Let's Build a Big One
I was two years old when this idea was hatched. The concept of building an airplane that had a wing-span that was longer than a football field actually originated with a gentleman named F. H. Hoge, Jr. Henry Kaiser got behind it and asked for help from billionaire Howard Hughes. The project was stamped with approval in 1942, and the rest is history. This lens shows a little bit of that history in words and pictures.
The idea intrigued the industrialist and shipbuilder Henry Kaiser, famous for building the Liberty Ships during World War II. In July, 1942, he suggested that the United States build an "aerial freighter" of at least seventy tons, a "gigantic flying ship" beyond anything imagined by the nineteenth-century science fiction writer Jules Verne. Kaiser asked for help from the billionaire Howard Hughes, a crack designer and pilot who had broken several airspeed records during the 1930's.
The project was approved in October, 1942. A team from Hughes Aircraft Company would design the craft and build one prototype and two additional planes. Once tests were completed, Kaiser's companies would begin regular production. The project was initially designated the HK-1 (HK for Hughes/Kaiser). Once design work had begun, Hughes employees voted to name it the H-4 Hercules. Hughes himself disliked the popular name of "Spruce Goose" and preferred to call the aircraft "the Flying Boat."
The project fell well behind schedule very early, mainly due to a multitude of design and construction problems. Kaiser dropped out of the project, and Hughes was forced by various government bodies to defend the project. Only continued support from the War Production Board and the personal intervention of President Franklin D. Roosevelt kept the project going.
The problems involved in designing and building such an airplane were massive. Kaiser had suggested that the overall size of the first prototype be seventy tons, but Hughes made the work more challenging by changing the size to some two hundred tons. The goal was an aircraft that could carry 130,000 pounds of cargo or 750 troops (twice the passenger load of a modern Boeing 747).
Working at the Hughes Aircraft Company plant in Culver City, California, and at other sites, the Hughes team tested a variety of shapes for air and water efficiency. The final design model, based on decisions largely made by Hughes himself, recorded the lowest air drag of any seaplane ever tested at the National Advisory Committee for Aeronautics' Research Center at Langley Field, Virginia. Instead of a double-hulled plane, Hughes choose a single-hulled design which would require a wingspan 50 percent larger than the next largest plane of the time, the Martin JRM Mars. It was also decided that the aircraft would have a sizeable single vertical tail.
The final design divided the interior of the fuselage into two decks connected by a spiral staircase: a flight control deck for the operating crew and a cargo deck. Two railroad cars could fit in the interior cargo space, on a floor that was designed to carry 125 pounds per square foot. If planks were provided for its tracks, a 60-ton army tank could drive inside, under its own power, without the need to dismantle any part of the tank. The hull also contains eighteen watertight compartments, twelve of which might flood without sinking the craft.
In its final design, the Spruce Goose has an overall length of 218 feet. Its 320-foot wingspan exceeds even that of the U.S. Air Force's modern transport, the Lockheed C-5A Galaxy. The tail alone, at 113 feet, is more than eight stories high. The hull is 265 feet wide and the wings, at their thickest, are more than 11 feet thick. The craft has a gross weight of 400,000 pounds and a range of 3,500 miles. It cruises at 175 miles per hour and has a landing speed of 78 miles per hour.
Hughes chose to power the plane with Pratt & Whitney R-4360 engines. Eight of these twenty-eight-cylinder, 3,000-horsepower engines were mounted in the wings. The engines, radial in shape, sport four-blade Hamilton Standard propellers more than 17 feet in diameter. There are a total of 448 spark plugs to service and maintain. Although the total engine horsepower of 24,000 is impressive, the engines' ability to lift a craft of more than 400,000 pounds is a real achievement for both their makers and the Hughes team's overall design efforts.
Flight controls that would respond reliably and quickly were a special problem for such a gigantic aircraft. The layout of the flight controls on the flight deck is conventional- a dual column and wheel to turn the elevator and ailerons, and pedals for the rudder. Less conventional is the way that the craft was designed to respond to these controls. Instead of a mechanical system, Hughes and his team chose a hydraulic system in which pressurized oil moves the control surfaces. Purely mechanical links between the flight deck and the rest of the plane would have required the strength of 150 to 200 men just to turn the controls. Mechanical links also are unreliable in such a massive aircraft. The Spruce Goose is so large that changes in temperature could cause metal parts to expand and contract, possibly jamming in the process.
In addition to wing fuel tanks, there is a central fuel system in the hull. Fuel lines in the wings, however, have slip joints to allow for wing deflections of as much as 13 feet during flight.
The Spruce Goose pioneered the use of a 120-volt DC electrical system in airplanes. This relatively high voltage leaves a safety margin in case of electrical leakage in any of the 32 miles of wire inside the Spruce Goose. It also allows manageable wire sizes to be used. (A 24-volt system, the engineers calculated, would have required solid aluminum rods 2 inches in diameter in order to carry the current.) Electrical relays are specially designed to work at high altitudes.
The Actual Flight:
On November 2, 1947, a test of the plane was scheduled which involved taxiing the craft across Long Beach Bay. Some members of the press were invited to ride aboard the plane, and Hughes took the controls. After two successful trips across the bay, Hughes increased the plane's speed during the third attempt. He delighted a sizeable crowd of onlookers by lifting the plane off the water. After traveling for a mile at a height of about 70 feet, the craft landed smoothly. Although it was the only flight ever made in the Spruce Goose, it became a memorable moment in aviation history.Although Hughes described the test flight as "just great," he never flew the craft again. There are varying opinions as to why he made no further attempts. Some argue that the plywood construction was not totally satisfactory (some workers claimed that Hughes attempted to address this by adding a corrugated aluminum skin and metal stiffeners into the gigantic wing). Others believe that Hughes saw congressional criticism as a challenge and lost interest after the successful flight.Yet Hughes continued to spend money on the aircraft. Although the original plans had called for three Spruce Gooses, no other versions of the planes were ever produced. The prototype remained in Hughes's control for the remainder of his life, sitting in a hangar that was air-conditioned to provide the proper humidity to preserve the wood.The craft was kept airworthy and the engines were fired up every month. The Spruce Goose was painted white. Hughes continued to make improvements, such as installing more powerful engines. When flooding damaged the Spruce Goose, Hughes built a larger hangar. While the United States government spent some $22 million on the project, Hughes spent an estimated $7 to $18 million dollars of his own money to complete and maintain the Spruce Goose.