You know, I was trying and trying to find the book where the designer of the P-40D stated that the chin was a big problem for level flight speed directional stability, but I cant find it. Go figure. Anyways, just wanted to point out that even he thought that was the problem. So they came up with the XP-40K-CU-15, the forerunner to the P-40Q. I also read somewhere that North American 'borrowed' Curtiss's data on that ship (before it was built), and hence the P-51 was born.