The earth isn't a sphere, and even in relatively flat areas (widwest USA, for instance) the topography of the landscape is far more important than the standard curvature. At sea, I suppose it might be significant once one starts considering distances of a couple miles... but at that point, the curva...

How much does the lack of nitrogen (or other buffer gas) affect the run-up distance? A lot. The propane-O2/run-up-distance/spark-ignition/pipe research I remember seeing was indicating one or two pipe diameters for a C3H8-O2 mixture. (centered ignition) I think. I'd have to check to be sure. I think...

The effect of an early exit has been exaggerated in this thread.

In reality, it doesn't matter, because the reduced-pressure-'wave' does not have time (only traveling at the speed of sound) to reach the projectile in the other tubes before they exit too.

I've covered this before in more detail.

The wall never gets very hot, because the gases don't transfer heat to the wall very fast, at least compared to the rate of heat conduction inside the wall. This holds true even in plastics.

The TI-86 runs a z-80 processor overclocked to 6megahertz. I run a Inspiron 1150... which has a Celeron at 2,600 MegaHertz So the clockspeed is 430 times faster. Further, I believe the celeron has pipelining, whereas the Z80 doesn't (another factor of two in speed there) Oh, and I expect that the ce...

Density of the anchor is irrelevant. Volume of the anchor is irrelevant. The boat (which, in our analysis, includes anchor; the anchor is part of the "boat"), if the downwards force is constant, must always displace a certain quantity of water. If you lower the anchor into the water, the downwards f...

...this whole concept of "experience" is really getting old. Especially when it comes to combustion cannon construction. Let's see here, skills needed to build spray&pray (in rough order of difficulty): 1) Gluing 2) Threading holes 3) Cutting And an advanced launcher (with fan, pressure-regulated me...

Well, I dunno the velocity-weighted mean gas temperature in the barrel... but I'd expect that it's below the average temperature in the gun.

Jimmy, I think you are missing a point: if the gas temperature is higher, the heat is transfered into the pipe wall faster, so the wall gets hotter. I suspect Wall-temp vs gas temp is roughly linear. Is it? Temp change at T + .025 seconds : Temp differential 55:100 110:200 274:500 550:1000 Yes, at l...

Eh, jimmy, it heats up 170k if the temperature difference is 1000k. That's a 17% difference in heat transfer rate. If we are correct about the... shortness... of the latke curve being primarily due to heat loss, that's a significant difference. That said, there are two main differences between PVC a...

Unless you are just doing the calculations for the lolz... I'm going to recommend you use the GGDT. In the case that you are doing it just to do it: 1) Your projectile is heavy and muzzle velocity is low. With any type of sane valve you can probably convince yourself to ignore opening time and press...

I'll explain it like this: Heat transfer from 1300k gas to 300k (metal) wall = 1 unit/unit of time And even steel isn't a superconductor of heat, so the wall would be a bit warmer than that. Heat transfer from 1300k gas to 470k (PVC) wall = .83 unit/unit of time .83 is fairly close to 1, and that's ...

C:B ratio is indeed the volume ratio... it'll be a calculated value, not directly measured.

The volume of the latke chambers (what I use as of EVBEC 1.6, anyways) is as follows:
.75" test: 25.3 cubic inch
1.5" test: 176 ci
2.5" test: 194 ci

Heh, looks like I may have miscalculated Re. I needed to calculate it again, and this time I'm getting about 36,000 In other news, it looks like treating the pipe wall as always being 300k would be a significant mistake - within a millisecond, the wall reaches 110*C above initial temperature. (stabi...

The Cd of a sphere is <a href="http://aerodyn.org/Drag/speed-drag.html ... ">somewhat dependent</a> upon mach number.

.42 is a good guess.