[Spaceships] VDS Came Early

[Anthony]

Originally Posted by Langy

Max Air Speed:
SQRT ( 2500 * Acceleration * Length )

Assuming non-air breathing engines; air breathing engines have variable performance depending on speed and scale as the cube root of power / area. Not sure how plausible the constant term is, there.

Originally Posted by Langy

Max Underwater Speed:
CubeRoot( 100 * Acceleration * Length )

Square root, actually, unless dealing with a water breathing engine, which has variable performance based on speed. Also, the constant should be much different (given relative densities, assuming the 2500 above is correct, 3).

[Langy]

Originally Posted by Anthony

Assuming non-air breathing engines; air breathing engines have variable performance depending on speed and scale as the cube root of power / area. Not sure how plausible the constant term is, there.

The constant term was a cludge to get it so that it fits decently, yielding Move 750 for a 1.5G engine on an SM+5 craft, though that was supposed to match an air-breathing engine.

Good point about it needing to be cube root, though - I'll see if I can come up with formulas for air-breathing engines and non-water breathing engines.

Square root, actually, unless dealing with a water breathing engine, which has variable performance based on speed. Also, the constant should be much different (given relative densities, assuming the 2500 above is correct, 3).

That formula matches almost exactly (with at most +/- 2) the figures from the Pyramid article, which is a water-breathing engine, so that constant is probably correct. The air one isn't, then.

[Anthony]

Originally Posted by Langy

That formula matches almost exactly (with at most +/- 2) the figures from the Pyramid article, which is a water-breathing engine, so that constant is probably correct. The air one isn't, then.

It's probably correct for matching the Pyramid article. That doesn't make it actually correct.

[Langy]

Good point, Anthony.

Anyways, here's some new formulas. Hopefully they'll be 'more correct'. Not sure.

Max Air Speed (Non-Air Breathing):
SQRT ( 20000 * Acceleration * Length )

Max Air Speed (Air Breathing):
CubeRoot( 2800000 * Acceleration * Length )

Max Water Surface Speed:
????

Max Underwater Speed (Non Water-Breathing):
SQRT( 20 * Acceleration * Length )

Max Underwater Speed (Water-Breathing):
CubeRoot( 100 * Acceleration * Length )

Supercav Threshold (No Bubble Generator):
SQRT( 225 * (Length/15 + 4) )

Supercav Threshold (Bubble Generator):
SQRT( 225 * (Length/30 + 2) )

Max Supercav Speed (Non-Water Breathing):
SQRT( 100 * Acceleration * Length )

Max Supercav Speed (Water Breathing):
CubeRoot( 1000 * Acceleration * Length )


Also, here's a TL10 supercavitating aerospace/underwater fighter (based on one from an old proposal for a TV series or something like that called Deep Angel), and some design features:

Front Hull
[1] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[2] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[3] Tactical Sensor Array (Array Level 6, $300K)
[4] Defensive ECM ($300K)
[5] Defensive ECM ($300K)
[6] Control Room (Emergency Ejection, C6, S/C 4, 1 Control Station, $560K)

Central Hull
[1] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[2] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[3] Weapons, Medium Battery (Hidden, 2x VRF Laser Turrets, 1x Missile Launcher, $225K)
[4] Weapons, Medium Battery (Hidden, 3x Missile Launchers, $225K)
[5] Submarine Ballast Tank (0.5 Tons, 5mps Delta-V, $12K)
[6] Submarine Ballast Tank (0.5 Tons, 5mps Delta-V, $12K)
[Core] Submarine Ballast Tank (0.5 Tons, 5mps Delta-V, $12K)

Rear Hull
[1] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[2] Armor, Nanocomposite (dDR 5, Hardened, $300K)
[3] Defensive ECM ($300K)
[4] Maneuver Enhancement ($50K)
[5] Fusion Torch (1.5G, Ram-Rocket, Water-Fueled, $3M)
[6] Fusion Torch (1.5G, Ram-Rocket, Water-Fueled, $3M)
[Core] Fusion Reactor (1PP, 400 Year Endurance, $150K)

Features: Winged, Supercavitating Hull, Bubble Generator, Stealth Hull, Dynamic Chameleon Hull

TL   Vehicle             ST/HP    Hnd/SR   HT     Move       LWt.    Load    SM    Occ.   DR     Range        Cost         Notes
9    UF-8 Peacemaker     200      0/4      12     3G/15mps   30      0.1     +5    1SV    100    -            $11,376K     [1], [2], [3]
     Air                          1/4             30/1000    
     Air                          1/4             30/3000                                        1500 miles                [2]
     Underwater                   0/4             30/36      
     Supercavitation              0/4             30/77                                                                    
     Supercavitation              0/4             30/212                                         100 miles                 [2]

[1] Minimum Supercavitation move is 24
[2] When using water in ballast tanks for fuel rather than ram-rockets.
[3] Crush Depth of 3,300 yards

New Design Features:
Supercavitating Hull: Allows you to supercavitate if you have a high enough move while underwater, increasing your maximum speed significantly. Cost is twice that of the Winged feature.

Bubble Generator: Lowers your Supercavitation Threshold. Supercavitating Hull required. Cost is twice that of the Winged feature. Requires 1/3 of a Power Point.

Supercav Threshold (in Yards per Second - double to get MPH)
SM                      4    5    6    7    8    9    10   11   12   13   14   15
No Bubble Generator	    32   34   35   37   41   44   49   56   62   73   92   107
Bubble	Generator       23   24   24   26   29   31   35   40   44   52   65   75

[Anthony]

So, since I've been poking at this for a while, I put together a google docs spreadsheet that does aerodynamic calculations for winged flight. I made it shared but non-editable (sorry), but you can download it and edit from there. Find it here.

For a SM +4 vehicle with a mass of 30T, 1G of deceleration occurs at 364 m/s (about move 400) and requires 107 megawatts of power (minimum).

[wabishtar]

I think I've noticed a bit of a problem with the rules in Pyramid 34. I've been trying to design a submarine that has a comparable performance to a U-Boat. So I looked up a U-Boat in my copy of GURPS WWII : Motor Pool and I found a crush depth of 330 yards. Using the formula provided for crush depth, I can't get anywhere close to 330 yards without using force fields! Using the formula of dDR * 150 / (hull length in feet) = Crush Depth, I can't begin to approach 330 yards, or any reasonable crush depth at all. I'm not sure what the mistake is, but I'm pretty sure there is one. Can someone who knows more about this crunchy stuff help me?

[dataweaver]

I would put one more tweak in play:

When using the Armor Facings option, you don't get to put your armor systems wherever you feel like. Instead, Forward and Rear armor systems must go in the fore and aft sections; and half of each of the remaining armor systems must go in the middle section, with the remaining half split evenly between fore and aft.

The other option would be to redistribute the vehicle spaces with three spaces in each of six facings instead of six spaces in each of three sections. The space combat rules would need some adjusting to this new layout; but I suspect that could be done without too much trouble. The main complication that would arise from this is that the option that lets you declare the fore section to be a spaceship unto itself wouldn't translate properly: the existing mechanism relies on the fact that one step down the Size scale has one-third of the mass.


I've also been working on a house rule that let's you fine-tune a vehicle's size, by allowing fractional Sizes for most purposes — specifically, Size can be decreased by 0.2, 0.4, 0.6, or 0.8, reducing the mass to 80%, 65%, 50%, and 40%, respectively. These same reductions apply to just about everything: anything that follows some sort of 1-3-10-30… progression gets the same reduction, while anything that follows a 1-2-5-10… progression gets more lenient reductions: 85%, 75%, 65%, and 55%, respectively; and anything that follows the even slower 1-1.5-2-3-5-7-10… progression (such as HP) gets an even more modest reduction: 90%, 85%, 80%, and 75%, respectively. Tabulated:

        Progression
Size  Fast Mod  Slow
-0.0  100% 100% 100%
-0.2   80%  85%  90%
-0.4   65%  75%  85%
-0.6   50%  65%  80%
-0.8   40%  55%  75%
-1.0   30%  50%  70%

And these numbers are close enough to each other that if you want even more precision, you can usually interpolate between a pair of them. (The percentages were adjusted to a convenient 5% mark for ease of use; if anyone wants more precise percentages, I can provide them.)

When using this in conjunction with the option of more compact heavily armored ships found in Pyramid 3/34, you might want to revise the latter rule's table to allow for fractional Size reductions, which would of course be cumulative with the above size reductions: ships with up to six spaces of armor would still get no reduction in Size; but each step after that on the Armor and Size Table would be good for -0.2 Size.

Likewise, you could use this option in conjunction with the facings-based spaces option above to handle the possibility of the front or top being a separate craft: but instead of that craft being -1 Size, it would be -1.6 Size.