I've just now started looking over the design rules and did some computations. My take is the speed advantages of the turbine + jet vs. fusion + grav are reduced by other considerations such as fuel, anti-grav ability, more space for other gadgets, and no need of an atmosphere. Please tell me if I'm computing something wrong-
Using orginal poster's TL's and plants, I compared a 10 m3 Turbine-8 plant vs a Fusion-12 plant of the same size.
Turbine-8 10m3 gives 260 power, 900 kg mass.
Fusion-12 10m3 gives 240 power, 1500 kg mass.
Advantage to the turbine for performance due to large difference in weight and slight bonus in power.
But now factor in fuel. For easy comparison, going to give both plants 10 hours of operation time. Turbine-8 needs 800 litres of fuel with a mass of 800 kg. Fusion-12 needs 100 litres of fuel with a mass of 100 kg.
Refiguring with fuel:
Turbine-8 10m3 gives 260 power, 1700 kg mass. .8 m3 for fuel.
Fusion-12 10m3 gives 240 power, 1600 kg mass. .1 m3 for fuel.
Turbine has slight advantage of power, Fusion has slight advantage of mass due to carrying less fuel. It appears to start to even out when only plants are compared.
Now throw in the drives. For argument's sake, using a 50m3 craft which seems fitting for a 10 m3 powerplant:
Jet: 7.5 m3, 750 kg mass.
Grav: 2.5 m3, 450 kg mass.
So adding powerplant, fuel, and engine togather gives:
Turbine Jet: 18.3 m3, 260 power, 2450 kg.
Fusion Grav: 12.5 m3, 240 power, 2050 kg.
Grav fighter's drive system is taking up less space and mass with only a slight reduction in power.
But now figure speeds. I'm going to use a ballpark figure of 5000 kg mass for the fighter + powerplant, engine, fuel for both. The grav fighter, built with higher technology, would probably be lighter due to a lighter hull. But, keeping them the same because the argument is to use the Jet Turbine even at TL 12 due to its speed advantage.
Turbine Jet Fighter: 7450 kg, 260 power, base 250 kph =
2180 kph top speed.
Fusion Grav Fighter: 7050 kg, 240 power, base 200 kph =
1360 kph top speed.
Final: The older Jet Turbine Fighter, if placed in the same futurisitc hull as the Fusion Grav Fighter, will leave it behind. But, the Fusion Grav Fighter will have a significant amount of space advantage for other systems (in this example around 6 m3 in a 50 m3 craft). The Fusion Grav Fighter is also a VTOL craft, can hover without needing a runway. The Fusion Grav Fighter also does not need an atmosphere, while the Jet Turbine Fighter does. One is faster, the other more versatile (more space, hovers, doesn't need an atmosphere).
I think the best combination for an atmospheric fighter built at TL 12 is the Jet engine with a Fusion powerplant. The Jet gives the best speed combined with the lower fuel requirements of the Fusion powerplant.
Fusion Jet Fighter: 7350 kg, 240 power, base 250 kph =
2040 kph top speed. Nearly same top speed as the Turbine Jet with option of greatly increasing range due to much lower fuel requirements (fusion takes 1/8th the fuel of the turbine). Another option for the Fusion Jet Fighter is to add a Lifter propulsion in addition to the Jet propulsion. "Lifter" in Civilian Vehicles is a poor man's Grav drive that can only hover and move at a slow speed (such as a cargo platform). In the example above it would take only .5 m3 volume and add 10 kg mass. But, this would give hover ability to your high speed jet. You might argue that the Jet + Lifter would be able to operate without atmosphere since wing lift would no longer be needed? Fusion Jet Lift Fighter anyone?
Seems the best of both worlds.
Note1: Shouldn't a Jet engine require much more fuel then a Grav engine regardless of the powerplant used? Nothing in Civilian Vehicles about this, all fuel requirements based solely upon the powerplant unless I missed something.
Note 2: I was surprised how fun it was tinkering with the design system in Civilian Vehicles, glad I looked into it finally.
