Misplaced Pages

#785214

61-512: The RMI-1 was a low wing, twin-engined aircraft with two turboprop Cs-1 engines slung under the wings. It was designed to have a crew of two or three. The tail section was of the conventional type with a single vertical stabilizer . Data from Repülő Muszaki Intézet Varga RMI-1/ X / H General characteristics Performance Hungarian military aircraft from the same era Aircraft of comparable role, configuration, and era Related lists Turboprop A turboprop

122-406: A constant-speed propeller increase their pitch as aircraft speed increases. Another benefit of this type of propeller is that it can also be used to generate reverse thrust to reduce stopping distance on the runway. Additionally, in the event of an engine failure, the propeller can be feathered , thus minimizing the drag of the non-functioning propeller. While the power turbine may be integral with

183-416: A large amount of air by a small degree than a small amount of air by a large degree, a low disc loading (thrust per unit disc area) increases the aircraft's energy efficiency , and this reduces the fuel use. Propellers work well until the flight speed of the aircraft is high enough that the airflow past the blade tips reaches the speed of sound. Beyond that speed, the proportion of the power that drives

244-426: A special ball-bearing helicoidal ramp at the root of the blades for easy operation. Walter S Hoover's patent for a variable pitch propeller was filed in the U.S. Patent Office in 1934. Several designs were tried, including a small bladder of pressurized air in the propeller hub providing the necessary force to resist a spring that would drive the blades from fine pitch (take-off) to coarse pitch (level cruising). At

305-570: A suitable airspeed a disk on the front of the spinner would press sufficiently on the bladder's air-release valve to relieve the pressure and allow the spring to drive the propeller to coarse pitch. These "pneumatic" propellers were fitted on the de Havilland DH.88 Comet aircraft, winner of the famed long-distance 1934 MacRobertson Air Race and in the Caudron C.460 winner of the 1936 National Air Races , flown by Michel Détroyat  [ fr ] . Use of these pneumatic propellers required presetting

366-575: A test-bed not intended for production. It first flew on 20 September 1945. From their experience with the Trent, Rolls-Royce developed the Rolls-Royce Clyde , the first turboprop engine to receive a type certificate for military and civil use, and the Dart , which became one of the most reliable turboprop engines ever built. Dart production continued for more than fifty years. The Dart-powered Vickers Viscount

427-640: A variable-stroke pump) in 1924 and presented a paper on the subject before the Royal Aeronautical Society in 1928; it met with scepticism as to its utility. The propeller had been developed with Gloster Aircraft Company as the Gloster Hele-Shaw Beacham Variable Pitch propeller and was demonstrated on a Gloster Grebe , where it was used to maintain a near-constant RPM. The French firm Ratier produced variable-pitch propellers of various designs from 1928 onwards, relying on

488-429: Is a turbine engine that drives an aircraft propeller . A turboprop consists of an intake , reduction gearbox , compressor , combustor , turbine , and a propelling nozzle . Air enters the intake and is compressed by the compressor. Fuel is then added to the compressed air in the combustor, where the fuel-air mixture then combusts . The hot combustion gases expand through the turbine stages, generating power at

549-404: Is a variable-pitch propeller that automatically changes its blade pitch in order to maintain a chosen rotational speed, regardless of the operational conditions of the aircraft. This is achieved by use of a constant-speed unit (CSU) or propeller governor , which automatically changes the propeller's blade pitch . Most engines produce their maximum power in a narrow speed band. The CSU allows

610-533: Is credited in Canada for creating the first variable pitch propeller in 1918. The French aircraft firm Levasseur displayed a variable-pitch propeller at the 1921 Paris Air Show . The firm claimed that the French government had tested the device in a ten-hour run and that it could change pitch at any engine RPM. Dr Henry Selby Hele-Shaw and T.E. Beacham patented a hydraulically-operated variable-pitch propeller (based on

671-466: Is identical to the centrifugal governor used by James Watt to control the speed of steam engines . Eccentric weights were set up near or in the spinner, held in by a spring. When the propeller reached a certain RPM, centrifugal force would cause the weights to swing outwards, which would drive a mechanism that twisted the propeller into a steeper pitch. When the propeller slowed, the RPM would decrease enough for

SECTION 10

#1732837515786

732-418: Is identical to the centrifugal governor used by James Watt to limit the speed of steam engines . Eccentric weights were set up near or in the spinner, held in by a spring. When the propeller reached a certain RPM, centrifugal force would cause the weights to swing outwards, which would drive a mechanism that twisted the propeller into a steeper pitch. When the propeller slowed, the RPM would decrease enough for

793-482: Is normally a constant-speed (variable pitch) propeller type similar to that used with larger aircraft reciprocating engines , except that the propeller-control requirements are very different. Due to the turbine engine's slow response to power inputs, particularly at low speeds, the propeller has a greater range of selected travel in order to make rapid thrust changes, notably for taxi, reverse, and other ground operations. The propeller has 2 modes, Alpha and Beta. Alpha

854-399: Is pumped through the propeller shaft by the governor to push on a piston that drives the mechanism to change pitch. The flow of oil and the pitch are controlled by a governor, consisting of a gear type pump speeder spring, flyweights, and a pilot valve . The gear type pump takes engine oil pressure and turns it to a higher pressure which is in turn controlled in an out of the propeller hub by

915-494: Is sacrificed in favor of shaft power, which is obtained by extracting additional power (beyond that necessary to drive the compressor) from turbine expansion. Owing to the additional expansion in the turbine system, the residual energy in the exhaust jet is low. Consequently, the exhaust jet produces about 10% of the total thrust. A higher proportion of the thrust comes from the propeller at low speeds and less at higher speeds. Turboprops have bypass ratios of 50–100, although

976-404: Is the mode for all flight operations including takeoff. Beta, a mode typically consisting of zero to negative thrust, is used for all ground operations aside from takeoff. The Beta mode is further broken down into 2 additional modes, Beta for taxi and Beta plus power. Beta for taxi as the name implies is used for taxi operations and consists of all pitch ranges from the lowest alpha range pitch, all

1037-740: The Hamilton Standard Division of the United Aircraft Company , engineer Frank W. Caldwell developed a hydraulic design, which led to the award of the Collier Trophy of 1933. de Havilland subsequently bought up the rights to produce Hamilton propellers in the UK, while Rolls-Royce and Bristol Engines formed the British company Rotol in 1937 to produce their own designs. The French company of Pierre Levasseur and Smith Engineering Co. in

1098-616: The P-3 Orion , and the C-130 Hercules military transport aircraft. The first turbine-powered, shaft-driven helicopter was the Kaman K-225 , a development of Charles Kaman 's K-125 synchropter , which used a Boeing T50 turboshaft engine to power it on 11 December 1951. December 1963 saw the first delivery of Pratt & Whitney Canada's PT6 turboprop engine for the then Beechcraft 87, soon to become Beechcraft King Air . 1964 saw

1159-830: The Piper Meridian , Socata TBM , Pilatus PC-12 , Piaggio P.180 Avanti , Beechcraft King Air and Super King Air . In April 2017, there were 14,311 business turboprops in the worldwide fleet. Between 2012 and 2016, the ATSB observed 417 events with turboprop aircraft, 83 per year, over 1.4 million flight hours: 2.2 per 10,000 hours. Three were "high risk" involving engine malfunction and unplanned landing in single‑engine Cessna 208 Caravans , four "medium risk" and 96% "low risk". Two occurrences resulted in minor injuries due to engine malfunction and terrain collision in agricultural aircraft and five accidents involved aerial work: four in agriculture and one in an air ambulance . Jane's All

1220-590: The Tupolev Tu-114 can reach 470 kn (870 km/h; 540 mph). Large military aircraft , like the Tupolev Tu-95 , and civil aircraft , such as the Lockheed L-188 Electra , were also turboprop powered. The Airbus A400M is powered by four Europrop TP400 engines, which are the second most powerful turboprop engines ever produced, after the 11 MW (15,000 hp) Kuznetsov NK-12 . In 2017,

1281-456: The CSU will typically use oil pressure to decrease the pitch. That way, if the CSU fails, that propeller will automatically feather, reducing drag, while the aircraft continues to be flown on the good engine. An "unfeathering accumulator " will enable such a propeller to return to fine pitch for an in-flight engine restart. Operation in a single engine reciprocating aircraft is as follows: Engine oil

SECTION 20

#1732837515786

1342-596: The Continental and Lycoming engines fitted to light aircraft. In aircraft without a constant speed unit (CSU), the pilot controls the propeller blade pitch manually, using oil pressure. Alternatively, or additionally, centrifugal weights may be attached directly to the propeller as in the Yakovlev Yak-52 . The first attempts at constant-speed propellers were called counterweight propellers, which were driven by mechanisms that operated on centrifugal force . Their operation

1403-519: The Soviet Union had the technology to create the airframe for a jet-powered strategic bomber comparable to Boeing's B-52 Stratofortress , they instead produced the Tupolev Tu-95 Bear, powered with four Kuznetsov NK-12 turboprops, mated to eight contra-rotating propellers (two per nacelle) with supersonic tip speeds to achieve maximum cruise speeds in excess of 575 mph, faster than many of

1464-645: The United States also developed controllable-pitch propellers. Wiley Post (1898–1935) used Smith propellers on some of his flights. Another electrically-operated mechanism was developed by Wallace Turnbull and refined by the Curtiss-Wright Corporation . This was first tested in on June 6, 1927, at Camp Borden, Ontario, Canada and received a patent in 1929 ( U.S. patent 1,828,348 ). Some pilots in World War II (1939–1945) favoured it, because even when

1525-530: The United States. A number of early aviation pioneers, including A. V. Roe and Louis Breguet , used propellers which could be adjusted while the aircraft was on the ground . This was also the case during World War I with one testbed example, "R.30/16" , of the Zeppelin-Staaken R.VI German four-engined heavy bomber. In 1919 L. E. Baynes patented the first automatic variable-pitch airscrew. Wallace Rupert Turnbull of Saint John, New Brunswick, Canada

1586-448: The World's Aircraft . 2005–2006. Propeller governor In aeronautics , a variable-pitch propeller is a type of propeller (airscrew) with blades that can be rotated around their long axis to change the blade pitch . A controllable-pitch propeller is one where the pitch is controlled manually by the pilot. Alternatively, a constant-speed propeller is one where the pilot sets

1647-458: The aircraft can continue flying using the other engine(s). In a single-engine aircraft, if the engine fails, feathering the propeller will reduce drag and increase glide distance, providing the pilot with more options for the location of a forced landing . Three methods are used to vary the pitch: oil pressure, centrifugal weights, or electro-mechanical control. Engine oil pressure is the usual mechanism used in commercial propeller aircraft and

1708-400: The blade will be at too low an angle of attack. In contrast, a propeller set for good cruise performance may stall at low speeds, because the angle of attack is too high. A propeller with adjustable blade angle is more efficient over a range of conditions. A propeller with variable pitch can have a nearly constant efficiency over a range of airspeeds. A shallower angle of attack requires

1769-417: The compressor intake is at the aft of the engine, and the exhaust is situated forward, reducing the distance between the turbine and the propeller. Unlike the small-diameter fans used in turbofan engines, the propeller has a large diameter that lets it accelerate a large volume of air. This permits a lower airstream velocity for a given amount of thrust. Since it is more efficient at low speeds to accelerate

1830-459: The control system. The turboprop system consists of 3 propeller governors , a governor, and overspeed governor, and a fuel-topping governor. The governor works in much the same way a reciprocating engine propeller governor works, though a turboprop governor may incorporate beta control valve or beta lift rod for beta operation and is typically located in the 12 o'clock position. There are also other governors that are included in addition depending on

1891-435: The desired engine speed ( RPM ), and the blade pitch is controlled automatically without the pilot's intervention so that the rotational speed remains constant. The device which controls the propeller pitch and thus speed is called a propeller governor or constant speed unit . Reversible propellers are those where the pitch can be set to negative values. This creates reverse thrust for braking or going backwards without

Varga RMI-1 X/H - Misplaced Pages Continue

1952-423: The engine to operate in its most economical range of rotational speeds , regardless of whether the aircraft is taking off or cruising. The CSU can be said to be to an aircraft what the continuously variable transmission is to the motorcar: the engine can be kept running at its optimum speed, regardless of the speed at which the aircraft is flying through the air. The CSU also allows aircraft engine designers to keep

2013-493: The first jet aircraft and comparable to jet cruising speeds for most missions. The Bear would serve as their most successful long-range combat and surveillance aircraft and symbol of Soviet power projection through to the end of the 20th century. The USA used turboprop engines with contra-rotating propellers, such as the Allison T40 , on some experimental aircraft during the 1950s. The T40-powered Convair R3Y Tradewind flying-boat

2074-546: The first deliveries of the Garrett AiResearch TPE331 , (now owned by Honeywell Aerospace ) on the Mitsubishi MU-2 , making it the fastest turboprop aircraft for that year. In contrast to turbofans , turboprops are most efficient at flight speeds below 725 km/h (450 mph; 390 knots) because the jet velocity of the propeller (and exhaust) is relatively low. Modern turboprop airliners operate at nearly

2135-504: The flyweights to move inward due to a lack in centrifugal force, and tension will be released from the speeder spring, porting oil out of the propeller hub, decreasing pitch and increasing rpm. This process usually takes place frequently throughout flight. A pilot requires some additional training and, in most jurisdictions, a formal sign-off before being allowed to fly aircraft fitted with a CSU. CSUs are not allowed to be fitted to aircraft certified under light-sport aircraft regulations in

2196-558: The gas generator section, many turboprops today feature a free power turbine on a separate coaxial shaft. This enables the propeller to rotate freely, independent of compressor speed. Alan Arnold Griffith had published a paper on compressor design in 1926. Subsequent work at the Royal Aircraft Establishment investigated axial compressor-based designs that would drive a propeller. From 1929, Frank Whittle began work on centrifugal compressor-based designs that would use all

2257-455: The gas power produced by the engine for jet thrust. The world's first turboprop was designed by the Hungarian mechanical engineer György Jendrassik . Jendrassik published a turboprop idea in 1928, and on 12 March 1929 he patented his invention. In 1938, he built a small-scale (100 Hp; 74.6 kW) experimental gas turbine. The larger Jendrassik Cs-1 , with a predicted output of 1,000 bhp,

2318-511: The ignition system simple: the automatic spark advance seen in motor vehicle engines is simplified, because aircraft engines run at a roughly constant RPM. Virtually all high-performance propeller-driven aircraft have constant-speed propellers, as they greatly improve fuel efficiency and performance, especially at high altitude. The first attempts at constant-speed propellers were called counterweight propellers, which were driven by mechanisms that operated on centrifugal force . Their operation

2379-403: The least torque, but the highest RPM , because the propeller is not moving very much air with each revolution. This is similar to a car operating in low gear . When the motorist reaches cruising speed, they will slow down the engine by shifting into a higher gear, while still producing enough power to keep the vehicle moving. This is accomplished in an airplane by increasing the angle of attack of

2440-406: The model, such as an overspeed and fuel topping governor on a Pratt & Whitney Canada PT6 , and an under-speed governor on a Honeywell TPE331 . The turboprop is also distinguished from other kinds of turbine engine in that the fuel control unit is connected to the governor to help dictate power. To make the engine more compact, reverse airflow can be used. On a reverse-flow turboprop engine,

2501-657: The most widespread turboprop airliners in service were the ATR 42 / 72 (950 aircraft), Bombardier Q400 (506), De Havilland Canada Dash 8 -100/200/300 (374), Beechcraft 1900 (328), de Havilland Canada DHC-6 Twin Otter (270), Saab 340 (225). Less widespread and older airliners include the BAe Jetstream 31 , Embraer EMB 120 Brasilia , Fairchild Swearingen Metroliner , Dornier 328 , Saab 2000 , Xian MA60 , MA600 and MA700 , Fokker 27 and 50 . Turboprop business aircraft include

Varga RMI-1 X/H - Misplaced Pages Continue

2562-418: The need to change the direction of shaft revolution. While some aircraft have ground-adjustable propellers , these are not considered variable-pitch. These are typically found only on light aircraft and microlights . When an aircraft is stationary with the propeller spinning (in calm air), the relative wind vector for each propeller blade is from the side. However, as the aircraft starts to move forward,

2623-416: The pilot not being able to see out of the rear of the aircraft for backing and the amount of debris reverse stirs up, manufacturers will often limit the speeds beta plus power may be used and restrict its use on unimproved runways. Feathering of these propellers is performed by the propeller control lever. The constant-speed propeller is distinguished from the reciprocating engine constant-speed propeller by

2684-423: The pilot valve, which is connected to the flyweights, and a seeder spring which presses against the flyweights. The tension of the spring is set by the propeller control lever, which sets the RPM. The governor will maintain that RPM setting until an engine overspeed or underspeed condition exists. When an overspeed condition occurs, the propeller begins to rotate faster than the desired RPM setting. This would occur as

2745-428: The plane descends and airspeed increases. The flyweights begin to pull outward due to centrifugal force which further compresses the speeder spring, which in turn ports oil to the hub back to the engine, decreasing engine rpm and increasing pitch. When an underspeed condition occurs, such as a climb with a loss of airspeed, the opposite takes place. The airspeed decreases, causing the propeller to slow down. This will cause

2806-403: The point of exhaust. Some of the power generated by the turbine is used to drive the compressor and electric generator . The gases are then exhausted from the turbine. In contrast to a turbojet or turbofan , the engine's exhaust gases do not provide enough power to create significant thrust, since almost all of the engine's power is used to drive the propeller. Exhaust thrust in a turboprop

2867-494: The propeller that is converted to propeller thrust falls dramatically. For this reason turboprop engines are not commonly used on aircraft that fly faster than 0.6–0.7 Mach , with some exceptions such as the Tupolev Tu-95 . However, propfan engines, which are very similar to turboprop engines, can cruise at flight speeds approaching 0.75 Mach. To maintain propeller efficiency across a wide range of airspeeds, turboprops use constant-speed (variable-pitch) propellers. The blades of

2928-601: The propeller to fine pitch prior to take-off. This was done by pressurizing the bladder with a bicycle pump, hence the whimsical nickname Gonfleurs d'hélices (prop-inflater boys) given to the aircraft ground-mechanics in France up to this day. A Gloster Hele-Shaw hydraulic propeller was shown at the 1929 International Aero Exhibition at Olympia. American Tom Hamilton of the Hamilton Aero Manufacturing Company saw it and, on returning home, patented it there. As

2989-477: The propeller. This allows for propeller strike or similar damage to occur without damaging the gas generator and allowing for only the power section (turbine and gearbox) to be removed and replaced in such an event, and also allows for less stress on the start during engine ground starts. Whereas a fixed shaft has the gearbox and gas generator connected, such as on the Honeywell TPE331 . The propeller itself

3050-469: The propeller. This means that the propeller moves more air per revolution and allows the engine to spin slower while moving an equivalent volume of air, thus maintaining velocity. Another use of variable-pitch propellers is to feather the blades of the propeller, in order to reduce drag. This means to rotate the blades so that their leading edges face directly forwards. In a multi-engine aircraft, if one engine fails, it can be feathered to reduce drag so that

3111-446: The propulsion airflow is less clearly defined for propellers than for fans. The propeller is coupled to the turbine through a reduction gear that converts the high RPM /low torque output to low RPM/high torque. This can be of two primary designs, free-turbine and fixed. A free-turbine turboshaft found on the Pratt & Whitney Canada PT6 , where the gas generator is not connected to

SECTION 50

#1732837515786

3172-413: The relative wind vector comes increasingly from the front. The propeller blade pitch must be increased to maintain optimum angle of attack to the relative wind. The first propellers were fixed-pitch, but these propellers are not efficient over a range of conditions. If the propeller blade angle is set to give good takeoff and climb performance, the propeller will be inefficient in cruising flight because

3233-585: The same speed as small regional jet airliners but burn two-thirds of the fuel per passenger. Compared to piston engines, their greater power-to-weight ratio (which allows for shorter takeoffs) and reliability can offset their higher initial cost, maintenance and fuel consumption. As jet fuel can be easier to obtain than avgas in remote areas, turboprop-powered aircraft like the Cessna Caravan and Quest Kodiak are used as bush airplanes . Turboprop engines are generally used on small subsonic aircraft, but

3294-413: The spring to push the weights back in, realigning the propeller to the shallower pitch. Most CSUs use oil pressure to control propeller pitch. Typically, constant-speed units on a single-engine aircraft use oil pressure to increase the pitch. If the CSU fails, the propeller will automatically return to fine pitch, allowing the aircraft to be operated at lower speeds. By contrast, on a multi-engine aircraft,

3355-493: The spring to push the weights back in, realigning the propeller to the shallower pitch. Small, modern engines with a constant speed unit (CSU), such as the Rotax 912 , may use either the conventional hydraulic method or an electrical pitch control mechanism. Hydraulic operation can be too expensive and bulky for microlights . Instead, these may use propellers that are activated mechanically or electrically. A constant-speed propeller

3416-410: The way down to zero pitch, producing very little to zero-thrust and is typically accessed by moving the power lever to a beta for taxi range. Beta plus power is a reverse range and produces negative thrust, often used for landing on short runways where the aircraft would need to rapidly slow down, as well as backing operations and is accessed by moving the power lever below the beta for taxi range. Due to

3477-454: Was destroyed in a bombing raid. In 1941, the engine was abandoned due to war, and the factory converted to conventional engine production. The first mention of turboprop engines in the general public press was in the February 1944 issue of the British aviation publication Flight , which included a detailed cutaway drawing of what a possible future turboprop engine could look like. The drawing

3538-686: Was operated by the U.S. Navy for a short time. The first American turboprop engine was the General Electric XT31 , first used in the experimental Consolidated Vultee XP-81 . The XP-81 first flew in December 1945, the first aircraft to use a combination of turboprop and turbojet power. The technology of Allison's earlier T38 design evolved into the Allison T56 , used to power the Lockheed Electra airliner, its military maritime patrol derivative

3599-629: Was produced and tested at the Ganz Works in Budapest between 1937 and 1941. It was of axial-flow design with 15 compressor and 7 turbine stages, annular combustion chamber. First run in 1940, combustion problems limited its output to 400 bhp. Two Jendrassik Cs-1s were the engines for the world's first turboprop aircraft – the Varga RMI-1 X/H . This was a Hungarian fighter-bomber of WWII which had one model completed, but before its first flight it

3660-593: Was the first turboprop aircraft of any kind to go into production and sold in large numbers. It was also the first four-engined turboprop. Its first flight was on 16 July 1948. The world's first single engined turboprop aircraft was the Armstrong Siddeley Mamba -powered Boulton Paul Balliol , which first flew on 24 March 1948. The Soviet Union built on German World War II turboprop preliminary design work by Junkers Motorenwerke, while BMW, Heinkel-Hirth and Daimler-Benz also worked on projected designs. While

3721-481: Was very close to what the future Rolls-Royce Trent would look like. The first British turboprop engine was the Rolls-Royce RB.50 Trent , a converted Derwent II fitted with reduction gear and a Rotol 7 ft 11 in (2.41 m) five-bladed propeller. Two Trents were fitted to Gloster Meteor EE227 — the sole "Trent-Meteor" — which thus became the world's first turboprop-powered aircraft to fly, albeit as

SECTION 60

#1732837515786
#785214