You want to calculate your own trajectories? Ok, I can help you with the more basic stuff. We are writing for a teacher who probably scarcely remembers that F=CdAV², not the department of defense, so that's fine. First off, there are two ways to calculate drag-inclusive ballistics: 1) Cal...

Ah, didn't know your heat transfer model ignored the fluid velocity's role in heat transfer rate. Some searching on wikipedia (for lack of good engineering resources around here) indicates that the following might be reasonably applicable: Total heat transfer = 1/(1/"gas-wall" + 1/"wall-bulk pipe") ...

Yeah, it's odd.

Phase transitions don't make any sense, considering that the temperature at a c:b ratio of .8:1 is about 650k. (PV=NrT, P=1atm)

The water vapor-liquid phase transition at 10 psi is about 355k...

Further, phase transitions take considerable amounts of energy, don't they?

OTOH, a 1x scope with illuminated reticle could be made for 5$. Yeah, at that price range the lenses would almost certainly be plastic... not much we can do about that. While you are making your own reticle, you might as well put fall-adjustment marks at the proper points. There are any number of wa...

Well, for an actual red-dot optic, you'd need a specially curved surface. I don't know what this surface curve is, so I don't know how available it would be, but you'll be paying 10$ shipping on (unless you find a suitable surplus lenses) a 20$+ piece of glass. However, 1x fixed-power scopes are eas...

I fired up EVBEC and figured out the performance, performance/cost, and performance/weight of launchers with a fixed overall length, but variable chamber length and chamber diameter. What I found is that (in my rather simplistic modeling of combustion) vastly oversized chambers are cost and mass eff...

Jimmy: precisely.

The way this thread is developing, I feel the need to get some smoke, a camera, a fan, and a clear 4" tube.

I suppose the tube doesn't even need to be pressure tight, which makes everything much easier.

Interesting; even without a fan, EVBEC predicted better-than-actual performance. It seemed that for the longest time, the assumption was that filling the chamber with air was roughly equivalent to the use of a chamber fan. Anyways, I'm not too upset with that prediction either - both the high-veloci...

Drag is caused, generally, when the projectile has to impart energy to move the air, for instance: 1) Out of the way of the nose cone 2) Into turbulent eddies behind the projectile 3) To generate lift off a wing 1: Because the diameter and velocity of the projectile are constants in our optimization...

Might a chamber-sized fan act like a centrifugal blower to some extent?

"air diffusion into the tube to sustain combustion - that's why it took so long"

I bet not. Laminar flame front speeds in poor fuel-air mixtures are slow.

Just for fun, try capping the ignition end with something solid. I bet you'll see faster prorogation with all fuel mixtures.

What type of effort would it take to direct a piston down onto a load cell/strain gauge?

I don't know the typical frequency response times of these things, but I thought I'd throw it out there.

(of course, this is probably how they make commercial "digital" pressure gauges)

Sorry to sidetrack the discussion of the model, but I'm not so sure the projectile starts to move early on in the launch sequence... Initial accelerations in combustion launchers is HIGH. <a href="http://img.photobucket.com/albums/v611/car2/pressvspos.png">Old graph</a> Ignore the pink line, the "14...

I noticed that (per the research cited in the Gexcon Gas Explosion Handbook) that the run-up distance of hydrocarbon-air detonations is roughly inversely proportional to pipe diameter; 4" pipe requires twice the length distance to undergo DDT compared to 2". If one accepts the premise that DDT is fa...

The formulas on that website are for figuring out <i>flow</i> given <i>Cv</i>. Since the GGDT already does those calculations, you don't need them. They have a table of CV values at the end of their .pdf, but that won't do you any good... you don't even know their valve geometry, and I'm sure you do...