Sikorsky is actually working jointly with NASA and the other helicopter manufacturers to develop low noise proprotors for tiltrotors. The Comanche has five blades in its rotor that how it is quieter. The first test was mostly as system checkout test. The second test entry is to acquire the research quality data. However, we are quickly scrambling to look at the data from the first test.
More rotors move the air continuasly and les rotors kindof let the air slow down and speed up.
I do my coin collecting just for fun, and my save my most valuable coins to use for college. There all very interesting, but CIA spy planes would probably be my most favorite. If you haven't seen Aviation Week magazine before you should get hold of copies. I never heard of them until I started working at Ames. My first tiltrotor work was in 84.