So about Engine Sizes...
It's nice that we got some more options for really small missile engines in 6.30, but it did turn the drop down menu into quite a mess.
While it's nice and important to be able to make a distinction of a 0.10 MSP and a 0.11 MSP engine (the latter being 10% larger) it is not so critical to be able to specify the difference between a 4.00 MSP and 4.01 MSP engine (the latter being only 0.25% larger) or a 4.99 vs 5.00 MSP engine.
Suggestion 1:Change missile engine sizes to a (roughly) 10% size difference basis for clarity.
0.10 MSP
0.11 MSP
0.12 MSP
...
0.20
0.22
0.24
...
1.00
1.10
1.20
...
3.00
3.25
3.50
and so on...
Suggestion 2:Adapt this to small (Fighter and FAC) Engines, and also change their fuel consumption values to matter as design choices. Currently you can get decent range / flight times out of Fighters even with 50% of total size being engine, Max Engine Power Mod and very small fuel-tanks (5% or less of total size). To get a feel closer to real fighters that regularly carry 25%+ of their weight as fuel and burn it in a matter of hours I think these changes would be welcome.
Size 1.0 (50 ton) still minimum size of a normal engine = x3.00 fuel consumption (using same formula as missile engine design size)
Size 1.1 (55 ton) = x2.81 fuel consumption
Size 1.2 (60 ton) = x2.65 fuel consumption
Size 1.3 (65 ton) = x2.51 fuel consumption
...
Size 2.0 (100 ton) = x1.87 fuel consumption
Size 2.2 (110 ton) = x1.75 fuel consumption
Size 2.4 (120 ton) = x1.65 fuel consumption
...
Size 5.0 (250 ton) = x1.00 fuel consumption
Note1: This also retains the option to build fighters and FACs that have fuel efficiency close to currently, but restricts it to engines size 4-5 or larger (200-250 ton).
Note2: If the same formula is used all the way down to size 50 engines it would lead to fuel consumption = -79% and mirror missile engine fuel consumption formula, but that might not be desirable. Even if it's not I think it would be useful to develop a formula that is balanced and fits for both applications though. Distinctions between missiles/ships are ensured by the different max power mod values used (and can be balanced through these as well if needed).
Note3: I actually found some more information on
real fighter planes here. It seems that fighter jets use 25-45% of weight for internal fuel and frequently add droptanks on top of that!!!