Some time ago, I noticed how disproportionately massive cockpits were to other aircraft parts, resulting in nose heavy planes in the absence of a rocket engine on the back. What started as a rampage against heavy cockpits metamorphosed into something much more sinister. Using 3ds Max, I created and weighed aircraft structure to create a frame of reference, and thus the games began.
Aircraft parts have all been measured and "weighed" using the "volume" of their surface area, including external and internal structure. A considerable weight reduction for airplanes has resulted. Flight deck components such as switch panels, computers, seats, and pilot interface have also been accounted for in part mass.
Fuel tanks were measured, and internal structures modeled from scratch to determine fuel capacity. Fuel capacities have also been added to additional wings. Applying rules learned for aircraft has also resulted in dry-mass reductions for all fuel tanks. Liquid Fuel, Oxidizer, and Monopropellant were removed from the game, replaced by JetA-1, KeroLox, HydroLox, and MMH/NTO. This is where Firespitter comes in: each fuel tank has several variants, but now only carries one type of fuel per tank.
As a friend kindly stated, I went "Vlad the Impaler" on reaction wheels; they have been removed.
Engines have had their masses tweaked, placing them on a steady TWR curve, with the most powerful engines featuring the highest TWRs. Many liquid fuel engines can no longer throttle below 70%, so stages and burns must be planned accordingly.
MechJeb is not required, but the module has been integrated into command modules, as well as Kerbals on EVA.
Requires Module Manager and Firespitter