there's demand.

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I can practically gaurentee you that no original drawings exist of the FN5 or FN5a. There are number of turrets reverse-engineered in CAD, much as I did mine, but they're all proprietry, eg Peter Jackson (of hobbit fame) has an aircraft modelling company that had drawn the FN20 in CAD. Despite my offering to sacrifice my first-born, they were sadly unwilling to let me have their CAD drawings of it!

The Imperial War Museum may have replica RAF posters which shew annotated cut-away drawings of various wartime RAF turrets, but they're always non-isometric, so not easy to dimension from.

It's just possible that the Yanks held onto the drawings they were given in 1940along with specimen turrets, to kick-start the US turret programmes. Amusingly the Americans took one look at our turrets, declared they could do better, (not unreasonable) and then quite independently made all the same errors we had in developing them ourselves before coming up with the very clever and reliable electric barbettes on the B29, Sperry Ball turret and so forth.

If you search youtube for Fidd88 or go here, you find all the little films I made as they went together - triumphs and diasters!

Fidd's FN5 model build films

Edited by Fidd88
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On 12/7/2019 at 7:14 PM, Bomber_County said:

Stunning modelling congrats, just a quick question, where do you source your drawings from, prior to drawing the up in an appropriate package. I have access at work to all the Autodesk products via the company license, just have to install them. Would be good to know where to find measured plans.......

I've had a shufti at my now considerable collection of FN5 pictures, and found the two drawings from which derived (eventually!) the CAD drawings used to build the model. A number of changes had to be made to aid construction, but dimensionally they were initially correct to these drawings until experimentation proved that there are errors in these drawings if it's mechanically built as per the drawing. Hence a lot of faffing about making corrections until all the moving parts acted as they should, and didn't hit anything around them, or the inside of the cupola.

These images are 600 pixels high, if you need higher res I can supply to an email address.

plan2.jpg

plan1.jpg

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...and here's a shot of our the line-drawings above were scaled and used as "canvases" within Fusion 360 to start relating the plan form of one with the side-elevation  of the other, to start making 3d sense of the drawings. This was only the very start of the process and some 2.5 years were spent, most evenings, in refining the drawings little by little until the 3d model worked mechanically, and resembled as closely as possible, photographic references. There's upwards of 1300 distinct versions of the main assembly drawing, and around 3 times that for individual drawings of components. The reason for this is that with such a large multi-part assembly drawing, making new parts within the assembly drawing made my computer grunt with the strain, so sometimes I'd export a cluster of parts alone, make the new part in that drawing to conform with the exported parts, before importing the new part alone back into the assembly drawing.

redcanvases.jpg

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I'm self-taught on Fusion 360, via few tutorials online and then experimentation. I fear I don't even know what "parametric" means without looking it up! I did classical draftsmanship at school 40 years ago, but nothing since. If I can help with anything, I will, but such talents I have with Fusion are a consequence of sheer stubbornness, not training! In other words, there may others better placed to help.

I used to the same scaled canvases in x y and z planes to work out the shape of the fuselage, and interpolate the shape of temporary bulkheads on which the curved geodetic panels can be built. In order to generate the MDF shapes around which each member has to be curved (a largely theoretical exercise currently) the fuselage shape with be sliced laterally along the lines of the 4 tubular longerons, and then those portions sliced again at 45 degrees to the vertical. 

fueslage v71 fwd end 2.jpg

fueslage v38halfleft.jpg

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If you are an old drawing board draughtsman, then you are an in-born parametric designer. You thinks 2D dimensions and angles before thinking 3D ... Don’t even think about using Blender. Designing a shape without entering dimensions seems .... very very very alien to me :blink:

Hubert

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 I was fortunate to have access to the microfilm archives at Brooklands, so I had the assembly drawings for the "five and half", "twelve and a half", "twenty-two and a half", and "fifty", and "eighty five" frames bulkhead drawings. But not the 90 frame, nor the "wishbone" pair of frames which supported the deleted ventral turret. So most of the internal shapes I knew, and it was a matter of interpolating between them to attain smooth curvatures without any "lumps". In my drawings the frames coloured silver relate (in shape) to the known dimensioned drawings, the wooden shapes being interpolated values between them which correspond to the known vertical and lateral extents of each shape at each interval.

So, these shapes replicate - as far as I can achieve, the space within the geodetic channels on the Wellington. They're in two parts because the floor over bomb-bay is plywood covered geodetic channel. On the model, the geodetic channel is roughly 1/2" on the long axis of the rectangular cross-section, and about 1/4" deep. I had to vary from the scale size owing to potential difficulties getting a rivet-gun into some of the areas required, and the need to thicken the metal over scale to reduce the risks of metal-fatigue.

Once the turrets are finished, the next project is to source some extrusion, some prototype alloy shear and gusset fittings, and some more metalwork tools, before building  prototype structures - most likely a ball and a short length of cylinder to fatigue test before committing to fully building the model.

My wife says I "think well in 3d", as I can do aerobatics "on the fly" and roll out at a particular point in space in relation to another aircraft (only on the pc these days!) but am hopeless in 2d - I get lost in London within seconds, much to her amusement! She, on the other hand, has the navigation abilities of a homing-pigeon crossed with a bat!

PS what it "Blender"?

pf.jpg

pilotsframecontours.jpg

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Urgh. I'm not surprised most "free" 3d software is worse than useless. Fusion 360, which is free for non-commercial use, was the first one I found that was decent. I must have tried 10 or so free ones before that, all were as much use as a chocolate tea-pot!

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24 minutes ago, HubertB said:

On the contrary, Blender is very good and very capable. It just requires a mind frame I have not. But if you are in organic design or 3D animation, you can produce wonders with Blender. Check it online to see what you can do.

Hubert

Thanks, I may. Attached is a picture of the fuselage from aft. The tail-end is still not quite right, as I need the dimensions of the 90 frame, but it's getting closer all the time. The wishbone frames need trimming too - they're poking out at the bottom currently!

fueslage v93.jpg

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This next image shews the method of interpolation. The lines (by inspection) represent the paths of the longerons, which could be defined in space both laterally and longitudinally. Wherever these were plotted, these formed a point to use the "spline" command in fusion 360, with other points at top and bottom. The ratios between these were kept constant as the fuselage tapered iirc which helped smoothly transition the shapes. Probably, accidentally, what you call "parametrics"? A similar plan drawing operated in the same way. The results aren't perfect, but they're pretty close, in terms of constructing the 3d shape from 2d drawings. The picture was named "loo-seats" as my wife said that's what I'd drawn when shown the initial drawing!

looseats.jpg

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8 hours ago, FME erk said:

Its almost scientific this modelling but what stunning results . . . .

Wellingtons are a favourite as they were stationed at the airfield located just a couple of miles away  . . . .

You probably can't throw a stick In Lincolnshire without it landing within two miles of an ex Wimpy field!

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