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Frazer Nash FN5 gun-turrets


Fidd88
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bloody hell....

 

I thought this thread was a question about turrets in the wrong bit of the forum...

 

what I stumbled on is absolutely exquisite - you do what I try and do which is replicate every single bit, bob and doodad in an aeroplane structure, only you do actually do it!

 

bravo

 

...(oh and please don't ever put it in a model that actually leaves the ground...)

 

Peter

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Kind of you to say so Peter, I don't think we're comparable in that respect. All your work is highly skilled and careful - proper modelling and scratch-building really - whereas mine is simply creating shapes on the PC and printing them. It's time consuming and looks good, but it really isn't in the same league as what you've done with the P51. My approach is limited by the few materials I use, whereas you move heaven and earth to recreate a "whatyamacallit" in breath-taking detail - and then hide it! (the very definition of a 1st class modeller?)

Hehe.

For me, it's the engineering of the Wellington that is my primary interest, it's just such an elegant piece of design. I got into it when I realised that the issues which killed this technology stone dead in 1945, namely speed of jet aircraft being higher than the necessarily flexible fabric covering could withstand, and, a better understanding of metal fatigue, which didn't affect Wellingtons as most were struck-off-charge or lost in combat inside 2 months; but which certainly would have affected airliners in longer service. Lastly, it really wasn't possible to pressurise, which put the tin-lid on this technology.

I realised a while back that this technology would be ideal for cargo drones, as it confers a great weight-saving over stressed-skin, is easier to assemble and provides around 30% more "usable space" within the airframe. It's also very tolerant of failures within the structure, and "fails soft" as we might say now, rather than breaking up.

Looking at that problem led me to the Wellington. My father was an RAF fighter pilot at the end of the war, but like many would be aircrew waiting to be sent overseas to train (he went to 1BFTS in Terrel, Tx) he was sent to bomber-stations to assist with the marathon daily efforts to re-arm, re-bomb, service, repair and air-test aircraft for the next mission. He was put with a Wellington squadron, and it was far and away his favourite aircraft, because like me, he was something of an inventor/tinkerer/amateur-engineer

In fact the whole reason he ended up in the RAF was because in 1940, as a teenager he, aided by his brother, had built a home-made bomb, in case the Germans invaded. He didn't forsee that detonating it would set off most of the local sirens, after-which he and his brother were given a 1st class bollocking and invited to join up without delay!

It's certainly my intention  to fly the turrets, within what is in effect, a miniature Wellington, with the geodetics similar to the original but at scale. I admit I shall be rather relieved when the aircraft has a few flights under its belt, and it's quite likely that I'll do early flights with the turret positions fared over and ballasted. Just in case! Because fixings- rivets and bolts - have different properties at scale from a metallurgical point of view, and they cannot be miniaturised to the same degree as the rest of the structure, I've had to accept using what are in effect over-size rivets,  and that impelled a lot of changes to the geodetics sheer and gusset fittings so as not to introduce weaknesses through over-size rivets being set too close together.

To the untutored eye, however, it should look pretty close. One day! For now I've just enjoyed researching, fabricating the turrets. I attach an early test of the infamous "bomb". Sadly no footage or still of the one that caused all the trouble exists. I gathered from my uncle that it "weighed several pounds" and took out several windows. It did, however prove that the Anderson Shelter was "fit for purpose" as they detonated it on top with them inside! The logic of which you probably have to be male,  17 and at war, to follow!

have you seen the films on youtube Peter?

bw1.jpg

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Just so. There's obviously a ton of "show-stoppers" that if I can't find solutions for will render it incapable of safe flight. The first is if I can accurately curve extruded alloy channel without great deformation of the cross-sectional shape. I have some ideas for that, but it remains to be seen if that can be achieved. The intention, once the turrets are finished is to attempt to make a geodetic "football" circa 2 feet in dimeter, and then test it to destruction with vibration and shock-loads to see roughly how robust - or otherwise - the structure is. If it's still a go at that point, then the next issue is calculating the wing-loading/weight, and if that comes in ok, calculation of the likely C of G. If all that elicits positive answers, then building the fuselage will commence. In the meantime, I have the turrets done. I started with those as it gave me more time to think about the rather more tricky aspects of wrangling the geodetics.

But as Voltaire said "no problem can withstand the assault of sustained thinking".

My wife says of this project "it's not the destination, it's the journey", meaning that the endless technical problems to solve are fascinating in their own right. She says other things when  I float the idea of hanging the completed fuselage from the sitting room ceiling! :banned:

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5 hours ago, Fidd88 said:

My wife says of this project "it's not the destination, it's the journey", meaning that the endless technical problems to solve are fascinating in their own right. She says other things when  I float the idea of hanging the completed fuselage from the sitting room ceiling! :banned:

I think she’s been taking to my SO - it’s a conspiracy! 

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Truly. Today I started assembling the "cosmetic" ie non-functioning hydraulic pipes. In order to save money by being able to make the "nests" of parts more efficiently packed with parts, I had omitted all straight sections. These were very accurately made from 1/16" K & S metals brass tube which could be glued onto very fine lugs on the ends of 3d printed plastic parts. For now these will be painted and salted away for later fitting. This is because fitting the windows is liable to involve a lot of test-fitting of the cupola, and I don't want to damage the hydraulic lines by fitting them too early.

Film:

and the preceding one of the working pneumatically driven mechanism for raising and lowering the guns:

EDIT: I forgot to mention that I sourced the brass tube first, which was K and S metals 1/16th" which comes out as 1.581mm in foreign. All the torturous 3d printed "pipes" were made from some 8 stock shapes, so as not to have to construct every last "wiggle", and were drawn at the same diameter. Finally lugs were added to the 3d printed lengths to be glued inside the ends of the straight brass tubes. If the lugs were lost in printing, simply drilling a 0.75mm hole and inserting a bit of broken drill-bit of the same size remade the missing lug. Although there's a slight textural difference between the two, once painted they ought look like a contiguous pipe. If not I shall invoke the "4 foot decorators rule", namely if one can't see a blemish at more than 4 feet, it isn't there:secret:

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Thanks, but I try not to think about the  "scope" of it. It's more a case of 'putting one foot in front of the other' rather than working on the entirety of the project, not thinking much beyond which beans need to be in a row before the next tasks can be got under-weigh. If I thought through the whole project from stem to stern, I'd be driven potty!

This will likely be about it for now, as aside from painting and test-fitting the cosmetic hydraulic pipes, there's only the windows left to do, and they'll take months to make, as I need to:

Make an MDF "plug" of the desired shape reduced by 1mm (the maximum thickness of the Perspex), then cover that in resin and micro-balloons, before sanding it back, then sealing it with a glass coat and bringing to a highly polished finish. Then a two part glass or carbon-fibre mould is made of the MDF shape. Then that has to be similarly fettled with to make pristine. Then a resin and powdered aluminium cast is made from the two moulds bolted together. This is then fettled with to make, yet again, a smooth and blemish-free finish. Finally hot Perspex in a frame is vacu-formed over the alloy/resin plug. Then the real work begins cutting up those windows into panels and bolting them to the sub-structure of the turret. Oh, and I need to do all that twice for two different moulds to make the windows for both turrets.

And that is why I don't think about the "scope"! :icon_eek:

 

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This evening I've been getting ready for the Gaydon and Brooklands events, and I thought it might be fun to take a picture of the model from a similar angle to a book illustration, and greyscale both. There are a fair number of differences. Not all of them are "errors", as the turrets were in perpetual development, so nowadays you will not find two museum examples that are the same, or even similar in some cases! Furthermore, as many museum turrets are only accessible from certain angles, and historical ones are taken often from very similar angles, the models are necessarily a "composite" design taken from features in probably several dozen FN5's.

fn5-2.jpg

fn5-1.jpg

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Cheers, yep the bottom one is real. You should do the same with your and close-up shots of the wheel-bays etc on your P51. Yesterday I received a photograph of the engraved text on the console of R for Robert's (The Wellington raised from Loch Ness) front turret.. My first thought was to simply retype the test on a suitable background and put that on a decal. Instead I decided to manipulate the photograph itself into a decal. The model photograph was in very strong artificial light, in daylight the colour and contrast are darker and more respectively, and by naked eye, much clearer.

 

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Hi all,

Lately I've been painting the "tub" for the rear-turret, although I can't fit it until some packing-pieces arrive. In the meantime I've assembled and painted the dozens of "hydraulic" pipes. I've found that they're almost impossible to fit with the pneumatic hoses in situ, so all that has been stripped out and one set of "hydraulic" pipes fitted - but not glued. Gluing will only occur once the pneumatic hoses have been also fitted.

 

 

helimadkentub600.jpg

fitted pipes stack600.jpg

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The detailing is exquisite.

as Peter mentioned, you are actually doing what the rest of us only try to sculpt.

in a sense, every model we build is a “sculpture”.  It’s an approximation of the real thing, more or less limited by the combination of modeler skill, aftermarket doodads and kit contents.

what you are doing transcends this - you are sculpting some components - albeit at a level of detail the rest of us can mostly only imagine - while actually making the overall unit functional.

it would not surprise me in the least to learn that you’d somehow managed to incorporate some .17 caliber rounds and functioning actions into those scale brownings...!

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You may laugh, but the Brownings do actually incorporate a spring loaded "working parts" which have a sliver of very fine plastic, a "reed" if you will, protruding from underneath. This was supposed to flick against 2-3 similar "reeds" within a sound-box for want of a better phrase, so that when the guns were cocked (with the modelled cocking wire), as the working parts flew forwards or were drawn back, it was supposed to make an approximation  of the sound of the guns cocking. Unfortunately, as the guns were the first part that I made, I hadn't quite got the required tolerances correct, nor indeed the mechanism, so it didn't work. Silly, but great fun to try and devise and make.

Admittedly I had an O level (roughly high school pass) in technical-drawing, so had some basic skills to learn CAD via Autodesk Fusion 360, which you can still download and use free via the start-up/hobby use license, and it took me a month of doing tutorials to learn the basics, and 6 months to get really quick, by the end of the year I'd 'slain the beast' of constructing compound curvatures. This is something all of you can do, it's just a matter of a few weeks hard graft learning the basics. One of the really nice things about fusion 360 is that there are several ways of drawing the same 3d model, some are efficient, some less so. After a time you experiment with as-yet-unused commands and discover the faster methods. Coupled with 3d printing, it's a very powerful model-making tool. What's currently lacking is the definition, relative to injection moulding. So any cylinder less than 0.8mm diameter is likely to be very weak, if it successfully prints at all, any feature less than 0.5mm may be lost, and tolerances are circa +/- 0.1mm. Sheets of material can deform at the corners due different cooling rates. In short, you have to experiment a bit to find the limits of what is possible. In SLS Nylon, the finish is approximately that of an "extra-strong mint", so if putting two parts together I under-size each by 0.1mm on the abutting faces. When attached to each other, the overall dimension across the two parts then comes out as per the drawing.

Fusion 360 has excellent tutorials, and a very active forum for getting help. There are specific tools available to facilitate others following your drawing methods, and making changes, although I only needed to use this once - with compound curvatures.

I think I succeeded with this model on the "bumble-bee" principle, I never realised I couldn't do it, and just kept battering away at problems and learnt new skills until it nevertheless started to take shape.

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No laughter here!  I like that you even thought about the sound effects!  
 

I finally have a PC with enough horsepower to take on CAD, and I’ll have some time over the holidays to focus on it.   Some of the things I want to build/modify simply don’t exist, so it’s either rely on the kindness of those hereabout or roll my own, so to speak 

you’re a great example and set the bar high!

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Well I'm very happy to assist, either in queries about fusion 360, or simply drawing your (or anyone's) parts and preparing .stl files for uploading to a 3d printer. It's usually a pretty quick process. For a demonstration, the other day, I drew a fairly accurate caged electric-fan, and it took about 15 minutes to do and another 2 to ready the .stl file and upload it to a printing site. Of course when you first learn expect it to take a great deal longer!

One thing our American cousins will have to take into account is that most printers are configured to work in metric (mm), rather than Imperial, and so your drawings would likely need to be rendered in metric mm as well. It may be that US printing services do offer Imperial, but please check before you start. Fusion can be configured to either, and having configured it, all further drawings remain in the configured measurement system.

 

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A few more pictures of the cosmetic hydraulic lines now glued in situ. Very bloody fiddly, if you'll pardon the pun. Next job is to restore the pneumatic lines, then the front-turret will be as complete as it can be with the parts I have. Following that I'll be working on the rear-turret to remove the pneumatic lines temporarily, fit the hydraulic lines and then restore the pneumatic hoses. After that, the initial plug for the fabricating the windows in 0.5mm sheet Acrylic, and at some point fitting the two "tubs" for the turrets. I'll probably make some form of temporary stand for them to display in the house, unless she-who-must-be-obeyed happens to spot them!

 

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bowdens1.jpg

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..and a few pictures of the newly made an installed oxygen pipes. One plain one goes from the economiser in the bottom of the turret to a fitting in the port stanchion (front turret) and then a ribbed or "corrugated" one goes from the fitting to the gunner's oxygen mask. The ribbed one was made by taking single core electrical cabling with 3mm OD insulation, and then threading 600 O-rings of 3mm ID and 1mm cross-section (5mm OD), all then having heathshrink tape warmed to close over it, the o-rings providing the effect of the ribs. It did work, but the effect is a little too subtle.

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Cheers, I really only needed half those, so the remaining lengths are now salted away for future use, Actually I spent a very agreeable couple of hours listening to Classic FM on the wireless and sculling coffee as I did the 600 rings. The effect is 'good enough', but not, I fear, 'great' as far as the ribbed hoses go. Still, it was a fair stab at it, I'm glad you've enjoyed following my "triumphs and disasters" as Kipling puts it, as the turrets neared  completion. Frankly there'll not be anything else to report for some considerable time now, but I might post the odd update as the mould-making for vacu-forming the Perspex gets going, except maybe the front-turret "tub" which is a bit more interesting than the one for the rear.

I'll certainly be keeping an eye on all your incredible modelling projects here, If anyone needs parts drawing in CAD, at any scale, let me know, and if needbe I can advise on whether or not the part is viable to print in SLS Nylon. It's occasionally nice to do something not Wellington or turret related! I'm also pretty knowledgeable on the Wellington airframe if you need questions answering.

Thanks all of you for all your kind words, as you know modelling is a solitary battle conducted in sheds, so it's great to have had some feedback after years of boring the family to tears with the minutiae of turret-design!

Still, some of it has 'rubbed off' as my daughter has just started an engineering apprenticeship, and came home with this that she'd made from steel rods and plate at the end of week 1.

All parts are hand-filed by her with no observable "rounding" from the file being out of square to the work. Impressively if I reversed one of the two plates on the threaded rods, both the two hole centers, the four edges, and the four radii remain perfectly aligned! Easy to make, hard to make this well. She's also the only girl in 41 other apprentices! (Dead chuffed Dad)

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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 !

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