I’ve seen several kinds of aircraft from Cesar Chavez Park, but never saw one of these before. It looks like a type of Vertical Take Off and Landing (VTOL) machine, a Tiltrotor, where the axis of the large, helicopter-like propellers can rotate 90 degrees. The shaft is vertical for takeoff and landing and then gradually swivels toward the horizontal for flight, as in the photo. I don’t know anything about these machines but I’m guessing, from looking at Wikipedia, that this may be a Bell-Boeing V22 Osprey. I saw it on 3/12/19 at 2:58 p.m.