Update:
From simple guidance in Discord I am able to locate (and extract) engine RPMs. However they are of little use because they are directly tied to wheel speed (and doesn't idle) and thus does not reflect the actual power output.
The game's even worse than I had thought.

woah woah woah this topic is getting quite hot actually. not expecting it.

@SnoWFLakE0s
Fantastic work on documentation. I will read it.

Ha. There is a typo on "list of variables". The GS entry have the "the" typed wrong.
Wait. Brake is a boolean value? What the $#&*

@jamesPLANESii
That's interesting. I was wondering what the variable tabs are for.
It's a bit like in CAD where you can create your own labels and variables and use them in your designs (in case say you need to scale a part)

@WormWithLegs
I understand there are a wheel rpm limit. That's something visible in the "part editor" where you can specify the maxwheelrpm. Obviously there are code associated with it, just as it's obvious car engines have a rpm variable.
__
Yes. We have the "brake" .. wait.
Yes, we have the brake input as a variable (so we have gauges and stuff pre-cockpit update, good job dev) but ew never actually have a part that has a brake with a "brake" input field where you can input the control for braking (e.g. you might want a parking brake you can engage while you are revving up the jets), except airbrakes.
That will actually be very cool. Just like old Cessna you can now brake your plane wheels no matter what else it is doing. Heck we even have these new VR handles and switches.

So far limiting wheel rpm the only way I have found to limit the speed of a ground vehicle (if you want something slow but powerful, like a tank or a truck)
I overheard a conversation about people modding engines to include "power multiplier" and max power (if that's the case) and how it affects engines. I know it affects Jet engines, but I also heard discussions on car engines yet I cannot find them

@WormWithLegs
Ah.

@ZeroWithSlashedO as in we should be able to choose the input that controls the brakes instead of it always being 'brake'. We should be able to change it to something like activation group 1 so we could make a handbrake or something.

@WormWithLegs
wdym?

NOW IF ONLY WE HAD THE ABILITY TO CONTROL BRAKES THROUGH FT

also instead of car engine rpm you can find the rpm of the wheel by going into the resizeable wheel variable menu
almost every interactive part has some sort of variables you can mess with

yes just click on the prop engine and there should be a variable menu button next to the connections menu button
click on it and there should be an option to name its rpm a certain name and you can refer to that name at any time in funky tree code.

@CDRxavier You call the prop rpm things like "RPMEngine1" etc. The RPM thing works through variables.

Yes

There is a discord server devoted to funky trees research, discovery and coding. Check the pinned forum with all the discords

Funky Trees Documentation

Not quite up to date with 1.11 & 1.12 yet, I've'nt had the time--but expect them to come fairly soon.
EngineRPM should be an output variable for individual parts, you can assign a variable name to carry the data, and that variable can be used for reference.

Also, regarding prop rpm:
What will happen if I have multiple propeller engines? There is no way to select which propeller rpm it is. I would assume it's the last prop engine you put on the plane that counts.
What about multiple car engines for that sake?