In the 1970s, I read a sci-fi novel in high school, where the main character was a black girl, a point purposely not made clear until late in the book. It takes place in a post-apocalyptic (is there any other kind?) Earth. She meets a white boy, and they discover a helicopter, which, miracle-of-miracles, works! I don't remember more than that, except that I enjoyed the book. If that description rings any bells, could you tell me the title? (and, yes, I did numerous web searches, but, couldn't find anything even close) Thanks!