Well, my copy of McCormick showed up, and the section regarding power effects on longitudinal stability didn't really tell me anything I don't already know, but the book seems to still be worthwhile, though- there's a lot of other good information in there about things I haven't even thought about yet.

So for the time being, I'm using the data for that specific Hamilton Standard prop in Perkins and Hage for lack of anything better. I would like to get data that is more pertinent to the aircraft I am designing, but for now I feel I can get away with using these charts because a) the prop used to generate those charts is probably very similar to what a T-28 was originally equipped with, and b) my scale T-28's prop would have thinner blades than a real T-28 prop scaled down to 70%, so in using this data, I am slightly overestimating the propeller effects. Somebody tell me that's a bad idea if it is.

In doing that, I have calculated a NP shift of about 1.8%MAC forward for a windmilling prop, which seems reasonable. My calculated full-power shift is nonsense though...22% AFT. That cannot possibly be right. Either I've got an unrealistic number in my spreadsheet, or there's an error in the calculation, or I need to find an alternate method of calculating this quantity to check it. The equation I'm using is out of my stability and control notes from college, and seems to be my professor's combination of a couple different methods. I can post it if someone wants to see it. There appears to be a massive dependence on the vertical location of the prop with respect to CG, and even varying that number slightly (6" up or down) drastically changes the calculated NP shift. Hopefully someday I'll figure this out.