Originally published under Baum's pseudonym Edith Van Dyne, which he also used for Aunt Jane's Nieces and Mary Louise, his series books marketed specifically to girls. It's included in the third volume of Oz-Story Magazine, which is how I read it. Baum wrote this in the early days of aviation, with inventor Stephen Kane working on a new kind of biplane that he thinks will be a vast improvement over the others. The real protagonist, however, is his sister Orissa, who is working as a secretary to a real estate mogul to help support the family. She finds out that her boss, Mr. Burthon, is in a rivalry with his brother-in-law Mr. Cumberford, and is trying to rip him off. When Burthon learns about the aircraft, he at first tries to buy into it, only for Cumberford to offer a much better deal. He then resorts to trickery and sabotage, and even proposes marriage to Orissa. I hadn't realized when I started reading this that much of the conflict is centered around cutthroat business practices. Orissa ends up flying the plane after Stephen is injured, and becomes famous as the Flying Girl (although the characters are quick to point out that she isn't the first female aviator). I know there's a sequel, The Flying Girl and Her Chum.