Great question. I actually asked this exact question to someone who believed in the Helliocentric model, and got nothing. Experiments have already been done, the case is closed, but the debate rages on for some reason.
Basically the easiest way is measuring the curvature on a lake, measuring the curvature of a large body of earth, takes new survey technology, or a lot of time, and money.....
I will try to run my experiment this weekend, if weather cooperates.
I will show how I did it, and conclusions.
Anyways.....
With new surveying technologies, measuring the curvature of the earth is in reach. I lost the youtube link, but with new survey tools, one can do a large survey of the earth. When I find it, I will post it.
This video pretty much proves ocean water goes up (Concave Hollow Earth), not down (convex earth), or is flat (flat earth). It's really game over. Concave Hollow Earth wins so many times, that why it can't be discredited, and is ignored. It's true.
A long time ago the curvature of the earth was measured with a Rectilineator. Video below gives full details on how it was done in Florida. There a whole book written about the Concave Hollow Earth with proof. It's called, Cellular Cosmogony, Earth is a Concave Sphere, with proof. You can get it on Amazon. Author is Cyrus Teed.
I posted this video, even though I risk it from being deleted, so I hope someone appreciates it.