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Oct 25, 2015, 05:45 PM
Melbourne, Australia
Thread OP
Build Log

Mark 15 tubular airship...

I'm trying a new approach to building a tubular airship, trying to reinforce the inner channel with a 'geodetic' mesh of carbon fibre tubing.

I had a crack at building the geodetic mesh this weekend. I wrote a program to calculate the intersection points for the rods, and then printed out a blueprint with the intersection points on it. I also designed and printed a small six-way 'clip' to anchor the mesh into position, and glued the clips in place on the latitudinal struts to provide anchor points at the correct geometric places, and then marked the intersection points with a white marker on the long 'winding' pieces.

It went ok for awhile, but ultimately failed as weaving the carbon fibre together and clicking lengths into the printed clips proved too stressful, and a couple of the 1mm cf rods snapped.

... I have a new technique which I'll try soon that shouldn't stress the rods quite as much; as you can see from the 'completed' structure it *almost* worked... :-/ . Instead of weaving, I'll try simply 'wrapping' the cf rods... which should be easier, and put less stress on the rods (although it makes the calculations harder, as the inner rods will need to be slightly shorter than the outer rods...

(TL:DR; - I'm not much good at basket weaving)
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Oct 26, 2015, 05:04 AM
Registered User
Thatīs a pretty nice idea. Rigids are the way to go!

Iīve tried something similar in small scale following the approach of Rettig from 1909. For that one I used Balsa wood rather than CFK, since itīs more leight weight and easier to glue and put in shape.
The final product is pretty nice to look at but it never actually went in service and is now throwing nice shadows at my ceiling

Good luck with your project, Iīm happy to see more!
Oct 26, 2015, 05:59 AM
Melbourne, Australia
Thread OP
Wow - that's fascinating! I knew about the Schütte-Lanz SL1, but I've never come across Rettig's airships. What's the book your photo is from? I take it from my rudimentary German that he was also using wood?

Your frame is very fine by the way - you should mount a light inside it :-). Did you have a plan to attach a gas bag?

Maybe I should give balsa a shot - cf is great stuff but it's a little tricky to work with some times - I spend a lot of time messing around trying to 3D print clips...
Oct 26, 2015, 07:00 AM
Registered User
Rettig never built an actual airship, but as a carpenter he proposed to fully build it in wood with an internal structure like the one in the picture.
The pic is from this book

This balsa frame was only a test on how strong and leightweight this way of building could be. Itīs somehow nice, but much more flexible than the common way, and extremely painful to calculate and to make. Further it possibly has the same drawbacks in aerodynamics like the SL1.
So this one never flew, but we have built a couple of other small scale rigids like this one:
Maiden flight of the Argo (3 min 1 sec)

CFK getīs interesting once you build larger airships, but for all rigids below 3 m length I would only use Balsa wood. Itīs easy to glue, cut and to repair. And itīs much cheaper than CFK.
Oct 26, 2015, 03:13 PM
Potential Future Has-Been
Seems like the printed nodes would break apart pretty easily unless you are doing high temperature PETG or something. Maybe you could make some kind of heated crimping tool that re-melts the nodes and compresses them into a solid blob. Such a tool would also have to cool the plastic before removing itself though, which would make it a challenge.
Nov 02, 2015, 01:46 AM
Melbourne, Australia
Thread OP
So... the latest attempt has been another 'learning experience' :-).

On the plus side, I was able to get the inner geodetic frame 'sorta' together - it isn't as accurate as I would like, but that was due to my limitations as a craftsman; the computer model held up nicely. The main problem is my clips - the 1mm cf is bendy, but tends to crack when I try to 'snap' it into my home-designed-and-made clips.

... However stretching the foil over the frame does *not* give the smooth channel I was hoping for :-(. I'll need to find some other fabric that's smooth and stretchier.. maybe I can steal someone's stockings... (ok, I've just been informed that no, I cannot steal someone's stockings... but that maybe I should go and buy some lycra and try that...)

In the meantime here are some piccies showing construction, and the awesomely smooth interior that is bound to encourage laminar airflow though the middle, she'll be right mate, no worries at all...


The next step is to construct the gasbag to go around the channel, and then finish my measuring rig - I've got some cheap domestic scales and a (not so cheap) anemometer, I've constructed a 'traditional airship' of the same dimensions and volume (1m x 50cm), and I hope to do some comparative drag calculations to determine once and for all whether this nutty scheme interesting concept is worth proceeding with.

P.S. Thanks so much for the book reference Wemperor (Andreas?) - it looks fascinating, and I've ordered it from Time to see if I can still read German :-).

P.P.S. A heat seal crimping tool would be nifty Pyro, but probably beyond me - I think a better design of clip that doesn't involve a press-fit is maybe the go... I'm thinking of a three piece clip that would allow me to exactly position things *before* bending things around... maybe for next time! It turns out that the actual stress on the thing *once* it's together isn't too bad (in fact it's almost negligible) - the problem is the transient stress when I'm trying to weave the thing together :-/.
Last edited by pegacat; Nov 02, 2015 at 01:57 AM. Reason: typo
Nov 02, 2015, 12:20 PM
Go small or go home
ruzam's Avatar
Just my observations.

Wouldn't it make more sense to put the cf frame 'inside' the tunnel and let the envelope pressure press against it? Maybe even simplify the envelop into a single seam tube and let it form to the frame on it's own under pressure. You'll use a little more envelope material, but you'll also have fewer seams to get air tight.

I can imagine weaving and aligning the frame is a frustrating task. I would use thread loops tied around the joints. Just tight enough to hold the rods 'in place' so they can be shifted and adjusted as the weave grows. Then touch each joint with crazy glue when it's in the right position. I don't know if that's any easier than using clips.
Nov 02, 2015, 01:47 PM
Melbourne, Australia
Thread OP
Yeah - I agree about having the gas bag press against the outside, and you're right about being able to simplify the construction of the gasbag - I hadn't thought of that!

... however the notion of covering the frame was to try to get a smooth inner channel; left to itself we'd just have the bumpy frame exposed... which might still be better than the crinkly foil!

I was wondering about tying the intersections, but I couldn't figure out how to do it accurately - I was trying to get the mesh to be an exact shape as calculated on the plan, hence the attraction of being able to click them into place. I glued the connectors on the lateral rods at exact positions, and then used a white marker for the intersection points on the wrapping wires. It looked good in theory, but got a bit muddled when I tried to assemble it.

I thought about using wire wraps (like bread ties or something) but I was also worried about it puncturing the gas bag....

... anyway, it's getting better. (Except I'm now out of carbon fibre and the tape I like...!)
Nov 02, 2015, 02:51 PM
Go small or go home
ruzam's Avatar
Use wire wraps to put it together, then replace the wire with thread/glue wraps one intersection at a time.

I've been having fun with UV activated glue. It can be used thick (instant plastic). Freezes as fast as instant clue when you hit it with the UV, but it's a workable gooey liquid until then. I'm picturing a drop placed at an intersection and cured in place. Should provide more than enough strength and support without having to take any more steps.
Nov 02, 2015, 05:50 PM
Potential Future Has-Been
I would ditch the frame idea and just use purely a pressurized envelope. Use PU since it stretches and can be heat sealed from both sides, then make tension bulkheads inside that run between the outer wall and the inner wall so that the inside hole can not constrict itself. Have about eight bulkheads symmetrically spaced, kind of like catenary curtains but continuous from top to bottom. The bulkheads ideally would be made from film that does not stretch so that it holds the profile shape of the hole, although such a wide sheet would take a lot of force to stretch so you can probably get away with using PU for that too.

A drawing would make it a lot easier to see what I'm talking about, but alas I'm too lazy to make one so hopefully the description is good enough.
Nov 03, 2015, 03:52 AM
Melbourne, Australia
Thread OP
Hi Pyro,

... indeed, see attached piccie of the mark 14 :-). Most of the ones I've tried so far have used internal panels (with holes cut in them for weight saving).

... however, you get bowing (you can see with the attached pic which is an 8-gore model). The notion with the frame was that it would weigh about as much, but maybe give a smoother surface... I'd love to get the 'ideal' shape, but I'm beginning to think it isn't possible at a small scale for a reasonable weight....

However what you say about PU has merit; I've been using this aluminised plastic stuff with limited success, maybe I should try PU. Do you use any particular sort, or is this the stuff that's used as painters drop sheets you can buy at a hardware store?

@Ruzam - the UV glue stuff sounds fascinating; I've never used it - I had a shot with glue guns and found them pretty useless (for me anyway!) Do you have a link?
Nov 03, 2015, 10:02 AM
Go small or go home
ruzam's Avatar
I started with one of these kits. I ordered online at the time but you can find them at nearly any hardware store. Comes with the LED UV light.

Since then I've bought just the replacement glue off ebay eg It's used very commonly to glue the glass face to phone screens.
Jan 07, 2016, 07:20 AM
Melbourne, Australia
Thread OP
So I'm back to building the scale models; trying to build some comparison shapes.

I'm getting better at making the geodetic mesh for the interior (much easier with the UV setting glue - thanks @Ruzam!), however I'm still having trouble covering it with material. I'm trying a thermally sealed polyethylene bi-layer (otherwise known as 'covering it in cling wrap and sticking it in the oven') however the stress of the heat shrinking process tends to snap the carbon rods. (I'm beginning to think carbon fibre rods are a sucky material to build the inner channel out of, but I can't think of a better material that's light weight and strong. They're not really made for bending though.)

Anyway, I've kind of got something that will do for initial testing I think, although it's still pretty rough on the inside. It's a shame that I can calculate mathematically perfect shapes, but I don't have the skill to turn them into a physically accurate channel. I'm tempted to try to 3D print a mesh, but the sort of open, curved mesh I want is very difficult for my cheap 3D printer to produce.

Here are some photos, including a curious one involving an oven and an airship... next step is to make up the envelope, and then start trying to get some data...

- Chris
Jan 08, 2016, 01:12 AM
Go small or go home
ruzam's Avatar
Presumably the oven doesn't get 'too' hot? Carbon fibre rods won't take kindly to heat.

My go to for lightweight smaller projects is split bamboo. You can pick up a bag of skewers from the dollar store and split the cross section into more workable dimensions. Sometimes you have to make a pile of bamboo splinters before you get some nice straight consistent lengths, but they're much lighter than CF and usually more than sufficient for the strength you need. You can refine the final split widths to match your strength requirements. And, well, bamboo skewers are cheaper than dirt so no worries about breaking a few in the creative process . I don't know how you'd find the longer pieces you need. Rattan would come in longer rolls and should work more or less the same way for splitting. Many years ago, the only rattan I could get locally was from a furniture outlet for wicker chair repair and it was some crazy expensive price per foot. With the right source I would think rattan should be cheaper than postage.
Jan 09, 2016, 05:55 AM
Melbourne, Australia
Thread OP
It was only in the oven for about 30 seconds :-). (I tried using a hair dryer, but it blew the cling wrap around too much.)

Bamboo / ratan is an interesting idea.. I'll look into it!

The good thing about cling wrap was even a double a layer of it was very light - altogether the 70cm long internal channel between ~35cm and 16cm in diameter was only 38g, up from a base weight of around ~25g for the cf frame.

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