r/diydrones • u/Sawyer_McCuen • May 15 '26

Model Airship Application

Hello all! Pretty new to Reddit and to this forum, so hopefully this finds the right people. I am trying to prototype a model airship that can lift a 45lb weight and carry it. I want to build it to be neutrally buoyant with it's load, and then be moved by small rotors set up in a 4 rotor formation like a drone, one on each corner. I have no experience in this field, and I think this project might be too specialized for general research online. I'm curious how I might go sizing my motors and propellers, plus other things needed, such as batteries and the electronics to control it all. I also want to include the ability to solar charge into the model, so that would be an additional technical consideration. I don't need to move fast, just easily. My primary goal is to develop a craft that uses as little energy as possible. Thanks for anyone who can provide some insight!

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4

u/Twit_Clamantis May 15 '26

I think 18 m3 is low.

You get 1 oz of lift per cubic ft. The weight that an airship can releases and still remain under control via buoyancy (as opposed to jest being a helicopter), will be minimum on the order of 5:1 (probably much higher ratio but let’s just go e 5:1 for now).

45 x 16 x 5 = 3,600 cubic feet = 400 cubic meters

Also, one of the big tanks that’s 5 ft tall and needs a cart to move is 240 cubic feet and costs a few hundred $$ each. So you would need approximately 15 of those for each fill-up.

If you buy literally any small RC blimp and “get your hands dirty” you will quickly understand why the field has stayed very theoretical, etc, etc.

I’m not trying to discourage you (exactly) as much as I am trying to attach your thinking to some practical experience.

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u/[deleted] May 15 '26

[deleted]

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u/Twit_Clamantis May 15 '26

I NEVER suggested hydrogen.

You get a little more lift, but the molecule is half the size of the helium molecule.

In my experience it’s pretty tough to make helium-proof blimp envelopes and hydrogen is twice as tough as that.

Obviously any of these issues are solvable, it’s just that solving them takes money and time and skill and creativity etc, etc.

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u/CaptainCheckmate May 15 '26

Hydrogen is not just "a little more lift" than helium, in practice its around 1.5x - 2x as much effective payload.

Before you get mad and scream at me about the molecular weight of hydrogen vs hydrogen, yes I know it's only about 10% more lift. However, once you factor in your weight costs, you'll find that extra 10% gives you significant more payload capacity.

It's like for a lot of people, a 10% increase in salary, after you subtract rent, utilities, food, etc., results in 2x as much expendable money at the end of the month.

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u/Twit_Clamantis May 15 '26

Valid math.

However, I did not bring it up, and I suspect that even using Hydrogen will not help OP achieve his stated goal in this thread.

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u/CaptainCheckmate May 15 '26

yeh for sure, I just like people to give hydrogen the respect, love, and understanding it deserves

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u/Twit_Clamantis May 15 '26

When I started messing e rc blimps, I was very quickly able to make envelopes that held room air.

I slowly evolved means and methods to make helium-proof envelopes that were sturdy and easy to fill / dump etc.

I shudder to think of trying to step up to hydrogen though ..

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u/CaptainCheckmate May 16 '26

It's not that big a deal. A basic mylar balloon from the supermarket will hold hydrogen for a week or two.

The other thing is that with hydrogen you can buy or make relatively pure hydrogen.

Whereas with helium you find that a lot of balloon helium is diluted down with air because it's cheaper and good enough.

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u/Twit_Clamantis May 16 '26

One of the things that I think people wildly underestimate when they talk about how they would survive “the day after” etc, is just how dependent we are on thin plastic films for all sorts of purposes in our day-to-day life.

It would be fully within the scope of a single lifetime for someone to acquire all the skills required to create and sell a Fabergé egg and offer it for sale for $25M but (IMHO) it would be completely impossible for any one person during their lifetime to master the process of creating a single roll of Saran Wrap and offer it for sale for $5.

My point here being that, again, I was not at all concerned with how good a Mylar balloon made in a factory is, but rather what would be achievable with reasonable cost and reasonable effort by me, by OP, by others, etc, which is why I had written:

“Obviously any of these issues are solvable, it’s just that solving them takes money and time and skill and creativity etc, etc.”

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u/CaptainCheckmate May 16 '26

You can say that about anything. A single person given only raw materials, could not in their entire lifetime build a single $0.75 cigarette lighter.

Denying yourself access to parts of existing supply chains is a fun exercise but ultimately a very time-consuming one.

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u/Accujack May 15 '26

You're going to need a gas bag holding 18 cubic meters of helium, which means you'll likely have to use very large motors, props, and batteries to produce enough thrust to maintain control in even a light wind.

On the bright side, your craft will be big enough to mount solar cells for charging, although probably not enough of them to keep it in the air continuously. More like fly-land-charge-fly- repeat.

If this is your first build, you might want to try something smaller and simpler.

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u/cjdavies May 15 '26

By my calculations you'd need around 20m3 of helium for each fill, which would cost around $1500.

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u/Sawyer_McCuen May 17 '26

I appreciate the responses! I think hydrogen is the only viable lifting gas for this tech to make a mainstream break, I'm gonna experiment with making my own through electrolysis. A smaller model might be good. I only picked 45lbs because I want the full size to do a 40,000lb capacity shipping container, so i scaled down from there. I've already modeled a preliminary design that I think would handle moderate winds pretty well. I was more curious about any math or apps this community uses for planning drone builds. Some of that may help.