Welcome to my useful fromulas post. If you haven't already, check out the build i uploaded to explain everything more intuitively. There's some stuff there i'm not gonna get into here because it aint all that interesting maths-wise.

FunkyTreesStuffz
HomungCompass (comming)

My first useful formula is
clamp(Activate1,0,1)
It seems a bit silly to even put here, but it's pretty cool. This term turns 0 when Ag1 is deactivated and 1 if it's activated. If you multiply an input, say VTOL, you can activate and deactivate it. The true usefulness comes to the surface when you use multiple inputs tho
Example:
(clamp(Activate1,0,1) * VTOL) + (clamp(-Activate1,0,1) * Throttle)
Activating or deactivating Ag1 makes the input switch between VTOL and Throttle. You could also for example excange Throttle for a PID function

Next is a counter function:
sum(abs(rate(Activate1)))/2
The value of this function increases by 1 every time you hit Ag1. You can use it to stage multiple detachers, parachutes, engines etc. using just one boolean input. to get a proper high or low, you just have to compare it to a number, like this:
(sum(abs(rate(Activate1)))/2)>=1

another thing i love are non-linear functions. They increase the acuracy and stability of any vehicle, without limiting the agility
sign(Pitch)*pow(abs(Pitch),2)
This function behaves just like Pitch, 0 is 0 and 1 is 1. However, anything in between is non linear. A 0.5 input outputs a 0.25, Thus making you plane pitch slower the smaller your input is. You can change the "2" for any positive number you like, but 1.5 - 2 work best. Numbers below 1 would invert the non linear effect

Do you miss working with piston engines? i don't.
sum(Throttle*2)
can be used as an input to a rotator to make it spin continuously without having the problem of it going reverse when you power down- Thank me later

have you been bugged out that there's no easy way to make choppers super stable? Well adding a PID to the main rotor to stabilize altitude ain't that hard, but x and y movement are a bit more complicated
i present:
cos(Heading)*rate(Latitude)+sin(Heading)*rate(Longitude)
and
cos(Heading)*rate(Longitude)-sin(Heading)*rate(Latitude)
the first formula outputs the speed at which you're moving forewards in metres per second. A number below 0 means that you're moving backwards
the 2nd formula indicated movement to the right, again in metres per second. A number below 0 shows that you're moving to the left

If you're ever lost, just use this handy formula an put it into a rotator:
((atan( (sum(rate(Latitude)*clamp((Time>1),0,1))) / (sum(rate(-Longitude)*clamp((Time>1),0,1))) )+sign( (sum(rate(-Longitude)*clamp((Time>1),0,1))) )*90)-Heading)/90
it shows you the way back to the location where you started (in 2d space), just like a compass in minecraft. You have to set the rotation angle to 90 degrees
this one was quite alot harder to create than i woulda thought, because of the nature of tan functions

last and perhaps least, a timing function
smooth(Activate1,0.5)=1
this delightful function activates 2 seconds after the input turns high. For higher delays, change the 0.5 for a lower number above 0