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TOPIC: 3D printed model for Jetex/Rapier/Tender

3D printed model for Jetex/Rapier/Tender 6 months 3 weeks ago #907

  • TerryInBavaria
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There is a lot of work involved but once that's done copies can be run off without too much effort. (Useful for crashes and flyaways :) )
One advantage of the 3D draughting approach is that the model can be resized quickly. I thought this would be useful for Jetex/Rapier where we have limited power options.
Also, didn't one of the guys on here use a 3D printer to create a Jetex/Sebel style 'tailored' model? He printed a form and then wrapped it in softsheet balsa.
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3D printed model for Jetex/Rapier/Tender 6 months 1 week ago #928

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Just to let you know, work continues on the 3D printed model.
I decided to make the model a little larger and change the geometry a little. My goal now is a 270mm span model with a tgt weight, including motor ready to fly, of 40 grams.

The original aircraft seems to have anhedral which I expect would destabilise it. The wing undersurface is pretty flat but it tapers in thickness of course. My initial glide checks with the smaller model proved to be a bit unstable. So the new wing is a little thinner and rerigged without the anhedral.

I've also made the foreplanes a bit thinner and these plug into holes in the fuselage sides. I'll try and use these for trimming and then glue them in place if I can get a good glide with a loaded motor.

The motor mount itself, will have a couple of pegs which push into corresponding holes in the fuselage to ensure line up. I may decide to hack out a trough if things look promising. That would also loose a bit of weight.

In addition to changes to the 3D model I've also been playing with the print settings. The first prints had two layers of plastic at the start of the print. These, when the two halves were stuck together made 4 layers which didn't contribute much useful strength so I've been finding settings that work without these initial layers.

I've also tried the lowest volume I can that works with LW-PLA for the interior support.
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3D printed model for Jetex/Rapier/Tender 6 months 1 week ago #951

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This morning I discovered that our little village stationers, which also serves as a post office was open. I was determined to first discover the German for Blu-tac and then try some test glides. So, it's Patafix and it's not blue but white but it is ferociously sticky stuff and with it I was able to take my latest 3D printed effort and try some test glides. In the end I stuck the foreplanes in place and used the Patafix to get a resonable glide out of it.

This one weighs in at 37gms with a used motor but I think I can get lighter yet. Tomorrow though I'm going to try a few catapult launches. My first attempts were dogged by the fact that the only thing even slightly elastic was some (knicker) elastic that I found in the grocery store! With the stationers to plunder I was able to find some largish elastic bands to chain together. I did order some vinyl tube which is supposed to be pretty good for powering catapults but that hasn't arrived yet.

My idea is to try a few catapult launches before I start trying Rapiers. While traditional deltas tend to be pretty stable I'm not sure how the foreplane will effect things. And the model is rather hard to grip for a good hand launch. The best I can do is grip the rear of the engine nacelles and then launch it by shoving it forward like a dart. Hopefully, with the cat I can get it aloft and then see if it sorts itself out and establishes a decent glide.
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3D printed model for Jetex/Rapier/Tender 6 months 1 week ago #962

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I thought I’d share a few more thoughts about my 3D printing process and progress.

3D printing is sometimes called additive manufacture. For centuries we have taken our supplies and cut them down to make the parts we need. But 3D printing is a bit like brick laying, the bricklayer builds the structure up in layers, if he needs a thicker wall he uses several layers of bricks . He must start with a level surface and add several courses of bricks until the wall is heigh enough.

With 3D printing we also need to start with a flat surface and these are pretty rare in aeroplanes. So, when I’ve been printing desktop models, in order to achieve one I take an existing 3D computer model and split it down the middle. And then the print starts from this newly derived vertical centre (side view profile) and proceeds out to the wing tips. See the pictures in some of my earlier posts.

When I decided to make a larger model I commenced by removing the wings and fore planes from the original 3D model and cutting the front 120 mm off the nose. This left me with a left and right rear fuselage and a left and right front fuselage to glue together, then I had to add the wings and fore-planes. By the time this was printed out and glued back together it was all pretty heavy, almost 40 grams including the weight of a used motor.

Then I had a look at printing the fuselage halves vertically. I still couldn’t print the full length in one go so this time I cut the model apart by removing the first 180mm of the fuselage. The rear section prints vertically from this cut.

For this part I was rather surprised to discover that I could use a special printer mode called vase mode. Vase mode, or Spiralise first prints the a base (in this case the fuselage cross section at the 180mm point) and then in a continuous spiral prints out the rest of the shape. The shape must be more or less circular, as aeroplane fuselages tend to be, and as the printing proceeds the height of the extruder continuously, and gradually increases. This has the advantage of giving a very smooth finish which is also be very light. It must be as it is only 0.4mm thick.

A rear fuselage printed in vase mode weighs 5 grams whereas conventional, layer at a time printing came out at 13 grams. Quite promising. These thin parts are a little like vacuum formed styrene parts and are really not too stiff. However, not all parts can be printed in vase mode and I had to do the front section the old fashioned way and that, much shorter part, weighs in at 12 grams. Of course it is stronger which is an advantage in the front fuselage of a Jetex model.

Fusion 360, the drawing software I use, has a feature called Loft. (Lofting derives from boat and aircraft design where two (or more) profiles shapes are drawn and lengths of slender, springy wood are used to find and generate intermediate profiles.) I used the Loft process to generate a 3D shape between my root and tip profiles.

I was pleased to find I could also print the main wings in vase mode. I’d already scrapped the wings that came with the original 3D model. They had had lots of (very authentic) lumps and bumps on for mounting missiles and tanks but I thought it simpler to do without these. I also wanted to eliminate an anhedral effect created by the flat undersurface. The spiral mode wing weighs 4 grams as opposed to 7 gram for an earlier attempt.

The fore planes could not be spiral printed, they are now just flat plates with a peg on one end to plug into a matching socket, set at the correct angle, in the front fuselage.

The vertical stabiliser and the little shoulder it sits on is also printed vertically but not in vase/spiral mode.

Other parts - underneath the fuselage, just aft of the air intake, is another printed part to take the motor. And probably in front of that will be a printed hook for a catapult.

I did actually print a rear fuselage with a trough but lining the shape with aluminium foil was going to be very difficult. Now I’ll stick foil across the width of the rear fuselage I think.
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3D printed model for Jetex/Rapier/Tender 6 months 1 week ago #968

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I emailed the filament manufacturers Colorfab to ask if they would consider doing an aluminium/grey version of the filament.

I got a nice replying this morning saying they'd be happy to do that for a minimum order of 50 Kg of filament. As the current weight per model is 30 grams, including wastage, sadly this is not on!

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3D printed model for Jetex/Rapier/Tender 6 months 1 week ago #970

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50 Kg of grey filament is enough for over 1,500 models! We should support Terry in this venture, so please put in your orders now!
:lol:

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