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| [[File:Flying boat.png|thumb|Francesco Lana de Terzi's flying boat concept c.1670]]
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| A '''vacuum airship''', also known as a '''vacuum balloon''', is a hypothetical [[airship]] that is [[Vacuum|evacuated]] rather than filled with a lighter than air gas such as hydrogen or helium. First proposed by Italian monk [[Francesco Lana de Terzi]] in 1670,<ref>{{Cite web | title = Francesco Lana-Terzi, S.J. (1631-1687); The Father of Aeronautics | url=http://www.faculty.fairfield.edu/jmac/sj/scientists/lana.htm | accessdate = 13 November 2009}}</ref> the vacuum balloon would be the ultimate expression of displacement lift power.
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| ==Principle==
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| An [[airship]] operates on the principle of [[buoyancy]] where air is the fluid in contrast to a [[ship]] where [[water]] is the fluid. The [[density of air]] at standard temperature and pressure is 1.28 g/L and 1 L of displaced air has sufficient buoyant force to lift 1.28 g. Airships use an airbag to displace a large volume of air; the bag is usually filled with a lightweight gas such as [[helium]] or [[hydrogen]]. The total lift generated by an airship is equal to the weight of the air it displaces, regardless of the materials used in its construction or the gas used to fill the airbag; However for flight it is necessary for the total lift capacity to exceed the ship's weight, which includes the weight of the gas used to fill the airbag.
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| Using the [[molar volume]], the mass of 1 L of [[helium]] (at 1 atmospheres of pressure) is found to be 0.18 g, since every displaced liter provides 1.28 g of lift the effective lift is reduced by 14%.
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| Vacuum airships would theoretically replace the helium gas with a near-vacuum environment and would theoretically be able to provide the full lift potential of displaced air. The main problem with the concept of vacuum airships however is that with a near-vacuum inside the airbag, the outside pressure would exert enormous forces on the airbag, causing it to collapse if not supported. Though it is possible to reinforce the airbag with an internal structure, it is theorized that any structure strong enough to withstand the forces would invariably weigh the vacuum airship down and exceed the total lift capacity of the airship, preventing flight.{{citation needed|date=May 2012}}
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| ==Material constraints==
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| Following the analysis by Akhmeteli and Gavrilin:<ref name="Akhmeteli">AM Akhmeteli, AV Gavrilin - US Patent App. 11/517,915, 2006. Layered shell vacuum balloons</ref>
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| The total force on a spherical shell of radius <math>R</math> by an external pressure <math>P</math> is <math>\pi R^2 P</math>. Since the force on each hemisphere has to balance along the equator the compressive stress will be
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| :<math>\sigma = \pi R^2 P / 2 \pi R h = R P / 2 h</math>
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| where <math>h</math> is the shell thickness.
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| Neutral buoyancy occurs when the shell has the same mass as the displaced air, which occurs when <math>h/R = \rho_a/(3 \rho_s)</math>, where <math>\rho_a</math> is the air density and <math>\rho_s</math> is the shell density, assumed to be homogeneous. Combining with the stress equation gives
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| :<math>\sigma = (3/2)(\rho_s/\rho_a)P</math>.
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| For aluminum and terrestrial conditions Akhmeteli and Gavrilin estimate the stress as <math>3.2\cdot 10^8</math> Pa, of the same order of magnitude as the compressive strength of aluminum alloys.
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| Unfortunately this disregards [[buckling]]. Using the formula for the critical buckling pressure of a sphere
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| :<math>P_{cr} = \frac{2Eh^2}{\sqrt{3(1-\mu^2)}}\frac{1}{R^2}</math>
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| where <math>E</math> is the [[modulus of elasticity]] and <math>\mu</math> is the [[Poisson ratio]] of the shell. Substituting the earlier expression gives a necessary condition for a feasible vacuum balloon shell:
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| :<math>E/\rho_s^2 = \frac{9P_{cr}\sqrt{3(1-\mu^2)}}{2\rho_a}</math>
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| The requirement is about <math>4.5\cdot10^5 kg^{-1} m^5 s^{-2}</math>.
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| This cannot even be achieved using diamond (<math>E/\rho_s^2 \approx 1\cdot 10^5</math>). Dropping the assumption that the shell is a homogeneous material may allow lighter and stiffer structures (e.g. a [[honeycomb structure]]).
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| ==Arthur De Bausset==
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| From 1886 to 1900 [[Arthur De Bausset]] attempted in vain to raise funds to construct his "vacuum-tube" airship design, but despite early support in the United States Congress, the general public was skeptical. Illinois historian Howard Scamehorn reported that [[Octave Chanute]] and [[Albert Francis Zahm]] "publicly denounced and mathematically proved the fallacy of the vacuum principle", however the author does not give his source.<ref>{{cite book|last=Scamehorn|first=Howard Lee|title=Balloons to Jets: A Century of Aeronautics in Illinois, 1855-1955|year=2000|pages=13–14|publisher=SIU Press|isbn=978-0-8093-2336-4}}</ref> De Bausset published a book on his design<ref name='De Bausset 1887'>{{cite book | last1 = De Bausset | first1 = Arthur | title = Aerial Navigation | publisher = Fergus Printing Co. | year = 1887 | location = Chicago | url = http://www.archive.org/details/aerialnavigatio00chicgoog | accessdate = 2010-12-01}}</ref> and offered $150,000 stock in the Transcontinental Aerial Navigation Company of Chicago.<ref>{{cite journal | title = Aerial Navigation | journal = New York Times | date = February 14, 1887| id = | url = http://query.nytimes.com/mem/archive-free/pdf?res=F60E16F93E5C10738DDDAD0994DA405B8784F0D3 | format = PDF | accessdate = 2010-12-01}}</ref><ref>{{cite journal | title = To Navigate the Air | journal = New York Times | date = February 19, 1887| id = | url = http://query.nytimes.com/mem/archive-free/pdf?res=F20917F9345D10738DDDA00994DA405B8684F0D3 | format = PDF | accessdate = 2010-12-01}}</ref> His patent application was eventually denied on the basis that it was "wholly theoretical, everything being based upon calculation and nothing upon trial or demonstration."<ref>{{cite book | last1 = Mitchell (Commissioner) | title = Decisions of the Commissioner of Patents for the Year 1890 | publisher = US Government Printing Office | year = 1891 | pages = 46 | accessdate = 2010-12-01 | quote = 50 O. G., 1766}}</ref>
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| ==References==
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| {{reflist}}
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| [[Category:Airship configurations]]
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| [[Category:Airship technology]]
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| [[Category:Hypothetical technology]]
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| [[Category:Vacuum systems]]
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If you present photography effectively, it helps you look much more properly at the globe around you. This means you can setup your mailing list and auto-responder on your wordpress site and then you can add your subscription form to any other blog, splash page, capture page or any other site you like. Should you go with simple HTML or use a platform like Wordpress. Keep reading for some great Word - Press ideas you can start using today. You can customize the appearance with PSD to Word - Press conversion .
Creating a website from scratch can be such a pain. If a newbie missed a certain part of the video then they could always rewind. Which is perfect for building a mobile site for business use. You can add new functionalities and edit the existing ones to suit your changing business needs. For a Wordpress website, you don't need a powerful web hosting account to host your site.
Photography is an entire activity in itself, and a thorough discovery of it is beyond the opportunity of this content. It was also the very first year that the category of Martial Arts was included in the Parents - Connect nationwide online poll, allowing parents to vote for their favorite San Antonio Martial Arts Academy. You can now search through the thousands of available plugins to add all kinds of functionality to your Word - Press site. Enough automated blog posts plus a system keeps you and your clients happy. For any web design and development assignment, this is definitely one of the key concerns, specifically for online retail outlets as well as e-commerce websites.
Word - Press installation is very easy and hassle free. But the Joomla was created as the CMS over years of hard work. To do this, you should link your posts to other relevant posts that you've created. So, we have to add our social media sharing buttons in website. Word - Press offers constant updated services and products, that too, absolutely free of cost.
As a open source platform Wordpress offers distinctive ready to use themes for free along with custom theme support and easy customization. As a website owner, you can easily manage CMS-based website in a pretty easy and convenient style. Offshore Wordpress development services from a legitimate source caters dedicated and professional services assistance with very simplified yet technically effective development and designing techniques from experienced professional Wordpress developer India. If you have any thoughts regarding where and how to use backup plugin, you can get hold of us at our own website. In addition, Word - Press design integration is also possible. Customers within a few seconds after visiting a site form their opinion about the site.