Related: Terminal velocity table for KSP v1.0 and later?
I like to build big fast rockets. I always get wind and heating effects on my way up. Prior to version 1, that was incredibly inefficient because of the severe effects of terminal velocity, but now (version 1.0+) it's not such a big deal because of the atmospheric remodeling.
Obviously, the less time you're affected by gravity the better so going fast has a measurable benefit. So does Terminal Velocity matter anymore?
Best Answer
It is important... on the way down :)
Getting off Kerbin got significantly easier. With the same ~2300m/s of LKO orbital speed, the actual fuel requirements accounting for the losses dropped from 4500 to 3500m/s of delta-V.
All but the absolutely fastest of rockets aren't bothered by the terminal velocity on the way up. If your TWR is less than ~8, you don't need to bother. If it is, you'll be still better off going over the terminal velocity over the short distance where your drag losses are higher than gravity losses, than suffering increased gravity losses over the remaining distance. Only with TWR exceeding something of order of 12 you might consider increasing your payload.(*). With TWR exceeding 16-18 (achievable with jet engines on small craft) air heating becomes a concern.
The situation is different on the way down. The low drag and high terminal velocity means low atmospheric deceleration. You need extra drag-inducing features like airbrakes, drogue chutes or such to reach a safe speed - only the last few kilometers have a terminal velocity below 250m/s which is safe to open the main parachutes, and if you're coming in too fast, or in a heavy, aerodynamic vehicle, you'll never reach that speed before lithobraking.
(*)Obviously flawed solutions like reducing the number of boosters or throttling the engines are against the Kerbal Way.