* Posts by rg20

12 posts • joined 6 Jan 2009

Man FLIES with Android-powered homemade bird wings

rg20

Gullable?

you mean Gullible.

You do realise of course that the word "gullible" is'nt actually in any dictionary !

Harvard boffins cause buzz with robot bee

rg20

Re: Brilliant...

Why do they pronounce "mirror" as "mrrrr", that girl on Mythbusters said it about 5 times in a row a few days ago, really annoying. Or President Bush saying "tourists" when he was talking about Terrorists!

I dont mind them saying aluminum or "fall" for autumn and lots of others as they were the original English words, but when they mangle the pronunciation of words that are used on both sides of the pond - annoying.

AirDroid

rg20

Camera control?

Can I turn on, watch and use the phones camera?

Would make a useful remote controlled camera!

Nuke support in UK hits record high

rg20

Radioactive waste

People keep banging on about the amount of radioactive waste produced by nuclear power, maybe someone can answer a question I've had for a while - "does the nuclear industry actually "create" more radioactive material than it had to begin with"

Uranium is mined in South Africa/Russia or wherever and is extracted from thousands of tons of rock/soil, if we were to take the radioactive waste back to the place where it was mined and it was ground very fine and mixed back in to the soil extracted, would the soil be more radioactive than it was originally?

I think the problem with the waste is that it is concentrated in a small area, if it could be diluted would the area be more or less radioactive overall than before it was extracted?

Maybe we could have a ship in the center of the Pacific mixing the waste into the seawater. If it was diluted sufficiently in enough water it would probably be undetectable above the baseline radioactivity of the water.

Or maybe I'm wrong! Can someone enlighten me?

Churlish HSBC drops atomic-scale accuracy

rg20

Postcodes different?

But the postcodes you typed in dont seem to match?

LOHAN to suck mighty thruster as it goes off, in a shed

rg20

I dont think the low temp will be a problem for the plastic pipe, I guess it will make it more brittle but as long as you dont hit it with anything too hard I think you'll find it is surprisingly tough.

You could always just leave it laying in the dry ice, there is no need for it to be vertical, just make sure it is not pointing at anything flammable for when the end cap pops off!

rg20

This is all getting a bit out of hand, you dont need no tig welding, burst disks etc

all you need is a length of plastic pipe and a couple of end caps.

Let me explain.

As I said in an earlier post we used a length of plastic waste pipe from B&Q to make

a test piece for our leak detector. The pipe says on the side "1.25/36mm BS EN 1455 B

ABS1.8mm" it has a diameter of 36mm and a wall thickness of approx 1.5mm. We bonded

some quick release flanges into the bore of the pipe using epoxy resin and this takes

a port pressure on our leak detector of 2x10-3mbar no problem, no leaks nothing,

remember the max external pressure it'll ever see is 14.7lbs/sq/inch.

This seems the right size pipe for you (your motor is 30mm dia?), place the motor in

the pipe bring the temp probe lead and ignition leads out the bottom through a hole

drilled in and aluminium plate. Seal this with epoxy resin. You will also need a hole

for the vac pipe fitting, attach this using epoxy resin. Attach to this a length of hose

from a acetylene welder or equivalent (this is designed to resist internal pressure but

will do the same for external pressure) attach this to a valve, then to a gauge then to

the pump.

Bond this plate to the bottom of the tube with epoxy resin, bond on the top cap too.

Lay this in your dry ice and monitor the temp, once it reaches temp you'll have to

let it "soak" for an hour or two to makes sure the core of the motor is at the correct

temp, remove and fit in a retort stand (or just leave it in the dry ice), vac it down,

this will only take a few seconds due to the small volume of the chamber. turn off the

pump close the valve and ignite.

The motor will probably burn thru the tube almost immediately but all you want to know

is if it will ignite at cold and altitude.

If you are worried about the assembly going bang, do not bond on the top cap, use a

rubber sealing ring instead to allow the top cap to pop off under the pressure.

This is a low cost disposable set-up but will do the job.

rg20

A rubber seal will be fine, I have a vacuum vessel in a "Thermotron", a large oven which also chills that we use for testing connectors at altitude and hot and cold, and we regularly test at 45mbar -55deg c. You dont need grease at all, in fact grease would cause the seal to slip and be pushed into the chamber (it happened to me once) a clean dry seal has the benefit of friction holding it in place.

rg20

Making a suitable chamber would be easy you simply need length of tubing of the right diameter a couple of o-ring seals and two flat plates for either end.

I recently had to make a long adaptor to fit long leads in our mass spectrometer/leak detector, we used a length of plastic waste pipe from B&Q with the correct flanges bonded in to either end with epoxy resin. This set-up will go to <6x10-3mbar with no probs (and no leaks).

Remember it is only going to be 14.7lbs/sq/inch which isnt a lot really, I dont know the diameter of the rocket but a length of plastic pipe of suitable thickness will be fine.

Remember it wont "blow-up" if it fails, it will buckle at most, the pressure is pushing in , not out.

rg20

You probably don't need to chill the whole chamber, just place the dry ice around the motor itself (sealed in a plastic bag) until it reaches temp then place it in the chamber. If you had a temp probe strapped to the side you could check the temp. You could overchill it, then wait til it reaches the correct temp before ignition.

It doesnt matter about the exhaust changing the pressure in the vessel as you only want to see if it ignites at that altitude and temp.

I use a chamber similar to this at work to test altitude sealed hi-voltage connectors for military aircraft, at altitudes of 70Kft and above and voltages of up to 60kv, my chamber has a vol of approx 3cubic ft and our edward series 8 vac pump can get it to 45mbar/70kft in about 30sec.

You could run any temp probe leads across the top seal under the top plate, as long at they are quite narrow (bellwire type dimensions) the pump will hardly notice the slight leak it'll cause, though it obviously wont hold altitude once the pump is switched off, ( i have trapped test leads under the lid of my chamber numerous times and not noticed til the pump was off!)

Columbia disaster 'not survivable', NASA concludes

rg20

DOH ! Meant Challenger !

DOH ! Meant Challenger above !

rg20
Flame

@ twat

"it's not the fall that kills you, it is hitting the ground at the end that does it"

Surely you mean the "offnominal deceleration situation" at the end that does it !

Also, remembering the Columbia disaster, when it exploded, the two boosters shot off in different directions, millions of pieces of burning debris falling to earth, and the commentator said :

"Obviously a major malfunction"

And I thought us Brits were the masters at understatement !

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