Inside the Gentle Giant

By David Brown

Imposing from any viewpoint, the Super Guppy can carry an amazing variety of shapes inside its 25 ft wide, 25 ft high, and 96 ft long cargo compartment. Based on the Boeing Stratocruiser and modified with a greatly enlarged fuselage, turboprop engines, reinforced landing gear, and a side-opening cargo nose, this is the only flying example of the five Super Guppies built. (NASA)When a giant turboprop cargo plane recently droned into Long Beach in Southern California, it marked the latest chapter in a fascinating tale.

When NASA needed to move a large box-shaped structure some 30 ft long and of 10,000lb weight across country from Southern California to NASA Langley in Virginia, they did not have to look far. As it happens, NASA owns and operates the sole remaining operational Turbine Super Guppy (out of the five built during the ‘60s to carry outsize pieces of cargo). The Super Guppy (NASA 941) is currently based at the NASA facility in El Paso, Tex., and flew from there to the west coast to pick up its cargo. The payload on this occasion was a composite, double-deck multi-bay box made for NASA’s Environmentally Responsible Aviation (ERA) project. This test article represents a 75 percent scale version of the center section of a hybrid wing-body aircraft (think of a scaled-up X-48, flown at NASA Dryden some years ago) but now built of a lightweight, damage tolerant stitched-composite structural concept dubbed PRSEUS (Pultruded Rod Stitched Efficient Unitized Structure) built by Boeing Research and Technology in Huntington Beach, Calif. and assembled in Long Beach. The innovative structure comprises carbon-epoxy panels, which are infused with resin and cured by vacuum pressure without having to use a large autoclave, which would normally be required.

ERA Project Manager, Fay Collier said, “Stitching the layers together in PRSEUS allows aircraft manufacturers to use fewer fasteners; this in turn will reduce cost, weight, and the likelihood of cracks developing.” After the layers are stitched, the carbon-fiber rods are inserted to add stiffening. Researchers estimate that PRSEUS should provide a 25 percent reduction in weight compared with state-of-the art aircraft composite applications.

The task was simple, fly PRSEUS to Langley, where it would be put into a test rig (COLTS), bent, pressurized, and eventually broken in the name of research. And how to get it there? According to Dawn Jegley, lead NASA engineer on the PRSEUS project, the Super Guppy was the obvious choice. It could easily accommodate the large structure, and its crew was well used to dealing with huge and ungainly items (the Super Guppies were used for years by Airbus to carry large portions of their airliners between construction sites in Europe).

The nose of the Super Guppy is opened to allow access to the cavernous interior. The cargo section is 25 feet wide at its widest point, 25 feet high, and almost 95 feet long. All the control runs have to be disconnected to allow the nose to be swung open and reconnected when the nose is closed. The entire flight deck is contained within the hinged nose section. (NASA)So recently the bulbous shape of NASA 941 appeared in the skies to the south of Long Beach airport, made a stately approach, and landed. When parked to the amazement of spectators, the nose of the aircraft, including the flight deck, started to open, pivoting about a hinge mounted on the left side. As the nose was slowly opened, the cavernous hold was revealed. PRSEUS was carefully loaded through the nose, the nose was moved back into position, and the controls reconnected.

What’s the Super Guppy like to fly? According to Astronaut and Super Guppy pilot, Greg Johnson, the rule is to do gently banked turns. It is a big airplane with lots of inertia. The basic design stretches back to the post-WWII Stratocruiser. This means that the controls are manual rather than hydraulic, so it takes a lot of muscle power to hand fly the Super Guppy. It’s a two-man effort to fly in rough air. The nosewheel steering is mechanical, controlled by the pilot through a large steering wheel down by his left knee, so taxiing is a slow and deliberate affair, bearing in mind the huge wingspan of more than 150 feet and the four big propellers out on the wings. On normal taxiways, the The test article being transported is a box-shaped structure, which represents the center-section of a hybrid wing-body design based on the X-48 (from Boeing), which was flown at NASA Armstrong in 2013 and is shown in its latest X-48C form in the accompanying photo (NASA)wingtips are out over the grass, and keeping the nosewheel on the yellow line is essential. Super Guppy crews generally fly at best cruise of around 220 knots and altitudes of 13,000 feet to 16,000 feet. The crew compartment is pressurized. The Super Guppy is limited to 250 knots airspeed. Range is limited, as the drag of the huge fuselage combined with the relatively low altitude contributes to a high fuel burn

Crosswinds are a limiting factor, both from the flying aspect, when a side wind will push against that great sail of a fuselage, and when opening and closing the nose on the ground. Opening and closing the nose is a precision operation involving multiple crew members, auxiliary jacks and extra wheels, and very careful lining up of marks on the hinged nose and on the fuselage. Use of checklists is mandatory because of the disconnection and reconnection of the controls required during the operation. NASA normally operates the Super Guppy with two pilots, one or two flight engineers and two or more ground crew, depending on the mission. A handful of seats is provided behind the flight deck for the extra crew or passengers

Originally sized to carry sections of the huge Saturn rocket, the Super Guppy has carried many exotic cargoes, including ISS and Airbus airliner components. Since it was acquired by NASA, one of the most interesting cargoes it has carried has been a pair of NASA T-38s. The needle-nosed jets were mounted cheek to cheek on a support framework, each still in one piece with wings attached, and gently slid into the cargo bay with room to spare.

As Long Beach lay under its accustomed morning maritime cloud layer, the Super Guppy took off and headed east on the first leg of its journey to NASA Langley. Over the next two days, it flew east, hop-scotching across the States and cruising around 220 knots IAS at an altitude of 13,000 feet, calling first at Williams Gateway, Ariz., and then flying another leg to Amarillo International airport in Texas. After an overnight stop at Amarillo, NASA 941 flew on to Campbell Army Airfield in Kentucky; then concluded its second day of flying with a final leg to NASA Langley, Va.

 At this point, the ground troops took over and unloaded the cargo from this gentle giant, moving it the five blocks to the building housing the COLTS (Combined Loads Test Section) test rig, its final destination. The next day, The Super Guppy was airborne again, flying on to Ellington and NASA HQ at Houston before concluding its odyssey with a final leg back to base at El Paso.

Super Guppy Specifications

Dimensions

Wingspan             156  ft  3 inches

Length                        143  ft 10 inches

Height                          48  ft  6 inches

Cargo bay dimensions:

Length                                    111 ft

Width                                      25 ft

Height                                      25 ft

Weights

Empty weight                       101,500lbs

Useful load                         54,500lbs

Max weight                      170,000lbs

Powerplants:  4 x Allison 501-D22C turboprops of 4680 hp each

Performance:

Max speed                                     250 knots

Cruise speed                                     220 knots

Range                                                 1734 nm

Service ceiling                         25,000 feet