Quote:
Originally Posted by Obltn Strand
Range is definetly not irrelevant when shooting long distances. It takes appox. 8 minutes for TI to reach 14 km. Ship traveling say 7kts covers distance of 1680 meters during that time. So ignoring distance is a definite miss.
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Actually, range is irrelevant with 0 degree gyro angle shots. If you have the AOB and speed correct, the torpedo will hit where you aim it.
Let's assume torpedo speed 30 knots, target speed 10 knots, 90 AOB at torpedo impact.
If range (to impact) is 1500 meters, you'd have to lead the target by 500 meters (target moves at 1/3 speed of torpedo). If the range (to impact) is 3000 meters, you have to lead it by 1000 meters (target moves at 1/3 speed of torpedo). In both cases, the lead angle is clearly the same (about 18,5 degrees with this torpedo/target speed ratio).
Even with AOB not equal to 90, the aiming point will be independent of range. You can see this easily by drawing a torpedo course and several target courses (parallel to each other) at different ranges. If you measure torpedo time to hit and calculate the distances each ship would move along its course during that time, you will see that all aiming points are on the same line. The lead angle does not depend on range. Every triangle formed by torpedo course, target course and aiming line is similar.
With anything else than 0 degree gyro angles torpedo tube parallax and torpedo movement before it turns to the correct heading will cause error. Higher gyro angles and shorter distances will cause a greater error in torpedo heading.
Edit: Range of course makes a difference in the error margin you have. If, for example, at 1000 meters, a ship covers 6 degrees in your periscope, this means your solution may be off by 3 degrees in either direction (assuming you aimed at the center of target). At 6000 meters range, the same ship would only cover 1 degree, allowing you an error margin of only 0,5 degrees in either direction. Thus, long distance shots are only possible with a very accurate speed and AOB/course solution.
Edit 2: Actually, even 0 degree gyro angle shots have torpedo tube parallax because of the aiming lead angle. Assuming a 10 degree lead angle and 30 meters between periscope and tube door, this amounts to an error of 5 meters or so in torpedo hit location. I'm not sure if the TDC actually corrects this error, but if it does, TDC range setting does have an effect on very long range shots. The correction for a 5 meter error at 500 meters would be 0,57 degrees, at 4000 meters it would be 0,07 degrees. So setting the TDC at 500 meters or 4000 meters would cause a 0,5 degree difference in torpedo path (again, assuming the TDC actually takes this error into account). At 4000 meters a 0,5 degree error in torpedo path would cause a 35 meter error in hit location.
This error is only relevant if the TDC is set for a very short range and the range to target is very long. In any case, the 0 degree gyro parallax error is much smaller than errors caused by large gyro angles and bad range settings, because the torpedo might well take a couple of hundred meters to turn towards the correct heading.