ASME International

Howard Hughes’ Flying Boat “Spruce Goose”

Historic Mechanical Engineering Landmark

July 20, 2002

Evergreen Aviation Museum The Captain Michael King Smith Educational Institute In July 1942, the world was at war. America had just lost 800,000 tons of her supply ships to German U-boats. Henry Kaiser, famed industrialist and builder of “Liberty” ships, proposed a fleet of flying The fuselage under construction transports to safely move troops and Adhering to the government mandate not to use materials critical to the war effort (such as steel and aluminum), the Hughes team materiel across the Atlantic. Kaiser constructed the Flying Boat out of wood. Testing new concepts for large-scale hulls and approached Howard Hughes with his control surfaces, plus the incorporation of complex power boost systems, delayed the construction process. idea. Together they formed the Hughes In mid 1944, Henry Kaiser withdrew from the project, and Hughes renamed the seaplane H-4, Kaiser Corporation and obtained an representing his aircraft company’s fourth design. After the war’s end in 1945 criticism of the project mounted. The Flying Boat prototype $18,000,000 government contract to had exceeded the government’s funding allowance and the U.S. Senate formed an construct three flying boats. investigation committee to probe alleged misappropriation of funds. Hughes invested $7,000,000 of his own into the project to keep it going. Hughes and his team of skilled engineers Meanwhile, the Hughes team assembled the Flying Boat in the Long Beach dry dock. Wishing to vindicate himself after a being designed a single hull flying boat interrogated by the Senate committee in Washington, D.C., Hughes returned to capable of carrying 750 troops. The California and immediately ordered the Flying Boat readied for taxi tests.

On November 2, 1947, a crowd of expectant plans called for eight 3,000 horsepower observers and newsmen gathered. With Hughes at the controls, the giant Flying Boat engines, a mammoth fuel storage and glided smoothly across a three-mile stretch of harbor. From 35 miles per hour, it cruised to 90 during the second taxi test when eager supply system, and wings 20 feet longer newsmen began filing their stories. During the third taxi test, catching the media and crowd unaware, Hughes lowered the wing flaps and than a football field. The aircraft was lifted the seaplane off the water flying her a little over a mile at an altitude of 70 feet for dubbed the HK-1, standing for the approximately one minute. The short hop proved to skeptics that the gigantic machine could, indeed, fly! Hughes Kaiser design number 1. Technical Aspects “Gunite” dies. Gunite is a patented process for from the tanks, located below the cargo deck, placing concrete mortar with compressed air. The creation of the Hughes Flying Boat to two 300-gallon wing tanks. One wing tank The Gunite process produced difficult shapes involved many engineering disciplines. Not fed the four inboard engines, and the other easily at a relatively low cost. only did mechanical engineers participate in wing tank fed the four outboard. The Flying Boat was also equipped with an emergency the numerous aspects of the aircraft project, Intensive research resulted in one of the fuel transfer and supply system in case of but their efforts ranged in breadth from the earliest practical uses of epoxy resins. The leakage or pump failure. models constructed for wind tunnel evaluation main structural material for the huge craft was and towing basin tests through to the final built up by bonding several plies of birch launching details of the completed seaplane. veneer with a ureaformaldehyde adhesive. In addition, some spruce, poplar, maple, and balsa Mechanical engineering was involved in were employed. Special corner angles were designing many elements of the Flying Boat: developed to replace glue blocks. Glue blocks the jigs and fixtures for molding the aircraft were a serious problem for the aircraft builders parts; the fire suppression systems; multiple because of differential expansion across and hydraulic components such as flareless tubing with the grain. Thousands (about eight tons) fittings and slip joints; the fuel and oil tanks; of small nails were used to provide pressure for the pumps and piping for the fuel and oil attaching the hull and wing skin. After the supplies; the oil cooling system; and the adhesive had cured, they were removed with cockpit instrumentation—not to mention the specially designed nail pullers. The result was design of the massive engines and full an immense wooden airframe able to withstand feathering propellers with reversing capability. the stresses of flight without being too heavy. Giant wings under construction Laminated wood Construction Fire Protection Engine Oil Supply System The principal structural material used for the Each of the seaplane’s eight engines had a 31- The wooden construction made fire protection Hughes Flying Boat was birch veneer. Members gallon oil lubricating tank. Each of these tanks a high priority. The amount of fire protection were built up using several plies of thin veneer was replenished from a central 281-gallon tank equipment aboard the Flying Boat is impressive. bonded together. When glued and steam located in the rear of the flight deck. The oil A total of 36 CO (carbon dioxide) pressure heated, birch held up better than spruce, and 2 containers are located on the cargo deck. supply system operated automatically with a it took the bolting stresses better. By laminating float in each individual tank or manually. The They provided both primary and auxiliary fire birch in multiple grain directions, the necessary oil piping in each engine nacelle consisted of a control to the fourteen fuel tanks and to each grip for bolts proved practical. Birch was also main engine-oil pipe, reserve-oil supply lines, of the eight engines. A complex manifold superior in terms of weight reduction in high vent lines and propeller-feathering piping. stress applications. allowed the gas to be directed to the plane’s various areas as needed. If required, all 36 Carburetor inlet scoops were placed below each engine nacelle, and oil coolers were placed in the Duramold, a lamination bonding process, was bottles could be discharged into one area for originally created for molding parts for smaller maximum effectiveness. inlets, which were enclosed by the air-scoop aircraft. The contoured surfaces were very fairings and temperature regulating doors. smooth and provided great aerodynamics. Electrical System Propellers Originally developed by Fairchild Aircraft Hughes and his team of engineers discarded Company, Howard Hughes purchased the the idea of using the conventional 24-volt Each of the eight Pratt and Whitney Wasp rights to use it in large aircraft. Because the direct current (D.C.) system for the aircraft, Major R-4360 air-cooled radial engines drove pieces required were so big, and the materials primarily because of weight, and designed a a Hamilton Standard four-bladed, hydromatic, for steel dies costly and in short supply, new 120-volt, three wire, redundant D.C. full-feather propeller measuring 17 feet 2 Hughes fabricated and experimented with system, which brought about a weight inches in diameter. The four inboard propellers reduction of 75 percent. Care also was taken could provide reverse thrust. The thrust to insure that all the electrical relays would reversing capability would assist the Flying perform at high altitudes. Two 30-kilowatt Boat back off the beachhead after loading or generators provided backup electrical power, unloading its cargo. and emergency battery power consisted of ten Engine Controls 12-volt batteries in two banks. Originally designed with four throttles—one Fuel System for each pair of engines, Hughes changed the To attain a range of 3,000 miles, the Hughes design to eight after the flight, one for each Flying Boat was equipped with fourteen tanks, individual engine. At first, all engines operated complete with baffles to minimize fuel by Pneudyne’s pneumatic system, or compressed sloshing. Each fuel tank had a 1,020-gallon air in place of hydraulic fluid. However, it was capacity, but to allow for expansion each was difficult to control them precisely, and no two valves would operate the same with identical Workers making Duramold parts filled to only 900 gallons. Fuel was transferred pressure. After the flight, Hughes had electric Control Surfaces throttles installed, along with servos for The enormous control areas (ailerons, flaps, throttle control on all eight engines, which elevators and rudder) cover 4,414 square feet, gave them a response time of 1/300 of a second. and all are fabric covered except the flaps.

Flight Controls Flareless Tubing Connectors Hughes and his team of engineers developed The Flying Boat was the first aircraft to utilize the first “artificial feel system” in the control flareless tubing connectors in the hydraulic lines. yoke, which gave the pilot the feeling he was flying a smaller aircraft, but with a force Wing Deflection multiplied two hundred times. For example, Fuel lines were equipped with “slip” joints and for each pound of pressure exerted on the “floating” fairleads to allow for the deflection control yoke by the pilot, the elevator received of the wings. The Hughes Flying Boat at the Museum 1,500 pounds of pressure to move it.

The Flying Boat required two auto-pilot systems Flight Deck Layout: and today, thanks to the many dedicated to her survival, she rests among other historic but Howard Hughes’ passion for safety required The pilot and co-pilot’s cockpit flight controls aircraft at the Evergreen Aviation Museum. five hydraulic control systems, which included are each equipped with a control column and two main systems, two auxiliary systems, a wheel, pedal operated rudder control, and The History and Heritage Program of hand pump system, plus an emergency flying- engine throttles between the two positions, ASME International tab system in case of complete hydraulic plus essential engine and navigation The History and Heritage Landmarks Program failure. Conventional control cables directly instruments. A starboard-side flight engineer’s of ASME International (the American Society connected cockpit controls to the control station is immediately behind the co-pilot’s of Mechanical Engineers) began in 1971. To surfaces, however, they did not move the seat and contains dials and gauges to monitor implement and achieve its goals, ASME control surfaces. They only provided a follow- the eight engines, throttles, alarm formed a History and Heritage Committee up to ensure the proper relationship between annunciators, fuel indicators and hydraulic initially composed of mechanical engineers, the pilot’s control positions and the actual status gauges. The radio operator’s console is historians of technology and the curator (now deflections of the control surfaces. The located on the port side, directly behind the emeritus) of mechanical engineering at the Hughes engineers used electrically driven, pilot’s seat and the flight test temperature Smithsonian Institution, Washington, D.C. high-pressure hydraulic pumps that provided recorder’s desk is behind it. Also on the port The History and Heritage Committee provides side is a table for the strain gauge calibration a public service by examining, noting, equipment. On the port side aft is the assistant recording and acknowledging mechanical flight engineer’s station, complete with the engineering achievements of particular more essential dials and gauges. The console significance. This Committee is part of for the propeller test equipment is located on ASME’s Council on Public Affairs and Board the starboard side aft. In addition, a number of on Public Information. For further information, chairs are provided as a “crew rest area.” please contact Public Information at ASME Bocking Elevator International, Three Park Avenue, New York, NY 10016-5990, (212) 591-7740. A novel elevator equipped with guardrails, located in the rear of the flight deck, is Designation designed to lift personnel through a top- Since the History and Heritage Program began opening hatch. Equipped with a microphone in 1971, 218 landmarks have been designated Flying Boat assembly connected to the aircraft’s communications as historic mechanical engineering landmarks, network, the personnel could supervise the operating power for the systems. When heritage collections or heritage sites. Each docking and mooring of the Flying Boat from a the pilot moved the controls, he actuated represents a progressive step in the evolution vantage point atop the fuselage. sensitive relay valves that transmitted of mechanical engineering and its significance metered, pressurized hydraulic fluid into Today to society in general. Site designations note an tubing that led to receiving relay valves event or development of clear historic Now commonly called the “Spruce Goose,” located at the control surfaces. The receiving importance to mechanical engineers. Collections the Hughes Flying Boat has endured to valves in turn permitted pressurized oil to flow mark the contributions of a number of objects become a popular cultural icon of American to the power cylinders, which actually moved with special significance to the historical history. She tells a story of wartime sacrifice, the control surfaces. To insure complete safety, development of mechanical engineering. determination and technological development. each control surface was operated by two She still is the largest wooden seaplane ever The Landmarks Program illuminates our independent, self-contained telecontrol built, and she proved that jumbo flying aircraft technological heritage and encourages the systems, which were supplied with electric and large lift capability were possible. She was preservation of the physical remains of power from two separate generators. decades ahead of her time in the early 1940s, historically important works. It provides an

Historic Mechanical Engineering Landmark Hughes Flying Boat, “Spruce Goose”

Constructed: 1943–1946 forms the airframe and surface structures of the seaplane, Assembled: 1946–1947 minimizing the use of critical war materials, such as Designed and built by Hughes Aircraft Company, this is aluminum. It was powered by eight Pratt and Whitney the largest wood constructed and the largest wingspan 3,000 horsepower engines. airplane ever built. Howard Hughes piloted the Flying Boat on its only flight, November 2, 1947, in Long Beach Harbor, Long Beach, Originally designated the HK-1 in 1942, the Flying Boat was designed to meet wartime troop and materiel California. The flight covered approximately one mile and transportation needs. Laminated wood (mostly birch) reached an altitude of approximately 70 feet above the water's surface.

annotated roster for engineers, students, William DeFotis Notable Hughes educators, historians and travelers. It helps Paul J. Torpey, Past President establish persistent reminders of where we Flying Boat Facts: have been and where we are going along the Herman Viegas, P.E. divergent paths of discovery. Diane Kaylor, Staff Liaison Cargo aircraft prototype The 125,000-member ASME International is a Largest wingspan: 319 feet, 11 inches with a Wil Haywood, Public Information Coordinator worldwide engineering society focused on wing area that covers 11,430 square feet technical, educational and research issues. ASME Oregon Section Features cantilever wing and tail surfaces ASME conducts one of the world’s largest Joy E. Conley, Chair Tallest aircraft: 79 feet, 3 3/8 inches publishing operations, holds some 30 technical Length: 218 feet 6 inches conferences and 200 professional development Joel Gillard, Vice Chair courses each year, and sets many industrial Largest seaplane J.D. Mitchell, Treasurer and manufacturing standards. Largest wooden aircraft—the entire airframe Thomas C. Gray, Secretary is composed of laminated wood ASME International The Hughes Flying Boat is owned by the Primary control surfaces, except the flaps, are fabric-covered Susan H. Skemp, President Evergreen Aviation Museum, located at 3685 The most reciprocating horsepower Dennis A. Armstrong, Vice President, NE Three Mile Lane, McMinnville, Oregon ever installed in an aircraft Region VIII 97128, USA, (503) 434-4180. Power: Eight Pratt & Whitney R-4360, Brian W. Doyle, P.E., History and Heritage Acknowledgements 3,000 horsepower engines Chair, Region VIII ASME thanks all those who have contributed Propellers: Eight, 17 feet, 2 inch diameter D. Yogi Goswami, EE., Senior Vice President, to the designation of the Hughes Flying Boat. Weight, empty: 284,000 pounds Public Affairs Special thanks to nominators of this landmark Weight, loaded: 400,000 pounds in 1986: Don Albrecht and Carson Dalzell of Stacey Swisher Harnetty, Vice President, (maximum take-off weight) ASME; Ray Hesser, Jack Whitehead and Public Information Capacity goals: 750 troops George Stawniczy. In 2000: Diane Kaylor of or two Sherman tanks Virgil R. Carter, FAIA, Executive Director ASME International; Brian W. Doyle, David P. Normal crew: 11 Lynden F. Davis, EE., Director, Western Taylor, J.D. MacEwan and Dennis A. Armstrong First and only flight: November 2, 1947 Regional Office of ASME Region VIII; Lyndon F. Davis of ASME Western Regional Office. Photographs Estimated Performance: ASME History and Heritage Committee provided by the Evergreen Aviation Museum. Brochure author Katherine Huit, Associate Cruise speed: 141 to 150 miles R. Michael Hunt, P.E., History and Curator, Evergreen Aviation Museum. Editorial per hour at 5,000 feet Heritage Chair assistance by Tracy Buckley, Curator, Evergreen Top speed: 227 to 231 miles Robert M. Vogel, Secretary Aviation Museum and Michael Wright, per hour at 5,000 feet John K. Brown Restoration Manager, Evergreen Aviation Range: 2,975 miles with Museum and museum staff. Brochure design by 12,500 gallons of fuel Christina Laliberté and Tyler Whitely, Service ceiling 17,400 to 20,900 feet Evergreen Aviation Corporate Communications. H219