Biomedical Engineering Reference
In-Depth Information
The supersonic pneumatic gun was also tested to determine velocity
repeatability using the steel shim discs as the diaphragm valve (Figure 54).
Using a sample size of fourteen, the standard deviation was calculated to be 46
ft/s. Average velocity was 1416 ft/s, with all values falling within 8% of the
average.
Steel Disc Speed Distribution, 0.001" Thickness
1600
1400
1200
1000
800
600
400
200
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Sample Number, n
Reproduced with permission. Copyright retained by Inderscience Publishers.
Figure 54. Velocity Distribution for Steel Shim Discs.
3.6. Experimental Data Collection from Supersonic
Pneumatic Gun
The maximum velocity achieved with the subsonic pneumatic gun was
812 ft/s, significantly lower than the desired supersonic velocities of over 1100
ft/s. Several approaches were considered to reach supersonic projectile
velocities, including the use of gases other than air, such as helium, and the
use of a CD nozzle. It is believed helium would have allowed for supersonic
velocities based on the higher speed of sound constant in the gas. The
analytical model (Ayars and Buchholtz, 2004) predicts velocities over 2500
ft/s can be achieved with the use of helium as a propellant gas, as opposed to
air (Figure 55). To calculate this, Eq. 1 and Eq. 2 were solved at various
pressures with the properties of helium in place of air. The use of helium was
avoided in this study because of its high relative cost, potential safety hazard,
and increases susceptibility to leaking. Although pressures were not recorded
with the supersonic pneumatic gun, velocities of up to 1488 ft/s were recorded
