09222017, 10:57 AM  #31 
Join Date: Feb 2005
Location: Berkeley, CA

Re: Binary propellant and Standard TL 8 guns?
The problem with solving for half velocity is that GURPS 1/2D range bears pretty much no relation to the actual range at which projectile velocity is halved.

09222017, 11:32 AM  #32 
Join Date: Aug 2004
Location: Austin, TX

Re: Binary propellant and Standard TL 8 guns?
Google docs are easy to share:
https://docs.google.com/spreadsheets...it?usp=sharing You can't edit it, but you should be able to duplicate it and then edit the copy. How it works: You put the bullet diameter in mm in cell C1, bullet mass (in grams) in C2, muzzle velocity in m/s in C3, and the bullet aspect ratio* in H1. The spreadsheet will take a guess for the coefficient of drag** and do a lot of math. Eventually, it will spit out the results in cells D6 to D9: 1/2d range and max range, for firing at a 10 degree angle (basically horizontal) and at a 45 degree angle (maximum possible range). It uses 400 rows to calculate the first 4 seconds of travel time in 0.01 second increments, and uses another 600 rows to calculate the rest of the flight time. deltaT for those rows is variable based on muzzle speed, and you can scale the deltaT by putting a value in F10 ("DelTFudge"). The deltaT is based on the flight time of the projectile in a vacuum, so it's usually longer than necessary and you can usually shorten the deltaT to get more precise results. By default, it calculates shots from 0 m above ground level, at 10 degrees and at 45 degrees. You can change the height and vary the angle with cells C5 and C4. Cells P1Z6 have some sample values for various projectiles, with the numbers for mass and muzzle velocity taken from wikipedia. Compared to GURPS standard, pistol bullets have roughly 2x the 1/2d range, but 2/3rds the max range; rifles are with +/ 20%. Wikipedia and GURPS HighTech disagree on a lot of those numbers, so I don't know. * This is 1 for round shot like cannonballs, 2 for pistol bullets and shotgun slugs, and 3 or more for rifle bullets but see the note on coefficient of drag. ** Coefficient of drag varies with bullet shape and velocity. I'm assuming a static CoD based on the numbers from the wikipedia article and some rough curve fitting. You can adjust the CoD by putting a value in H10 ("CoD Fudge"). If anyone has better data on CoD I'd love to see it; I know you can theoretically do stuff with a ballistics coefficient but it's been a long, long time since fluid dynamics and I can't resolve the equations on wikipedia.
__________________
Read my GURPS blog: http://noschoolgrognard.blogspot.com 
09222017, 10:02 PM  #33 
Join Date: Aug 2004
Location: Buffalo, New York

Re: Binary propellant and Standard TL 8 guns?
I was able to download it as an XLSX file without a problem. The next step for me is to try and figure out what the formulas you are using are, what the numbers are used in the formula, and maybe recreate it sufficiently enough that I can write a VBA code or VB.NET code to do the same thing.
The good news is that I have Doug's updated balistics sheet, and I have yours, and that should keep me busy trying to understand what they're doing. My theory is that if your methodology and Doug's methodology show two different paths to the same goal, I can maybe use one method to check against the other. It may well be they're both enough alike to be the same for all intents and purposes. I don't know. Thanks both of you for the spreadsheets. :) 
09222017, 10:12 PM  #34  
Join Date: Aug 2004
Location: Buffalo, New York

Re: Binary propellant and Standard TL 8 guns?
Quote:
I wasn't expecting that the velocity would be halved as such. Using an actual example... A round designated as .45 Colt, developed and released for public sales in 1873 that weighed 255 grains, and had a muzzle velocity of 855 feet per second, its average damage worked out to be 8.5 points, or 2d6+1 damage. In order to reduce the average damage to 8.5/2 or 4.25... The velocity must now become: 440 feet per second. Not half the velocity to be sure, but that's what I had to change the velocity value to get a damage of 4.25. I'm guessing however that this is not necessarily what you meant. Am I right? 

09232017, 01:24 AM  #35  
Join Date: Dec 2008

Re: Binary propellant and Standard TL 8 guns?
Quote:
__________________
HMS OverflowFor conversations off topic here. 

09232017, 03:06 AM  #36 
Join Date: Feb 2005
Location: Berkeley, CA

Re: Binary propellant and Standard TL 8 guns?
Yes. GURPS 1/2d range incorporates elements of both damage and accuracy, and thus doesn't accurately represent either one.

09232017, 07:59 AM  #37 
Join Date: Oct 2010
Location: Cambridge, UK

Re: Binary propellant and Standard TL 8 guns?
In 3e, the Acc bonus was lost at 1/2D range, but this is not the case in 4e. Or did you mean some other aspect of accuracy?
__________________
Indexes: DFRPG Characters, Disadvantage of the Week, Skill of the Week, Techniques. 
09232017, 08:01 AM  #38  
Join Date: Aug 2007

Re: Binary propellant and Standard TL 8 guns?
Quote:
__________________
Fred Brackin 

09232017, 08:16 AM  #39  
Join Date: Aug 2004
Location: Austin, TX

Re: Binary propellant and Standard TL 8 guns?
Quote:
Calculate the static portions of the drag equation as 0.5*1.23*(object coeffecient of drag, roughly 0.47/object aspect ratio)*cross sectional area/mass. 1.23 is the density of air, more or less. Calculate subsonic drag static portion as 1.4* the previous value. For each row, calculate instant velocity as the square root of the sum of the squares of the previous row's horizontal and vertical velocity, and current angle of the inverse tangent of vertical velocity/horizontal velocity. Calculate instant horizontal and vertical acceleration as the square of instant velocity times static portions of the drag equation (using the subsonic number if instant velocity is below the speed of sound) times the cosine or sine of current angle, and add the static acceleration due to gravity for the vertical accel. Instant horizontal and vertical velocity are the previous horizontal or vertical velocity plus instant horizontal or vertical acceleration times deltaT, and total distance traveled in the horizontal and vertical are the sums of horizontal and vertical velocity times deltaT. I calculate 1/2d range as the horizontal distance when instant velocity has dropped below muzzle velocity * square root (1/2), since that velocity gives you half damage in Doug's formula. With a little approximation of the coeffficient of drag, the current spreadsheet gets the maximum range for the RIA M2A1 105mm howitzer within 10 yards, and the maximum height and range of a 5"/38 cannon within 2%, so I'm pretty satisfied with it. I just need to speed it up a bit.
__________________
Read my GURPS blog: http://noschoolgrognard.blogspot.com 

Thread Tools  
Display Modes  

