One idea for Final Verdict about Convex ou Concave Earth
I thought about an easy experiment to try, and also not very expensive (I guess).
The experiment is not valid unless it is possible to measure distance between two ballons at great distances (100 to 300km aprox.).
From point A0 let a balloon (or a plane, if possible) go straight up let's say about 30km high
From point B0 let a balloon go straight up 30 km high, too
Measure the distance between A0 and B0 (let's say, exactly 200km) at sea level.
Measure the distance between the two ballons when they are both at 30km high (both strraight up) at A30 and B30, I hope that must be easy why sound wave technology or other. Maybe there are many ways, some more precise than others.
Now, the FINAL VERDICT:
If the distance between A30 and B30 is less than 200km the Earth is Concave
If the distance between A30 and B30 is more than 200km the earth is Convex
The higher you measure and the larger the distance is between A0 and B0 and more conclusive will be your final verdict.