What is the explanation for why the spinning atmosphere, (that is spinning around the axis of the Earth at the same rate as the surface) which supposedly explains why plane and helicopter trajectories do not have to compensate for Earth spin, doesn't have the same effect on projectiles? Even if you believe in the Coriolis effect, Sandokhan has already shown that the Coriolis effect doesn't prove the Earth spins rather it could be the ether that spins (see his posts on Mach's principle.)
If I may offer just a point of clarifiaction
Except in business, poetic or literary settings, I think "trajectory" is generally more used on things that reach their destination without the need of the air.
In other words, rockets, bullets, etc. They are launched at a high speed and either momentum carries them or a solid fuel rocket propels them, but they could just as easily (if not more easily) "fly their course" and reach their destination without air. Think of the word ballistic.
Airplanes and helicopters on the other hand are supported by air constantly. I mean, if the air were to suddenly vanish mid flight, you could say an airplane had a trajectory since it has mass and velocity so it would move forward briefly before dropping down, but it wouldn't reach its destination and that's not how they fly.
Airplanes and helicopters do not have a trajectory in the normal sense, because they are constantly accelerating air downward to produce lift. If they are producing more lift than their weight, they climb. If less lift, they sink. If equal lift, they maintain altitude.
The pilot or the autopilot constantly watches the altimeter and constantly adjusts throttle and other controls to maintain the desired altitude. Without that, the plain would go higher and higher or lower and lower till it crashed.
It really doesn't have anything to do with the earth rotating or not or curved or flat - it's just how you fly a plane. I used to build and fly model planes so this is a first hand experience for me.
This really is all a side note from the question, but hopefully brings some clarity.