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Frank Colver wrote:II personally would not want to fly any craft that had any chance for divergent pitch or roll under some flight condition unless i could avoid that condition.
Me too! I don't want to work that hard to have fun!
In this case, I brought up the question of divergence as a thought experiment to test whether the high hat's pitch control was due purely to a static drag difference or a dynamic drag difference or both.
I proposed a configuration where the drag of the high hat would decrease with pitch down. All that's needed for that to be true is that the high hat be tilted forward rather than vertical or tilted aft. When tilted more forward, further pitch down would reduce its profile more quickly than when it is tilted less forward.
The problem that I had with that configuration was that the wing would also be reducing its drag as it pitched down, so it wouldn't be clear as to which would be reducing its overall drag faster. This is especially true since the wing is much larger than the high hat (and in the steeper part of the sine curve). But if the wing were already at a negative angle of attack, then it's drag would no longer be decreasing with further pitch down. That's the mental exercise that led to flying at a negative angle of attack. And it was only a marginally useful exercise if the high hat were raked forward. If the high hat were raked backward - even slightly - then it would be very difficult to put it in the region where pitch down would be reducing its drag at all.
Having gone through this exercise, I think that Kai Martin's original explanation of static drag differences is correct and leads to the stability that we saw in the video. I also think that this stability is further enhanced by the dynamic drag differences that result from pitch rotation.
The process of science is largely a process of challenging assumptions. You have to question everything. That's the path to finding the truth. I hope no one was offended in the process.
