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Aerogel Cannon

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LAN_403

Self Defenestrate

Tue Mar 07 2006, 06:08AM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Okay, heres the big one. My overall plan is to build an air cannon to shoot a small 1/4"d 3/8"l cylinder of aerogel. Components of choice would be a stainless or aluminum sample cylinder (might be able to borrow one for a while), a full flow 1/4" solenoid valve, and a good length of 1/4" stainless tubeing. The end of the barrel will be essentialy capped off so the air infront of the projectile can be evacuated to some degree. I haven't toyed with the idea of lubricants on the barrel just yet, but if anyone has any input there, that would be great. Also in the barrel will be a set of sensors to detect the projectiles velocity near the end of the barrel, and barrels of different length will be used in accordance to pressure used. The solenoid and the sensors will be serviced via basicstamp2 on my laptop. Now, my questions. Will the aerogel expand/deform/hold up at all at lower than average pressures(think hand vaccum pump)? How hard might the aerogel be to cut and sand to shape? Will the aerogel be crushed or otherwise ruin itself under fast acceleration? Under the proposed pressures? Is there any way to coat the aerogel with a lubricant, like a teflon spray, that won't wear off in three feet of barrel friction? The ideal aerogel "bullet" of its size would weigh in at a tenth of a milligram (.05g per cubic inch), so would lubricants/sealers of some sort actually weigh it down and do more harm than good? Would a longer or shorter projectile be better, more stability vs. weight? If longer is better, would hollowing the projectile out some be a compromise? the projectile will remain in the barrel the entire time, so it won't actaually come flying out, hence recording data at the end of the barrel, something to keep in mind. Some of these can't really be answered without physical testing, but if you have a good idea of the outcome it would really help. Aerogel isn't cheap, so any projectile improvements need to be solid, maybe five projectiles will be fired, and fired again in a perfect world. Anyone want to tackle these questions? Thanks in advance!

-Dan

Bored Chemist

Tue Mar 07 2006, 06:53AM

Registered Member #193 Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022

I suspect the range won't be very good. Have you ever tried throwing cotton wool?

Bjørn

Tue Mar 07 2006, 01:48PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Most lubricants does little good under very low load conditions when it comes to reducing friction. They are designed for fairly high loads. Graphite works well at low loads but I am not sure if it will help in this case.

Aerogel handles low pressures very well. It will hold up well to acceleration since it has a high strength to weight ratio.

I am sure your valve will be the limiting factor in this experiment, not the weight of the projectile.

Dr. Shark

Tue Mar 07 2006, 01:52PM

Registered Member #75 Joined: Thu Feb 09 2006, 09:30AM
Location: Montana, USA
Posts: 711

What is the point of the exercise, if I may ask?

Self Defenestrate

Tue Mar 07 2006, 02:52PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Range isn't a concern, speed will be measured while the projectile is still in the barrel. The cotton stops due to wind resistance, and I'd like to try firing into a partial vaccum. I'm curious as to how fast I can get an object to go. The cylinder can take about 1800psi, and the valve will be a fast acting full flow solenoid with an ID the same as the barrel, so no worrys there. The ports on the cylinder are 1/4 inch, hence all the 1/4 inch measures. I geuss the thing creeping in the back of my mind is to hit mach one, and study how the aerogel holds. I have all the parts at my fingertips, so why not try? Lubricants look out now, although a shot with a graphite projectile to lightly coat the barrel and get a measure to compare tomight be good.

...

Tue Mar 07 2006, 03:03PM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

not to rain on your parade, but...

The KE of a piece of aerojel is tiny. The drag of a piece of aerogel is huge. That is not really a good combination... Even it you got it up to 400m/s, a .1mg I am calculating about .00002j...

Also, have you ever felt a piece of aerogel? It is not all that strong, it has a good strength to weight ratio because it has almost ho weight... It should hold up to an air cannon, but I doubt it will take hitting into much at any decent speed; I would bet even water would do it in.

Also, what pressure are you planning to run? If using a sample bottle you could handle a few thousand psi? If you are looking for a flow through sollenoid you are going to have problems... A 1/4" section will have about 100lbs of force on it @2kpsi... The biggest sollenoid I have seen for a decint price are circle seal ones like this one (but if you weight you can get them for <$50).

Good Luck!

Bjørn

Tue Mar 07 2006, 04:45PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

Higher pressure does not automatically give higher speeds. The speed of sound in the gas pushing the projectile will set a clear limit to the maximum speed. A different type of gas or a warmer gas may give much higher speeds at a lower pressure.

If the projectile is fired in a vacuum then Mach 1 gives little meaning since sound does not travel in vacuum.

If you want maximum speed then use hydrogen or helium and make sure it is as hot as possible. If your pump does not give you a good vacuum then fill your barrell with a light gass and/or a very hot gass.

A normal solenoid valve will open so slowly that the experiment would be over long before it has opened significantly. The large drop in pressure through a partly open valve will cool the gass and significantly reduce the speed of sound in the gas.

Carbon_Rod

Tue Mar 07 2006, 10:19PM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

It may be rather disappointing if its anything like putting a toy Nerf arrow on a shop compressor duster.

I think the structure will crumble to dust under the combined forces of acceleration, barrel friction, heat, air pressure, resonant acoustics, and or air resistance.

Anyone who tried special 12-gauge shell shot can confirm this stuff.

Are you trying to embed particles into the gel?

Self Defenestrate

Tue Mar 07 2006, 11:19PM

Registered Member #87 Joined: Thu Feb 09 2006, 01:36PM
Location: San Jose
Posts: 191

Okay, I'm not trying to shoot it at anything, I'm trying to get a good high speed, hence me not caring too much about haw many joules it will impart on a target. In fact, its a good thing that it won't destroy anything, I won't have to worry about what stops the projectile as much, and could probably let it slow down to near nothing in a short distance. I still infact have yet to handle the material, but its just another challenge, right?

Getting a solenoid is already covered, I can get pretty much any solenoid I'll need. I probably won't top over 100psi on the first setup, but after parental aproval I might venture far beyond that number with system revisions, but lets keep talk under 100psi. Hot gasses would be interesting, but wouldn't the sudden pressure drop cool the gasses pretty quick?

The overall goal is to go as fast as possible with what I can get. Well, since we have a vote that the cylinder will crumble and crush, would there be any way to reinforce it, or to help keep its shape?

Carbon_Rod

Wed Mar 08 2006, 12:59AM

Registered Member #65 Joined: Thu Feb 09 2006, 06:43AM
Location:
Posts: 1155

Still too vague man. But its sounds like you want to use it as a carrier for a gaseous payload of some sort

Lower acceleration and a jacket may work. A solenoid may even be to fast for the 130psi off a shop compressor. Or a Burn rate controlled Potato cannon. =]

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