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Project 1.4 - Free Air Pressure Measurements at Altitudes - Lt. Col. J.A. Fava
OBJECTIVE
The objective of Project 1.4 was to obtain basic free air peak overpressure measurements vertically above an air burst megaton weapon,
Information was sought covering the range of 20 psi to 1 psi.
This data
was needed to further the study of the effect of altitude on the propagation
of the shock wave so that safe ranges for delivery aircraft could be specified more accurately.
INSTRUMENTATION
Twelve parachute-borne pressure-instrumented telemetering canister,
were deployed in a vertical array above intended ground zero.
of altitudes at burst time was 930 feet to 33,560 feet.
The range
The large
horizontal bombing error precluded the canisters being in the range of
primary interest.
RESULTS
All twelve canisters telemetered useful data. Ten of the twelve
were in the "free air" (regular reflection) region, and two were in the
mach reflection region below the triple point path.
The assumption MkTLL.
whiten::«-: optimum agreement between measured and computed
peak overpressures, and with this assumption the r.m.s. percentage
deviation between measured and computed values is 7%, which is considered
highly satisfactory for measurements of this type.
However, if lower
estimates of the actual yield obtained by other methods are confirmed, the
higher apparent yield obtained from these blast pressure measurements will
indicate a need for revision of current methods of calculating the effects
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of altitude on blast overpressures,
Measurements of the amplitude and time
of arrival of the reflected shock were obtained, but because of the large