Login    Register
User Information
Username:
Password:
We are a free and open
community, all are welcome.
Click here to Register
Sponsored
Who is online

In total there are 73 users online :: 3 registered, 1 hidden and 69 guests


Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Google [Bot], Yahoo [Bot] based on users active over the past 5 minutes

The Team
Administrators
Global Moderators
global_moderators.png CS

Supersonic Airsoft BB's

A place to ask general spud cannon related questions.
Sponsored 
  • Author
    Message

Unread postAuthor: Spudinator » Mon May 17, 2010 4:38 pm

That's a sweet gun but...

Not sure you are hitting supersonic with room-temp gas. Dont know if any of you old members are lurking around who remember the many discussions on the flow of gas at room temperature. The way I recall it, gas can not exceed the speed of sound at room temp, thus a projectile fired by said room temp gas cannot either. It must be heated through either compression or chemical means (the latter of which we will not go into)..

Thats how some break-action pellet rifles can fire beyond the speed of sound. A very large powerful spring slams a quantity of air into a very small space heating it far beyond room temp, which then allows the gas (and pellet) to travel beyond the speed of sound.

Unless of course you are heating your gas bottles to a couple hundred Fehrenheit :shock:

Perhaps the cracks you are hearing is merely your superb large hammer valve doing its job? :wink:

just my 2 cents
  • 0

"This is so fun it should be illegal... Oh wait..."
User avatar
Spudinator
Donating Member
Donating Member
 
Posts: 70
Joined: Sun Feb 13, 2005 4:50 pm
Location: WA
Reputation: 0

Unread postAuthor: Biopyro » Mon May 17, 2010 4:44 pm

Even if this is not theoretically possible, there is something going on here which does appear to be causing supersonic projectiles, because I think we had this discussion in a thread where muzzle blast was hunted for as a culprit but not found. It may be beyond our understanding (for now) but I think it could really be happening.
  • 0

Those who would give up Essential Liberty to purchase a little Temporary Safety, deserve neither Liberty nor Safety. -Benjamin Franklin
User avatar
Biopyro
Colonel
Colonel
 
Posts: 656
Joined: Fri Aug 04, 2006 5:32 am
Location: UK
Reputation: 0

Unread postAuthor: Dave_424 » Mon May 17, 2010 5:17 pm

Spudinator:

I'm aware that at room temperature, a projectile cannot exceed the speed of sound in that gas.

I'm definatley going supersonic, I can shoot the 31 grains at 950 fps with my silencer and all I hear is a PFFFT......

As soon as I stick in a 3 grain airsoft BB, There is a woosh then and keoooowwww that echoes all around. I will do a video tomorow showing the diffrence between a 31 grain pellet and an airsoft BB with chrony readings.

My thoughts is that as the air exits from the valve, and reaches the pellet/bullet it compresses rapidly and heats up. That seems to be the only explanation.

Because heavier and tighter fitting pellets create a back pressure, holding the valve open for longer, I can keep pellets supersonic up to around 19 grains, and after that they are slightly below 1100fps.

This platform is so efficient, massive power can be produced. I have personally seen 18 grain BSA parylam pellets going 1400 + fps when I was testing a high power valve for a customer, lets just say that he is happy with the valve.

Dave
  • 0


Dave_424
2nd Lieutenant
2nd Lieutenant
 
Posts: 220
Joined: Thu Aug 02, 2007 7:45 am
Reputation: 0

Unread postAuthor: Spudinator » Mon May 17, 2010 6:10 pm

Hmm, what type of gas are you using then? Helium or hydrogen are the only gases that could exceed mach 1 at room temperature, and I kinda doubt you are pumping pure compressed hydrogen into your pellet rifles...

On your argument that it is compressed against the BB/pellet. Wouldn't the release of temperature upon exiting the valve negate any compressive effects against the projectile? I know for a fact that using room temperature gas at any pressure is not capable of supersonic velocities. Period. I guess at this point vids of shots and chrograph would be a big help.

Perhaps Dave Hall could apply his proffesional opinion on the matter?
  • 0

"This is so fun it should be illegal... Oh wait..."
User avatar
Spudinator
Donating Member
Donating Member
 
Posts: 70
Joined: Sun Feb 13, 2005 4:50 pm
Location: WA
Reputation: 0

Unread postAuthor: Dave_424 » Mon May 17, 2010 6:22 pm

Im using just normal AIR, mix of Oxygen, Nitrogen etc.

Im not sure whats happening in my gun.

Chrony videos will follow tomorrow, I will shoot a range of pellet weights to rule out any chrony errors to show that the readings are correct and consistant, then run one or two BB's through (My neigbours don't really like the muzzle crack when it goes supersonic.

Just to say, The gas is regular ambient air, at room temperature etc. all standard condidions.

Dave
  • 0


Dave_424
2nd Lieutenant
2nd Lieutenant
 
Posts: 220
Joined: Thu Aug 02, 2007 7:45 am
Reputation: 0

Unread postAuthor: DYI » Mon May 17, 2010 6:48 pm

Supersonic flow is not physically impossible, it just requires good design and/or very high pressure to achieve. A more solid limit is imposed by the particle speeds in the gas (mean of around 500m/s for room temperature nitrogen).

What's happening here is not unusual considering the high pressure, fast valve, and light projectiles.
  • 0

Spudfiles' resident expert on all things that sail through the air at improbable speeds, trailing an incandescent wake of ionized air, dissociated polymers and metal oxides.
User avatar
DYI
Lieutenant General
Lieutenant General
 
Posts: 2861
Joined: Sat Jul 07, 2007 8:18 pm
Location: The People's Republic of Canuckistan
Country: Turks and Caicos Islands (tc)
Reputation: 9

Unread postAuthor: Gippeto » Mon May 17, 2010 7:07 pm

@ spudinator;

I was coming pretty darn close...with only 400psi air. After further testing with dry fires, I do believe I actually succeeded.

http://www.spudfiles.com/forums/x-1-1-m ... 16607.html

As mentioned, I did some "dry" firing at the same pressure to determine whether the sensors on my chrony were reading the muzzle blast. Every "dry" shot had a non result. The sensors are NOT detecting the muzzle blast.
  • 0

User avatar
Gippeto
Donating Member
Donating Member
 
Posts: 2393
Joined: Sat Jan 19, 2008 10:14 am
Location: The Great White North...Canada eh!
Reputation: 11

Sponsored

Sponsor
 


Unread postAuthor: Lentamentalisk » Tue May 18, 2010 7:52 pm

The issue is that the "speed of sound" is how quickly sound travels, on average, not, as DYI said, the speed of the individual particles.
The particles have a mean speed of the SoS, but then there is an approximately normal distribution on either side of that. It is theoretically possible to accelerate an object to the speed of the very fastest particle, but efficiency drops rapidly, as the projectile is traveling faster than a greater portion of the population of particles.
  • 0

Do not look back, and grieve over the past, for it is gone;
Do not be troubled about the future, for it has not yet come;
Live life in the present, and make it so beautiful that it will be worth remembering.
User avatar
Lentamentalisk
Brigadier General
Brigadier General
 
Posts: 1202
Joined: Tue Aug 07, 2007 5:27 pm
Location: Berkeley C.A.
Reputation: 0

Unread postAuthor: Ragnarok » Tue May 18, 2010 11:01 pm

Spudinator wrote:The way I recall it, gas can not exceed the speed of sound at room temp, thus a projectile fired by said room temp gas cannot either.

That's not actually true. Gas can quite easily exceed the speed of sound at room temperature - it just has to not be at room temperature itself.

It is true to say that under practical restraints, a gas normally cannot expand faster than its SoS. These restraints include microscopic imperfections in the barrel - a supersonic flow hitting these forms a shockwave, and this spreading shockwave then disrupts supersonic gas flow through it, slowing it down.

For those reasons, it is reasonable to make the assumption that gas flow does not exceed the speed of sound for its temperature. However, that does not mean the gas in the system is the same temperature as the ambient gases outside the system.

Things such as adiabatic heating and shock effects can raise gas temperatures to the point that the internal speed of sound is significantly higher than that of outside the system. (That said, most spudguns do not harness these effects, and have a lower internal SoS.)

The AirForce Condor is actually marketed as a supersonic PCP - and you can be sure there'd be some stink if they weren't capable of it.

Yes, it's hard to go supersonic when your gas bottle is only at room temperature, but if you will, imagine the internal science of something that is capable of it somewhat like the spring piston airguns you've already mentioned.
The difference is that instead of the piston being a large spring driven lump of steel, it's replaced by the gases coming from the reservoir, which similarly compress and heat the gases ahead of them - those already between the pellet and valve.

This is also magnified to some extent by shock effects - sound waves travelling through the gasses in the barrel heat it. Progressive soundwaves travel through slightly warmer gas, thus travel faster, catching up with one another, eventually combining into a supersonic shock front.
The shock effect is well known, and can be observed in a laboratory using a "shock tube" - which is basically a pneumatic burst disc cannon without a projectile.

Anyway, as has been said - supersonic with room temperature air is hard, but not impossible if high pressures and good design are involved.
I know I'm one of the chief sceptics when it comes to debunking supersonic claims on this forum, but that's largely because many of the designs involved seem unlikely candidates to harness these effects.
A modified AirForce Condor however - damn, you'd better believe that's capable of it!

This post brought you by the "Ragnarok gets rather loquacious when tired" foundation.
  • 0

Last edited by Ragnarok on Wed May 19, 2010 8:42 am, edited 1 time in total.
Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: Technician1002 » Wed May 19, 2010 12:21 am

Well put. This is on my drawing board to use the 2.5 inch QDV as the "spring" to drive a secondary piston in a second cylinder to compress and heat the air in front of it to drive a small projectile at supersonic speed. I'll start with a marshmallow (2.5 inch piston valve to drive a marshmallow.. :D ) and then see if I can get a golfball supersonic. Getting the golfball supersonic will be a maybe. The marshmallow should be no problem.

Math is showing the marshmallow launch at over 1,000 PSI and a high compression temperature. The compression ratio will be higher than a diesel engine.
  • 0

User avatar
Technician1002
Chief of Staff
Chief of Staff
 
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: 12332123 » Wed May 19, 2010 2:43 am

On Wikipedia -I know, not the most reliable source - it claims that:

'In non-ideal gases, such as a van der Waals gas, the proportionality is not exact, and there is a slight dependence of sound velocity on the gas pressure.'

Given that air is mostly composed of diatomic molecules (N2, O2), which tend to behave in a non-ideal manner, could this perhaps account for supersonic velocities (i.e could the local speed of sound in the propellant gas be greater than the ambient speed of sound)?
  • 0


12332123
Private
Private
 
Posts: 7
Joined: Thu Apr 15, 2010 8:35 am
Reputation: 0

Unread postAuthor: Ragnarok » Wed May 19, 2010 8:59 am

12332123 wrote:i.e could the local speed of sound in the propellant gas be greater than the ambient speed of sound?

That's basically what my post above said, along with the reasons why that can be the case.

As it is, an increase in pressure does increase the speed of sound. However, at the same time, an increase in density reduces the SoS.
Normally, simply compressing a gas (then allowing the temperature to equalise) means these two effects pretty much cancel out.
Things such as the compressibility factor and moisture content of the air mean that density and pressure are not completely linearly related, but the difference is usually pretty small - meaning that the SoS in a gas bottle at 10 bar is near as dammit the same as that of the normal atmosphere.

To actually significantly change the SoS, you need to change pressure and density independently - either by heating it (which in a confined gas will increase pressure, but doesn't change density), or by using a lower molecular weight gas such as helium (which doesn't increase pressure, but lowers density).

As it is, it's possible for the temperature of the gases in a launcher to increase (my above post explains why), giving the launcher a higher internal gas temperature. Hard, but possible.
  • 0

Does that thing kinda look like a big cat to you?
User avatar
Ragnarok
Chief of Staff
Chief of Staff
 
Posts: 5339
Joined: Tue Dec 19, 2006 8:23 am
Location: The UK
Reputation: 8

Unread postAuthor: Spudinator » Thu May 20, 2010 5:18 pm

Hmm news to me, guess these theories never surfaced during my time on spudtech. I didnt consider a "dead" space between valve and breach, assumed they were connected very closely. Does make sense the air would heat under compression in between the two...

I dont remember any mention whatsoever of room-temp air exceeding SoS in the old discussions, but then we didnt have Ragnarok on at that time either I believe. I think it was Pacogoatboy, D_Hall, a few others...
  • 0

"This is so fun it should be illegal... Oh wait..."
User avatar
Spudinator
Donating Member
Donating Member
 
Posts: 70
Joined: Sun Feb 13, 2005 4:50 pm
Location: WA
Reputation: 0

Previous

Return to General Spud Cannon Related

Who is online

Registered users: Bing [Bot], Google [Bot], Yahoo [Bot]

Reputation System ©'