Airship design ideas.
The most potent airship is the weather balloon. It’s main feature is expandability. It can automatically change volume as it changes altitude. No rigid airship could do this in the past and no rigid airship does it well enough today to be functional.
Some have proposed gigantic airships and they have built smaller demonstrator model rigid ships which are able to adjust buoyancy by adjusting the volume of an inner lifting gas envelope, while the envelope remains itself fully contained – ‘trapped’ as it were – within a rigid airframe structure. This design limits altitude to the volume of the airframe and it also makes the airship at lower altitudes unnecessarily over exposed to the wind. Principle: The smaller the airship the less the wind affects the airship.
So instead the ideal airship can change its volume in the extreme, yet has a rigid structure, can expand to climb and can shrink to be as small as possible to be less susceptible to the wind.
So Hybrids are a facinating design idea. You get some lift from the lifting-gas envelope, and some dynamic lift from airfoils. But so far the only human carrying-sized airships that are called hybrids and made with poorly shaped airfoils. And because they are not volume-adjusting, they are altitude limited. Why stay at 500 feet when you can otherwise ascend 3 times higher than Mount Everest? The only awesome hybrid design I have seen was a remote control model that resembled a manta ray. This was a proper airfoil flying-wing, that could also float neutrally buoyant. But it was still of course unable to adjust volume and thus altitude limited.
The furthest the big hybrids have gotten is very limited. They basically look like two or three cylinders attached at the hip, or a shape approximating a desk top mouse. None of these shapes produces much lift when in forward motion, and yet they are no longer very big volume of lifting gas, because they have cut a cylinder shape down into a thinner shape. If you use a calculator and do some volume calculations of shapes, the Sphere is the best, the cylinder is the best for airships and the airfoil shape is one of the worst because its volume is very little. Airships need size. That is their strength. As soon as an airship’s shape moves away from a cylinder, its lifting power decreases very much, unless it is morphing the other way into a sphere. For example: Fill a wing with lifting gas and drop it and it will drop to the ground. Fill a sphere with lifting gas and it will get to space. So the wing is not efficient at lifting by containing lifting gas within it’s small slim volume, and is best suited to making lift through movement through the relative airflow. So the next question is: What if you change the airfoil away from its ideal shape and kind of expand it Michelin man style, to be a literally ballooned up airfoil? Well the answer is it increases its lifting-gas capability by a miniscule amount, yet loses most of its Bernouli effect generating airfoil properties, by its new found bulkiness. TLDR: It dont work good. The one exception to this is the proven manta-ray shape. Alternatively you could go for a traditional airship shape – think Zeppelin, R101, Acron etc, but then attach some normal wings to it. But then this style of airframe cant go much faster than 100kmh, and at that velocity wings dont make much lift. Thats probably why the pure airship design style has strides in development over these other styles. It presents minimal frontal area to the airflow and it’s lifting gas volume, in long-cylinderical form is massive.
Comparison to sailing ships
Sailing ships did not have engines and moved their hundreds of tons of weight around the World by wind-sail propulsion. If you got wind in your sails you can go anywhere.
Hitherto rigid airships stay around 3000 feet and move under engine power. Yet their massive size – which is so susceptible to the wind – is also an ideal sail. The worst thing for an airship is motoring at 100kmh airspeed, against a 35kmh head wind. Such a negative yet frequent occurrence. Better for the airship to actually go by the principle of not trying to minimise size, and not trying to avoid strong winds, but rather to know, like old ship’s captains, the trade winds of the World, and how they move across the vast distances, from season to season. There should be a trade-wind handbook or encyclopedia for airship captains, that details all the known wind patterns around the World and include things like expected speed and direction at different altitudes. To expand the Wind book idea further an actual weather channel type app that can give real time data on airship specific winds anywhere any time. There would undoubtedly be permanent wind paths that would be discovered and they would emerge as reliable routes for airship travel between all locations. In particular the higher altitude winds would be the most useful owing to their greater speed and the known fact that higher altitudes have less weather. In this way if you were good, you could fly your ship without even running the engines, by ascending straight up to the altitude where your desired wind route is and then flying along on that, like a leaf on a stream, until you get to above your destination and descend to land. So here the two main factors are: Knowledge of high altitude wind streams and the ability to ascend and descend from sea level to great altitudes.
A rigid ship with expanding sails
The needed design style could simply be same as Richard Branson’s high altitude round the World hot air balloon with its pressurised cabin and lifting gas top envelop and its jet stream travel routes that carried it around the entire World. The down side to that is limited takeoff and landing autonomy. Also if one wanted to manoeuver closer to sea level in wind and weather, a rigid ship is the way to go.
So I propose a rigid ship with the same appearance of the classic airships, yet with an ability to expand lifting volume with ascent. How to do this? Visualise a rigid airship which climbs to around 10,000 feet and then at this point weather balloon shaped massive balloons emanate from the top of the rigid structure – A Hindenburg sized rigid airship, with 40 steadily expanding loose balloons expanding out of the top of the airship rigid structure. This seems crude, but it would succeed in getting the ship to very high altitudes. As the ship descends from 50,000 feet down to 10,000 feet the balloons decrease volume and finally they are stowed back in the rigid structure. This follows the notion that a weather balloon the size of a phone booth, will expand to fill a suburban swimming pool in volume at its highest altitude. This ship can contain its size from sea level up to lower altitudes, but can expand volume to ascend to altitudes where the weather is less and the fast wind streams are.
Lifting gas – The biggest problem
So the whole reason airships work is because the gas in them is much lighter than air. Many gases are lighter than air, but they are still ‘heavy’ as far as the spectrum of lighter than air gases goes. The two best lifters are Hydrogen and Helium. Actually Hydrogen is the lightest of them all, but Helium is almost as light. The Holy Grail of lifting gases would be cheap and abundant plentiful Helium, OR Hydrogen that doesnt burn. Because Helium is rare and expensive/uneconomical, while Hydrogen is cheap producible, abundant, very good at lifting, BUT its flammable. For airships to actually work a cheap inert and efficient lifting gas is required. These two gases also are so small and slippery on a small scale – atoms of molecules of the gas or whatever – that only the best materials in the best condition will contain them for any period of time. For example somehow lifting gas manages to escape through a rubber or latex balloon wall through ozmosis or whatever, within a short period of time – maybe a few days to a week. To make a small airship that lifts one man and a small engine and the mass of the airframe it self, would require $7000 of Helium. By comparison Hydrogen would be much cheaper – perhaps $1000.
This is probably a problem for the physiscists and the chemists to create a solution for. Either figure out a Helium production process that is cheap enough or make either a new substitute lifting gas or make a mixture of Hydrogen with an inert and light gas that is in sufficient ratio to render the Hydrogen safe. On that last idea, how about mixing Helium with Hydrogen – would at some ratio, the Helium make inert the Hydrogen? In a similar (not the same) way to the concept used in underground mines where so much air is pumped down and through the mine that even if a flammable gas seeps in, and even if a naked flame is present, that flammable gas still is not able to ignite due to the excessive ratio of air to the contaminant flammable gas. A mixture of the two lifting gases would eventually separate with the lighter moving to the higher level like oil on water, and so youd have Helium at the bottom and Hydrogen resting on the ceiling of the envelope. The difference being that in the airship situation you want an inert gas to mix well with the Hydrogen and you want to prevent the Hydrogen from mixing with air. This might actually make a safety buffer between the Hydrogen and the working parts of the ship such as the engines and the crew areas including the galley. A compound lifting gas, might be inert and cheap.
In the same way some cars have tyre pressure sensors in their wheels that display a pressure gauge in the dash panel, new airships could have a series of gas constituent sensors inside the lifting envelopes, which can indicate the type of gas that is there. This could be useful in sensing if air has contaminated the envelope, indicating its percentage.
What about hot air? Certainly it works, hot air balloons even in the 1700s, were setting serious altitude records – often getting so high that the adventurer went higher than human physiology can handle. So yes hot air lifts well. But it does require energy to heat the air and heres the deal, if you want a ship that can fly for two weeks at a time, hot air may not be so useful. The big perspective on hot air, is that its best lifting ability is much less than Helium and Hydrogen. For this reason a Helium or a Hydrogen balloon is always going to be much smaller and less volume than a hot air balloon even though they lift the same mass to the same altitude. Hot air balloons are bigger, because hot air still lifts well but you need a much bigger volume of it. Branson’s balloon was an interesting and exciting hybrid hot air balloon with a lifting gas envelope atop the hot air envelope. So the hot air would also rise and heat up the helium envelope (I assume it was Helium). This is good because you get the synergy of the hot air energising the Helium and making it even less dense and keeping it hot compared to the outside air temperature at altitude which is freezing cold.
Although Hot air is less efficient it still got Branson and also Fosset around the World. And also I have heard that hot air balloons are not expensive to heat.
To throw in a wild card type thing: Vacuum balloons are a concept. If you could create a strong yet light envelope and then suck most of the air out of it, while still maintaining its volume undiminished, and if the envelope was light enough, youd get airborne.
Theres also the idea to use solar electric heating to heat a lifting gas. At altitude temperature can be – 57 degrees Celsius. So keeping the lifting gas from getting frozen might render further lifting power.
Pumps and taps could be used to maintain the ships attitude, by sending gas forward and aft to keep it balanced and also to sequester lifting gas into compression tanks to diminish inner envelope volume within the airframe, to descend. Taps/valves could provide safety cut-offs for stopping gas escaping if one segment of the lifting envelope failed, (Such as one of the big expanding balloons at high altitude).
Importance of the right volume
The sphere volume formula for different diameter, gives astounding results. For example a 2 meter sphere – A ‘2m Balloon’ lifts 4kg of weight. Change balloons now and get a 6 m balloon. Does it then lift 12kg? Because that would be commensurate with the tripling of the diameter….No, it lifts actually 113kg! 2m balloon lifts 4kg, while 6m balloon lifts 113kg. And so it goes, while a linear increase in diameter gives a much increased – probably exponential increase in lifting power.
So a 100kg man would be able to get airborne with a 6m diameter balloon. A 40kg ballerina would get airborne on a 4.4m diameter balloon. If you made a balloon of the combined diameters, for a 10.4m diameter balloon, you would have a lifting power of five men and 2 ballerinas – some 590kg of lifting power.
Rain, ice, snow. A b alloon in the documentary below, had to put down in the sea, because it became heavy from snow. Such big surface areas as ballons and airships need some method to address water on the surface, particularly to stop ice forming.
Aeroplanes use de-icer systems to remove ice from wings. Now I see the value of hot air for Helium balloons – it can prevent the balloon from icing.