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Fuelless Flight with Air Submarine?
An anonymous reader writes "Using the same physics principles as submarines, a new company is planning a fuelless air ship. Recent advances in ultra light and strong materials are making this concept a practical reality." There's no question that changes in buoyancy can be used to propel a vehicle, but "fuelless" is going to be tricky.
All the same, it's still a cool idea. I want a small one to fly to work in (maybe add pedals for all the compression-> decompression stuff and you'll have a human powered plane ;)
Looks can be deceiving. Or CAN they?
However, just because it may not use fuel to continue on it's journey doesn't mean it didn't need some power to get it started...
Physics 101. Law of thermodymanics. Etcetera.
This issue is a bit more complicated than you think.
Well this PhD smells a quack (from the link on the page http://www.fuellessflight.com/techno/tech.htm):
"We humans can rarely invent any process that nature does not already use. Most of the science we know today merely copies nature. Our thermodynamic laws were formed by observation of nature. They are not proven, merely not disproved. Within this section of our website you will be taught a new science that mimics the earth's weather, by harnessing the dual forces of gravity -- buoyancy and gravity acceleration. Harnessing gravity may be more technically described as the science of harnessing mass differentials. High density mass falls within a low density lifting fluid, like rain falls from the sky, and low density mass rises in a high density lifting fluid, like a bubble rises in water or helium rises in air."
I think I understand the technology he is proposing (I'm confident it still requires input energy, beyond the environment), but he really should tone down the quack-o-meter. I think we can rest easily that the thermodynamic laws are intact.
-Sean
you need energy.
That would be the helium in this case. You could argues that it takes energy to build the thing, during which contained energy would be loaded via fuel powered vihicals, but thats a little overly semantical.
I mean, I can fill a ballon with helium, and it will rise without power.
The Kruger Dunning explains most post on
Even if you ignore the fuel needed to pump the helium in and out of the storage, they will need the power to propel the "gravy"-plane forward
They don't plan on pumping the helium in and out. It looks like they plan on leaving the helium static in the tanks, and pumping air in and out of other tanks, making the plane weigh more and less. However, it's not really the weight of the plane that matters, it's the density. The goal is to get the average density of all the materials onboard i.e. the people, instruments, seats, structure, tanks, etc to be less than the density of the air around it. This is where I think they will have problems.
Anyone familar with aviation or the atmosphere knows that the atmosphere gets much less dense as you go up. Here in Columbus, altitude 1,000 feet, the density of air is 1.2 kg/m^3 At 10,000 feet the density is 0.88 kg/m^3 and at 30,000 feet it is 0.41 kg/m^3. This plane would have to have an average density less than those values to reach those altitudes, and keep in mind that simply having the cabin pressurized for humans will make the entire cabin a bubble of "heavy" air.
The energy to pressurize air will come from a wind powered turbine which will be deployed when the plane is descending, but I don't know how much power they expect to get from this. Any power produced by this turbine would affect the plane in the form of drag, which decreases speed and range. This would have to be a very flexible air storage system, since the requirements would change every day depending on high and low pressure systems, temperature, and the weight of whoever is on board.
They may also have stability and control issues. I assume that this would have to be a large plane, even with today's light weight materials. Just look at how big blimps have to be to carry their minimal cargo. A plane like this with huge wingspan and extreme buoyancy would be affected by every gust of wind and bit of turbulence that affected it, and although it could be very stable, control inputs would have to combat huge wind loads, and control effectiveness would be marginal, to say the least.
From my armchair view of this project, it seems possible on a small scale, but not to the point of carrying "massive loads" of people and cargo as the website claims.
My $0.02
The idea that an airplane can fly endlessly carrying heavy loads of passengers and cargo without burning any fuel
So far so good.
The new hybrid "gravity-powered aircraft"
Starting to get bogus.
is formed by merging the capabilities of the following devices into a single new aircraft apparatus:
(1) an aircraft capable of aerostatic (lighter-than-air) lift to gain altitude; and,
Still OK.
(2) a glider aircraft capable of aerodynamic lift, having a high glide ratio to accomplish long range gliding; and,
Starting to get bogus.
("Glider"? Using diving planes to add a significant forward component to upward/downward motion is well understood. But a "glider" is something else - a high-speed device with significant aerodynamic lift - initially powered by atmospheric thermal energy in the form of updrafts storing energy by raising a NON-bouyant craft against gravity, then trading this stored energy for momentum as necessary by gliding downward. Raising a neutrally-bouyant object stores no energy.)
(3) a (patented, new design of Robert D Hunt) wind turbine that is capable of harnessing the force of wind to generate power as the aircraft glides downward. This cycle can be repeated indefinitely to allow the craft to stay aloft virtually forever.
Bingo! Perpetual motion.
You CAN get a lot of forward motion out of lift-driven vertical motion. But it takes ENERGY to adjust the lift. The submarines described in the original Slashdot posting are one example. Zepplins with diving planes that achieved speeds in excess of 200 MPH by this mechanism also existed in the mid 20th century.
But the Zepplins BURNED FUEL to change their bouyancy (by heating some of their bouyancy gas), just as the submarines use energy to compress or expand gas in their bouyancy tanks. This makes them a heat engine (though a slowly cycling one) and subject to the carnot cycle limit.
This craft proposes to use a turbine to collect energy from the wind of its passage and use that to adjust its bouyancy, use the bouyancy to produce forward motion, creating the wind to drive the turbine. Like a generator with its shaft connected to a motor which is also wired to its output, the energy goes around and around, with some being lost in every pass.
This is not to say it won't fly at all. But to the extent that it DOES fly it's getting its basic power from vertical air currents, just like any other glider. By being nearly neutrally bouyant it sacrificed the ability to store energy in the gravitational potential of its own weight at altitude, and it's replacing that by being able to convert the wind of its passage to stored electricity, then feed that back into forward motion via bouyancy adjustments rather than propulsive fans.
But I expect this to be more expensive and less efficient than other alternatives - such as an equivalent modification to the original 200-MPH zepplins WITHOUT the fixed wings.
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
Honestly, after reading this site, it smacks of all the hype around the Segway (and many similar, less-successful "revolutionary breakthrough" schemes).
Yes, it is possible to create a fuel-less aeroplane that can still maintain forward motion. Advanced glider technology certainly fits this description. However, there are a couple of things that are missing from the adware:
The physics of underwater motion are similar those of flight - basic fluid dynamics here. The problem is he's ignoring fundamental environmental differences between water and air. The density differences between the two make it possible to move large masses underwater, but only tiny masses in the air using the same principles. Not to mention that the fluid consistency and motion between air and water are radically different, which invalidates using the ocean as a model for the sky.
He's a fraud. Pure and simple.
-Erik
There are always four sides to every story: your side, their side, the truth, and what really happened.
You're forgetting that lift capacity goes by the cubic footage of the lifting body, not the length.
I'm too lazy to do the math, but a longer body would have a far larger volume in the lifting body than liner.
7.5 ft per person on a 30ft version != 75ft for 10 ppl.
"You worthless post!"
-Shakespeare, 2 Gentlemen of Verona, 1. 1. 147
Not quite. The idea is to use a large area of vacuum to provide normal lift. Then a second ballast tank can be adjusted will cause the thing to decend. When it decending, it uses the forward energy to spin the turbines which then powers the compressors. The steady state of this thing will be floating at 100,000 ft or so.
I think it can work if they can solve the "magical box that can hold a total vacuum that weighs less than the air its going to displace" part of the problem but thats been know about since the days of Boyl and Dalton.
This system uses the energy of the wather system to move around a device that wants to float at a n altitude above ground level. In that way its much like a sail boat. The reality is if anyone can build a large vacuum chamber, they can stick engines on it and get from LA to London much quicker than current jets if they can get up high enough. I figure this will happen about the time someone finds the right stuff to make a space elevator out of.
The work required to pump all the air out of the ship to make it buoyant and rise to some height is more than the work required to just lift the ship that distance. Drag and any forward kinetic energy given to the plane implies that the energy recovered by the turbines during fall is not sufficient to pump all the air out of the ship again to once again make it rise, thus you will have to carry along fuel to run an engine to drive the pump that changes your buoyancy. If you use external power to evacuate the buoyancy chambers on the ground, then it can be said that the pressure differential represent stored energy. As the ship rises, gas pressure potential energy is traded for gravitational potential energy (altitude) and kinetic energy (forward motion).... So both the compressed helium and the evacuated chamber represent stored energy which must be loaded onto the ship while on the ground, thus this ship requires fuel like any other ship. Not only this but the inefficiencies in recovering kinetic and gravitational potential energy demand that the ship carry much more stored energy that that required to lift the ship through one up and down cycle.... So you may not hear the phrase "filler up" that the air park, but "emptier out" if effectively the same thing DN
My goodness, that video is so verbally twisted virtually anyone not having a clue would buy into it.
Of course that is the intent. Their perpetual motion is a complete farce. If you listen to the explanation (I know, it's ludicrous) they're basically saying you can get more air going down then you can going up.
Some other fallacies is the "lighter than air" effect. If you've ever seen a blimp, then you realize the size this craft would have to be in order to carry even the lightest loads. Helium is only "lighter than air" when it's density is lower. This is the whole "which weighs more, a pound of lead or a pound of feathers" argument.
Along those lines, you'd also need to take into account the expansion effect. Let's use weather balloons as an example. The higher they go, the bigger they get. Air pressure drops as you go up, therefore the greater air pressure in the balloon expands it outward. If it didn't, then the balloon would reach an equilibrium and go no higher. This craft would need to also take this into consideration. This could be quite a technical hurdle, gliding an aircraft that is constantly changing dimensions.
Regardless, the craft would at least need to carry some onboard power source.
I take this "article" with a big salt lick.
~X
Random Quote:"If it's too good to be true, then somebody is getting rich and it isn't you."
~X~
>To be safe they re-ran the numbers three times to be absolutely, positively sure the refuelers hadn't made any mistakes; each time using 1.77 pounds/liter as the specific gravity factor. This was the factor written on the refueler's slip and used on all of the other planes in Air Canada's fleet. The factor the refuelers and the crew should have used on the brand new, all-metric 767 was .8 kg/liter of kerosene.
Lessons: a triple-check doesn't help you if there's a systematic error. Standardized measurements are a Good Thing.
>the EICAS issued a sharp bong--indicating the complete and total loss of both engines. Says Quintal "It's a sound that Bob and I had never heard before. It's not in the simulator."
Lesson: in a safety-critical system, train the users for "impossible" situations.
>Hydraulic pressure was falling fast and the plane's controls were quickly becoming inoperative. But the engineers at Boeing had foreseen even this most unlikely of scenarios and provided one last failsafethe RAT.
Lesson: when your engineers go paranoid, if there are lives at stake then for God's sake listen to them. "Belt and suspenders" engineering saved lives in this incident.
>Quintal "got busy" in the manuals looking for procedures for dealing with the loss of both engines. There were none..
Lesson: learn from experience. There have been incidents, like volcanic ash injection, that have forced shutdowns of all engines on a jetliner. If your statistics say the engines can't fail at the same time, and the graybeards say they can, then you left something out of the statistics.
>The avoidance of disaster was credited to Capt. Pearson's "Knowledge of gliding which he applied in an emergency situation to the landing of one of the most sophisticated aircraft ever built."
Lesson: there is no substitute for a wealth of experience. Downsize your 20-year veterans to save money, watch things go wrong.
Sorry for the diversion, but these are things I'm passionate about.
Actually modern jets are pretty good gliders. If I rember correctly they tend to have a glide ratio of somewhere around 20:1 The problem is that there best glide speed tends to be pretty fast so while if you are at say 20,000 feet you could glide 80 miles you might cover that in only 15 minutes. Not a lot of time to find a place to land. Once you drop the gear and flaps you are going to be landing in a hurry.
I rember a story about a Canadian 767 that ran out of gas and was lucky enough and had a very talented crew that managed to glide to an old airfield and made a dead stick landing.
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.
just as the submarines use energy to compress or expand gas in their bouyancy tanks. This makes them a heat engine (though a slowly cycling one) and subject to the carnot cycle limit.
The followup poster has exposed an error in the above, (though not the one he thought.)
Actually, as long as you compress and expand gas adiabatically, then the Carnot cycle is irrelevant.
Actually, adiabatic expansion and compression are two of the four cycles of a carnot engine. (The others are adding heat to the compressed gas at constant volume and removing it at constant volume.)
My carnot cycle argument applies to the case of the mid-20th-century airships where the bouyancy was adjusted by heating the gas. It IS irrelivant when you're adjusting the bouyancy by, say, using an electric motor to compress it into a tank. (Though other heat engine arguments do apply. See below.)
The conservation of energy argument also applies. I'll show you where the detailed physics of the process make it show up when we get a little further along.
Obviously you cannot make an engine that works in this way [losslessly], because the point of an engine is (1) to do net work or (2) to cause a heat transfer. So the efficiency of any engine cycle has a Carnot limit.
Right.
But the process you have described need not be an engine. In fact, this should be completely obvious. Since there is no net work being done, and no heat transfer, how on earth can you even define an thermodynamic efficiency for the cycle?
Even the process of compressing and expanding the gas makes this into a heat engine. Compressing the gas heats it. The heat must be dumped. Expanding the gas cools it, and heat must be applied from an external source to bring it back to temperature.
This doesn't make carnot apply, though. But it DOES lead to additional losses if you don't do your compression and expansion adiabatically.
You must compress slowly, and dump the resulting heat without forcing it across a significant temparature difference. Similarly you must scavange the energy when it expands by running it through an airmotor to extract the energy and recharge your energy storage. (Otherwise the energy gets dumped.)
But the temperature change takes place in the compressor/airmotor. This makes it very hard to add or dump the heat across negligible temperature gradient in order to perform the operation adibatically.
(You also get losses in the generator/motor/battery system, or whatever you're using to store the energy for reuse. The total of these losses is so high you're probably ahead to do the bouyancy adjustments with heat in the first place. But then you ARE a carnot cycle heat engine.)
All of the above are efficiency issues, however. They represent precentage losses of useful energy as it it transferred from one form to another (gas pressure, temperature, height of mass in gravity field, momentum, etc.)
You ARE an engine, by the way, because you're doing work: Lifting and lowering the mass of the vehicle, driving the vehicle against air resistance.
And you don't even need to get this complicated. (Slow) compression and expansion of an isolated volume of a gas is reversible and adiabatic. Hence it is isentropic.
Right.
But that doesn't mean the total cycle is reversible.
In the airship case, the compression occurs when the ambient pressure is low, and the expansion when the ambient pressure is high. Even if your compressor/airmotor was perfect, the difference represents a loss of energy - specifically, the energy necessary to raise and lower the vehicle, which is lost to air friction from the vehicle's motion. (Thus conservation of energy is not violated.)
So why not just use a propeller?
If you're heating the gas to adjust the bouyancy, on the other hand, you ARE a heat engine. So you don't beat carnot, (and have to input maybe three or more times as
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
One thing that everyone keeps forgetting is drag / weight / size. The type of equipment that this guy is talking about is going to take up a lot of space. Usually things that take up space weight something. Things that also take up space require energy to move them through the air. His only form of propulsion is gliding / compressed air, but gliders are usually extremely aerodynamic vehicles with a high glide ratio. Drag and the weight of the aircraft are directly related to such a ratio. So in theory, the super marine would go up, glide a foot, and then have to repeat. Not to mention maneuverability. Highly impractical.