Approximating High-Tech and Ultra-Tech with Spaceships

[ericbsmith]

Originally Posted by ericthered

The dDR is concentrated on the cock pit using a house rule not fully explained yet... It'd be nice to have.

I'm assuming that it's just 5 systems in the core plus two control rooms in the same section, as I set up in my example. Using a house rule shouldn't really offer an improvement above this, since at that point you've already got a section of the ship that's essentially an armored bathtub with the pilots inside.

Originally Posted by ericthered

Where are the rules on converting Gs of acceleration into actual vehicle speeds? I could do some math on that, but It'd be nice to have an official source...

GURPS Spaceships, p. 35, lists how to get Air Performance figures, including vehicle speed. Turbofans have a maximum air speed of 2,000mph (see p. 10 of Spaceships 7). Here's my workup of the design using my spreadsheet.

[ericbsmith]

F-15 'EAGLE'
PILOTING/TL7 (HIGH-PERFORMANCE AIRPLANE) Page:

TL      Name      dST/dHP  Hnd/SR  HT  Move  LWt.    Load   SM    Occ     dDR   Range    Cost   
 7  F-15 'Eagle'     20       —    12    —    30   0.2 [1]  +5  2SV [2]  0/5/0    —    $3.075M

Length: 30 yd. (90 ft.) Crush Depth: 0.0 Atmospheres (0 ft.)
Air Performance #1: aAccel: 1G (22 mph/s) aSpeed: 2,000 mph Hnd/SR: +5/4
Air Performance #2: aAccel: 1.5Gs (33 mph/s) aSpeed: 2,000 mph Hnd/SR: +5/4

SHIP SYSTEMS

   FRONT     
[1-3]        Defensive ECM
               -6 to Hit
[4]          Tactical Comm/Sensor Array
               Array level: 3
[5]          Major Battery
               one fixed mount 2.5cm improved very rapid fire conventional gun
[6]          Medium Battery
               three fixed mount 16cm missile launchers

   CENTER    
[1-5]        Light Alloy Armor
               dDR 5
[6, Core]    Control Room
               Comp: C0 / Comm/Sensor: 1 / 2 Stations

    REAR     
[1-2]        Maneuver Enhancement
               +2 Handling
[3-4]        Afterburning Turbofan
               1 G / 1.5 Gs & 4x Fuel Use / 1.5 hr Fuel [3,4,5]
[5-6, Core]  Fuel Tank
               4.5 Tons of Jet Fuel

Design Switches, Features, & Notes: Ammunition Cost: $1,023,330; Fuel Cost: $18,000; Total Cost: $4,116,330
SHIP OPTIONS: Streamlined, Winged, Emergency Ejection Pod
[1] Load includes: 0.2 tons of Crew & Passengers
[2] Crew Requirement: 2 Control Stations (1 Pilot, 1 Navigator)
PERFORMANCE PROFILES: [3] Air #1, [4] Air #2
FUEL USED: [5] Jet Fuel (4.5 tons)
TROOP STRENGTH (TS): (217) CLASSES: Air FEATURES: Night, Sealed

WEAPONS TABLE
Range Scale: Basic Combat Ranges Turn Length: 20-sec

Qty.       Location            Weapon       Mount      Options       Size     Damage      sAcc [1]   Rcl    RoF    Shots  MPS  Accel  Projectile   Range  
                                                                                                                                           SM             
   1   Front [5] - Major  Conventional Gun  Fixed  Very Rapid Fire  2.5cm  3d+2 (2) cr  -8 (+8) [2]   3   200 [4]  1,400   1               -8        C    
   3  Front [6] - Medium  Missile Launcher  Fixed                    16cm  6dx4 (2) cr     +1 [2]     1    3 [3]     15    6     6G        -1        X

[1] Parenthetical value is the Rapid Fire bonus (p. SS1:60), [2] Includes +2 sAcc for Fixed Mount, [3] RoF Already multiplied by number of mounts, [4] Includes x2 RoF for Improved
Created using the GURPS Spaceship Design Spreadsheet Version 2.0 RC 13 based on the GURPS Spaceships series of books. http://gurpsland.no-ip.org/#GURPSSpa...ignSpreadsheet

[Michael Thayne]

Originally Posted by ericbsmith

I get $3.115M and only dDR5 at SM+5. The Defensive ECM and Tactical Array cost $300k each, so $1.4M just for those four systems. You also left out Emergency Ejection. I suspect you forgot to add Streamlining (lowers dDR) and Wings (increases cost somewhat, as well as giving a big Handling bonus).

Three Maneuver Enhancements is overkill. Base Handling for SM+5 is 0, +0 for being 1G, -1 for TL 7, +4 for Wings gives a handling of +3. Maximum Handling bonus is +5, so two Maneuver Enhancements maxes out the bonus. A third only acts as a redundancy in case of damage; it would be better off with some more fuel.

Also, Spaceships standard layout is to list which section each module is installed in. It makes it easier to check/test designs if you use something approximating the standard layout; it also helps if you make sure to list the SM and TL. E.g.:
Center
[1-5] Light Alloy Armor
[6,Core] Control Room

Whelp, you're right about all these points. Must not have been fully awake this morning when I wrote this.

Originally Posted by ericthered

and the resulting stats would be nice.

Its worth noting that sensor arrays are a base of $60K, but tactical arrays are multiplied by x5 for final cost.

The dDR is concentrated on the cock pit using a house rule not fully explained yet... It'd be nice to have.

Where are the rules on converting Gs of acceleration into actual vehicle speeds? I could do some math on that, but It'd be nice to have an official source...

Working on getting my own stats for this jet.

No house rule, I just forgot to reduce DR for streamlined (though I was using the armor and volume rule again).

[Anthony]

Originally Posted by ericbsmith

GURPS Spaceships, p. 35, lists how to get Air Performance figures, including vehicle speed.

Note that the listed performance is divorced from reality, as it discounts SM completely.

[ericbsmith]

Originally Posted by Michael Thayne

No house rule, I just forgot to reduce DR for streamlined (though I was using the armor and volume rule again).

Armor/Volume rule only takes it from dDR 5 to dDR6, since five units of armor doesn't significantly increase dDR. If using my optional rules for partial dDR a SM+5 streamlined ship would qualify for dDR 1.5 each, giving dDR 7.5 for five systems of Light Alloy, and a final dDR 9 after adding them together and multiplying for Armor/Volume.

[ericthered]

Originally Posted by Anthony

Note that the listed performance is divorced from reality, as it discounts SM completely.

How SHOULD SM effect top speed? I'm not seeing any particular reason why it should.

[ericbsmith]

Originally Posted by ericthered

How SHOULD SM effect top speed? I'm not seeing any particular reason why it should.

The bigger the SM the smaller the front cross-section so the smaller the surface area that's exposed causing drag, which should allow larger ships to go faster given similar other stats (thrust to mass, etc).

[Anthony]

Originally Posted by ericthered

How SHOULD SM effect top speed?

Drag scales with surface area (second power of linear scale), thrust at any given acceleration scales with mass (third power of linear scale). Max speed is the speed at which drag is equal to thrust. Thus, on average you want to multiply top speed by the square root of linear scale.

There are other limiting factors -- notably, air-breathing engines have variable thrust depending on velocity, and stagnation temperature of air exceeds the melting point of aluminum at a bit under mach 3, iron at around mach 4, and any known materials by mach 6, which limits speed by what your hull is made out of.

[David Johnston2]

Originally Posted by ericbsmith

The bigger the SM the smaller the front cross-section so the smaller the surface area that's exposed causing drag, which should allow larger ships to go faster given similar other stats (thrust to mass, etc).

I kind of doubt that has much relevance to tanks.

[ericbsmith]

Originally Posted by David Johnston2

I kind of doubt that has much relevance to tanks.

No, but it does to F-15's and most other flying planes and spaceships (which is what we started talking about in post #8 or so).