Question: William Harper Jr. was a pioneer aviator and aviation engineer with which two American brothers, inventors, and aviation pioneers who are generally credited with inventing, building, and flying the world's first successful airplane?

Context articles: Neta Snook
Hilder Florentina Smith
Wright brothers
Vecihi Hürkuş
John Henry Towers
William J. Powell
Aviator Monument (Stockholm)
William Harper Jr.
The Wright Brothers (book)
John Robertson Duigan

Neta Snook Southern (February 14, 1896 – March 23, 1991) was a pioneer aviator who achieved a long list of firsts.
 She was the first woman aviator in Iowa, first woman student accepted at the Curtiss Flying School in Virginia, first woman aviator to run her own aviation business and first woman to run a commercial airfield.
 Yet "Snooky", as her friends called her, was fated to be remembered for her relationship to Amelia Earhart.
 Her autobiography "I Taught Amelia to Fly" aptly captures the essence of her fame, she was forever linked to the Earhart mystique as her first instructor.
Hilder Florentina Youngber Smith (August 10, 1890 – January 11, 1977) was a pioneer aviator.
 She was one of California's first female pilots and the first woman to fly an airplane from LAX.
 She was a member of a flying aerial team called The Flying Sylvesters.
The Wright brothers, Orville (August 19, 1871 – January 30, 1948) and Wilbur (April 16, 1867 – May 30, 1912), were two American brothers, inventors, and aviation pioneers who are generally credited with inventing, building, and flying the world's first successful airplane.
 They made the first controlled, sustained flight of a powered, heavier-than-air aircraft on December 17, 1903, four miles south of Kitty Hawk, North Carolina.
 In 1904–05 the brothers developed their flying machine into the first practical fixed-wing aircraft.
 Although not the first to build and fly experimental aircraft, the Wright brothers were the first to invent aircraft controls that made fixed-wing powered flight possible.
Vecihi Hürkuş (6 January 1896 – 16 July 1969) was a pilot fought at World War I and Turkish Independence War, aviation engineer and aviation pioneer in Turkey.
 He designed and built the first airplane in Turkey.
 He also founded the first Airline company in Turkey.
John Henry Towers (January 30, 1885 – April 30, 1955) was a United States Navy admiral and pioneer naval aviator.
 He made important contributions to the technical and organizational development of naval aviation from its very beginnings, eventually serving as Chief of the Bureau of Aeronautics (1939–1942).
 He commanded carrier task forces during World War II, and retired in December 1947.
 He and Marc Mitscher were the only early Naval Aviation pioneers to survive the extreme hazards of early flight to remain with naval aviation throughout their careers.
 He was the first naval aviator to achieve flag rank and was the most senior advocate for naval aviation during a time when the Navy was dominated by battleship admirals.
 Towers spent his last years supporting aeronautical research and advising the aviation industry.
William Jenifer Powell (July 27, 1897 – July 12, 1942) was an American engineer, soldier, civil aviator and author who is credited with promoting aviation among the African American community.
 Along with Bessie Coleman and James Banning, he is recognized as a pioneer aviator and a civil rights activist.
 Powell was optimistic about the prospects of African-Americans in aviation, and believed that their involvement in the industry would help end racial prejudice at a time of widespread segregation under the Jim Crow laws.
The Aviator Monument (Swedish: Flygarmonumentet ) is a statue that stands at Karlaplan in central Stockholm, Sweden.
 The statue was a gift from the Swedish Aeronautical Society in memory of different Swedish aviation pioneers who fell in both the North Pole expedition and in the first time of the Swedish aviator era in 1917.
 The task to build the monument was given to the famous sculptor Carl Milles.
 The Aviator Monument was finished in 1931.
William Harper Jr. was a pioneer aviator and aviation engineer with the Wright brothers.
The Wright Brothers is a 2015 non-fiction book written by the popular historian David McCullough and published by Simon & Schuster.
 It is a history of the American inventors and aviation pioneers Orville and Wilbur Wright.
 The book was on "The New York Times" Non-Fiction Best Sellers list for seven weeks in 2015.
John Robertson Duigan MC (31 May 1882 – 11 June 1951) was an Australian pioneer aviator who built and flew the first Australian-made aircraft.
 Duigan was born in Terang, Victoria, and grew up in Melbourne attending Brighton Grammar School.
 He travelled to the United Kingdom in late 1901 to study electrical engineering at Finsbury Technical College in London (1902-1904) and Motor Engineering at Battersea Polytechnic (1905).
 He worked for the Wakefield & District Light Railway Co. until 1907 when he returned to Australia.
 From 1908 he lived at 'Spring Plains', a sheep station owned by his father near Mia Mia in central Victoria.
 After seeing a postcard of Wilbur Wright's flights in France in late 1908 he began experimenting with aviation, first constructing a Wright-type glider, and then a powered aircraft.
 The 20-25 horsepower, four-cylinder engine was made in Melbourne by J.E. Tilley.
 This Farman-type biplane made a short flight on 16 July 1910, but Duigan never considered this to be a fully controlled flight.
 He regarded his longer flight of 7 October 1910 as his first successful attempt.
 This was followed by ever longer and higher flights.
 His younger brother, Reg Duigan assisted with most aspects of the construction and testing of the biplane and later flew it about a dozen times.
 The biplane was flown in public at Bendigo Racecourse on 3 May 1911 where it completed its only circling flight as the paddock at Spring Plains was surrounded by hills and trees.