I've been in discussions on another board with a physicist and he contends that a pilot in a plane will need to put a 1 degree downward direction input to the controls to account for the 1 degree of curvature rate at 500mph. as small as those control inputs are required, he says that the control surfaces need to conform to the shape of the earth. I disagree I contend that no control is needed due to the aircraft being in level flight, with gravity pointing straight down. the plane flies level, the atmosphere is curved and no adjustment is ever needed. (all other factors remaining constant when comparing a suppose flat earth vs round earth set of conditions) I equate the condition to that of a control line airplane.... the airplane just stays perpendicular to the centripetal force of the string... it follows the circular path naturally with no control input. can the board here add some color to the example and correct me if I am wrong in my analysis? thanks! ps as a side note, our discussion started to talk about the ISS . how does it rotate around the earth .. does it have a natural rotation about its own axis to match 1 revolution every 90 mins? or is it effectively tidally locked to the earth via how it was launched?