Busbar Capacitance Calculation Help and is Transposition Worth It?

What stops you from building it and measuring it ??

The capacitance will be tiny due to the air being the dielectric. HyperPhysics shows the simple math for calculating parallel plates capacitance. I like much better the diagrams from MIT but as you should expect, the math is not as simple.

I almost forgot, if stray capacitance is a problem in your circuit then you do not want air as a dielectric because the humidity and dust levels will change the dielectric constant considerably.

Why would you use a busbar system for this application? Clipped direct to the airframe a 3 core 4.0mm² cable will carry 36 amps, and is fully insulated. The additional weight of the insulation will be more than offset by simplification of the mounting brackets, and the flexibility of a cable must help with installation. The cores of a cable spiral around each other so capacitance is not an issue. I would also be concerned about the effect of vibration on rigid busbar connections. A 56 x 0.3mm² multi-stranded core with crimped connections would be far better for this duty.

Maybe.

This is an aircraft and the bussing system may be type approved and permit type approved tapping along route.

If it is a type approved bussing system then the capacitance data should be in its specs too.

If it's a replica or prototype then it's back to LCR first principals.