The Ryan X-13 "Vertijet"

The airplane made history on April 11, 1957, when it completed its first full-cycle flight at Edwards AFB, California. It took off vertically from its mobile trailer, rose into the air, nosed over into a level attitude, and flew for several minutes. It then reversed the procedure to vertical flight and slowly descended to its trailer for a safe landing.

The X-13 on display, one of two built, was the Vertijet which made the full-cycle flight on April 11, 1957. It was transferred to the U.S. Air Force Museum in 1959.

SPECIFICATIONS
Span: 21 ft.
Length: 24 ft.
Height: 15 ft.
Weight: 7,200 lbs. max.
Armament: None
Engine: Rolls-Royce "Avon" of 10,000 lbs. thrust.

PERFORMANCE
Maximum speed: 350 mph.
Minimum speed: 0 mph.
Service Ceiling: 20,000 ft.

The Avon MK 203 is an axial flow turbojet engine similar to the Avon RA.28-49 used to power the vertical landing Ryan X-13 "Vertijet" aircraft. This engine was donated to the Museum in July 1986 by Rolls Royce, Ltd., Glasgow, Scotland.

Development of the Rolls Royce Avon turbo jet was started in 1945 under the Rolls Royce designation AJ-65 (Axial Jet 65 hundred pounds). This was Rolls Royces first axial flow engine. It was designed by Alan Arnold Griffith as a single spool design with a 15 stage compressor and a design thrust of 6500lbs.

Developed as a potential replacement for the Rolls Royce Nene engine, first prototypes of the Rolls Royce Avon appeared in 1947. Due to a number of minor problems production did not get underway until 1950. The first production version, the Rolls Royce Avon RA.3/Mk.101 provided 6500lbs of thrust and was used in the English Electric Canberra B.2.

The Rolls Royce Avon would continue to be developed for some time. While the early versions had 8 canular combustion chambers, later versions had a can-annular combustion chamber. On some engines a simple two-position eyelet nozzle reheat system was used, giving around 30% more power. Production of the Avon for aircraft would continue until 1974, by which time an impressive total of over 11,000 had been built. The Avon was still in operational service with the RAF in the Canberra PR.9 until 23 June 2006.

Derivatives of the Rolls Royce Avon continue to be used in static industrial applications, and are still marketed by Rolls Royce as a compact high reliability power source. For example, in 2003 two electrical generating sets were ordered for the Petroleum Authority of Thailand (PTT) to provide additional power for PTT's Mab Ta Phut, Rayong, gas plant, which introduced Rolls-Royce Avon power in 1984.

The Rolls-Royce Avon was the first axial flow jet engine designed and produced by Rolls-Royce. Introduced in 1950, it went on to become one of their most successful post-World War II engine designs. It was used in a wide variety of aircraft, both military and civilian, ending production after 24 years in 1974.

Design and development

The Avon design team was headed by Cyril Lovesey, who had previously been in charge of Merlin development. The engine was intended both as an experiment in axial-flow engines, as well as (if successful) a replacement for the 5,000 lbf (22 kN) Nene. Originally known as the AJ.65 for Axial Jet, 6,500 lbf which was designed by Alan Arnold Griffith, the engine developed as a single-spool design with an 8, later 10 stage compressor, mass flow rate of 150 lb/s (68 kg/s) and a pressure ratio of 7.45. Development started in 1945 and the first prototypes were built in 1947. Introduction was somewhat slowed by a number of minor problems.

Early Marks had eight can-type combustion chambers whereas later Marks had a single can-annular combustion chamber and a 15 stage compressor.

Operational history

The engine eventually entered production in 1950, the original RA.3/Mk.101 version providing 6,500 lbf (29 kN) thrust in the English Electric Canberra B.2. Similar versions were used in the Canberra B.6, Hawker Hunter and Supermarine Swift. Uprated versions soon followed, the RA.7/Mk.114 producing 7,350 lbf in the de Havilland Comet C.2, the RA.14/Mk.201 of 9,500 lbf (42 kN) in the Vickers Valiant and the RA.26 of 10,000 lbf (44 kN) used in the Comet C.3 and Hawker Hunter F.6. An Avon-powered de Havilland Comet 4 flew the first scheduled transatlantic jet service in 1958. The line eventually topped out with the 12,690 lbf (56,450 N) and 16,360 lbf (72,770 N) in afterburner RA.29 Mk.301/2 (RB.146) used in later versions of the English Electric Lightning. Other aircraft to use the Avon included the de Havilland Sea Vixen and Fairey Delta.

The Avon was also produced under license by Svenska Flygmotor as the RA.3/Mk.109 as the RM5, and an uprated RA.29 as the RM6 with 17,110 lbf (76,110 N). The RM5 powered the Saab Lansen, while the RM6 was the main powerplant of the SAAB Draken.

In the US, the Avon was used to power the vertical landing Ryan X-13 Vertijet aircraft (in RA.28-49 form).

In Australia, the Avon was used by Commonwealth Aircraft Corporation to power its heavily modified variant of the F-86 Sabre, known as the CA-27 Avon-Sabre.

The Avon continued production, mostly for the use in the Sud Aviation Caravelle and English Electric (BAC) Lightning, until 1974, by which time over 11,000 had been built. The engine garnered an impressive safety record over that time. The Avon was still in operational service with the RAF in the Canberra PR.9 until 23 June 2006.

The war against gravity has been fought on various battlefields. On one, designers try to get heavier-than-air machines off the ground vertically, or at least in a very short space. On the other, designers strive to achieve, regardless of the length of takeoff, the greatest altitude possible.

VTOL (Vertical Takeoff and Landing) demands both vertical and horizontal thrust components. With a few exceptions these components have been provided by the same power plants, either by tilting wings (and usually their attached engines), diverting or ducting engine thrust, or tilting the entire aircraft to a vertical takeoff and landing position.

As for high altitude, the heavier-than-air achievers in that field have been military designs - 'black', or highly secret, at that - very different from the VTOL types, and uniquely advanced for their time.

After their investigations of a tail-sitting VTOL aircraft in 1947 and later evaluation of two J33-powered test rigs, Ryan was contracted to build the X-13 research aircraft. The X-13 was intended to take off vertically, being suspended from a mobile trailer by a hook under the forward fuselage.

The delta-winged design first achieved conventional take-off and flight on 10 December 1955 with temporary landing gear attached. By 1956 it had made vertical take-offs, and simulated landings by engaging the hook below the nose on a nylon cable.

The X-13 made its first transition from vertical to horizontal flight and back to a vertical landing in April 1957. VTOL control was achieved by a combination of thrust deflection and thrust variation.

Two prototypes were built, and both were preserved when the test program finished.

The experience of the two big tail sitting turbojets immediately raised the question: was it possible to design a jet aircraft to take off and land in the vertical mode? In theory, of course, there could be no doubt; all that would be required would be a jet engine capable of delivering more thrust to an aircraft than the combined weight of airframe and engine--i.e., a favorable thrust-to-weight ratio.

Commonplace today, this was not so easy to achieve in the mid-1950s. Until the present generation of high performance jet engines came along, delivering enormous thrust derived from high internal heat and pressures, aircraft depended upon light airframes, restricted payloads and superb streamlining in order to reach reasonable performance levels. With the modest engines then available, the only answer was to develop the smallest feasible airplane and, even then, to be content with moderate performance levels.

Based on the Ryan Aeronautical Company’s successful combination jet-and-piston engine FR-1 Fireball fighter for the Navy, and impressed with the company’s interest in developing higher thrust levels, the Air Force signed a contract for a pure-jet VTOL research aircraft on 28 July, 1954. The project expanded with the Navy and NACA joining as sponsors during various phases of the effort. The X-13 Vertijet which resulted was to be a proof-of-concept vehicle only and, in spite of overheated enthusiasm in some quarters, in no way was it ever a prototype fighter.

Minimalism was the key to the X-13's success. To begin with, it was tiny--24 ft long with a wingspan of only 21 ft, weighing a maximum of only 7,200 lbs--and numerous items found in conventional airplanes were omitted here: landing gear, flaps, dive brakes, no catapult or arresting gear, limited space for test instrumentation and absolutely none for armament. Fuel capacity was strictly limited, too, as one pilot found out to his discomfiture. During a demonstration flight from Andrews AFB to the Pentagon grounds in July, 1957, Peter Girard found that the plane carried barely enough fuel to do the job; a flubbed landing attempt would mean a prompt climb to altitude and ejecting. Nevertheless, he overcame Potomac boat traffic, blinding water spray and an unruly hedge in order to made history’s first and only landing of a fixed-wing jet aircraft at the Pentagon.

For all its design limitations, the X-13 was a fully-functioning airplane with operational controls, a simple delta-wing, tailless design. Being jet-propelled, it had to deal with control problems which its tail sitting turboprop cousins never faced. The XFV-1's heavy prop blast washed over its wing and tail surfaces, making its rudder and elevators effective at zero airspeed. Whenever the X-13 perched atop its dynamic column of jet exhaust, however, its conventional flight controls were useless. In order to be able to maneuver while hovering, it used the first gimbaled nozzle ever mounted in an aircraft to control pitch and yaw; wingtip nozzles provided roll control.

In place of landing gear, casters or a skid, the X-13 relied upon a simple hook mounted under its nose; instead of a launching pad or runway, it was mated to the flat bed of a truck. In preparation for a launch, the truck bed was hydraulically raised to a vertical position, like a dump truck, and the pilot would rotate his seat up to 45 degrees to compensate. At launch, the tiny jet would simply lift off vertically, rise to a few hundred feet, and arch over into horizontal flight, where its conventional controls would become effective. Its landing technique was equally simple and effective. Approaching the recovery trailer along a medium or low (usually low) profile, the pilot would point the aircraft’s nose to the vertical, gradually slow to a zero airspeed a few feet above the ground, and then delicately “walk” his plane a few feet forward until the nose hook engaged a raised wire. With its engine cut, the X-13 would settle against the flatbed, ready to be lowered to the horizontal and trucked away.

The Vertijet was clearly a technical success. It proved its design concept and demonstrated that a VTOL flight with a jet aircraft was indeed possible. Practicality, however, was a different matter. The gallant little jet also proved to be a technological dead end; its feats were never replicated and no X-13 successors grace today’s skies. Instead, aircraft designers took another and totally different approach to the problem of jet-propelled VTOL: directed thrust. Today’s Harrier attack planes, widely used in several nations, take to the air on columns of vectored thrust, directed by gimbaled nozzles. However little a burly Marine Corps Harrier may resemble the elegant and delicate X-13, it nevertheless can claim the Vertijet in its design ancestry.

Throughout the 1950s, most major aircraft manufacturers in the United States were anticipating the application of Vertical Takeoff and Landing (VTOL) technology to many types of military aircraft. The armed forces expended considerable sums to develop VTOL aircraft that could remain safely dispersed at small operating sites without the need for cumbersome and vulnerable airbases or aircraft carriers in an age of intercontinental ballistic missiles and thermonuclear weapons. An aircraft with a thrust-to-weight ratio greater than one could launch vertically, and once airborne, transition to horizontal flight for completion of its mission, and return for a vertical landing without expensive, easily targeted runways. The Ryan Aircraft Corporation attempted to convert this idea into a practical fighter for the Air Force with its X-13 Vertijet. However, like most other VTOL aircraft, the performance compromises made for their unique capabilities did not warrant its introduction in place of more capable conventional aircraft.

The idea for the Vertijet originated just after World War Two when engineers for Ryan casually debated whether or not their FR-1 Fireball, which had a thrust-to-weight ratio of one at low fuel quantities, could take off vertically. The vertical take-off idea soon advanced beyond the discussion stage. In 1947, the Navy's Bureau of Aeronautics awarded Ryan a contract to investigate the technical challenges involved in the development of a vertically-launched jet fighter as part of a program to evaluate the feasibility of submarine-based aircraft. The Navy also funded a series of "tail-sitter" aircraft that centered on conventionally-configured airplanes, equipped with large counter-rotating propellers that would rest vertically on a strengthened tail section. These designs, which included the Convair XFY-1 (see NASM collection) and Lockheed XFV-1, were to use their high-thrust propellers to rise vertically from a broad range of naval vessels, thus allowing defensive air cover without aircraft carriers.

Click on Picture to enlarge

Ryan's engineering studies revealed that a similar jet-powered design was feasible with a reaction control system that diverted exhaust gasses in the appropriate direction to allow control during hovering and low-speed flight. A subsequent Navy contract funded construction of an unmanned flying demonstrator, which first flew on October 20, 1950. This ungainly contraption, powered by an Allison J33 turbine, and known affectionately as the "beast in the back yard," used a ball mounted nozzle to provide reaction control while hovering. Ryan engineers converted a B-47 fuel tank into a cockpit to allow test pilot Peter Girard to evaluate the test-bed's suitability as a manned research aircraft, which sat on its tail to take off vertically. On November 24, 1953, Girard made the first manned hovering flight in a jet aircraft with this unusual machine.

After Navy funding ran out, the Air Force became interested in Ryan's experiments and in July 1954 issued a contract to the company to construct two VTOL tail-sitter demonstrators, designated as the X-13 Vertijet. This project, based on the earlier Navy design proposal, was to demonstrate the suitability of easily dispersible VTOL fighters. The X-13, designed and built under the direction of Chief Engineer Curtiss Bates, emerged as a compact, single-engine delta-wing fighter. The only unusual feature visible to the casual observer was a set of winglets and the fixed landing gear. The Ryan Technical Section, led by Robert Fuhrman, designed the aircraft to travel on a special trailer, which would tilt vertically for the launch and recovery of the X-13 during vertical takeoffs and landings.

By late 1955, Ryan completed the first Vertijet (s/n 54-1619), and on December 10, Girard took off for its maiden flight. For its initial testing, the X-13 sported a fixed tricycle landing gear and flew as a conventional airplane. Fuhrman and his team did not want to risk vertical flight-testing until they had thoroughly explored the conventional handling characteristics of the X-13. After the installation of dampers had solved oscillation problems revealed during this phase of the testing, engineers added a temporary steel-tube truss with castering wheels to the rear of the X-13. This allowed the aircraft to sit on its tail during the vertical flight-testing phase without the need for the complex launch and recovery procedures inherent to the launch trailer. Pete Girard made the first vertical takeoff and landing on May 28, 1956. On the same day, the second X-13 made its first flight. The aircraft was agile and responsive in conventional flight.

Click on Picture to enlarge

In conventional flight, elevons and a rudder controlled the X-13. As the aircraft transitioned to a nose-high attitude to "hover" on the thrust from its own engine, a vectorable exhaust nozzle linked to the controls provided a simple and effective means of control. Small bleed-air thrusters mounted on the wingtips allowed for the small adjustments to the pitch and yaw of the aircraft when required by the tricky landing process. A stability augmentation system integrated the conventional and VTOL control systems together without requiring any abrupt changes to pilot control inputs. The vertical takeoff procedure consisted of elevating the bed of the launch trailer vertically, which allowed the X-13 to hang from a cable suspended by two arms on the top of the trailer, with a partially retractable hook. For vertical operations, a flat bumper replaced each of the main wheels on the fixed landing gear, which kept the underside of the fuselage from damage if it swung into the bed of the trailer, which made transport easier. The pilot then simply increased throttle until the hook lifted off the launch cable, backed away from the trailer and then accelerated vertically, smoothly pitching over to conventional flight.

However, vertical landings were more difficult and were probably the most impractical part of the Vertijet concept. Its greatest flaw, as with the earlier tail-sitters, was the obscuration of the pilot's vision by the airframe, which made it extremely difficult to judge the distance to the ground adequately without outside assistance. Although the pilot's seat pivoted 45 degrees towards vertical during landing, the pilot still had to approach the recovery trailer blind with the underside of the fuselage facing the surface of the trailer. Constant radio communication with a ground observer was essential to talk the X-13 into position during the cumbersome process. A 6 meter (20 foot) long folding pole with marked gradations attached to the top of the recovery trailer gave the pilot a clear indication of the distance remaining before he contacted the trailer. Once in position, the pilot slowly retarded the throttle until the nose hook caught the recovery cable.

On May 28, 1956, the X-13 made its first vertical hovering flight, and during that summer, Girard and fellow test pilot, Lou Everrett, began practicing the techniques required to catch the cable on the launch-and-recovery trailer by hooking a one-inch thick rope strung between two towers. For these tests, the Ryan engineers fitted X-13 with a wooden nose that was easily replaceable if damage occurred while the aircraft docked with the trailer. On November 28, Girard made the first transition from horizontal to vertical flight and back again in the X-13. On April 11, 1957, he launched from the trailer, transitioned to conventional flight, and returned for a vertical landing, thus completing the X-13's mission profile. On July 30, 1957, to illustrate the dispersed operating site concept the second X-13 put on an impressive display at the Pentagon for over 3,000 military officers and journalists.

Click on Picture to enlarge

However, competing programs reduced the funds available to continue the project, and the X-13 took to the air for the last time on September 30, 1957. While later programs, such as the XV-6 Kestrel (see NASM collection) and AV-8 Harrier, experienced greater success by resulting in operational aircraft, the X-13 was an effective solution to the problems of creating a VTOL fighter, given the limitations of jet technology at the time of its construction. The Vertijet accomplished all tasks specified for it and undoubtedly succeeded as an experimental demonstration aircraft, in spite of the inherent impracticality of the operational concept. Ironically, by the end of the twentieth century, the thrust vectoring system, initially pioneered on the X-13, would become an essential component of advanced combat aircraft. In 1960, Ryan donated the first X-13, along with its launch trailer, to the Smithsonian Institution.

National Air and Space Museum

After remote controlled tethered rig tests from 1947 to 1950 and a flying rig in 1951, Ryan was awarded an Air Force contract in 1953 to develop an actual flying jet-powered VTOL aircraft, which was given the designation X-13. It was only 24 ft long - just large enough to accommodate a cockpit (again with a tilted seat) and the 10,000 lb thrust Rolls-Royce Avon turbojet. Its high mounted delta wing had a wingspan of only 21 ft, capped with flat endplates. At the tip of the nose was a short pole ending in a hook. The hook was used to capture a wire on a vertical trailer bed. Once captured, the trailer was lowered to horizontal and could be transported on the ground. Engine thrust was vectored to provide pitch and yaw control in hover, while roll was provided by puffer jets outboard of the endplates. The first prototype was fitted with a temporary landing gear and made its first horizontal flight on 10 December 1955. It later made full conversions to vertical attitude and back at altitude. The landing gear was then replaced by a rear mounted castoring framework, known as the "roller-skate" and hooking practice was conducted. The second prototype followed a similar progression; on 11 April 1957, it made a vertical take-off from the raised trailer, transitioned to horizontal flight and back, ending with hooking on the wire "trapeze." On 28-29 July of that year, the X-13 was demonstrated in Washington, hovering across the river to the Pentagon. The Air Force chose not to continue development of the Vertijet because of the lack of an operational requirement