i = incident angle: the angle between the source-target line and
a line normal to the skin surface
L = heat-loss factor
p = density, lb/ft
Cp = specific heat, Btu/lb-F
t = skin thickness, feet
Similar relationships were established for the B-47 tests. In addition to the theoretical calculations above, thermal effects on certain critical panels were determined by
experimental furnace testing. The limiting thermal response for the B-36 was a 400 F
rise in the 0.020-inch magnesium hat panels of the elevator. For the B-47, the critical
thermal response was a 370 F rise in the 0.020-inch aluminum skin of the ailerons.
The characteristic: of the blast wave in free air include a sharp rise to its peak posi-
tive pressure (the shock front), followed by a relatively slow decrease through the initial
ambient value to a minimum of approximately a third of the peak positive value and a
slow return to initial ambient pressure. The difference between the peak-positivetransient and initial-ambient values is the overpressure. For the B-36 in Castle, this
was expressed empirically as:
1/3
‘
AP = 31.3 V— [18 (<3) -0.88 1/2
R
wis
(6.3)
Where: AP = peak overpressure, psi
W =yield, ibs TNT equivalent
R
= Slant range, ft
(mm)’”
Pb 4b
p = air density, slugs/ft®
a = speed of sound, ft/sec
h = altitude of the measurement
b = burst altitude
Equation 6.3 was used only for overpressures less than 2 psi. Both equations 6.1 and
6.3 were derived from limited test data from previous operations.
The second important property of the blast wave is the material, or gust, velocity —
the air movement behind the shock front. The equation used to predict material velocity
was:
u=1.89a,
AP
——
“2B, (
ap \~1/2
{|7+6—
Ph )
Where: u = material velocity, ft/sec
%;, = speed of sound at measurementaltitude, ft/sec
AP = peak overpressure, pai
Py = initial ambient pressure at measurement altitude, psi
14
(6.4)