Inside the ‘Spruce Goose’

Those were the first words out of my mouth when I laid eyes on the Hughes Flying Boat, aka the Hercules, colloquially known as the Spruce Goose. Not terribly poetic, I know, but it was from the heart.

The last time I was inside the Evergreen Aviation & Space Museum in McMinnville, Oregon, was 20 years ago, when the facility was under construction. At the time, the Spruce Goose was across the street in pieces, shrink-wrapped and waiting for installation. The museum was in the excavation stage, and I stood in the 7-foot deep pit that had been dug to hold the hull of the behemoth aircraft. 

On Friday, November 4, 2022, I was back, and face to face with one of the most iconic and impressive feats of aeronautical engineering ever achieved. Up until that moment, the largest airplane I had been physically close to was a Lockheed C-5 Galaxy that Dad had taken me to see when I was a kid. For the record, the Spruce Goose wingspan bests the C-5 by approximately 97 feet, and the tail of the wooden behemoth is over 100 feet tall. I submit the exclamation was warranted.

The museum campus sports three buildings: a theater, a wing for more modern aircraft, spacecraft and the SR-71 Blackbird, and the structure that houses the Hughes Flying Boat. There are also several aircraft outside on static display, including multiple military jets, a Douglas C-47 that towed gliders on D-Day, a Boeing 747 painted in the livery of Evergreen Flying Service, and a McDonnell-Douglas VC-9C that served as Air Force Two for decades. There is also a waterpark, Wings and Waves, for those who desire a more kinetic experience.

The star of the museum, of course, is the Flying Boat, the largest seaplane in the world, which was apropos for my visit on a really rainy day even by western Oregon standards—ducks were donning rain gear and frogs were wearing flotation devices. 

Barry Greenberg, the secretary/treasurer of the museum, chairman of the collection and acquisitions committee, and founder of the Spruce Goose Advisory Board, escorted me to the center of the main building where the Flying Boat reigns supreme.

I had been warned that the aircraft is so large that it’s hard to comprehend as you approach it. This is true. It takes you a moment to realize that the big silver-gray thing that is overhead is a wing. The aircraft sports eight Pratt & Whitney R-4360 Wasp Major 28-cylinder, air-cooled radial piston engines with four-bladed propellers—each blade longer than I am tall. I was told the hull measures 265 feet wide and the mid spar of the wings measures 322 feet.

Although the hull is countersunk into the floor by about 7 feet, a staircase is necessary to reach the main boarding door of the aircraft. There is a platform there with an informational plaque and a cadre of well-informed docents waiting to show you the aircraft.

We were greeted by Wayne Swanson, one of the docents who specializes in tours of the Spruce Goose. The docents at the museum wear green vests covered with military patches. The first thing Swanson showed me was a sample of the material from which the airframe is crafted—Duramold. The sample Swanson pulled from his pocket looked more like the layers from a Kit Kat candy bar rather than a slice of modern plywood. Duramold is a composite material made from birch wood impregnated with phenolic resin, then laminated and put under heat and pressure resulting in something as light and strong as steel.

"The skin is made of nine plies, but don't call it plywood," he said, as he tapped gently on the fuselage. The sound is unmistakably wooden. According to Swanson, 8,000 nails were used to hold the wood layers together as the three different types of glue and heat were combined to cure the material that would become the wings. A special nail gun was developed to put the nails in and another tool created to take the nails out when the wood and glue layers had cured.

You enter on the cargo deck and the ceiling is high above you. It is almost like stepping into a cathedral. The aircraft smells different from the other restorations I have been aboard—it took me a moment to realize I was smelling the wood. Most large aircraft smell of plastic and metal. The first thing you want to do when you enter the flying boat is look towards the aft section. The museum has taken care to light the aft deck so you can see allllllll the way down the tail—a distance of approximately 200 feet down a tunnel of ribs that become progressively narrower. You get the impression of looking into infinity.

Using a flashlight—a necessity as for the most part, the lighting inside the Spruce Goose is subdued—Swanson pointed out the details of the great airplane. For example, the

I-beams are made from laminated wood and are "super strong," and the corner brackets—also made of wood, some of which are as thin as a playing card or a credit card, depending on the angle.

How can something so thin be so strong? Swanson explained, "In the 1940s they rotated the grain of each ply. The first one was vertical, the second was 45 degrees off, then 90, so everytime they put a ply in, they rotated the grain. Today they call that engineered plywood."

Swanson proceeded to tap on the aircraft as he described the ribs of the aircraft, which measure 3 by 5.5 inches and larger where the wing joins the fuselage.

"That wing is 322 feet long," he continued. “That's end to end, and so big that you can't build it in one piece. You have to build it in at least two pieces. They had a left half and a right half as you couldn't even transport a 322-foot I-beam."

The aircraft has a gross weight of 400,000 pounds. "[It’s] the same as a 747 and could hold 120,000 pounds of cargo," he said.

A lighted hatch leads to a bilge that holds the fuel tanks. The aircraft burned the 130 octane aviation gasoline available in the period. "Each tank has 900 gallons, and there are 14 tanks, which gives you 12,600 gallons," Swanson said, adding, "Multiply that by 7 because each gallon weighs 7 pounds and that gives you almost 100,000 pounds of fuel." (I did the math: it comes out to 88,200 pounds of fuel.)

Fuel hoses run from the bilge to each engine. Electric pumps moved the fuel. Hughes liked redundancy, noted Swanson. "Everything is in parallel. There are two fuel hoses and two pumps on each engine so if one fails, the other one takes over. He did an analysis of everything that could fail on the airplane, everything that could keep the engines from running and made sure it had two sources so there are two fuel sources, two oil sources, two hydraulic sources, two electric sources."

The wings and the engine compartments are large enough for a man to stand in. The engines are placed at 20-foot intervals on the wings. According to Swanson, the original engines were rated at 3,000 hp, but then they were modified to 3,500 hp.

"A person can go to that engine in flight and adjust the throttle or tighten up hoses and things as all the accessories are on the back of the engine," he continued. "A series of intercom radios enabled Hughes to communicate with the crew, which on the flight consisted of a pilot, [a] copilot, and [an] engineer for engine instruments, and a second engineer for utilities such as hydraulic pressure."

A hydraulically actuated control system—developed by Hughes—was a necessity, as the size and therefore the weight of the control surfaces were far beyond anything that had come before. The ailerons, for example, measure 140 feet long. Although they were covered with fabric, it was said it would take the strength of 200 men to move them if the aircraft was rigged with cables and pulleys like the multiengine bombers of the day.

Inside the cargo hold just behind a stanchion rope there are 16 red fire extinguishers—two for each engine—and a pile of inflated red, yellow, and blue beach balls. The beach balls are there for buoyancy should the aircraft go down on the water.

The application of the beach balls was a take on Hughes’ 1938 around-the-world flight where concerns about ditching at sea inspired him to load his aircraft with 80 pounds of ping-pong balls in the wings and fuselage to keep the aircraft afloat in the event of a water landing.

"He couldn't get enough ping-pong balls for this airplane so he went with beach balls," Swanson said, "although there is some controversy as to if they were on board during the one and only flight."

Another Hughes engineering marvel was an electrical system of 120 volt DC, which allowed for the use of smaller cables and wires, saving considerable weight despite the miles of wiring required for the system.

The flight deck is above the cargo hold, accessed through a circular staircase. One of the first things you will notice when you get there are rows of what look like theater seats behind the raised platform where the pilots sit. This flight deck is spacious in every sense of the word. On the port side, there is a series of plexiglas windows that were installed when the aircraft was on display in Long Beach, California—the other side is solid bulkhead, leading a person to wonder how dark the aircraft was back in the day, when the only source of natural light came from cockpit windows.

The aircraft featured built-in coffee urns. [Courtesy: Meg Godlewski]

Hughes was known for eccentricities but he did like his comforts—there are built-in coffee urns on the flight deck.

The flight engineer's station is located aft of the pilots’ seats on the starboard side of the fuselage. It is a wall of dials stacked 11 high and eight across next to panels of annunciator lights and switches. The dials measure manifold pressure, tachometer, oil temperature and pressure, fuel pressure, cylinder head temperature, and fuel flow—that's how you keep track of eight engines. The other panels display the output of the three electrical generators, and monitor the aircraft systems for fire—a bad thing in any aircraft but particularly dangerous in one that is made primarily of wood.

Across from the engineer's station are monitors for a series of strain gauges installed for the taxi tests. "They ran the engines when the aircraft was under construction but they couldn't run them under load until the test flight," Swanson explained, adding that the wing load of the aircraft had an arc of 13 feet "so they needed to structurally test where it was overbuilt or underbuilt."

The information from each strain gauge was recorded on magnetic tape.

I was offered the chance to try out the left seat—and, of course, I had to put on the Hughes-esque hat that you must wear when you do this. Barry graciously took the right seat for the full effect.

The first thing struck me about the left side of the cockpit was the throttle quadrant—eight levers in all. As a multiengine pilot, I've had the experience of having to bring both throttles up simultaneously. I very gingerly stretched my hand out to see if I could get all eight levers at once. I didn't move them—but hovered over them. The answer is yes, I can reach all eight at once. I share this as one of my siblings, when we were watching the movie, The Aviator, asked if I would be able to fly the Spruce Goose. I said yes, as it was all physics—bring the throttles up to get enough thrust to get airflow over the wings and up she goes.

There is another set of throttle levers on the copilot's side—Hughes’ redundancy again.

The arrangement of the instrument panel is confusing by today's standards. Most of the aircraft I have flown are post-1967 designs with the standardized placement of the so-called six pack: airspeed on the top row, far left; the attitude indicator then altimeter; then on the second row, left to right, the turn coordinator/slip skid indicator, heading indicator, and vertical speed indicator.

On the Spruce Goose, I had to spend a few minutes looking for these instruments—trying to do an IFR scan in this airplane would definitely be difficult. Some of the instruments are located below the pilot's field of view, underneath the yoke.

The airplane has a slip skid indicator—two actually—without the upside-down “doghouse” markings, although there is a yaw indicator next to the one on the pilot's side at eye level. The attitude indicator is the 1940s-style black ball with tick marks at the top to indicate bank angle and a stylized aircraft for pitch. The vertical speed indicator is located directly beneath the attitude indicator.

On the lower part of the panel there is the other slip-skid indicator, a radio direction finder and another AI.

There are dials to show aircraft trim for aileron, elevator, and rudder, which are managed by a joystick on the left side of the cockpit. There is a centralized gauge to indicate pitch. “DOWN” is in red. In addition, there is a mark on the windscreen, sort of a first-generation “heads up display” to help the pilot determine aircraft attitude.

The avionics, which were likely state-of-the-art at the time, consist of an ADF (automatic direction finder), an RMI (radio magnetic indicator), and a radio direction finder. (Hughes didn’t like getting lost.)

To the right of the pilot's seat is a console filled with toggle switches and annunciator lights for all the aircraft systems—Hughes was known for always wanting to be in control, and this console is a testament to that. By comparison, the copilot's panel feels rather sparse in instrumentation.

Directly over the cockpit is a roof hatch, which, if you are tall enough, gives you a great view of the top of the aircraft—and/or the harbor when you're on the water.

During the one and only flight of the Spruce Goose, it only flew for 1 mile at an altitude of approximately 70 feet above the surface of the water; some say it never got out of ground effect. We will never know what its service ceiling was or how it handled during maneuvers—but that doesn't take away from the feat(s) of engineering required to build it.

I was not the only visitor that rainy Friday—there were several children, a few accompanied by parents and at least one school group. The children were as impressed as I was—I heard the exclamation "WHOAAAAA!" several times as they walked around the museum. One can only hope the next generation is inspired.