(and why does friggin spell check underline fletch?)

It underlined it because you improperly used the word as a noun. Fletching would be the proper terminology in that sentence and you would use the word fletch strictly as a verb when you would say you are going to fletch your arrows. I also believe what you stated in your response about BH flight is accurate, although I'm a novice in archery compared to your many years of experience.