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88-556: The Hawker Hart is a British two-seater biplane light bomber aircraft that saw service with the Royal Air Force (RAF). It was designed during the 1920s by Sydney Camm and manufactured by Hawker Aircraft . The Hart was a prominent British aircraft in the inter-war period, but was obsolete and already side-lined for newer monoplane aircraft designs by the start of the Second World War, playing only minor roles in

176-481: A Rolls-Royce F.XI water-cooled V12 engine (the engine that later became known as the Rolls-Royce Kestrel). It had, as the specification required, a metal structure, with a fuselage structure of steel-tube covered by aluminium panels and fabric, with the wings having steel spars and duralumin ribs , covered in fabric. The crew of two sat in individual tandem cockpits, with the pilot sitting under

264-653: A W shape cabane, however as it does not connect the wings to each other, it does not add to the number of bays. Large transport and bombing biplanes often needed still more bays to provide sufficient strength. These are often referred to as multi-bay biplanes . A small number of biplanes, such as the Zeppelin-Lindau D.I have no interplane struts and are referred to as being strutless . Because most biplanes do not have cantilever structures, they require rigging wires to maintain their rigidity. Early aircraft used simple wire (either braided or plain), however during

352-412: A biplane aircraft, two wings are placed one above the other. Each provides part of the lift, although they are not able to produce twice as much lift as a single wing of similar size and shape because the upper and the lower are working on nearly the same portion of the atmosphere and thus interfere with each other's behaviour. In a biplane configuration with no stagger from the upper wing to the lower wing,

440-464: A compression ratio of 6:1, and 'B' engines a high compression ratio of 7:1. The Kestrel was designed to be fitted with a gear-driven supercharger , in early Kestrel variants 'MS' engines were moderately supercharged and 'S' engines were fully supercharged. A number of Kestrel variants were produced by rebuilding or modifying earlier Marks. During 1927, once the prototype of the Kestrel was complete,

528-560: A documented jet-kill, as one Lockheed F-94 Starfire was lost while slowing down to 161 km/h (100 mph) – below its stall speed – during an intercept in order to engage the low flying Po-2. Later biplane trainers included the de Havilland Tiger Moth in the Royal Air Force (RAF), Royal Canadian Air Force (RCAF) and others and the Stampe SV.4 , which saw service postwar in the French and Belgian Air Forces. The Stearman PT-13

616-513: A faster and more comfortable successor to the Dragon. As the available engine power and speed increased, the drag penalty of external bracing increasingly limited aircraft performance. To fly faster, it would be necessary to reduce external bracing to create an aerodynamically clean design; however, early cantilever designs were either too weak or too heavy. The 1917 Junkers J.I sesquiplane utilized corrugated aluminum for all flying surfaces, with

704-588: A fighter version of the Hart was suggested, the Air Ministry selected the type as an interim fighter until higher-performance fighters could be bought in larger numbers. The new fighter variant added a second Vickers machine gun, while the coaming of the rear cockpit was angled to give a better field of fire, and a supercharged Kestrel IS engine was fitted. Evaluation of an initial batch of six aircraft, known as Hart Fighters by one flight of 23 Squadron during 1931

792-422: A given wing area. However, interference between the airflow over each wing increases drag substantially, and biplanes generally need extensive bracing, which causes additional drag. Biplanes are distinguished from tandem wing arrangements, where the wings are placed forward and aft, instead of above and below. The term is also occasionally used in biology , to describe the wings of some flying animals . In

880-525: A maximum speed of 160 mph (258 km/h). Designs were tendered by Hawker , Avro and de Havilland . Fairey , who had sold a squadron's worth of its wooden Fox bomber in 1925, was not at first invited to tender to the specification, and was sent a copy of the specification only after protesting to the Chief of the Air Staff , Hugh Trenchard . Hawker's design was a single-bay biplane powered by

968-507: A minimum of struts; however, it was relatively easy to damage the thin metal skin and required careful handling by ground crews. The 1918 Zeppelin-Lindau D.I fighter was an all-metal stressed-skin monocoque fully cantilevered biplane, but its arrival had come too late to see combat use in the conflict. By the 1930s, biplanes had reached their performance limits, and monoplanes become increasingly predominant, particularly in continental Europe where monoplanes had been increasingly common from

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1056-706: A need for a larger and more powerful engine was conceived for use in flying boats, and development began on an engine which utilised a 6" cylinder bore, compared to the Kestrel's 5", this became the Rolls-Royce Buzzard . The Buzzard (or "H") engine was further modified for use in the Schneider Trophy as the Rolls-Royce R engine. In 1935 the Kestrel design was used as the basis to develop the Rolls-Royce Merlin . The Kestrel design

1144-623: A range of 470 mi (757 km). It was faster than most contemporary fighters, an astonishing achievement considering it was a light bomber. It also enjoyed excellent manoeuvrability, making the Hart one of the most effective biplane bombers ever produced for the Royal Air Force. In particular, it was faster than the Bristol Bulldog , which had recently entered service as the RAF's front line fighter. This disparity in performance led

1232-555: A single Rolls-Royce Kestrel II engine, and had a max speed of 168 mph (270 km/h). Its armament consisted of a single forward .303 in (7.7 mm) Vickers machine gun and one .303 in (7.7 mm) Lewis gun. The Osprey joined the Fleet Air Arm (FAA) in 1932, with 103 being built, and ended its career in 1944 after serving as a trainer for FAA pilots during the Second World War. By December 1936, Ospreys were being deployed by 701 Squadron based at RAF Kalafrana in

1320-463: A small degree, but more often was used to improve access to the cockpit. Many biplanes have staggered wings. Common examples include the de Havilland Tiger Moth , Bücker Bü 131 Jungmann and Travel Air 2000 . Alternatively, the lower wing can instead be moved ahead of the upper wing, giving negative stagger, and similar benefits. This is usually done in a given design for structural reasons, or to improve visibility. Examples of negative stagger include

1408-473: A somewhat unusual sesquiplane arrangement, possessing a more substantial lower wing with two spars that eliminated the flutter problems encountered by single-spar sesquiplanes. The stacking of wing planes was suggested by Sir George Cayley in 1843. Hiram Maxim adopted the idea for his steam-powered test rig, which lifted off but was held down by safety rails, in 1894. Otto Lilienthal designed and flew two different biplane hang gliders in 1895, though he

1496-463: A team to introduce a new engine using the cast block, but set the goal to surpass the D-12. This would be accomplished using supercharging at all altitudes, allowing it to outperform naturally aspirated engines. Previously, supercharging (and turbocharging) was primarily used for high-altitude designs to offset the loss of ambient air pressure as the aircraft climbed, and thereby maintain power. But with

1584-560: Is better known for his monoplanes. By 1896 a group of young men in the United States, led by Octave Chanute , were flying hang gliders including biplanes and concluded that the externally braced biplane offered better prospects for powered flight than the monoplane. In 1903, the Wright Flyer biplane became the first successful powered aeroplane. Throughout the pioneer years, both biplanes and monoplanes were common, but by

1672-634: The Aeroplane and Armament Experimental Establishment at RAF Martlesham Heath on 8 September. It demonstrated good performance and handling, reaching 176 mph (283 km/h) in level flight and 282 miles per hour (454 km/h) in a vertical dive. The competition culminated in the choice of the Hawker Hart in April 1929. The de Havilland Hound was rejected due to handling problems during landing and because of its part-wooden primary structure. While

1760-524: The Avro Antelope demonstrated similar performance and good handling, the Hart was preferred as it was far cheaper to maintain, a vital aspect to a programme during defence budget constraints that the British armed forces faced during the 1920s. The Fairey Fox IIM (which despite the name was a new aircraft), delayed by Fairey's late start on the design compared to the other competitors, only flew for

1848-536: The Bristol M.1 , that caused even those with relatively high performance attributes to be overlooked in favour of 'orthodox' biplanes, and there was an allegedly widespread belief held at that time that monoplane aircraft were inherently unsafe during combat. Between the years of 1914 and 1925, a clear majority of new aircraft introduced were biplanes; however, during the latter years of the First World War,

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1936-474: The Curtiss CR won the 1923 Schneider Trophy . The CR was powered by the recently introduced Curtiss D-12 engine, which replaced the individual cylinders with a cast aluminum block. This gave the engine much greater strength, allowing the rest of the engine to be greatly simplified, making it much lighter overall, as well as easier to assemble as the two parts simply bolted together in a single operation. It

2024-653: The First World War -era Fokker D.VII fighter and the Second World War de Havilland Tiger Moth basic trainer. The larger two-seat Curtiss JN-4 Jenny is a two bay biplane , the extra bay being necessary as overlong bays are prone to flexing and can fail. The SPAD S.XIII fighter, while appearing to be a two bay biplane, has only one bay, but has the midpoints of the rigging braced with additional struts; however, these are not structurally contiguous from top to bottom wing. The Sopwith 1½ Strutter has

2112-703: The Grumman Ag Cat are available in upgraded versions with turboprop engines. The two most produced biplane designs were the 1913 British Avro 504 of which 11,303 were built, and the 1928 Soviet Polikarpov Po-2 of which over 20,000 were built, with the Po-2 being the direct replacement for the Soviet copy of the Avro 504. Both were widely used as trainers. The Antonov An-2 was very successful too, with more than 18,000 built. Although most ultralights are monoplanes,

2200-617: The Lite Flyer Biplane, the Sherwood Ranger , and the Murphy Renegade . The feathered dinosaur Microraptor gui glided, and perhaps even flew, on four wings, which may have been configured in a staggered sesquiplane arrangement. This was made possible by the presence of flight feathers on both forelimbs and hindlimbs, with the feathers on the forelimbs opening to a greater span. It has been suggested that

2288-556: The Nieuport-Delage NiD 42 / 52 / 62 series, Fokker C.Vd & e, and Potez 25 , all serving across a large number of air forces. In the general aviation sector, aircraft such as the Waco Custom Cabin series proved to be relatively popular. The Saro Windhover was a sesquiplane with the upper wing smaller than the lower, which was a much rarer configuration than the reverse. The Pfalz D.III also featured

2376-674: The North-West Frontier , British India during the inter-war period. Four Hawker Harts from the Swedish Air Force saw action as dive bombers during the 1939–1940 Winter War as part of a Swedish volunteer squadron, designated F19, fighting on the Finnish side. Though obsolete compared to the United Kingdom's opposition at the start of the Second World War , the Hart continued in service, mainly performing in

2464-501: The Sopwith Dolphin , Breguet 14 and Beechcraft Staggerwing . However, positive (forward) stagger is much more common. The space enclosed by a set of interplane struts is called a bay (much as the architectural form is used), hence a biplane or triplane with one set of such struts connecting the wings on each side of the aircraft is a single-bay biplane . This provided sufficient strength for smaller aircraft such as

2552-1155: The South African Air Force , the Royal Egyptian Air Force , the Royal Iraqi Air Force , the Imperial Iranian Air Force , the Straits Settlements and the Southern Rhodesian Air Force . During the Second World War the Audax saw limited service in Africa on the Kenya – Abyssinia border during the Second Italo-Ethiopian War . The Audax also saw service in Iraq, at RAF Habbaniya , west of Baghdad , after

2640-419: The lift coefficient is reduced by 10 to 15 percent compared to that of a monoplane using the same airfoil and aspect ratio . The lower wing is usually attached to the fuselage , while the upper wing is raised above the fuselage with an arrangement of cabane struts , although other arrangements have been used. Either or both of the main wings can support ailerons , while flaps are more usually positioned on

2728-756: The Air Force (CVM) who built 21. 1004 Harts were produced. The Hart entered service with No. 33 Squadron RAF in February 1930, replacing the larger and slower Hawker Horsley . No. 12 Squadron replaced its Foxes with Harts in January 1931, with a further two British-based Hart light bomber squadrons forming during 1931. Harts were deployed to the Middle East during the Abyssinia Crisis of 1935–1936. The Hart saw extensive and successful service on

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2816-514: The CR.42 was able to achieve success in the defensive night fighter role against RAF bombers that were striking industrial targets throughout northern Italy. The British Fleet Air Arm operated the Fairey Swordfish torpedo bomber from its aircraft carriers, and used the type in the anti-submarine warfare role until the end of the conflict, largely due to their ability to operate from

2904-528: The Caribou , performed the first non-stop flight between the Canadian mainland and Britain in 30 hours 55 minutes, although the intended target for this long distance flight had originally been Baghdad , Iraq . Despite its relative success, British production of the Dragon was quickly ended when in favour of the more powerful and elegant de Havilland Dragon Rapide , which had been specifically designed to be

2992-617: The East African theatre of World War II. Swedish Air Force General Björn Bjuggren wrote in his memoirs how his squadron developed dive-bombing techniques in the mid-1930s for their B4s. When the Hawker engineers found out, they issued a formal objection, saying that the aircraft had not been designed for that purpose. However, the Swedish pilots proved that the aircraft was up to the task and dispelled their concerns. The Hawker Audax

3080-514: The Egyptian government, powered by 750 hp (560 kW) Armstrong Siddeley Panther VIA radials. Acknowledging the amount of redesign work done, these were designated the Avro Type 674 . Audax I Audax (India) Audax (Singapore) Canadian Audax Egyptian Audax Iraqi Audax (Nisr) Persian Audax Hartebeest Hartebeest I The Hawker Demon was a fighter variant of

3168-515: The First World War, the British Royal Aircraft Factory developed airfoil section wire named RAFwire in an effort to both increase the strength and reduce the drag. Four types of wires are used in the biplane wing structure. Drag wires inside the wings prevent the wings from being folded back against the fuselage, running inside a wing bay from the forward inboard corner to the rear outboard corner. Anti-drag wires prevent

3256-577: The French Nieuport 17 and German Albatros D.III , offered lower drag than a conventional biplane while being stronger than a monoplane. During the Interwar period , numerous biplane airliners were introduced. The British de Havilland Dragon was a particularly successful aircraft, using straightforward design to could carry six passengers on busy routes, such as London-Paris services. During early August 1934, one such aircraft, named Trail of

3344-661: The Germans had been experimenting with a new generation of monoplanes, such as the Fokker D.VIII , that might have ended the biplane's advantages earlier had the conflict not ended when it had. The French were also introducing the Morane-Saulnier AI , a strut-braced parasol monoplane , although the type was quickly relegated to the advanced trainer role following the resolution of structural issues. Sesquiplane types, which were biplanes with abbreviated lower wings such as

3432-539: The Hart light bomber. During air defence exercises the RAF's Siskins and Bulldogs were often unable to intercept the new Hart bombers, which were sometimes instructed to restrict their height and speed in order to give the fighters a chance, which prompted the development of a fighter variant of the Hart. While the Hawker Fury offered better performance, lower production volumes made it more expensive and therefore it remained available only in small numbers, so when

3520-424: The Kestrel engine remain airworthy today. Earlier in-line engine designs were generally built on top of a cast aluminum crankcase, with the cylinders, individually-machined steel cylinders, bolted on top. Given the forces involved, the system connecting the cylinders to the crankcase had to be robust, adding weight, and as a whole the engine was reliant on the structure of the crankcase to hold it together. In 1923,

3608-512: The Merlin engine during the war. As a response to the fuel injection systems developed by Bosch, in 1936 a Kestrel engine was fitted with a pressurised carburettor system to improve fuelling at high altitudes. The resulting behaviour of the engine when flight tested by the Farnborough institute was seen to be "...one of the smoothest engines they had used at high altitudes". From Lumsden,

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3696-578: The RAF to gradually replace the Bulldog with the Hawker Fury . Demand was such that production was spread out among a wide selection of aircraft companies. Of the 962 built in the United Kingdom, Hawker produced 234, Armstrong Whitworth 456, Gloster 46, Vickers 226 and 42 were produced in Sweden under licence by ASJA who built 18, Götaverken who built three and the Central Workshops of

3784-774: The anti-submarine and anti-piracy role. The Osprey was also sold to the Swedish Air Force being used on the seaplane cruiser HSwMS  Gotland , which carried six Ospreys. Ospreys were also sold to the Portuguese Naval Aviation and the Spanish Republican Air Force . Data from The British Bomber since 1914 . General characteristics Performance Armament Related development Related lists Biplane Biplanes offer several advantages over conventional cantilever monoplane designs: they permit lighter wing structures, low wing loading and smaller span for

3872-407: The biplane naturally has a deep structure and is therefore easier to make both light and strong. Rigging wires on non-cantilevered monoplanes are at a much sharper angle, thus providing less tension to ensure stiffness of the outer wing. On a biplane, since the angles are closer to the ideal of being in direct line with the forces being opposed, the overall structure can then be made stiffer. Because of

3960-420: The boiling point of water decreases with altitude . The amount of heat rejected by an air-to-air cooling system is a function of the maximum coolant temperature and volume, so the resulting decrease in cooling capacity became a limiting factor for aero engine power in this period, as the coolant has to be kept below boiling point. The solution was to pressurise the engine's entire cooling system, thereby raising

4048-602: The communications and training roles until being declared obsolete in 1943. The Hart proved to be a successful export, seeing service with the Royal Egyptian Air Force , Royal Indian Air Force , South African Air Force , Estonian Air Force , Southern Rhodesia , Sweden (where it was designated B4) and the Kingdom of Yugoslavia . The Rhodesian Hardys saw service on the Allied side during the opening moves of

4136-608: The competition aerobatics role and format for such a biplane well-defined by the mid-1930s by the Udet U 12 Flamingo and Waco Taperwing . The Pitts Special dominated aerobatics for many years after World War II and is still in production. The vast majority of biplane designs have been fitted with reciprocating engines . Exceptions include the Antonov An-3 and WSK-Mielec M-15 Belphegor , fitted with turboprop and turbofan engines respectively. Some older biplane designs, such as

4224-569: The conflict before being retired. Several major variants of the Hart were developed, including a navalised version for the Royal Navy 's aircraft carriers . Beyond Britain, the Hart would be operated by a number of foreign nations, including Sweden, Yugoslavia , Estonia , South Africa , and Canada. In 1926, the Air Ministry stated a requirement for a two-seat high-performance light day-bomber, to be of all-metal construction and with

4312-470: The drag from the number of struts used. The structural forces acting on the spars of a biplane wing tend to be lower as they are divided between four spars rather than two, so the wing can use less material to obtain the same overall strength and is therefore lighter. A given area of wing also tends to be shorter, reducing bending moments on the spars, which then allow them to be more lightly built as well. The biplane does however need extra struts to maintain

4400-549: The end of World War I . At the start of World War II , several air forces still had biplane combat aircraft in front line service but they were no longer competitive, and most were used in niche roles, such as training or shipboard operation, until shortly after the end of the war. The British Gloster Gladiator biplane, the Italian Fiat CR.42 Falco and Soviet I-153 sesquiplane fighters were all still operational after 1939. According to aviation author Gianni Cattaneo,

4488-459: The first production aircraft were delivered to 30 Squadron in January 1935. The Hardy saw some service during the Second World War, in Africa and the Middle East; the Hardys performing a number of operations against Italian-occupied Abyssinia as well as other areas of Africa. The Hardy also saw service with Southern Rhodesia . The last operational sortie by a Hardy was on 9 May 1941 and most of

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4576-468: The first time on 25 October 1929, long after the Hart had been selected. A total of 992 aircraft were built as Harts. It became the most widely used light bomber of its time and the design would prove to be a successful one with a number of derivatives, including the Hawker Hind and Hector . There were a number of Hart variants, though only slight alterations were made to the design. The Hart India

4664-416: The gap between the wings, which add both weight and drag. The low power supplied by the engines available in the first years of aviation limited aeroplanes to fairly low speeds. This required an even lower stalling speed, which in turn required a low wing loading , combining both large wing area with light weight. Obtaining a large enough wing area without the wings being long, and thus dangerously flexible

4752-423: The hind limbs could not have opened out sideways but in flight would have hung below and slightly behind the fore limbs. Rolls-Royce Kestrel The Rolls-Royce Kestrel (internal type F ) is a 21.25 litre (1,295 in³) V-12 aircraft engine from Rolls-Royce . It was their first cast-block engine, and used as the pattern for most of their future piston-engine designs. Used during the interwar period , it

4840-561: The late 1930s allowed the engine to be boosted to higher power levels without suffering from detonation . The mark-XVI engine used in the Miles Master M.9 prototype delivered 745hp (500kW), and the XXX variant of 1940 saw service at 720hp (537kW). One key advance in the Kestrel was the use of a pressurised cooling system. Water boils at 100°C at standard atmospheric pressure , but this pressure decreases as altitude increases, and therefore

4928-639: The low speeds and simple construction involved have inspired a small number of biplane ultralights, such as Larry Mauro's Easy Riser (1975–). Mauro also made a version powered with solar cells driving an electric motor called the Solar Riser . Mauro's Easy Riser was used by "Father Goose", Bill Lishman . Other biplane ultralights include the Belgian-designed Aviasud Mistral , the German FK12 Comet (1997–),

5016-519: The lower wing. Bracing is nearly always added between the upper and lower wings, in the form of interplane struts positioned symmetrically on either side of the fuselage and bracing wires to keep the structure from flexing, where the wings are not themselves cantilever structures. The primary advantage of the biplane over a monoplane is its ability to combine greater stiffness with lower weight. Stiffness requires structural depth and where early monoplanes had to have this provided with external bracing,

5104-453: The most famed copies was the Siemens-Schuckert D.I . The Albatros D.III and D.V , which had also copied the general layout from Nieuport, similarly provided the backbone of the German forces during the First World War. The Albatros sesquiplanes were widely acclaimed by their aircrews for their maneuverability and high rate of climb. During interwar period , the sesquiplane configuration continued to be popular, with numerous types such as

5192-439: The new construction technique, the engine would be so strong that it could be supercharged at all altitudes without overstressing the cylinders, allowing a smaller engine to operate as if it was larger, and thus improving its power-to-weight ratio . The prototype Kestrel engine was first run in 1926, and one first flew in 1927, with a power rating of 450hp (335kW). The engine was normally aspirated in its initial form. The engine

5280-422: The night ground attack role throughout the Second World War. In the case of the Po-2, production of the aircraft continued even after the end of the conflict, not ending until around 1952. A significant number of Po-2s were fielded by the Korean People's Air Force during the Korean War , inflicting serious damage during night raids on United Nations bases. The Po-2 is also the only biplane to be credited with

5368-420: The nose. Many were fitted with a hydraulically-powered turret in the rear gunner's position, which had been tested on the Hawker Hart. Demons were also sold to the Royal Australian Air Force . It saw only second-line operations during the Second World War. Production of the Demon was undertaken by Hawker and by Boulton Paul Aircraft at their Wolverhampton factory, where their last example of 106 to be completed

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5456-438: The outbreak of the First World War biplanes had gained favour after several monoplane structural failures resulted in the RFC's "Monoplane Ban" when all monoplanes in military service were grounded, while the French also withdrew most monoplanes from combat roles and relegated them to training. Figures such as aviation author Bruce observed that there was an apparent prejudice held even against newly-designed monoplanes, such as

5544-424: The reduced stiffness, wire braced monoplanes often had multiple sets of flying and landing wires where a biplane could easily be built with one bay, with one set of landing and flying wires. The extra drag from the wires was not enough to offset the aerodynamic disadvantages from having two airfoils interfering with each other however. Strut braced monoplanes were tried but none of them were successful, not least due to

5632-457: The relatively compact decks of escort carriers . Its low stall speed and inherently tough design made it ideal for operations even in the often severe mid-Atlantic weather conditions. By the end of the conflict, the Swordfish held the distinction of having caused the destruction of a greater tonnage of Axis shipping than any other Allied aircraft. Both the German Heinkel He 50 and the Soviet Polikarpov Po-2 were used with relative success in

5720-442: The series of Nieuport military aircraft—from the Nieuport 10 through to the Nieuport 27 which formed the backbone of the Allied air forces between 1915 and 1917. The performance of the Nieuport sesquiplanes was so impressive that the Idflieg (the German Inspectorate of flying troops) requested their aircraft manufacturers to produce copies, an effort which was aided by several captured aircraft and detailed drawings; one of

5808-415: The structural problems associated with monoplanes, but offered little improvement for biplanes. The default design for a biplane has the wings positioned directly one above the other. Moving the upper wing forward relative to the lower one is called positive stagger or, more often, simply stagger. It can increase lift and reduce drag by reducing the aerodynamic interference effects between the two wings by

5896-409: The survivors were scrapped, although some continued in service as communications aircraft. On 14 May 1941, the Belgian Colonial authorities obtained a Hawker Hardy from the South African Air Force. Painted in Belgian colours, the machine was used for observation missions, but unfortunately overturned while landing at Gambela airfield on 26 May 1941, effectively writing off the aircraft. The Hawker Hind

5984-423: The temperature at which the coolant would boil: not only does this help mitigate the decrease in cooling performance with altitude, but allows a smaller cooling system to be used in the aircraft for the same heat load. The Kestrel was built to maintain coolant pressure to keep the boiling point at about 150°C. In early Kestrel variants, unsupercharged engines were available in two compression ratios, 'A' engines had

6072-434: The time, none of the British aero engine manufacturers could offer an engine which offered a similar power rating which was also as light and compact as the D-12. The D-12 was licensed by Fairey and introduced to the UK as the Felix. Arthur Rowledge , Chief Designer at Napier and the designer of the Napier Lion engine, joined Rolls-Royce in 1921 to take up the role as "Chief Assistant to Mr F. H. Royce". Rowledge built

6160-614: The two planes when the high pressure air under the top wing and the low pressure air above the lower wing cancel each other out. This means that a biplane does not in practice obtain twice the lift of the similarly-sized monoplane. The farther apart the wings are spaced the less the interference, but the spacing struts must be longer, and the gap must be extremely large to reduce it appreciably. As engine power and speeds rose late in World War I , thick cantilever wings with inherently lower drag and higher wing loading became practical, which in turn made monoplanes more attractive as it helped solve

6248-400: The upper and lower wings together. The sesquiplane is a type of biplane where one wing (usually the lower) is significantly smaller than the other. The word, from Latin, means "one-and-a-half wings". The arrangement can reduce drag and weight while retaining the biplane's structural advantages. The lower wing may have a significantly shorter span, or a reduced chord . Examples include

6336-588: The uprising there, during the Anglo-Iraqi War . In the days leading up to that battle crews began to upgrade the Audaxes stationed there, despite having received orders forbidding such actions. They fitted some to carry 250 lb (113 kg) bombs instead of 20 lb (9 kg) bombs. The Audax ended its service by 1945. A derivative of the Audax, the Hawker Hartebeest , a light bomber,

6424-513: The wing trailing edge, and operating a single .303 in (7.7 mm) Vickers machine gun mounted on the port side of the cockpit. The observer sat behind the pilot, and was armed with a single Lewis gun on a ring mount, while for bomb-aiming, he lay prone under the pilot's seat. Up to 520 pounds (240 kg) of bombs could be carried under the aircraft's wings. The prototype Hart, serial J9052, first flew in June 1928, being delivered to

6512-434: The wings from folding up, and run from the underside of the outer wing to the lower wing root. Conversely, landing wires prevent the wings from sagging, and resist the forces when an aircraft is landing, and run from the upper wing centre section to outboard on the lower wings. Additional drag and anti-drag wires may be used to brace the cabane struts which connect the fuselage to the wings, and interplane struts, which connect

6600-421: The wings from moving forward when the aircraft stops and run the opposite direction to the drag wires. Both of these are usually hidden within the wings, and if the structure is sufficiently stiff otherwise, may be omitted in some designs. Indeed many early aircraft relied on the fabric covering of the wing to provide this rigidity, until higher speeds and forces made this inadequate. Externally, lift wires prevent

6688-519: Was a Hart variant, designed for army cooperation, seeing much service in the British Empire . The first Audax flew in late 1931 and over 700 Audaxes were produced (including export). The Audax was similar to the Hart, though had some modifications, including a hook to pick up messages. It was armed with a single Scarff ring -mounted .303 in (7.7 mm) Lewis gun and a fixed forward-firing .303 in (7.7 mm) Vickers machine gun and

6776-460: Was a derivative of the Hart and was intended to replace it. The Hawker Hector was a variant of the Hind and was used in the army co-operation role. It saw only limited service during the Second World War with the Royal Air Force. Hectors were also sold to Ireland. The Hawker Osprey was the navalised carrier-borne version of the Hart, performing in the fighter and reconnaissance roles. The Osprey had

6864-495: Was a tropical version, the Hart Special was a tropical Hawker Audax , a Hart variant with desert equipment; a specialised Hart Trainer was also built which dispensed with the gunner's ring. Vickers built 114 of the latter model at Weybridge between 1931 and June 1936. The production Hart day bomber had a 525 hp (390 kW) Rolls-Royce Kestrel IB 12-cylinder V-type engine; a speed of 184 mph (296 km/h) and

6952-471: Was also easy to convert existing assembly lines to the new system as the cast blocks were already being produced for the crankcase, and all that was required was new machines to mill the blocks to the accuracy needed for the pistons. The Curtiss D-12 was one of the most powerful engines of its era, and continued to exchange records with other contemporary high-power engines such as the Napier Lion . At

7040-630: Was built for the South African Air Force with modifications made from the Audax. Sixty-nine of these aircraft were built, the majority in South Africa. The aircraft saw action in East Africa during clashes against Italy who occupied Abyssinia. A.V. Roe built 287 Audaxes as part of the RAF expansion scheme during 1935–1937. These did not warrant an Avro type number but between 1937 and 1938, Avro built 24 modernised Audaxes for

7128-519: Was delivered to the RAF in December 1937. The Hawker Hardy was a general-purpose variant of the Hawker Hart tropicalised to meet Air Ministry Specification G.23/33 as a Wapiti replacement in Iraq. The prototype was a production Hart which was modified with a modified radiator, a message pick-up hook, water containers and a desert survival kit. The prototype first flew on 7 September 1934, and

7216-535: Was first produced in 1927 at 450 hp (335 kW), which was soon improved in the I-B version to 525 hp (390 kW) by increasing the compression ratio to 7:1. The I-B variant saw widespread use in the Hawker Hart family of aircraft, a mainstay of British air power during the early 1930s. Development continued and the V model introduced the centrifugal supercharger, increasing power to 695hp (520kW). Increased availability of higher octane aviation fuels in

7304-703: Was fitted to a number of British fighters and bombers of the era, including the Hawker Fury and Hawker Hart family, and the Handley Page Heyford . The Kestrel engine was also sold to international air force customers; in this role it was used to power prototypes of the German Messerschmitt Bf 109 and the Junkers Ju 87 "Stuka" dive-bomber, as the Junkers Jumo 210 engines were not ready to be fitted. Several examples of

7392-404: Was more readily accomplished with a biplane. The smaller biplane wing allows greater maneuverability . Following World War I, this helped extend the era of the biplane and, despite the performance disadvantages, most fighter aircraft were biplanes as late as the mid-1930s. Specialist sports aerobatic biplanes are still made in small numbers. Biplanes suffer aerodynamic interference between

7480-724: Was powered by a version of the Kestrel engine and had a maximum speed of 170 mph (274 km/h). A number of variants of the Audax were produced, including the Audax India , a tropicalised version of the Audax for service in India and the Audax Singapore for service there. Other air forces which also used the Audax included the Royal Canadian Air Force , the Royal Indian Air Force ,

7568-474: Was successful, and larger orders followed for the fighter Hart, now known as the Hawker Demon. The production Demon's first flight was on 10 February 1933. 305 Hawker Demons were built, including 232 for the RAF. The Demon was powered by versions of the Kestrel engine. It had an armament of a single rear .303 in (7.7 mm) Lewis Gun with two fixed .303 in (7.7 mm) Vickers machine guns in

7656-747: Was used as a base for both the Goshawk , however the aircraft which were intended to be fitted with the Goshawk engine were cancelled, so the project was scrapped. The Kestrel was also used as the basis for the Peregrine (and therefore the Vulture ), all utilising the same 5" piston bore and 5.5" piston stroke. In practice, development of the Peregrine and Vulture engines were curtailed, before eventually being cancelled, to allow increased resource developing

7744-777: Was widely used by the United States Army Air Force (USAAF) while the US Navy operated the Naval Aircraft Factory N3N . In later civilian use in the US, the Stearman became particularly associated with stunt flying such as wing-walking , and with crop dusting, where its compactness worked well at low levels, where it had to dodge obstacles. Modern biplane designs still exist in specialist roles such as aerobatics and agricultural aircraft with

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