Torpedo Data Computer: Difference between revisions

Revision as of 08:13, 12 January 2019

Revision as of 18:31, 18 April 2019

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===The problem of aiming a straight-running torpedo===

[[Image:FiringGeometry.png|noframe|thumb|Figure 2: Illustration of general torpedo fire-control problem]]

A straight-running torpedo has a [[gyroscope]]-based control system that ensures that the torpedo will run a straight course.<ref name="straight">Straight after an initial turn to course, as explained below.</ref> The torpedo can run on a course different from that of the submarine by adjusting a parameter called the gyro angle, which sets the course of the torpedo relative to the course of the submarine (see Figure 2). The primary role of the TDC is to determine the gyro angle setting required to ensure that the torpedo will strike the target.

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*The torpedo moves on a fixed course and speed

[[Image:Intercept.svg|noframe|thumb|Figure 3: The torpedo fire control triangle]]

As can be seen in Figure 2, these assumptions are not true in general because of the torpedo ballistic characteristics and torpedo tube parallax. Providing the details as to how to correct the torpedo gyro angle calculation for ballistics and parallax is complicated and beyond the scope of this article. Most discussions of gyro angle determination take the simpler approach of using Figure 3, which is called the torpedo fire control triangle.<ref name="clear"/><ref name = "wahoo"/> Figure 3 provides an accurate model for computing the gyro angle when the gyro angle is small, usually less than 30°.<ref name = SmallGyro>{{harvnb|COMSUBATL|1950|loc=&sect; "Theory of Approach and Attack", pp. 8-8, 8-9}}</ref>

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{{math|''θ''_Track}} is the angle between the target ship's course and the torpedo's course.

[[Image:DeflectionAngle.png|noframe|thumb|Figure 4: Deflection angle versus track angle and target speed ({{math|1=''θ''_Gyro = 0°}}).]]

A number of publications<ref name = OptimumTrackAngle>{{harvnb|COMSUBATL|1950|loc=&sect; "Theory of Approach and Attack", p. 8-9}}</ref><ref name="Clear2">{{harvnb|O'Kane|1977|p=303}}</ref> state the optimum torpedo track angle as 110° for a Mk 14 (46 knot weapon). Figure 4 shows a plot of the deflection angle versus track angle when the gyro angle is 0° (''i.e''., {{math|1=''θ''_Deflection=''θ''_Bearing}}).<ref name="track">Most work on computing intercept angles is done using track angle as a variable. This is because track angle is a strictly a function of the target's course and speed along with the torpedo's course and speed. It removes the complexities associated with parallax and torpedo ballistics.</ref> Optimum track angle is defined as the point of minimum deflection angle sensitivity to track angle errors for a given target speed. This minimum occurs at the points of zero slope on the curves in Figure 4 (these points are marked by small triangles).