I've been following this on another forum and am planning to build a non-propeller design to sidestep the sailing references. I accept that the vehicles in the videos linked in the other two threads presented on this forum are doing what it looks like they are doing without any trickery. I also feel that the treadmill test is a valid way to test and refine a design. However, it appeared that there was some disagreement about that before the previous thread here was locked. My understanding is that general tone of the disagreement is what caused the thread to be locked, not the topic or actual disagreement, so I'm hoping that this thread won't be automatically shut down. I've read and agreed to the conditions of this forum and will abide by the guidelines. I feel I have a pretty good understanding of what is happening but would like to make sure that I haven't overlooked something that could affect the outcome of my experiments with a non-propeller design. I want to observe and measure the various forces and interactions of this under controlled conditions to optimize a small device before attempting to scale this up. Is the treadmill test a valid substitute for an outdoor test? If not, why not?