btrettel wrote:I've only skimmed this thread, but you should find the links on this page to be extremely helpful D_Hall: http://trettel.org/bags/other-models.html
You might find this to be the most interesting (and may even have a printed copy already available to you): http://www.dtic.mil/srch/doc?collection=t3&id=AD0475660
The high muzzle velocities will require more complicated modeling much like what I plan for BAGS 2 and what Rag has done with Apocalypse. The simplest way is to assume velocity, density, pressure, etc. varies down the length of the barrel (this is 1D).
There are a number of ways to solve an unsteady compressible 1D problem... the books I have listed primarily use the method of characteristics, as does Rag's Apocalypse. I'm been thinking about going that route myself, but I really don't have the patience for it. Ragnarok must have significantly more patience than me because the MoC is a PAIN IN THE ASS to work with. I'm sure that when it works well, it works well, but it's another layer of complexity in an already complex problem. I can give you some good references in addition to what I already have listed if you want to go this route.
For that reason what'll be released will likely use what's called a finite difference of finite volume scheme... which aren't too difficult to implement but you run into the problem of the scheme being a "black box" in that you don't really know how it works or when it's working well. So I have much highly mathematical reading ahead of me. The end result surely will be worthwhile.
@ Jack, The 3 gallon launcher would consume a huge amout of gas for a 200 PSI shot. GGDT does make wonderful predictions for it. The 7 gallon at 200 PSI would perform even better but use about 12 cubic feet of gas per shot. It may get the ball supersonic, but doesn't answer the question, can I do it with just air?
The links are great but some of the links on the pages have changed. I have found the NASA pages with some of their simulations. They are not as easy to use or as intuitive as GGDT.
The modeling is very complex, but to assist I've been modeling the acceleration of a projectile piston in GGDT to give an acceleration curve, then reversing the process to find the chamber size necessary to reverse the process lossless in say 1/4 the barrel length. This gives a higher pressure than I started with in a smaller volume. I then use these values to see the "temperature drop if it was launching and look to that as a temperature rise instead.
Then I take the hot gas temperature with the small virtual chamber and high pressure and use that to model the ejection of the small projectile out the small barrel with the high pressure high temperature "light gas" in the chamber. Next projectile weight diameter and such is adjusted to give the exact same time to launch as the first piston takes to stop in the compression end.
I know there will be massive losses due to the temperature changes, friction, piston blow by, recoil causing incomplete energy transfer etc etc, but the preliminary numbers are looking real good.
Taking 70 degeree air at 200 PSI and dumping it on a 3 inch piston gives it energy, which then comes to a sudden deceleration in 1/4 the distance compressing air to over 800 PSI which heats it a lot, which transfers energy to the projectile 1/4 the mass of the piston as a light gas at theoretically over 3X the speed.
A 500 FPS piston into the light gas tube in theory can launch the golf ball at well over 1500 FPS. My burning desire is to be the first here to try it.
Since I've launched apples at over 700 FPS on only 100 PSI the required energy on a relatively massive 3 inch piston at 200 PSI is easily done. Imagine a golf ball with an 800 PSI light gas behind it for 10 feet. This is the type of figures I am getting.
Keeping it from blowing up will be the trick.