= incident angle: the angle between the source-target line and
a line normal to the skin surface
L = heat-loss factor
p = density, 1b/ft®
Cp = specific heat, Btu/ib-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 characteristi: of the blast wave in free air include a sharp rise to its peak positive 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 pusitive value and a
slow return to initial ambient pressure. The difference between the peak-positivetransient and initilal-ambient values is the overpressure. For the B-36 in Castle, this
was expressed empirically as:
1/3
AP = 31.3
R
logo (—) —0.88
wi/3
1/2
(6.3)
Where: AP = peak overpressure, psi
W =yield, lbs TNT equivalent
R
= Slant range, ft
( Ph ) i/2
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 pai.
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, veloc{ty —
the air movement behind the shock front. The equation used to predict material velocity
WaB:
_
AP
ap \~142
Where: u = material velocity, ft/sec
&, = speed of sound at measurementaltitude, ft/sec
AP = peak overpressure, psi
P), = initial ambient pressure at measurement altitude, psi
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