The Hughes Flying Boat – Museum Centerpiece and Aviation Icon

Big Plans for a Wartime Military Transport

The Hughes H-4 “Hercules” Flying Boat, popularly known as The Spruce Goose, is an archetypal icon of American aviation technology. The latter name, one Howard Hughes hated and rightly so, was initially coined by the Press to illustrate the widely held belief (propagated by them and members of Congress), that the plane was a “flying lumberyard” and that it was too big to ever fly. (*NOTE: Consequently, I will refer to the flying boat by its proper name.) Their misinformation and unfounded trashing of the project was so effective that my own father, an engineer himself who was a young man during that era, always told me the same thing. Well, not only did the plane fly—it was designed by aeronautical engineers and Mr. Hughes to do exactly that—but it introduced cutting edge aviation technology that can be found in modern commercial and military aircraft.

Hughes Flying Boat
The Hughes Flying Boat at Evergreen Aviation Museum, McMinnville, Oregon August 2016
“…it wasn’t underpowered at all; it performed exactly like it was designed to.” – David Grant, co-pilot and engineer

The Hughes Flying Boat has been at the center of my aviation interests since boyhood. I remember talking to my Dad about it many times growing up, probably after having seen it on a TV documentary or reading about it in a book. I would ask him why it only flew once and only just above the water’s surface. Dad, being a Lehigh engineer (as I’ve mentioned in previous posts) would say something like it was too big to get out of its own way. Of course, you wouldn’t have jet engines on a wooden aircraft, but the assertion by most people that the plane was underpowered is actually not true. You’d have to ask the engineers who designed it and someone did just that. Co-pilot David Grant, an engineer who designed the hydraulic systems for the plane, said that the one and only flight was “ecstasy all the way, like walking on air.” Interviewed at a gathering marking the 40th anniversary of the flight, he said that The Flying Boat “wasn’t underpowered at all;  it performed exactly like it was designed to.”[1] Now, there’s a guy who would know. Mr. Grant died in 2001.

Port-side wing and engines
Hughes Flying Boat Port-side wing and engines

The Hughes Flying Boat has 8 Pratt & Whitney R-4360 Wasp Major engines for its power plants. At 3,000 horsepower each, that’s a total of 24,000 hp. The plane did fly, at an altitude of about 25 ft., the height noted in the official flight log (most accounts indicate 70ft., including Boeing’s Historic Snapshot page on the plane, although they indicate an initial height of 33ft., which seems more realistic). Initially I had thought, after watching many documentaries and also Martin Scorcese’s excellent film, The Aviator, that the Flying Boat barely had the power to achieve the required 90 mph take-off speed. This misconception owes more to myth propagated over the decades than fact. The R-4360 represented the cutting edge in aircraft engine technology in its day, which is certainly why Howard and his chief engineer, Glenn Odekirk, would have spec’d it for the flying boat and also the legendary XF-11 reconnaissance plane.

Heavy Lift Capability

flight engineer's station
Howard Hughes at the flying boat’s flight engineer’s station.

The H-4 Hercules was designed with a floor to carry 125 pounds per square foot.[2] Its maximum take-off capacity is 400,000 pounds. This capacity could be divided up in a number of configurations for tanks, ordnance, men and other heavy military vehicles. The diagrams at the exhibit detailing these arrangements are indeed fascinating. It could even carry 2 heavy full-sized Sherman Tanks, plus men and other vehicles. That load capacity, in addition to the 24,000 horsepower from the 8 engines seems like more than enough to do the job. I can’t do the calculations but Hughes’ engineers did, and they designed the Flying Boat around them. So, when people said “it’s too big to fly,” they were basing that opinion on an emotional response. In actuality, Mr. Hughes and his engineering team designed and built a plane that could lift all that heavy cargo and deliver it across the Atlantic.

Hughes Flying Boat Gallery

Delays and Lack of Management

However, the Spruce Goose wasn’t completed in time to be used in the war and would never go into production. The delay was due to Howard’s perfectionist oversight of every detail in its design and construction. This obsessive involvement caused delays and work progressed slowly—employees at Hughes Aircraft had to wait for Howard to decide to show up at the plant in Culver City, California, and no one knew when that would be. Oftentimes, his engineers had to wait until late at night for Hughes to review sketches and modifications.

Hughes Aircraft also lacked the corporate structure and organization needed for building production airplanes. After my recent visit to the Boeing assembly plant in Everett, Washington, I see how this is absolutely necessary. More on that in another post! At Hughes Aircraft, Howard continued to work as he had in the 1930’s—in total control and dividing his time among his many projects, showing up when he had the inclination or the time. This practice was bad for production schedules but ultimately resulted in building the best airplane possible.

“”I’ve put the sweat of my life into this thing…” – Howard Hughes

The H-4 Hercules was designed as a counter-strategy to offset the heavy loss in war supplies inflicted by German U-boats in the North Atlantic. But even by the time the government signed the development contract in 1942 with Hughes and Henry Kaiser (Hughes’ partner in the project at the beginning), the tide was already turning against the U-boats. So, the need for a huge transport plane declined well before the end of the war. But it was still a project that had significant application to the future of military transport…and to aviation in general. Unfortunately, Congress killed the project after its first and only flight since it was no longer needed. Hughes had already sunk millions of his own money into its development and he kept it perfectly maintained and flight-ready for decades at considerable personal expense.

Howard considered the Hercules to be his greatest achievement in and contribution to aviation.

Technological Innovation Decades Ahead of Its Time

model of Hughes Flying Boat's construction
A model exhibit of the Hughes Flying Boat’s construction.

Although the government project was cancelled Hughes kept a small army of people employed specifically to maintain and continue modifications on the flying boat. It was his prized accomplishment. Had the project moved forward, it could have possibly been redesigned to incorporate jet engines. Large military transport planes are commonplace now and the flying boat, decades ahead of its time in the 1940’s, could have realized its full potential given more money and development time. But as is suggested in the final sequence of The Aviator, Howard was already looking forward to other projects using new jet engine technology, which makes sense. Also, the whole senate hearing scandal was a big drain on Hughes, having violated is prized privacy and he was likely wanting to put it all behind him. Nonetheless, Howard considered the Hercules his greatest achievement in aviation. He would proudly show it off whenever he wanted to impress someone. The systems that Hughes and his engineers developed had a far-reaching application in the development of military and commercial airplanes. The most obvious one is the design and build of the first super-sized military transport plane. Other important innovations include hydraulic-assisted flight controls that delivered 200 times the pressure the pilot exerted at the controls to the flight control surfaces. Hughes and his team called this the “artificial feel system,” which gave the pilot the feeling of flying a much smaller aircraft. This was the first-ever system of its type (and equipped with multiple redundancy), and is used in every commercial and military aircraft flying today. The flying boat also has a central CO2 fire control system. Fire control was of utmost importance in a plane made of wood, but modern aircraft also use these types of systems.

The Hughes Flying Boat from under the empennage

An Enduring Legacy

If you’re an airplane geek like me, I highly recommend reading this awesome document, prepared by the American Society of Mechanical Engineers, that commemorates the designation of the Hughes Flying Boat as a Historic Mechanical Engineering Landmark, and details its innovative technical specifications and systems. You can also visit this page on the ASME website for additional information on the plane.

One of Howard Hughes’s foremost desires was to make a significant contribution to the field of aviation, and with the Hughes Flying Boat he more than succeeded. I like this touching tribute by Robert W. Rummel, who worked with Hughes as a young engineer and later as a TWA executive:

“He was an outstanding pilot, and in the cockpit, he seemed to exult in the freedom of flight. Of course, he was an astute businessman, and making money was one of the things that motivated him. But he had a sincere and abiding interest in aviation, and I think it was his one and only true love.” [3]

– Robert W. Rummel
Hughes Engineer, TWA Executive

I highly recommend going to see this national treasure and aviation icon. Museums like Evergreen depend on visitors for their continued existence, and it draws about 150,000 people a year. So be one of them…you’ll be very glad you went.

Works Consulted
1. “Hughes H-4 Hercules.” Wikipedia, Accessed 7 Sept. 2016.
2. “H-4 Hercules Flying Boat.” Boeing, Accessed 7 Sept. 2016.
3. “Howard Hughes’ Flying Boat, Spruce Goose.” American Society of Mechanical Engineers, July 20, 2002, Accessed 12 Sept. 2016.
4. “Spruce Goose Flies.” History, Accessed 7 Sept., 2016.

Works Cited
1. Oliver, Myrna. “David Grant, 84; Spruce Goose Co-Pilot.” Obituary, Los Angeles Times, 26 Sept., 2001, Accessed 17 Sept., 2016.
2. “Spruce Goose.” What-When-How Accessed 16 Sept. 2016.
3. Lerner, Preston. “Howard Hughes’ Top Ten.” Air & Space, November 2004, Accessed 12 Sept. 2016.

Author: jamestcallahan

James T. Callahan is a commercial and fine art photographer based in Hillsborough, New Jersey. His specializations are in product, industrial and architecture. His fine art work takes a poetic look at the American Landscape through 19th Century architecture, historic and abandoned railroads and the American Small Town. You can see his work on his website at, and on Instagram at

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