Could it be Newton had some ideas with respect to the cannonball thought experiments prior to the famous apple story?
The thought experiment goes like you shoot an ordinary cannonball tangential to the Earth. Assume the Earth is smooth, and, the cannon is mounted at a certain height above the ground. The cannonball takes a standard projectile motion path (a curve) and crashes into Earth a few distance away from where it was launched. For the second trial, you can increase the fire power and repeat the experiment and observe that the curve elongates a little, and, the cannonball has displaced farther. You can keep repeating the experiment in this manner such that you will find that the cannonball will eventually follow the curvature of Earth, and, if you stand long enough by the fire cannon mount, the cannonball might hit you from behind.
If so, why was such a thing never expressed in Principia? Did any of his close associates or contemporaries express such a thought experiment?