Talk:QF 13-pounder 9 cwt

Shell speeds do not make sense

I deleteted the following because the numbers simply do not add up. The muzzel velocity was 660m/s, so 10 seconds should give about 6600m, or 20,000 ft. Worse, the shell seems to speed up as the height and angle is increased. Tuntable (talk) 03:32, 29 November 2011 (UTC)

The shell took 10.1 seconds to reach 5,000 ft (1,500 m) fired at 25° above horizontal, 15.5 seconds to reach 10,000 ft (3,000 m) at 40°, 22.1 seconds to reach 15,000 ft (4,600 m) at 55°.

Take a piece of paper and draw the lines at the degrees indicated. You will discover that at 25° the shell spends most of its time travelling horizontally and little vertically (i.e. long range at low altitude), wheras at 55° it spends most of its time travelling vertically (short range at high altitude). Hence at 25° it travels 11,831 feet in total in attaining 5,000 feet altitude (5000 / sin 25), while travelling 10,723 feet horizontally; and 18,312 feet in total in attaining 15,000 feet altitude at 55° (15000 / sin 55) while travelling 10,503 feet horizontally. This assumes the shell travels in a straight line whereas it actually travels in a parabola, the mathematics of which are beyond me, but the straight-line calculations are close enough. I have restored the original text. Rod. Rcbutcher (talk) 05:06, 29 November 2011 (UTC)

oops. Brain fart. Mind you, Sin 30° is 0.5, so one would expect roughly 10,000' after 10 seconds at 25°. Air resistance must be fierce. Tuntable (talk) 08:37, 29 November 2011 (UTC)

References