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Old Oct 22, 2008, 04:25 AM
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Lifting capacities

Hey all, I'm thinking of building a blimp, and was wondering if you could tell me the lifting capacity of Helium and Hydrogen, like, how many grams per cubic centimetre or something like that. Thanks

-R
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Old Oct 22, 2008, 05:17 AM
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I think I found it!! Please confirm

Hydrogen has a lifting capacity of 1.1 kg/m, and Helium has a lifting capacity of 1.02 kg/m.

thats:
1100gram/ cu. m

cu. m. = 100 cubed = 1,000,000 cu. cm.

therefore:

Hydrogen: 0.0011g/cu. cm
Helium: 0.00102g/cu. cm

-R
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Old Oct 23, 2008, 07:28 AM
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helium lifts ~1oz per cu ft
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Old Oct 23, 2008, 06:42 PM
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One cubic foot of helium will lift about 28.2 grams, so multiply the volume of the balloon by 28.2.
Divide by 448 -- the number of grams in a pound -- to determine the number of pounds it can lift.
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Old Oct 24, 2008, 01:16 AM
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Thanks I just wanted to confirm those weights and you guys did Cheers is my hydrogen value correct?
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Old Oct 24, 2008, 01:23 AM
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Actually it's not the "lifting gas" that lifts weight. It's the air that provides static lift, while the lifting gas just produces weight. Maybe you know the fun question "What's lighter: one kg of lead or one kg of feathers?" It's similar with buoyancy. Question: What gives more buoyant lift, one cubic meter of helium or one cubic meter of hydrogen? Answer: both the same. Even one cubic meter of concrete gives the same buoyant lift as one cubic meter of helium. It's just concrete is heavier than helium, and helium is heavier than hydrogen. Both weight and buoyancy are forces due to gravity, I guess that's why they are mixed up from time to time.
<nitpicking mode off>

The word 'lifting capacity' is quite a telling term for what one actually wants from a lifting gas: it's buoyancy less weight ;o)

Best, Johannes
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Old Oct 24, 2008, 01:32 AM
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arghh...too many words for a friday arvo!!
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Old Oct 24, 2008, 03:04 AM
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Quote:
Originally Posted by inventing_man
One cubic foot of helium will lift about 28.2 grams, so multiply the volume of the balloon by 28.2.
Divide by 448 -- the number of grams in a pound -- to determine the number of pounds it can lift.
That would be 454 there's 453,59 grams in a pound.
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Old Oct 24, 2008, 03:39 AM
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Quote:
Originally Posted by microtaylorcraft
arghh...too many words for a friday arvo!!
The weekend is near, hang in there ;o)

Here are definitions from the Airship Design Criteria (FAA-P-8110-2):

SUBPART I - GENERAL
1.2 Definitions
(f) Weight of pure gases at standard sea level atmospheric condition of 29.92 inches Hg. pressure and 15 C temperature:
(1) Dry air = .07647 lb/ft3.
(2) Dry helium = .01054 lb/ft3.
(g) Unit lift - The value used should be identified in the analysis of the design. In the absence of a rational analysis, 0.0635 lb/ft3 (96% purity) should be used for helium.
Best, Johannes
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Old Oct 24, 2008, 11:38 AM
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Quote:
Originally Posted by Chickenthief
That would be 454 there's 453,59 grams in a pound.
Yes but helium does have weight too. The helium weight is subtracted out to give a answer of real lift potental for a given volume.
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Old Oct 24, 2008, 11:46 AM
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Dont know if this will help.But a 5.5 foot dia. will lift 2.2 lbs...RTR http://www.balloonbasics.com/JUMBO_BALLOONS.html
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Old Oct 24, 2008, 08:20 PM
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Ok thanks for the help guys, me and a mate are looking at building a 6metre rigid airship and I wanted to know how big to make it to be able to lift all the RC gear and a wireless camera.
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Old Oct 25, 2008, 05:41 AM
Mostly harmless
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A rigid ? why? Do you have any particular reason for making the airship rigid? A rigid frame only adds unnecessary weight to the aircraft. If you are looking up to build an RC airship with camera, Blimp or semi-rigid would be much easier to build and more resilient on the long run...
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Old Oct 25, 2008, 06:06 AM
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Well....i personally don't fancy building such a large envelope for a blimp...so Rigid is the way to go.

-R
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Old Nov 10, 2008, 10:38 AM
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Quote:
Originally Posted by microtaylorcraft
Well....i personally don't fancy building such a large envelope for a blimp...so Rigid is the way to go.
-R
6m rigid sounds very intriguing. What is the volume or diameter you're aiming at? I always thought an iglu- tent or folding boat like design should make sense for this size of a 'collapsible' rigid.
Best, Johannes
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