Zero gyro shooting

[Dorjun Driver]

This is the quick and not–so–dirty method I use. I've found it quite handy when the tactical situation gets chaotic.

Plug the formula into your fx-5000F or smart phone and Bob’s your uncle. Heck, grab a pack of Lucky’s, a cup a joe, whip out the old slip-stick and do it old school!

http://imageshack.us/a/img62/2599/torpedosolutionsimple.png

Don't let the trigonometry intimidate you. After a couple of patrols you may find yourself solving this in your head.

I hope you find it useful.

[Carrollsue]

Yep, that's it:yeah::yeah::D

[fireftr18]

Thanks for all the work. :know: :salute:

[TorpX]

I see someone else has been putting their high school geometry to good use. :up:

I like your diagram there. I assume the " fx-5000F " is your calculator. I have used my TI-85 very successfully since my SHCE days, but now, every time I want to add something to it, I have to find something to delete. :-?

[Dorjun Driver]

I see someone else has been putting their high school geometry to good use. :up: .
.
.


There are some interesting hacks one may use to eliminate the above trig functions altogether. But seeing as this formula is only executed a couple of times per hour, the effort to include them far outweighed their utility.:D

[Dignan]

Hey Dorjun. Do you know if the "asin" function is the same as "arcsin"? I'm trying to replicate your formula in a smartphone calculator and it only has an asin function. I'm not getting the correct solution in my tests and I'm wondering if this is why. Math was never my strength.

EDIT: another question... I am building my formula using letters for my variables. V for ship velocity, T for Torp speed. This seems to work fine but for track angle do I need to attach some trig function so the calculator knows its an angle and not a quantity? I've just been using "A" for track angle but I don't know if the formula is understanding this as an angle. Is this my problem by chance?

[Pisces]

Asin, arcsin, sin with superscript -1 aka inv(erse) sine, all means the same function. It calculates an angle that corresponds with the slope of a vertical edge divided by the length of the sloping side (hypotenusa) in a right angled triangle. Though it can also be used with triangles that have no right angle (90 degrees) in them. The 'slope' must have a a value between -1 and 1, or else the angle cannot be calculated. No butts, no ifs, it can't!

In everyday household uses, the sine/cosine/tangent functions are calculated on degrees. As such the reverse kind of function: asin/acos/atan result in degrees. But most scientific calculators also have an option make them use angles in radians. A radian is the angle made when you wrap the radius of a circle around the circumference. Radians are a big thing in engineering and science. It's 57.29577951 degrees, or 180 degrees divided by Pi. 2 Pi radians make a full circle. On Casio calculators there should be a small 3 character abreviation in the top of the display: deg for degrees, rad for radians and gra for gradians (http://en.wikipedia.org/wiki/Gradian). Gradians are a big thing in surveying.

To test your calculator for degree or radian mode: 0.707 asin should result in near 45 degrees, or 0.785398163 radians (=Pi/4), or 50 gradians (90 degrees angle is 100 gradians. The French trying to be funny there.)

So that could be the cause for unexpected results from the formula. Or the order of precedence in arithmetic: multiplication/division precedes adding/subtracting.

[Carrollsue]

Asin, arcsin, sin with superscript -1 aka inv(erse) sine, all means the same function. It calculates an angle that corresponds with the slope of a vertical edge divided by the length of the sloping side (hypotenusa) in a right angled triangle. Though it can also be used with triangles that have no right angle (90 degrees) in them. The 'slope' must have a a value between -1 and 1, or else the angle cannot be calculated. No butts, no ifs, it can't!

In everyday household uses, the sine/cosine/tangent functions are calculated on degrees. As such the reverse kind of function: asin/acos/atan result in degrees. But most scientific calculators also have an option make them use angles in radians. A radian is the angle made when you wrap the radius of a circle around the circumference. Radians are a big thing in engineering and science. It's 57.29577951 degrees, or 180 degrees divided by Pi. 2 Pi radians make a full circle. On Casio calculators there should be a small 3 character abreviation in the top of the display: deg for degrees, rad for radians and gra for gradians (http://en.wikipedia.org/wiki/Gradian). Gradians are a big thing in surveying.

To test your calculator for degree or radian mode: 0.707 asin should result in near 45 degrees, or 0.785398163 radians (=Pi/4), or 50 gradians (90 degrees angle is 100 gradians. The French trying to be funny there.)

So that could be the cause for unexpected results from the formula. Or the order of precedence in arithmetic: multiplication/division precedes adding/subtracting.

:har: OMG….you took me back 45years to Trig class, with me with the huh look on my face!!:O:
Thanks:yeah:

[Dignan]

Asin, arcsin, sin with superscript -1 aka inv(erse) sine, all means the same function. It calculates an angle that corresponds with the slope of a vertical edge divided by the length of the sloping side (hypotenusa) in a right angled triangle. Though it can also be used with triangles that have no right angle (90 degrees) in them. The 'slope' must have a a value between -1 and 1, or else the angle cannot be calculated. No butts, no ifs, it can't!

In everyday household uses, the sine/cosine/tangent functions are calculated on degrees. As such the reverse kind of function: asin/acos/atan result in degrees. But most scientific calculators also have an option make them use angles in radians. A radian is the angle made when you wrap the radius of a circle around the circumference. Radians are a big thing in engineering and science. It's 57.29577951 degrees, or 180 degrees divided by Pi. 2 Pi radians make a full circle. On Casio calculators there should be a small 3 character abreviation in the top of the display: deg for degrees, rad for radians and gra for gradians (http://en.wikipedia.org/wiki/Gradian). Gradians are a big thing in surveying.

To test your calculator for degree or radian mode: 0.707 asin should result in near 45 degrees, or 0.785398163 radians (=Pi/4), or 50 gradians (90 degrees angle is 100 gradians. The French trying to be funny there.)

So that could be the cause for unexpected results from the formula. Or the order of precedence in arithmetic: multiplication/division precedes adding/subtracting.

:hmmm: <-- is my face right now.:haha: I think I am beginning to understand what you are saying. I'm going to re-read this later and try to digest. Thanks for the explanation. So what I've done is plug this formula by Dorjun into an app called MagiCALc. It's a scientific calculator for the iphone. Here's what I've got.

Lead Angle = asin (V sin A / (V ^ 2 + T ^ 2 - 2VT cos A) ^ 1/2)
V= Target speed
T= Torpedo Speed
A= Track angle/Intercept angle.

The program automatically recognizes my variables and asks for input. When I input the following values for each as a test...

V(Target speed) = 9
T (Torp speed) = 30
A (Intercept angle) = 75

...it spits out (= -0.11)
I take this to mean an 11 degree lead angle. Is that how I should be doing this?

I tried it with a different lead angle variable again to be sure.
V(Target speed) = 9
T (Torp speed) = 30
A (Intercept angle) = 135

and it spit out (=0.02). or a 2 degree lead angle
That doesn't seem right to me. Can anyone see what I've done wrong here? Is my formula off? Do I need to make the calculator see my output "Lead Angle" as an angle and not a straight number value or something?

Pisces, thanks again for the trig refresher. While I love playing this game, this has reminded me why I was a "social science" person.

[Dorjun Driver]

:hmmm: <-- is my face right now.:haha: I think I am beginning to understand what you are saying. I'm going to re-read this later and try to digest. Thanks for the explanation. So what I've done is plug this formula by Dorjun into an app called MagiCALc. It's a scientific calculator for the iphone. Here's what I've got.

Lead Angle = asin (V sin A / (V ^ 2 + T ^ 2 - 2VT cos A) ^ 1/2)
V= Target speed
T= Torpedo Speed
A= Track angle/Intercept angle.

The program automatically recognizes my variables and asks for input. When I input the following values for each as a test...

V(Target speed) = 9
T (Torp speed) = 30
A (Intercept angle) = 75

...it spits out (= -0.11)
I take this to mean an 11 degree lead angle. Is that how I should be doing this?

I tried it with a different lead angle variable again to be sure.
V(Target speed) = 9
T (Torp speed) = 30
A (Intercept angle) = 135

and it spit out (=0.02). or a 2 degree lead angle
That doesn't seem right to me. Can anyone see what I've done wrong here? Is my formula off? Do I need to make the calculator see my output "Lead Angle" as an angle and not a straight number value or something?

Pisces, thanks again for the trig refresher. While I love playing this game, this has reminded me why I was a "social science" person.


What Pisces said. It appears your calculator wants radians as input. Sooo:

asin (V sin RADIANS(A) / (V ^ 2 + T ^ 2 - 2VT cos RADIANS(A) ^ 1/2)

Or something to that effect. The output of asin(whatever), may be considered a scalar. But it ain't.

Your inputs from above should spit out 17.4 and 9.9 respectively.

Now. Who's working on the Q and D spread calculator? :subsim:

[Dignan]

What Pisces said. It appears your calculator wants radians as input. Sooo:

asin (V sin RADIANS(A) / (V ^ 2 + T ^ 2 - 2VT cos RADIANS(A) ^ 1/2)

Or something to that effect. The output of asin(whatever), may be considered a scalar. But it ain't.

Your inputs from above should spit out 17.4 and 9.9 respectively.

Now. Who's working on the Q and D spread calculator? :subsim:

Ok, thanks. I'll see if I can figure out how to switch it to Radian output. :hmmm:

Before I try, doesn't putting "sin" before my A make it read that input as radians?

[Dorjun Driver]

No no no! Just use the radians() function to convert your degree input to the format your calculators sin()/cos() functions want.

While hell is breaking loose we don't want to be dividing stuff by transcendental numbers! Next thing you know, you'll want to compute just how close you can shave that shot. Anywhere in the engine room will be fine. Honest.

[Dignan]

No no no! Just use the radians() function to convert your degree input to the format your calculators sin()/cos() functions want.

While hell is breaking loose we don't want to be dividing stuff by transcendental numbers! Next thing you know, you'll want to compute just how close you can shave that shot. Anywhere in the engine room will be fine. Honest.

Ha! 10-4 on that. The calculator I'm using removes the parentheses from the sin(A) and Cos(A)when I try to save it. That seems to be my problem. I'll putz with it some more. Thanks

[Pisces]

To switch between degrees and radian and gradians on a Casio you have to press the mode button and then 4, 5, or 6. See the legend under the display.

Your inputs from above should spit out 17.4 and 9.9 respectively.Agreed. If you get a number like 0.11 as a result for degrees, then it will infact be 0.11 degrees, NOT 11.

If it was a logarithmic sliderule then that decimal point fudging might make sense. But that method doesn't hold with a digital scientific calculator.

[Pisces]

Oh yeah, I forgot to add:

Dorjun Driver's formula can be significantly simplified if you know the AOB:

Deflection = arcsin ( Vship * sin AOB / Vtorpedo)

[Dorjun Driver]

The object of the exercise was to develop a solution with as little information about the target as possible, i.e., speed. All other data are up to the sub driver.

[Dignan]

Oh yeah, I forgot to add:

Dorjun Driver's formula can be significantly simplified if you know the AOB:

Deflection = arcsin ( Vship * sin AOB / Vtorpedo)

When you say AOB for this formula do you mean the AOB Of the target at the given moment you compute the solution or do you mean the intercept/track angle formed by the sub course and target course? I guess I dont understand the difference between aob and track angle in this situation.

EDIT: I continue to have a hell of a time getting this formula to work on my scientific calculator. It just doesn't want to recogize my A input as radians. I've tried everything. What would I have to multiply my angle input (A in this case) by to convert it to RADIANS within the formula? Maybe I'll have to do it that way. For instance:

Lead Angle = asin (V sin (conversion value for Radians)A / (V ^ 2 + T ^ 2 - 2VT cos (conversion value for Radians)A) ^ 1/2).

what would this value have to be? pi/180? A(pi)/180? A*(57.29577951 / pi), as mentioned before by pisces? I appreciate all the help thus far.

[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.:sunny:

http://img132.imageshack.us/img132/8963/torpedosolution.png

[Dignan]

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.

[Dignan]

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

"The Dude abides" :up:

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:D, 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.

[Dorjun Driver]

No parallax, no reach, and no turning radius. KISS:yep:

[BigWalleye]

Since it would take far better eyesight than mine to set the firing bearing to within less than one degree, your equation is accurate enough for me. My point was that SLM-1 was the official USN publication on the subject, the one R/L sub officers were taught from, and that their plots, with Heaven only knows what unspecified second- and third-order refinements, agreed with your analysis to an accuracy better than we can use.

Although I prefer KISMIF.:)

[Dignan]

What Pisces said. It appears your calculator wants radians as input. Sooo:

asin (V sin RADIANS(A) / (V ^ 2 + T ^ 2 - 2VT cos RADIANS(A) ^ 1/2)

Or something to that effect. The output of asin(whatever), may be considered a scalar. But it ain't.

Your inputs from above should spit out 17.4 and 9.9 respectively.

Now. Who's working on the Q and D spread calculator? :subsim:
Ok, I think I'm close to cracking this. I figured out the radian functions on my calculator are a different set of buttons with the "degree symbol" after it, ironically (see below)

La = asin˚ (V sin˚ A / (V ^ 2 + T ^ 2 - 2VT cos˚ A) ^ 1/2)

V=target speed
T=Torp speed
A=track angle

When I input the following like before
V=9
T=30
A=75
...I get 15.5 for a lead angle. Not the 17.4 Dorjun said I should get but closer. Anyone see any flaws with this formula now that the trig functions are set to radians?

[Dorjun Driver]

I don't know what to tell ya. Using your formula above I keep getting 17.4. I could be entering the same wrong numbers repeatedly, but...:hmmm:

[BigWalleye]

Maybe the point of confusion is that the intercept angle in Dorjun Driver's original diagram is NOT the track angle, but 180-the track angle. And what is marked as "theta sub track" in DD's second diagram is actually the intercept angle, again 180-the track angle. Track angle - whether ownship track angle or torpedo track angle - is equal to the AoB at the point where the tracks intersect, either ownship track and target track or torpedo track and target track. In either case, the intercept angle is 180-(AoB at intercept). I'm pretty sure Dignan will get the correct result if he uses 180-Track angle in his calculations. And DD's formula is correct for intercept angle not AoB and not track angle.

BTW, I believe that what is marked as "theta sub torpedo track" is in fact the torpedo track angle. It is only "theta sub track" which is on the wrong side of ownship track line.

Or I'm trying to figure this out too late at night and have it all wrong....:)

"I'm getting too old for this ****"! - Danny Glover, Lethal Weapon

Further clarification: Please see the diagram on Page 1-12, SLM-1.

[TorpX]

BW, you are right about the angles not being marked off right. The track angle should be taken from where the target is going to where the sub is. The torpedo track angle, TTa is not always the same as the track angle, Ta, but as this thread is titled "Zero gyro shooting", the TTa should be the same as the Ta. Trying to make use of formulas derived for zero gyro shots in non-zero gyro shots will likely lead to disappointment and frustration.


BTW, for this:
V=target speed
T=Torp speed
A=track angle

When I input the following like before
V=9
T=30
A=75

I get a lead angle of 15.05 deg.

[Dorjun Driver]

Or I'm trying to figure this out too late at night and have it all wrong....:)

Too late? Way too early my friend, way too early. Late or early, I think my second diagram is correct.

Whatever the correct nomenclature, if the target is steaming along the green line, and you fire your torpedo when the target arrives at the intersection of the green and blue lines, and the torpedo travels down the red line, the torpedo and target will meet at the intersection of the red and green lines. Much to the target's chagrin.

And for the record, using “the formula” as written, I achieve accuracy sufficient to put my torpedoes pretty much where I aim—under the stack, 5’ below indicated draft—every shot. Discounting duds and deep runners, I’ve yet to use more than one fish to sink ships displacing, up to and including, 8150 tons. So there.

TorpX, I'm still getting 17.4 degrees. Perhaps I transcribed my "working" Casio/Excel formula improperly. I'll check into it.

If I were Bill O'Reilly, I'ld be tempted to let this whole thing go with a simple "You can't explain that!" But I'm not, so I won't.:nope:

TMC/RSRDC/OTC

[Dorjun Driver]

I can find nothing amiss on either platform.

If anyone knows how to attach an Excel sheet, I'll be happy to share.

[Dignan]

[QUOTE=BigWalleye;2022126] In either case, the intercept angle is 180-(AoB at intercept). I'm pretty sure Dignan will get the correct result if he uses 180-Track angle in his calculations. And DD's formula is correct for intercept angle not AoB and not track angle.

QUOTE]

That did it :yeah:. When I subtract my angle input from 180 i get 17.4 also. To be clear, the angle I am using in my formula is what DD calls "track angle" in his second diagram, the angle formed by the intersection of my course and the target course. So to make this work we need the angle on "the other side" of that intersection, right? Hence subtracting from 180.

Dorjun, "prefered nomenclature" aside, that seems to be the way to go. "That" being using the angle formed by sub course and target course, subtracted from 180. I appreciate this guide. It's something I've been trying to find for a while.

Thanks BigWalleye and thanks DD, Pisces and TorpX for guiding my torps in the right direction throughout this. I've been "Mozarting" the heck out of this over the past few days (Mozarting is when you get obsessed with finishing a project or solving a problem and block out all other distractions and influences in your life...not good). Now hopefully I can actually play the dang game. :ping:

[BigWalleye]

Dorjun Driver,

1. The diagram in your OP is a correct representation of the trigonometric problem you were addressing.

2. The equation in your OP is a correct solution for the trigonometric problem illustrated in the diagram.

3. The angle labeled ‘theta sub intercept’ in your OP diagram is the intercept angle and inserting a value for that angle in the final equation of your OP will yield a correct solution for the deflection angle.

4. The angle labeled ‘theta sub intercept’ in your OP diagram is not the ‘track angle’ (aka Ta, aka A, aka ‘AoB at intercept’) per SLM-1, Page 1-12. It is the supplement of that angle and equals (180-Ta).

5. The angle labeled ‘theta sub Track’ on your second diagram is equivalent to the angle labeled ‘theta sub intercept’ in your OP diagram. It is on the same side of ownship track. It is not the track angle Ta, at least not as SLM-1 defines the term. Please see the diagram on Page 1-12.

6. The angle labeled ‘theta sub Torpedo Track’ is equivalent to TTa, the “torpedo track angle’” as defined in SLM-1, Page 1-12. The intercept angle for the torpedo track. ‘theta sub intercept’ is the suplement of that “torpedo track angle” and equals 180-TTa. Inserting that intercept angle in the last equation of your OP diagram will yield a correct result for the deflection angle.

7. The OP diagram provides a correct solution for a zero-gyro-angle torpedo run. Your second diagram provides a correct solution for firing at small non-zero gyro angles.

8. Except for the mislabeled ‘theta sub Track’ in your second diagram, which is not essential to the calculation of deflection angle in the non-zero-gyro case anyway, I believe everything you have posted is correct.

9. I believe Dignan’s incorrect results came from confusing Ta and intercept angle. His results are consistent with substituting track angle into your equation in place of the (correct) intercept angle. The error was not yours.


Comparing the deflection angles generated from your equation with deflection angles picked off Plate XVIII from SLM-1 yields small discrepancies, which increase somewhat at higher target speeds. I had always assumed that Plates XVII and XVIII in SLM-1 were accurate. The text implies that they include various correction factors and that they are substantially the results generated by a WW2-vintage TDC. The text does not indicate directly how the curves were generated, or what factors were included in the calculations. I had also assumed that the curves were somewhat more accurate than a first-order trigonometric analysis, such as the one in your OP. Apparently, my assumptions were incorrect. I would appreciate if you could tell me why the SLM-1 data are not to be trusted. I do agree that a first-order analysis is perfectly adequate for our purposes.

(Edit: Sorry, I tried to post data for comparison from an Excel spreadsheet and it didn't post properly. I'll be happy to provide the data some other way.)

Slightly OT: Living in the upper Midwest, I made my last post after 11:00 CST. For this 70-year-old, that is well past my normal bedtime. That’s why I made my comment about it being “too late at night....” and added the Danny Glover quote. Sorry if you mis-interpreted it.

[Dorjun Driver]

BigWalleye,

No, my apologies. My attempts at humor often fall short of the mark. Probably ‘cause I’m always up.

I don’t mean to imply the U.S. Navy is in error, just my Q&D formula works with great effect when time is short. It shouldn’t be too difficult to derive the curves shown in plates XVII and XVIII. I’ll give it a shot. After all, that’s why Stephen gave us Mathematica!:yeah:

[BigWalleye]

Q & D? Nah! I'd call it a neat little analysis. And even after 35 years as a engineer, not something I could do in this head!

"10 degrees. 15 if he's going fast." Now THAT is Q & D! (IIRC, actual words of a WW2 skipper describing how he set up deflection. Almost cetainly NOT what he actually did, although he may not have even been aware of his own instinctive adjustments.)

BTW, I have printed out tables, one for each torpedo speed, showing deflection angle for every 2.5 kts and 15 degrees AoB. Easy to interpolate on the fly. Accurate enough for my preferred tactic of normal approach to head-butting range.:)

I would really be interested to know if you succeed in reproducing the curves in SLM-1 and what parameters are included. Reluctant to attempt it myself. As it is, I find so many side issues to get involved in, I never seem to have enough time for the game!

[TorpX]

TorpX, I'm still getting 17.4 degrees. Perhaps I transcribed my "working" Casio/Excel formula improperly. I'll check into it.


I think the difference is because you designate your angles differently. When someone says "track angle", I use the track angle as per the USN. I keep to using it, and it has made my SH life much simpler. :) When you first posted your formula, it gave me the right answer, but I had to see how you marked the angle, first.



Comparing the deflection angles generated from your equation with deflection angles picked off Plate XVIII from SLM-1 yields small discrepancies, which increase somewhat at higher target speeds. I had always assumed that Plates XVII and XVIII in SLM-1 were accurate. The text implies that they include various correction factors and that they are substantially the results generated by a WW2-vintage TDC. The text does not indicate directly how the curves were generated, or what factors were included in the calculations. I had also assumed that the curves were somewhat more accurate than a first-order trigonometric analysis, such as the one in your OP. Apparently, my assumptions were incorrect. I would appreciate if you could tell me why the SLM-1 data are not to be trusted. I do agree that a first-order analysis is perfectly adequate for our purposes.

I took another look at plates XVII and XVIII. I then broke out my trusty TI-85 and set it to graphing my formula for lead angle using their parameters. The results, as near as I could see, looked close to what the plates showed, but not exactly. This puzzled me at first, but on closer thought, I think I know why.

We are solving a simplified problem, where no allowance is made for the distance between the torpedo tube and the periscope, and none for any launch delay, torpedo acceleration and such. Any delay or sluggishness of the torps would have the effect of increasing the deflection angle and could account for the discrepancy.



"10 degrees. 15 if he's going fast."

Speaking of Q & D, in WAR IN THE BOATS, the author mentions using a rule of thumb, "speed plus three". It certainly has the advantage of being simple, but I haven't tried it. :)

[BigWalleye]

Speaking of Q & D, in WAR IN THE BOATS, the author mentions using a rule of thumb, "speed plus three". It certainly has the advantage of being simple, but I haven't tried it. :)


Captain Ruhe wins the kewpie doll! For a straight shot, his rule-of-thumb is within one degree of the calculated result from 7 to 20 kts target speed. Agrees with SLM-1 up to 16 kts, too. Embarrassing (to me, anyway) but typical. We have been wrestling with this problem to find a correct analytical solution, applying the trig we learned years ago like this was a physics lab problem. But the guy with the eye at the periscope used a much simpler approach that, in the real world of a sub in combat probably worked just as well. I used to do engineering work for the Air Force. The fighter jocks would pull stuff like this, too.

[Dorjun Driver]

I believe I've found the "margin of error."
http://img26.imageshack.us/img26/9819/tubesv.jpg
If you look closely at the lower right–hand corner, there's moth.

And don't get me started about my TI Silent 700!

[BigWalleye]

Presuming that what you have pictured is a digital computer, there can be no margin of error. Digital devices either work or they don't. The programming can be wrong, but if the device works at all, it does exactly what it was programmed to do, every time.

Now, the TDC was an analog electro-mechanical device. It had plenty of room for error. A moth on one of the integrator plates could raise merry Hell. How they kept all the little balls and rollers aligned through a depth-charging is amazing to me.

But are you suggesting that Plate XVIII was created using a moth-eaten TDC?:)

[Dorjun Driver]

You'ld have to ask Grace about that.
http://img7.imageshack.us/img7/7331/graceos.jpg

[Dignan]

You'ld have to ask Grace about that.
http://img7.imageshack.us/img7/7331/graceos.jpg

Yikes

[BigWalleye]

IIRC, the moth caused the entire section to fail and go offline. QED.

Did you know Grace? (Excuse me, Admiral Hopper, sir...er, ma'am...er....)

[Dignan]

Moths or no moths...Grace or no Grace. I just wanted to post a little shot showing my success with DD's formula. This was from about 2300 meters. Fired two, one prematurely detonated and the other found it's mark, splitting the vessel in two. Thanks again Dorjun!

Target speed = 13
Torp speed = 30
As you can see in this pic, the Ta = 96 (after my formula subtracts it from 180 I get a lead angle of 22.4.) Right on the money.

Oh ya, if you hadn't figured it out, this is SH5. I switch back and forth between 4 or 5. SH5 has come a looooong way with all the mods. It's completely playable now.

http://www.mediafire.com/conv/d925c4f8cd0b04a6db299cec301fc9a39bbc777cce88814736 89146521c4aed26g.jpg

[Dorjun Driver]

Hey! I'm not that old!

Although, there was this one gal at NUSC. She was the lead for the MK-117 project, and I was doing acoustic analysis of the MK-48...

I'ld go on, but I'ld have to kill myself.:ping: And you and all you hold dear.

[BigWalleye]

I'ld go on, but I'ld have to kill myself.:ping: And you and all you hold dear.

Shame on you! That line's old and tired and been used too often by the guys who couldn't buy a ticket.

[Dorjun Driver]

Moths or no moths...Grace or no Grace. I just wanted to post a little shot showing my success with DD's formula. This was from about 2300 meters. Fired two, one prematurely detonated and the other found it's mark, splitting the vessel in two. Thanks again Dorjun!

Target speed = 13
Torp speed = 30
As you can see in this pic, the Ta = 96 (after my formula subtracts it from 180 I get a lead angle of 22.4.) Right on the money.

Oh ya, if you hadn't figured it out, this is SH5. I switch back and forth between 4 or 5. SH5 has come a looooong way with all the mods. It's completely playable now.


Well thank the Blessed Oliver Plunkett!

"Let's go Beanie Boy. Our job is done here."

[Dorjun Driver]

Shame on you! That line's old and tired and been used too often by the guys who couldn't buy a ticket.

Yeah, but grounders are so easy at this time of the morning. It is morning, isn't it?

[BigWalleye]

Oh ya, if you hadn't figured it out, this is SH5. I switch back and forth between 4 or 5. SH5 has come a looooong way with all the mods. It's completely playable now.



Figured with 30-kt torpedos you weren't USN. ATO not my cuppa joe.

[BigWalleye]

Yeah, but grounders are so easy at this time of the morning. It is morning, isn't it?

It is here. They turn the air on out there yet?

[Dignan]

Figured with 30-kt torpedos you weren't USN. ATO not my cuppa joe.

Ya, I prefer playing fleet boats but the graphics are stunning in SH5 and the gameplay is as good as SH4 now in my opinion. I do feel a sense of betrayal at times sailing around sinking allied ships, though. All in the name of recreation, right.

[BigWalleye]

Ya, I prefer playing fleet boats but the graphics are stunning in SH5 and the gameplay is as good SH4 now in my opinion. I do feel a sense of betrayal at times. All in the name of recreation, right.


Yup! That's a pretty chromy sewerpipe!:D

[Dignan]

Yup! That's a pretty chromy sewerpipe!:D

I know, I know. SH5 doesn't have the best reputation but there are about 3 or 4 must have mods that make it a good game.

[BigWalleye]

I know, I know. SH5 doesn't have the best reputation but there are about 3 or 4 must have mods that make it a good game.

Please post them. (Names that is!) I might give it a try just for the eyecandy. Thanks.

(Have we now gone OT? Waiting for the beadle.:))

[Dignan]

Please post them. (Names that is!) I might give it a try just for the eyecandy. Thanks.

(Have we now gone OT? Waiting for the beadle.:))

No problem. Here are what I would consider the basic "must haves". Install in this order. There are many, many others you'll probably want to pick up but these are the foundational mods you need.

[WIP] FX_Update by TDW.
http://www.subsim.com/radioroom/showthread.php?t=174511
- mostly improves effects but does include some bug fixes

[REL] Multiple UIs for SH5 with TDC
http://www.subsim.com/radioroom/showthread.php?t=166093
- Does too many things to list here. Basically fixes 90% of the bugs and unusable parts of the game, to include the broken stadimeter.
[WIP] IRAI (Intelligent Random AI)
http://www.subsim.com/radioroom/showthread.php?t=171973
- Makes the AI challenging (think TMO for SH5).

[TEC] SH5.exe patches to fix bugs and add functionality
http://www.subsim.com/radioroom/showthread.php?t=181433&highlight=TDW+Generic+Patcher
- fixes other broken aspects of game, like the hydrophone...that's a big one.

[BigWalleye]

Thanks, Dignan. You da man!:up: