Early vertical take-off and landing fighters from southern California, part 2: Ryan's jet-powered tail-sitters

As I discussed in my previous post, the Convair XFY and Lockheed XFV were touted by their respective companies as magic-bullet solutions to overcome the speed limitations of helicopters by combining the vertical lift of a helicopter with the combat performance of a fighter plane. However, these aircraft were handicapped by the pilot having difficulty landing the plane (in other words, figuring out how close he was approaching the ground), and the Convair and Lockheed "Pogos" also would have been no match for Soviet fighter planes even if they had gone into production due to the turboprop powerplant around which were designed. However, US aircraft manufacturers in southern California did not completely give up on the tail-sitter concept, instead merely choosing to design tail-sitting VTOL fighters powered by a jet engine rather than a propeller engine. While the Ryan Aeronautical Company of San Diego is best known for taking the lead in jet-powered tail-sitting VTOL aircraft design, the very Convair and Lockheed that had created the turboprop-powered "Pogo" aircraft also undertook design studies for tail-sitters with jet propulsion. Therefore, this post will focus on jet-powered designs for tail-sitting VTOL fighters from southern California.

Artist's impression of the Ryan Model 38 VTOL jet fighter project

In January 1947, the Ryan Aeronautical Company of San Diego began design studies for a single-seat VTOL fighter, the Model 38, in response to a Pentagon requirement for a prototype jet-powered, single-seat VTOL fighter. The first Model 38 design, the Model 38-1, was to use either one Rolls-Royce Nene or Allison J33 turbojet (both of which had a thrust of 5,000 lb [22.2 kN]) and had a gross weight of 7,700 lb (3,492 kg). Because the weight of the proposed aircraft exceeded the available thrust of the turbojet, Ryan's chief designer, Benjamin Salmon, proposed to equip the Model 38-1 with four rocket-assisted take-off (RATO) boosters that would be used in take-off mode until the aircraft reached sufficient altitude in order to conduct a transition to forward flight. By February, two additional Model 38 proposals were envisaged, the Model 38-2 with an X-shaped tail and tip-mounted jets, and the Model 38-3 with a tail empennage featuring four fins. In April 1947, the US Navy awarded Ryan a contract for further development, with the aim being to construct two prototypes. A test rig was built by Ryan to use an Allison J33 for VTOL testing in late 1948, and Ryan carried out wind tunnel tests of various configurations for the Model 38 for the next few years. By September 1951, a somewhat larger Model 38 design was envisaged with delta wings, a weight of 17,500 lb (7,937 kg) and one 21,000 lb (93.4 kN) thrust General Electric J53 turbojet. The proposed production Model 38 would be armed with four 20 mm cannons and air-to-surface missiles. Unusual features for vertical take-off and landing included a vectorable exhaust outlet for providing low-speed pitch and yaw control, plus ducts feeding engine compressor air to outlets in the wings for low-speed roll control. The aircraft would have flown at subsonic speeds at an altitude of 50,000 feet (15,240 meters). By late 1951, however, the Navy chose not to fund full-scale development of this proposal, largely due to concerns about cost and performance, not to mention that the J53 had earlier begun test runs. Ryan then sought to win back Navy support in 1953 by conceiving the Model 38R with a T-tail delta wing planform and one Pratt & Whitney J67 turbojet, but this design did not progress beyond the drawing board (Miller 2001). 

Left: Ryan X-13 Vertijet prepared to hook itself to a flatbed launch/transport trailer after a test flight, 1957
Center: Second X-13 Vertijet (serial number 54-1620) on display at the National USAF Museum in Dayton, Ohio.
Right: First X-13 Vertijet (serial number 54-1619) on display at the Gillespie Field Annex of the San Diego Air and Space Museum in San Diego, California.

Although the Navy lost interest in Ryan's VTOL jet fighter design, the US Air Force was very interested in Ryan's proposal, so Ryan itself proposed the Model 69 VTOL technology demonstrator with one non-afterburning 10,000 lb (44.4 kN) thrust Rolls-Royce Avon turbojet, a high-mounted delta wing spanning 21 feet (6.4 meters), small wingtip stabilizers, and a large vertical stabilizer. In 1953, the US Air Force awarded Ryan a contract to build two experimental aircraft (serial numbers 54-1619/1620) designated X-13, and the aircraft was officially christened Vertijet. Assembly of the first X-13 began in early 1954 and was completed by the fall of 1955. The Vertijet made its first flight on December 10, 1955 with Ryan test pilot Pete Girard at the controls; this was a brief horizontal flight to prove airworthiness, with an improvised, fixed tricycle landing gear. As flight tests progressed, the tricycle undercarriage was replaced by the tail-mounted Roller Skate apparatus with dampened wheels, and on May 28, 1956, the first X-13 vertical take-off and landing was conducted with the Roller Skate. The second X-13 (54-1620) was completed in early 1956, differing from the first aircraft in featuring a modified cockpit with improved visibility for the pilot when the Vertijet was in an upright position. It was shipped to Edwards Air Force Base on a trailer in the spring of 1956 and fitted with fixed tricycle landing gear, making its first flight on May 28 in horizontal takeoff and landing mode. After initial flawless flights in horizontal mode, the aircraft was fitted with necessary attachment gear that would allow it to operate from a special 'pogo rig', prompting the addition of an attachment hook below the X-13's nose that would engage with a small trapeze when the aircraft was at rest. A trailer system featuring a vertical flatbed was built to serve as a launch and recovery platform for the second X-13, and on November 28 the aircraft made its first transition from level flight to hover at 6,000 feet (1,828 meters), before returning to level flight. On April 11, 1957, a vertical take-off from the trailer was carried out followed by a transition to horizontal flight and a vertical return to the pogo rig. By July, the second X-13 was ferried to Pentagon via the Panama Canal aboard the USS Young America to conduct demonstration flights for the military top brass, with Pete Girard as well as Ryan test pilots William "Lou" Everett and William Immenschuh taking part in those flights. After several short demonstration flights at Andrews Air Force Base in Maryland, Girard himself carried out a demonstration flight on July 30 before 3,000 Pentagon officials and media reporters lasting 7 minutes, aiming to prove to the Air Force the potential combat applications of the X-13. The flight unexpectedly ended in mishap just as the X-13 was to land in front of the Pentagon, as Girard noted that the fuel meter was low, so he decided to land the plane in a rose garden. The X-13 program was terminated in early 1958 and the two aircraft subsequently were given to museums, with the first aircraft now on display at the Gillespie Field Annex of the San Diego Air and Space Museum in San Diego, and the second aircraft displayed at the National Museum of the US Air Force at Wright-Patterson Air Force Base in Dayton, Ohio.

By the late 1950s, the US Air Force and US Navy had come to the conclusion that the tail-sitter idea was conceptually a dead end when it came to operational practicality, and after hearing the new of flight tests of the Rolls-Royce Thrust-Measuring Rig (nicknamed the Flying Bedstead) realized that the best way for jet fighter to achieve vertical take-off and landing was to use swiveling jet engines, lift jets, and lift fans. In other word, by allowing a jet fighter to rise vertically above the ground through means of downward air, lift fans, swiveling jet engines, and separate jets could give the pilot visibility during the process of landing his/her plane vertically. Thanks to the British, the US armed forces and the aircraft industry in southern California could now look in this new approach to vertical take-off and landing for jet fighters.

References:

Buttler, T., 2007. American Secret Projects: Fighters and Interceptors 1945 to 1978. Hinckley, UK: Midland Publishing.

Miller, J., 2001. The X-Planes: X-1 to X-45 (3rd Edition). Hinckley, UK: Midland Publishing.