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back to article Got a few minutes to help LOHAN suck?

As we recently reported, El Reg's Low Orbit Helium Assisted Navigator (LOHAN) team has taken delivery of an AeroTech RC 32/60-100NS rocket motor – the proposed power plant for our Vulture 2 spaceplane. Click here for a bigger version of the LOHAN graphic However, no one – including AeroTech – is sure whether the thing will fire …

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Old air compressor?

Perhaps an old air compressor with the feeds reversed? (i.e. sucking the air out of the receiver tank). Might be fun adapting the air inlet though.

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this

or anything with a piston in it. Old engine perhaps.

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Anonymous Coward

Schools...

Most secondary schools have these for science demonstrations, Magdeburg hemispheres are fun!

There are about 2000 secondary schools around the uk should'nt be too hard to find one..maybe even a physics teacher reading el reg.

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Magdeburg hemispheres

don't need high vacuum to become inseparable.

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Anonymous Coward

Well that depends on size! the smaller spheres need more vac.. but our school pump was also capable of stopping (not just quiet) the sound of an alarm clock escaping from a bell jar... that's high enough vacuum for 100k feet..

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Newcomen

Maybe you don't need a pump... fill the tube with steam, seal the top, then stick it in the dry ice etc. I've no idea how low a vacuum this will generate, and the humidity may not help matters. I suppose you could use the same approach with a large separate vessel - reduce the pressure via condensation of steam, then connect the low-pressure vessel to REHAB in the same way that you currently propose to connect the vacumm pump.

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Anonymous Coward

I came to comments to suggest the exact same thing. You get my vote!

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No Pump needed Use Charles' Gas Law

I agree you shouldn't need a vacuum pump. In a sealed environment as the outside air temperature decreases so to will the volume of air in the sealed environment. If simply cooling REHAB with dry ice doesn't decrease your air volume to meat your criteria then plum a preassure cooker in place of your air compressor. Remember the steam created will need to be vented to normal air as the preassure cooker comes up to temperature. Once the required temp is reached shut off the heat, close the vent to air and cool the preasure cooker. This will draw air out of REHAB to equalize the preassure between the two enclosed containers creating a vacuum in both the preassure cooker and REHAB.

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Boffin

After condensing the steam

you're still left with quite a lot of air, which was inbetween the steam before it condensed

Better to let the steam condense in a cylinder with a piston, which pulls on another piston (with a smaller diameter) which pulls air out of the test vessel via a one-way valve. Repeatedly introducing fresh steam into the first cylinder, then condensing it will gradually lower the air pressure in the test vessel, simultaneously enlightening you as to why James Watt is credited as the inventor of the modern (reciprocating) steam engine, instead of Thomas Newcomen.

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Better waterproof the camera if you take that approach. It'll be sitting in a puddle, or possibly even a block of ice (depending on a number of unknown variables) in the bottom of the chamber by the time the vaccum is formed.

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As the vacuum is formed and held the boiling point of the water will reduced and the water will be drawn out as water vapour.

In any case the camera will not be in the chamber, but outside it watching the experiment through a mirror.

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Anonymous Coward

Water trump pump

What about this : http://en.wikipedia.org/wiki/Aspirator_%28pump%29

Use a garden hose for the water, create the vaccum, start firing.

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Boffin

Limited by water vapour pressure

so, if the aspirator is at 25C, the best you can get is about 24mmHg.

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Boffin

Well....

I don't know if they go as low as you require, but pretty much every diesel car out there has a vacuum pump to generate the vacuum for the brake servo. Normally mounted on the end of the camshaft, on the cars I've played with. Might be worth a look.

GJC

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Happy

Why the downvote?

That someone has something against Volvos?

I know... troll bait. But at least trolls and Volvos are from the same neck of the woods.

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Schools labs can do this !

http://en.wikipedia.org/wiki/Aspirator_%28pump%29

A bit of plumbing is required (I think you will need to use a garden hose), but this can make enough vaccum for the test.

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Alert

Vacuum pumps

I've got an old "extension" pump if you want and you could probably have the Mrs' old breast milk pump as well.

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Cooling even necessary?

Looks like fun. I'm wondering if you need to cool the environment though - my expectation would be that at that altitude, you'll have such a rarified environment that a dark-coloured rocket body might get quite toasty. Not done the calc, but my guess is that 99% of your "coldness" will escape REHAB altogether..

Be interesting to see about the pressure effects. I assume your rocket doesn't carry oxidiser, so it'll be fun to see if you can get ignition or not!

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(Written by Reg staff) Silver badge

Re: Cooling even necessary?

The rocket does have its own oxidiser, I'm assured. Just as well, at that altitude...

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Boffin

All rockets have oxidizer, by definition. In this case the fuel is APCP, the same stuff as Space Shuttle SRBs.

If you have two compressors that individually cannot generate such a high vacuum, can you connect them in series to improve performance?

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FAIL

Solid fuel rocket motors

from the humblest model rocket to the Space Shuttle boosters DO carry oxidiser. It's part of the stuff that goes *fwoosh*, making it go *fwoosh* without complexities such as air inlets or oxygen tanks.

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£40 Pond Pump?

how about connecting the test chamber to a sealed reservoir and then pumping out the water?

You'll have to work out the proper ratio of chamber to reservoir, but it should be cheap and easy to reset.

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Boffin

Limited by water vapour pressure - again

24mmHg

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Boffin

I'm wondering if the vacuum chamber will have enough oxygen to sustain the engine ignition. Unless the engine comes with its own oxydant...

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Ditch the 'boffin' icon

because those guys think before they post.

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Alert

Danger, sciencetards at work...

The Chinese knew it in 998 A.D. (and probably 2,000 years earlier).

Robert Goddard knew in in 1926.

An essential characteristic of a rocket is that IT CONTAINS ITS OWN FUEL AND OWN OXIDISER.

That is why they work in space where there is no oxygen.

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Freezer

Get the compresser out of an old freezer.

Don't know 'how low it will go', but they're basically free and suck pretty hard so worth a pop.

(for the sake of respecting the law, I believe you'll want a freezer that has already lost its refrigerant - that way you're not responsible for its release.)

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Vic
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An engine.

Go to the nearest scrapyard and grab a small engine.

Plumb one of the cylinders inlet to the chamber, put some sort of exhaust on the manifold, and find something to turn the crankshaft (an old electric motor, for example).

If the cylinder you chose leaks - pick another one. Scrap engines have a habit of being knackered...

Don't run it for too long unless you've also sorted the cooling system. It will get hot...

Vic.

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Go

Micra lump

I'm reliably informed the the K11 Micra 1.0 and 1.3 litre lumps are so smooth that it's tricky to notice when they are running on three cylinders, unless you're fairly mechanically minded.

So just pop the injector feed and HT coil from one cyl, run your vacuum 'feed' from the tank into the intake manifold chamber having banked it off as best you can with JB weld and bits of washing machine bodywork, and wang that legendary powerhouse of an engine up to it's sweet, sweet peak power point of 6000rpm.

If nothing else, the resulting explosion/implosion/fire/injury would look cool in high framerate, high definition video.

Steven R

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Do what the RC modellers do...

When making composite wings, RC modellers use an old fridge compressor which pulls and holds much more vacuum than 15mmHg if you want it. These things are often left running overnight while resin sets under pressure inside a vacuum bag.

For an example:

http://www.paragoncode.com/shop/vacuum_pump/

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Boffin

What to expect from a fridge compressor

According to this site: http://www.paragoncode.com/shop/vacuum_pump/

a fridge compressor maxes out at 100mb, or about 75 mm of mercury, so its probably not good enough.

@PC Paul: if you sucked down to 15mm Hg (0.98 bar) when vac-bagging a foam wing you'd end up with a very thin wing. I have an AutoVac II system I bought from ASP which was set to pull 5" (128mm) of mercury when I got it (0.16 bar): that's plenty for vac-bagging wings. I vac-form carbon shells on Dow blue foam male moulds and pull about 11" (0.36 bar) but this is much stiffer foam than anything you'd make a wing out of: its sold for under-floor insulation and is rated to support something like 260kG/m^2 load with a hard floor surface on top of it to spread the load.

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Don't know what you can use, but if you use any name except LOVELACE for the part that sucks mightily there's no justice in the world.

Contrived acronyms are somewhat beyond me at current caffeine levels.

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I don't think

Ada deserves that.

Oh, wait. . .

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Low Orbit Vacuum Experimental Lab And Cooling Environment

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Fridge Compressor

There seem to be quite a lot of Google hits for home made vacuum pumps made from old fridge compressors. The only problem might be getting a hold of one, because the disposal regulations surrounding the refrigerant gasses.

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Boffin

Fridge compressor?

A bit of searching around the web suggests they're capable of sucking about 25 inches. That's not even in the same ballpark as the air pressure at 80k feet, but I doubt that lack of air pressure would affect the firing; temperature would be the prime concern. And once the motor fires it's a self-sustaining reaction, it doesn't need outside air (that'd be quite a problem with pressures inside the motor casing being a tad unfavorable in letting air _in_). So there's probably no need to create near-absolute vacuum, and a fridge compressor would be good enough.

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Paris Hilton

vacuum pump bodge

Instructables is a good source of the kind of bodging el reg would be proud of.

And this might do the trick for you:

http://www.instructables.com/id/convert-a-tire-inflator-type-air-compressor-into-a/

<Insert Paris/Lohan related pump joke here>

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Paris Hilton

Ask the project's namesake? Just give her 15 feet of garden hose...

Paris, also...

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Boffin

Cheap little sucker...

...here http://www.berkut13.com/sucker.htm (The plans seem to fit in beautifully with the LOHAN ethos...

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Gauge on wrong side of valve?

Physical engineering isn't my thing but don't you risk false positives if you have the valve and the gauge in their current positions? I would prefer see the gauge reading conditions *inside* the container, not conditions between the valve and the pump.

I am assuming the case where the required vacuum is reached and the valve closed. Either way, its better to move it, in my opinion.

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Only if you have plenty of pressure gauges ...

... or if you can find one with "Not wrecked by rocket exhaust or your money back" written on it.

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(Written by Reg staff) Silver badge

Re: Only if you have plenty of pressure gauges ...

Correct. That's our thinking on closing off the vacuum chamber and isolating the gauge and pump before firing. I doubt the gauge would survive the sudden rise in pressure...

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Aspirator is it.

As above. Nothing fancy needed at all. An aspirator pump will get down to the pressure you need. A good quality one will get down to 20mmHg, which is 80,000 feet altitude.

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Submerge the whole thing in liquid hydrogen with the result that the air inside condenses in a moment. Fire the motor - with no moving parts or electronics there is literally nothing that can go wrong.

Post the video.

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Mushroom

Liquid hydrogen + lit rocket motor.

I can think of at least one thing that can go wrong...

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Ensure plenty of air supply to the liquid hydrogen to ensure complete combustion and remove the requirement to dispose of the waste hydrogen (or any thing else for that matter).

Light blue touch paper and retire....

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Vacume Pump

I use an old compressor from a Freezer as a vacume pump for doing composite layups for rocketry, I got it from my local scrap yard ony cost a Fiver, then a bit of pipe and a pressure gauge and it will do what you want. If you want more details on what I have then let me know and Ill help you out with a few photos of the vacume pump.

The freezer compressor is just a pump that normally pumps refrigerant gas from one side to the other, they are quite good pumps too. so using it to pull a vacume is no problems for it. If I can find any links on the web on how to use the compressor as a vacume pump ill let you know.

Roy

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Anonymous Coward

Old refridgerators

Use an old fridge pump.

See http://www.dream-models.com/eco/vacuumpump.html

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Boffin

geoff, you're half way there

Now Geoff's idea will work with almost every car, put a t-junction into the brake servo line and you got a vacuum pump. Just don't forget to seal it up again afterwards!

As another idea: Your test rig isn't all that big. Take one of these £10 electric tyre inflator compressors, put it in an airtight sturdy container and lead the supply cable and pressure hose outside. seal around them. now drill one more hole, fix nipple to it and attach vacuum hose.

The air that the compressor pumps outside has to come from somewhere, so you got yourself a vacuum pump. As they all do loads of pressure and little volume, it might take a few minutes, but I'm sure it'll do the trick under £25. It's easier to move than a car and might, if you put a bit of effort in, even look vaguely scientific.

Good suck!

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Boffin

Local Garage or HVAC Contractor?

Well-stocked auto mechanic shops qualified to do air conditioning repairs have vacuum pumps that are used to evacuate the air conditioning system prior to refilling the system with refrigerant.

You may also be able to convince a local HVAC (Heating, Ventilation, and Air Conditioning) contractor to come out with an A/C service truck, and use some engineering tomfoolery to connect its A/C evacuation pump up to REHAB.

You may even be able to pay for the job by offering to run an advert for the company providing the equipment on LOHAN's side...

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