Ryan X-13

The Ryan X-13 'Vertijet' was a jet powered single seat aircraft designed to investigate the feasibility of jet powered VATOL combat aircraft.

Initial development
During April of 1947, the US Navy awarded the Ryan Aeronautical Company a contract to "explore the feasibility of reaction control for jet aircraft". Navy interest in vertical takeoff and landing (VTOL) configurations had been spawned by the obvious shipborne mission advantages of an aircraft with this capability: there would be no need for large, flat surfaces beyond a relatively small platform as a carrier ship could be made significantly smaller  and lighter and therefore more maneuverable and much more difficult to spot; and the feasibility of carrying an aircraft aboard a  submarine might suddenly prove a very attractive option.

The April contract was the result of a late 1946 meeting on the subject of jet-powered VTOL aircraft held between T Claude Ryan (president of Ryan Aeronautical) and the Chief of the Bureau of Aeronautics for the Navy, RADM Stevens. During the meeting, Stevens and Ryan discussed the Navy's strong interest in possibly acquiring dedicated VTOL aircraft that were small enough to permit operation from submarines. At the time, the Navy had narrowed its configuration choices to three designs: a convertiplane with a single, stowable rotor, a very low-aspect ratio all-wing aircraft of basically disk-type planform (effectively a developed version of Vought's XF5U-1) and a purejet VTOL design of advanced configuration and performance.

The latter Navy study, which offered the greatest promise of the three, proved of sufficient interest to Ryan to merit an in-house effort to generate a design capable of accommodating the Navy preliminary specification. Ben Salmon, one of Ryan's chief design engineers, was assigned the project and within days of receiving a go-ahead from the company, began looking at preliminary configurations and powerplant combinations that might fill the Navy's need.

Seven potential powerplant options had been chosen by December 3, and within weeks of that date, this selection had been narrowed to one — the Rolls-Royce Nene 8c. Remaining in contention was the General Electric J33-GE-25, but development was on-going and it appeared that availability would be at least a year in the future. With the powerplant effectively chosen, Salmon was quick to create a complementary aerodynamic shell under the company Model 38 designator. By January 10, 1947, he estimated its gross weight to be 7,700 lb. This created very tight performance margins for the Nene 8c, so a solution was created by mounting four RATO bottles, to be used only during lift-off, on the aft end of the aircraft.

During the last two weeks of January, preliminary drawings were completed under the designation Model 38-1. By early February, three configurations had been created to give the Navy a variety of options. These included the original Model 38-1, the Model 38-2 with an X-type tail and tip-mounted jets; and the Model 38-3 with a  more conventional cruciform tail. During March of 1947, Salmon made a presentation outlining his conclusions to the Navy's Bureau of Aeronautics. Though several of his early studies had by now, been modestly revised (the Model 38 no longer required RATO bottles for lift-off), he had stuck with the basic Model 38 configuration and had pursued reaction control as the primary means of maintaining aircraft stability during hover and non-aerodynamic flight.

Less than a month after Salmon's presentation, the Navy, on April 24, 1947, granted Ryan a contract for $60,000 to study the reaction control concept for VTOL aircraft stability (some 80 configurations had been explored by mid-1948). Many facets of this idea now were examined by Ryan's engineering staff, including exhaust bifurcation, rotatable rocket motors, articulated nozzles using engine compressor section bleed air, tailpipe gas bleed, auxiliary compressed air  sources, articulated vanes in the jet exhaust, and eyelid-type exhaust nozzles.

Consequent to the control system research, Ryan elected also to begin preliminary wind tunnel work and basic performance estimates. Additionally, studies exploring various takeoff and landing techniques were completed, and conclusions that eventually would bear on actual hardware, several years later, were reached. A second proposal was shipped to the Navy on June 24, 1948, following completion of the original study contract. The new proposal requested funding for a full-scale  horizontal test stand to permit studies of jet  reaction forces and associated moments of  inertia. A General Electric J33 turbojet engine would be necessary for these tests  and Ryan agreed to make the results available to the Navy in report form by the end of 1949.

The Ryan proposal was accepted and by late 1948, the test stand was in operation and generating a viable data base. With the stand now functioning with favorable results, Ryan again went to the Navy and  asked that funding be allocated for the construction of a full-scale vertical test stand. The company argued, convincingly, that a J33, mounted in a special, tethered skeletal support rig, would provide extensive hardware experience while permitting the  company to fully explore the control system  design it thus far had executed only on  paper  A year after the Ryan request had been approved, the vertical test rig, assembled at the company's San Diego facility, was in operation and undergoing preliminaiy  VTOL testing. Remotely piloted, it was a strange affair consisting of the J33 engine suspended in a maze of structural tubing, a pair of large bleed pipes for controlling yawing moments, and a large l-beam frame that sewed as the main tether constraint for the  entire mechanism. Large structural cables supported the test article, and additional electrical cables provided remote input for  control from some 40 ft away.

On October 20, 1950, following months of preliminary work, the Ryan test rig flew under three-axis control for the first time,  though still suspended by a gimbal arrangement from the l-beam support structure. This was followed, on May 31, 1951, by the first free, controlled hover by a jet-powered  vehicle. Though still tethered, the attachment was primarily for control system input wiring, and not physical constraint; the gimbaled framework had been removed. Following the successes of the tethered testbed, Ryan, on September 12, 1951, proposed to the Navy a new version of their original Model 38 study. Though effectively a new design bearing the old designator, it still utilized most of the basic control system ideas first proposed by Salmon some five years earlier.

The new Model 38 was larger by a substantial margin than its predecessor, and also the beneficiary of significant advances in technology. Weighing 17,500 lb, it was nearly five times heavier than its predecessor, and being equipped with four 20mm  guns and 600 rounds of ammunition, was substantially more suitable for the fighter role. General Electric's still-under-development J53-GE-X10 turbojet, rated on paper at 24,900 lb th while weighing only 5,293 lb, was the proposed powerplant. With an engine of such extraordinary power-to-weight-ratio, the Model 38 was expected to be capable of exceptional performance; and vertical takeoffs and landings were expected to present virtually no problem.

Somewhat surprisingly, the Navy turned down the initial Ryan proposal. The company quickly followed it with another, however, which called for the development of a testbed aircraft that would be used as a prototype for a follow-on aircraft that was tactically-capable. Though a full-scale hardware contract was not immediately forthcoming, the Navy, during February of 1953, agreed to provide funding for the construction and testing of several wind tunnel models. This was followed, during June, with the release of minimal funding for preliminary testbed design studies, which Ryan now was calling the Model 38R.

Early Model 38R configuration studies called for the use of the 14,800 lb th Pratt & Whitney J67-PW-11 turbojet engine. It was installed in a T-tailed delta wing design which in retrospect, looked like a large version of the aircraft that eventually was to become the X-13. Navy interests notwithstanding, Ryan, while courting Navy funding, also approached the Air Force with a proposal for  a similar design to accommodate Air Force  needs. Concomitantly, it was proposed that the Air Force fund an experimental, testbed-type prototype, to be powered by a non-afterburning Rolls-Royce Avon turbojet, to be followed by a developed tactical version powered by an afterburner-quipped Avon.

Later development
By late-1953, Navy post-Korean War budget cuts had begun to have an affect on  Navy research and development projects. Funding became scarce, and by the end of summer many programs had been canceled or severely reduced in scope. The navalized Ryan Model 38, though not the first to go, was not long in the running. During the summer, word arrived at Ryan that Navy money simply had run out. Air Force interest, fortunately, had taken root by now and during August of 1953, an initial study contract, AF33(600)-25895 (to be followed by a firm contract on July 28, 1 954), was awarded calling for the construction and flight test of two Ryan Model 69 research aircraft to be designated X-13 (the aircraft was also referred to initially as Project 603A, then Project 1227, and finally, Project 693A).

The new project was turned over to a "new" team of Ryan engineers, including  Bob Fuhrman, chief of the company's engineering technical section; Charles Ackerman, chief project engineer; D H  Williams, chief of design; and William lmmenschuh, chief of test operations. Others involved included Herman Braasch, chief of aircraft projects for the company; Bruce Smith, vice-president of engineering;  Art Akers, electronics engineer (who developed the X-13's autostabilization system);  and William White, flight control system engineer.

Experimentation now resumed with the Navy's old vertical test stand and following a modification effort in which the framework was given simple wing skins and an empty  B-47 fuel tank to serve as a rudimentary  fuselage, flight tests with a pilot onboard  (Ryan test pilot P F "Pete" Girard strapped to a Ryan Navion seat) were initiated for the  first time. At this stage of the testbed's development the pilot provided no control input and actually was along basically for the ride. Once hover characteristics had been documented, however, the cockpit was equipped with an independent control set and a new, tilting seat. At the same time, the jet reaction control system was modified, the stabilization system was further improved, and a new tailpipe was installed. With these changes, the Ryan testbed made its first controlled, free, piloted jet hover on November 24, 1953.

Construction
Ryan now began to formalize plans to acquire a Rolls-Royce Avon turbojet engine for use in the new test aircraft, having learned of its development through Navy  sources. This powerplant, offering perhaps the highest thrust-to-weight ratio of any turbojet engine in the world at the time of its unveiling, was to prove the key ingredient in  the many X-13 successes that were to follow. On January 20, 1954, assembly of the first X-13 parts was begun at the Ryan plant in San Diego. This was followed, during June, by a final mock-up inspection and approval, and shortly afterwards, by the arrival of the first Avon engine. By the fall of 1955, the first aircraft was nearing completion. This aircraft, 54-1619, on August 17, was placed on a flatbed truck, covered with canvas, and moved by convoy (that included one of the first pre-production Convair F-102As built at the near-by Convair facility at Lindbergh Field) to Edwards AFB for initiation of its flight test program. As the X-13's conventional flight characteristics were unknown at the time, a decision was made by Ryan to flight test the aircraft in conventional mode before attempting actual VTOL operations. In order to accommodate this decision, a temporary tricycle landing gear was built and attached to the underside of the fuselage.

Initial Tests
On December 10, 1955, with the landing gear in place and Ryan test pilot "Pete"  Girard in the cockpit, the X-13 became airborne for the first time. Lasting only seven minutes, the first hop proved short, as Girard had noted quickly that the aircraft had a serious oscillation problem about all three  axis. Just over two weeks later, the solution — a roll and yaw damper — was installed, and flight testing was resumed. Following the abbreviated conventional flight program, the X-13 was mounted vertically in a tubular structure that was to serve  as its initial vertical attitude landing gear. Known as the "pogo" gear, this unit permitted the X-13 to takeoff, hover, and land while in a vertical attitude. As if to underscore the fact that the aircraft could not be flown conventionally with this rig attached, the unnecessary ailerons and rudder were removed.

While mounted in the "pogo" assembly, tests were undertaken to explore the reaction control system, general maneuverability and handling, and pilot visibility with the aircraft in a vertical attitude. It was quickly discovered that powerplant spool-up lag, similar to a phenomenon experienced in the static vertical test rig, continued to be a problem with the actual X-13. Basically the pilot was forced to chase thrust settings due to slow engine throttle  response. if rapid descent was noted and throttle was applied, the tendency was for the pilot to over-control due to the lag in thrust response to throttle input. The result was usually the aircraft ballooning to a higher altitude than desired.

Solutions to the throttle/thrust lag problem consisted of a Ryan-developed servo system to smooth and effectively slow down throttle movement response times, and a pilot-designed throttle quadrant which permitted power inputs but allowed the throttle handles to be returned by feel to their previous thrust settings. A problem of concern, but which eventually proved to be exaggerated, was the gyroscopic effect of the Avon 's internal turbine wheels. "Pete" Girard had studied this theoretical difficulty with some intensity and had concluded there was potential for trouble. in consultations with the X-13's trailer manufacturer, Freuhauf Trailer Company, a decision had been made calling for the cable support arms, to which the X-13 was to attach itself during takeoff and landing, to  swing up and capture the aircraft's nose hook, rather than visa versa. As flight tests later proved, the gyroscopic problem was relatively small, at worst, and not in the least bit troublesome.

Flights
On May 28, 1956, the first X-13 completed its first test hop in vertical mode. Girard kept the mission conservative, reaching a maximum altitude of less than 50 ft while keeping the horizontal speed to under 30 mph. initial spot landing tests were encouraging, as overall accuracy was better  than 2 ft, and on many occasions, Girard was able to get within 6 in of the target point. Practice hook landings were conducted during succeeding flights, utilizing a one-inch thick section of manila rope suspended between two 50 ft tall towers and a plywood, break-away nose hook on the X-13. Many successful practice runs were made utilizing this training set-up, these generating great confidence in the system and giving Girard an excellent experience base.

During the spring of 1956, the second X-13, 54-1620, arrived at Edwards and was prepared for flight tests. Following a first flight in conventional mode on May 28, 1956, 54-1620, like 54-1619, was mounted on top of a "pogo" rig for preliminary hover testing. Incremental advances were undertaken to slowly work the aircraft into its full flight envelope. Following the hook tests using 54-1619, the temporary tricycle landing gear arrangement was reinstalled for the next flight test  program stage. On November 28, 1956, following several preliminary flights leading up to the actual event, the X-13, with Girard in  the cockpit, ascended to 6,000 ft and slowly pitched nose-up until it effectively was hovering in space. For many seconds the aircraft sat in a vertical attitude, and then  slowly pitched over again and regained flying speed. This was the first such VTOL transition of a jet-propelled aircraft, ever.

The ultimate test came four months later. On April 11, 1957, the X-13 took off vertically on its most important flight. Hovering away from its support trailer, it ascended to altitude over Edwards AFB, pitched over into conventional flight attitude, performed a  series of conventional flight maneuvers, slowed, pitched nose-up into a hover, and then slowly descended back to the Edwards South Base ramp. Maneuvering into position, its hook slipped over the support trailer suspension cable and within seconds, the first horizontal flight-to-vertical-attitude landing in history was completed without incident.

Further transition flights now were undertaken with significant regularity, leading Ryan, during late July, to load the cocooned second X-13, 54-1620, aboard the USS Young America for transport to Washington, DC, via the Panama Canal. There, with Ryan test pilots Lou Everett, Bill lmmenschuh, and "Pete" Girard splitting cockpit responsibilities, it was demonstrated in front of the Pentagon. Eight demonstration/practice flights (excluding the single mission from the Pentagon) eventually were logged at Andrews AFB during the week of July 20. On July 26, several complete VTOL demonstrations were undertaken, these being viewed  by numerous Department of Defense observers. The actual Pentagon demonstration was short, but impressive. Taking place on July 30, it lasted just seven minutes. The route was historic, and purposely chosen to underscore the technology advances so vividly represented by the X-13's capabilities—it retraced the course flown by Onville Wright and Lt Benjamin Foulois some 48 years earlier when making the final acceptance flight of the first US military aircraft. Though successful, well-attended (over 3,000 were on hand), and newsworthy, the Pentagon flight proved the X-13's last hurrah. Following return to California on September 12, 1957, it was delivered by truck to Edwards AFB to rejoin 54-1619 in a pilot indoctrination program optimized to expose Air Force and Navy pilots to the  peculiarities of VTOL aircraft.

These operations continued through the end of the year (though Ryan had suspended all related X-13 work on September 27), until funding and legal constraints terminated even this activity during the first few  months of 1958. By mid-1958, the X-13 and its technology base had effectively been forgotten. Only the NACA remained interested in the hardware and delays in turnover commitments and the NACA's inability to receive proper pilot indoctrinations, eventually eliminated even this final option.

Post flight
After a total expenditure of $9.4 million, no other support for the two X-135 was  attainable and the NACA and the Air Force  had, by now, diverted their interests to space  activity and the X-15 program. As a result, surveys were made to determine the best  means of disposition. It eventually was decided that 54-1 61 9 would be loaned to the  USAF Orientation Group to serve as a mobile static display for two years, following  which it would be turned over to the Air Force  Museum. The second aircraft, 54-1620, was to be turned over immediately to the  Smithsonian institution. As luck would have it, the number 2 aircraft, 54-1620, was inadvertently prepared for use by the Orientation Group as their static display and was delivered during 1959 with a modified erecting cradle mounted on  a flatbed trailer. This aircraft, in turn, was later turned over to the Air Force Museum. The number 1 aircraft, 54-1619, was delivered to the Smithsonian institution, together with one ground support vehicle and miscellaneous extras.

Construction, System, and Equipment
The X-13 was an all-aluminum aircraft with titanium structure in high—heat-sink engine bay areas. The delta wing, with the exception of the ducting to accommodate the wing tip yaw and roll control nozzles, was of conventional construction and had a 60° leading edge sweepback; 4° angle-of-incidence; and 0° dihedral. In its VTOL configuration, the X-13 had no conventional landing gear, but instead had two small, non-retractable tube-mounted bumpers on the fuselage under-side along with a small, semi-retractable nose hook. In conventional mode, a conventional tricycle landing gear could be attached for horizontal attitude take oﬁs and landings. When the conventional landing gear was fitted, the main gear tread was 7.9 ft.

The nose hook supported the entire aircraft from a short section of steel cable that was normally suspended between two mechanical arms attached to the articulated (it could be moved vertically 90" from horizontal) ﬂatbed portion of a specially manufactured Fruehauf trailer. This cable also could be suspended between any two  strong, stationary objects such as large trees or poles. For trailer launching and  retrieval, the flatbed of the trailer could be  raised, with the X-13 in place, to a vertical position by two large, segmented hydraulic rams.

In order to enter the conventional horizontal ﬂight mode, the X-13, following liftoff from the trailer cable normally hovered into acceleration position and then began a vertical ascent. As airspeed and altitude increased and the aerodynamic control surfaces became effective, the aircraft rapidly pitched over into conventional horizontal flight. Landings were accomplished in reverse order. The aircraft would decelerate and the nose would slowly pitch up to a vertical attitude, transitioning from aerodynamic to jet thrust lift. Descent now was made slowly, and once in proximity of the trailer, the air-  craft would hover into position for hook-up.

A hover/taxi procedure would slowly bring the X-13 to within range of the trailer  and its supporting cable. A ground observer, to assist in directing the X-13 to the cable, was situated in a cage mounted on the  flatbed's upper left corner. Constant radio contact was maintained at this point as it  was necessary for the pilot to receive audio,  as well as visual clues. A 20-ft-long pole with colored distance markings protruded horizontally from each  side of the vertical portion of the trailer. As the X-13 neared the support cable, the pilot  could see this pole and thus judge his height  and distance from the hook point. Additionally, a specially designed task velocity measuring unit (TVMU) on the tip of  the nose probe (consisting of two free-swiveling ring-type pitch and yaw vanes)  provided motion references at very low speeds (down to 8 knots).

Small wing tip nozzles utilizing engine compressor section bleed air provided fine yaw and pitch control inputs during hover. Course pitch and yaw control needs were input by the pilot via the articulated main  engine exhaust nozzle. All control inputs were integrated with a simple, but efficient stability augmentation system. The cockpit was unpressurized and equipped with a multi-piece canopy that opened vertically. The pilot's ejection seat was a swiveling unit (in pitch, only) offering  45° of movement in concert with the rotation  of the aircraft between vertical and horizon-  tal flight. lt had limited zero/zero capability and initially was equipped only with a right-hand actuator. At a later date, Stanley Aviation of Colorado Springs, Colorado  modified the seat to accommodate actuators on both sides.

The basic avionics complement included an Aircraft Radio Corporation Type 12 VHF command radio; an R-19 receiver; a T-1 1 B transmitter; and T-1 3A transmitter. Aerodynamic surfaces for the X-13 were basically conventional for a delta wing aircraft. Single-piece trailing edge elevons were attached to each wing, and the large vertical fin (the product of a short coupled fuselage) had a single-piece rudder. Tip fins were attached to each wing tip providing increased vertical surface area and consequently improving chord-wise airflow at high speed and elevon control at low speed.

During various stages of its flight test program, the X-13 was equipped with an anti-spin chute mounted in a bullet fairing at the base of the vertical fin. This also could be used as a drag chute during conventional horizontal landings to shorten landing roll-out. Late in the flight test program, a pair of retractable airbrakes (which were integral  with a new, small main landing gear) in the  form of two hydraulically-actuated under-fuselage panels, were added to facilitate  deceleration during horizontal flight.

Powerplant
The X-13 was powered by a single, non-afterburning Ftolls-Royce Avon RA.28-49 axial-flow turbojet engine. The engine specification number was TSD 510. Maximum thrust rating was 10,000 lb at 8,000 rpm for 10 min. Military thrust rating was 9,350 lb at 7,800 rpm for 30 minutes. Normal thrust rating was 8,650 lb at 7,600 rpm continuously. The engine was 113.3 in long and had a diameter of 41.5 in. lt's dry weight was 2,897 lb. Fuel was standard JP-4. All fuel in the X-13 was carried in a single wing tank with a  capacity of 271 gal. A single engine oil tank held 1 .8 gal.

Summary
The X-13 program represents one of the two most successful VTOL research aircraft programs of the 1950s. Along with the X-14, the X-13 represents a high water mark in the history of vertical takeoff and landing aircraft development. The X-13 program proved beyond doubt that VTOL flight, on jet thrust alone, was  both technically feasible and practical. The ease with which the aircraft routinely transitioned from vertical to horizontal attitude,  and back again, left little question as to the operational utility of such flight capabilities. Among the advances realized during the course of X-13 development were:
 * 1) a  fully functional and mechanically practical vectorable exhaust nozzle;
 * 2) bleed air  thrusters for yaw control during hover;
 * 3) cockpit ergonomics in tune with the unique  vertical attitude of the aircraft;
 * 4) the application of a delta wing to a VTOL-capable  aircraft; and
 * 5) a sufficiently high thrust-to-weight ratio.

Perhaps the only failing of the X-13 program was its lack of success in generating follow-on production aircraft contracts. This was due in part to the aircraft's small payload envelope, powerplant limitations, a conservative military establishment, and in retrospect, program mistiming. It worked, and worked well. Unquestionably, it was ahead of its time.

With Ryan test pilot "Pete" Girard at the controls, the first X-13, 54-1619, became airborne in conventional mode for the first time on December 10, 1955, from Edwards AFB, California. The second X-13, 54-1620, became airborne in hovering mode for the first time on May 28, 1956, also from Edwards AFB.

Both X-13s survived the flight test program. The first aircraft, 54-1619, is currently on long term loan from the Smithsonian Institution's National Air & Space Museum to the San Diego Aerospace Museum in San Diego, California. The second aircraft, 54-1620, is currently on display at the US Air Force Museum's annex section at Wright-Patterson AFB, Ohio.

Aircraft of comparable role, configuration, and era

 * Rolls-Royce Thrust Measuring Rig
 * Short SC.1
 * Snecma C.450 Coleoptere