Props do not lose efficiency with altitude, they lose effectiveness. If the air is 1/2 the density you get half the thrust when the prop turns at the same speed with the same setting of pitch. But by the same token the drag on the blades is also halved and so the torque and hence power demand too. Since an engine with no supercharger would have its air and (with an old-fashioned carburator) fuel draw also halved and thus power output reduced accordingly it all works out great for an airship-because an airship is only concerned with drag and that too is halved. From this we conclude that when an airship is at its ceiling, the pressure height where its lift gas has filled the available volume, it is actually more efficient at a given speed--its fuel consumption is reduced in proportion to the reduced density of the air it plows through. The props are less effective but just as efficient, the engine is less effective but more efficient since you cover the same miles with less fuel and as a bonus the engine runs cooler.
There is a lot of confusion on these threads from people who do not understand airships. There are a lot of assumptions that are correct for airplanes but not airships. A cruising airplane needs to generate the same thrust at all altitudes and to stay at the optimum lift/drag ratio it needs to fly faster in thinner air; for these reasons their props do indeed need to work harder as they climb and they do indeed lose efficiency. (They are flying faster though so they cover more ground sooner; this pays off).
An airship's speed is limited by the danger of damaging its necessarily light structure; the forces that threaten it happen at higher and higher airspeeds as the air gets denser. If we maintain constant drag instead of constant speed as we rise, the props start out with a very easy job and the engines will be practically idling and as we climb we must indeed increase power as we speed up, at the inverse square root of the density ratio. But now we are going faster. If instead of turning the prop at constant speed and increasing pitch we held the pitch and turned the prop faster in proportion to airspeed we'd clearly maintain constant thrust, constant torque, and have the power demand rise with speed because the prop rotation speed rises with it. Again clearly the _prop_ has constant efficiency in this case! (The engine may slip).
A very high altitude airship will need to be very light and will be fragile at low altitudes. Wind speeds tend to rise as you climb but then at the bottom of the stratosphere there is a sweet spot where the wind _forces_ have a minimal average, though the speeds may seem high by sea level standards. This thread is correct the airship has to pass through levels with rougher winds--but it does not need to fight them, it can limit itself to its maximum safe airspeed at that density. If the adverse winds exceed that it gets blown downwind some that 's all. It does not suffer any wind forces its engines and props don't create except when the wind shifts rapidly and inertia is felt. Presumably you call it down on calm days and chase it down whereever adverse winds in the middle layers have blown it to.
All the above remarks apply to any airship.
I have posted my denunciation of the stupidity of using spherical airships that have no boundary layer control; Techsphere's website continues to post the fairy tale that the drag of the sphere matters less in thinner air. True absolute drag is lower but so what? What matters is performance relative to streamlined alternatives; at any altitude a sphere without BLC has over 12 times the drag of a streamline of the same volume hence lift! If the air is 1/10 the density hence drag at a given speed is only 1/10 what it would be down at sea level--well, static lift is reduced by the same proportion so in terms of relative weight of components it is the same as making a ship of the same mass 1/10 the volume for use at sea level or filling the big ship up with lift gas down here and needing ten times the power to handle the same speed.
But I have seen sites that suggest Techsphere may be belatedly working on BLC; if so their scheme may work at last.
http://designnews.com/article/CA412219?nid=2335& ri d=832757878
Hey, I'm new to Slashdot and I am having trouble figuring things out like how I can just relpy to you directly. I need to take care of some things right now but would love to respond on these things later.
A very general response--airships rarely have serious stability problems. They tend to have a very long moment arm between the center of lift (in the middle of the gas bag) and the center of mass, because fuel, payload, and a lot of structural weight tends to be down on the bottom. Combine that with their big scale and corresponding long moment arm and you have tremendous pendulum stability against roll. Also they move at such low speeds and can turn only slowly so there would be very little centrifugal force--insofar as there is any the ship just gently rolls to keep down facing the cabin floor, and rolls back. Oscillations are well damped by the tail fins.
Pitch and yaw would be big problems except that the tail fins solve it pretty well. Again the forces are not like those on airplanes though they do have to be managed with good piloting.
Response times are very slow--blimp pilots have to anticipate their moves a long time in advance.
The Hindenburg gave a very smooth ride and even blimps are remarkably stable.
"The "answer" was given here.[See up thread for link, I use plain text-Foxwell] It basically amounts to more weight == more thrust required. A fair enough stance, but I still don't buy it."
Good for you! I did answer this person--he seems to think a ton of aluminum weighs more than a ton of Dacron! A less efficient structure would indeed have to be bigger to lift a given payload and hence have more drag and need even more lift for more fuel. But there is no reason at all to say a blimp would weigh less empty and deflated than a rigid would, and lots of history that contradicts that mindless assumption. You might think a blimp ought to be lighter but they aren't. And I think the same investment in effort that would lighten blimps to the degree already achieved in the 1930s with rigids would if applied to a rigid project yield really fantastic results. There are gripes against rigids that have some merit but rarely does anyone bring them up.
This guy was not even talking about a classic Zeppelin type airship but apparently guessing at a structure like Upson's Metalclad ZMC-2. Which by the way itself skewers his argument--the "Tin Balloon" as the Navy guys at Lakehurst liked to call it was too small and had some other weird issues but it was a sound structure, being basically a skin of aluminum sheet minimally reinforced by some bracing rings (mainly for attaching things I think) and a small pressure to keep its sides from creasing, but the resistance to bending or collapsing came from the mechanical strenght of the egg-shaped metal sheet itself--think of it as a very thin-walled tube or pipe. It also held helium very well and plenty of folks today think it is the true future of serious LTA.
BTW--you or anyone else interested in airships might check this site out:
http://spot.colorado.edu/~dziadeck/airship/lists er v.htm
That's the page for joining the listserv, but check out the rest of the site first. John himself rarely posts except to help people asking the list for help and advice, and there are no archives so you just have to dive in and see if you like it. Lurk a while. But this is the main place I have ever found for serious airship talk. I learned a lot from it. Onward!
"I *still* think that a rigid airship is the way to go for a truly large vessel."
Well sure. Actually I am not a fanatic and I like to see as many options developed as possible. I believe in giant blimps too. But honestly first of all, only rigids have ever been made and worked in the big size ranges. Second, I think they are subject to great economies in fabrication using modern automated industrial methods. Third, taking an old design and just substituing in more modern materials (largely for the fabric--much of the weight of a Zeppelin was fabric!) would improve their good lift ratios even more. Bottom line--if you want a big airship ASAP the rigid beckons. It has been done! I think that is part of the problem--no one wants to be known as a great imitator or updater.
"Hey, since you seem to have spoken with quite a few airship designers,"
I read books and then found the listserv above. This did lead to conversations with actual airship designers but I never buy into every part of any of their individual visions. Diversity is good I think but in LTA it often is more like radical parochialism!
"... let me pose a question to you. One of my dream ideas has always been to build a carrier in the sky. The way I figure it, the sides of the deck would be lined with large rigid frame balloons that would provide buoyancy for the craft. With its entire weight lightened, it could then use turbofans built into the bottom of the craft to provide the actual lift power. These turbofans would be powered by the onboard nuclear reactors. (Who else would need an aircraft carrier other than the miliatary?) I'm still thinking about how forward thrust would be applied, but it could be accomplished by building the turbofans to "ti
"Rigid airships could have very small air pressure and get away with it, but blimps wouldn't stay inflated."
Maybe it is because I have not been sleeping enough lately but I'm confused trying to figure out what the premise of this statement is.
Let's review some airship fundamentals!
In concept, rigid airships are rigid structures that shelter simple flexible gas bags (ideally containing pure lift gas like helium and no air whatsoever) from the wind of the slipstream, but the air within the hull that they float in (providing lift) communicates freely with the air outside and is at the same _static_ pressure as a parcel of air that is not in relative motion would be.
This is a bit tricky to accomplish because when the airship is moving the motion of air around it creates a varying pattern of air motion and complimentary static pressure variation--the air right on the nose has been rammed up to full speed and has extra static pressure due to that, the air flowing past the sides has lower than average static pressure, due to the Bernoulli effect. There is some pair of regions, one aft the nose and one somewhere ahead of the tail tip (ideally) where the variations cancel out and you might just make some holes there, but that area will shift around if the hull tips out alignment with the slipstream as when turning in any direction. If you let high pressure air in one place and out to low pressure areas elsewhere you get a wind inside the rigid which defeats the point of a hull--except you do want a little air circulation.
Anyway in the ideal rigid the air is a calm zone inside the hull that is moving along with the ship, and any pressure variations outside due to ascent, descent, changing temperature, or anything else are reflected by air freely entering or escaping the hull to ideally maintain the same static pressure--the only forces on the skin are due to aerodynamics, the motion through the air. Great.
Now the gas bags--to a first approximation they just match the prevailing pressure which, since they are closed bags, means they expand and contract freely. (There are also lags in responding to changing temperature. But any variations resolve into the bags taking on whatever volume matches their internal pressure with the prevailing one inside the hull).
In detail--in any column of still air, the density and pressure at the bottom is greater than at the top, because the molecules respond to gravity in that way. This is the way that aerostatic lift actually occurs. In any lift gas--hot air, hydrogen, methane, helium, steam, whatever--the rate of fall-off of pressure and density is lower--with hot air because its molecules are more energetic being hotter, and in others because their molecules are lighter hence faster at the same temperature so their energy denisty can match that of air molecules. So there is no way a bag of helium can exactly match the pressure of the column of air it is in exept at one point--on the bottom they match, and going up the pressure of the helium falls more slowly, so there is a net pressure out--and up. This is how we get static lift in a limp balloon. To that extent the cells of any rigid airship need to endure a pressure variation. This variation is such that if it continued linearly going up it would rise to a full atmospheric pressure at about 10,000 meters (10 KM, 6 miles) up, so since the avarage atmosphere is about 100,000 Pascals (Newtons per meter squared) the pressure difference between the top and bottom of a flaccid helium bag would be 10 Pascals/meter of height, about 1/10,000 atmospheric pressure. A cell 100 meters in height would be bearing 1 percent atmospheric pressure at the top _if_ it were filled at sea level. (but then the ship could not rise without venting gas--its pressure height would be zero.) The biggest cell ever used a rigid would be the 40 meter diameter ones in the last big rigids, the American ZRS naval ships and the last 2 Zeppelins (Hindenburg and Graf Zeppelin II). So with big cells you already have signif
" 'Still, if you compress the gas {helium} and let it cool, eventually it should condense, if the temperature is low enough.' {me}
So, like, you'd need a compressor and a refrigerator (let's say "ice box"). Wouldn't you also need an expander somewhere in the process? Just guessing."
To be honest I am hazy on the details too but the technical challenge I think you are indicating is indeed formidable. How to make a heat pump that removes heat from the substance with the coldest condensation temperature in the universe? They use all kinds of ultra-exotic techniques to peel away at those last few degrees Kelvin! It is incredibly difficult and expensive. Thermodynamically speaking yes there is something like "expansion" going on but in very exotic contexts--electron gases in semiconductors, weird quantum effects, stuff like that. I'd have to do a lot of research to be more specific. It is done in stages, each one stranger and harder than the last.
"I think you might be somewhat confused. The question was not why they shaped it like a sphere, but rather why they didn't use a rigid airship instead of a blimp. Someone stated that the biggest problem is fuel, and then expanded on that answer. " I came late to this thread having been out of town. But "fuel" is a totally irrelevent answer to the question you point to--it does not matter how an airship is structured how much drag it has, which is what dictates the power/thrust requirements for a given performance target. OTOH the sphere (without Boundary Layer Control to change the picture) has tremendous drag compared to a normal streamline and "fuel" would be a very relevant answer to that. Spheres are wonderful structurally but not nearly enough so to overcome that huge drawback.
How could the difference between a blimp or a rigid have any bearing on its power supply or the demands of the mission as they would affect fuel/power demands??
Please point me to the answer--either I missed it, answered it, or dismissed it as hopelessly confused. Rigids historically had very good useful lift ratios and the best a blimp might hope to do is match that. Being generous to the blimp I just assume there is no difference. No other characteristic that distiguishes them favors a blimp either--they are not easier to make good shapes out of, there is just no overwhelming advantage except that the industry, such as it is, is geared toward thinking about blimps and making them and not rigids. For this project a rigid is clearly the quick and dirty solution and if not abandoned will I bet retain the lead forever. It solves a lot of problems the blimps pose.
And if you want a sphere I can tell you what might make it workable. These Techsphere guys don't even acknowledge the problem, they just change their name every few years so people don't connect them with their last fiasco!
"Out here in western USA, we get loads of wild fires. rather than flying tankers and people, it would be very useful to use these to get huge volumes of water in. In addition, they may be able to drop off fighters in close to the action.
Now, lets hope that somebody does not come up with the idea of using hydrogen and doping for this."
Any LTA use must remember, the lift gas always lifts the same weight, you can't vary it, so if you drop weight you must vent the lift gas that used to lift it too, or you are on a one-way trip to the stratosphere. (in real life all kinds of airships have escape valves that prevent pressure from getting to dangerous levels as the ship rises past the altitude where the gas fills the ship--this is called "pressure height" and as you pass it gas will be vented one way or another--either through valves or seams will split and spill it! Assuming it is the valves that do their job, clearly you lose lift as the gas is lost and so you come into equilbirium and stop rising--lift now matches weight. But helium is expensive and operations with it always try to avoid this.
One idea I like is using _steam_ for a lift gas. It has 60 percent the lift of helium--see
www.flyingkettle.com
You can vent the steam, or if you are patient condense it into water--which is now more ballast!
For firefighting the real danger is, the air is terribly turbulent above a big fire. Also hot air lifts less than cool air so you will lose lift flying above a fire.
Of course one way to correct for that is to drop ballast--say a lot of water...
"Too, blimps are NOT kept at high pressure. Actually, the ideal is having them as vacuous as possible while still maintaining their shape - too little pressure and they'll collapse in on themselves, and thus increase in density. Too much pressure and you're increasing the density another way."
No, no no! the pressure involved in a pressure ship is just a percent or so of atmospheric--it is not about varying density at all, you just can't do that significantly except by heating or cooling the gas, not in a structure light enough to be lifted by the air!
There is no way that a failure of pressure leads to "increased density" of the lift gas due to collapse. What you lose when pressure fails is _structure_ in a pressure ship. It goes limp and this is very bad if you have airspeed--something like that happened to the Navy's big ZPG-3W that crashed in the early 60's with a loss of most hands aboard. But if you stop engines and avoid crashing and have not lost a lot of lift gas, you become a limp balloon if pressurization fails, but a floating one.
"Pressure is probably just slightly over atmospheric - think of a balloon with just enough air in it to be round, not one that's fully inflated."
Yes!
Except that you are thinking of a rubber balloon, where the pressure comes from tension. I think the pressure of a blimp would feel quite firm to human touch. But atmospheric pressure is like that of water thirty feet deep, quite high.
"Not trying to troll, but, isn't Helium the most abundant resource in the universe next to hyrdogen?"
Yes, but not on Earth. A lot was probably created in the Big Bang and the stars have been creating it since they formed. But it is so light and unlike hydrogen not prone to form compounds and so tends to escape planets more easily. I'm sure the gas giants have a lot of it but a small rocky planet like ours loses it--most of ours would arise from radioactive decay of heavy elements.
People who want to create more by nuclear processes would do better to devise a fission recipie to optimize the output of alpha particles (helium ions that is!) rather than develop fusion. Fusion would create so much energy we'd probably either use helicopters or jets for veritical lift alll the time and laugh at LTA--or use the energy for _thermal_ (very hot air) airships rather than mess around with helium!
I don't want to rely on any of these nuclear processes for my helium!
"As I understand it, one minor problem with blimps is containing the Helium used to fill it. The molecules are so small they eventually pass through most materials."
Yes.
"Is "need more Helium" another argument for developing workable cold fusion?"
No. If we could employ fusion of any kind on the scale that would be needed to create that much helium we'd be generating or wasting so much energy we could just power rocket jets or something. Probably we'd develop a civilization that basically cooks away the atmosphere anyway or something equally drastic!
Besides the types of fusion reaction considered most likely to be workable soonest don't typically create Helium-4 unfortunately.
What we need to do is conserve the helium we've got better or turn to mining the atmosphere to recover it. Airships will retain helium way better than the normal uses we put most helium to today!
"I think this technology is under-utilized. A friend of mine from Alaska bid to provide materials for the Trans-Alaska Gas pipeline and crane services by using blimps. He felt he could cut millions off the estimated bill and eliminate the need for a truck road by using blimps. Needless to say, no visionaries were on the bid committee.
Blimps should be ideal for overland hauling, and they could make a great platform for cranes in many instances."
I think it is really a challenge to make airships serve these functions well, though certain rather bizarre-looking designs may be more workable than they look.
However, your friend should have considered interesting gas field developers in using airships to _ship the gas_ directly inside them, as a gas. Methane (most of natural gas is this) is actually itself considerably lighter than air. Serious proposals to do this have been made. To do it really well you'd need really big airships and the smaller they are the bigger the fleet of them you'd need, so it is really extreme in that sense. But it is not difficult at all to match or beat the fuel-economy of a surface ship, and fly 5 times faster than that ship can steam, and of course fly over land and sea ice. And this application avoids a lot of the complications of most niches we LTA fans try to develop for big cargo airships. You just design those big smokestack things that are standard in gas fields for venting away to serve as adequate "high masts" for the ship to moor to--this would involve strengthening them to be sure. But then moor the ship to the top of the stack/mast in the way developed by Britain and the US Navy in the 1920s, and run a very broad hose to an intake, and through a manifold fill sub-cells within the ship's helium cells with the product. Unmoor, and off the ship goes, burning its own payload in turbine engines. (Since natural gas is LTA you'd need some condensed cargo for ballast too--say, some precipitated heavy petroleum from the gas itself, or some oil from a nearby well, or if all else fails water or sand or whatever is readily available! Hopefully the ballast would be oil though). Burning a percent or so of its cargo (gotta burn the liquid a bit too to match the loss of lift from the burnt gas) you cruise at 65 knots or so to a market. Flexible, safe, fast, secure--an excellent system and entirely workable with known technology.
"Yes, you are the only one surprised by use of a blimp instead of a rigid airship."
The only one surprised maybe, but not the only one scandalized.
"Rigid airships are a lot more complicated to build structurally, since they are carrying a bunch of rigid structure that does nothing to generate lift and can bend and break under stress."
it ain't necessarily so. In concept a blimp is simpler (though actually a workable blimp has a lot of subparts) but to successfully design and fabricate that nonrigid structure turns out not to be so easy, judging from the cost and long development times of non-rigid projects which if anything seem more difficult and expensive than rigids. A lot of confusion arises because blimps tend to be much smaller and of course it is easier to make something small than large. Easier for more peopel to try, easier to gain experience--all as a pure matter of scale. Also, blimps have historically been seen by most decision-makers as quick, dirty, expendible solutions to problems while rigids have been national priorities and the projects have often suffered from the surrounding politics.
I'd shut up about this if blimps have in fact ever proved out to have greater proportions of useful lift than the better rigids achieved, in the case of the last Zeppelins better than 50 percent of the lift was available for payload and fuel. Show me a blimp that comes close to that! Generally blimp useful lifts are like a quarter, maybe a third, of total lift. Of course today we have helium and then they mostly used hydrogen, but today we would make rigids out of somewhat lighter materials too. BTW--a friend who loves blimps over rigids often says that we've had way more progress with fabrics than with metals--but in fact a lot of the structural weight of a rigid was not the frame but the fabric, skin, cells, and rigging, and all of these would _definitely_ be much lighter, stronger, more gas-tight, and probably cheaper too today.
But even comparing a 1933 model helium rigid (USS Macon) with a 2004 model pressure ship, do you really assert the overall structure is lighter relative to the lift volume on the blimp? The skin of a blimp is the whole show pretty much--if it rips or leaks you have big problems with every aspect of the ship's operations, so its specifications are stringent and the safety factors with fabrics must be high because it is hard to verify the integrity of fabrics without testing them to destruction. You may satisfy yourself that the design is sound by doing that to a long sequence of samples, you may adopt stringent quality control to prevent flaws (all this clearly helps explain the high costs involved!) but in the end you risk that the next sample you make has one and that's the patch you install in the ship--only high safety factors bring down the risk. The same would be true of rigids made of composites but with metals you can X-ray the girders to confirm they are sound! The division of labor betweent the parts also provides both a sort of safety factor (structure is not dependent on pressure for instance) and can contain the scope of damage.
As for "design," a pressure ship designer I corresponded with got indignant that I wished he had included some principles of rigid design in a modern book on airships--he said first of all no one makes rigids today (Catch-22!) and second, the _standard_ design methods used for airplanes and other structures were sufficient-in other words many elements of rigid airship design are "off the shelf" for an experienced engineer. But stresses in fabric pressure designs are much more unpredictable and the field is arcane and underresearched.
"Blimps are not just one big ballon, but can and are compartmentalized for disaster containment."
I'm pretty familar with modern blimp design and practice, as a fan though I am no professional. I can't imagine a single pressure ship flying that meets these specs. It is easy to imagine but no one does it. Actually the best scheme like this I have ever seen speculat
I may be wrong, underestimating the ability of the Germans in a last ditch all-out effort but I doubt very much this period was at the end of the war. No, the time the Germans could really close down US coastal shipping was when we entered it. Guess what we used to break that grip? Blimps! No U-boat liked the idea of attacking a ship or doing anything that might draw the attention of our "kleine Zeppelins." True there was reason to doubt the blimp itself could prevail against the sub (although there is good reason to think sometimes they did make kills, and the US Navy suppressed the fact since there were a lot of airship haters in the Navy who wanted to shut down LTA, these eventually got their way) but once spotted a sub was in grave danger and far less likely to make a kill of its targets. (One blimp is known to have been shot down by a sub--but its machine gun had jammed--it is very frustrating to wonder what might have happened if it had not. But however glorious shooting down a "little Zeppelin" might seem it would do little harm to the Allied war effort!) The fact was, convoys guarded by blimps were never attacked by submarines. Same was true in WWI with the British blimps. The Germans, who knew something about potential uses of airships, were very worried about our blimps.
Of course there were other ways of supressing subs, including seaplanes and landplanes, blimps were just very effective--and cost-effective. Our problem at the beginning of the war was that first of all we had few of any of these resources (the Navy had all the blimps and just a handful of them--they drafted the fleet of Goodyear advertising blimps and sent them out armed with rifles on the Pacific coast!) of any kind. Much worse the Navy didn't make merchant shipping protection a priority; convoys were not even adopted until many ships had already been sunk. the Navy wanted warships to go fight Japan and regarded everything else as a sideshow--to the point that the _Army_ had the most numerous fleet by the end of the war since the Navy would not do the job of transporting troops or carrying supplies for the Army in the Pacific! The Army ships were not capital warships of course but there were a whole lot of them.
No, all kinds of LTA were used in WWI. Actually I don't know how much balloons were used--I don't pay a lot of attention to stuff about unpropelled balloons, I like airships. BTW any airship, rigid or not, is a "dirigible" because the word means the craft can be made to move in some controlled direction--this is the essence of an airship, it is dirigible. True, the grander term was fashionably applied to rigids but an airship is a dirigible is an airship, whether it is a blimp, a rigid, a metalclad, a semirigid, or a number of other structural schemes.
But during "the Great War" while the Germans were almost alone in using rigids (which were large but not all made by Zeppelin--some were made by Schütte-Lanz) except for some essentially experimental British ones, nearly everyone was using semirigids or blimps. And the British had an especially good quick-and-dirty blimp program to patrol the sea lanes. They did the same jobs the more advanced American blimps (all made by Goodyear, and using helium instead of hydrogen as the WWI era airships all did) did. The most numerous airship fleet was this American one of course, and I think it rivaled the Zeppelin fleet in volume of lift gas enclosed. During WWII lots of uses were found for tethered balloons too--and these were generally filled with hydrogen (being unmanned).
Yes and no. What actually happens with fossil resources of any kind is, as the easy to mine sources give out, the harder known ones are all that is left--the difficutly of getting the stuff increases and if there is a demand the price rises, thus making more marginal extraction more profitable and exploration for more sources a more attractive risk. I think what you want to know is, how much would the easy sources we know now yield and how fast are we approaching that limit? I don't know, but helium is used for lots of stuff besides balloons and most of its uses throw it away--only airships strive to retain it and keep it pure. So we'd be better off from the conservation POV if airships were its major use.
When the extraction costs of mining it rise high enough we could then extract it directly from the atmosphere, then we'd have a "renewable" source since any lost gas goes back into the supply pool, But such helium would be terribly expensive.
How to make liquid helium? with great difficulty, that's how. Essentially the way any other gas is liquefied but it is very hard because helium atoms are very light (hydrogen is hard to liquefy too) and _also_ are noble gases--the helium atom has a filled shell of electrons and is very symmetrical so it has little tendency to interact with other atoms by the various molecular bonds that affect others, mainly because they are 'dissatisfied" with their electron arrangements.
Still, if you compress the gas and let it cool, eventually it should condense, if the temperature is low enough. It is very hard to get the temperature that low however. The stuff boils away very easily.It also can exhibit very weird behavior that is explained only by means of quantum mechanics.
First of all--there is no reason why rigidity or flexibility of a substance has anything to do with whether it is heavy or light. You can have a very heavy fur coat and a very light aluminum soda can.
As for the whole "vacuum" thread-look, suppose for a moment you have some wonderful substance that _can_ form a shell that can hold the air out of a vacuum. It has some finite weight, would you not assume so? Say it weighs a quarter what the air excluded from the inside would weigh. (this is not bad at all for an airship.) Thus you have 3/4 that weight as "useful lift" for payload or fuel. (ignoring the detail of the weight of other things that form the essential structure like engines, cabin walls, props, etc). Groovy. But now you fill this shell with helium. Oops! you just added weight to no purpose, because it didn't increase the volume of air displaced any. But wait! before your shell was holding out a pressure equal to the weight of ten tons of material on one square yard--that is a lot of force. If you flood the inside with helium it relieves all that stress. Since you probably won't want to drive your airship much faster than speeds that exert pressures like 1 percent of the atmosphere on it, maybe 10 percent tops (10,000 Pascals) you can throw away 9/10 the shell's thickness, thus saving.225 percent of the total available lift. The weight of the helium is only 1/7 or so that of air of the same volume so about a third of that discarded shell weight is useful lift despite deducting the weight of the helium.
Obviously if the best substances available would not weigh only 1/4 that of the air but something worse, the corresponding weight savings by using helium would be even greater.
Whether vacuum can work or not, its advantage over helium is too small to be worth using. Helium practically is a vacuum, but one that exerts pressure.
No blimp can change the density of the craft to make it ascend or descend, except to the limited extent that heating the gas can vary the density. As a practical matter that method is limited. But lots of people seem to believe that the ballonets of blimps can gulp in extra air to make the ship heavier or squeeze the helium to a lower volume or something. To the extent that the hull materials can bear overpressures both things happen--but a typical blimp (or any other airship--most of the fastest airships were rigids but the very fastest ever was a US Navy ZPG-2W, a blimp) is designed around overpressures of about 1 percent sea level atmosphere pressure. One measly percent! That is how much latitude you have for pressure variation hence that is the limit for "buoyancy control." And to strenghten the hull to take more pressure would make it much too heavy to lift anything else, or even itself. Airships cannot be compared to submarines on this point of buoyancy control. Practically speaking their buoyancy is a function of how much gas they have, period. A kilogram (mass) of helium lifts the same amount of weight whenever its pressure and temperature are the same as the air outside, no matter what
Tremendously. Factor of 12.5. In fact the power supply--not just the energy storage but whatever transforms it into force--ie not just the fuel but the engine, not just the battery but the motors--and the props would all have to be that much bigger than for a well-streamlined conventional airship turned into the wind. A sphere has high drag because the airflow loses some energy to friction as it passes over the surface, and then it has not got the energy left to reach the center of the far side--it stalls and the flow separates, leaving a large area in the back at a low pressure. Most drag on most real objects in the air has this cause but a streamline trades off more surface drag (more length) for a smaller radius area of separated flow--the pointed tail also helps minimize that. I believe a sphere might in principle have its drag lowered by techniques known as "boundary layer control" but these Techsphere guys have never heard of that apparently. (Nor has anybody ever demonstrated a drag-reduced sphere by means of BLC either, maybe that won't work.) But a factor of 12 for a bare sphere is conservative--it might be more like a factor of 30.
These spheres--how do you keep them from blowing away in stiff winds? How can reasonable amounts of power installed in them enable them to keep station? (To keep station an airship must be able to counter the wind's airspeed, it is the same as flying at that speed in a calm.)
For me these are rhetorical questions, because I believe an answer would be-"boundary layer control!" With that I bet the drag per volume might be brought _below_ normal streamline levels. And you would reap great structural advantages, need no fins, and be able to turn around pretty quick. (Don't say you don't have to--any reasonable BLC system I can imagine would need to work on one axis only. But you would have smaller moment arm than an elongated airship.)
But this only works_ with_ the BLC system. These bozos don't know from BLC apparently and are stuck with the normal amount of drag any sphere would have. Which is terrible compared to a streamline turned into the wind even with its fins and accessories--a factor of 12 I think. Not good at all. That is how much extra power you need compared to a normal airship at the same tonnage and altitude, that shows how strong the forces are.
To be fair, the Techsphere guys do say their airships should be thought of as being to other airships as helicopters are to airplanes. What they either don't understand or don't want to draw attention to is, the amount of power and the size of the rotors they need to use that efficiently would be about the same as for a helicopter of similar mass. They would basically _be_ helicopters, with some buoyancy.
Bad, bad idea without BLC. I have tried to tell these gentlemen that and they show no sign of listening. Watch the DoD's projects blow away the way the Sanswire sphere did--these guys did that one too and made the same promises.
Slashdot Mirror
Props do not lose efficiency with altitude, they lose effectiveness. If the air is 1/2 the density you get half the thrust when the prop turns at the same speed with the same setting of pitch. But by the same token the drag on the blades is also halved and so the torque and hence power demand too. Since an engine with no supercharger would have its air and (with an old-fashioned carburator) fuel draw also halved and thus power output reduced accordingly it all works out great for an airship-because an airship is only concerned with drag and that too is halved. From this we conclude that when an airship is at its ceiling, the pressure height where its lift gas has filled the available volume, it is actually more efficient at a given speed--its fuel consumption is reduced in proportion to the reduced density of the air it plows through. The props are less effective but just as efficient, the engine is less effective but more efficient since you cover the same miles with less fuel and as a bonus the engine runs cooler.
& ri d=832757878
There is a lot of confusion on these threads from people who do not understand airships. There are a lot of assumptions that are correct for airplanes but not airships. A cruising airplane needs to generate the same thrust at all altitudes and to stay at the optimum lift/drag ratio it needs to fly faster in thinner air; for these reasons their props do indeed need to work harder as they climb and they do indeed lose efficiency. (They are flying faster though so they cover more ground sooner; this pays off).
An airship's speed is limited by the danger of damaging its necessarily light structure; the forces that threaten it happen at higher and higher airspeeds as the air gets denser. If we maintain constant drag instead of constant speed as we rise, the props start out with a very easy job and the engines will be practically idling and as we climb we must indeed increase power as we speed up, at the inverse square root of the density ratio. But now we are going faster. If instead of turning the prop at constant speed and increasing pitch we held the pitch and turned the prop faster in proportion to airspeed we'd clearly maintain constant thrust, constant torque, and have the power demand rise with speed because the prop rotation speed rises with it. Again clearly the _prop_ has constant efficiency in this case! (The engine may slip).
A very high altitude airship will need to be very light and will be fragile at low altitudes. Wind speeds tend to rise as you climb but then at the bottom of the stratosphere there is a sweet spot where the wind _forces_ have a minimal average, though the speeds may seem high by sea level standards. This thread is correct the airship has to pass through levels with rougher winds--but it does not need to fight them, it can limit itself to its maximum safe airspeed at that density. If the adverse winds exceed that it gets blown downwind some that 's all. It does not suffer any wind forces its engines and props don't create except when the wind shifts rapidly and inertia is felt. Presumably you call it down on calm days and chase it down whereever adverse winds in the middle layers have blown it to.
All the above remarks apply to any airship.
I have posted my denunciation of the stupidity of using spherical airships that have no boundary layer control; Techsphere's website continues to post the fairy tale that the drag of the sphere matters less in thinner air. True absolute drag is lower but so what? What matters is performance relative to streamlined alternatives; at any altitude a sphere without BLC has over 12 times the drag of a streamline of the same volume hence lift! If the air is 1/10 the density hence drag at a given speed is only 1/10 what it would be down at sea level--well, static lift is reduced by the same proportion so in terms of relative weight of components it is the same as making a ship of the same mass 1/10 the volume for use at sea level or filling the big ship up with lift gas down here and needing ten times the power to handle the same speed.
But I have seen sites that suggest Techsphere may be belatedly working on BLC; if so their scheme may work at last.
http://designnews.com/article/CA412219?nid=2335
Hey, I'm new to Slashdot and I am having trouble figuring things out like how I can just relpy to you directly. I need to take care of some things right now but would love to respond on these things later.
A very general response--airships rarely have serious stability problems. They tend to have a very long moment arm between the center of lift (in the middle of the gas bag) and the center of mass, because fuel, payload, and a lot of structural weight tends to be down on the bottom. Combine that with their big scale and corresponding long moment arm and you have tremendous pendulum stability against roll. Also they move at such low speeds and can turn only slowly so there would be very little centrifugal force--insofar as there is any the ship just gently rolls to keep down facing the cabin floor, and rolls back. Oscillations are well damped by the tail fins.
Pitch and yaw would be big problems except that the tail fins solve it pretty well. Again the forces are not like those on airplanes though they do have to be managed with good piloting.
Response times are very slow--blimp pilots have to anticipate their moves a long time in advance.
The Hindenburg gave a very smooth ride and even blimps are remarkably stable.
Wow, what fun things to reply to!
"The "answer" was given here.[See up thread for link, I use plain text-Foxwell] It basically amounts to more weight == more thrust required. A fair enough stance, but I still don't buy it."
Good for you! I did answer this person--he seems to think a ton of aluminum weighs more than a ton of Dacron! A less efficient structure would indeed have to be bigger to lift a given payload and hence have more drag and need even more lift for more fuel. But there is no reason at all to say a blimp would weigh less empty and deflated than a rigid would, and lots of history that contradicts that mindless assumption. You might think a blimp ought to be lighter but they aren't. And I think the same investment in effort that would lighten blimps to the degree already achieved in the 1930s with rigids would if applied to a rigid project yield really fantastic results. There are gripes against rigids that have some merit but rarely does anyone bring them up.
This guy was not even talking about a classic Zeppelin type airship but apparently guessing at a structure like Upson's Metalclad ZMC-2. Which by the way itself skewers his argument--the "Tin Balloon" as the Navy guys at Lakehurst liked to call it was too small and had some other weird issues but it was a sound structure, being basically a skin of aluminum sheet minimally reinforced by some bracing rings (mainly for attaching things I think) and a small pressure to keep its sides from creasing, but the resistance to bending or collapsing came from the mechanical strenght of the egg-shaped metal sheet itself--think of it as a very thin-walled tube or pipe. It also held helium very well and plenty of folks today think it is the true future of serious LTA.
BTW--you or anyone else interested in airships might check this site out:
http://spot.colorado.edu/~dziadeck/airship/lists er v.htm
That's the page for joining the listserv, but check out the rest of the site first. John himself rarely posts except to help people asking the list for help and advice, and there are no archives so you just have to dive in and see if you like it. Lurk a while. But this is the main place I have ever found for serious airship talk. I learned a lot from it.
Onward!
"I *still* think that a rigid airship is the way to go for a truly large vessel."
Well sure. Actually I am not a fanatic and I like to see as many options developed as possible. I believe in giant blimps too. But honestly first of all, only rigids have ever been made and worked in the big size ranges. Second, I think they are subject to great economies in fabrication using modern automated industrial methods. Third, taking an old design and just substituing in more modern materials (largely for the fabric--much of the weight of a Zeppelin was fabric!) would improve their good lift ratios even more. Bottom line--if you want a big airship ASAP the rigid beckons. It has been done! I think that is part of the problem--no one wants to be known as a great imitator or updater.
"Hey, since you seem to have spoken with quite a few airship designers,"
I read books and then found the listserv above. This did lead to conversations with actual airship designers but I never buy into every part of any of their individual visions. Diversity is good I think but in LTA it often is more like radical parochialism!
"... let me pose a question to you. One of my dream ideas has always been to build a carrier in the sky. The way I figure it, the sides of the deck would be lined with large rigid frame balloons that would provide buoyancy for the craft. With its entire weight lightened, it could then use turbofans built into the bottom of the craft to provide the actual lift power. These turbofans would be powered by the onboard nuclear reactors. (Who else would need an aircraft carrier other than the miliatary?) I'm still thinking about how forward thrust would be applied, but it could be accomplished by building the turbofans to "ti
"Rigid airships could have very small air pressure and get away with it, but blimps wouldn't stay inflated."
Maybe it is because I have not been sleeping enough lately but I'm confused trying to figure out what the premise of this statement is.
Let's review some airship fundamentals!
In concept, rigid airships are rigid structures that shelter simple flexible gas bags (ideally containing pure lift gas like helium and no air whatsoever) from the wind of the slipstream, but the air within the hull that they float in (providing lift) communicates freely with the air outside and is at the same _static_ pressure as a parcel of air that is not in relative motion would be.
This is a bit tricky to accomplish because when the airship is moving the motion of air around it creates a varying pattern of air motion and complimentary static pressure variation--the air right on the nose has been rammed up to full speed and has extra static pressure due to that, the air flowing past the sides has lower than average static pressure, due to the Bernoulli effect. There is some pair of regions, one aft the nose and one somewhere ahead of the tail tip (ideally) where the variations cancel out and you might just make some holes there, but that area will shift around if the hull tips out alignment with the slipstream as when turning in any direction. If you let high pressure air in one place and out to low pressure areas elsewhere you get a wind inside the rigid which defeats the point of a hull--except you do want a little air circulation.
Anyway in the ideal rigid the air is a calm zone inside the hull that is moving along with the ship, and any pressure variations outside due to ascent, descent, changing temperature, or anything else are reflected by air freely entering or escaping the hull to ideally maintain the same static pressure--the only forces on the skin are due to aerodynamics, the motion through the air. Great.
Now the gas bags--to a first approximation they just match the prevailing pressure which, since they are closed bags, means they expand and contract freely. (There are also lags in responding to changing temperature. But any variations resolve into the bags taking on whatever volume matches their internal pressure with the prevailing one inside the hull).
In detail--in any column of still air, the density and pressure at the bottom is greater than at the top, because the molecules respond to gravity in that way. This is the way that aerostatic lift actually occurs. In any lift gas--hot air, hydrogen, methane, helium, steam, whatever--the rate of fall-off of pressure and density is lower--with hot air because its molecules are more energetic being hotter, and in others because their molecules are lighter hence faster at the same temperature so their energy denisty can match that of air molecules. So there is no way a bag of helium can exactly match the pressure of the column of air it is in exept at one point--on the bottom they match, and going up the pressure of the helium falls more slowly, so there is a net pressure out--and up. This is how we get static lift in a limp balloon. To that extent the cells of any rigid airship need to endure a pressure variation. This variation is such that if it continued linearly going up it would rise to a full atmospheric pressure at about 10,000 meters (10 KM, 6 miles) up, so since the avarage atmosphere is about 100,000 Pascals (Newtons per meter squared) the pressure difference between the top and bottom of a flaccid helium bag would be 10 Pascals/meter of height, about 1/10,000 atmospheric pressure. A cell 100 meters in height would be bearing 1 percent atmospheric pressure at the top _if_ it were filled at sea level. (but then the ship could not rise without venting gas--its pressure height would be zero.) The biggest cell ever used a rigid would be the 40 meter diameter ones in the last big rigids, the American ZRS naval ships and the last 2 Zeppelins (Hindenburg and Graf Zeppelin II). So with big cells you already have signif
" 'Still, if you compress the gas {helium} and let it cool, eventually it should condense, if the temperature is low enough.' {me}
So, like, you'd need a compressor and a refrigerator (let's say "ice box"). Wouldn't you also need an expander somewhere in the process? Just guessing."
To be honest I am hazy on the details too but the technical challenge I think you are indicating is indeed formidable. How to make a heat pump that removes heat from the substance with the coldest condensation temperature in the universe? They use all kinds of ultra-exotic techniques to peel away at those last few degrees Kelvin! It is incredibly difficult and expensive. Thermodynamically speaking yes there is something like "expansion" going on but in very exotic contexts--electron gases in semiconductors, weird quantum effects, stuff like that. I'd have to do a lot of research to be more specific. It is done in stages, each one stranger and harder than the last.
"I think you might be somewhat confused. The question was not why they shaped it like a sphere, but rather why they didn't use a rigid airship instead of a blimp. Someone stated that the biggest problem is fuel, and then expanded on that answer.
"
I came late to this thread having been out of town. But "fuel" is a totally irrelevent answer to the question you point to--it does not matter how an airship is structured how much drag it has, which is what dictates the power/thrust requirements for a given performance target. OTOH the sphere (without Boundary Layer Control to change the picture) has tremendous drag compared to a normal streamline and "fuel" would be a very relevant answer to that. Spheres are wonderful structurally but not nearly enough so to overcome that huge drawback.
How could the difference between a blimp or a rigid have any bearing on its power supply or the demands of the mission as they would affect fuel/power demands??
Please point me to the answer--either I missed it, answered it, or dismissed it as hopelessly confused. Rigids historically had very good useful lift ratios and the best a blimp might hope to do is match that. Being generous to the blimp I just assume there is no difference. No other characteristic that distiguishes them favors a blimp either--they are not easier to make good shapes out of, there is just no overwhelming advantage except that the industry, such as it is, is geared toward thinking about blimps and making them and not rigids. For this project a rigid is clearly the quick and dirty solution and if not abandoned will I bet retain the lead forever. It solves a lot of problems the blimps pose.
And if you want a sphere I can tell you what might make it workable. These Techsphere guys don't even acknowledge the problem, they just change their name every few years so people don't connect them with their last fiasco!
"Out here in western USA, we get loads of wild fires. rather than flying tankers and people, it would be very useful to use these to get huge volumes of water in. In addition, they may be able to drop off fighters in close to the action.
Now, lets hope that somebody does not come up with the idea of using hydrogen and doping for this."
Any LTA use must remember, the lift gas always lifts the same weight, you can't vary it, so if you drop weight you must vent the lift gas that used to lift it too, or you are on a one-way trip to the stratosphere. (in real life all kinds of airships have escape valves that prevent pressure from getting to dangerous levels as the ship rises past the altitude where the gas fills the ship--this is called "pressure height" and as you pass it gas will be vented one way or another--either through valves or seams will split and spill it! Assuming it is the valves that do their job, clearly you lose lift as the gas is lost and so you come into equilbirium and stop rising--lift now matches weight. But helium is expensive and operations with it always try to avoid this.
One idea I like is using _steam_ for a lift gas. It has 60 percent the lift of helium--see
www.flyingkettle.com
You can vent the steam, or if you are patient condense it into water--which is now more ballast!
For firefighting the real danger is, the air is terribly turbulent above a big fire. Also hot air lifts less than cool air so you will lose lift flying above a fire.
Of course one way to correct for that is to drop ballast--say a lot of water...
"Too, blimps are NOT kept at high pressure. Actually, the ideal is having them as vacuous as possible while still maintaining their shape - too little pressure and they'll collapse in on themselves, and thus increase in density. Too much pressure and you're increasing the density another way."
No, no no! the pressure involved in a pressure ship is just a percent or so of atmospheric--it is not about varying density at all, you just can't do that significantly except by heating or cooling the gas, not in a structure light enough to be lifted by the air!
There is no way that a failure of pressure leads to "increased density" of the lift gas due to collapse. What you lose when pressure fails is _structure_ in a pressure ship. It goes limp and this is very bad if you have airspeed--something like that happened to the Navy's big ZPG-3W that crashed in the early 60's with a loss of most hands aboard. But if you stop engines and avoid crashing and have not lost a lot of lift gas, you become a limp balloon if pressurization fails, but a floating one.
"Pressure is probably just slightly over atmospheric - think of a balloon with just enough air in it to be round, not one that's fully inflated."
Yes!
Except that you are thinking of a rubber balloon, where the pressure comes from tension. I think the pressure of a blimp would feel quite firm to human touch. But atmospheric pressure is like that of water thirty feet deep, quite high.
"Not trying to troll, but, isn't Helium the most abundant resource in the universe next to hyrdogen?"
Yes, but not on Earth. A lot was probably created in the Big Bang and the stars have been creating it since they formed. But it is so light and unlike hydrogen not prone to form compounds and so tends to escape planets more easily. I'm sure the gas giants have a lot of it but a small rocky planet like ours loses it--most of ours would arise from radioactive decay of heavy elements.
People who want to create more by nuclear processes would do better to devise a fission recipie to optimize the output of alpha particles (helium ions that is!) rather than develop fusion. Fusion would create so much energy we'd probably either use helicopters or jets for veritical lift alll the time and laugh at LTA--or use the energy for _thermal_ (very hot air) airships rather than mess around with helium!
I don't want to rely on any of these nuclear processes for my helium!
"As I understand it, one minor problem with blimps is containing the Helium used to fill it. The molecules are so small they eventually pass through most materials."
Yes.
"Is "need more Helium" another argument for developing workable cold fusion?"
No. If we could employ fusion of any kind on the scale that would be needed to create that much helium we'd be generating or wasting so much energy we could just power rocket jets or something. Probably we'd develop a civilization that basically cooks away the atmosphere anyway or something equally drastic!
Besides the types of fusion reaction considered most likely to be workable soonest don't typically create Helium-4 unfortunately.
What we need to do is conserve the helium we've got better or turn to mining the atmosphere to recover it. Airships will retain helium way better than the normal uses we put most helium to today!
"I think this technology is under-utilized. A friend of mine from Alaska bid to provide materials for the Trans-Alaska Gas pipeline and crane services by using blimps. He felt he could cut millions off the estimated bill and eliminate the need for a truck road by using blimps. Needless to say, no visionaries were on the bid committee.
Blimps should be ideal for overland hauling, and they could make a great platform for cranes in many instances."
I think it is really a challenge to make airships serve these functions well, though certain rather bizarre-looking designs may be more workable than they look.
However, your friend should have considered interesting gas field developers in using airships to _ship the gas_ directly inside them, as a gas. Methane (most of natural gas is this) is actually itself considerably lighter than air. Serious proposals to do this have been made. To do it really well you'd need really big airships and the smaller they are the bigger the fleet of them you'd need, so it is really extreme in that sense. But it is not difficult at all to match or beat the fuel-economy of a surface ship, and fly 5 times faster than that ship can steam, and of course fly over land and sea ice. And this application avoids a lot of the complications of most niches we LTA fans try to develop for big cargo airships. You just design those big smokestack things that are standard in gas fields for venting away to serve as adequate "high masts" for the ship to moor to--this would involve strengthening them to be sure. But then moor the ship to the top of the stack/mast in the way developed by Britain and the US Navy in the 1920s, and run a very broad hose to an intake, and through a manifold fill sub-cells within the ship's helium cells with the product. Unmoor, and off the ship goes, burning its own payload in turbine engines. (Since natural gas is LTA you'd need some condensed cargo for ballast too--say, some precipitated heavy petroleum from the gas itself, or some oil from a nearby well, or if all else fails water or sand or whatever is readily available! Hopefully the ballast would be oil though). Burning a percent or so of its cargo (gotta burn the liquid a bit too to match the loss of lift from the burnt gas) you cruise at 65 knots or so to a market. Flexible, safe, fast, secure--an excellent system and entirely workable with known technology.
"Yes, you are the only one surprised by use of a blimp instead of a rigid airship."
The only one surprised maybe, but not the only one scandalized.
"Rigid airships are a lot more complicated to build structurally, since they are carrying a bunch of rigid structure that does nothing to generate lift and can bend and break under stress."
it ain't necessarily so. In concept a blimp is simpler (though actually a workable blimp has a lot of subparts) but to successfully design and fabricate that nonrigid structure turns out not to be so easy, judging from the cost and long development times of non-rigid projects which if anything seem more difficult and expensive than rigids. A lot of confusion arises because blimps tend to be much smaller and of course it is easier to make something small than large. Easier for more peopel to try, easier to gain experience--all as a pure matter of scale. Also, blimps have historically been seen by most decision-makers as quick, dirty, expendible solutions to problems while rigids have been national priorities and the projects have often suffered from the surrounding politics.
I'd shut up about this if blimps have in fact ever proved out to have greater proportions of useful lift than the better rigids achieved, in the case of the last Zeppelins better than 50 percent of the lift was available for payload and fuel. Show me a blimp that comes close to that! Generally blimp useful lifts are like a quarter, maybe a third, of total lift. Of course today we have helium and then they mostly used hydrogen, but today we would make rigids out of somewhat lighter materials too. BTW--a friend who loves blimps over rigids often says that we've had way more progress with fabrics than with metals--but in fact a lot of the structural weight of a rigid was not the frame but the fabric, skin, cells, and rigging, and all of these would _definitely_ be much lighter, stronger, more gas-tight, and probably cheaper too today.
But even comparing a 1933 model helium rigid (USS Macon) with a 2004 model pressure ship, do you really assert the overall structure is lighter relative to the lift volume on the blimp? The skin of a blimp is the whole show pretty much--if it rips or leaks you have big problems with every aspect of the ship's operations, so its specifications are stringent and the safety factors with fabrics must be high because it is hard to verify the integrity of fabrics without testing them to destruction. You may satisfy yourself that the design is sound by doing that to a long sequence of samples, you may adopt stringent quality control to prevent flaws (all this clearly helps explain the high costs involved!) but in the end you risk that the next sample you make has one and that's the patch you install in the ship--only high safety factors bring down the risk. The same would be true of rigids made of composites but with metals you can X-ray the girders to confirm they are sound! The division of labor betweent the parts also provides both a sort of safety factor (structure is not dependent on pressure for instance) and can contain the scope of damage.
As for "design," a pressure ship designer I corresponded with got indignant that I wished he had included some principles of rigid design in a modern book on airships--he said first of all no one makes rigids today (Catch-22!) and second, the _standard_ design methods used for airplanes and other structures were sufficient-in other words many elements of rigid airship design are "off the shelf" for an experienced engineer. But stresses in fabric pressure designs are much more unpredictable and the field is arcane and underresearched.
"Blimps are not just one big ballon, but can and are compartmentalized for disaster containment."
I'm pretty familar with modern blimp design and practice, as a fan though I am no professional. I can't imagine a single pressure ship flying that meets these specs. It is easy to imagine but no one does it. Actually the best scheme like this I have ever seen speculat
I may be wrong, underestimating the ability of the Germans in a last ditch all-out effort but I doubt very much this period was at the end of the war. No, the time the Germans could really close down US coastal shipping was when we entered it. Guess what we used to break that grip? Blimps! No U-boat liked the idea of attacking a ship or doing anything that might draw the attention of our "kleine Zeppelins." True there was reason to doubt the blimp itself could prevail against the sub (although there is good reason to think sometimes they did make kills, and the US Navy suppressed the fact since there were a lot of airship haters in the Navy who wanted to shut down LTA, these eventually got their way) but once spotted a sub was in grave danger and far less likely to make a kill of its targets. (One blimp is known to have been shot down by a sub--but its machine gun had jammed--it is very frustrating to wonder what might have happened if it had not. But however glorious shooting down a "little Zeppelin" might seem it would do little harm to the Allied war effort!) The fact was, convoys guarded by blimps were never attacked by submarines. Same was true in WWI with the British blimps. The Germans, who knew something about potential uses of airships, were very worried about our blimps.
Of course there were other ways of supressing subs, including seaplanes and landplanes, blimps were just very effective--and cost-effective. Our problem at the beginning of the war was that first of all we had few of any of these resources (the Navy had all the blimps and just a handful of them--they drafted the fleet of Goodyear advertising blimps and sent them out armed with rifles on the Pacific coast!) of any kind. Much worse the Navy didn't make merchant shipping protection a priority; convoys were not even adopted until many ships had already been sunk. the Navy wanted warships to go fight Japan and regarded everything else as a sideshow--to the point that the _Army_ had the most numerous fleet by the end of the war since the Navy would not do the job of transporting troops or carrying supplies for the Army in the Pacific! The Army ships were not capital warships of course but there were a whole lot of them.
No, all kinds of LTA were used in WWI. Actually I don't know how much balloons were used--I don't pay a lot of attention to stuff about unpropelled balloons, I like airships. BTW any airship, rigid or not, is a "dirigible" because the word means the craft can be made to move in some controlled direction--this is the essence of an airship, it is dirigible. True, the grander term was fashionably applied to rigids but an airship is a dirigible is an airship, whether it is a blimp, a rigid, a metalclad, a semirigid, or a number of other structural schemes.
But during "the Great War" while the Germans were almost alone in using rigids (which were large but not all made by Zeppelin--some were made by Schütte-Lanz) except for some essentially experimental British ones, nearly everyone was using semirigids or blimps. And the British had an especially good quick-and-dirty blimp program to patrol the sea lanes. They did the same jobs the more advanced American blimps (all made by Goodyear, and using helium instead of hydrogen as the WWI era airships all did) did. The most numerous airship fleet was this American one of course, and I think it rivaled the Zeppelin fleet in volume of lift gas enclosed. During WWII lots of uses were found for tethered balloons too--and these were generally filled with hydrogen (being unmanned).
Yes and no. What actually happens with fossil resources of any kind is, as the easy to mine sources give out, the harder known ones are all that is left--the difficutly of getting the stuff increases and if there is a demand the price rises, thus making more marginal extraction more profitable and exploration for more sources a more attractive risk. I think what you want to know is, how much would the easy sources we know now yield and how fast are we approaching that limit? I don't know, but helium is used for lots of stuff besides balloons and most of its uses throw it away--only airships strive to retain it and keep it pure. So we'd be better off from the conservation POV if airships were its major use.
When the extraction costs of mining it rise high enough we could then extract it directly from the atmosphere, then we'd have a "renewable" source since any lost gas goes back into the supply pool, But such helium would be terribly expensive.
How to make liquid helium? with great difficulty, that's how. Essentially the way any other gas is liquefied but it is very hard because helium atoms are very light (hydrogen is hard to liquefy too) and _also_ are noble gases--the helium atom has a filled shell of electrons and is very symmetrical so it has little tendency to interact with other atoms by the various molecular bonds that affect others, mainly because they are 'dissatisfied" with their electron arrangements.
Still, if you compress the gas and let it cool, eventually it should condense, if the temperature is low enough. It is very hard to get the temperature that low however. The stuff boils away very easily.It also can exhibit very weird behavior that is explained only by means of quantum mechanics.
First of all--there is no reason why rigidity or flexibility of a substance has anything to do with whether it is heavy or light. You can have a very heavy fur coat and a very light aluminum soda can.
.225 percent of the total available lift. The weight of the helium is only 1/7 or so that of air of the same volume so about a third of that discarded shell weight is useful lift despite deducting the weight of the helium.
As for the whole "vacuum" thread-look, suppose for a moment you have some wonderful substance that _can_ form a shell that can hold the air out of a vacuum. It has some finite weight, would you not assume so? Say it weighs a quarter what the air excluded from the inside would weigh. (this is not bad at all for an airship.) Thus you have 3/4 that weight as "useful lift" for payload or fuel. (ignoring the detail of the weight of other things that form the essential structure like engines, cabin walls, props, etc). Groovy. But now you fill this shell with helium. Oops! you just added weight to no purpose, because it didn't increase the volume of air displaced any. But wait! before your shell was holding out a pressure equal to the weight of ten tons of material on one square yard--that is a lot of force. If you flood the inside with helium it relieves all that stress. Since you probably won't want to drive your airship much faster than speeds that exert pressures like 1 percent of the atmosphere on it, maybe 10 percent tops (10,000 Pascals) you can throw away 9/10 the shell's thickness, thus saving
Obviously if the best substances available would not weigh only 1/4 that of the air but something worse, the corresponding weight savings by using helium would be even greater.
Whether vacuum can work or not, its advantage over helium is too small to be worth using. Helium practically is a vacuum, but one that exerts pressure.
No blimp can change the density of the craft to make it ascend or descend, except to the limited extent that heating the gas can vary the density. As a practical matter that method is limited. But lots of people seem to believe that the ballonets of blimps can gulp in extra air to make the ship heavier or squeeze the helium to a lower volume or something. To the extent that the hull materials can bear overpressures both things happen--but a typical blimp (or any other airship--most of the fastest airships were rigids but the very fastest ever was a US Navy ZPG-2W, a blimp) is designed around overpressures of about 1 percent sea level atmosphere pressure. One measly percent! That is how much latitude you have for pressure variation hence that is the limit for "buoyancy control." And to strenghten the hull to take more pressure would make it much too heavy to lift anything else, or even itself. Airships cannot be compared to submarines on this point of buoyancy control. Practically speaking their buoyancy is a function of how much gas they have, period. A kilogram (mass) of helium lifts the same amount of weight whenever its pressure and temperature are the same as the air outside, no matter what
Tremendously. Factor of 12.5. In fact the power supply--not just the energy storage but whatever transforms it into force--ie not just the fuel but the engine, not just the battery but the motors--and the props would all have to be that much bigger than for a well-streamlined conventional airship turned into the wind. A sphere has high drag because the airflow loses some energy to friction as it passes over the surface, and then it has not got the energy left to reach the center of the far side--it stalls and the flow separates, leaving a large area in the back at a low pressure. Most drag on most real objects in the air has this cause but a streamline trades off more surface drag (more length) for a smaller radius area of separated flow--the pointed tail also helps minimize that. I believe a sphere might in principle have its drag lowered by techniques known as "boundary layer control" but these Techsphere guys have never heard of that apparently. (Nor has anybody ever demonstrated a drag-reduced sphere by means of BLC either, maybe that won't work.) But a factor of 12 for a bare sphere is conservative--it might be more like a factor of 30.
"Fuel" indeed.
These spheres--how do you keep them from blowing away in stiff winds? How can reasonable amounts of power installed in them enable them to keep station? (To keep station an airship must be able to counter the wind's airspeed, it is the same as flying at that speed in a calm.)
For me these are rhetorical questions, because I believe an answer would be-"boundary layer control!" With that I bet the drag per volume might be brought _below_ normal streamline levels. And you would reap great structural advantages, need no fins, and be able to turn around pretty quick. (Don't say you don't have to--any reasonable BLC system I can imagine would need to work on one axis only. But you would have smaller moment arm than an elongated airship.)
But this only works_ with_ the BLC system. These bozos don't know from BLC apparently and are stuck with the normal amount of drag any sphere would have. Which is terrible compared to a streamline turned into the wind even with its fins and accessories--a factor of 12 I think. Not good at all. That is how much extra power you need compared to a normal airship at the same tonnage and altitude, that shows how strong the forces are.
To be fair, the Techsphere guys do say their airships should be thought of as being to other airships as helicopters are to airplanes. What they either don't understand or don't want to draw attention to is, the amount of power and the size of the rotors they need to use that efficiently would be about the same as for a helicopter of similar mass. They would basically _be_ helicopters, with some buoyancy.
Bad, bad idea without BLC. I have tried to tell these gentlemen that and they show no sign of listening. Watch the DoD's projects blow away the way the Sanswire sphere did--these guys did that one too and made the same promises.