I actually thought of this many years ago, and tried working up a design for one. I couldn’t get under the weight limit. I assumed that’s weight without lifting gas, although I didn’t look it up, because obviously with lifting gas in it, it has negative total weight. Even using Hydrogen, for the added lift, any gasbag (plus seat, engine, etc.) that was large enough to provide the required lift, wound up weighing too much. Modern gasbag materials may allow it, now, but when I thought of it 25? years ago, nothing available at a reasonable price could do it.
Quoth Polycarp:
Not true, on two counts. It is true that a helium atom weighs four times as much as a hydrogen atom, but on the other hand, there are two hydrogen atoms in a molecule, but only one helium. So helium gas (at a given temperature and pressure) is twice as dense as hydrogen (conveniently, the density of a gas is directly proportional to its molecular mass). Second, it’s not the densities themselves that are important, but the difference in density from air. Air has an average molecular mass of around 29, hydrogen has a molecular mass of 2, and helium has a molecular mass of 4. So hydrogen’s lifting strength is 27/25 times greater than helium’s, or 8% greater. Which helps, but isn’t really a huge difference.
Right, so with new information, and having been aimed properly by the kind and knowledgeable people hereabouts, I have some figures I’d like to double check.
Using either hydrogen or helium, which I found gives about 9.2 newtons of lift, I would need to contain approximately 572 cubic feet of the gas. This is based on my weight, around 200 pounds, plus likely weight for a harness and small propulsion setup. I was unable to find any likely weights for gas bag materials, but that still seems sizable.
Have I missed anything thus far? Or perhaps someone knows the likely weight of materials for the balloon?
You’re missing a “per” there. 9.2 newtons per what? You can get any amount of lift you want, with enough gas.
sorry, 9.2 newtons per cubic meter.
Oh, the humanity!
Possibly.
9.2 N/m[sup]3[/sup] equates to 2.06 lb/m[sup]3[/sup]. If we (rather optimistically) assume the envelope, harness, propulsion system, etc. weigh the same as you, there’s 400lbs to lift. This requires 194 m[sup]3[/sup], which is 6854 cuft. That’s the volume of a cylinder 15 ft in diameter and not quite 40 ft long.
You need more than the minimal positive buoyancy combined with ballast to maintain control of something using helium. For airships, you usually need to be able to shift weight for attitude control. In order to land safely you will have to be able to dump some of the helium. Perhaps heat can be added to increase buoyancy during flight, so dumping gas is not required for landing, but for a very small craft maintaing neutral buoyancy would be very difficult. Maybe a hot air/helium mix using balloonet chambers like the Goodyear blimp would be a good compromise.
Also, helium will leak out of anything you material you use, so you need enough to maintain lift, and, at least on the ground, a system to recycle the gas by removing the air that mixes in with it.
Oh yeah, another problem to consider, lighter than air craft have a natural tendency to head for power lines when descending. Something not so likely to be problem 100 years ago. I still think the lawn chair and leaf blower is the way to go.
You don’t necessarily need to get actual positive buoyancy. You could also go with just slightly less, and couple it with fans or the like to produce the remainder in active lift.
And ballast isn’t strictly necessary, either, if you have some way of pumping the helium back into high-pressure tanks.
The Goodyear blimp can fly with slightly negative buoyancy, but it also carries spare helium, ballast, and inflatable/deflatable balloonets to change the attitude. Without that, an engine failure turns the craft into a very light rock. Now add in the helium pumping system and you have a larger, heavier craft, needing a larger engine, larger control surfaces, and so on. Pretty soon you have a Goodyear Blimp. Aircraft design is always like this. Maybe a Diamond Age style vacuum balloon is the answer.
Noted.
Don’t forget the weight of your goggles.
The trouble with lighter-than-air craft is the sqaure-cube law. Volume is the cube of length. So if I build a machine half the size of the Hindenburg, it will have 1/8 the lift ability. 1/4 the size, 1/64 the lift power. Surface area etc. is the square of length. Assume the infrastructure of a Hindenburg is related to surface area - so many struts per hundred feet, the gasbag material weight determined by square footage (unless you make it thinner), etc. SO a zeppelin half the size weighs 1/4 the weight but has 1/8 the lift; 1/4 size gets 1/16 the weight but 1/64 the lift, etc.
So you can see a really small zeppelin will not work - not enough lift power. The zeppelins had separate gasbags inside the rigid shell, so you could inflate/deflate without changing the shape and stiffness of the craft. DIrigibles (Goodyear) use the gas pressure to maintain their shape. (Although I imagine you could alter the lift and maintain the pressure by having an internal gasbag which inflates or defaltes inside the helium bag and holds plain no-lift air.)
Does the 9th ray work on Jasoom?
Good question! I don’t believe it’s ever been put to the test.
Updating this thread (although the OP seems to have unfortunately left us):
Unfortunately its $4 million price (payable in yearly million dollar installments) is a bit high for me.
Top Gear had an episode on this with James May.
There’s a 2-person “home made” blimp on display at the Tillamook Air Museum, the “Thompson Experimental Airship Model #28”. It was FAA certified: Thompson Alien Blimp.
The other question I suppose is whether modern materials could create a much more robust but lighter craft - carbon fibre rather than aluminum structures that look like a collection of old TV antenna triangular masts; modern no-rip materials that are airtight, thin but serviceable plastic windows for crew quarters, light but strong electric motors, hydrogen fuel cells (!) for power for those motors, etc. The question is whether you want a fair-weather friend or something designed to last in whatever conditions it encountered.
One of the fun details about the original airship was that they were big enough that there were catwalks in the interior, etc.
Keep in mind that storms seem to have done in many of the old-timey zeppelins, and if you have an acre of surface you can accumulate a lot of water, ice or snow in the wrong weather - certainly enough to negate your buoyancy no matter how drip-dry the skin is. Icing is already a serious problem for fixed-wing aircraft.