It would seem one of the biggest drawbacks to balloons and lighter-than-air ships is how they can deal with strong winds and gusts. It makes me wonder have they theorized on what is the best design to manage this problem?
Is the traditional cigar shaped design the optimum design? Or would it be better if they were shaped like a saucer or a wing?
And since it’s what everyone uses then I guess the sphere is the best design for a balloon? Why don’t they make balloons in the cigar shape or wing shaped like a parafoil?
And bonus question is have they figured out how to make balloons steerable at all or is up and down the only control they are able to exert?
They generally make balloons round because it’s easiest to do that way (and it distributes the strain equally), but if you think there aren’t other shapes you haven’t been to the supermarket or Party City to see the other shapes on hand, or been to a hot air balloon festival. Look it up.
Recent efforts to make commercial balloons have explored various different shapes, but they all tend not to diverge too far from the “classic” cigar. I don’t know what advantage there would be for a wing shape – you’re not depending on traditional wing lifting forces, and not going fast enough to bring it much into play.
As for steering (“dirigible” means “directable”, so the name “dirigible” refers to this steerable capability, not to shape or design), there has been well over a century of experiment and design. Heck, exactly how to steer a balloon was a plot point in Jules Verne’s novel Robur the Conqueror back in the 1870s. Certainly a lot of results have been obtained beyond “up” and “down”. What do you think the ailerons and rudders on blimps and zeppelins are for?
Using drag ropes combined with a sail for steering is an old idea, which, unfortunately, turned out not to work very well for Andrée and his companions on Örnen.
Hot air balloons are steerable in some general sense in that, in today’s world at least, the pilot may have information on wind direction at various altitudes, and rise or fall to catch the desired drift. When I went up as a passenger (as part of a festival), pilots were exchanging information about this by radio.
One problem with Zeppelins was that they were rigid (aluminum?) frames so susceptible to breakage - especially from side winds when ground maneuvering. The lift bags are inside. Craft like the Goodyear Blimp keep their shape through air pressure, so a strong side gust would shake it up a little but no do structural damage; Bu you need some basic structure to attach ropes to. While balloons (usually, hot air balloons) don’t need to by symmetrical, radial symmetry helps distribute the load evenly on all the ropes attached to the envelope.
There are two options for a dirigible - the cigar shape minimizes wind resistance going forward, which considering the size, that’s a major factor for fuel consumption. Another is shaping the dirigible as a lifting body (such as the “flying bum” being tested in Britain). there are a few debatable benefits to this - you don’t need as much buoyancy lift with heavy cargo - but you probably need enough to get off the ground so what’s the point?
A Zeppelin uses gas bags inside it’s fixed frame - so one method of steering I read about was to selectively compress helium(we hope) from the front or back airbags to make the craft lighter or heavier so it goes up or down. As it floats up or down, if the front is pointed in the direction, then it will cause the rear fins to have some control capability as the air flows over them. Not sure if this is more efficient fuel-wise than simply running a propeller.
Balloons work by having a lower mass:volume ratio than air. The surface of a balloon has to be a solid (else your lifting medium just floats away leaving the craft behind) so it’s really about volume to surface ratio. The natural (i.e. requires least energy) shape of a pressurized vessel is a sphere, so to get any other shape, you have to selectively reinforce, stiffen or otherwise constrain parts of the balloon and that adds weight. More weight means more volume is required. More volume means more surface area. More surface area means increased resistance to turning and/or acceleration, and greater sensitivity to winds. It’s a nasty cycle.
The problem with saucer and parafoil shapes is that they have a rather high ratio of surface area to volume.
Indeed they have. More than 100 years of intensive development has led to the conclusion that it’s best to scrap the whole lighter-than-air boondoggle, and go with something like this: B-787.
Yes, in the sense of “lightest and cheapest”.
Steerability implies propulsion, which is heavy, expensive and slow. It has never produced results that make anyone very happy.
You can try to make a balloon of any shape (just ask Macy’s). However, imagine making a cube balloon by stitching 6 squares together. As you over-pressure it, the centers of each square will bulge - just as loading a plank, even equally, will cause it to sag in the middle. The blimp is the best compromise - Since equal pressure in every direction produces circles, an ellipse shape or cigar shape is not much more difficult than a sphere to make hold its shape.
I’ll go out on a limb here, and say that it’s all about Gaussian curvature.
As long as it’s a constant – whether positive or negative – you are usually fine. And as long as it’s sslowly changing in any direction you should also be fine. But when it changes drastically – or, worse indeed, approaches infinity (as it would have to do along an edge or in a corner) – you have a Big Problem of Structural Integrity.
There are three types of balloons:
[ul]
[li]Hot-air balloon - Envelope (the fabric) is filled w/ ambient air which is then heated via the burner to make it less dense than the air outside of the envelope. These are the colorful balloons that most people are aware of & the ones you can buy a ride in or watch at a balloon festival.[/li]
[li]Gas balloon - Lighter than air gas (helium, hydrogen, etc) inside. Filled with enough LTA gas to make the envelope, & anything suspended from it rise. On the small scale, this is a balloon you buy at a party supply place for a birthday or graduation. On a large scale it’s basket, equipment, & person/people on a long distance flight, like last week’s America’s Challenge. Those balloon are up to 1000 m[sup]3[/sup] & fly much higher than a typical hot air balloon flight to take advantage of the higher winds at altitude.[/li]
[li]Rozière - essentially a combination of the above two, where the LTA gas is heated to give it more buoyancy. These are used for extremely long distance flights (trans-oceanic, circumnavigation of the globe).[/li][/ul]
As dstarfire stated, the natural shape is a sphere as every part is equally as strong / no one spot has any more pressure than any other. Yes a balloon can be made into a special shape but this means extra fabric on the inside to either act as baffles &/or keep it in the desired shape. The legs on the polar bear hot air balloon contribute to the shape of it but not to it’s buoyancy. Yes the air in the legs will be a little warmer than outside air because of convection, but not enough to lift the weight of the fabric of the legs. The body/torso has enough ‘extra’ lift to also lift the legs. Think of a special shape kind of like a Ferrari. It’s less practical than a minivan, but it’s more fun. A special shape weighs more because of the extra fabric from both internal baffles & whatever may be necessary for the design, which means you can’t take an many passengers as a similarly sized regular shaped balloon but they’re more fun to look at because of their unique shape. Normal balloons are not wing shaped because that’s less than ideal for heating the air inside (hot air balloon) & creates more pressure at some points than at others.
When you are flying in a balloon in flight, there is no wind in your face because you are moving with the wind / at the same speed as the wind. The winning balloon in the above referenced America’s Challenge averaged just under 40mph & was flying over 80mph at one point. There are two times in a flight that wind speed comes into play: when inflating/taking off, & when coming in for a landing.
Part of the procedure when setting up the balloon is to anchor it; typically, this is done with a large diameter, specialty-purpose rope that’s tied off to the multi-thousand pound chase vehicle. If it’s too windy when setting up, the wind wants to blow the balloon over/keep it from standing up &/or blows the mouth (partially) closed. This makes it hard to aim the burner & keep it from scorching the bottom of the envelope. (The bottom one or two rows is typically Nomex, but Nomex is fire resistant, not 100% fire proof, especially with that kind of flame.)
When you come in for a landing, you’re moving at whatever the wind speed is while the ground is not moving (ignoring earth’s rotation). The higher the windspeed, the faster you’re moving, & in general, the bigger the landing area you want. In rural Iowa or Kansas, in the off-season, you’ve got hundreds of acres of unplanted fields in all directions & can therefore fly in somewhat higher winds than a more suburban setting where you have buildings & power lines & lights & trees & other areas that you don’t want to land in (planted crops, near livestock, etc.)
Blimps are moored to a single point on the nose; they also have a horizontal wheel underneath that allows the blimp to roll, causing it to act like a windsock in that it’s always pointing into the wind.
Any device that is lighter than air has to deal with problems of wind and air pressure. No matter what the shape powerful engines and controls would be needed to counter those effects. Combined with engine power, airfoils and traditional control surfaces would be best, so something that resembled a conventional aircraft. By increasing weight an buoyant craft gets closer and to a very light airplane. At some point you have something that is only slightly heavier than air and actually is a very light airplane. Unfortunately because of it’s size it will still need powerful engines and large control surfaces to avoid being tossed about by the wind. You could perhaps have a lighter than air craft tethered to a much heavier vehicle on the ground which could lift great weights and transport them under control, but the system in total is much heavier than air. The problem in general is that a buoyant object becomes just a contained portion of the air itself. An airplane is similar in nature to that, they are carried with the air they operate in, but they are much smaller and more easily controllable within that air because the small size reduces the drag that must be overcome to make them move counter to where the air is taking them.
What I think you mean by balloons, by definition, are not steerable, although some limited control is available by changes in altitude.
With respect Zeppelins used hydrogen, Google “Zeppelin” or The “Hindenberg” (I am using an Android tablet, I regret I have not figured out how to link to a different site on this platform.)
If you wanted maximum lift, one large balloon is better than two small ones with the same combined diameter. However, if you wanted to do a special shape balloon you’d overpressurize one area & under pressurize another if it were all one chamber.
However, helium is scarce & therefore expensive. Hydrogen is basically a throw-away gas & is used more frequently.
The Hindenberg and other Zeppelins were designed to use helium. However, most of the world’s helium supply came from the USA - from the Texas oil fields in those days, IIRC. Once Hitler came to power and began making waves, the USA decided that airships could have military uses (how quaint) and denied export permits for helium. As a result, the Germans switched to more risky hydrogen.
Helium IIRC imposes a slight lift penalty in return for a much greater safety factor. A mole of H2 is about 2, a mole of He (monatomic) is about 4, and a mole mix of N2 and O2 is about 30 - so the lift difference is somewhere around 14:15 vs 13:15