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

3D printed model for Jetex/Rapier/Tender 3 months 2 weeks ago #974

  • TerryInBavaria
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Thank you Roger!

Incidentally, the material cost of each model would be about 1.70 GBP.

I'll have to insist, when I get up and running, that there be no panic buying. Certainly no more than 10 models per customer. :whistle: :lol:

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3D printed model for Jetex/Rapier/Tender 3 months 1 week ago #992

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This week I've been doing some more work on the 3D printed flying model. And I've been doing some flying!

By now I've got the weight of the model down, including a loaded motor to 41gms. This includes a thin piece of 1mm balsa underneath the heat shield and some of that sticky backed aluminium foil.

I keep redesigning the parts and trying to find ways of making them lighter. The nose section is the heaviest at the moment (12gm), and the strongest, but I think I can get it lighter.

I've also taken a leaf out of Wilmot Mansours's book and printed a alignment jig. The idea is to align the two fuselage parts, the wings and the foreplanes. It needs a bit more work but it's coming along. With Fusion 360, the CAD software, it's possible to use any existing parts as tools to cut their outline in another shape. So I line up the parts as they are in the finished assembly and then use that part as a tool to cut its own shape out of the bulkheads that will make up the jig.

Similarly, after cutting out a place from the rear fuselage for the balsa heat shield I used that shape as a printed cutting template for its balsa equivalent.

And then we get to the flight testing! Some time ago I ordered some vinyl tube so that I could make a catapult and I also printed a few hooks but the tube hasn't arrived yet. As I have a release system on my drone I decided to use it to haul the model aloft. After doing a few chuck arounds I decided the thing seemed stable enough in roll but I wasn't sure about the pitch stability. In the end I got the CG in what I thought was the right place. Stuck the foreplanes on with a bit of pitch up and decided to tow it aloft. (If its good enough for the Space Shuttle it's good enough for Jetex.) I figured any model that could be released tail first vertically and sort it self out and glide must have some promise.

Now believe me I have tried to video this but the combination of simultaneously hitting the release button on the drone while starting the video and tracking the descending model with my phone was challenging. (of course that's why we have grandchildren) I do have a video and if I can find a way to 'blow up' the tiny white dot in the middle of a blue sky I'll do so. However it was a useful test. I spontaneously manufactured a couple of elevons out of masking tape for the second attempt and things were looking ok.

The next iteration of the wings will have a little up to the outer trailing edges.
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3D printed model for Jetex/Rapier/Tender 3 months 1 week ago #994

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Hi Terry,
great stuff! Launching by drone. Wow! his must be a first for a Jetex type model (though the Jetex team did launch their large Javelin (made for the MOD as a 'spin test model ') from a captive balloon.



But you missed out some (to me) important stuff: what difference did the low-tech elevons make to the flight pattern and why did you fit them? Please tell us :kiss:

I have often thought I would like to begin powered flight testing from a great height. Our vicar wasn't too keen about me using his church tower. But a drone ... that's the way to go.:lol:
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3D printed model for Jetex/Rapier/Tender 3 months 1 week ago #995

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What a great picture. These were the early days of those new fangled delta wings so why not. Do you know, was the model controllable?

Which reminds me. After the first model release I had to put the drone controller down and leave it to its own devices. Otherwise I found myself pushing on the sticks trying to control the free flying test model!

The spontaneously manufactured elevons pointed the way to moving the motor to the rear. (I'd already poked as much up onto the fore-plane as seemed reasonable.) Luckily I have an unmade up kit of Steve Badge's Mig 21 to look at. And I'm not too proud to copy, especially from people who know what they are doing. I had a look for where Steve had put the Rapier and guesstimated where that should be on my model. Then modified the motor mount tube.

Roger adds:

thanks Terry, that explains things. You could always try wings with a reflex. I seem to remember 'Jedelsky' wings are quite sensitive to Reynolds numbers and CG. As to the Javelin, it was free flight, but programmed, using a clockwork mechanism, to go into a spin, and then, with different settings, to come out of it. Bert Judge tells the story that one day, the mechanism malfunctioned and this large and heavy 'model' went off in a straight line. It glided quite a way ... towards an inhabited area. Woops, but fortunately 'landed' without incident or damage.




They did things differently in the 'Old Days'. :dry:
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3D printed model for Jetex/Rapier/Tender 3 months 15 hours ago #1014

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For this weeks instalment I have to report that I finally had a go at flying the 3D printed Typhoon under rocket power. This was with the version with the Rapier mounted, external stores style under the belly.

This attempt, perhaps unsurprisingly, suggested a need for large amounts of down thrust. As motors are in shorter supply than 3D printer filament I went back to the Fusion 360 software and created another Typhoon version this time with a trough. I had tried that before but couldn’t figure out then how to line the trough. This time I made it a bit wider and lined it with balsa.

I’d also discovered that my printed motor holder wasn’t much good. It got soft under fire!

So I redesigned the fuselage with a trough with a steepish curve to introduce down thrust. Moving the motor inside makes for a higher thrust line and thus less thrust induced pitch up moment. And I redesigned the motor mount to leave the motor free to cool.

The trough is lined with balsa and sticky aluminium foil but as you’ll notice things went a bit pear shaped aft of the trough.

This one has a lovely flat glide with a full motor on board and I had high hopes. It weighs in at 40gms with a loaded motor and all necessary ballast! Span 245mm and length 370mm.

But the next trial under power still showed too much pitch up. I did think, as I walked home dejected, that I could raise the thrust line still further by giving it an aluminium lined printed augmenter tube. But then it would need a little hatch for loading and maybe remote electrical ignition. All doable but another rabbit hole to go down.


Another of the problems is the current model is that it is a little awkward to hand launch. Maybe I’m just cack handed but I was wishing that my catapult elastic would arrive. Then I could just have a post in the ground, pull back and let go. And think of the duration boost!

But I think the next move is to sort out the motor mount. So that I’m sure of a consistent thrust line.

While I was waiting for the weather I did start looking at another type. And the Blackburn Buccaneer, the Banana Bomber, came to mind. Compared to the Typhoon its wings are tiny things but it looks like it gets a bit of fuselage induced lift.

I had another 3D model to start from. I immediately started chopping it up according to what now seems a satisfactory formula: front fuselage to be printed with a 2 layer shell, rear fuselage to be printed in single layer spiral mode, wings also in spiral mode and the vertical and horizontal surfaces 3mm and 2mm thick respectively to be printed flat. I had to remove the fin from the original 3D file to have a chance of printing the rear fuselage in spiral mode.


I haven’t tried adding a trough yet. I thought I’d see what I got to with the Typhoon.



I also recall that there was an all white version so that matches the filament colour. Now I just need a set of transfers!
And it does glide rather nicely.
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3D printed model for Jetex/Rapier/Tender 3 months 12 hours ago #1017

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Terry, you might want to try what I call a downthrust tab as showing here at the rear underside of my little Depron foam Hawk, which you filmed once years ago of Old Warden. It hardly shows in flight and only needs to protrude 1", made from .5mm ply 0.25" wide , set at a steep angle to really pay off.

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