|Kamov Ka-22 "Vintokryl"|
In 1951 various attempts were being made to increase the effective range of helicopters, notably by towing them in the outward direction behind an Li-2, with the lifting rotor autorotating. The idea occurred to Kamov designer Vladimir Barshevsky that it would be possible to dispense with the tug aircraft if a helicopter could be provided with wings and an aeroplane propulsive system. After obtaining permission from Kamov, his deputy V. V. Nikitin took a proposal to the Kremlin and in a matter of days the OKB had a Stalin directive to get started. The engines were to be TV-2 (later TV-2VK) turboshafts supplied by N. D. Kuznetsov, and many organizations were involved in research for this challenging project, starting with model tests in the T-101 tunnel at CAHI. The final go-ahead was issued on 11th June 1954. An order for three Ka-22s was placed on the factory at Ukhtomskaya, which had been derelict since Kamov was evacuated from there in October 1941. Concentration on the small Ka-15 (the OKB's first production helicopter) and other problems so delayed the programme that on 28th March 1956 prototypes 2 and 3 were cancelled. In June 1958 the LD-24 rotor blades began testing on an Mi-4. The Ka-22 itself first lifted from the ground on 17th June 1959, and made its first untethered flight on 15th August 1959, the test crew being led by pilot D. K. Yefremov. Serious control difficulties were encountered, and the Kamov team were joined by LII pilots V.V.Vinitskii and Yu.A.Garnayev. Though still full of problems the Vintokryl was demonstrated on 11th October 1959 to MAP Minister P.V.Dement'yev and VVS C-in-C K.A.Vershinin. Gradually difficulties were solved and in July 1960 an order was received to manufacture three Ka-22s at GAZ No.84 at Tashkent, with D-25VK engines. On 23rd May 1961 a speed of 230km/h was held for 37 minutes. On 9th July 1961 the Ka-22 caused a sensation at the Aviation Day at Tushino. On 7th October 1961, with spats over the wheels and a fairing behind the cockpit, a class speed record was set at 356.3km/h, followed on 12th October by 336.76km/h round a 100km circuit. The spats and fairing were then removed and on 24th November 1961 a payload of 16,485kg was lifted to 2,557m. Preparations were then made to ferry AM 0I-01 and the third machine AM 0I-03 from Tashkent to Moscow for Nil acceptance testing. Both departed on 28th August 1962. While making an intermediate stop at Dzhusaly 0I-01 rolled to the left and crashed inverted, killing Yefremov and his crew of six. The cause was diagnosed as 'disconnection of No 24 cable joint of the linkage with the starboard lift rotor collective-pitch control unit'. At Tashkent and in Turkestan the cable joints and cyclic-pitch booster brackets were inspected on 0I-02 and 0I-03 and found to be incorrectly assembled. Changing the direction of rotation of one lifting rotor did little at lower speeds and caused problems at higher speeds - 'When', said lead engineer V.S.Dordan, 'Shockwaves off the blades sounded like a large machine gun'. To improve stability and controllability the complex AP-116 differential autopilot was installed, continuously sensing attitude and angular accelerations, feeding the KAU-60A combined flight-control unit. On 12th August 1964 the heavily instrumented 0I-03 took off on one of a series of tests conducted with VVS (air force) and GVF (civil) crews. Take-off was in aeroplane mode, and 15 minutes later at 310km/h the aircraft suddenly turned to the right, 'not arrested by full rudder and aileron...the aircraft turned almost 180° when Garnayev intervened, considering the problem was differential pitch of the propellers... turn rate slowed, but the aircraft pitched into a steep dive...the engineer jettisoned the flight-deck hatches, and one struck the starboard lift rotor causing asymmetric forces which resulted in separation of the entire starboard nacelle. Garnayev ordered the crew to abandon the aircraft'. Three survived, but Col S.G.Brovtsev, who was flying, and technician A.F.Rogov, were killed. By this time the Mi-6 heavy helicopter was in wide service, and the Ka-22 was ultimately abandoned. Several years later the two surviving machines, 0I-02 and 0I-04, were scrapped. An article about the Ka-22 in Kryl'ya Rodiny (Wings of the Motherland) for November 1992 does not mention the fact that two crashed, which is not widely known even in the former Soviet Union.
The Ka-22 was basically an aeroplane with its engines on the wingtips, with geared drives to both propellers and lifting rotors. The airframe was all light alloy stressed-skin, the high wing having powered ailerons and plain flaps. The fuselage had a glazed nose, three-seat cockpit above the nose and a main cargo area 17.9x3.1x2.8m for 80 seats or 16.5 tonnes of cargo. The entire nose could swing open to starboard for loading bulky items or a vehicle. The original prototype was powered by 5,900shp TV-2VK engines, but these were later replaced by the 5,500shp D-25VK. These had free turbines geared via a clutch to the main rotor and via a front drive to the four-blade propeller and a fan blowing air through the oil cooler from a circular inlet above the nacelle. The two free-turbine outputs were interconnected by a 12-part high-speed shaft 'about 20m long'. The main rotors were larger derivatives of those of the Mi-4. In helicopter mode the propeller drive was declutched and the flaps were fully lowered. Flight control was by differential cyclic and collective pitch. In aeroplane mode the lifting rotors were free to windmill and the aircraft was controlled by the ailerons and tail surfaces. The twin-wheel landing gears were fixed.
Apart from prolonged dissatisfaction with the engines, the problems with the Ka-22 were mechanical complexity, severe losses in the gearboxes and drives and the fact that each lifting rotor blew straight down on top of the wing. Similar charges could be levelled against today's V-22 Osprey.
Y.Gordon, B.Gunston "Soviet X-Planes", 2000
Vintokryl (screw-wing) compound helicopter, project 1955, flown (D.Yefremov and crew of 5) 20 April 1960. Stressed-skin airframe with engine propeller rotor group on each tip of large wings with flaps depressed 90° in helo mode, auto control linking fuel flow with prop pitch in cruise. Wing high on fuselage with interior 17.9 x 3.1 x 2.8 for 16.5t cargo or 80 seats (not fitted). Glazed nose for nav, high flight deck for two pilots and radio engineer. High-mounted wing with slight taper, outboard ailerons and inboard flaps which were not lowered in hovering displays. Conventional aeroplane tail, used only in aeroplane mode. Power group comprising turboshaft engine with drive capable of being progressively clutched to either four-blade propeller or four-blade rotor, latter being used for vertical flight and propellers for cruise, with lift shared between wing and windmilling rotors. Selected engine normally has rear drive from free turbine; installation has rear jetpipe and air from inlet ducted round underside of cowling, driving at rear to high-speed shaft to reduction gearbox under rotor shaft, from which front drive goes to propeller. Upper circular inlet feeds fan-assisted oil cooler. Fixed tricycle landing gear with twin main wheels. Superficially rotors and hubs resembled those of Mi-4 and Yak-24, but with trailing-edge tabs inboard; handed, left rotor being clockwise seen from above.
Public display (confident) Tushino 9 July 1961, D.K.Yefremov. Same pilot, assisted by V.V.Gromov, set world 15/25km record 7 Oct 1961 at 356.3km/h, with spatted landing gear, followed by record lift on 24 Nov of 16,485kg to 2km. OKB testing complete early 1964. ASCC name "Hoop".
Bill Gunston "The Osprey Encyclopedia of Russian Aircraft", 2000
The development of helicopter design at home and abroad opened up the prospects of using rotorcraft as a means of transportation of heavy-weight cargoes on the vast territory of the USSR. In the mid-50s, in response to a GOR issued by the Ministry of Defence, the OKB took a revolutionary decision to build an experimental compound helicopter, the Ka-22. Dubbed "Vintokryl" (lit. "screw-wing"), it featured two lifting rotors and two tractor propellers for forward thrust, both mounted at the wingtips. This was an aircraft of a basically new type for our country's aviation, combining the advantages of the helicopter capable of vertical take-off and landing and of the aeroplane possessing greater lifting capacity, range and speed as compared to the helicopter.
N.I.Kamov focused the attention of the Vintokryl's creators on the design of high-speed lifting rotors which would enable the compound aircraft to cruise at 400-450km/h. At high forward speeds the wing was intended to decrease rotor disc loading as much as possible, ensuring low drag factors. This allowed the tips of the main rotor blades to reach the speed of sound and the rotor to work in a mode close to autorotation. N.I.Kamov's decision to retain minimum required rotor disc loading at high speed sufficient for damping rotor oscillations and for ensuring stable rotor behaviour during manoeuvers proved to be of fundamental importance.
Development and construction of the Ka-22 called for a lot of theoretical and experimental work. Under the leadership of S.Ya.Finkel' a whole set of methods was developed to determine the aircraft's parametres, rotor blade configuration, the basic performance characteristics of the rotorcraft and its aerodynamic design, to calculate aerodynamic loads, aerodynamic balancing etc. Special research was made to ensure optimum characteristics in transitional flight modes, to select structural stiffness characteristics of the airframe components, to prevent rotor blade flutter and "ground resonance". Much attention was paid to the problems associated with the compound rotorcraft's stability and controllability. Kamov's engineers succeeded in corroborating the results of theoretical methods of calculation through the use of numerous models, test rigs and special devices, as well as in the process of flight tests. A major contribution to the creation of the Ka-22 was made by S.B.Garshtein, AI.Dreizin, Z.Z.Rosenbaum, A.G.Satarov, E.A.Petrosian, L.A.Potashnik, V.N.Kvokov and other members of the OKB staff, as well as by TsAGI specialists M.K.Speransky, I.O.Faktorovich and E.V.Tokarev.
Work on the unique powerplant and systems of the aircraft was headed by deputy chief designer N.N.Priorov, and deputy chief designer M.A.Kupfer was responsible for the rotor system and the airframe. Yu.S.Braginsky was appointed Ka-22 leading designer and V.B.Al'perovich was the leading engineer of the flight test programme.
Test pilot D.K.Yefremov was the first to put the unusual aircraft into the air on August 15, 1959. First deputy chief designer V.I.Biryulin was responsible for all the work on the compound helicopter. LII staff, including test pilots Yu.A.Garnayev and V.V.Vinitsky, rendered great assistance to the Kamov organization in perfecting the Vintokryl's stability and handling, especially at low transitional flight speeds.
In 1961 an OKB test crew captained by D.K.Yefremov set eight world records on the Ka-22, including the world helicopter speed record (356km/h) and the payload to 2000m altitude record (16485kg); the latter achievement still stands as of this writing. The compound helicopter was impressive by any standards: maximum take-off weight was 42500kg; the cargo cabin was 17.9m long, 2.8m high and 3.1m wide. To get an idea of the magnitude of the task solved by the OKB, suffice it to compare the maximum take-off weight of the Ka-22 and that of the then biggest Kamov helicopter, the Ka-25 (7000kg).
Sadly, the fate of the Ka-22 was sealed by two tragic crashes, the cause of which could not be determined beyond doubt at the time. After that, the Air Force leadership could not overcome the mistrust that had arisen towards this flying machine and never gave the OKB a chance to complete development. Nevertheless, the design, construction and testing of such a complex and large rotorcraft took the company's specialists to a new, higher scientific and technical level.
G.Kuznetsov "OKB Kamov - 50 years", 1999
The Hoop was an interesting Soviet effort to develop a Convertiplane, resulting in a vehicle that looked amazingly like a conventional aircraft, that is, with the exception of the two wingtip rotors. Otherwise, the fuselage with a single vertical stabilizer and a normal tail assembly made it look quite "normal". A tricycle landing gear featured a forward-fuselage gear along with a spindley-appearing pair of landing gears hanging from the inner wing locations.
The propulsion system, in the form of a pair of 5600 horsepower Ivchenko turbine engines, provided the propulsive force for both the lifting flat-mounted rotors and the normally-positioned forward-pushing propellers. The tailpipes of these powerplants are assessed to have tail pipes that can be deflected downward to provide additional lift during the vertical flight phase of the trajectory.
The wingtip-mounted rotors are located some distance above the upper wing surfaces such that they cleared the smaller vertically-mounted propellers. They are estimated to each have a span of about 28m.
The entire trailing edge of the high-set cantilever wing is made up of ailerons and flaps, with the rear of the craft fitted with a conventional-type tail.
Making use of the An-10 transport fuselage design, the Hoop theoretically could have had an impressive passenger capacity of 80 to 100. Also, the fuselage design, with its swept-up lower rear fuselage could incorporate a loading ramp for vehicles and freight.
Little is known about the actual test program of the Hoop as it was designed and developed during the era of secrecy of the Cold War era.
The Ka-22 demonstrated a significant speed capability, setting a world record for a rotorcraft of over 350km/h in October 1961. That same year, the model was first displayed in the 1961 Soviet Aviation Day display.
S.Markman & B.Holder "Straight Up: A History of Vertical Flight", 2000
The Ka-22 combined a square fuselage with a 20m wing span. At the tips of the wings were two nacelles containing Ivchenko TB-2 engines delivering over 5600shp each of which could power a 20m four-blade rotor or four-btade tractor propeller. The fuselage was similar in size to the Antonov An-12 transport and could carry 100 passengers or a 16000kg load. The rotors apparently autorotated during horizontal flight. The Ka-22 (NATO reporting name Hoop) won the world speed record for rotary wing craft in October 1961 when it exceeded 365km/h. It was not mass produced.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
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Technical data for Ka-22
Crew: 5, engine: 2 x D-25VK turboshaft, rated at 4050kW, rotor diameter: 22.5m, fuselage length: 27m, height: 2.8m, take-off weight: 42500kg, payload: 16500kg, max speed: 356km/h, service ceiling: 5500m, range: 450km