[hharney]

Cessna never made the same Skymaster throughout it's manufacturing process. That's why there is Straight, A's, B's, C's etc. models. They continued to make changes to try to market the airplane. The gross weights changed throughout the years also, it increased as the models increased. My personal understanding is because of marketing. They may have had to spend some money to add these extras (changes in certification) but it must have made sense to them to do it. The 1971 F model has the highest gross weight and therefore useful load too. It was the last of the swing door models and therefore had the latest and greatest stuff. Structurally, was it the same as the D as you asked? I am sure there must have been something to convince the FAA that the gross weight could be increased, what those are I am not 100% sure. But something justified it. The F model is the one to get if you can find one, rare birds. They only made 83 F models in 1971 and 64 F models in 1972. That is if you want a swing door model, but they were lighter planes and had the luggage door too. The 1973 and after got heavier and they eliminated the luggage door. There are some other differences to like the front prop blades are 2 inches longer than the rear prop blades. Why? To even the score on the single engine climb and ceiling for each engine. The rear was always better than the front so the solution was to put a longer blade on the front. Too bad because it really made the blade clearance close to the ground.

I have never seen any angle/pitch info on the Robertson STOL mod. Not sure it would be eas to do with all the models and differences that were made over the years. AOA would have helped back then but no one used those much for testing.

Hope that helps too