On Thursday, 10/8/2010, the Blue Angels spent about an hour doing survey and practice flights over SF bay prior to their scheduled Fleet Week shows on Saturday and Sunday. All were shot with the new Sigma SD15 and 50-500mm OS. The Friday, Saturday and Sunday shots will be added soon.
John: Thanks for the kind words. I've never used the 170-500, I shoot with the 50-500mm on my Sigma cameras and the 150-500mm on my Nikons. My settings when I shoot airshows is from 500s to 1250s, at f8 to f10. Recently most are shot at 1000s at f8. F8 to f10 seems to get the sharpest shots on my Sigmas. I usually shoot hand-held, especially planes, and I'll use a monopod sometimes for car, motorcycle and car shots, but most of those are shot hand-held, too. Only rarely will I go above 200ISO with the SD15, shooting most shots at 100ISO if possible.
If you're really serious about getting the sharpest possible shots with the 170-500 and the SD15, and the settings I suggested aren't doing the trick, you might consider sending both the camera and lens to Sigma for calibration. I did that with an SD15 and my 50-500mm, and the results were great. All the Sigma SD15/50-500mm calibrated shots can be seen in my 2014 and 2015 galleries.