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The Focke-Achgelis Fa 223 Drache (English: Dragon) was a helicopter developed by Germany during World War II. A single 750-kilowatt (1,010 hp) Bramo 323 radial engine powered two three-bladed 11.9-metre (39 ft) rotors mounted on twin booms on either side of the 12.2-metre-long (40 ft) cylindrical fuselage. Although the Fa 223 is noted for being the first helicopter to attain production status, production of the helicopter was hampered by Allied bombing of the factory, and only 20 were built. The Fa 223 could cruise at 175 kilometres per hour (109 mph) with a top speed of 182 km/h (113 mph), and climb to an altitude of 7,100 m (23,300 ft). The Drache could transport cargo loads of over 1,000 kg (2,200 lb) at cruising speeds of 121 km/h (75 mph) and altitudes approaching 2,440 m (8,010 ft). Henrich Focke had been removed by the Nazi regime from the company he had co-founded in 1936. Though the ostensible reason was that he was "politically unreliable", the RLM decision to phase Focke-Wulf into the production program of the almost-ready Messerschmitt Bf 109 necessitated an influx of capital to fund the immediate expansion of the company's production capabilities. Focke-Wulf was reorganized into a limited company (G.m.b.H.) in June 1936. After Focke-Wulf formally signed a contract to produce the Bf 109C in November 1937, the American company International Telephone & Telegraph (ITT), through its German subsidiary C. Lorenz, bought a 28 percent share of Focke-Wulf in 1938, making it the controlling interest. However, the Air Ministry was so impressed by the Focke-Wulf Fw 61 helicopter that it suggested Focke establish a new company dedicated to helicopter development and issued him with a requirement for an improved design capable of carrying a 700 kg (1,500 lb) payload. Focke established the Focke-Achgelis company at Hoykenkamp on 27 April 1937 in partnership with pilot Gerd Achgelis, and began development work at Delmenhorst in 1938. They first produced an enlarged, six-occupant version of the Fw 61, designated Fa 226 Hornisse (Hornet), while contracting out development of the engine, transmission, and rotor hub to BMW's Berlin works. The Fa 226 was the world's first transport helicopter and was ordered by Lufthansa in 1938. The Fa 226 attracted the attention of the Air Ministry, who redesignated it Fa 223 in 1939 before the first prototype flew.[8] The Navy was also interested in the Hornisse and briefly considered it as a replacement for their Schnellboote. In September 1939 the first prototype, the V1, left the Delmenhorst factory. Now nicknamed Drache ("Dragon") it had a twin-rotor layout similar to the Fw 61, but had a fully enclosed cabin and load bay, with the single Bramo engine mounted in the middle of the tubular-steel body. Initial hovering tests showed problems and the V1 was not to fly until 1940. The engine initially specified, a BMW Bramo 323D proved too fragile when run at high speed for any length of time, and was replaced with a more robust 1,000 hp Bramo 323Q3 in the later prototypes to improve reliability and lifting capability. The biggest problem, however, was the severe vibration caused by unbalanced driveshafts when the rotors moved out of phase, and this could only be fixed by greater attention to detail on the part of BMW. For more details of development, operational history and variants, click here.

The Vickers Type 56 Victoria was a British biplane freighter and troop transport aircraft used by the Royal Air Force. The Victoria flew for the first time in 1922 and was selected for production over the Armstrong Whitworth Awana. The Victoria was a twin-engined biplane transport with a conventional landing gear with a tailskid. The design mated a similar fuselage of the earlier Vernon transport with the wing of the Virginia bomber, which was developed in parallel. It was also powered by two Napier Lion engines. The enclosed cabin had room for 24 troops on collapsible canvas seats arranged along the sides of the fuselage. In April 1921 two prototypes were ordered by the Air Ministry to Specification 5/20. The first prototype, allocated serial number J6860, was built as a Type 56 and designated as Victoria I, the second J6861 was built as a Type 81 Victoria II. The Type 56 had two 450 hp (340 kW) Napier Lion engines with large frontal radiators and were fitted directly onto the lower mainplanes, the fuel tanks were placed under the inboard section of the bottom mainplane. The prototype J6860 first flew from Brooklands, Surrey on 22 August 1922. The Type 81 flew in January 1923, and initially differed only in having the fuel tanks under the top mainplane.[5] It was later modified by replacing the flat sided engine cowling with more streamlined nacelles with the radiators between the undercarriage legs, as fitted in the Virginia II bomber. In March 1925, it was decided to place an order for 15 production aircraft. By this time, the Virginia design had evolved to incorporate swept-back wings, and the production Victoria IIIs incorporated this change. Another improvement first introduced in the Virginia was the introduction of metal structures instead of the all-wooden airframes of the early aircraft, with an order being placed for a prototype Victoria with a metal structure (serial number J9250) in September 1927, this being delivered in October 1928. The metal airframe proved much more suitable for the hot and humid areas where the Victoria served, with Victoria IV and Vs with metal structures produced by conversion and new production respectively. The final version was the Mark VI, which substituted modern, more powerful Bristol Pegasus radial engines for the Napier Lions. The Vickers Valentia was a further improved version with a stronger structure, capable of operating at higher weights. 97 Victorias were built, many of which were later converted into Valentias. Variants Type 56 Victoria Mk I The first prototype. Powered by two 450 hp (340 kW) Napier Lion IAX W12 engines. Type 81 Victoria Mk II The second prototype. Type 117 Victoria Mk III The first production version. Military transport aircraft for the RAF. Powered by 450 hp Napier Lion II engines. 46 built. Type 145 Victoria Mk IV Metal wing structure. One prototype powered by Bristol Jupiter radials.[19] Thirteen Lion-engined conversions from earlier marks. Type 169 Victoria Mk V New production aircraft with metal structure, powered by two 570 hp (430 kW) Napier Lion XIB engines. 37 new-built. Type 262 Victoria Mk VI Final production - powered by 660 hp (490 kW) Bristol Pegasus IIL3 engines instead of Lions. 11 new-build, 23 by conversion.

The Vickers Vimy was a British heavy bomber aircraft developed and manufactured by Vickers Limited. Developed during the latter stages of the First World War to equip the Royal Flying Corps (RFC), the Vimy was designed by Rex Pierson, Vickers' chief designer. Only a handful of Vickers Vimy aircraft had entered service by the time the Armistice of 11 November 1918 came into effect, so the type did not serve in active combat operations during the war, but the Vimy became the core of the Royal Air Force (RAF)'s heavy bomber force throughout the 1920s. The Vimy achieved success as both a military and a civil aircraft, the latter using the Vimy Commercial variant. A dedicated transport derivative of the Vimy, the Vickers Vernon, became the first troop-transport aircraft operated by the RAF. During the interwar period the Vimy set several records for long-distance flights, the most celebrated and significant of these being the first non-stop crossing of the Atlantic Ocean, performed by John Alcock and Arthur Brown in June 1919. Other record-breaking flights were made from the United Kingdom to destinations such as South Africa and Australia. The Vimy continued to be operated until the 1930s in military and civil capacities. The Vickers F.B.27 Vimy is an equal-span twin-engine four-bay biplane, with balanced ailerons on both upper and lower wings. The engine nacelles were positioned mid-gap and contained the fuel tanks. It has a biplane empennage with elevators on upper and lower surfaces and twin rudders. The main undercarriage consists of two pairs of wheels, each pair carried on a pair of tubular steel V-struts. There is a tail-skid and an additional skid mounted below the nose of the fuselage to prevent nose-overs. The aircraft was designed to accommodate a three-man crew and a payload of 12 bombs. In addition to the pilot's cockpit, which was positioned just ahead of the wings, there were two positions for gunners, one behind the wings and the other in the nose, each with a pair of Scarff ring-mounted Lewis guns; the rear cockpit mounting was commonly not fitted during the interwar period. Provision for a maximum of four spare drums of ammunition were present in the nose position, while up to six drums could be carried in the rear position. The majority of the Vimy's payload of 250 lb (110 kg) bombs were stowed vertically inside the fuselage between the spars of the lower centre section; a typical load consisted of 12 bombs.[1] In some variants further bombs could be stowed externally for a total of 18 bombs, if the particular engine used provided enough power. For anti-surface warfare in the maritime environment, the Vimy could also be armed with a pair of torpedoes. To improve bombing accuracy, the Vimy was equipped with the High Altitude Drift Mk.1a bombsight. Standard equipment also included two Michelin-built Mk.1 flare carriers. The Vimy was powered by a range of different engines. Owing to engine supply difficulties, the prototype Vimys were tested with a number of different engine types, including Sunbeam Maoris, Salmson 9Zm water-cooled radials, and Fiat A.12bis engines, before production orders were placed for aircraft powered by the 230 hp (170 kW) BHP Puma, 400 hp (300 kW) Fiat, 400 hp (300 kW) Liberty L-12 and the 300 hp (270 kW) Rolls-Royce Eagle VIII engines, with a total of 776 ordered before the end of the First World War. Of these, only aircraft powered by the Eagle engine, known as the Vimy IV, were delivered to the RAF.[5] Due to the number of engine types used there are multiple conflicting official reports on the production numbers of each sub-variant of the Vimy. Design and production of the prototypes was extremely rapid; the detailed design phase of what had become internally designated as the Vickers F.B.27 and the manufacture of the three prototypes was completed within four months. Long-distance flights The most significant of the Vimy's many pioneering flights was the first non-stop crossing of the Atlantic Ocean, made by Alcock and Brown in June 1919. An example was specially constructed for the attempt, with additional fuel tanks to extend its range and a revised undercarriage. Only one such aircraft was built; it is preserved and displayed in the London Science Museum. In 1919, the Australian government offered £10,000 for the first All-Australian crew to fly an aeroplane from England to Australia. Keith Macpherson Smith, Ross Macpherson Smith and mechanics Jim Bennett and Wally Shiers completed the journey from Hounslow Heath Aerodrome to Darwin via Singapore and Batavia on 10 December 1919. Their aircraft G-EAOU is preserved in a purpose-built, climate-controlled museum in the grounds of the airport in Smith's home town Adelaide, Australia; "The trip from Darwin to Sydney took almost twice as long as the flight to Australia." Vickers Vimy Reserve in Northgate, a suburb of Adelaide, is named in honour of the place the plane landed on its return to South Australia in 1920. In 1920 Lieutenant Colonel Pierre van Ryneveld and Major Quintin Brand attempted the first England to South Africa flight. They left Brooklands on 4 February 1920 in Vimy G-UABA, named Silver Queen. They landed safely at Heliopolis, but as they continued the flight to Wadi Halfa they were forced to land due to engine overheating with 80 miles (130 km) still to go. A second Vimy was lent to the pair by the RAF at Heliopolis, and named Silver Queen II. This second aircraft reached Bulawayo in Southern Rhodesia, where it was badly damaged when it failed to take off. Van Ryneveld and Brand then used a South African Air Force Airco DH.9 to continue the journey to Cape Town. The South African government awarded them £5,000 each. Variants F.B.27 Vimy Prototypes; four built, powered by two 200 hp (150 kW) Hispano-Suiza 8 piston engines.. F.B.27A Vimy II Twin-engine heavy bomber aircraft for the RAF, powered by two 300 hp (220 kW) Rolls-Royce Eagle VIII piston engines. Vimy Ambulance Air ambulance version for the RAF.[36] Vimy Commercial Civilian transport version, powered by two 300 hp (220 kW) Rolls-Royce Eagle VIII and later 360 hp (270 kW) Rolls-Royce Eagle IX piston engines. A.N.F. 'Express Les Mureaux' Vimy Commercial No.42 re-engined with 2x 370 hp (280 kW) Lorraine 12Da V-12 engines by ANF Les Mureaux. For more details of background, production, operational history and operators, click here. This aircraft is on display at Adelaide Airport.

Not to be confused with Piasecki H-16 Transporter. The Piasecki 16H was a series of compound helicopters produced in the 1960s. The first version of the Pathfinder, the -1 version, first flew in 1962. The similar but larger Pathfinder II, the 16H-1A, was completed in 1965. Variants Model 16H-1 Pathfinder one PWC PT6B-2 with one 405 shp turboshaft engine Model 16H-1A Pathfinder II Specifications below larger version with one 1,250 shp (930 kW) T58-GE-8 Model 16H-1C Pathfinder III proposed conversion of the 16H-1A with one 1,500 shp (1,100 kW) T58-GE-5 Model 16H-3J nine-seat development, not built.

The Bell HSL (Model 61) was an American 1950s anti-submarine warfare (ASW) helicopter built by Bell Helicopter for the US Navy. The prototype first flew in 1953, but the type became obsolete during development and was found unsatisfactory upon entering service in 1957, resulting in the cancellation of the production contract; many of the 50 production aircraft were delivered directly into storage. The last HSL was retired in 1960. It was the only tandem rotor type designed by Bell. The prototype Bell Model 61 first flew on 3 March 1953; it had been designed to meet a United States Navy requirement for an anti-submarine warfare helicopter. In June 1950, the Model 61 was announced as the winner of the competition, and three XHSL-1 evaluation aircraft were ordered. The Model 61 had a rectangular-section fuselage structure and four-leg, six-wheel landing gear.[citation needed] It was powered by a Pratt & Whitney R-2800 radial engine mounted in the aft fuselage. Crew included two pilots and two sonar operators. The main rotors were at either end of the fuselage tube, linked by a transmission. The front rotor shaft was slightly ahead of pilots in the front cockpit. Because of the urgency of the requirement, low-rate production was ordered almost immediately after Bell received a contract for three XHSL-1s. The Navy eventually contracted for at least 160 production aircraft, including 18 intended for the British Royal Navy. Bureau Numbers were assigned for a total of 234. Because of development problems that resulted in poor schedule performance to the contract, only 50 were built. Although all were delivered, after service test and acceptance only a handful were used, for the development of airborne mine sweeping. The rest were delivered directly into storage and were subsequently struck off. Variants XHSL-1 two experimental flight test and one static test article HSL-1 production version, 50 built. Bell Model 61 Company designation for the HSL Bell D-116 A proposed civil variant of the Model 61, not proceeded with. Bell D-216 A proposed variant of the HSL, not proceeded with. Bell D-238 A proposed variant of the HSL, not proceeded with.

Vertical Aerospace Ltd. is an aerospace manufacturer based in Bristol, England. It designs and builds zero emission, electric vertical take-off and landing (eVTOL) electrically powered aircraft. The company was founded in 2016 by Stephen Fitzpatrick, an ex-Formula One team owner, and founder and CEO of OVO Energy. In June 2018, the company flew its first prototype aircraft — an electrically powered quadcopter that weighed 750 kg (1,650 lb), named VA-X1. In 2019, the company became Honeywell's first eVTOL customer, buying their fly-by-wire aircraft control systems for a future Vertical Aerospace aircraft, the VA-X4. in February 2021, the company announced it was partnering with Solvay S.A. for the development of the composite structure of its vehicle. In March, the company announced it was partnering with Rolls-Royce for the development of its electrical power system. In the period between 2020 and 2022, under the leadership of Chief Engineer, Tim Williams, Vertical Aerospace successfully designed, built, and flew the VX-4 prototype aircraft. This achievement marked a historic moment in the aerospace industry, as it was the first of its kind – a new technology, electric-powered aircraft – to be created in the United Kingdom in living memory. The aircraft accomplished its first takeoff and landing while tethered to the ground in September. In 2023, the VX4 successfully completed an unmanned test flight at Kemble Airport, Cotswold UK. The aircraft demonstrated its capabilities by lifting off, hovering, flying, and landing solely through the thrust generated by Vertical's proprietary battery packs. The prototype was damaged during uncrewed flight testing on 9 August 2023 at Cotswold Airport. The company attributed the accident to a fault with the propeller, but said it was an older design that had since been replaced. In 2024 the second full-scale prototype of the VX4 was revealed. It was claimed to use a proprietary battery and a powertrain system with 20% greater power. The prototype also included redesigned carbon fiber propellers to lower noise and improve performance. In January 2025, piloted hover flight tests were successfully carried out. The next testing stage is low-speed manoeuvres. Vertical Aerospace says that the VX4 is a piloted, zero emissions electric vertical take off and landing (eVTOL) vehicle with an expected range of over 100 miles (160.9 km), capacity for 4 passengers and a pilot, and runs quieter than a helicopter. The proposed aircraft is intended to operate in and out of cities and other confined locations. It would rely on its fixed wing for lift during most of a flight. This shift follows the eVTOL industry, which is shifting towards wing-borne lift + cruise and vectored thrust concepts, due to the efficiency gains wing-borne lift offers while cruising. It features eight propellers mounted to the wing. The four front-mounted propellers shift from providing lift in take-off mode to providing forward thrust while cruising. The rear motors operate only during take-off and landing. No specifications are available at this time.

The Airbus Vahana (Sanskrit: Vāhana, or Vahanam literally means "vehicle") was an electric-powered eight-propeller VTOL personal air vehicle prototype, or eVTOL, financed by A³ (pronounced "A-cubed"), by Airbus and Airbus Urban Mobility. The Vahana project started in 2016 as one of the first projects at A³, the advanced projects and partnerships outpost of Airbus Group in Silicon Valley. Airbus "envision[s] Vahana being used by everyday commuters as a cost-comparable replacement for short-range urban transportation like cars or trains". It was planned to be a part of urban air mobility. The project was finished in December 2019. The convertiplane aircraft design, funded by the European aircraft manufacturer Airbus, called Vahana (Sanskrit: "vehicle"), started in 2016. It was being developed at A³ (A-cubed), the expanded project and partnership outpost of Airbus in Silicon Valley. Airbus said "Our work on this demonstrator confirms our belief that fully autonomous vehicles will allow us to achieve the scale required of Urban Air Mobility."[6] Then-CEO Tom Enders said: "I'm no big fan of Star Wars, but it's not crazy to imagine that one day our big cities will have flying cars making their way along roads in the sky." To test the Vahana concept, small models flew in Santa Clara, USA in 2017. Vahana was planned to become part of urban air mobility. In June 2017 at the Paris Air Show the prototype Vahana Alpha One (registration N301VX) was publicly presented for the first time. 31 January 2018 the first flight took place in Pendleton, Oregon. The full-scale aircraft Alpha One demonstrator reached a height of 5 meters within 53 seconds. By August 2018, more than 25 hover flights had been completed and the transition to forward flight had been tested. By January 2019, the second aircraft, Alpha Two, was completed, while the first was testing transitions to forward flight, but was not yet flown with the wings horizontal. On 3 May, it achieved its first full transitions to forward flight, reaching 90 kn (170 km/h) on its 58th flight. Airbus will not produce serial versions of the Vahana or the ducted-rotor CityAirbus demonstrators. Airbus finished the Vahana project in December 2019 in favor of the CityAirbus. The last flight took place on 14 November 2019, after 138 test flights with a total flight time of over 13 hours and a distance of 903 km were made. The longest single flight duration until then was 19 minutes, 56 seconds and the longest single distance covered has been 50,24 km. Configurations include electric helicopter and eight fan tilt-wing. For both configurations the hover performance estimates were based on blade element momentum theory. Vahana found the electric helicopter configuration superior at low ranges, and the tilt-wing configuration superior at longer ranges. The designer has not finalized the Vahana project and hope that "the electric tilt-wing configuration provides a DOC advantage and many other advantages such as reduced noise and enhanced safety for urban mobility". For both vehicles a common payload weight will be 200 lb (90 kg). A helicopter gearbox power density is assumed to be 6.3 kW/kg. Both configuration will assume 15 kg for avionics components and 15 kg for a crash rated seat. electrical actuators will take 0.65 kg each (8 units for helicopter and 12 units for tilt-wing). Additionally, the tilt-wing has two actuators (4 kg each). An additional 10% is for fittings and miscellaneous hardware. The cruise power of the tilt-wing is lower than the cruise power of an electric helicopter. The disk loading for both configurations is similar to those of many existing light helicopters. The electric helicopter hover power at short ranges is lower than those of the tilt-wing. Some drawings and explanations of Vahana can be seen under SELF-PILOTED AIRCRAFT FOR PASSENGER OR CARGO TRANSPORTATION. One of the reasons why Vahana was being developed as a self-steering aircraft was because the developers expected the available human pilots would not be sufficient in number for the anticipated volume of flights. Another reason was the higher payload and saving on labour expenses. In contrast to autonomous driving, autonomous flying has to be navigated at a significantly higher speed and in three instead of two dimensions. This requires higher computing speed and faster sensors and actuators. Autonomous navigation is carried out with a Lidar system, together with cameras and radar.

The Boeing 720 is a retired American narrow-body airliner produced by Boeing Commercial Airplanes. Announced in July 1957 as a 707 derivative for shorter flights from shorter runways, the 720 first flew on November 23, 1959. Its type certificate was issued on June 30, 1960, and it entered service with United Airlines on July 5, 1960. A total of 154 Boeing 720s and 720Bs were built; production ended in 1967. As a derivative, the 720 had low development costs, allowing profitability despite relatively few sales. Compared to the 707-120, it has a length reduced by 8.33 feet (2.54 m), a modified wing and a lightened airframe for a lower maximum takeoff weight. Originally designed to be powered by four Pratt & Whitney JT3C turbojets, the initial 720 could cover a 2,800-nautical-mile [nmi] (5,200 km; 3,200 mi) range with 131 passengers in two classes. The reconfigured 720B, powered by JT3D turbofans, first flew on October 6, 1960, and entered service in March 1961. It could seat 156 passengers in one class over a 3,200-nautical-mile [nmi] (5,900 km; 3,700 mi) range. Some 720s were later converted to the 720B specification. It was succeeded by the Boeing 727 trijet. Shorter range 707 Boeing announced its plans to develop a new version of the 707 in July 1957. It was developed from the 707-120 to provide for short- to medium-range flights from shorter runways. The model was originally designated 707-020 before being changed to 720 at the input of United Airlines. Compared to the 707-120, it has four fewer frames in front of the wing and one fewer aft: a total length reduction of 8 feet 4 inches (2.54 m). The new model was designed to a lower maximum takeoff weight with a modified wing and a lightened airframe. The wing modifications included Krueger flaps outboard of the outboard engines, lowering take-off and landing speeds—thus shortening runway length requirements—and a thickened inboard leading edge section, with a slightly greater sweep. This modification increased the top speed over the 707-120. It had four Pratt & Whitney JT3C-7 turbojet engines producing 12,500 lbf (55.6 kN) each. At one point in the development phase, it was known as the 707-020, then 717-020, although this was the Boeing model designation of the KC-135 and remained unused for a commercial airliner until it was applied to the MD-95, following Boeing's merger with McDonnell Douglas in 1997. Because the aircraft systems were similar to the Boeing 707, no prototype Boeing 720 was built; any different systems were tested on the Boeing 367-80. The first 720 took its maiden flight on November 23, 1959. The type certificate for the 720 was issued on June 30, 1960. It first entered service with United Airlines on July 5, 1960; 65 of the original version were built. The 720B version of the 720 had JT3D turbofan engines, producing 17,000 lbf (75.6 kN) each. The JT3D engines had lower fuel consumption and higher thrust. The maximum takeoff weight for the 720B was increased to 234,000 lb (106,000 kg). The 720B first took to the skies on October 6, 1960, and received certification and entered service with American Airlines in March 1961;[7] 89 720Bs were built in addition to conversions of American's 10 existing 720s. As a modification of an existing model, the 720 had minimal research and development costs, which allowed it to be successful despite few sales. The company built 154 Boeing 720s and 720Bs from 1959 to 1967. The 720's wing modification was later added on the 707-120B and on 707-120s retrofitted to the B standard. Design The Boeing 720 is a four-engined low-wing cantilever monoplane. Although it was similar to the Boeing 707, compared with the 707-120, it was 8 ft 4 in (2.54 m) shorter in length, and had a lighter structure through use of lighter forged metal parts and thinner fuselage skins and structures. Fuselage The rearmost of the 707's over-wing emergency exits was deleted on each side, which reduced passenger capacity, while two over-wing exits were an option for higher-density configurations. Wings The 720 uses an improved wing based on the 707 wing. The wingspan remained the same as the 707-120. For the 720, the wing was changed between the fuselage and inner engines by adding a wing root glove. This glove reduced the drag of the wing by decambering the root, which reduced the "middle effect", thereby increasing the effective local wing sweep. The wing root glove reportedly increased the drag divergence Mach number of the wing by Mach 0.02. Engines Though initially fitted with turbojet engines, the dominant engine for the Boeing 720 was the Pratt & Whitney JT3D, a turbofan variant of the JT3C with lower fuel consumption and higher thrust. JT3D-engined 720s had a "B" suffix; some of American's 720Bs were conversions of JT3C-powered 720s. Like the 707, the 720/720B used engine-driven turbocompressors to supply high-pressure air for cabin pressurization. The engines could not supply sufficient bleed air for this purpose without a serious loss of thrust. The small air inlets and associated humps are visible just above the main engine inlets on the two inner engine pods of all 720s and 720Bs; the lack of the turbocompressor inlet on the outer starboard pod (number 4 engine) helps spotters distinguish 720/720Bs from most 707s, which had three turbocompressors. For Operational History, click here. Variants 720 First production variant with four Pratt & Whitney JT3C turbojet engines Several high-density seat configurations delivered to Eastern Airlines included four over-wing escape hatches and brake cooling fans to effect quick turns on short-haul sectors.[citation needed] These aircraft, designated "720-025", were certificated to carry up to 170 passengers, provided that certain safety requirements were met. 720B Improved variant with four Pratt & Whitney JT3D turbofan engines; American Airlines converted its 720s to 720B standard.