Mark 18 Tubular Airship - RC Groups
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May 08, 2017, 07:03 PM
Melbourne, Australia
Discussion

Mark 18 Tubular Airship


Hi Folks,

it's been awhile since I posted about the tubular airship (https://www.rcgroups.com/forums/show...ubular-airship). I haven't given up on trying to make one with a 'geometrically perfect' annular airfoil shape, but I was finding it very hard to build, so I've made a rather more 'rough-and-ready' design based on a ring of multiple inflated cells, in order to test the general concept.

We took the 'Mark 18' for a fly in the local school hall on the weekend, and I'm pretty happy with how it worked out. This version uses little steering fans in the trailing edge webbing (they're a bit loud and buzzy - they're stolen from a quadcopter!) and a main internal fan. There are a lot of design compromises here, but it still seems to fly pretty well...

Anyway, people should find it interesting, it certainly looks a bit different! Attached are some youtube links, and a still photograph of my expert aircrew piloting the craft.

cheers,

- Chris

doing doughnuts with the mk18 (0 min 17 sec)


steph general flight (1 min 39 sec)
Last edited by pegacat; May 08, 2017 at 07:22 PM.
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May 09, 2017, 10:54 PM
Build and rebuild
Brainstorm's Avatar
Well done, Chris! That's a very effective proof of concept. Looks great, and flies fantastically well.

Kudos!

-Roland
May 09, 2017, 11:52 PM
Go small or go home
ruzam's Avatar
Good stuff!

How do you find the stability in high speed forward flight? I've found all my blimps to be highly maneuverable at low speed, but trying to flat out gun it from one end of the gym to the other usually ends with a spin out.
May 10, 2017, 02:25 AM
Melbourne, Australia
Thanks guys!

Embarrassingly I've got an electrical problem with my motor which was cutting out when I went over about 1/4 throttle, so I'm not actually sure about high speed flight. Certainly at the speeds we were playing with on the weekend it was fine - I'm hoping to get stability similar to a 'flying ring', but this is based on wishful thinking rather than engineering....

The only other evidence I have is that if I give it a push (with no engine) it flies straight - but again, low speeds only...
May 10, 2017, 10:15 AM
Build and rebuild
Brainstorm's Avatar
Hope you can resolve your electrical issue! If you were flying at quarter throttle indoors, I would think it worthwhile to give it a try outside on a calm day. There's nothing like testing in real life how your design will handle at higher throttle and faster speeds.

On a related note, a cousin of mine, many years ago, designed a small blimp made up of a simple bundle of pressurized tubes. It was similar to yours, except that it forewent your annular concept, and instead had an additional (longer) cell at the center. This made for a very simple and stable structure.

In terms of the individual cells, he made them tubular, and simply tied off the ends, just like the sausages you put on the grill. Without the two longitudinal seams, the cells could handle more pressure, which improved rigidity and obviated the need for a ballonet (at intended full scale).

I seem to remember that somebody here in the Blimp forum has played with tubular cells before as well. I think it might have been pyronaught. Tubular cells might work for your ring-shaped design, too!
May 10, 2017, 07:55 PM
Melbourne, Australia
Tubular cells are interesting - they're certainly easy to construct and very robust!

Part of the idea of this design though is to try to minimise drag, and that's best done with a tapered trailing edge. The design goal is to try to double the speed of an equivalent conventional airship, which is a tough ask because of the cube law problem - but getting drag under control is a key concern.

Re the engine - yup, I'm learning a lot about ESCs! I don't want to fly it outside until it's reliable, because if the engine cuts out I lose the airship. (The predecessor to the one in the video had to be fished out of a fern, which is why I flew this one indoors :-)...)
May 12, 2017, 04:22 PM
Registered User
What is the function or purpose behind the tubular envelope? Is it to reduce drag, make the prop more efficient by virtually shrouding it, or what?

Edit to add, I totally missed the post above. Blame it on the new baby and ensuing sleep deprivation.
Last edited by thx712517; May 12, 2017 at 04:32 PM.
May 13, 2017, 03:25 AM
Melbourne, Australia
Yup, there's a few ideas here:
1. reduce drag with an annular airfoil
2. get a more efficient engine with a 'ducted fan' approach
3. make it more manoeuvrable by having as much of the weight as possible close to the centroid, to reduce the angular moment...

... this isn't the ideal shape I'm after (the ducted fan has gaps around it, the cells aren't a perfect annular ring etc.) but it's getting there :-)
May 26, 2017, 05:36 AM
Registered User
this looks really awesome! more pics please!


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