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					                           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.       to two 300-gallon wing tanks. One wing tank
The creation of the Hughes Flying Boat
                                                     The Gunite process produced difficult shapes       fed the four inboard engines, and the other
involved many engineering disciplines. Not
                                                     easily at a relatively low cost.                   wing tank fed the four outboard. The Flying
only did mechanical engineers participate in
the numerous aspects of the aircraft project,                                                           Boat was also equipped with an emergency
                                                     Intensive research resulted in one of the
but their efforts ranged in breadth from the                                                            fuel transfer and supply system in case of
                                                     earliest practical uses of epoxy resins. The
models constructed for wind tunnel evaluation                                                           leakage or pump failure.
                                                     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                                                                             Engine Oil Supply System
                                                     Fire Protection
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 CO2 (carbon dioxide) pressure
heated, birch held up better than spruce, and                                                           supply system operated automatically with a
                                                     containers are located on the cargo deck.
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
Duramold, a lamination bonding process, was                                                             engine nacelle, and oil coolers were placed in the
                                                     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
Originally developed by Fairchild Aircraft
                                                                                                        Propellers
                                                     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
               Workers making Duramold parts         filled to only 900 gallons. Fuel was transferred   valves would operate the same with identical
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
but Howard Hughes’ passion for safety required                                                            her survival, she rests among other historic
                                                    The pilot and co-pilot’s cockpit flight controls
five hydraulic control systems, which included                                                            aircraft at the Evergreen Aviation Museum.
                                                    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
failure. Conventional control cables directly                                                             The History and Heritage Landmarks Program
                                                    instruments. A starboard-side flight engineer’s
connected cockpit controls to the control                                                                 of ASME International (the American Society
                                                    station is immediately behind the co-pilot’s
surfaces, however, they did not move the                                                                  of Mechanical Engineers) began in 1971. To
                                                    seat and contains dials and gauges to monitor
control surfaces. They only provided a follow-                                                            implement and achieve its goals, ASME
                                                    the eight engines, throttles, alarm
up to ensure the proper relationship between                                                              formed a History and Heritage Committee
                                                    annunciators, fuel indicators and hydraulic
the pilot’s control positions and the actual                                                              initially composed of mechanical engineers,
                                                    status gauges. The radio operator’s console is
deflections of the control surfaces. The                                                                  historians of technology and the curator (now
                                                    located on the port side, directly behind the
Hughes engineers used electrically driven,                                                                emeritus) of mechanical engineering at the
                                                    pilot’s seat and the flight test temperature
high-pressure hydraulic pumps that provided                                                               Smithsonian Institution, Washington, D.C.
                                                    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,”               importance to mechanical engineers. Collections
located at the control surfaces. The receiving
                                                    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                                                                   technological heritage and encourages the
                                                    built, and she proved that jumbo flying aircraft
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.                                                                       historically important works. It provides an
                                                    decades ahead of her time in the early 1940s,
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
educators, historians and travelers. It helps
                                                                                                                Notable Hughes
                                                 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.                                                                                             Cargo aircraft prototype
                                                 Diane Kaylor, Staff Liaison
The 125,000-member ASME International is a                                                            Largest wingspan: 319 feet, 11 inches with a
                                                 Wil Haywood, Public Information Coordinator             wing area that covers 11,430 square feet
worldwide engineering society focused on
technical, educational and research issues.      ASME Oregon Section                                    Features cantilever wing and tail surfaces
ASME conducts one of the world’s largest                                                                      Tallest aircraft: 79 feet, 3 3/8 inches
                                                 Joy E. Conley, Chair
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                                                                                                  Primary control surfaces, except
                                                 The Hughes Flying Boat is owned by the
Susan H. Skemp, President                                                                                              the flaps, are fabric-covered
                                                 Evergreen Aviation Museum, located at 3685
                                                 NE Three Mile Lane, McMinnville, Oregon                     The most reciprocating horsepower
Dennis A. Armstrong, Vice President,
                                                                                                                    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                                                                                       Propellers: Eight, 17 feet, 2 inch diameter
                                                 ASME thanks all those who have contributed
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                           (maximum take-off weight)
Stacey Swisher Harnetty, Vice President,
Public Information                               ASME; Ray Hesser, Jack Whitehead and                                   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                                                                                         per hour at 5,000 feet
                                                 Curator, Evergreen Aviation Museum. Editorial
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

				
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