Hughes H-4 Hercules
Hughes H-4 Hercules
Heavy Transport Aircraft
Number Built
1 (Prototype)

Hughes H-4 Hercules Program Milestones
First Flight
November 2, 1947
Aircraft Retirement
November 2, 1947

Hughes H-4 Hercules Aircraft Dimensions
Wing Span
319 feet 11 inch (97.54 m)
218 feet 8 inch (66.65 m)
Fuselage Height
30 feet (9.1 m)
79 feet 4 inch (24.18 m)

Hughes H-4 Hercules Weights
Empty Weight
300,000 lb (136,079 kg)
Maximum Payload
400,000 lb (181,439 kg)

Hughes H-4 Hercules Powerplants
8 x PW R-4360 Wasp Major
3,000 hp

Hughes H-4 Hercules Radius & Performance
3,000 nm (4,800 km)
Endurance (Projected)
20.9 hours
Service Ceiling
20,900 feet (6,370 m)
Maximum Crusing Speed
220 mph (353,98 km/h)

Flight Deck of the Hughes H-4 Hercules
Hughes H-4 Hercules Information
The Hughes H-4 Hercules is built and designed by the Hughes Aircraft company and flew for the first and only time on 2 November 1947. The aircraft was built from wood due to wartime raw material restrictions to the use of aluminium and was granted the nickname "Spruce Goose" by its critics, mainly because some accused Howard Hughes of misusing government funding to build the aircraft. The Hercules is the largest flying boat ever built, and has the largest wingspan and height of any aircraft in history. At this moment the aircraft is stationed at the Evergreen Aviation Museum in McMinnville, Oregon.

Although the aircraft was build of materials other than metals, the H-4 was built almost entirely of laminated birch, not spruce as its nickname suggests. The aircraft was considered a technological tour de force. It married a soon-to-be outdated technology, flying boats, to a massive airframe that required some truly ingenious engineering innovations to function. Ultimately, however, the project was an expensive failure and, at the end of the war, was cancelled.


Hughes H-4 Hercules Design
During the second world war, the United States Department of War was faced with the need to transport war material and personnel to Britain. Due to German U-boats, allied shipping across the Atlantic Ocean suffered major losses so a requirement was issued for an aircraft that could cross the Atlantic with a large payload. The H-4 Hercules was designed by Henry J. Kaiser who later teamed with aircraft designer Howard Hughes to create what would become the largest aircraft built. When completed, the aircraft was capable of carrying 750 fully-equipped troops or several M4 Sherman tanks. The original designation, the "HK-1", reflected the collaboration between Kaiser and Hughes.

Initially, the HK-1 contract called for three aircraft to be constructed under a two-year deadline in order to be available for the war effort. Seven different configurations were considered including twin-hulled and single-hulled designs with combinations of fours, six and eight, wing-mounted engines. The final design chosen was a behemoth, eclipsing any large transport yet built or even envisioned. In order to conserve metal, it would be built mostly of wood hence, the "Spruce Goose" nickname.

Although Kaiser had originated the "flying cargo ship" concept, he did not have an aeronautical background and deferred to Hughes and his designer, Glenn E. Odekirk. Development dragged on which frustrated Kaiser who blamed delays partly on restrictions placed for the acquisition of strategic materials such as aluminium but also placed part of the blame on Hughes' insistence on perfection. Eventually, Kaiser withdrew himself from the project.

Hughes continued the project on his own under the designation "H-4 Hercules", signing a new government contract that now limited production to only one example. Work continued at a slow pace with the end result that the H-4 was not completed until well after the war was over. There were many reasons for this, including Hughes' mental breakdown during development of the aircraft.

In 1947, Howard Hughes was called to testify before the Senate War Investigating Committee over the usage of government funds for the aircraft. Even though he encountered skepticism and even hostility from the committee, Hughes remained unruffled.

During a break in the Senate hearings, Hughes returned to California in order to execute some taxi tests on the H-4. On 2 November 1947, after a series of taxi tests with Hughes himself at the controls and co-pilot Dave Grant next to him, the Hercules lifted off from the waters of Long Beach, remaining airborne 70 feet off the water at a speed of approximately 135 mph. At this altitude, the aircraft was still experiencing ground effect and some critics suggested that the aircraft lacked the power necessary to climb above the ground.