FaT activation distance vs. TDC range - Q

[Keelbuster]

I've had a long-standing wonder about the FaT pattern activation setting. When you set the TDC range, that's the current range, and the TDC computes the course of the torpedo. The run-distance until impact of the torpedo will be shorter than the range set in TDC, because the range you set is the hypotenuse (at least for a 90 AoB shot). However, I fear the the FaT activation range is a real run distance and hence if you set the FaT range to the same setting as the TDC range, the pattern will always activate beyond the target. While this isn't a massive problem for shots that are close to 90 AoB (and you do want the pattern to activate slightly beyond the target so that it has the best chance for a hit on the first pass), it would be good to have a way to set the FaT activation so it would reliably be say...150-200m past the predicted impact point.

Does this make sense? Am I using the FaT wrong?

[RoaldLarsen]

I've always thought that the TDC range setting was range to impact point from firing point, not current range to target. If I'm correct, then you don't have the problem you thought you had about FAT run distances. If I'm incorrect, then perhaps I've been lucky with my manual targetting.

Actually, range shouldn't be one of the parts of the firing solution, should it? The determination of the correct firing angle is distance independent. What matters is target's course and speed, and the course and speed of the torpedo. The solution is the target bearing relative to torpedo course at time of firing.

Given this, there seems to be only two reasons to input a range:
1. to calculate expected run time, and
2. to set the initial leg length of a FAT torpedo.

[Mittelwaechter]

The TDC shows actual distance to target!

Checking the distance lets you choose the correct torpedo and speedsetting to hit the target. A target in 5400 meters distance at 90 AOB can't be hit with a G7e or a fast G7a.

And the constant update function shows - under certain circumstances - the target is travelling out of range when turning the periscope to AOA.

In close combat the distance setting is completely irrelevant.

For the FAT and LUT inicial turning point you'll have to calculate the travelling distance by youself and put it into the individual torpedo data setting above the tube indicator.

Hehe: now tell me - the turning point halves the laddern pattern (i.e. 800m) and makes the torpedo run 400 meters "on both sides" of the turning point? Or does it turn and starts to run 800 meters until it comes back?

[Hitman]

Actually, range shouldn't be one of the parts of the firing solution, should it?

Yes and no. For zero Gyro Angle shots you are more or less correct, but for angled shots the problem exists and the TDC will solve it based on the distance to target in the moment of shooting (Which is what you input in the TDC, and not distance to target in the moment of torpedo impact)

See this thread:

http://www.subsim.com/radioroom/showthread.php?t=121744

[RoaldLarsen]

Originally Posted by Hitman

Yes and no. For zero Gyro Angle shots you are more or less correct, but for angled shots the problem exists and the TDC will solve it based on the distance to target in the moment of shooting (Which is what you input in the TDC, and not distance to target in the moment of torpedo impact)

See this thread:

http://www.subsim.com/radioroom/showthread.php?t=121744

Thanks for setting me straight!

I had forgotten that the torpedo starts ahead of the bearing point, and that it needs to travel through an arc before moving straight to the target. Therefore the torpedo's course will be different from the bearing to impact point at time of firing. The amount of this deviation is a function of the distance to target at time of firing.

So let's see if I've got this correct. For firing a FAT torpedo:

First set the TDC for bearing to target, range to target, AOB and target speed, all as they are at time of firing. This will determine what the torpedo does before it starts its pattern run. Until then it acts just like a normal torpedo. Then set FAT controls as follows. (I know this is not the order of operations one will actually follow - I'll get to that later. Right now I'm just going through the controls in the order they affect the torpedo.)

Straight run determines the distance the torpedo will run at its initial gyroangle (as determined by non-FAT TDC settings) before it adjusts course to be perpendicular to target's course. If this initial gyroangle is not zero, then you should make sure the straight run distance is at least as long as the distance from firing point to expected impact point, otherwise the torpedo will start to turn to adjust course before reaching the target.

Once the torpedo has run its straight run distance, it will adjust course to be perpendicular to target's course as indicated by your AOB input. It will then run 1/2 of the distance indicated by the Leg setting. It will then turn 180 degrees and run the whole distance indicated by the Leg setting, and then turn 180 in the opposite direction. It will continue to run the whole Leg distance and make 180 degree turns in alternating directions until it runs out of power, or hits something.

The direction of the initial turn is indicated by the Second Gyroangle setting. Set Second Gyroangle to 90 Port or 90 Starboard to determine whether the ladder progresses in the direction of target's travel, or opposite it.

When you are actually setting up a shot you will not set these controls in the order in which they take effect. You will probably set them in an order something like this.

Second Gyroangle can be set as soon as you know whether target is moving left to right or right to left.

Leg can be set as soon as you know what else is around the target.

AOB and Speed can be set once you have made a couple of observations of the target. AOB will be correctly updated whenever you have a lock on target and TDC Manual Input is off. Bearing is set whenever you have a lock on target and TDC Manual Input is off.

Range must be determined just before you fire.

Since Straight Run length is dependent on the firing solution, an accurate calculation can only be done after all the other inputs have been made. For practical purposes this might be too late, so you may want to estimate the Straight Run distance just before setting the Range.

[Keelbuster]

I read all of your responses. And i got the sense that nobody knew the answer to my question: is the FaT range the same as the TDC range. Still, we're all gamers, and we're all probably drunk, so i sorta forgive you for being lazy and ignorant.

Anyway, perhaps more importantly, I've been away from this forum for a while because i didn't dig the sh4 vibe, and because my SH3 system bricked. Anyway, I'm moving up in the world and will be likely able to run SHV. I am really looking forward to it. I expect UBI romania to **** it up, but I also expect (hope maybe) that it will be workable as a community project. The SH3 project was insane. The game came so so far. It was awesome. Huge even. ****.

KB