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May 19, 2018, 05:48 AM
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Discussion

2000 cu.ft Thermal Airship


I've been working on a 2000 cu.ft RC thermal Airship for the better part of 7 years. What started out as a small project to learn CAD wound up snow-balling into years of torment and problem solving (it turns out that some aspects of full size Hot Air Balloons and Thermal Airships become pretty complicated when scaled down).

Attached are a few images of the first (mostly successful) flight.
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May 20, 2018, 03:41 AM
Go small or go home
ruzam's Avatar
Wow! That's a pretty amazing project!
May 20, 2018, 07:47 AM
Melbourne, Australia
Good Work!

How did the flight go?
May 21, 2018, 08:02 AM
Gaftopher
Gary Mortimer's Avatar
Well done! Your dad would have been super proud. Can you remember the 105 that was kicking about here? Nashua or Xerox I can't remember which. That looks a little like the Lanseria area?
May 27, 2018, 03:31 AM
Registered User
Thread OP
@ Pegcat:

The images are of the first successful flight, so it went a lot better than previous (attempted) flights... In the previous 2 tests I managed to scorch the envelope and then we got the pressure wrong so I popped it (learning curve).

It seems to fly tail heavy, but we were pumping cold air into the tailfins to keep them rigid (also making them heavy).

@ Gary:

I remember that thing well, I also remember the pilot complaining that it was a horrible thing to fly. I must be honest, even flying the model seems to require a PHD and 3 hands. It's pretty busy.
Mar 29, 2019, 11:55 PM
Potential Future Has-Been
Nice. I built a large thermal blimp RC model myself so I know how difficult it is. It is pretty well documented on this forum somewhere if you dig back far enough. You did great on the fins, making them look just like the real thermal blimps. I simplified my own fins and didn't make them inflatable.
Mar 30, 2019, 08:58 PM
Melbourne, Australia
... also nice to see someone posting here, gosh it's been quiet!!

Is anyone building airships? I'm still grinding along, but my envelope making skills still suck and I always have trouble finding leaks...
Mar 30, 2019, 11:07 PM
Go small or go home
ruzam's Avatar
Haha, designing, designing, designing...

Need to spend more time on the building!
Mar 31, 2019, 04:34 AM
Registered User
Thread OP
It's been a few months since I've been able to dig into the project. That work thing really gets in the way.


The fins definitely added a whole lot of complexity. It still wants to fly tail heavy & I'm not sure if it's due to the weight of the fabric that makes up the tail or the weight of the cold air that's pumped into the tail to keep it rigid. The easiest solution to the pitching issue seems to be to move the gondola forward which I'm in the process of doing. We added ballast to the nose in an attempt to keep it down on the last test flight but even with a kilogram of sand tied to the nose ring it still wanted to point skyward. If it still points up after moving the gondola I'll probably rebuild the tail out of lighter fabric.

Other (now solved) snags have been speed control issues (we managed to burn an ESC for the pressurization fan which caused a lot of black smoke and a mild panic).

I've also been fighting a burner control issue. Initially I used 24V solenoid valves but they had a habit of freezing so eventually i resorted to the trusted method of Servo's and small Festo ball valves for the blast valves.

The pilot lights are pretty reliable but they do still flame out on the odd occasion, to counter this I've made a rudimentary auto relight system using a micro controller. The re-light sparks every time you open the blast valve and again every time you close it, the idea being that if the burners flame out they will re-light as the gas velocity slows down when you close the blast valves.

An unexpected design flaw with this system is that the spark igniters produce massive electromagnetic interference which causes the servo's to go haywire. The shorter the servo wires, the less the problem (which meant a re-design of the gondola). It also seems that analog servo's are less prone to interference than newer digital ones.


@ Pegacat: Keep going....

@ Pyronaught: I followed your posts from start to finish (might have even commented, can't remember).


Hopefully I'll get a few hours to play late next week...


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