Laurence Yep, the author of Dragonwings, intervenes here to clarify some points. He specifies what he means by Tang as the dynasty that ruled from 618 to 907 A.D. Yep suggests that "Tang" might be more accurately written "T'ang" (Afterword.1).
The author shares that the book was based on accounts of a young Chinese flier, Fung Joe Guey. Yep also shares that little is known about Fung Joe Guey and other early Chinese Americans. He has tried to imagine what life was like for these individuals that history sometimes forgets or lumps into a faceless group. He's also tried to be true to the time period.
Yep writes that this book was meant as an intervention against other stories that are written about Chinese people in America, namely Dr. Fu Manchu and Charlie Chan, both of which are characters that have created stereotypes about Chinese and Chinese American people.