Making Gyrocs Great

[Humabout]

Originally Posted by Anthony

1900 yards per second isn't that high, with a 50% fuel fraction it requires a propellant with an iSP of about 250. It's pretty optimistic for a micro missile but not what you're making it.

ISP of 250 is solidly (pun!) in the realm of composite solid rocket fuels.

Also, 1900 yd/s is about Mach 5ish, not 35.

[Varyon]

Originally Posted by Humabout

Also, 1900 yd/s is about Mach 5ish, not 35.

Yeah, I'm not sure where I got that extra factor of 7 from. Also, it occurs to me that they don't have to reach their maximum speed at 10 yards out, but rather just need to reach their maximum damage at this point. The 440 yd/s from the first post is how fast the projectile is moving at the end, when it runs out of fuel. Using the way collision damage (as it relates to mass) works in Spaceships as a guide, final velocity of 400 yd/s calls for a 1.5 HP (0.016 lb) projectile, while final velocity of 500 yd/s calls for a 1.2 HP (0.008 lb) projectile; these correspond to 84% and 92%, respectively, of the gyroc's mass being fuel, which is far above what I anticipated. A fully-fueled 2.8 HP gyroc needs a velocity of around 215 yd/s for 6d damage, so that would be our actual goal at 10 yards, requiring around 230G. Considering it's below Mach 1 to start with, we might as well keep it below such (to match the UT description), with a final velocity of 375 yd/s (just on the edge of the speed of sound). That calls for a final HP of around 1.6, or 0.019 lb (~80% fuel). Using Douglas Cole's old spreadsheet (c. 2011, the equation may have been updated since then), a 0.1 lb, 15 mm projectile would need to be moving at around 335 yd/s to get 6d damage. With a final speed of 375 yd/s, keeping constant kinetic energy (which is necessary with Doug's spreadsheet, as damage there is a function of KE and cross section, and the latter doesn't change), you'd need a final mass of 0.036 lb, or around a 65% mass fraction as fuel. Assuming I haven't screwed up the math somewhere (which is possible; my first attempt gave me 5% of mass as fuel).