Lots of fun
Sometimes you can learn an awful lot just by playing around. Looks like this was one of those occasions. Thanks for letting us "watch".
Tuesday saw the Paper Aircraft Released Into Space (PARIS) team down at QinetiQ's hypobaric chamber in Farnborough, testing the crucial Vulture 1 aircraft release mechanism. As we've previously explained, just how to get the Vulture 1 to separate from the main payload at a more-or-less predetermined height has given us plenty …
Pretty obvious failure of the ground-glass syringe... you thought it would form a perfect seal?
You need a rubber diaphragm as the seal and something lubricated as the slide, so there's very little stiction. Alternatively you *may* get away with wetting the ground-glass surfaces with a gloopy but low-vapour-pressure oil.
Put a balloon inside the syringe? Well sealed, containing at least 15cc air but not inflated.
In fact, you can probably do away with the syringe altogether and use, say a toilet roll carton tube core, closed from one end, containing the balloon and some sort of an actuator (a pencil?).
My thought was that to keep it in tune with the rest of the project, a condom containing some air and with a knot tied in the end, ought to expand at a reasonable enough rate so that if contained in a toilet roll tube, would push something out of the end quite readily.
I have memories of a night in the pub many years ago when someone decided to inflate a condom and it was well over beach ball size when it finally exploded so it'll take the strain.
"....the air had time to sneakily escape between the ground glass plunger and the syringe interior wall."
What happened to the placcy one? Those usually have a ridged rubber thingy* on the end of the plunger which should give a better seal. You might want to apply a smear of silicone grease to the thing first (you want the plunger to move smoothly and contamination of the syringe contents isn't an issue).
I'm impressed with the chamber though. 8,000 to 65,000 feet in 0.1 seconds? Makes my ears hurt just thinking about it.
*Stop laughing at the back there.
> I'm impressed with the chamber though. 8,000 to 65,000 feet in 0.1 seconds?
> Makes my ears hurt just thinking about it.
I cringe when I think about these things because the Nazis put actual living people (well before anyway) in these things.
Makes me ashamed to be a German.
BB icon because he looks a bit like Hitler.
Nah, the cheap and cheerful method is to use an extremely loose-fitting plunger, such as a large syringe with the rubber bit removed, and a tied-up balloon inside. The balloon will be fairly leak-proof at low pressures, and the loose-fitting piston has very low friction.
Should spend a little time looking at how people actually build low-temp Stirling Engines.
Of course, ripping apart an old pressure gauge is arguably more reliable, and not exactly expensive compared to the electronic kit.
Go down to Halfords, distract the sales-weasel, and steal one of those cheap'n'nasty turbo boost gauges (or even better, a manifold pressure gauge for a non-turbo car, since they have better resolution). Take the glass off, and use the needle to trigger your release mechanism.
You're looking for about 5kPa at 20,000 metres; another trip to your friendly hypobarycist will confirm the actual position of the needle.
... put a small sealed balloon to contain the air reservoir inside the syringe? Something thin but very strong would be required. Probably latex would be best, if it were lubricated it might help the movement of the plunger ....
... Hey. now there's an idea that ties into the Paris theme quite well.
Could you use a common-or-garden balloon in a tube - partially inflated? As the pressure drops - regardless of the rate of ascent - the balloon will expand, and push against whatever it is you want to push at the end of the tube at the right time.
Or, why not just use a good old-fashioned altimeter? Is it too high-tech for this project?
for those who remember the above equation: are you sure that you can take temperature into account properly? Can be really low up there or rather high if you get a bit of sunlight.
Anyway, what'as wrong with a membrane-type manometer? Engineers have optimised devices for the application 200 years ago. A sliding design is obviously plagued by stiction(*) problems and so, said engineering forefathers used a rotating design. You amateur approach to this buys you no geek points.
I'm really interested in the actual craft! When are we being treated to drafts of the paper Aeroplane, please?
P.S. Yes I'm taking this way to seriously: but we all want to see this thing work.
P.P.S Paris icon because <insert pressure-related sexual double-entendre here>
(*) that word rolls off the tounge quite easily if you've heard it before
What about a knotted partially inflated condom as the air reservoir insider the cylinder/piston assembly? No leaks that way, and you can use a simple and light unit as the piston seal is non-critical. This has to be the way to go if only because of the awesome double-entendre potential.
I'm no expert (hence eminently qualified to spout forth on this forum), but I'd imagine that rubber balloons would freeze at such chilly altitudes, presumably the reason a glass syringe was chosen.
I reckon the PARIS team should have a 20,000 ft tether and a simple trigger release...
I see a potential problem that could ruin the mission. Civilian GPS units have built in hardware limitations, and won't track if the speed exceeds 999 mph, or altitude goes above 60000'. This to prevent the ilks of Kim Jong-il etc. from building a cheap missile guidance system.
The suggestions above to use an altimeter are good, but I have a simpler and probably lighter alternative.
Basically we need the pressure at 20,000m (at 16km it's 0.1 atm) to trigger the release. That implies a 10x expansion... for now I'll imagine the last 4km of pressure change will be consumed by the trigger's mechanical force, to keep things simple.
The problem with the syringe is the small piston area compared with the volume contained therein. Also, the glass syringe is delicate, expensive and fiddly. But if you had a large plunger, say 10cm diameter, the force it exerts will increase by the square of the diameter ratio, so you could get a much larger force to do the work.
Let's suppose you chose a tuna can. Now, obviously an opened tuna tin is lousy at containing pressure, but if the edges were machined smooth it could be a dandy container for a semi-inflated condom (PARIS never leaves home without one, natch). As the rubber expands it will press on the lid; on the lid, perhaps soldered or welded in place, is a single-edged razor blade. The pressure from the lid will push the blade into one or more monofilament fishing lines, which are tensioned and connected to release the plane and what-have-you.
The expansion force from this cylinder should be well above what any syringe can muster, its operation will be basically frictionless and I can't see it weighing as much as a glass syringe. The response of the lid to pressure can be controlled by springs and by the initial volume of air, thereby allowing a pressure response tailored to your needs (another thing PARIS is good at).
The only question to determine is the response to –60°C temperatures found at that elevation. Perhaps latex is not the best choice there, but a latex-free condom may work better. I guess you need to buy a lot of condoms and test them out!
However, I'm not sure how repeatable that would be.
While 'preservatives' are individually tested at manufacture, I don't know what tolerances they work to.
So that's something to try out at Qinetiq - put an entire boxful of thin-walled balloons blown up to equal pressure into the chamber and see whether they burst almost together or widely spaced.
Using this idea but without the need for razor blades and fishing lines:
A Tupperware or similar container with a press on lid.
Container or lid (or both) perforated to allow pressure to equalise.
Container attached to lifting balloon.
Insert semi-inflated balloon into container.
Attach lid to plane and seal container with semi-inflated balloon inside.
When pressure causes balloon to expand enough to pop lid from container, separation has been achieved.
Not sure what container would be best. Perhaps old plastic 35mm film canister?
Also not sure if having lid attached to plane is within percentage of craft made of paper tolerances, but if you're attaching all sorts of electronics I can't see it being a problem.
So rubber is going to go like "flaky pastry" and batteries will probably die halfway through the journey without protection. So..
..what about those chemical hand warmers that you'll see in hunting and fishing shops? Expose the bag to air and give it a shake and it gets nice and toasty for a couple of hours. Maybe wrap the sensitive components up with a couple of these and something fluffy? How long's the flight expected to be?
For the lovely QinteQ people to offer us another day, and throw it open to Reg readers to design and build devices that'll work at -56C and 70000'. Then we can all get boffining in our sheds, and test the whole darn lot in one go. I think we all //really// want this to work, don't we?
I believe I saw this experiment on a talk show--or was that YouTube? It was something to do with toy balloons and water. Can't think of what might happen if you mixed those two.
I could have sworn my science instructors did the same things at university, but only in demonstrations to the incoming classes. The upper-classmen would have laughed at these sorts of things.
Re-entry: After decades of research, astrophysicists and aeronautical engineers have identified several fatal flaws in what is commonly called "Non Rigid Technology, or NRT". Strange, and poorly understood, forces come into play at sub-sub-sub-sonic speeds - particularly at the atmospheric littoral. Crumpling, wrinkling, and flapping are common but lesser known forces such as trailing-edge tattering - that can lead to dog-earing - have also been modeled. Moderate to severe dog-earing is predicted to cause such great aerodynamic stresses that the structural integrity of load-bearing creases can no longer be relied upon and catastrophic failure is predicted in nearly all scenarios. Without its rigid heat shields, the Space Shuttle would crumple like a used tissue on re-entry.
Approach: Without a doubt, and unknown to most lay folk, atmospheric transit is the most dangerous stage of any space mission. At post-reentry speeds bird-strike is an ever-present and deadly risk. For NRT craft, bird-peck and bird-crap further threaten the chances of a successful mission. The massive forces of the Earth's atmospheric air currents are also a source of danger. "The Trade Winds", "The Roaring Forties", "Twister Alley", "The Tropical Easterly Jet", "The Middlesborough Zephyr", "The East Covington Highstreet Eddy". An aircraft will be tossed about and beaten a dozen times before it even has a hope of landing.
Landing: Seventy percent of the Earth's surface is covered by ocean. A further twenty percent is covered in seas, lakes, permanent ice, rivers, ponds, hidden bends of streams where summer romance blossoms beneath the willows, standing puddles, half drunk cups of tea, and beer (both pre- and post-micturition). This means that there is a 90% chance of a water-landing. Even with a hull rated to depths in excess of 0.000546806649 fathoms a splash-down is a high-risk exercise for an NRT. A landing on solid ground is similarly fraught. Assuming a suitable landing site can be found with the pre-requisite length, width, and load bearing characteristics, keeping the site clear of vehicles, pedestrians, onlookers and curious puppies, until the NRT can be made safe will be nigh on impossible.
Conclusion: I think few will disagree that the chances of a successful mission outcome are negligible. It is more likely that the PARIS crew will suffer some horrendous calamity upon re-entry or, perhaps more terrible, remain trapped in Low Earth Orbit awaiting rescue, cannibalism, or a ringside seat as the Earth is finally destroyed by some massive global climatic event or nuclear calamity. All that we can hope for, for their sake, is that they might see the insurmountable risk before them, be steeled by resolve and camaraderie, and take their emergency cyanide pills as they sit, waiting, on the launch pad.
.. hosting you lot while you mess about. Not exactly cutting edge technology.
And there is another thing, as pointed out 75000ft and -56C. So you have a paper airplane at 60% moisture content at ground level and you increase the height, the temperature drops humidity rises until -. Well we have all arrived back in the office after the weekend to find all the paper in all the printers is distorted, that is what will happen. As you rise further the temperature drops further the paper will freeze.
Now when you release said distorted frozen lump with all the aerodynamic quality of a brick into the thin air of 75000ft, how will it fly? Very well, straight down. Gravity is a fine thing, makes you keep a sense of proportion, unless, of course, you are on acid.
Could you not just use vasoline on the plunger in order to stop air escaping? Assuming that you hadn't already thought of the blisteringly obvious? Or you could just use an air bladder / balloon of some kind, which will expand at lower pressures. If you place that inside a tube sealed at one end, it'll work pretty much the same as the syringe.
Some further study in the gospel truth of google searches, reveals
Meaning only one of the limits need apply, and by judicious choice of GPS, and keeping speed well below mach 2 it should be possible to track the craft, even above 60000'
Another possibly obvious thought - the air bladder doesn't need to be made of elastic material so if rubber does go 'bad' in any way at low temps (further research needed) then just use any non-elastic flexible airtight material - whatever hot air balloons are made of would do fine.
I think the precision of a (properly-sealed) syringe-based mechanism should be hard to beat, though.
I believe metallised mylar would be what you're looking for. That's the stuff that "foil" helium balloons (both small and very, very large) are made out of, and I'm pretty sure you get it being used as Christmas present wrapping after suitable patterns have been printed.
I still think using chemical heat pads to protect batteries and such is a good idea though. If only because it's my idea.
Can you please stop the frightening headlines about Paris ?
I was initially scared that something awful had happened to Paris Hilton involving something to do with a crazy steam-punk-relaxation-drug-chamber or something horrible.
Then I saw the article was about paper airplanes, space and science.
I am so happy that Paris Hilton is well !
Taking a look at the phase diagram of carbon dioxide I note that it is likely that in the pressure regime of this experiment the sublimation rate of dry ice increases with altitude (i.e. with lower atmospheric pressure). A spring loaded mechanical link incorporating a suitably shaped piece of dry ice could be used to release Paris at a known density altitude. Temperature also plays a part in sublimation rate, but that could taken out of the picture by enclosing the mechanism in a foam insulating container and placing a chemical warmer inside immediately prior to launch.
Have one of your boffins with more time on his hands than I have do a bit of calculation and I imagine that you could with reasonable reliability expect a piece of frozen CO2 of a given size and shape to disappear by the time it reaches a predetermined density altitude.
But then again, maybe this is all bollocks.
My experience of reading paperback books on flights is that the paper tends to warp due to the slightly lower air pressure in the cabin compared to ground level. At 20,000' the low air pressure may be catastrophic to the PARIS craft. The next time you visit Qinetiq could you take it and test its ability to maintain structural integrity at altitude?
I would hate to think of all your detailed and dedicated engineering research effort and the enormous budget potentially going to waste.
You'll probably want this grease instead. Unlike the Corning one (limited at -40 C), it is certified for temperatures as low as four (4) K. Which is really not much at all (-269 on the good ol' Celsius scale).
As in the inside of some types of barometer.
They are made of welded metal sections in a concertina arrangement. Although designed for a much lower pressure variation range, it should be possible to use a strongish spring to limit movement.
Perhaps link the bellows to the trigger of a cap-gun? - assuming you are going for bodge?
Alternatively, a precision machined mouse-trap?
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