1904 in aviation

• Frenchman Robert Esnault-Pelterie flies a glider based on the Wright brothers' glider designs but employing ailerons rather than wing-warping for control. His glider is the first full-sized aircraft to employ ailerons.
• The French Navy disbands its balloon branch.Layman 1989, p. 15.
• During the Russo-Japanese War, the Imperial Japanese Army uses two Japanese-designed kite balloons during the Siege of Port Arthur (which begins on 1 August); they make 14 successful flights. It is Japan{{'}}s first combat use of military aviation of any kind.{{cite book |last=Francillon |first=René J. |title=Japanese Aircraft of the Pacific War |location=Annapolis, Maryland |publisher=Naval Institute Press |year=1979 |isbn=0-87021-313-X |page=29}}
• At Vladivostok, Imperial Russian Army engineer Captain Fyodor A. Postnikov and his crews make frequent ascents in spherical balloons and a kite balloon from Russian ships, and the armored cruiser Rossia tests various forms of air-sea communications from balloons and the use of shipboard balloons for directing gunfire against shore targets and in detecting naval mines.
• The Royal Swedish Navy commissions Ballondepotfartyg Nr 1 ("Balloon Depot Ship No. 1"), a barge designed to operate one kite balloon. She is the first watercraft designed and built specifically for aeronautical purposes.Layman 1989, p. 106.

• January – Before the beginning of the Russo-Japanese War, the Imperial Russian Navy conducts many experiments with towing balloons and man-lifting kites from its warships.Layman 1918, p. 91
• 22 and 24 March – The Wright brothers apply for patents for their flying machine in France and Germany.{{cite book |last=Renstrom |first=Arthur George |title=Wilbur & Orville Wright: A Reissue of A Chronology Commemorating the Hundredth Anniversary of the Birth of Orville Wright, August 19, 1871 |url=https://history.nasa.gov/monograph32.pdf |series=Monographs in Aerospace History |volume=32 |others=NASA Publication SP-2003-4532 |publisher=U.S. Centennial of Flight Commission, National Aeronautics and Space Administration |date=September 2003 |orig-date=First published 1975 |page=7 |lccn=2003051363 |access-date=10 April 2022}}
• 1 April – Captain Ferdinand Ferber makes a failed attempt to fly an Archdeacon glider at Berck sur Mer, Picardy.
• 3 April – Gabriel Voisin successfully flies a modified Archdeacon glider at Berck sur Mer, Picardy.{{cite web |url=https://www.lartigue.org/archives/us2/actualites/annees_passees/actu-avia4.html |title=Jacques Henri Lartigue and the early days of aviation |website=lartigue.org |publisher=Ministère de la Culture et de la Communication - France/AAJHL |access-date=10 April 2022}} Voisin added a canard to the design. His longest flight on this day is 25 seconds.
• 23 April – Thomas Scott Baldwin makes a flight with August Greth's dirigible The California Eagle at San Francisco. This flight predated his efforts with the California Arrow.
• April–May – John J. Montgomery and Thomas Scott Baldwin work together at Santa Clara College in California using a wind tunnel to refine propeller designs for dirigibles. These propeller designs were used on Baldwin's successful California Arrow later in 1904 and the wind tunnel was the first of its kind on the west coast of America.
• 9–11 May – The Imperial Russian Navy armored cruiser Rossia carries a balloon on a raiding cruise against Japanese ships into the Sea of Japan in the first use by a warship of a balloon on the high seas in wartime. The balloon makes 13 successful ascents before it breaks its mooring lines and is damaged after landing on the sea.Layman 1989, p. 93.
• 23 May – The Wright brothers make their first flight attempt in the Wright Flyer II. They are not successful.Renstrom, p. 8.
• 25 May – In Tandil, Argentina, Guido Dinelli flies his "Aeroplano apparatus" glider attached to a bicycle for {{Convert|180|m}}.{{cite web |url=http://www.aeroclubsanpedro.com.ar/guido%20dinelli.htm |last=Campos |first=Eduardo |title=8 de Octubre de 2004, Salón de la Sociedad Italiana de San Pedro Charla sobre el primer vuelo de un aparato mas pesado que el aire en Ibero América, el "25 de Mayo de 1904" |trans-title=8 October 2004, Salon of the Sociedad Italiana de San Pedro Talk about the first flight of a heavier-than-air aircraft in Ibero America, the "25 May 1904" |archive-url=https://web.archive.org/web/20130810202554/http://aeroclubsanpedro.com.ar/guido%20dinelli.htm |archive-date=10 August 2013 |publisher=Aero Club San Pedro |year=2004 |language=es |access-date=10 April 2022}}{{cite web |url=https://airandspace.si.edu/support/wall-of-honor/guido-dinelli-may-251904 |title=Guido Dinelli - May 25, 1904 |website=National Air and Space Museum |department=Wall of Honor |access-date=10 April 2022}}{{Unreliable source?|reason=Page includes disclaimer: "Wall of Honor profiles are provided by the honoree or the donor who added their name to the Wall of Honor. The Museum cannot validate all facts contained in the profiles."|date=April 2022}}
• 26 May – The Wright brothers make their first successful flight in the Wright Flyer II. It is the first of 105 flights they will make in the Flyer II during 1904.{{cite web |url=http://www.century-of-flight.net/Aviation%20history/aviation%20timeline/1904.htm |website=Century of Flight |title=Aviation Timeline: World Aviation in 1904 |access-date=10 April 2022 |archive-url=https://web.archive.org/web/20190303215350/http://www.century-of-flight.net/Aviation%20history/aviation%20timeline/1904.htm |archive-date=3 March 2019 |url-status=dead}}
• June – The British Army tests Samuel Cody's person-carrying kites at Aldershot.
• June – John J. Montgomery makes a series of successful test flights with his tandem-wing glider design near San Juan Bautista, California as a prototype to his successful 1905 gliders that were used to make the first high-altitude flights in heavier-than-air flying machines in the world.
• August – An Imperial Japanese Navy observer in an Imperial Japanese Army kite balloon spots fire for a naval shore battery against Russian ships in the harbor at Port Arthur during the Siege of Port Arthur. It is the first time in history that an observer in any kind of aerial device directs gunfire against a purely naval target.Layman 1989, p. 85.
• 3 August – Major Thomas Scott Baldwin demonstrates the first successful U.S. airship, California Arrow, at Oakland, California.
• 20 September – Wilbur Wright makes the world's first circuit flight, in the Wright Flyer II.
• November – The Imperial Russian Navy begins conversion of the passenger ship Lahn into an aviation ship named Russ capable of handling a spherical balloon and eight kite balloons and of supporting aerial photography. Russ is the first self-propelled, seagoing ship intended specifically for aeronautical services and the first ship to employ multiple aeronautic devices.Layman 1989, p. 94.
• 9 November – Wilbur Wright flies the Wright Flyer II a distance of {{Convert|2.75|mi}} near Dayton, Ohio, the first flight of longer than five minutes.
• Date not known – Horatio Phillips in the United Kingdom experiments with a slat-winged multiplane aircraft. It is a fully self-propelled, autonomous take-off fixed wing aircraft using an internal combustion engine and a single tractor propeller that includes its own wheeled landing gear and modern looking tail empennage. It flies for a short hop but is unstable.{{cite book |last1=Angelucci |first1=E |last2=Matricardi |first2=P. |title=World aircraft: Origins - World War I |publisher=Sampson Low |year=1977}}

{{reflist|33em}}

• {{cite book |last=Layman |first=R.D. |title=Before the Aircraft Carrier: The Development of Aviation Vessels 1849-1922 |location=Annapolis, Maryland |publisher=Naval Institute Press |year=1989 |isbn=0-87021-210-9}}

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