On 7 Jul 2015 at 19:22, Kurt Feltenberger wrote:

> So here's my question:  Just how fast would the railguns or coilguns
> reasonably be?  50,000m/s?  100km/s?  More?

Realistically, there are two limits.

First, energy. The "gun" has to impart that impact energy to the
rounds *and* supply any losses. As well as dissipate those losses.

An "interesting" calculation is to figure out how long the projectile
is in the "barrel. Then divide that into the energy required to give
you the *power* consumption during a shot.

The results are generally pretty scary.

The other limit is acceleration. This is limiting two ways. First,
the projectile can only handle so much before it starts to deform
under its own "weight".

Second, those acceleratyion forces are exerted one the structure of
the *gun*. Which tends to try to rip it loose from the ship.

It's not too hard to take the formulas for accel vs distance and
velocity versus accel to get one that will give you the accel
required for a given "muzzle velocity" in a given length of barrel.\

Again, the figures will scare you.

v = a * t
d = 0.5 * a * t^2

v/a = t

so substituting...

d = 0.5 * a * (v/a)^2

d = 0.5 * a * v^2 /a^2
d = 0.5 * v^2 / a
d * a = 0.5 * v^2
a = 0.5 * v^2 /d
a = v^2 / 2* d

d in meters
v in m/s
a in m/s^2

go ahead and feed in the figures and be prepared to swallow your
teeth.

Lets try your 50,000 m/s and a 500 m barrel.

a = (5e4)^2 / (2 * 500)

a = 25e8 / 1e3
a = 25e5
a = 2.5e6

so that's an acceleration of a quarter of a million gees. Your
projectiles will flow like water and jam up the barrel.

--
Leonard Erickson (aka shadow)
shadow at shadowgard dot com