You don't always need to be able to do the math quickly. On the flying side you can get a feel for a lot of the envelope. Angle of attack, speed. Air density at take off can be a problem though because you can't feel the aircraft until you are already hurtling down the runway. Don't forget angle of attack, hopefully your aircraft gives you some signs before it gets too far.
Now design is a whole different matter if you are tying to meet several requirements, that can take a lot of math but if your only goal is to make it fly you don't need a lot of math.
I thought you just had to get the DeLorean to 88ph, under the clock.