[justlurking]

What is the length of rope needed to encircle the earth at its largest diameter assuming the earth is a perfectly flat sphere?

It depends on whether you are raising the rope a foot above the surface at a single point, or the entire rope.

For the former, it's exactly 2 feet (1 up and 1 down).

For the latter, you are simply increasing the diameter by 2 feet, so the circumference will increase by 2 * Pi, or about 6 feet, 3 inches.

This is the correct answer for a sphere or circle of any size.

[MosesKnows]

It depends on whether you are raising the rope a foot above the surface at a single point

...how much additional rope is required to raise the rope exactly one foot off the earth’s entire surface?