Hiller switched to tip mounted ramjets but American Helicopter went on to develop the XA-8 under a U.S. Army contract. It first flew in 1952 and was known as the XH-26 Jet Jeep. It used XPJ49 pulsejets mounted at the rotor tips. The XH-26 met all its main design objectives but the Army cancelled the project because of the unacceptable level of noise of the pulsejets and the fact that the drag of the pulsejets at the rotor tips made autorotation landings very problematic.
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The high noise levels usually make them impractical for other than military and other similarly restricted applications.Jan Roskam, Chuan-Tau Edward Lan; Airplane aerodynamics and performance, DARcorporation: 1997, , 711 pages However, pulsejets are used on a large scale as industrial drying systems, and there has been a resurgence in studying these engines for applications such as high-output heating, biomass conversion, and alternative energy systems, as pulsejets can run on almost anything that burns, including particulate fuels such as sawdust or coal powder. Pulsejets have been used to power experimental helicopters, the engines being attached to the ends of the rotor blades. In providing power to helicopter rotors, pulsejets have the advantage over turbine or piston engines of not producing torque upon the fuselage since they don't apply force to the shaft, but push the tips.
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Pulsejets are used today in target drone aircraft, flying control line model aircraft (as well as radio-controlled aircraft), fog generators, and industrial drying and home heating equipment. Because pulsejets are an efficient and simple way to convert fuel into heat, experimenters are using them for new industrial applications such as biomass fuel conversion, and boiler and heater systems. Some experimenters continue to work on improved designs. The engines are difficult to integrate into commercial manned aircraft designs because of noise and vibration, though they excel on the smaller-scale unmanned vehicles.
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American soldier guarding a captured Heinkel He 162 Spatz. Model of pulsejet- powered He P.1077 Romeo. Pulsejets vibrated excessively and needed help to start. Model of Junkers EF 128, one of the last jet-powered projects before the fall of the Reich Focke-Wulf Volksjäger 2.
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The second type of pulsejet is known as the valveless pulsejet. Technically the term for this engine is the acoustic-type pulsejet, or aerodynamically valved pulsejet. Valveless pulsejets come in a number of shapes and sizes, with different designs being suited for different functions. A typical valveless engine will have one or more intake tubes, a combustion chamber section, and one or more exhaust tube sections.
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Originating in 1949, the XK5DG-1 first flew in 1950, and was tested at the Naval Air Test Center in Point Mugu, California. By 1952, however, the speed requirements for target drones had increased to the point that the KD5G was considered too slow for operational service, while pulsejets also lost efficiency quickly at higher altitudes; as a result the XK5G-1 project was cancelled.
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There are two basic types of pulsejets. The first is known as a valved or traditional pulsejet and it has a set of one-way valves through which the incoming air passes. When the air-fuel is ignited, these valves slam shut, which means that the hot gases can only leave through the engine's tailpipe, thus creating forward thrust. The cycle frequency is primarily dependent on the length of the engine.
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The behavior is difficult to model and to predict, and research is ongoing. As with conventional pulsejets, there are two main types of designs: valved and valveless. Designs with valves encounter the same difficult-to- resolve wear issues encountered with their pulsejet equivalents. Valveless designs typically rely on abnormalities in the air flow to ensure a one-way flow, and are very hard to achieve in a regular DDT.
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Rotor-tip propulsion has been claimed to reduce the cost of production of rotary-wing craft to 1/10 of that for conventional powered rotary-wing aircraft. Pulsejets have also been used in both control-line and radio- controlled model aircraft. The speed record for control-line pulsejet-powered model aircraft is greater than 200 miles per hour (323 km/h). The speed of a free-flying radio-controlled pulsejet is limited by the engine's intake design.
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By properly 'tuning' the system (by designing the engine dimensions properly), a resonating combustion process can be achieved. While some valveless engines are known for being extremely fuel-hungry, other designs use significantly less fuel than a valved pulsejet, and a properly designed system with advanced components and techniques can rival or exceed the fuel efficiency of small turbojet engines. In 1909, Georges Marconnet developed the first pulsating combustor without valves. It was the grandfather of all valveless pulsejets.
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Reaction engines generate the thrust to propel an aircraft by ejecting the exhaust gases at high velocity from the engine, the resultant reaction of forces driving the aircraft forwards. The most common reaction propulsion engines flown are turbojets, turbofans and rockets. Other types such as pulsejets, ramjets, scramjets and pulse detonation engines have also flown. In jet engines the oxygen necessary for fuel combustion comes from the air, while rockets carry oxygen in some form as part of the fuel load, permitting their use in space.
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The Argus Company began work based on Schmidt's work. Other German manufacturers working on similar pulsejets and flying bombs were The Askania Company, Robert Lusser of Fieseler, Dr. Fritz Gosslau of Argus and the Siemens company, which were all combined to work on the V-1. With Schmidt now working for Argus, the pulsejet was perfected and was officially known by its RLM designation as the Argus As 109-014. The first unpowered drop occurred at Peenemünde on 28 October 1942 and the first powered flight on 10 December 1942.
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In 1942, the RLM had ordered Heinkel to abandon the HeS 8 and HeS 30 to focus all development on a follow- on engine, the HeS 011, a more advanced and problematic design. Meanwhile, the first He 280 prototype was re-equipped with pulsejets and towed aloft to test them. Bad weather caused the aircraft to ice up, and before the jets could be tested pilot Helmut Schenk became the first person to put an ejection seat to use. The seat worked perfectly, but the aircraft was lost and never found.
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Retrieved: 23 July 2010. Ramjets can be particularly useful in applications requiring a small and simple engine for high speed use, such as missiles, while weapon designers are looking to use ramjet technology in artillery shells to give added range: it is anticipated that a 120-mm mortar shell, if assisted by a ramjet, could attain a range of . They have also been used successfully, though not efficiently, as tip jets on helicopter rotors. Ramjets are frequently confused with pulsejets, which use an intermittent combustion, but ramjets employ a continuous combustion process, and are a quite distinct type of jet engine.
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The engine produced of static thrust and approximately in flight. Ignition in the As 014 was provided by a single automotive spark plug, mounted approximately behind the front- mounted valve array. The spark only operated for the start sequence for the engine; the Argus As 014, like all pulsejets, did not require ignition coils or magnetos for ignition — the ignition source being the tail of the preceding fireball during the run. The engine casing did not provide sufficient heat to cause diesel-type ignition of the fuel, as there is insignificant compression within a pulsejet engine.
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The aircraft was designed as Messerschmitt project P.1073 in 1941, and was originally conceived as a cheap and simple escort fighter, to either be towed aloft by a Heinkel He 177 heavy bomber or Junkers Ju 388 using a semi-rigid bar (the Deichselschlepp, which was also considered for towing winged auxiliary fuel tanks), or carried on a Me 264 in a Mistel type fashion.Me.328 (in Russian) Three versions were proposed: an unpowered glider, a version powered by Argus pulsejets, and a version powered by a Jumo 004 turbojet.Wood & Ford, pp. 41-42 Its construction was to be mainly of wood.
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Valveless pulsejet engines have no moving parts and use only their geometry to control the flow of exhaust out of the engine. Valveless pulsejets expel exhaust out of both the intakes and the exhaust, but the majority of the force produced leaves through the wider cross section of the exhaust. The larger amount of mass leaving the wider exhaust has more inertia than the backwards flow out of the intake, allowing it to produce a partial vacuum for a fraction of a second after each detonation, reversing the flow of the intake to its proper direction, and therefore ingesting more air and fuel. This happens dozens of times per second.
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Test pilot Hanna Reitsch carried out a test programme on the two prototypes of the glider version, releasing from its carrier aircraft at altitudes of . Ground launches, using both cable-type catapults and rocket- assisted carriages on rails were also successful. Even with a reduced wingspan the aircraft had a very satisfactory performance, and it was planned to build up to 1,000 for use as disposable bombers to be flown by volunteers from 5/KG200, the so-called Leonidas Squadron. Seven prototypes powered by two Argus As 014 pulsejets, as used on the V-1 flying bomb were built by glider manufacturer, Jacobs-Schweyer of Darmstadt.
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Project SQUID was a United States defense effort post-World War II effort to develop and improve pulsejet and rocket engines, run by the Office of Naval Research. It was started by discovery of the German Argus As 014 pulsejet used on the V1 buzzbomb, which was reverse-engineered as the Republic Ford JB-2, the first American cruise missile. It produced extensive research in the areas of computational flow dynamics , and was used to improve the design of the experimental Fairchild XH-26 Jeep Jet, which used pulsejets on the rotor tips instead of a central engine. The research led to development of pulse detonation engines, which have been suggested as the engines powering the postulated Aurora spyplane.
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Furthermore, it was already well known by the time the Miniaturjäger competition was announced that, as they didn't produce enough power at low speeds for takeoff, the Argus pulsejets were unsuitable for manned aircraft that would have to takeoff unassisted. Since additional launch schemes would have to be added to the project, such as towplanes, catapults or rocket boosters, the goal of the program would be defeated as complexity and expense would be far higher. Thus the Miniaturjäger project never saw mass-production, being abandoned by December 1944. Even so, aircraft manufacturers Heinkel, Blohm & Voss and Junkers came up with light fighter designs using a strict minimum of materials before that date.
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It was intended for use as a fighter aircraft, to be armed with two 20 mm MG 151/20 cannons. However, during static testing it soon became apparent that the same problems which were to plague the early development of the V-1 flying bomb - namely, excessive vibration - would make the project difficult to bring to a successful conclusion, and the manned flight programme was suspended in mid-1944, after only a few test flights had been made. Some sources say two prototypes were destroyed by inflight structural failure caused by vibration. Despite this, planning continued, and a version was projected, which would use four Argus pulsejets, two mounted below the wings in addition to the original pair mounted above the rear fuselage.
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A wide variety of roles were suggested for the aircraft, ranging from a point-defence interceptor, to a version with folding wings and twin pulsejets to be launched from a catapult on a U-Boat, to a ground-attack aircraft. Various modifications to the prototypes were made to evaluate their suitability for these missions, and different engine configurations were tested. Despite all this, the vibration problem simply could not be overcome and the program was abandoned in early 1944, even as production facilities were being readied to construct the aircraft at the Jacobs Schweyer sailplane factory in Darmstadt. According to Thomas Powers's book Heisenberg's War the idea of using the Me 328 as a parasite bomber within the Amerika Bomber program was explored.
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Valved pulsejet engines use a mechanical valve to control the flow of expanding exhaust, forcing the hot gas to go out of the back of the engine through the tailpipe only, and allow fresh air and more fuel to enter through the intake as the inertia of the escaping exhaust creates a partial vacuum for a fraction of a second after each detonation. This draws in additional air and fuel between pulses. The valved pulsejet comprises an intake with a one-way valve arrangement. The valves prevent the explosive gas of the ignited fuel mixture in the combustion chamber from exiting and disrupting the intake airflow, although with all practical valved pulsejets there is some 'blowback' while running statically or at low speed, as the valves cannot close fast enough to prevent some gas from exiting through the intake.
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The P.1079 Messerschmitt designs span from 1941 to 1944, the latter being the year in which the High Command of the Luftwaffe took to call attention to the need of a strong defense against the devastating allied bombing raids, with its Emergency Fighter Program. Since pulsejets were cheaper to build, the possibility of using them to power aircraft was explored, owing to the overstretched industry and materials shortages of the Third Reich at that stage of the war. Thus the main German aircraft manufacturers were asked by the Luftwaffe to produce light fighter designs (Miniaturjäger), using a strict minimum of materials that would be fitted with one Argus As 014 pulsejet engine per unit. The projected planes were small, spartan creations, with no landing gear, no radio and almost no electrical equipment, but the mostly propaganda-based aim was to produce them cheaply and in large numbers so as to overwhelm the Allied bomber formations that flew daily over Germany's skies.
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Ulrich Albrecht: Artefakte des Fanatismus; Technik und nationalsozialistische Ideologie in der Endphase des Dritten Reiches All the P.1079 Messerschmitt designs remained on paper, but Junkers built the Ju EF 126 Ellie the only pulsejet-powered fighter project that reached the prototype stage right before the end of the war. For this venture Heinkel would use a He 162 airframe, powered by a pulse jet and Blohm & Voss submitted the Blohm & Voss P 213 At any rate the Argus pulsejets proved themselves unsuitable for manned aircraft that would have to take off unassisted, for they did not produce enough power at low speeds for takeoff. Since additional launch schemes would have to be added to the project, such as towplanes, aircraft catapults or rocket boosters, the goal of the program would be defeated and expenses would be far higher than projected. Thus the pulsejet-powered fighter project never saw mass production, being brought to a close already before 1945.
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Bomber versions of both types were proposed, and work continued on them at the insistence of Adolf Hitler long after the point when anything other than token use could have been made of them. Moves were made to revive the Me 328 again in 1944 as a piloted flying bomb based on the Me 328B, fitted with a bomb, but it was dropped in favour of the Fieseler Fi 103R (Reichenberg). Two differing revised versions - one designated as the Me 328C, to be fitted with a Jumo 004 turbojet — and another, in-house proposal that did not receive a letter suffix, used two As 014 pulsejets mounted on pylons mounted onto the rear fuselage sides — refitted with a twin tail empennage design — along with a Porsche 109-005 single-use turbojet of thrust in the same dorsal rear location as meant for its use on the V-1, allowed with the new twin-tail designMe 328 proposal for two As 014/Porsche 109-005 propulsion — but neither of these proposals came to anything. Owing to the basic idea of short-life reaction propulsion units to power it, the Me 328 project is often listed as a suicide weapon, however the aircraft was not intended as such.
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