Hi!
As promised I would like to discuss with you in this thread the idea of a new kind of low cost Space Tower: the Space Hose.
In a nutshell it is about using a lightweight hose made from PE foil which is blown trough from the bottom and is using the frictional forces of the flowing air to produce continuous lift for supporting the weight of the hose.
It was designed as an alternative approach to solving the N-prize problem which is about putting a 9,99 gram satellite into space for 9 orbits and winning £ 9999,99 when staying within the £ 999,99 budget.
Because of the geostationary orbit a space tower offers it would mean keeping the tower upright for a total of 9 days.
You can find a brief presentation including most of the relative simple math in the Technical Advice section of the official N-prize forum.
I'm aware that this approach is not a very realistic one due to the huge stability problems when going for a single hose, but the math showed that it could be feasable to support a 100km hose and the needed raw material and energy consumption would be within the N-prize budget, hence I think it is worth sharing with you.
By using plain air at a reasonable blowing speed as the medium for continuously transfering the frictional force to the hose it overcomes most of the limitations of the existing inflatable space tower and the space fountain concept. A head diffusor is making the air blowing out sidewards on top with only a small downward momentum to support the payload and prevent tearing the hose.
And it was fun to find such a new solution and do the math to support it, so I think it is worth sharing the concept!
Have fun reading the slides and Input is welcome !
gutemine/buzz
PS: Sorry, for the bad graphics - I had to compress heavily to get below the 256k limit of the forum for attachments-- gutemine, Sep 10 2010 Vent the atmosphere Vent_20the_20Atmosphere[marked-for-deletion] redundant: "the proposed device is essentially a large hose, it would be supported from the inside by the rushing air" [ldischler, Sep 11 2010] Flettner rotor http://en.wikipedia.org/wiki/Rotor_shipPrior Art [8th of 7, Sep 12 2010] Magnus effect http://en.wikipedia.../wiki/Magnus_effectTake note ... [8th of 7, Sep 12 2010] Inflatable Space Tower study http://pi.library.y...vol62_pp342-353.pdfInflatable Space tower study [gutemine, Sep 12 2010] [+] to offset crotchetyness.-- DrWorm, Sep 11 2010 Another [+] to set off crotchetiness.-- rcarty, Sep 11 2010 [-] to offset cheery blather.-- Grogster, Sep 11 2010 + if you actually add those graphics-- zeno, Sep 11 2010 <link> ?-- FlyingToaster, Sep 11 2010 [+] for no link.-- Grogster, Sep 11 2010 I see what you mean.-- nineteenthly, Sep 11 2010 The paragraphs starting "In a nutshell..." and "By using plain air" are the actual posting.
Much as I like the idea, I dislike jumping through the hoops necessary to actually get around to finding out what the idea is... and further hoops to find the math that's been done on it by the poster. [-]-- FlyingToaster, Sep 11 2010 Except... the air is coming out the top, which generates thrust, forcing the hose downward.
You could redirect the thrust by putting a bell over the top, in which case you've invented the air-powered version of the Water Wiggle (q.G.).
Except... the mass of the air in the hose is not negligible for this effort, since the mass of escaping air is what's being accelerated to provide the upward force. I'd be very surprised to see it go up 1km.-- lurch, Sep 11 2010 First thank you for your feedback!
Second I decided not to post a direct link because the N prize forum is easy to find and I asked there for technical advice because it was designed for the N-prize competition. And the owner didn't run away laughing when I first showed him the idea - so I owe him something.
Third if you would have a look at the slides (feel free to download and post them somewehere else for a public link) you would know that the current design includes a diffusor on top making the air blowing out sidewards with only a very small downward momentum to prevent the top from falling and supporting the payload while not tearing the foil with too much pulling. I now editied this part of information into the original post to prevent further confusion.
Finally the amount of air needing to be moved to generate sufficient friction is amazingly low - but yes, it will take some time to erect it. But the math is easy - the volume of the suggested 10" hose 100km long is about 5000m³ - and the needed blowing in the calculated example is 618,5m³/h This would mean if the hose is laying on the ground it would be blown up in about 8h (so I added an extra day to the energy bill for winning the competition).
But you are right a single hose probaly would not go beyond 1-2km - already taller then any current building on this planet. So probably the N-prize money is still safe.
But please continue to find the mistakes I did in my calculation - there MUST be plenty!
BTW I'm sorry for the math, but I had to find out if it is realistic.
If you prefere pratical experimental verification:
Take a condom and put it over an adhesive strip tape roll and then blow trough the hole of the roll upwards. This gives a nice upright position :-)
But you now have the problem of the inflatable space tower - pressure will increase dramatically with height, and you end up with expensive kevlar balloons to hold the pressure (but is is not that worse - so a big thumbs up for their idea!)
Then you do the same after cutting away with a scissor the small repository piece at the top. Blow again - you have to blow faster, but it still works to hold the upright position. The remainder on the top works as a pretty bad diffusor. This is what the space hose would be (even when in our experiment the pressure increase of the diffisor does the job, not the friction - but you cann't buy that long condoms to verify) - so the experiment is cheating a little bit.
If you then cut away the entire head so that the opening at the top has the same diameter then the rest of the hose/condom you will fail - no matter how hard you blow. The Bernoulli effect is aginst us.
As soon as somewhere in the hose/condom the diameter shows a small imperfection making it smaller, then the flow speed will have to be slightly higher, which means at that place the pressure will drop within the hose and as soon as this happens the athmosperhic pressure will win and the hose will collapse at that place. The air then still flows but it would be totally instable even when friction gives still the upward lift (then you really have a space flag not willing to stay upright). Hence a small pressure surpluss is a must, but this is the way a hose works.-- gutemine, Sep 11 2010 //the air is coming out the top, which generates thrust, forcing the hose downward.////current design includes a diffusor on top making the air blowing out sidewards with only a very small downward momentum to prevent the top from falling//
air blowing out the top won't push the tower down. Why would you think it would ? [edit: 'cuz it's going to be moving around due to atmospheric conditions, nvm]
//the owner didn't run away laughing// he has practice.-- FlyingToaster, Sep 11 2010 OK so let's ruin the typical 'how works a rocket' experiment:
Take the usual garden hose, attach a 10cm diameter plate in front of the nozzle which is attached to the nozzle via wires so that the water will be reflected by the plate and will spill out radially.
Then turn on the water and don't be dissapointed that the hose doesn't move backwards as usual.
Eating up momentum is easy, every ball dancing in a fountain knows how to do this-- gutemine, Sep 11 2010 hmm, you're right, but only because your pipe will be flapping all over the place for various reasons anyways: if it was straight it wouldn't be pushed down at all: objection removed.-- FlyingToaster, Sep 11 2010 If you blow only slightly higher then the equilibrium of hose weight and lift due to friction you get a continuous force keeping the host upright. And the diffusor can easily also produce lift/pull by blowing slightly downwards. Make a light cone out of the plate of in front of your garden hose and see what happens.
But you are right - the force always goes in the same direction as the hose - so you need to tell it continuously where UP is (well the centrifugal force would know) - but this is easy doable if the diffusor on top is held horizontal with a pendular weight below it. If it then goes sidewords it will blow more on this side and would regain equilibrium. Upright pendualars are a pain, but this problem is also solveable, especially because you have an entire apmosphere providing the damping.
But yes, doing this for a hose 100km long is not that easy, even on a windless day. But the Inflatable space tower people already got this solved and their patent granted. If you use the straw pack approach you can get a sufficiently stiff structure.
But I think a single hose should be erectable at least with 1-2km height to proof the concept. The rest is beyond of what a halfbakery can do.
The really idea is not about the head or keeping it stable - it is that flowing air friction gives a lift even in vacuum (and especially in vaccuum because of the high speed due to the expanding air) - and THAT is the real interesting and new point of this approach.-- gutemine, Sep 11 2010 Cool.
So, what are the numbers (mass of tubing, power of fan) needed for a 2km hose? It would be a truly awesome proof of concept... If you build it, they will bun...-- MaxwellBuchanan, Sep 11 2010 This is what I had in mind for a test flight - you can buy at the next grocery store the 10" PE foil with 12 µm up to 5000m in lenght as plain packaging material for less then 100 EUR.
Add the Fan at one end and blow it up when laying on the ground. Then add the diffusor to the open end blowing reasonable downwards with pendular stabilisation to produce lift and then point this end to the sky and see how far it goes on a windless day.
The fan power in this case is not that exciting either because the weight of a 5km hose is only 1/20 of the 100km Space Hose = 280/20 multiplied with 3 because we use 12 µm foil = 42kg. And a 1km hose (just to beat the tower at the gulf with a slightly higher construction budget) would be only 8kg - a normal model plane propeller and engine can probably do this. If you use only a 300m hose you don't even need any permissions for such a strange 'experimental kite'
If this works you are back to testing the slogan on the first page of the slides :-)-- gutemine, Sep 11 2010 //10" PE foil with 12ym up to 5000m//
Is this a sheet or a tube, though? But in any case I guess a heat-sealer could seal two layers into a tube. ym = µm?-- MaxwellBuchanan, Sep 11 2010 All PE foil is produced by blowing extrusion to a hose. It then is either simply falted and rolled and sold as hose for packaging purpose or it is cut to a foil and rolled. Stress the product search engines with PE foil and you find lots of vendors offering all dimensions and thickness.
The lenghts you can buy are simply dependent to the thickness so that you get easy shippable amounts. But it would be no problem to ask them not to stop the extrusion before 100km are done either.
All this is standard technology and I though it would be a nice message for the N-prize to say you can reach space with a (long) plastic bag, because cheap plastic bags are produced from such hoses by cutting the hose to pieces and welding one end.
PS: If somebody is willing to give it really a try I would bring the beer :-)
PPS: and I edited the µm - I was just layzy in typing. And the blank between Hi and ! is now gone too.-- gutemine, Sep 11 2010 Thanks - but I was first very tempted to add a second blank ;-)-- gutemine, Sep 11 2010 I like this idea . [+ ]-- MaxwellBuchanan, Sep 11 2010 I knew I shouldn't have written that about the safe N-prize money :-)
But I hope that somebody soon finds a real flaw in the friction lift concept.-- gutemine, Sep 11 2010 // recursive illiteracy. //
Sp. "repetetive illiteracy."-- 8th of 7, Sep 11 2010 what are you expecting from somebody who insists on ignoring that names always start with capital letters ?-- gutemine, Sep 11 2010 [-] for the link.-- Grogster, Sep 11 2010 OK, so I voted [-] myself for not beeing able to make an attachment here-- gutemine, Sep 11 2010 <gratuitous pedantry>
Amongst others:
// excpeting //
Sp. "expecting"
// insists to ignore //
Gr. "Insists on ignoring"
// names are always starting //
Gr. "names always start"
</gp>
// capital letters //
It's the Teutonic bloodline that does that.-- 8th of 7, Sep 11 2010 By the way, [21Q], I like the idea of Space Hoes -- it seems fitting that "the oldest profession" should have the first crack [at/in] space...-- Grogster, Sep 11 2010 <throws ball of crumpled paper at [Grogs]>-- 8th of 7, Sep 11 2010 Oh come on, surely a little slack is allowed for people whose first language is neither American nor English?-- MaxwellBuchanan, Sep 11 2010 Actually I suppose not. Pednatry rules.-- MaxwellBuchanan, Sep 11 2010 [+] for pednatry.-- Grogster, Sep 11 2010 Careful there, [Grogs], pednatry is still an offence in some less liberal jurisdictions, and would probably be so in others if they knew what it meant.
// first language is neither American nor English? //
<placeholder for witty remark>-- 8th of 7, Sep 11 2010 [+] to offset pednatry-- Voice, Sep 11 2010 //what are you expecting from somebody who insists to ignore that names are always starting with capital letters ?//
Actually 8th, the proper grammer/spelling is:
"What are you expectorating from somebodily who's insistifitory on ignorifizing that names be in startification of capitalistic letterizatiousness?"
Anybody with half a brane learns that in skool.-- doctorremulac3, Sep 11 2010 Typos are free of charge :-)
And if I would post and discuss in my mother language it would be easier for both sides. Unfortunately this is not the case and we cann't change this even when going to space. I can only excuse and try to avoid difficult words. Having said this I changed my own vote to [+] again because I don't want to be resentful towards myself. PS: I needed a full minute and a dictionary to understand the pednatry joke - so be patient with me.-- gutemine, Sep 11 2010 All in good fun gute. Welcome to the Halfbakery.-- doctorremulac3, Sep 11 2010 [doc], you're channeling the spirit of George W. again. Snap out of it !
// half a brane learns that in skool. //
Any fule kno that.-- 8th of 7, Sep 11 2010 Don't worry, my understanding of humor is crispy with honey sauce
"supported from inside" sounds more like a politic thriller then an engineer's description - could somebody find a better one ?
Air traveling at this low speed would end up at the top with almost the same temperature and pressure as outside the hose, and as long as you don't blow out with more then 2nd cosmic speed this hose would not do anything harming to the atmosphere which doesn't happen already on a daily basis-- gutemine, Sep 11 2010 In that case could I get a croissant delivered to one of my ideas prepared with your understanding of humour?-- rcarty, Sep 11 2010 // it would be easier for both sides. //
Hah !
"I believe you find life such a problem because you think there are the good people and the bad people. You're wrong, of course. There are, always and only, the bad people, but some of them are on opposite sides." (Havelock Vetinari, "Guards ! Guards !" by Terry Pratchett).-- 8th of 7, Sep 11 2010 // In that case could I get a croissant delivered to one of my ideas prepared with your understanding of humour? //
You got one for the perforated Newspaper - I like practical thinking (and Terry Pratchet & Douglas Adams too)!-- gutemine, Sep 11 2010 //pednatry// Thank you for filling a badly needed gap in my idiolect. Definition: pedantic criticism which leaves an opening for more of the same.-- mouseposture, Sep 11 2010 < still trying to think up witty remark>-- 8th of 7, Sep 11 2010 Well isn't the whole life about learning new words ?
The last one your learn is: death
And thanks for pointing me to the Venting idea. It is really pretty close, it just overestimated the needed effort by avoiding the math and forgot to point out that it works also nicely in vaccum. But I liked really the spectacular auroras part!
So in this case the N-prize budget limit at least added some value :-)-- gutemine, Sep 11 2010 // isn't the whole life about learning new words //
Only for the dull; for everyone else, it's about sex and drugs and rock and roll.-- 8th of 7, Sep 11 2010 don't you learn these words at adolescence ?
PS: I'm not willing to discuss bloodlines, I'm sorry - too many vampire stories already around for making a good idea out of them. BTW if I have to correct all my typos and miswordings I would spend all the time editing and beeing lost for the discussion-- gutemine, Sep 11 2010 Space hoes? Begin SNL transcript:
Announcer: "Astronuat Jones"! Tonight's episode: "Episode 6: The Ice Planet".
[ dissolve back to scene ]
Astronaut Jones: I can't talk right now, Earth! I'm making contact with a Krilgarian woman!
Krilgarian Woman: Earth creature...
Astronaut Jones: Right.
Krilgarian Woman: You have ventured into the Krilgarian Galaxy without permission.
Astronaut Jones: Say what?
Krilgarian Woman: I am Xerba the Beautiful...
Astronaut Jones: Dig it.
Krilgarian Woman: ...and I have been instructed by my leaders to take you my hostage and keep you as my prisoner.
Astronaut Jones: Drop it like it's hot.
Krilgarian Woman: Do not attempt to escape...
Astronaut Jones: Jump on you!
Krilgarian Woman: My powers are great, and I will not hesitate to use them against you.
Astronaut Jones: Make me hungry!
Krilgarian Woman: No Earth creaturee has escaped from Krilgar...
Astronaut Jones: Word, say word!
Krilgarian Woman: You will be placed in our testing laboratory...
Astronaut Jones: Where?
Krilgarian Woman: ...'til you are no longer of use.
Krilgarian Woman: Then, you will be eaten.
Krilgarian Woman: What say you to this, Earth Man?
Astronaut Jones: I say you drop down that skirt, and let me get that green dugout!
Krilgarian Woman: [ a beat ] This is not possible. Krilgarians do not have vaginas.
Astronaut Jones: What they got?
Krilgarian Woman: Instead, we possess something more like your Earth Man penis, only bigger.
Astronaut Jones: Hey! We're in space, baby -- penis, vagina, it's all good!-- daseva, Sep 11 2010 **************** this post has beend censored for content not suitable for people of the age below 100-- gutemine, Sep 11 2010 Welcome to the 'bakery gutemine! ;-)-- daseva, Sep 11 2010 Thanks for the welcome, but I would like to have also some more (technical) critics and advice - croissants are not everything for a good breakfast.-- gutemine, Sep 11 2010 Except It isn't a technical forum for a single collaborative effort.-- FlyingToaster, Sep 11 2010 But surely it is? Half the reason I post ideas here (well, the less obviously ludicrous ones) is that I can count on informed feedback from expert 'bakers. Which, amazingly, often happens.....-- MaxwellBuchanan, Sep 11 2010 A device like this -- but only about 6 meters tall -- is used as an advertisement by a local business. A cloth cylinder, open at both ends, with an upward-pointing fan blowing air in at one end. It does stand upright, but it wriggles dramatically. So perhaps instability is a problem.-- mouseposture, Sep 11 2010 except the post is all bluster, no substance... like a marketing campaign looking for a product.-- FlyingToaster, Sep 11 2010 //So perhaps instability is a problem.//
I'd say so. Considering that pointing down would be more stable than pointing up. Most likely it would lie on the ground like a sausage as the pressure built up. Then it would explode.-- ldischler, Sep 11 2010 Yes [MP], a local garage uses them on its forecourt. They have smaller hoeses on the side for arms which finish with tiny hoesicles for fingers. And they have inane grinning faces painted on their main section. This might be a useful addition to the space hose.-- pocmloc, Sep 11 2010 [pocmloc] Yes! A scarecrow for alien invaders.-- mouseposture, Sep 11 2010 I might have missed it, but how do you keep the upper end of the hose cutting through the upper atmosphere at 10,000 mph+ from burning up?-- Zimmy, Sep 12 2010 I haven't actually looked at the numbers, but how big is the fan at the base of this. Simply pushing air through 100 feet of horizontal 10" round duct takes a fairly heavy duty fan. I'm not convinced you aren't going to stall out a fan due to back pressure trying to do this.-- MechE, Sep 12 2010 Regarding the fan power - 15kW is not what you would call heavy duty (only 10x what you household vacuum cleaner can do). If this would be a permanent installation I was even thinking about using two 10x10x10m steel chambers which would be filled alternating with water to blow out the air on the top at 618 m³/h. Water is much easier pumpable and you could store it for a pump/electricity failure in a simple water depot tower nearby. But the blown air should be very dry (to prevent rain and snow in the hose) so I stayed with a commercial fan running at a dry place (Death Valley for example, but Cerro Paranal would be better because of the 2635m height ?)
Regarding the wiggeling - the petrol station device is there for entertainment and catching your eye - meaning the wiggeling is intentionally. The hose there is reduced slightly continuously in diameter to produce this effect (faster flow = reduced pressure = instabillity). It is a kind of upright pendular, because if the hose is folding sidwards the pressure increase caused by the diameter reduction re-errects it. But this effect would not work for a km long structure.
The suggestet space hose uses a diffusor 'nozzle' on the top for creating an upwards pull and a continuous pressure surpluss in the entire hose. The classic space tether uses the centripedual force of the counterweight at the top for stabilisation - here the lift of the blowout diffusor can be used.
Regarding the speed on the top - there is a slide on this in the presentation. The speed difference for 100km is only 27km/h and the air pressure is very low there (1/1000 of surface pressure) - this is nothing the diffusor nozzle on top cann't produce with 618m³/h of air expanding into vacuum, because you only need to create this speed difference during errection and then you only need to compensate the loss and because as soon as the hose and the air move at the same speed the loss will be pretty low.
Regarding the sun - actually the slides suggest a black foil hose - all the heating from sun and turbulant flow losses will create additional flow upwards due to the chimmney effect (heating up is just another reason for the gas to expand ... upwards when you blow from the bottom). So the sun actually should add positively to your energy bill.
And yes, I'm aware that this is not a technical advice forum and not a marketing plattform either :-)-- gutemine, Sep 12 2010 10" dia. 100km long...
250,000 sq ft. sail.-- FlyingToaster, Sep 12 2010 //250,000 sq ft. sail.//
Of which only the first 20% is in a dense atmosphere (ie, below 60,000ft), so call it a 50,000sq ft. sail. Also, since this is a cylinder, I'd guess it has a lot less drag than the equivalent area of sail in a conventional ship - maybe half of what you'd expect, based on area alone (guess)?
I'd guess a big sailing ship has maybe 10,000sq. ft of sail, so this isn't really such a big deal.-- MaxwellBuchanan, Sep 12 2010 [MB] Sailing ship doesn't ordinarily encounter 100 kpm winds; this thing would encounter the jet stream, would it not? Really, [gutemine] has already acknowleged the instability problem, and asked to take that objection off the table.-- mouseposture, Sep 12 2010 Fair point. Might one suggest, therefore, not building this thing under one of the jet streams?-- MaxwellBuchanan, Sep 12 2010 //since this is a cylinder// oh, then 750,000'ish sq ft if you want to do entire area.
10" is roughly .25m x 100km = 25,000 sq meters, or roughly 250,000 sq ft.
//a big sailing ship has maybe 10,000 sq ft// and how much does the ship weigh and how fast does the wind push it ?-- FlyingToaster, Sep 12 2010 //750,000'ish sq ft if you want to do entire area. //
No, my point was that the frontal area is indeed 250,000 sqft, but I would bet that a long, thin cylinder has considerably less drag than a flat, square sail of the same [frontal] area.-- MaxwellBuchanan, Sep 12 2010 //considerably less drag//
hope so: I plugged "50,000 sq ft" and "10kph"[edit: sry, that should be 10 knots, not ten kph] into a sail wind-load calculator and got
21,500 lbs force.-- FlyingToaster, Sep 12 2010 // long, thin cylinder has considerably less drag //
If the cylinder is rotated about its primary axis, then a lateral force is exerted.
<link>-- 8th of 7, Sep 12 2010 So it's subject to, conservatively, 10,000 lbs lateral force, and this is resisted by putting it in tension. How much tension does it need to be under to be even approximately straight? Remember, it's made of polyethylene film. (It cannot be allowed to curve too much, otherwise it kinks.)-- mouseposture, Sep 12 2010 Thanks for all your feedback and input !
Jetstream only goes up to the stratosphere (approx 15km) and the air pressure is there down to almost 1/10th of the pressure at sea level for which your sail force calulator was built for.
A sail actually is built to generate force so the drag coefficient is up to 1 or even higher. A smooth sphere which is close to an infinite tube has 0.1
So you are making here a mistake of the order of almost 100 in calculating the windforce. And actually a flexible tower would simply bow until the wind produces also a lift (then you could even lower the fan).
I'm not understanding the point how on a cylinder any rotating force should be excerted. And the slide about Dyneema string strengthening is included intentionally, these fabric offer 4000N/mm² - which is about 400kg on a single mm² with approximately same weight then normal PE
But that doesn't mean I'm ignoring the problem (and pray for a windless day). As I already said, the Inflatable Space tower people already did the math for this problem and came up that if you use a pack of such cyclindrical structures you can survive but could end up with a bundled structure 150m in diameter.
Google with this text for finding their study: Design and Feasibility of a 20 km Free-Standing Pneumatically-Supported Space Tower - Raj Seth
BTW - Dyneema strings are now also used to hold sails and woven to sails
I just have read the comment about not building under a Jet stream - that is another reason why the studies are always suggesting the aequator for a space elevator. Jet stream originates there because of the tropical warming - meaning this wind doesn't blow there and also no hurricanes. And if you go for a mountain there as suggested you can save another few km of wind pressure. Mount Kenya for example would bypass 30-50% of the wind problem - but for good locations you need to check some scifi literature, I think Peru and Ecuador are also high on their lists.-- gutemine, Sep 12 2010 // how on a cylinder any rotating force should be excerted //
See "Magnus Effect" <link>
But you're right about the Jet Stream - it's a fairly localised phenomenon.
<aside>
// Google with this text //
It's considered polite to provide a hyperlink in the "links" section, rather than a search string. Unless, that is, you actually like being stalked by a rampaging mob of angry HalfBakers wielding torches and pitchforks....
</aside>-- 8th of 7, Sep 12 2010 Isn't the Magnus effect about an object already (!) rotating beeing able to create a sidewards force (Beckham was famous for such shots which drive the goalies crazy ?)
And sorry for the Search string, but there are so many potential links (and I still didn't figure out how your linking works - remember this costed me already some fisbones)
EDIT: Cool - I managed to add the link - thanks for pushing my nose into the sand - But I'll leave the full reference also - the author earns admiration. Their study and patent were a good inspiration for the Space hose!-- gutemine, Sep 12 2010 //so you are making a mistake on the order 100//"My" mistake ? You mean the specifically mentioned "sail windforce calculator" ? Are you under the impression that people wouldn't notice the word "sail". What they might not notice is that the calculation was for a 20km length, not a 100km length.
Seriously doubt it'd be off by even one order of magnitude: your "sphere is equal to a cylinder" doesn't even deserve to be called "bollocks".
So, you've got a tonne of sidewards loading in a 10 knot wind.-- FlyingToaster, Sep 12 2010 // able to create a sidewards force //
Yes, if you put it like that.
// remember this costed me already some fisbones //
It could cost you more than that. Look out of your window. See that flickering orange light in the distance ? Hear the growing "Rhubarb, rhubarb, rhubarb" chant, and the stomp of heavy boots ? That's the HalfBakery Regional Serious Inquisition Squad, out to solve their latest baffling case, by their ususal fire-and-the-sword method.
(See also under "Shoot first and dodge questions later").-- 8th of 7, Sep 12 2010 I didn't want to be impolite - 20km length should be OK (15 would be more realistic), but then still the drag coefficient of a cylinder should be up to a factor of 10 wrong, and the air pressure drops almost 50% every 5000m - so in 15km height your should be already down to almost 1/8 - which reduces the 'sail force' further.
But you are right something like a few tons of wind pressure could remain even under optimal circumstances. This is the reason why I said that the N-prize money is probably still safe. The needed dyneema strings would be very likely to blow the budget.
And regarding the armed forces - I was more scared to be wrapped in PE foil and dumped into the recycle bin when I posted the idea.-- gutemine, Sep 12 2010 //drag coefficient of a cylinder.... factor of 10// factor of 1.75 - 2.-- FlyingToaster, Sep 12 2010 [gutemine] I was the one who mentioned jet stream (to my present chagrin); [FlyingToaster]'s figure was based on a 10 kph wind. So how much tension?
I question your reliance on inflatable space tower calculations. That structure is to be built of Kevlar- polyethylene composite, not 10" PE foil from the grocery store. That's not fatal, though it might put you over the £ 999.99 limit.
But there's another difference. The inflatable space tower is composed of multiple closed cells: the more it's bent, the greater the restoring force. As for the space hose, if it's bent too much, it kinks, obstructing the flow of gas: beyond that angle, the more it bends, the *less* the restoring force (above the kink).-- mouseposture, Sep 12 2010 // wrapped in PE foil and dumped into the recycle bin //
You were SCARED ? There are people who pay good money for that sort of thing ....-- 8th of 7, Sep 12 2010 You are right, but the slides contain also some math on this.
Worst case is the hose is closed on the top, with Dyneema strengthed PE foils it could stand this pressure increase. They inflatable people don't have that much pressure reserve eigther, because they have to hold the structural weight too.
And PE is pretty elastic - which means even if you close the hose the flow will continue some time because of the suggested supressure partly stored in the elastic hose. BTW kinking a hose with a surpressure is quite difficult. That's the good thing about wind - it doesn't excercise punctual pressure.-- gutemine, Sep 12 2010 //10 kph// actually it was 10 knots, my typo.
//Magnus// one of the sites I went to for a sail windforce calculation used a variable that was valued at 2 for a flat surface (ie: a sail), 1.2 for a cylinder (spars) and 1 for untethered cylinder (rope).-- FlyingToaster, Sep 12 2010 A sail calculator is not such a good idea, the formular for calculating the wind force with the drag coefficient is much more accurate and there you could also enter the changing gas densitiy correctly. Unfortunately you would endup with an integral very similar to the wall effect.
Actually after some thinking this probably would be the worst case - the hose shaped like the velocity curve of the wall effect. Which would not be that bad, because then the problematic first few km would be 'almost' horizontal. And the bowing radius would be in the km range so there is no danger of folding. Then having a hose actually would be a benefit to what the inflatable space tower people had to withstand. Cool - I didn't event think about this possibility jet !
The only real problem is that the pressure in the hose would need to be able to withstand the stagnation pressure of the wind (the rest would be pulling forces) - which brings us back to a suitable surpressure for stability and the strings from Yuri's pravda picture.
But the cause of the trade winds is mainly an equatorial upwards flow of warm air - which would be to the hose's benefit and actually increase stability and improve the energy bill.
but tomorrow is a working day - 8n-- gutemine, Sep 12 2010 //first few kilometres would be almost horizontal// at which time all the vertical forces come into play and a few kilometres away some poor sod looking out his living-room window watches as a tube falls from the sky and blows his chicken-coop off into the distance.
//budget// condom manufacturers will be lined up to sponsor: just don't tell them about the hole in the top.-- FlyingToaster, Sep 12 2010 [FlyingToaster] This thing is an erection in both the civil engineering and the medical sense.-- mouseposture, Sep 12 2010 <pedant>
Civil engineering, or aerospace engineering ?
</pedant>-- 8th of 7, Sep 12 2010 //civil engineering, or aerospace engineering ?// Oh, civil, civil: that goes to the very heart of the idea. Think about how weight is transmitted through the structure to the foundation.-- mouseposture, Sep 12 2010 //Think about how the weight is transmitted to the foundation// through the column of air ?-- FlyingToaster, Sep 13 2010 Well, perhaps I'm missing something -- here's how I understood it: Friction of upward-flowing air against the (in- )sides of the tube is what counters its weight. The flow of air is generated by a fan on the ground. The weight of the structure is transmitted through the air, thence through the fan, to the foundation.-- mouseposture, Sep 13 2010 but it's not actually transmitted through the structure: the air column is what's holding everything up: if you had a horizontal fan blowing into a plenum, the weight would be on the bottom of the plenum... transmitted by the air, not by the sides of the plenum... and on the fan blades 'cuz that's what's pushing all the air in.-- FlyingToaster, Sep 13 2010 OK, I was counting the air as part of the structure, which is maybe not so legitimate. Point is, I figured if it rests on the ground, it's a tower, not a tethered- balloon, -kite, or -satellite still less a rocket or an airplane. Also, I wanted an excuse for the pun.-- mouseposture, Sep 13 2010 Regarding the weight of the air. Within a flexible open hose the pressure should be alwyays the same then outside. If you add a diffusor nozzle at the end you can have a pressure surplus which would add the needed stability. Then the only 'weight' that you need to hold ist the surplus air that generates the pressure. That's the funny thing about our athmosphere. You get 100000N/m² pressure at sea level. but nobody cares because our bodies contain the same pressure.
Regarding the wind forces I found the time to use the proper air resistance force formular:
A=0,25*15000=3750m² (the 15km we agreed multiplied with the 10" diameter) C=0,1 (drag coefficient) v=13,89m/s² (a 50km/h "breeze") F=airdensity*v²AC/2 = 1,293*13,89²*3750*0,1/2=46766N actually this still is too high because air density goes down to already 50% in 5km and 1/8 in 15km - but let us stay with this, because maybe the C value is too optimistic or the wind blows harder.
If I read the Dyneema Wiki entry right a single 8mm thick Dyneema string could hold this (58000N tearing strength, and 50kg/km) This string would have a weight of 750kg on these 15km. Probably your would use a bundle of smaller strings for better structural support (see the Pravda picture) but the weight strength ratio would be the same.
The Dyneema strengthening would make the structure approximately 4x heavier as planned, but because friction force goes with the square of velocity this would mean blowing approximately 2x harder to keep it upright.
Not so bad for withstanding a 50km/h wind. And don't forget that the 10" limit and the missing Dyneema Strings is more because of the budget limits of the N-prize - not because of good engineering. To get Paul's money we better wait for a windless day :-)
And regarding the shape of the hose under such strong winds. It would end up with a nice exponential line going to space and find it's optimal shape for standing the wind itself - I didn't even think about this, because I was carried away by the straw approach the inflatable space tower paper suggests.
So thanks for pointing me in the right direction. Maybe I will add a slide on this in the next version of the presentation!-- gutemine, Sep 13 2010 + I like your spunk.-- Zimmy, Sep 15 2010 well, I'm fully aware that the idea is a little bit ... strange, but I had fun making it up, and even when doing the math, so I thougt it would be worth sharing it with you (both the idea and the fun).
Let's see where the hose will blow us :-)-- gutemine, Sep 15 2010 The customary place is around front, near the middle.
And a location exciting yet discreet.-- baconbrain, Sep 15 2010 And in the back of a very uncomfortable automobile.-- daseva, Sep 15 2010 I think young couples find backseats of cars still pretty entertaining ...-- gutemine, Sep 16 2010 of course if you *started* at 30km up, you wouldn't have some of the problems... of course you also wouldn't have much atmosphere to pump.
alternatively as long as you have a hose you might as put something useful through it... hydrogen and oxygen for instance.-- FlyingToaster, Sep 16 2010 what is the problem with the first 30km ?
The typical ones (wind, stability,...) we already discussed - and it doens't look unhandable - especially for a small hose - because then the windforce and involved mass is not that high compared to the pull force it can hold with some strengthening and pull is also stability.
The trick of the hose is actually to get an usable airpressure BEYOND the normal reach of balloons.
So you can balloon or parachute inside nicely up to 100km or more. And due to the air expansion caused by the decreasing hydrostatic pressure you even get quite an acceleration on the journey upwards.
Theoretically it could be up to hypersonic speed - remember in a few hundred Pascal this is not such a big thing.
And air is the perfect (!) medium - always balanced from the static pressure outside (up to 100km, when it is so low that you don't have a problem anymore), not dangerous, poisonous, and not a problem to blow it out from the top (you will not loose it because of gravity)-- gutemine, Sep 17 2010 random, halfbakery