09-05-2007, 08:06 AM
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#128 (permalink)
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Military Professional
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Scotch taster
Join Date: 08-06-03
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I've found some references to the stereoscopic and coincidence range finders
Quote:
From The M1A1 Tank: Its Role In The Marine Corps
The M-60A1 has a coincidence range finder that requires the
tank commander to manually crank the superelevation on the
gun tube, until the double image of the target is brought
together or zeroed-out, much like a pair of binoculars. The
problem with this system is that it is time consuming and
the tank commander can over-crank the target. The existing
range finder is more affected by temperature, moisture and
needs constant adjustments. A well trained crew can get a
round on target at 2000m, or closer, in approximately 7 to
10 seconds.
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Quote:
From M48 Patton
When first deployed, the M48-A3 had for the 1960s a state-of-the-art fire control system. At the time computers were mechanical, and range to the target was provided by a stereoscopic range finder, which functioned similarly to a 35mm camera. An end-box on each side of the turret exterior held a prism-type mirror. Turning a hand-crank on the range finder would pivot these mirrors until the double-image in the range finder merged. As the distance between the mirrors is exactly known, a little trigonometry provided the range (in meters) to the target. This information was displayed on a range indicator, and also fed to the ballistic computer by a rotating shaft. The ballistic computer was a collection of gears and cams--nothing was solid-state--which had a handle so that the gunner could select the type of ammunition that was to be fired. Each round had a different muzzle velocity, and therefore the computer had a different cam for each type. The computer would take the range data, merge it with the velocity data, and via a set of rotating shafts, supply this information to the gun's super-elevation mechanism, resulting in the gun being elevated above the gunners line of sight sufficiently for the round to overcome the downward pull of gravity on its way to the target. The gunner's sight however remained locked onto the target.
A good crew in Europe was able to put the first round on target 90% of the time, but this required excellent teamwork and communication on the part of the entire crew. In peacetime qualification, it was possible to stop from a speed of 20 mph, acquire the target, and get off a first round kill at 2,000 yards in seven seconds.
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For the Indians in defence and hull down, they should've already had the ranges marked and saved themselves 3-5 seconds.
FAS also goes on to explain that the range finder is useless when dealing with short ranges
Quote:
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This precision fire control system was almost irrelevant in Vietnam where typical engagement ranges could be measured more reasonably in feet than in yards. So in Vietnam it was common to take the gunner out of the turret and put him on the back deck with an M16 or M79 for close-in protection. This also afforded him some protection from mines, and indeed the tank commander and loader often rode on the turret roof or the hatch lips when mines were expected. The TC laid the main gun by eye, and fired using the commander's override control or a lanyard to the manual trigger on the main gun.
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__________________
Chimo
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