Zero gyro shooting

[TorpX]

Dignan,

I'm not sure whether you are using a scientific calculator or something else. Any dedicated calculator should have a degree mode. If not it would be computing in radians. Check this by trying this:

sin 90 = 1 and arcsin 1 = 90 [degree mode]

sin (3.1415927/2) = 1 and arcsin 1 = 1.570796... [radian mode]

[pi radians = 180 degrees]

Be careful about the track angle, intercept angle and the AoB. They are all different angles. IMO, the track angle is less confusing to use. This is a good way to calculate the Lead Angle:

La = arctan((Vt sin Ta)/(Vp + Vt cos Ta))

where
Vt is target speed,
Vp is torpedo speed
Ta is track angle

or, if you must use radians and convert:

Ta1 = Ta * (pi/180):
La1 = arctan((Vt sin Ta1)/(Vp + Vt cos Ta1)):
La = La1 * (180/pi)

There are diagrams which show the geometry of the set-up at the start of the Algebraic Firing Solution thread.

[I didn't get the right answer when I tried Pisces formula. Either he left something out or I'm fouling it up tonight.]

[Dorjun Driver]

Yeah, the intercept angle is simply 180-track angle (in degrees) or 3.1416-track angle (in radians). See complete diagram below—when I submitted the original post, I was still into the whole brevity thing.

[Dignan]

Originally Posted by Dorjun Driver

when I submitted the original post, I was still into the whole brevity thing.

"The Dude abides"

Thanks for the new diagram. Just for my own edification, in your new diagram, the target AOB at the point of impact = the track angle, correct? And the Intercept angle is formed by the target course and your torpedo track course, correct?

[Dorjun Driver]

That's a big ten–fore, Dignan.

[BigWalleye]

Small quibble on nomenclature: In SLM-1, the Submarine Torpedo Fire Control Manual (http://www.hnsa.org/doc/attack/index.htm), what you are referring to as the "track angle", (theta sub track on your diagram) is designated the "torpedo track angle". This is distinct from the track angle, which SLM-1 defines as "The angle at the point of intercept target ships course and the submarine's course measured to port or starboard of the target ship's bow toward the submarine. Symbol: Ta." That is, track angle, as used in the WW2 USN and in many first-person accounts, is relative to the submarine's course, not the torpedo's course. Using the two interchangeably might cause confusion to someone reading first-person accounts or patrol reports.

[Dorjun Driver]

Correct. The first diagram represents a special case where they are the same. And indeed, the second diagram is mislabeled. Thanks for the heads up.

[BigWalleye]

The formula in your OP is correct (IMAO!), or at least agrees with my own analysis. It produces results which agree closely - but not exactly! - with the results shown on Plates XVII and XVIII in SLM-1. There are small differences, usually less than 1 degree, which I think are due to corrections for parallax and what SLM-1 calls "torpedo advance" - the distance the torpedo travels before it settles on its gyro-dictated course. It is interesting that the equation in your OP does not appear anywhere in SLM-1, and that the method used to calculate the curves of Plates XVII and XVIII is not specified either.

[Dignan]

Originally Posted by TorpX

Dignan,

I'm not sure whether you are using a scientific calculator or something else. Any dedicated calculator should have a degree mode. If not it would be computing in radians. Check this by trying this:

sin 90 = 1 and arcsin 1 = 90 [degree mode]

sin (3.1415927/2) = 1 and arcsin 1 = 1.570796... [radian mode]

[pi radians = 180 degrees]

Be careful about the track angle, intercept angle and the AoB. They are all different angles. IMO, the track angle is less confusing to use. This is a good way to calculate the Lead Angle:

La = arctan((Vt sin Ta)/(Vp + Vt cos Ta))

where
Vt is target speed,
Vp is torpedo speed
Ta is track angle

or, if you must use radians and convert:

Ta1 = Ta * (pi/180):
La1 = arctan((Vt sin Ta1)/(Vp + Vt cos Ta1)):
La = La1 * (180/pi)

There are diagrams which show the geometry of the set-up at the start of the Algebraic Firing Solution thread.

[I didn't get the right answer when I tried Pisces formula. Either he left something out or I'm fouling it up tonight.]

Ah, I think I see my mis-step. I was failing to convert the final La result into radians too. I converted the input (Ta in your formula above) to radians but not my final La output. Regarding my calculator, its something I downloaded for free on my phone. It's possible the person who made it did not do it correctly or did not include a way to automatically convert to radians. Some of them are better than others.

Thanks a lot. I'll try this tonight. If it doesn't work I"ll probably just go back to drawing it out on the nav map. Not that big of a deal. I try to remind myself that somewhere under all this putzing around with mods and formulas and stuff there's a game to be played.