USA (1964)
Oversized Cargo Aircraft – None Built

The Aero Spacelines PG-2 was an oversize cargo aircraft with an extremely large cargo hold, designed to airlift the first and second stages of the Saturn V rocket from their factories to Cape Canaveral, Florida, for final assembly. To save on costs, the aircraft would use components from existing aircraft, and most interestingly would use several key components from the British Saunders Roe Princess flying boat, hence the nickname “Princess Guppy”. Unfortunately, due to opposition from Congress, and the deterioration of the Princess aircraft, none of the type would be built.

NASA and the Transportation Problem

The race to the moon in the 1960s between the United States and Soviet Union introduced a number of challenges upon the growing aerospace industry. The task at hand was one of the biggest endeavors in human history, requiring manpower, materials, logistics, training, and calculations never used before to achieve such a tremendous goal. In America, the Apollo program was well underway, composed of the Apollo spacecraft and the massive Saturn V rocket it would be launched from. The Saturn V (at this point called the Saturn C-5), was a multistage launch platform with 3 different stages. Logistically, there was a problem with its design. The Saturn V was meant to be assembled and launched from Cape Canaveral in Florida, but the first and second stages of the rocket were assembled in completely different states. The first stage, S-IC, was assembled in New Orleans by Boeing, while the second stage, S-II, was produced on the opposite end of the country in California by North American Aviation. This created a massive challenge regarding transportation. The two stages were massive in size, each having a diameter of 33 ft (10 m). The first stage had a length of 138 ft (42 m) while the second stage had a length of 83 ft (24.9 m). Transporting these two components was a major issue, as almost nothing could quickly move these to Cape Canaveral. This led to NASA deciding to use an aircraft to transport the 1st and 2nd stages. However, this brought on yet another problem. At the time, no aircraft then in service could carry such a large and ungainly cargo, leading several aircraft companies to propose concept aircrafts to complete such a task. Due to the nature of the challenge, the proposals often were unorthodox in their design to accommodate the large load. One company, however, was formed deliberately to fill NASA’s airlifting needs.

Aero Spacelines was formed in 1960 by Jack M. Conroy with NASA as their main customer in mind. Jack, being a former Air Force and commercial pilot, knew of their transportation issue regarding rocket components even before the Saturn V rocket, beginning with their previous multistage rocket designs. He proposed using modified Boeing 377 Stratocruiser airliners with large overhead cargo holds to carry these rocket components from their manufacturers to their assembly points. The first of his “Guppy” designs as they were called, the Pregnant Guppy, first flew in 1962 and was awarded contract work for NASA as an airlifter. The Pregnant Guppy was still too small, however, to carry the large 1st and 2nd stages of the Saturn V, and so a larger design began to be drawn up. An early study was done with an entirely new fuselage using B-36 wings and control surfaces to save on parts. This design would have a cargo hold with a diameter of 40 ft (12.2 m), allowing it to carry both boosters. Little is known of this design outside of this but it would be quickly changed on January 30th, 1964 when John M. Conroy announced Aero Spacelines would design a new oversized load airlifter based on the Saunders Roe Princess.

The Saunders Roe Princess: A Dead Dream Revived.

The Saunders Roe Princess was the biggest flying boat design built in Britain, and the biggest all metal flying boat ever built. Originally designed as an innovative transatlantic passenger liner, it would first fly in August of 1952. However the Princess encountered two major issues. The ten Proteus engines used were underpowered, causing performance to suffer. On a more pressing matter, the Princess found itself being quickly outdated as it was developed. With the arrival of the De Havilland Comet, the world’s first jet powered airliner, in the same year as the Princess, it was quickly shown that piston-engine airliners, let alone floatplanes, was a dying breed of travel. Jet aircraft could fly faster, smoother, and further than piston engine airliners, and the Princess couldn’t find buyers because of this change in the market. In addition, the amount of airfields left in Britain after the Second World War nullified the benefits of flying boats and their lack of need for airfields. A single Princess would be built and tested, with two more being completed, but not flown, when the program was ended. The three Princesses were put into storage, cocooned away in hopes that a buyer would eventually come and save them.

Over the years several interested parties would look at the Princesses but no deal ever came to fruition. The three airframes would sit in storage for a decade (1954-1964) when they came to the attention of Jack M. Conroy. Interestingly, this wouldn’t be the first time the US considered acquiring the three aircraft, as the Navy had once proposed to convert the three into flying nuclear-powered test beds, but this plan never progressed past a few models and drawings. At the time, Conroy was still working on his booster carrier concept using B-36 components, but the large design of the Princess gave him an idea. Instead of the B-36, Conroy had the idea of reusing the same parts from the Princess. The plans were quickly reworked and came to be known as the PG-2 Princess Guppy. The PG-2 would reuse the wings from the Princess but had several enhancements. Instead of using the ten Proteus engines, these would be swapped out for six Rolls-Royce Tyne turboprop engines. The Tyne engines were originally planned for the Princess during its development, but the engines weren’t ready and couldn’t be used by the time the Princess was built. Now a decade later, the engine was fully operational and ready. The wing length would also be stretched to 40 feet (16.2 m), and the cargo hold would have a 38 foot (11.6 m) minimum diameter and a length of 100 feet (30.5 m). This reduction in length would no longer allow the aircraft to carry the S-IC booster. Maximum cargo capacity would be up to 200,000Ib (104,600 Kg). The aircraft would be reworked once again later in 1964 as the PG-3. The PG-3 would be reduced in size to some degree. The Princess wings would no longer be lengthened to save on costs, and the Tyne engines would no longer be used on the PG-3, instead they’d be replaced by jet engines. A total of eight jet engines would be used on this design, with 4 pairs of engines being used on B-52H engine pods. Other than wing design, the rear of the aircraft was also changed, with the fuselage not angling upward and instead being more of a straight point.

Aero Spacelines had full intentions of seeing this project through, and eventually a representative of the company was sent to inspect the three Princesses at their storage facility. However, a terrible revelation was discovered upon inspection. At some point, maintenance on the three Princesses in storage was stopped, and so they were left to rot for nearly a decade. Being near the sea and exposed to the elements, the three aircraft had deteriorated to such an extent they would no longer be usable. With this discovery, Aero Spacelines had to unfortunately cancel the project and the three Princesses were scrapped. Work on a large carrier was halted for Aero Spacelines and they focused on their smaller Super Guppy aircraft instead, which carried the 3rd stage of the Saturn V.

Design

The Aero Spacelines PG-2 was a large oversized cargo aircraft designed to carry the first and second stages of the Saturn V rocket. To do so, it would have a very large fuselage to accommodate the rocket stages. The aircraft would have an all metal fuselage that was 200ft (61 m) in length. The lower section of the fuselage contained the huge cargo bay for the rocket stages. On the original plan this section had a diameter of 40 feet (16.2 m) but was shortened to 38 feet (11.6 m) on the PG-2. Cargo was loaded into the aircraft by means of a ramp. The cargo bay had a large clamshell door in front of the aircraft. Landing gear was divided into six pairs of wheels on the underside. Two pairs of wheels were closer to the front of the aircraft while the remaining four were towards the rear. The cockpit and crew section was located above the cargo bay in the aircraft. The cockpit itself bears a striking resemblance to the cockpit section of the Douglas C-133. A crew of 3 to 4 was expected for operations. Initially, the wings would be reused from the Convair B-36 bomber. The engines for this version were never specified. On the PG-2, it was decided at this point that the wings of the Saunders-Roe Princess would be used over for the B-36’s. The wings would be lengthened an additional 40 feet in total for stabilization. The Princess’ original ten Proteus engines would be replaced with six Rolls Royce Tyne engines to improve performance. The tail section of the PG-2 would also be reused from the Princess.

The PG-2 would be reworked into the PG-3 design. The overall proportions were diminished to save on labor. The specifications of this version are relatively unknown aside from one or two estimates based on promotional images. The cargo bay was to remain the same in length. The cockpit section and most of the fuselage remain unchanged aside from the rear. The rear of the fuselage no longer tapered upward and instead transitioned straight back into a cone shape. The tail section of the aircraft remained in the same location but was now supported by a large support to accommodate the height difference of the rear of the aircraft. The wings of the PG-3 remove the 40ft (16.2 m) extension off of the Princess wings and keep the original length. The six Tyne engines were removed in favor of eight jet engines. These engines would be paired together in four B-52 engine pods on the wings. The jet engine intended for use isn’t stated but it’s likely they were Pratt and Whitney TF33 engines. Promotional art also depicts the PG-3 having wingtip mounted fuel tanks.

Conclusion

With the cancellation of the Princess Guppy, Aero Spacelines moved on to other means to assist NASA regarding transportation, however they weren’t the only company to offer an aircraft design to carry the larger rocket stages. Several other companies had offered proposals to NASA for the same function, such as Convair and Fairchild. Many of these designs reused existing aircraft as their base or for parts to save on costs. None of these would come to fruition either. Despite reusing components from existing aircraft, many members of Congress found building a new aircraft for this role unnecessary for the amount of funding it needed. Instead it was decided that the 1st and 2nd stages would continue to be transported to Cape Canaveral via barge. For the 2nd stage, this was a very long journey that involved going through the Panama Canal to reach Florida. Despite being time consuming, this method was one Congress found cost effective. No oversized aircraft proposals would be built aside from Aero Spacelines’ own Super Guppy design, which was used to transport the 3rd stage of the rocket, and one of which is still in service to this day by NASA.

The Princess Guppy was a well researched design using prior knowledge of Aero Spacelines’ Pregnant Guppy. The design would have brought back to life a decade-old dream but unfortunately it was crushed due to negligence. Had it been built, it would be questionable if the aircraft would even be airworthy. The immense size of the fuselage and the small amount of engines in comparison to said size could have prevented the aircraft from even lifting off. Regardless, none of the types were built.

Variants

• Early Design (PG-1?) – The first design of the booster carrying aircraft reused components of the Convair B-36 bomber. It would have a large cargo hold to carry the oversized load.
• PG-2 – Second design of the booster carrier. The PG-2 Princess Guppy would use the modified wings and tail components of the Saunders-Roe Princess and would be powered by six Rolls Royce Tyne engines.
• PG-3 – Reduced size version to lessen the work needed to build the aircraft. It was powered by 8 jet engines in B-52H engine pods. The Princess’ wing returns to its normal size for this version.

Operators

• United States of America – The Princess Guppy was designed specifically to be used by NASA for the transport of the first and second stages of the Saturn V rocket. None were be built.

Aero-Spacelines PG-2 specifications
Wingspan	259.8 ft / 79.2 m
Length	200 ft / 61 m
Height	86 ft / 26.2 m
Wing Area	6328 ft² / 587.8 m²
Engine	6 x 4,616 hp (3,442 kW) Rolls Royce Tyne RTy.12 turboprop engines
Propeller	6 x De Havilland 4-blade propellers
Powerplant Ratings	Horsepower output Altitude Take Off 5730 hp Sea Level
Weights	Useful 250,000 lb / 113398 kg Minimum Flying Weight 180,000 lb / 81646.6 kg Maximum Take Off 430,000 lb / 195044.7 kg Maximum Landing 400,000 lb / 181436.9 kg
Crew	3 to 4

Gallery

Artist Concept of the PG-2 by Godzilla

Credits

• Written by Medicman
• Edited by Henry H. & Ed J.
• Illustrations by Godzilla

Sources

• COX, G. (2019). AMERICAN SECRET PROJECTS 3 : u.s. airlifters since 1962. Place of publication not identified: CRECY PUB.
• Keeshen, J. & Hess, A. (2013). Secret US proposals of the Cold War : radical concepts in military aircraft. Manchester North Branch, MN: Crécy Publishing Limited,Distributed in the USA by Specialty Press.
• https://wightaviationmuseum.org.uk/princess-flying-boat/