I guess first off you should spell principal correctly.
Now, as a school principal, I've excused
Disney vacations probably a dozen or more times, but only after the work that the student has missed has been turned in and graded. My best piece of advice?? Don't BS in the letter. Go straight to what you are doing, if you feel like you need to do that. Actually, Flight has a pretty good letter too, but as a principal, I would want to know more, simply because if you are going to the beach for a week, there is no way that I would excuse it. However, Disney (and Sea World, and Kennedy Space Center, and Grand Canyon, and Yellowstone, etc...) is a little different simply because there is so much new "stuff" there that is highly educational. If he/she refuses to excuse the absences, as him/her if it is possible to excuse them after missed work has been turned in, along with the YES stuff that you will be doing. That should do it. Do know that some folks are real hard-butts about stuff like this (my own son's principal is that way, and I know her on a personal, first name basis & work in the same district). Also, a call or a visit to the principal works wonders, simply because it let's everyone know that you really do care about your child and his/her education. That's hard for a lot of folks because they feel intimidated, but still worth it in the long run.
Enjoy your time. If you went to my school, it would definitely be excused. Hope it works out for you.