The only data collection/test flights I ever went on, and I flew on several "missions", was in a Convair 580. I wrote the "navigation" software and it had an error in it that I didn't discover until some years later.. oh well, we got the data we were trying to gather in spite of the error. It's very interesting to be standing in the mostly empty cabin when the pilot goes into a 45-60 degree bank. You get rather heavy and things look strange, especially if you are looking up through the cockpit and out the windscreen, although seeing nothing but trees out the side window is also rather curious, or in one case an airport about a mile or two from my house, that we just happened to be over at the time.
WOW! Our pilots were a bit more "tame" :-)