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Registered Member #1329
Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53
Hey Guys,
Check this out. Here is how I see the problem with disc launchers. Please comment.
The pancake coil lends itself very nicely to launching a disc shaped object. But the disc shaped object really sucks aerodynamically. So how do fix the problem. Easy... make the projectile aerodynamic by adding fins, nose cone, cylindical etc. WRONG not easy at all. The instantaneous force at "lift off" shatters, breaks, bends, explodes stuff that is attached to the disc. I witnessed this today and just look at past post from Tristan.
Fast MHZ has had some luck with this and he may have a few tricks up his sleeve, Fast?? anything.
So I am thinking how does one acquire a nearly indestructable fairly aerodynamic projectile. While researching this today I came upon a picture of a golf ball being struck by a golf club. The golf ball was compressed to almost 1/2 its diameter due to the force of the striking club. Pretty tough I would say..
Than I found this
Play around with it it is fun.
Here is the crux of the issue. According to the applet if object A with a mass of one, at rest is struck by object B with a mass of 2 and a speed of 1, object A will travel away with a speed of 1.3333. Make object B have a mass of 5 and the speed of object A will travel at 1.66 times the speed of object B
So why then not have a disc of 2x mass hit a golfball with a mass of 1x?? Atleast the GB would be a much better projectile that the flat billboard of a disc.
I realze this is basic physic, but what am I reading wrong into this? If this worked you could build a very thick AL disc that would absorb lots of energy from the pancake coil and transfer it to a smaller better space traveller.
Registered Member #90
Joined: Thu Feb 09 2006, 02:44PM
Location: Seattle, Washington
Posts: 301
Think about using the aluminum platter to push a more balanced rocket-shaped projectile. This approach was used by the Discovery Channel for their big induction launcher. Worked great. Links and photos will be posted later after the show airs in Fall 2008. Look for the series "Ten Ways to Save the Planet" and try to find the episode named "Solar Sunshade".
The platter had a short range of motion, like six inches to launch and another six inches into a cushion. Measurements found the aluminum accelerated on the order of 1,000 - 10,000G, but it also seemed to try to flip like a tossed coin, too.
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
Yeah, I have long thought of ways to make an aluminum sabot and some kind of dart projectile. However if the aerodynamic projectile that separates from the aluminum is lighter than the aluminum you will loose a lot of energy, but perhaps aerodynamics makes up for some of that if your goal is long range and accuracy, as well as perhaps piercing power. At this point I am just waiting until I acquire some better shop equipment to start testing things (i.e. metal lathe).
Registered Member #1329
Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53
Barry, 1,000 to 10,000 G's... Hmm that explains it. When I put a ball of my son's silly putty on the AL disc and fired it at 6000 uf and 900 volts It flattened it into a thin sheet 3 miles in dia. and 1 molecule thick!!! :>)
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
w1vlf wrote ...
Barry, 1,000 to 10,000 G's... Hmm that explains it. When I put a ball of my son's silly putty on the AL disc and fired it at 6000 uf and 900 volts It flattened it into a thin sheet 3 miles in dia. and 1 molecule thick!!! :>)
LOL!
Yeah the acceleration is very fast with the IL's... I guess that's one advantage of the reluctance design is you can spread out the acceleration a little longer. I am sure it varies by each individual coil but most probably have a majority of their acceleration in less than half an inch. Not sure how much study has been done in this area but it should be easy to do, just put some thin plastic spacers between the coil and disk and measure the resulting velocities as the projectile is started further and further away. I haven't done this at all with my newer launchers but back in the day I found that at a starting distance of 1" the energy was reduced by more than 75%. I wouldn't be surprised if my newer coils are even tighter than that due to be much smaller (a little over 2" as compared to my old coils which were over 5" diameter - designed for the larger hard drive disks like my avatar).
The way I think about the quick acceleration and great force exerted is kind of like this... picture a record setting baseball player swinging a sledge hammer at your projectile which is suspended in air in front of him...
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
rp - could you elaborate your question in more detail? I'm not sure what or to whom your asking about. An induction launcher always has the projectile in front of the coil.
About the original post -
w1vlf wrote ...
Here is the crux of the issue. According to the applet if object A with a mass of one, at rest is struck by object B with a mass of 2 and a speed of 1, object A will travel away with a speed of 1.3333. Make object B have a mass of 5 and the speed of object A will travel at 1.66 times the speed of object B
So why then not have a disc of 2x mass hit a golfball with a mass of 1x?? Atleast the GB would be a much better projectile that the flat billboard of a disc.
I realze this is basic physic, but what am I reading wrong into this? If this worked you could build a very thick AL disc that would absorb lots of energy from the pancake coil and transfer it to a smaller better space traveller.
Its interesting, I've never really thought about the possibility to increase velocity by striking a lighter object, with the sabot style of course the velocity remains the same. Energy will be lost though unless both are of the same mass, and the lighter the final projectile the more inefficient the design becomes. In your example of the second object being 2X as heavy then the first, you loose about 15.5% efficiency if my math is correct. And in your 1:5 example then your loosing about 45% efficiency. If velocity alone is what your after than this might work, but the overall efficiency of the system will decrease. And of course the more complex design, etc. But then there is the advantage of aerodynamics, and the golf ball idea isnt half bad, they are designed for this type of application. I think it needs to be tested!
Registered Member #1329
Joined: Mon Feb 18 2008, 07:31PM
Location: Harwinton Connecticut
Posts: 53
Tristan...Yes efficiency suffers in the momentun transfer process, but still I am guessing the aerodynamics of the ball would make up for it.
Last night I did a little research about how far a golfball travels when struck by a club. In the LONG DRIVE COMPETITION people hit the ball over 470 meters. So today I will try to procure some golfballs and do a couple of crude tests. The reason I like the ball type projectile is it's simplicity. For example. On my first coil gun I spent a lot of time messing with projectiles, different length to diameter ratios, putting a hole in the back so a thin rod could be inserted for a stabilizer etc. Some improvements were made for sure. However at 20' they all would start to tumble. So the next set was to go simple, musket ball simple. I bought a couple of steel balls that fit reasonable well inside my launch tube. At 20 feet 10 shots would all fall inside a 1" square. No world benchrest record for sure but lots better than the tubular projectile. With out the gyroscopic effect of the spinning bullet, I will keep to the ball ammo for the moment, atleast until more is learned about this. Off to the golf course to acquire some balls PaulC W1VLF
Registered Member #1062
Joined: Tue Oct 16 2007, 02:01AM
Location:
Posts: 1529
with a coilgun. there is a coil around a coilform and barrel, when switched, the projectile goes down the tube, this lets you do a aerodynamic design. What prevents you from doing the same with induction? just move the coil back, and make the pancake coil a traditonal coil.
Registered Member #158
Joined: Sun Feb 12 2006, 09:53PM
Location: Central Ohio
Posts: 282
rp181 wrote ...
with a coilgun. there is a coil around a coilform and barrel, when switched, the projectile goes down the tube, this lets you do a aerodynamic design. What prevents you from doing the same with induction? just move the coil back, and make the pancake coil a traditonal coil.
I see what your saying now. This is something I am actually in the process of testing myself, delayed by my recent house purchase and move. I dont know the dynamics of such a device personally, but I've only seen 1 induction launcher here on 4HV(at least since I've been here) that worked well using a solenoid type coils where a projectile traveled through a barrel inside the coils. If you can get that style to work well then please let us know about your setup. And of course when I get back to experimenting will do the same. I think FastMHz tried using a coil from his good working reluctance coilgun with an aluminum round and could barely get the projectile to twitch.
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Disc launchers and Conservation of Momentum
