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62-398: The de Havilland DH.114 Heron is a small propeller -driven British airliner that first flew on 10 May 1950. It was a development of the twin-engine de Havilland Dove , with a stretched fuselage and two more engines . It was designed as a rugged, conventional low-wing monoplane with tricycle undercarriage that could be used on regional and commuter routes. A total of 149 were built; it

124-464: A bent aluminium sheet for blades, thus creating an airfoil shape. They were heavily undercambered , and this plus the absence of lengthwise twist made them less efficient than the Wright propellers. Even so, this was perhaps the first use of aluminium in the construction of an airscrew. Originally, a rotating airfoil behind the aircraft, which pushes it, was called a propeller, while one which pulled from

186-473: A childhood fascination with the Chinese flying top, developed a model of feathers, similar to that of Launoy and Bienvenu, but powered by rubber bands. By the end of the century, he had progressed to using sheets of tin for rotor blades and springs for power. His writings on his experiments and models would become influential on future aviation pioneers. William Bland sent designs for his "Atmotic Airship" to

248-644: A company demonstrator, and was tried by British European Airways in 1951 on its Scottish routes. Following the successful completion of the prototype trials as a regional airliner, series production of the Heron began. The first deliveries were to NAC, the New Zealand National Airways Corporation (later part of Air New Zealand ). Basic price for a new Heron in 1960 was around £60,000, minus radio. The first Heron, Series 1A suffered deficiencies, as NAC soon discovered. First,

310-461: A craft that weighed 3.5 long tons (3.6 t), with a 110 ft (34 m) wingspan that was powered by two 360 hp (270 kW) steam engines driving two propellers. In 1894, his machine was tested with overhead rails to prevent it from rising. The test showed that it had enough lift to take off. One of Pénaud's toys, given as a gift by their father , inspired the Wright brothers to pursue

372-416: A fixed-pitch prop once airborne. The spring-loaded "two-speed" VP prop is set to fine for takeoff, and then triggered to coarse once in cruise, the propeller remaining coarse for the remainder of the flight. After World War I , automatic propellers were developed to maintain an optimum angle of attack. This was done by balancing the centripetal twisting moment on the blades and a set of counterweights against

434-495: A further development, the company basically enlarged the Dove; the fuselage was lengthened to make room for more passengers or freight, and the wingspan was increased to make room for two more engines. The Heron was of all-metal construction, and was laid out as a conventional design; the resulting aircraft could use many of the parts originally designed for the Dove, thus simplifying logistics for airlines using both types. The emphasis

496-467: A large number of blades. A fan therefore produces a lot of thrust for a given diameter but the closeness of the blades means that each strongly affects the flow around the others. If the flow is supersonic, this interference can be beneficial if the flow can be compressed through a series of shock waves rather than one. By placing the fan within a shaped duct , specific flow patterns can be created depending on flight speed and engine performance. As air enters

558-528: A low- drag wing and as such are poor in operation when at other than their optimum angle of attack . Therefore, most propellers use a variable pitch mechanism to alter the blades' pitch angle as engine speed and aircraft velocity are changed. A further consideration is the number and the shape of the blades used. Increasing the aspect ratio of the blades reduces drag but the amount of thrust produced depends on blade area, so using high-aspect blades can result in an excessive propeller diameter. A further balance

620-415: A propeller efficiency of about 73.5% at cruise for a Cessna 172 . This is derived from his "Bootstrap approach" for analyzing the performance of light general aviation aircraft using fixed pitch or constant speed propellers. The efficiency of the propeller is influenced by the angle of attack (α). This is defined as α = Φ - θ, where θ is the helix angle (the angle between the resultant relative velocity and

682-453: A propeller suffers when transonic flow first appears on the tips of the blades. As the relative air speed at any section of a propeller is a vector sum of the aircraft speed and the tangential speed due to rotation, the flow over the blade tip will reach transonic speed well before the aircraft does. When the airflow over the tip of the blade reaches its critical speed , drag and torque resistance increase rapidly and shock waves form creating

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744-454: A sharp increase in noise. Aircraft with conventional propellers, therefore, do not usually fly faster than Mach 0.6. There have been propeller aircraft which attained up to the Mach 0.8 range, but the low propeller efficiency at this speed makes such applications rare. The tip of a propeller blade travels faster than the hub. Therefore, it is necessary for the blade to be twisted so as to decrease

806-417: A spring and the aerodynamic forces on the blade. Automatic props had the advantage of being simple, lightweight, and requiring no external control, but a particular propeller's performance was difficult to match with that of the aircraft's power plant. The most common variable pitch propeller is the constant-speed propeller . This is controlled by a hydraulic constant speed unit (CSU). It automatically adjusts

868-520: A wound-up spring device and demonstrated it to the Russian Academy of Sciences . It was powered by a spring, and was suggested as a method to lift meteorological instruments. In 1783, Christian de Launoy , and his mechanic , Bienvenu, used a coaxial version of the Chinese top in a model consisting of contrarotating turkey flight feathers as rotor blades, and in 1784, demonstrated it to

930-427: Is a family of air-cooled six-cylinder , horizontally opposed fixed-wing aircraft and helicopter engines of 541.5 cubic inches (8,874 cc) displacement, manufactured by Lycoming Engines . The engine is a six-cylinder version of the four-cylinder Lycoming O-360 . Producing between 230 and 350 horsepower (170 and 260 kW) these engines are installed in a large variety of aircraft. The main competitors are

992-455: Is hydraulic, with engine oil serving as the hydraulic fluid. However, electrically controlled propellers were developed during World War II and saw extensive use on military aircraft, and have recently seen a revival in use on home-built aircraft. Another design is the V-Prop , which is self-powering and self-governing. On most variable-pitch propellers, the blades can be rotated parallel to

1054-479: Is suitable for airliners, but the noise generated is tremendous (see the Antonov An-70 and Tupolev Tu-95 for examples of such a design). Forces acting on the blades of an aircraft propeller include the following. Some of these forces can be arranged to counteract each other, reducing the overall mechanical stresses imposed. The purpose of varying pitch angle is to maintain an optimal angle of attack for

1116-409: Is that using a smaller number of blades reduces interference effects between the blades, but to have sufficient blade area to transmit the available power within a set diameter means a compromise is needed. Increasing the number of blades also decreases the amount of work each blade is required to perform, limiting the local Mach number – a significant performance limit on propellers. The performance of

1178-489: Is used to help slow the aircraft after landing and is particularly advantageous when landing on a wet runway as wheel braking suffers reduced effectiveness. In some cases reverse pitch allows the aircraft to taxi in reverse – this is particularly useful for getting floatplanes out of confined docks. Counter-rotating propellers are sometimes used on twin-engine and multi-engine aircraft with wing-mounted engines. These propellers turn in opposite directions from their counterpart on

1240-529: The Continental IO-520 and IO-550 series. An AEIO version was developed for high-performance competition aerobatics aircraft. Starting at 260 hp (190 kW) the power was eventually increased to 300 hp (220 kW). The AEIO-540 family has achieved considerable success in aircraft such as the Extra 300 , CAP 232 , and Zivko Edge 540 . All engines have an additional prefix preceding

1302-545: The French Academy of Sciences . A dirigible airship was described by Jean Baptiste Marie Meusnier presented in 1783. The drawings depict a 260-foot-long (79 m) streamlined envelope with internal ballonets that could be used for regulating lift. The airship was designed to be driven by three propellers. In 1784 Jean-Pierre Blanchard fitted a hand-powered propeller to a balloon, the first recorded means of propulsion carried aloft. Sir George Cayley , influenced by

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1364-452: The Series 2 , featuring retractable landing gear, which reduced drag and fuel consumption, and increased the top speed marginally. The 2A was the equivalent of the 1A, the basic passenger aircraft while the 1B and its successor the 2B had higher maximum takeoff weight, the 2C featured fully feathering propellers, the Heron 2D had an even higher maximum takeoff weight, while the Heron 2E

1426-465: The Tupolev Tu-95 propel it at a speed exceeding the maximum once considered possible for a propeller-driven aircraft using an exceptionally coarse pitch. Early pitch control settings were pilot operated, either with a small number of preset positions or continuously variable. The simplest mechanism is the ground-adjustable propeller , which may be adjusted on the ground, but is effectively

1488-488: The Tupolev Tu-95 , which can reach 575 mph (925 km/h). The earliest references for vertical flight came from China. Since around 400 BC, Chinese children have played with bamboo flying toys . This bamboo-copter is spun by rolling a stick attached to a rotor between one's hands. The spinning creates lift, and the toy flies when released. The 4th-century AD Daoist book Baopuzi by Ge Hong (抱朴子 "Master who Embraces Simplicity") reportedly describes some of

1550-643: The 1970s and 1980s including N415SA , a Riley Heron still flying in Sweden as of 20 May 2012 and a Riley Turbo Skyliner, tail number N600PR currently registered in the United States (this example appeared in the 1986 movie Club Paradise ). The most radical modification of the basic Heron airframe was the Saunders ST-27/-28 , that changed the configuration as well as the "look" of the whole aircraft with two powerful turboprop engines replacing

1612-535: The Great Exhibition held in London in 1851, where a model was displayed. This was an elongated balloon with a steam engine driving twin propellers suspended underneath. Alphonse Pénaud developed coaxial rotor model helicopter toys in 1870, also powered by rubber bands. In 1872 Dupuy de Lome launched a large navigable balloon, which was driven by a large propeller turned by eight men. Hiram Maxim built

1674-592: The Heron range was relatively "leisurely", and after production at de Havilland's Chester factory ceased in 1963, several companies, most notably Riley Aircraft Corporation , offered various Heron modification kits, mainly related to replacing the engines, which greatly enhanced takeoff and top speed capabilities. Riley Aircraft replaced the Gipsy Queens with horizontally-opposed Lycoming IO-540 engines. One U.S. airline that carried out Riley-type conversions at their Opa Locka Airport , Florida, engineering facility

1736-399: The air in the propeller slipstream. Contra-rotation also increases the ability of a propeller to absorb power from a given engine, without increasing propeller diameter. However the added cost, complexity, weight and noise of the system rarely make it worthwhile and it is only used on high-performance types where ultimate performance is more important than efficiency. A fan is a propeller with

1798-428: The aircraft maintain speed and altitude with the operative engines. Feathering also prevents windmilling , the turning of engine components by the propeller rotation forced by the slipstream; windmilling can damage the engine, start a fire, or cause structural damage to the aircraft. Most feathering systems for reciprocating engines sense a drop in oil pressure and move the blades toward the feather position, and require

1860-501: The aircraft was generally underpowered. Its quite heavy engines (weighing about 490 pounds (220 kg) each), had an output of only 250 hp (190 kW) each. By comparison, later modifications or rebuilt aircraft had as much as 50% more power (in the case of the Saunders ST-27). Unlike the Dove, the Heron came with a fixed undercarriage and no nosewheel steering, which simplified maintenance, but reduced top speed. Secondly,

1922-405: The airflow to stop rotation of the propeller and reduce drag when the engine fails or is deliberately shut down. This is called feathering , a term borrowed from rowing . On single-engined aircraft, whether a powered glider or turbine-powered aircraft, the effect is to increase the gliding distance. On a multi-engine aircraft, feathering the propeller on an inoperative engine reduces drag, and helps

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1984-399: The aisle and large windows were also provided. Baggage was stored in an aft compartment with an additional smaller area in the nose. A few peculiarities appeared; passengers who filled the aft rows first would find that the Heron gently "sat down" on its rear skid. Pilots and ground crews soon added a tail brace to prevent the aircraft from sitting awkwardly on its tail. Performance throughout

2046-410: The angle of attack of the blade gradually and therefore produce uniform lift from the hub to the tip. The greatest angle of incidence, or the highest pitch, is at the hub while the smallest angle of incidence or smallest pitch is at the tip. A propeller blade designed with the same angle of incidence throughout its entire length would be inefficient because as airspeed increases in flight, the portion near

2108-407: The blade pitch in order to maintain a constant engine speed for any given power control setting. Constant-speed propellers allow the pilot to set a rotational speed according to the need for maximum engine power or maximum efficiency, and a propeller governor acts as a closed-loop controller to vary propeller pitch angle as required to maintain the selected engine speed. In most aircraft this system

2170-440: The blade rotation direction) and Φ is the blade pitch angle. Very small pitch and helix angles give a good performance against resistance but provide little thrust, while larger angles have the opposite effect. The best helix angle is when the blade is acting as a wing producing much more lift than drag. However, 'lift-and-drag' is only one way to express the aerodynamic force on the blades. To explain aircraft and engine performance

2232-403: The blade tips approach the speed of sound. The maximum relative velocity is kept as low as possible by careful control of pitch to allow the blades to have large helix angles. A large number of blades are used to reduce work per blade and so circulation strength. Contra-rotating propellers are used. The propellers designed are more efficient than turbo-fans and their cruising speed (Mach 0.7–0.85)

2294-496: The controls on 10 May 1950. The aircraft was unpainted at the time, and after 100 hours of testing was introduced to the public on 8 September 1950 at the Farnborough Airshow , still glistening in its polished metal state. By November, the prototype had received its formal British Certificate of Airworthiness and had flown to Khartoum and Nairobi for tropical trials. The prototype was then painted and fitted out as

2356-467: The dream of flight. The twisted airfoil (aerofoil) shape of an aircraft propeller was pioneered by the Wright brothers. While some earlier engineers had attempted to model air propellers on marine propellers , the Wright Brothers realized that a propeller is essentially the same as a wing , and were able to use data from their earlier wind tunnel experiments on wings, introducing a twist along

2418-433: The duct needs to be shaped in a different manner than one for higher speed flight. More air is taken in and the fan therefore operates at an efficiency equivalent to a larger un-ducted propeller. Noise is also reduced by the ducting and should a blade become detached the duct would help contain the damage. However the duct adds weight, cost, complexity and (to a certain degree) drag. Lycoming O-540 The Lycoming O-540

2480-575: The duct, its speed is reduced while its pressure and temperature increase. If the aircraft is at a high subsonic speed this creates two advantages: the air enters the fan at a lower Mach speed; and the higher temperature increases the local speed of sound. While there is a loss in efficiency as the fan is drawing on a smaller area of the free stream and so using less air, this is balanced by the ducted fan retaining efficiency at higher speeds where conventional propeller efficiency would be poor. A ducted fan or propeller also has certain benefits at lower speeds but

2542-431: The feathering process or the feathering process may be automatic. Accidental feathering is dangerous and can result in an aerodynamic stall ; as seen for example with Yeti Airlines Flight 691 which crashed during approach due to accidental feathering. The propellers on some aircraft can operate with a negative blade pitch angle, and thus reverse the thrust from the propeller. This is known as Beta Pitch. Reverse thrust

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2604-463: The front was a tractor . Later the term 'pusher' became adopted for the rear-mounted device in contrast to the tractor configuration and both became referred to as 'propellers' or 'airscrews'. The understanding of low speed propeller aerodynamics was fairly complete by the 1920s, but later requirements to handle more power in a smaller diameter have made the problem more complex. Propeller research for National Advisory Committee for Aeronautics (NACA)

2666-574: The fuselage – clockwise on the left engine and counterclockwise on the right – however, there are exceptions (especially during World War II ) such as the P-38 Lightning which turned "outwards" (counterclockwise on the left engine and clockwise on the right) away from the fuselage from the WW II years, and the Airbus A400 whose inboard and outboard engines turn in opposite directions even on

2728-414: The hub would have a negative AOA while the blade tip would be stalled. There have been efforts to develop propellers and propfans for aircraft at high subsonic speeds. The 'fix' is similar to that of transonic wing design. Thin blade sections are used and the blades are swept back in a scimitar shape ( scimitar propeller ) in a manner similar to wing sweepback, so as to delay the onset of shockwaves as

2790-519: The ideas inherent to rotary wing aircraft. Designs similar to the Chinese helicopter toy appeared in Renaissance paintings and other works. It was not until the early 1480s, when Leonardo da Vinci created a design for a machine that could be described as an "aerial screw" , that any recorded advancement was made towards vertical flight. His notes suggested that he built small flying models, but there were no indications for any provision to stop

2852-400: The length of the blades. This was necessary to maintain a more uniform angle of attack of the blade along its length. Their original propeller blades had an efficiency of about 82%, compared to 90% for a modern (2010) small general aviation propeller, the 3-blade McCauley used on a Beechcraft Bonanza aircraft. Roper quotes 90% for a propeller for a human-powered aircraft. Mahogany was

2914-634: The lethargic four-engine arrangement, a stretched fuselage, the shape of the windows changed and the wingtips squared instead of rounded. A De Havilland Heron, registration G-AOXL, is preserved on stilts outside Airport House (which incorporated the Croydon Aerodrome control tower) on Purley Way, Croydon, Greater London Data from De Havilland Aircraft since 1909 General characteristics Performance Related development Aircraft of comparable role, configuration, and era Propeller (aircraft) The propeller attaches to

2976-616: The lightweight aluminium alloy wingspars were prone to constant cracking due to the heavy loading on the wing caused by the overweight engines and rough landings on unpaved runways. NAC resolved this by replacing the aluminium spars with heavier steel spars, reducing the performance of the Heron Series 1A (re-classified 1B) to uneconomic levels for the services required of them in New Zealand. NAC disposed of them in 1957. After 51 Series 1 aircraft had been built, production switched to

3038-432: The other wing to balance out the torque and p-factor effects. They are sometimes referred to as "handed" propellers since there are left hand and right hand versions of each prop. Generally, the propellers on both engines of most conventional twin-engined aircraft spin clockwise (as viewed from the rear of the aircraft). To eliminate the critical engine problem, counter-rotating propellers usually turn "inwards" towards

3100-417: The pilot to pull the propeller control back to disengage the high-pitch stop pins before the engine reaches idle RPM . Turboprop control systems usually use a negative torque sensor in the reduction gearbox, which moves the blades toward feather when the engine is no longer providing power to the propeller. Depending on design, the pilot may have to push a button to override the high-pitch stops and complete

3162-484: The power source's driveshaft either directly or through reduction gearing . Propellers can be made from wood, metal or composite materials . Propellers are most suitable for use at subsonic airspeeds generally below about 480 mph (770 km/h), although supersonic speeds were achieved in the McDonnell XF-88B experimental propeller-equipped aircraft. Supersonic tip-speeds are used in some aircraft like

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3224-561: The propeller blades, giving maximum efficiency throughout the flight regime. This reduces fuel usage. Only by maximising propeller efficiency at high speeds can the highest possible speed be achieved. Effective angle of attack decreases as airspeed increases, so a coarser pitch is required at high airspeeds. The requirement for pitch variation is shown by the propeller performance during the Schneider Trophy competition in 1931. The Fairey Aviation Company fixed-pitch propeller used

3286-424: The rotor from making the craft rotate. As scientific knowledge increased and became more accepted, man continued to pursue the idea of vertical flight. Many of these later models and machines would more closely resemble the ancient bamboo flying top with spinning wings, rather than Leonardo's screw. In July 1754, Russian Mikhail Lomonosov had developed a small coaxial modeled after the Chinese top but powered by

3348-411: The same force is expressed slightly differently in terms of thrust and torque since the required output of the propeller is thrust. Thrust and torque are the basis of the definition for the efficiency of the propeller as shown below. The advance ratio of a propeller is similar to the angle of attack of a wing. A propeller's efficiency is determined by Propellers are similar in aerofoil section to

3410-410: The same wing. A contra-rotating propeller or contra-prop places two counter-rotating propellers on concentric drive shafts so that one sits immediately 'downstream' of the other propeller. This provides the benefits of counter-rotating propellers for a single powerplant. The forward propeller provides the majority of the thrust, while the rear propeller also recovers energy lost in the swirling motion of

3472-445: The wood preferred for propellers through World War I , but wartime shortages encouraged use of walnut , oak , cherry and ash . Alberto Santos Dumont was another early pioneer, having designed propellers before the Wright Brothers for his airships . He applied the knowledge he gained from experiences with airships to make a propeller with a steel shaft and aluminium blades for his 14 bis biplane in 1906. Some of his designs used

3534-433: Was Prinair , of Puerto Rico, which replaced the Gipsy Queens with Continental IO-520 engines. Prinair also considerably stretched Heron 2 N574PR to allow extra passengers to be carried. Connellan Airways also converted its Herons, using Riley kits. When available aircraft reached the end of their service lives, the engine conversions gave the elderly airliner a new lease of life as a number of examples were converted in

3596-510: Was a VIP version. In service, the Heron was generally well received by flight crews and passengers who appreciated the additional safety factor of the four engines. At a time when smaller airliners were still rare in isolated and remote regions, the DH.114 could provide reliable and comfortable service with seating for 17 passengers, in individual seats on either side of the aisle. With its larger fuselage, passengers could stand up whilst moving down

3658-644: Was also exported to about 30 countries. Herons later formed the basis for various conversions, such as the Riley Turbo Skyliner and the Saunders ST-27 and ST-28 . In the closing stages of the Second World War , the aircraft manufacturer de Havilland began development of a new small twin-engined passenger aircraft, the DH 104 Dove, intended as a replacement for the earlier Dragon Rapide and which soon proved to be successful. As

3720-616: Was directed by William F. Durand from 1916. Parameters measured included propeller efficiency, thrust developed, and power absorbed. While a propeller may be tested in a wind tunnel , its performance in free-flight might differ. At the Langley Memorial Aeronautical Laboratory , E. P. Leslie used Vought VE-7s with Wright E-4 engines for data on free-flight, while Durand used reduced size, with similar shape, for wind tunnel data. Their results were published in 1926 as NACA report #220. Lowry quotes

3782-469: Was on rugged simplicity to produce an economical aircraft for short- to medium-stage routes in isolated and remote areas which did not possess modern airports. The Heron was designed with a fixed undercarriage and Gipsy Queen 30 engines, which lacked potentially unreliable reduction gearboxes and superchargers . The Heron prototype registered to the de Havilland Aircraft Company, Hatfield , UK, as G-ALZL undertook its first flight with Geoffrey Pike at

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3844-447: Was partially stalled on take-off and up to 160 mph (260 km/h) on its way up to a top speed of 407.5 mph (655.8 km/h). The very wide speed range was achieved because some of the usual requirements for aircraft performance did not apply. There was no compromise on top-speed efficiency, the take-off distance was not restricted to available runway length and there was no climb requirement. The variable pitch blades used on

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