What is the meaning of "by up to a factor of two" in this sentence ? Thanks for your time.
we have characterized their aerodynamic performance and found that the drag coefficient can be reduced, on demand, by up to a factor of two.

Question

Answer

It means that you divide by 2. So reduce it by
 half of the original.
Reduce by a factor of 10 would mean to reduce it by a 10th. (divide by 10 and then subtract that number from the original number).