Hughes H-4 Hercules (Spruce Goose) Heavy-Lift Transport / Flying Boat Prototype

The Hughes H-4 Hercules, ridiculed as the Spruce Goose, remains the largest flying boat ever constructed and features the largest wingspan of any aircraft ever made.

Updated: 5/11/2016; Authored By Staff Writer; Content ©www.MilitaryFactory.com

This famous Howard Hughes flying boat aircraft - formally designated by Hughes Aircraft as the H-4 "Hercules" - only ever achieved a single flight (with Hughes himself at the controls) and was only produced in a single working example. The folly of the project garnered the H-4 the nickname of "Spruce Goose" and largely termed a failure in the scope of World War 2-era aircraft design. The primary drive behind such a large airframe was in providing the United States military - then committed to war in Europe and the Pacific - with an oversized transport capable of airlifting large quantities of battlefield equipment to the front. This was strengthened by regular losses of Allied shipping from German U-Boats in the Atlantic and elsewhere, taking their toll on vital supplies attempting trying to reach forces in Europe. As such, a military requirement was put forth for a trans-Atlantic freighter-type aircraft capable of a considerable payload.

Despite the seemingly promising nature of the H-4 design, it simply arrived too late in the war to serve much of a purpose, additionally adding to the image of the project as a complete failure for Hughes. The H-4 also suffered from the defense spending drawn down once the war had officially come to a close - many projects were either suspended indefinitely or cancelled outright. Hughes was then forced to appear before a Senate committee to answer for government funds spent on his H-4.

Upon its completion, the H-4 became the world's largest aircraft and largest flying boat ever designed and produced to that point. Power was served through 8 x Pratt & Whitney R-4360 28-cylinder engines developing 3,000 horsepower each. Four engines were fitted to a wing. Each wing was high-mounted in its installation and straight in its general design with the engine nacelles fitted at the leading edges. Each wing itself was the full wingspan of just one competing Boeing B-29 "Superfortress" four-engined heavy bomber. To demonstrate the internal carrying capacity of the H-4, the hold could service up to 700 combat infantry or two M4 Sherman Medium Tanks. Endurance of the aircraft was estimated to be approximately 21 hours of flight time. Its flying boat qualities - aided by its boat-like hull and outboard-mounted pontoon legs - allowed the H-4 to take-off and land from just about any water source. Additionally, the aircraft was constructed of wood (birch) which helped buoyancy and would not require heavy use of metals in its construction (metal proving a critical wartime resource). The wood approach was also spanned into another Hughes wartime project - the D-2 heavy fighter (detailed elsewhere on this site). The "Spruce Goose" ridicule is related to the product's heavy use of wood in its construction.

The initial H-4 concept was drawn up by Henry Kaiser while the direct design was put together by engineer Glenn Odekirk. Howard Hughes served as the project's overseer and would be the hands at the controls during her one and only flight. The one and only prototype was saved in the post-war draw down and can be seen in its full glory at the Evergreen Aviation Museum of McMinnville, Oregon, USA.

As much as aviation technology has advanced to this day (November 2013), the Hughes H-4 Hercules still maintains the largest wingspan of any aircraft ever built, let alone considered for production. This claim to fame includes even the mammoth American Boeing 747 and the Soviet/Russian An-225 Mriya offerings. Additionally, no other flying boat design has bested her dimensions.

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Hughes H-4 Hercules Technical Specifications

Service Year: 1945
Type: Heavy-Lift Transport / Flying Boat Prototype
National Origin: United States
Manufacturer(s): Hughes Aircraft - USA
Production Total: 1

Structural (Crew Space, Dimensions and Weights)

Operating Crew (Typical): 3
Overall Length: 218.67 feet (66.65 meters)
Overall Width: 320.01 feet (97.54 meters)
Overall Height: 79.33 feet (24.18 meters)

Weight (MTOW): 396,832 lb (180,000 kg)

Installed Power and Standard Day Performance

Propulsion: 8 x Pratt & Whitney 28-cylinder R-4360 propeller engines developing 3,000 horsepower each.

Maximum Speed: 199 mph (320 kph; 173 knots)
Maximum Range: 2,983 miles (4,800 km)
Service Ceiling: 20,899 feet (6,370 meters; 3.96 miles)
Rate-of-Climb: 1,000 feet-per-minute (305 m/min)

Armament / Mission Payload

None.

Global Operators / Customers

United States (cancelled)

Model Variants (Including Prototypes)

HK-1 - Original Design Designation that reflects the collaborative efforts of design and concept from Henry Kaiser and Howard Hughes ("HK").

H-4 - Base Designation with the wihtdrawal of Henry Kaiser from the project.

HFB-1 - Another designation attributed as a recognition of "Hughes Flying Boat - First Design".