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Specifically, this question relates to Gustave Whitehead's achievement, credited with first flight by one state and evaluated by a growing number of historians. This question is specific to Gustave Whitehead, and therefore is not a duplicate of previous general questions about the Wrights and anyone who might have flown before them. Gustave Whitehead, German immigrant and Connecticut resident, has been credited with the first successful powered flights of mankind by the State of Connecticut and many of his contemporaries.
According to substantial documentation, Whitehead flew powered aeroplanes successfully in 1901-1904, including predating the Wrights' flights by two years and three months. My book, "Gustave Whitehead: First in Flight" (2015), lists the evidence, showing why he wasn't more widely credited in recent decades. It includes extensive detail about how the Wrights managed to obtain credit, in order to win their lawsuit against Curtiss and gain broader patent rights. Mainstream historians dislike the Whitehead claim and point to what their competitor, Orville Wright, said about it.
Did Whitehead achieve powered flight before the Wrights?