1:3.7 scale Frazer Nash FN5 turrets

[Fidd88]

After nearly 5 years, I've just completed the pair of FN5 turrets for an RC model. The turrets are designed to be filmed from within, when the eventual model is in flight. So whilst the model isn't complete, a major portion of the effort is, in the form of the turrets.

I attach a single picture, in case it might interest you, and a film and still taken from within the turrets.

Cheers,

15 minute youtube film with narration

[GusMac]

Just stunning work and completely mind-boggling! 

[Fidd88]

Cheers Gusmac.

To be honest it's less complex than it looks, the elevation mechanism is surprisingly simple. Probably the hardest part was ensuring moving parts didn't collide with each other, and in particular, didn't collide with the underside of the cupola, whilst allowing the guns the full 105 degrees freedom of movement. Working at this scale meant being able to screw things together with tiny M1 screws and nuts, which allowed the build to be backtracked without causing damage, but also greatly added to the apparent detail. Sometimes there's "trickery" afoot, for example the control-handles are 3d printed as one solid unit, including the mounting of the handle. But I drilled, tapped and added screws nonetheless, as per the full-size turret which makes the control-handles appear as multiple small pieces screwed together, rather than one piece augmented by functionless screws...

 

[Bomber_County]

Absolutely stunning, a true work of art, congratulations........

[harv]

Amazing!!.......harv 

[Fidd88]

Thanks lads. Given the standards of modelling in here, that means a lot - especially after the best part of 5 years holed-up in the workshop or long hours at a PC doing the CAD work.

It's funny to be finally free of them, if you understand what I mean. The next phase promises to be a but tricky. The geodetics will be made from extruded alloy, rivetted and bolted together once curved and notched to the required shapes. There's a lot of show-stoppers inherent in this, which if I can't solve, means I may have to do away with the geodetics in alloy. Similarly, there's some expense involved in sourcing the miniature rivet gun/compressor and Avdel rivets, and even more in the alloy extrusion die. So I need to sequence all this very carefully so I don't get caught with tools I can't use, or extrusions which are wrongly sized for being able to get the rivet-gun into (from both sides), both the preceding okay, but unable to get the internal sheer and gusset fitting made at a sensible price. Finally there's the issue of getting the "chains" made, which will sit inside the geodetic channel whilst it's bent, whose function is to prevent the cross-section of the channel from collapsing.

All these things need to come together for the build method to work.

I attach a picture of the two types of geodetic joint, one to cross-members, and one to the tubular longerons.. These now need to be redrawn, owing to the change from 1:4.5 scale to 1:3.7 scale. The picture below is not a 100% accurate to the real thing, although the function of all the parts are. This arose due to the fact that rivets in particular could not be reduced in scale to the required amount, which meant hole-centres are necessarily further apart in mine.

 

[Clunkmeister]

Excuse me while I pick me jaw up off the deck.

 

[Fidd88]

Hehe. It looks worse than it is. I'm bloody hopeless with woodwork, so a balsa aircraft was never on the cards, but a very large model in metal is "doable". It's really the geodetic engineering that's my primary interest, so I've been thinking hard about this for around 7 years already. Although the Wellington's geodetics look very complicated to make, it's actually pretty simple. There are just two main types of joint on the whole aircraft, and once those are mastered, the only remaining obstacle is to define the required curvatures, and devise a method for making accurately curved members. Once those are solved, it'll go together as fast as I can bend them and rivet them into place. By the same token, once patterns are made for producing the curvatures, repairing crash-damage should be equally swift, just as it was on the original aircraft, assuming it's a hard-landing rather than an obliterating "lawn-dart" sort of a prang!

Once the issues above are solved, I'd estimate being able to produce around 3 feet of fuselage a day, and about the same span-wise for the wing. So it's all the preparation that takes forever, once actual building commences it should be pretty quick, not least because it's fundamentally going to be very repetitive.

[Fidd88]

One of the things I'm currently dealing with is the changes to scale that occurred during development of the turrets. I realised, early on, that at 1:4.5 scale, with the intended radial engines fitted, that there would be no gap between the cylinder-heads and the cowl. So the scale was changed to 1:3.7, and the CAD drawings changed to reflect this. Now that the turrets are complete I'm coming across all the consequential issues resultant from that change. First off, the Wellington will be just barely able to fit in my workshop with the wings removed, and then only with the turrets and supporting structure forward of the terminal rings at station 1A at the front, and 97 at the back, removed.

The second thing I twigged is the jig I built (yellow thing) and the datum bar (black) were now 30cm too short! So I need to let-in a 30cm length to the existing datum bar, ensuring it is perfectly oriented in relation to the end of the cut bar, and, similarly lengthen the 4 measurement bars, and then strip and repaint all the markings on the datum bar which of course are now wrong! Bugger! Pics to follow of the current jig when re-worked. I'll also try and take care of the sag in the measurement bars else I'll need a correction table based on length and rotation.

 

[Fidd88]

After a smelly, dusty and noisy week, I've cut the datum bar and let-in a 300mm length of 50mm square hollow square section steel, and likewise lengthened the 4 measuring bars. A foul job out of the way, with endless clamping and checking so as to get the extensions completely true to the original. Usual fun and games making tack-welds so the first continuous weld didn't contract and pull it all out of shape. I need to take a break now to attend to other things, but hope to start the next phase of the project by sourcing and learning to use a pneumatic rivet-gun for the miniature rivets. This needs to be done first so that I can ensure there's room to get tools into all the required confines when rivetting and bolting together the geodetic panels.