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and I'd be interested in knowing more precisely how these estimates for velocities and gun life were obtained.
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Mar 31 17 1:40 PM
Programs for ballistic
calculations I had, were not good enough for those graphs.
I found too large
differences between available historical range tables and
So I started mine, with
possibility of placing different atmosphere parameters (pressure,
temperature, and calculation of density from those values, or density
on sea level put manually).
interesting, but not exact match
with historical range tables. A
bit to small descend angle could be explained by “flat earth” in
my model, but difference in max range will be less than 0.5 degree,
so I could add correction later. But striking velocity differences?
Interesting that I have
virtually identical flight time as in historical tables if I use the
same initial values (temperature for example)
Some differences are
inevitable, but how large differences are acceptable – so in other
words did I use correct formulas for drag calculations?
And what atmosphere
parameters were used for historical calculations in various
US usually temperature 90 F, air density could be
calculated a bit less than 1.16
UK usually temperature 70 F
Germany? Italy? France?
I need data to normalize
For pressure with height up
to 11 km I used those formulas
= static pressure (pressure at sea level) [Pa]
temperature (temperature at sea level) [K]
temperature lapse rate [K/m] = -0.0065 [K/m]
= height about sea
= height at the bottom of atmospheric layer [m]
= universal gas constant = 8.31432
acceleration constant = 9.80665
= molar mass of Earth’s air
= 0.0289644 [kg/mol]
for higher altitudes
equations , , and correspond to the altitude, pressure, and
temperature at the bottom of the stratosphere. The pressure at the
bottom of the layer is determined from the user provided inputs of
the pressure and temperature at sea level knowing that the altitude
at the bottom of the layer is 11 km
for temperature up to 11 km
0.0065 K per meter.
Drag force = 0.5 *
shell_const * air_density * projectile_cross_section *
I know there was Bill
Jurens article about numerical ballistic calculations, but I can’t
find it now. Can anybody help?
I have enough graphs based
on range tables only “more or less” accurate (actually less than
more), so I want to avoid initial errors in range tables.
And to make it comparable I
really need to normalize atmosphere conditions for all guns, to make
it I need range table with corrected values.
Corrections are not so
small. For example 20 degree F in temperature corresponds to
something between 800 to 1000 yards
difference in max range (depends on gun and max elevation of turret),
and in any medium range different hit angle and striking velocity.
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