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The Mitsubishi Ki-46 was a twin-engine reconnaissance aircraft that was used by the Imperial Japanese Army in World War II. Its Army Shiki designation was Type 100 Command Reconnaissance Aircraft (一〇〇式司令部偵察機); the Allied brevity code name was "Dinah". On 12 December 1937, the Imperial Japanese Army Air Force issued a specification to Mitsubishi for a long-range strategic reconnaissance aircraft to replace the Mitsubishi Ki-15. The specification demanded an endurance of six hours and sufficient speed to evade interception by any fighter in existence or development, but otherwise did not constrain the design by a team led by Tomio Kubo and Jojo Hattori. The resulting design was a twin-engined, low-winged monoplane with a retractable tailwheel undercarriage. It had a small diameter oval fuselage which accommodated a crew of two, with the pilot and observer situated in individual cockpits separated by a large fuel tank. Further fuel tanks were situated in the thin wings both inboard and outboard of the engines, giving a total fuel capacity of 1,490 L (328 imperial gallons). The engines, two Mitsubishi Ha-26s, were housed in close fitting cowlings developed by the Aeronautical Research Institute of the Tokyo Imperial University to reduce drag and improve pilot view. The first prototype aircraft, with the designation Ki-46, flew in November 1939 from the Mitsubishi factory at Kakamigahara, Gifu, north of Nagoya.[3] Tests showed that the Ki-46 was underpowered, and slower than required, only reaching 540 km/h (336 mph) rather than the specified 600 km/h (373 mph). Otherwise, the aircraft tests were successful. As the type was still faster than the Army's latest fighter, the Nakajima Ki-43, as well as the Navy's new A6M2, an initial production batch was ordered as the Army Type 100 Command Reconnaissance Plane Model 1 (Ki-41-I). To solve the performance problems, Mitsubishi fitted Ha-102 engines, which were Ha-26s fitted with a two-speed supercharger, while increasing fuel capacity and reducing empty weight. This version, designated Ki-46-II, first flew in March 1941. It met the speed requirements of the original specification, and was ordered into full-scale production, with deliveries starting in July. Although at first the Ki-46 proved almost immune from interception, the Imperial Japanese Army Air Force realised that improved Allied fighters such as the Supermarine Spitfire and P-38 Lightning could challenge this superiority, and in July 1942, it instructed Mitsubishi to produce a further improved version, the Ki-46-III. This had more powerful, fuel-injected Mitsubishi Ha-112 engines, and a redesigned nose, with a fuel tank ahead of the pilot and a new canopy, smoothly faired from the extreme nose of the aircraft, eliminating the "step" of the earlier versions. The single defensive machine gun of the earlier aircraft was omitted not long into the production run. The new version first flew in December 1942, demonstrating significantly higher speed 630 km/h (391 mph) at 6,000 m (19,700 ft). The performance of the Ki-46-III even proved superior to that of the aircraft intended to replace it (the Tachikawa Ki-70), which as a result did not enter production.[8] During operational testing in March 1944, it was discovered that replacing the engines' single exhaust collector ring with individual pipes provided extra thrust and an increase in top speed to 642 km/h (399 mph). In an attempt to yet further improve the altitude performance of the Ki-46, two prototypes were fitted with exhaust driven turbosupercharged Ha-112-II-Ru engines. This version first flew in February 1944, but only two prototypes were built. Mitsubishi factories made a total of 1,742 examples of all versions (34 x Ki-46-I, 1093 x Ki-46-II, 613 x Ki-46-III, 4 x Ki-46-IV) from 1941 to 1944. For details of operational history and 18 variants, click here.

The Kamov Ka-26 (NATO reporting name Hoodlum) is a Soviet light utility helicopter with co-axial rotors. It looks like it has twin turbine engines in nacelles on each side of the body, but they are radial engines with turbofans for cooling. The Ka-26 entered production in 1969 and 816 were built. A variant with a single turboshaft engine is the Ka-126. A twin-turboshaft–powered version is the Ka-226. (All the Ka-26/126/128/226 variants are code-named by NATO as "Hoodlum"). The fuselage of the Ka-26 consists of a fixed, bubble-shaped cockpit containing the pilot and co-pilot, plus a removable, variable box available in medevac, passenger-carrying and crop duster versions. The helicopter can fly with or without the box attached for flexibility. It is powered by two 325 hp (239 kW) Vedeneyev M-14V-26 radial engines mounted in outboard nacelles. The Ka-26 is small enough to land on a large truck bed. The reciprocating engines are more responsive than turboshaft engines, but require more maintenance. It runs mostly at 95% power in crop dusting with usually excess payload, leaving little reserve power for emergencies. Due to frequent overloads, the interconnect shaft joining the two engines is prone to breakage and requires frequent inspection. The standard instrumentation of the Ka-26, like larger naval Kamovs, may be overkill for civilian or crop dusting use. The 18-dials cockpit panel masks a part of the right-downwards view, needed to avoid telephone and power lines at low altitudes. The instrument panel may be simplified to retain the six main dials. As there is a low rotor clearance at the aircraft front, it is approached from the rear when the rotors are turning. Due to the limitations of the Ka-26, USSR and Romania agreed under the Comecon trade to build a single-turboshaft engine version, the Kamov Ka-126, with better aerodynamics and range. The Ka-26 is eminently useful for civil agricultural use, especially crop dusting. The coaxial main rotor configuration, which makes the Ka-26 small and agile, also results in a delicate airflow pattern under the helicopter, providing a thorough, yet mild distribution of chemicals onto plants. The Ka-26 is often used to spray grape farms in Hungary, where conventional "main rotor and tail rotor" layout helicopters would damage or up-root the vine-stocks with their powerful airflow. Hungarian Kamov operators claim that coaxial rotors of the Ka-26 creates an airflow which allows well-atomized pesticides to linger longer in the air, causing more of the residue to settle underneath, rather than on top of, the leaves. This results in a more efficient distribution of pesticides, as most pests and parasites do not live on the top side of foliage. Additionally, the coaxial vortex system is symmetrical, allowing the distribution of the pesticide to be more uniform, without the side currents induced by the tail rotor, making it easier to avoid contaminating adjacent non-crop areas. In some Warsaw Pact armies, the Ka-26 was used only in the light paratroop or airborne role, but not the civilian agricultural role[citation needed]. In the military role, its slow (150 km/h) cruise speed compared with the Mi-2 (220 km/h) limits effective general-purpose military use, although its shorter length (7.75 m) compared with the Mil Mi-2 (11.9 m) and smaller rotor diameter (13 m vs. 14.6 m) are advantageous for military operations in an urban area. Its operational range is also greater than the Mil-2. On 30 June 2020, Moldovan police and prosecutors closed down an illegal factory producing unlicensed copies of the Ka-26. The factory had a production line with ten air frames in various stages of completion that were intended for sale to clients in former Soviet countries. Variants Ka-26 Hoodlum-A One- or two-crew utility light helicopter, powered by two 325-hp (239-kW) VMK (Vedeneyev) M-14V-26 radial engines. 850 built. Ka-26SS NOTAR technology testbed for the Ka-118 fitted with tail jet beams. Ka-126 Hoodlum-B One- or two-crew utility light helicopter, powered by one 720-shp (537-kW) OMKB "Mars" (Glushenkov) TVD-100 turboshaft engine. First flown in 1986, built and developed by Industria Aeronautică Română in Romania. 2 prototypes and 15 series helicopter built. V-60 A prototype light armed escort helicopter based on the Ka-126. Ka-128 One prototype, powered by a 722-shp (538-kW) Turbomeca Arriel 1D1 turboshaft engine. Kamov Ka-226 Six- or seven-seat utility helicopter, powered by two 450-shp (335-kW) Rolls-Royce (Allison) 250-C20R/2 turboshaft engines.

The Westland Welkin was a British twin-engine heavy fighter from the Westland Aircraft Company, designed to fight at extremely high altitudes, in the stratosphere; the word welkin meaning "the vault of heaven" or the upper atmosphere. First conceived in 1940, the plane was built in response to the arrival of modified Junkers Ju 86P bombers flying reconnaissance missions, which suggested the Luftwaffe might attempt to re-open the bombing of England from high altitude. Construction was from 1942 to 1943. The threat never materialised; consequently, Westland produced only a small number of Welkins and few of these flew. Westland put forward their P.14, essentially an adaptation of Westland's Whirlwind fighter layout (and a more experimental twin, the P.13) to meet Air Ministry Specification F.4 of 1940 for a high altitude fighter. The most obvious feature was the enormous high aspect ratio wing, with a span on the production aircraft of 70 feet (21 m). The compact but troublesome Rolls-Royce Peregrine engines of the Whirlwind were replaced by the more powerful two-stage Rolls-Royce Merlin Mk.76/77. The most significant feature was a pressurised cockpit, which took the majority of effort in the design. After extensive development a new cockpit was developed that was built out of heavy-gauge duraluminium bolted directly to the front of the main spar. The cockpit hood used an internal layer of thick perspex to hold the pressure, and an outer thin layer to form a smooth line. Heated air was blown between the two to keep the canopy clear of frost. In January 1941, the Ministry of Aircraft Production authorised the building of two P.14 prototypes DG558 & DG562. The F.4/40 specification was revised into F.7/41 that year. The Welkin design was now in competition with the Vickers Type 432 with Merlin 61 engines. The pressurisation system was driven by a Rotol supercharger attached to the left-hand engine (this was the difference between the Merlin 76 and 77), providing a constant pressure of 3.5 psi (24 kPa) over the exterior pressure. This resulted in an apparent cabin altitude of 24,000 feet (7,300 m) when the aircraft was operating at its design altitude of 45,000 ft (14,000 m). This cabin altitude was still too high for normal breathing, so the pilot had to wear an oxygen mask during flight. A rubber gasket filled with the pressurized air sealed the canopy when the system was turned on, and a valve ensured the pressure was controlled automatically. Moreover, the pilot also had to wear a high altitude suit as he might have been required to bail out at altitude. The Welkin required a sophisticated electrical system. This was to minimise the number of seals and points of entry in the cockpit for the controls and instrumentation. It took an electrician experienced in the features of the Welkin four hours to undertake a pre-flight check of this system. The wings were so large that the high lift Fowler flaps of the Whirlwind were not needed, and were replaced by a simple split flap. The extra wing area also required more stability, so the tail was lengthened to provide a longer moment arm. The armament − four Hispano 20 mm cannon − was the same as the Whirlwind's, but the Welkin carried the guns in a tray in its belly, which facilitated loading. In that position, muzzle flash was also less likely to dazzle the pilot. The Welkin was seriously handicapped by compressibility problems caused by its long, high aspect-ratio wing which needed to be thick at the root (thickness-to-chord ratio of about 19%) for strength reasons. Compressibility caused the flight envelope (flyable speed range) between high-incidence stall and shock-stall to become very small at high altitudes – any decrease in airspeed causing a "normal" stall, any increase causing a shock-stall due to the aircraft's limiting critical Mach number. This reduction of the speed envelope is a problem common to all subsonic high-altitude designs and also occurred with the later Lockheed U-2. When W.E.W. Petter came to design his next high-altitude aircraft, the English Electric Canberra jet bomber, the required wing area was distinguished by noticeably short wings, with thickness-to-chord ratio (t/c) at the root of 12%, a t/c ratio which delays compressibility effects to an aircraft speed of about Mach 0.85. Information on the Welkin was only released at the end of the war. A two-seat radar-equipped night fighter version known as the Welkin NF.Mk.II for specification F.9/43 was developed but only one was eventually produced as the variant was not ordered into production. By the time the Welkin Mk.I was complete and in production, it was apparent that the Luftwaffe was no longer conducting high altitude missions, due largely to successful interceptions by specially modified Supermarine Spitfires. Only 77 complete Welkins were produced, plus a further 26 as engine-less airframes.[10] Although two Welkins served with the Fighter Interception Unit based at RAF Wittering from May to November 1944, where they were used to gain experience and formulate tactics for high altitude fighter operations, the Welkin was never used operationally by the RAF. Variants P.14: Two prototypes built to meet Air Ministry Specification F.7/41. Welkin Mk.I : Single-seat twin-engine high altitude fighter aircraft, 75 built, further 26 aircraft were completed without engines. Welkin Mk.II : Two-seat night fighter prototype, one converted from Mark I.

The Buhl AirSedan was a family of American civil cabin sesquiplane aircraft developed and manufactured by the Buhl Aircraft Company in the late 1920s. One example completed the first transcontinental non-stop roundtrip flight, made in 1929 by the CA-6 Spokane Sun-God, and the first Pope to have flown did so in a Buhl Airsedan. The Airsedan series were designed by Etienne Dormoy following the departure of Alfred V. Verville from Buhl, with whom he had worked previously. Dormoy had worked with Deperdussin before World War I, flew combat operations during the war before returning to work with SPAD, travelled to the US to coordinate production of SPADs with Curtiss until the project was cancelled with the end of the war. He then worked with Packard on automobiles for a year in 1919 before working as a civilian with the United States Army Air Corps with Verville, who convinced him to work at Buhl. As a Frenchman, he was familiar with the advantages of the sesquiplane concept as it was a popular configuration in France, such as with the Breguet 26T airliner, but rare in the US. The fuselage framework, lower wing and empennage were welded chromium-molybdenum alloy steel tubes faired with wooden battens, with the lower wing integral with the fuselage structure. The upper wings were built around spruce spars, with built up ribs made from spruce and plywood. The entire airframe was covered with doped aircraft-grade fabric. To reduce control forces, projecting aerodynamic balance horns on rudder and elevators, while inset aerodynamic horns were used on the ailerons, which were fitted to the upper wing only. To provide trim control, the rudder was ground adjustable while the elevators could be adjustable in flight. Depending on the models, three different designs of lower wings were used - either constant chord with reversed N struts on the CA-5, a triangular wing with a vee strut on the CA-3, CA-6 and CA-8, or a constant chord wing with two rigged struts, on Canadian built CA-6Ms. All were conventional sesquiplanes with fully enclosed cockpits, fitted with dual controls in front of a passenger cabin. The number in the designation generally referred to the number of occupants as originally designed, with a larger number of seats corresponding to a larger airframe. The first variant built was the CA-5, while later variants had a much slimmer fuselage, a greatly improved windscreen design and a modified cockpit. The CA-5 had the undercarriage legs connected to the fuselage, and part way out from the fuselage, on the lower wing. The CA-3 had the undercarriage mounted solely to the fuselage, while the CA-6 and CA-8 had additional bracing struts from the top of the fuselage to the lower wing which allowed the undercarriage track to be widened. Buhl asserted that its undercarriage design reduced camber changes during landing, and the tendency to yaw due to bumpy ground. The CA-6 was certified to use Edo J-5300 floats. Canadian production. After Buhl had ceased operations in 1932 due to declining sales as the Great Depression deepened, the drawings and jigs were purchased by the Ontario Provincial Air Service (OPAS) in Canada who then built four CA-6M's for use as fire spotting aircraft at their facility in Sault Ste. Marie between 1935 and 1937. These differed from the original aircraft in having Canadian Vickers floats, a new fin and rudder and larger lower wings. Due to the excessive weight of the Canadian-Vickers built floats, the first Ontario Provincial Air Service-built CA-6M refused to leave the water until given a more powerful 440 hp (330 kW) Pratt & Whitney Wasp engine. For details of opertational history and 20 variants, click here.

The Vickers Warwick was a British twin-engined bomber aircraft developed and operated during the Second World War that was primarily used in other roles. In line with the naming convention followed by other RAF heavy bombers of the era, it was named after a British city or town, in this case Warwick. The Warwick was the largest British twin-engined aircraft to see use during the Second World War. The Warwick was designed and manufactured by Vickers-Armstrongs during the late 1930s. It was intended to serve as a larger counterpart to the Vickers Wellington bomber. The two aircraft share similar construction and design principles but development of the Warwick was delayed by a lack of suitable engines. Its first flight was on 13 August 1939 but delays to its intended powerplant and by the time adequate engines were available, it was obsolete. The Warwick entered production during 1942 and squadron service with the Royal Air Force (RAF). Barely a dozen aircraft were built as bombers. The type was used by RAF Transport Command as a transport, and by RAF Coastal Command as an air-sea rescue and maritime reconnaissance aircraft. The Warwick was also operated by the Polish Air Forces in exile in Great Britain and the South African Air Force. A civil operator, the British Overseas Airways Corporation (BOAC), also operated a handful of transport Warwicks. In October 1932, the British industrial conglomerate Vickers-Armstrongs tendered for the Air Ministry Specification B.9/32, which called for the development of a twin-engined medium bomber. During late 1934, when the company was already developing their Type 271 to meet Specification B.9/32, Vickers received a draft requirement for a larger bomber. The draft specification developed into Air Ministry Specification B.1/35, which sought a twin-engined heavy strategic bomber. It was intended to make use of more powerful engines, of 1,000 hp (750 kW), that were being developed, to enable the bomber to be faster and carry a heavier bomb load than the earlier B.3/34. Among the requirements of Specification B.1/35 was a speed of no less than 195 mph (314 km/h) while flying at 15,000 ft (4,600 m), a range of 1,500 mi (2,400 km) while carrying 2,000 lb (910 kg) of bombs, and the engines were to be furnished with variable-pitch propellers. It was designed in parallel with the smaller Wellington, both aircraft having been derived from the Vickers Type 271 design, developed for Specification B.9/32. By the end of July 1935, the Air Ministry was considering eight designs. These included Vicker's proposal, the Type 284, powered by a pair of Bristol Hercules engines, which exceeded the specifications. Vickers received an order for a prototype on 7 October 1935, while the Air Ministry also ordered prototypes from Armstrong Whitworth (the AW.39, a development of the Armstrong Whitworth Whitley) and Handley Page (the HP.55). These alternative designs were cancelled before being built, as Handley Page and Armstrong Whitworth switched to work on newer specifications released for medium (P.13/36) and heavy (B.12/36) bombers. For more details of development and design, operational history and 12 variants, click here. Total number built was 846.