This class of aircraft uses a single propulsion system that alters the direction of thrust for hover or cruise, or alters the attitude of the aircraft itself. Aircraft 9-14 rotated their powerplants, whereas all other aircraft in this wheel kept their engines stationary (except #30, the VJ 101C, which rotated four of its six engines).
These aircraft are convertiplanes using rotating blades that function like rotors in vertical flight and like propellers in forward flight. The rotors are long articulated blades which have cyclic pitch control for hover. The powerplants remain stationary with the power shaft pivoting from vertical to horizontal.
1. Transcendental Model 1G
The Transcendental Aircraft Company was formed by former Piasecki workers in 1945 to investigate tilting rotor technology. It built the single-seat open cockpit Model 1G in 1951. The 1G suffered from dynamic stability problems that were determined to be fundamental to the tilting rotor concept, so the Air Force funded research on rotors in transition including gyroscopic effects and oblique airflow. The 1G then made its first flight (as a helicopter) on 6 July 1954 and made its first conversion to horizontal flight that December. A single 160 hp Lycoming O-290-A engine powered three-bladed 17 ft rotors at each wingtip. The piston engine had a manual two-speed reduction box that powered shafts down each wing. At the pivot, three concentric shafts supplied input to the rotors for tilt angle, cyclic pitch, and collective pitch. At the maximum engine speed of 3,000 rpm, rotor speed for hover was 240 rpm, while for horizontal flight they rotated at 633 rpm. The rotors required three minutes to transition through 82° of tilt during conversion, including the gear change. The 1,750 lb (fully loaded) 1G had a 26 ft long fuselage and a wingspan of 21 ft. The height was only 7 ft; in fact, the 1G was so small, the pilot's head rose above the windscreen (see photo). The 1G flew over 100 flights and 20 hours before being lost in an accident on 20 July 1955 due to a rotor control mechanical failure. Top speed was about 160 mph. A 4,000 lb Model 2 with a 250 hp engine was tested in 1956-57, but the Air Force decided to not fund it further in order to pursue the competing Bell XV-3.
2. Bell XV-3
One of the founders of Transcendental left to take the lead on the design of the Bell XV-3, which began under a joint Army-Air Force program in 1951. The XV-3 used the reliable 450 hp Pratt & Whitney R-985 radial engine mated to a two-speed manual gearbox, similar in principal to that of the Transcendental 1G. The fuselage was 30 ft long and had a 31 ft wing span. It made its first flight as a helicopter in August 1955, but crashed two months later before completing a full conversion. Extensive wind tunnel and rig tests were conducted after this, with pilots practicing the conversion process and gear changes (which required significant manipulation of the pitch and throttle controls and took about 20 seconds) in the tunnel. Rotor instability concerns led to a change from 23 ft three-bladed full-articulated rotors to 24 ft two-bladed semi-rigid rotors. The second XV-3 made its first flight on 12 December 1958, with a full conversion only 6 days later. Conversions over the full 90° could be conducted in 10 seconds. Inadequate power and high weight growth precluded the XV-3 from hovering out of ground effect. The XV-3 made 110 full conversions and over 250 flights before it was damaged in a wind tunnel test in 1965 when a rotor housing separated from the aircraft. The ejection seats were thankfully never needed: they ejected downward.
3. Curtiss-Wright X-100
The X-100 was built primarily to flight test Curtiss-Wright's concept of using propeller "radial force" instead of wing lift for conventional flight. This phenomenon produces a large force at right angles to the airflow as the propeller angle of attack is increased. The X-100 used a 860 bhp fuselage-mounted Lycoming YT53-L-1 driving cross-shafts for the 10 ft diameter tilting fiberglass propellers at the wingtips. At the rear of its 24 ft fuselage, engine exhaust was used for pitch and yaw control in hover; roll control was provided by differential propeller pitch. Wingspan was 16 ft and gross weight was 3,500 lb. The X-100 first hovered in free flight in September 1959, and made its first short take-off and landing flight on March 1960. Its first (and only) transition from vertical to horizontal was performed in April 1960. Control in hover was weak due to the low exhaust gas velocity. Testing continued until October 1961, sufficiently proving the Tilt Prop concept to the extent necessary to proceed with what would become the X-19.
4. Curtiss-Wright X-19
Using the radial force lift concept proven by the X-100, Curtiss-Wright designed a six-passenger civil executive transport, originally designated the X-200. As part of the Army/Navy/Air Force Tri-Service Assault Transport Program, the Air Force contracted for conversion of two prototypes, designated X-19, extensively modified for military requirements with ejection seats, rescue hoist, mock refueling probe and a fuselage stretch for improved passenger access. The 44 ft long aircraft was powered by two Lycoming T55-L-7 turboshaft engines producing 2,650 shp each. At the end of each tandem wing was a 13 ft three-bladed wide chord, high twist propeller. In order to eliminate gyroscopic and torque effects, propellers located diagonally rotated in the same direction. Roll, pitch and yaw were all controlled by differential propeller pitch. Empty weight as flown reached 10,000 lb, and gross weight over 12,000 lb. The first aircraft hovered on 20 November 1963, but suffered a hard landing. It was repaired, but problems with the control system and a series of mechanical problems plagued the program. On 25 August 1965 a transmission part failure caused an asymmetric lift situation, which allowed the crew to validate the operation of their ejection seats. When the program was canceled four months later, the first aircraft had made 50 flights, but for a total of only four hours. The second aircraft was never flown.
5. Doak 16 VZ-4
The Doak 16, which received the Army designation VZ-4, was built in 1957. It was 32 ft long, had a gross weight of 3,200 lb, a tandem two-seat cockpit, and a 16 ft wingspan. Each wing ended in eight-bladed 4 ft wide propellers within tilting ducts; they were powered by a single 860 bhp Lycoming YT53 engine. The first flight was made on 25 February 1958. Transition from hover to 200 kt could be made in less than 20 seconds. Variable inlet guide vanes controlled roll in hover, and engine exhaust gases were deflected at the rear of the fuselage for pitch and yaw control. Deceleration and descent had to be carefully controlled in order to prevent the lip of the duct from stalling, as well as to manage a large upward pitching moment from the ducts acting as a wing at a high angle of attack. The Doak 16 suffered from a lack of control power, but completed over 50 hours of testing and proved the feasibility of the tilt duct concept.
6. Bell X-22A
The X-22A was the Navy contracted and managed portion of the Tri-Service Assault Transport Program. The Bell X-22A was 39 ft long, featured side-by-side pilot seats, and had a gross weight of 17,000, including six passengers or a 1,200 lb payload. It was powered by four 1,250 shp GE YT58-GE-8D turboshaft engines that were cross-linked and had 35% excess power in case one of the engines failed in hover. Span over the canard (including the 7 ft diameter three-bladed ducted propellers) was 23 ft; across the rear wingtip ducts it was 39 ft. The ducts rotated non-differentially from 0° to 95° and had spanwise elevons across the center of the duct. Differential propeller pitch and the elevons were used to control the X-22A in hover. In forward flight, the ducts provided a significant amount of the aerodynamic lift. The first aircraft was rolled out on 25 May 1965. It made its first hovering flight in March 1966, and was tested to transition angles of up to 30° at speeds of up to 100 kt. That August, the first prototype was lost in a hard landing after only three hours of flying time due to a hydraulic failure. The second prototype made its first flight in January 1967 and performed hundreds of complete transitions. It reached a maximum speed in forward flight of 315 mph, and had a range of 450 miles. In early 1968, the X-22A's variable stability and control system was demonstrated, which allowed for research into hover and transition flight characteristics of other possible V/STOL aircraft. On 30 July 1968, it set a record by hovering at an altitude of over 8,000 ft. Flying until 1980, it accrued about 200 hours in the air.
7. Nord 500 Cadet
In 1966, the French company Nord (later part of Aérospatiale) built two Cadets, each powered by two 317 shp Allison T63-A-5A engines. The Nord 500 Cadet was 22 ft long and 20 ft wide, weighed only 2,760 lb and used two relatively large five-bladed ducted propellers. On the exit end of the ducts, four control vanes in a diamond shape controlled pitch (collectively) and yaw (differentially). This configuration was selected to try to expand the airflow in hover and compress it during horizontal flight. The first aircraft was used for static tests while the second made a tethered hover on 23 July 1968. It was canceled without being tested further.
8. Vertol 76 VZ-2
The Vertol 76 received the Army designation VZ-2 in early 1956. The 26.5 ft fuselage was built of metal tube construction, and had a helicopter-like two seat cockpit. A single 860 bhp Lycoming YT53-L-1 was mounted on the fuselage, and drove the two 9.5 ft three-bladed propellers by a cross-shaft through the 25 ft span wings. In hover, pitch and yaw were controlled by two ducted propellers in the tail; in transition, aerodynamic controls were phased in until the tail propellers were no longer needed in horizontal flight. Ground testing began in April 1957. The first vertical flight was made on 13 August 1957, first horizontal flight on 7 January 1958, and first complete transition on 15 July 1958. It continued to fly until 1965, making over 450 flights, including 34 full conversions.
9. Hiller X-18
The Hiller X-18, begun in February 1957, used various components from existing aircraft. The fuselage was that of a Chase YC-122C transport. The two wing-mounted 7,100 eshp Allison T40-A-14 turboshafts came from the XFY-1/XFV-1 tailsitter (#23 and #24) program and could not be cross-linked. It had three engines, the two turboprops drove the 16 ft diameter counter-rotating three-bladed propellers and a 3,400 lb thrust Westinghouse J34 turbojet which produced pitch control thrust. The 33,000 lb loaded X-18 underwent extensive ground tests beginning in December 1958, and made its first conventional flight on 24 November 1959. It made partial conversions with wing angles of up to 33° (relative to the fuselage) -- with a 17° nose-up attitude, the wings had an effective 50° degrees of tilt (relative to the flight path). The turboprop engines had electric pitch controls and were too slow to provide adequate response in hover. On the 20th flight it had a propeller pitch control problem at 10,000 ft and went into a spin. It was recovered before impact, but was grounded, having never achieved hover. It continued to test ground effects before it was damaged by a test stand failure.
10. LTV-Hiller-Ryan XC-142
The XC-142 aircraft was the third aircraft evaluated in the Tri-Service Assault Transport Program. It used four cross-linked 3,080 shp General Electric T64-GE-1 engines, each driving a 15.5 ft four-bladed propeller. Roll was controlled by differential propeller pitch, and pitch by an 8 ft three-bladed variable pitch tail rotor. Yaw was provided by ailerons powered by propeller slipstream. The wing could tilt through 100° allowing the XC-142 to hover in a tailwind. The tail rotor folded to the port side to reduce the stowage length and to protect against accidental damage during loading. This cargo aircraft was 58 ft long, had a wingspan of 67 ft and was capable of transporting 32 troops and gear or 8,000 lb of cargo. It had a rear loading ramp and had a maximum gross weight of 41,000 lb for a vertical take-off, or 45,000 lb for a short take-off. It made its first conventional flight on 29 September 1964, first hover on 29 December 1964, and first transition on 11 January 1965. Air Force trials included cargo flights, cargo and paratrooper drops, and desert, mountain, rescue, and carrier operations. Five aircraft were built, but mechanical failures (primarily the cross-shaft and gear boxes which could be damaged during wing flexing) and operator error caused four of them to be damaged in hard landings. One crash occurred as a result of a failure of the drive shaft to the tail rotor, causing three fatalities. The XC-142 suffered from excessive vibration and noise, resulting in a high pilot workload. During the program, the XC-142 accrued 420 hours by 39 different pilots as an operational evaluation aircraft.
11. Canadair CL-84 Dynavert
The Canadian CL-84, begun in November 1963, was a quarter the size of the XC-142. It weighed 8,100 lb empty, could make a vertical take-off at 12,200 lb, or a short take-off at 14,700 lb. The wings were 33 ft long and housed two 1,450 shp Lycoming T53-LTC1K-4A turboprops which powered the cross-linked 14 ft four-bladed propellers. Pitch control was provided by two counter-rotating two-bladed horizontal propellers, which in horizontal flight were stopped and aligned to minimize drag. Roll control was by differential pitch, and yaw was controlled with ailerons. It made its first vertical flight in May 1965, and first conventional flight that December. A total of four aircraft were built, including one which was not flown. US pilots evaluated it extensively, including demonstrations on amphibious ships and the Pentagon helipad. Neither government was sufficiently interested to order production aircraft. Two aircraft were destroyed in non-fatal accidents due to mechanical failures.
12. Bell XV-15
Over twenty years after they began work on the XV-3, Bell received a contract to begin work on their 13,000 lb Research Tilt Rotor aircraft, which was designated XV-15. The 42 ft fuselage housed side-by-side pilot seats. At each tip of the 35 ft span wings, a 1,550 shp Lycoming T53-LTC1K-4K turboshaft engine powered a 25 ft diameter three-bladed rotor. The engines and rotors tilted through 90° and were cross-linked in the event of engine failure. The rotors were semi-rigid stainless steel with a high twist and no flapping hinges. Control at low speeds was by cyclic and collective blade angle adjustments. The first hover of the joint Army/NASA XV-15 was performed on 3 May 1977. The first aircraft was later tested extensively in the wind tunnel. Aircraft number two made its first hover on 23 April 1979. It made the first conversion to horizontal flight on 24 July 1979. In the next several years, the XV-15 conducted extensive tests, shipboard landings, and achieved a maximum speed (in a dive) of 397 mph. By 1986, it had made 1,500 conversions in 530 flight hours. The aircraft was flight tested aboard the USS Wasp in 1990 to evaluate shipboard compatibility issues of the tilt rotor concept.
13. Bell Boeing V-22 Osprey
In 1983, Bell, teamed with Boeing Vertol, was selected to develop their Tilt Rotor concept into the Army/Navy/Marine Corps/Air Force V-22. It is powered by two Allison T406-AD-400 engines which drive 38 ft three-blade rotors on a 45 ft wingspan. The cross-shafted engines are each rated at 6,150 shp for take-off with the maximum continuous rating of 5,890 shp; the transmission is rated at less than 5,000 shp for normal operations, but nearly 6,000 shp for emergencies. The Osprey made its first flight on 19 March 1989 and first transition on 14 September 1989. It is capable of transporting 24 troops or 864 cubic feet of cargo. A loading ramp is in the tail of the 57 ft fuselage. Normal vertical take-off weight is 47,500 lb, while maximum gross weight for a short take-off and landing can be as high as 60,000 lb, including up to 20,000 lb of internal or external payload. Combat range is about 600 miles, while maximum ferry range is 2,400 miles. Maximum speed is nearly 400 mph. By the end of 1996, over 1,100 hrs of flight testing had been conducted with five development aircraft; two aircraft crashed (1991 and 1992) the latter one killing seven people. The first of four "production representative" test aircraft began flying on 5 February 1997. A total of 523 aircraft will now be built for the Marine Corps, Navy, and Air Force, with the first V-22s becoming operational in 2000.
14. Bell 65 Air Test Vehicle (ATV)
In 1954, Bell built their Model 65 Air Test Vehicle (ATV) of parts from a number of commercial aircraft. A 1,000 lb thrust Fairchild J-44 missile turbojet engine mounted on each side of the aircraft under the wing could be tilted from vertical to horizontal. A Turbomeca Palouste turbocompressor provided reaction jets at the tail and wingtips for control in hover. It made its first hover on 16 November 1954 from a platform to prevent the ATV from reingesting its exhaust gases. The ATV was modified with a wheeled landing gear and made horizontal flights in 1955. It made partial conversions at altitude, but had inadequate engine thrust to complete the transition. Bell ended the program in 1955 in favor of its X-14 (#18), but used this tilt jet experience to develop the Air Force XF-109 V/STOL fighter concept; although canceled before being built, this concept was very similar to the later VJ 101C (#30).
15. Robertson VTOL
Robertson Aircraft Corporation was formed in October 1956 to build a four seat vertical take-off and landing (VTOL) aircraft powered by two supercharged 340 hp Lycoming GSO-480 engines. The wing had a sliding flap system with a double-slotted full span trailing edge flap providing all control. The flaps were retracted into the low aspect ratio wing for horizontal flight. All fuel and oil were carried in wing tip tanks which also acted as endplates. This capped the wing "buckets" and should have improved cruise efficiency. The aircraft made a tethered flight on 8 January 1957 but was not pursued.
16. Ryan 92 VZ-3 Vertiplane
The Ryan 92, designated VZ-3 by the Army in June 1956, was intended to be a reconnaissance and liaison aircraft able to operate from unprepared surfaces. It had a 28 ft metal fuselage and was powered by a 1,000 shp Lycoming T53-L-1 turboshaft engine driving a metal three-blade Harzell propeller on each side. The propellers were situated ahead of and below the wing, so the majority of the propeller slipstream flowed directly into the bucket formed by the extended double flaps and were turned downward for vertical lift. Differential propeller pitch was used for roll control. Engine exhaust was used at the tail for pitch and yaw before aerodynamic controls were effective. Ryan began taxiing trials on 7 February 1958. After extensive wind tunnel tests and aircraft modifications the first flight was made on 21 January 1959. The engines were unable to provide sufficient power to hover without a head wind. An accident the next month grounded it for repairs until its first test by NASA in February 1960; unfortunately the pilot ejected after an unplanned maneuver. It was again rebuilt to flying status: modifications after the crash led to a fabric nose section, an open cockpit, and a different landing gear. It continued flying in 1961, testing low-speed V/STOL handling characteristics.
17. Fairchild 224 VZ-5 Fledgling
The Fairchild M-224-1 Fledgling was powered by a 1,024 shp General Electric YT58-GE-2 turboshaft engine turning four three-bladed Harzell metal propellers. The open cockpit had room for the pilot as well as a jump seat. The aircraft could either sit on its forward tricycle landing gear or rest on its two main wheels and a tail skid, providing the Fledgling with 30° of inherent rotation to enhance the "bucket's" effectiveness. Small rotors at the top of the T-tail controlled pitch during hover. Tethered tests were made in late 1959, but it never flew.
18. Bell X-14
Built under a US Air Force contract, the X-14 used a planar array of diverter vanes to vector the exhaust of two Armstrong Siddeley ASV8 Viper engines (1,750 lb thrust each) at the center of gravity (c.g.). The vanes could be rotated to direct the exhaust from vertical to nearly horizontal. The 25 ft fuselage and tail were from a Beech T-34; the 34 ft span wing was from a Beech Bonanza. The lack of a ejection seat limited hover testing to very low and very high altitudes. The gross weight was originally only 3,100 lb. The landing gear had to be lengthened when the phenomenon of suck-down was first discovered. Engine gyroscopic effects and exhaust gas reingestion were also encountered. First hover flight was achieved on 17 February 1957; first transition was made on 24 May 1958. The Viper engines were replaced with higher power GE J85 engines when it was transferred to NASA in 1960. It was eventually fitted with a digital fly-by-wire control system and continued flying as a V/STOL testbed until 1981!
19. Hawker P.1127 Kestrel
The Hawker/Bristol funded P.1127 development began in 1957. The Bristol Pegasus engine (originally with only 11,000 lb thrust) was developed for the aircraft with heavy US funding support. It was based on the earlier Orpheus engine, and had a bifurcated jetpipe and vectoring front and rear nozzles. The P.1127 made its first hover on 21 October 1960 on tethers, but this was not considered to be beneficial to feel out the aircraft response, so the first untethered hover was made less than a month later, on 19 November 1960. First conventional flight was made on 7 July 1961 and first double transition on 12 September 1961. Control power was low about all axes, which, combined with suck-down and limited height control power, resulted in a high pilot workload in hover. Hot gas ingestion was overcome with a low forward speed in takeoff and landing. One of the two initial test aircraft crashed, with the pilot ejecting safely. The British government began supporting the development before the first flight, funding the first two prototypes, and later four more. Pegasus 3 power was increased to 13,500 lb thrust. In 1962, the UK, US and Germany initiated a tripartite program, funding nine improved P.1127 Kestrels for use by a UK-led tri-national squadron which conducted operational trials. These used Pegasus 5 engines, with thrust increased to 15,500 lb. The Kestrel paved the way for the Harrier (#21).
20. Yakovlev Yak-36 Freehand
The Freehand was powered by two non-afterburning Soyuz Tumanskiy/Khatchaturov R-27-300 turbojet engines (11,000 lb thrust each) mounted forward of and below the cockpit. They were fitted with louvered nozzles, which were vectorable through about 90º and exhausted at the center of gravity (c.g.), similar to the Bell X-14 (#18). Engine bleed air was used for reaction control nozzles at the tip of each wingtip fairing, on the tailcone, and at the tip of a ten foot long nose "probe." The overall length was 57.5 ft long (including the nose probe), with a wingspan of 27 ft. Empty weight was 12,346 lb, maximum take-off weight was 20,723 lb. The Yak-36 made its first untethered hover on 9 January 1963. From there, the flight envelope was slowly expanded, with a double transition from vertical take-off to forward flight and back to vertical landing performed on 16 September 1963. A number of retractable doors (including a large "apron" under the nose) were fitted to reduce hot gas reingestion. It was only capable of vertical take-offs and landings. The first public display was at the Soviet National Aviation day on 7 July 1967 at the Domodedovo Air Show. The Yak-36 was a technology demonstrator that eventually led to the operational Yak-38 Forger.
21. McDonnell Douglas/British Aerospace Harrier
Following the Hawker (later British Aerospace) Kestrel operational trials (#19), the first of six production-designed Harrier developmental aircraft flew on 31 August 1966. The production GR1 Harrier entered service with the UK Royal Air Force on 1 April 1969 powered by the 19,000 lb Bristol (later Rolls-Royce) Pegasus Mk 101. US Marine Corps AV-8As were purchased in 1969, powered by the 21,500 lb thrust Pegasus 11. A navalized version, the FRS1 Sea Harrier, entered service with the Royal Navy in 1980. McDonnell Douglas (later with British Aerospace) began developing the AV-8B GR5 Harrier II in 1974, and began flight testing in 1981. With a more powerful engine, a larger, composite supercritical wing, optimized Lift Improvement Devices (LIDs) and other improvements, the Harrier II was able to double the payload and range when making short takeoffs. The F402-RR-408 Pegasus 11-61 has now reached 23,800 lb thrust. Today, the Harrier is the only operational V/STOL aircraft in the world. In addition to the USMC, the UK RAF and RN, the Harrier is also operated by Spain, Italy, India and Thailand.
22. Boeing X-32
As part of the Joint Strike Fighter (JSF) program, the Boeing X-32 concept demonstrator (artist's drawing above) uses a derivative of the Pratt & Whitney F119 engine with Rolls-Royce lift components. The X-32 concept has a chin inlet and a blended delta wing. In short take-off and vertical landing (STOVL) mode, the engine closes the vectorable cruise nozzle and opens two lift nozzles at the aircraft c.g. First flight is planned for 2000. The winner of the JSF source selection in 2001 will then develop its operational STOVL version of the concept as a supersonic multirole aircraft to replace the Harrier. Boeing's design for the operational aircraft has an empty weight of about 22,000 lb, length of 45 ft and a wingspan of 30 ft; maximum take-off weight would be about 50,000 lb. During the Concept Development Phase that ended in November 1996, Boeing completed 11,700 hours of developmental testing and piloted simulations, including testing of a Pratt & Whitney YF119-powered 94% scale model in 1995.
23. Lockheed XFV-1
After World War II, the US Navy was looking for ways to improve ship defense by equipping merchant ships with vertical take-off aircraft. A 1950 design competition selected Convair (#24) and Lockheed to each build a single-seat tail sitting fighter aircraft. Each used the Allison YT40-A-14 engine (two coupled T38 power sections mounted side-by-side) driving two 16 ft counter-rotating three-bladed Curtiss-Wright propellers with electric pitch control. The engines produced 5,500 eshp with a 7,100 eshp take-off rating, resulting in over 10,000 lb of thrust. The 37 ft fuselage had mid-mounted 30 ft span wings. Control in hover was by the same large aerodynamic surfaces as in level flight, as each was bathed in propeller slipstream; the "X"-shaped tail arrangement minimized downwash masking. An erector trolley was used to stand the XFV-1 in the vertical position; the tips of each tail had a small castoring wheel. The aircraft was fitted with a temporary conventional attitude landing gear and made its first horizontal flight in March 1954. A total of 27 conventional flights were made, with the first full transitions made above 1,000 ft that Fall. Control in hover was very weak, and the pilot had difficulty in determining sink, climb, and rotation from normal visual cues. No vertical take-offs or landings were ever attempted. As with the Convair XFY-1 Pogo, the engine and control systems were judged to be insufficient.
24. Convair XFY-1 Pogo
As with the Lockheed XFV-1, the Pogo used the Allison YT40-A-14 engine and Curtiss-Wright counter-rotating propellers, but was somewhat more compact and less conventional in appearance. The Pogo was 31 ft long with a 26 ft wide delta wing. A large vertical stabilizer above the wing was matched by an equally sized ventral fin below which could be jettisoned for an emergency horizontal landing. The seat was inclined 45° toward the instrument panel for vertical flight. Control in hover for the XFY-1 were also the same as for conventional flight, but again this provided only limited control power. Almost 300 tethered tests hanging from the ceiling of Moffett Field's airship hangar were made in April 1954. First free hover was on 1 August 1954. The first double transition to horizontal flight and back to a vertical landing was made on 2 November 1954. The Pogo was flown until November 1956. As with the Lockheed XFV-1, the engine and control systems were considered inadequate.
25. Ryan X-13 Vertijet
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.
26. SNECMA C450 Coléoptère
In France, the Société Nationale d'Etude et Construction de Moteurs d'Aviation (SNECMA) began working on a jet powered tail-sitter in 1954. Various rigs were tested from 1955-1957 powered by the 6,400 lb thrust Atar D jet engine, each with increasing complexity. The C450 Coléoptère ("annular wing") was the final step in the program. It had a 22 ft fuselage surrounded by a 10.5 ft diameter annular wing with four small fins above castoring wheels. The airframe was built by the Nord company. Control in hover was provided by tilting vanes in the nozzle of the 7,700 lb thrust Atar 101E turbojet. In forward flight the small fins deflected the air for control. Two small strakes in the nose could be extended to facilitate a pitch-up moment in transition back to vertical. First tethered hover was on 17 April 1959; first free hover was on 3 May 1959, lasting for 3 1/2 minutes. The ninth flight was on 25 July 1959; it was to transition to about 36° from the vertical and then return to hover at 2,000 ft before beginning a vertical descent. However, the Coléoptère was unable to establish the hover and began descending faster than desired and fell into oscillations about all three axes. The pilot ejected at 150 ft but was badly hurt. The Coléoptère rotated to about 50° and accelerated horizontally, but did not quite complete the transition and crashed. Emphasis on both sides of the Atlantic changed from dispersal to air superiority and attack, roles for which the tail sitters, with their small payload and range, were ill-suited.
Same Propulsion System for Hover and Forward Flight (Aircraft # 1 - 26)
Separate Power Plant for Hover (Aircraft # 27 - 29)
Combined Power Plant for Hover (Aircraft # 30 - 37)
Augmented Power Plant for Hover (Aircraft # 38 - 45)
Vision For the Future (and Credits, etc)
V/STOL Aircraft and Propulsion Concepts (The V/STOL "Wheel of Misfortune")
(c) 1997 American Helicopter Society