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81-516: Passenger flights started with Sikorsky S-55 helicopters, with three Sikorsky S-58s added to its five S-55s in 1956; in 1958 the Boeing Vertol V-44, a 15-seat civil version of the Piasecki H-21 , took over. In 1962 they transitioned to the tandem rotor , twin turbine engine powered Boeing Vertol 107-II Turbocopter and later operated the twin turbine engine Sikorsky S-61 . In February 1955

162-408: A Lamb–Oseen vortex . A rotational vortex – a vortex that rotates in the same way as a rigid body – cannot exist indefinitely in that state except through the application of some extra force, that is not generated by the fluid motion itself. It has non-zero vorticity everywhere outside the core. Rotational vortices are also called rigid-body vortices or forced vortices. For example, if a water bucket

243-432: A boundary layer which causes a local rotation of fluid at the wall (i.e. vorticity ) which is referred to as the wall shear rate. The thickness of this boundary layer is proportional to √ ( v t ) {\displaystyle \surd (vt)} (where v is the free stream fluid velocity and t is time). If the diameter or thickness of the vessel or fluid is less than the boundary layer thickness then

324-406: A Sikorsky S-61L (N618PA), while on departure climbout from Newark International Airport, experienced a fracture of one of the tail rotor blades, resulting in severe vibrations and an immediate return and descent to the airport. At about 150 feet altitude, the entire tail rotor gearbox was torn from the aircraft, resulting in an immediate and radical center of gravity change to the aircraft. This caused

405-407: A convex surface. A unique example of severe geometric changes is at the trailing edge of a bluff body where the fluid flow deceleration, and therefore boundary layer and vortex formation, is located. Another form of vortex formation on a boundary is when fluid flows perpendicularly into a wall and creates a splash effect. The velocity streamlines are immediately deflected and decelerated so that

486-614: A day between JFK and the Port Authority building at the World's Fair, as La Guardia was still under construction. Scheduled flights to the top of the Pan Am Building (now MetLife Building ) began in December 1965; they ended in 1968, then resumed for a few months in 1977. In April 1966 23 flights a day flew nonstop to Pan Am's terminal at JFK, scheduled 10 minutes; passengers could check in at

567-597: A number of derivative designs including the Sikorsky H-34 , which was produced in even greater numbers. The H-19 had a long military career worldwide in the late 20th century and also proved popular with civil operators. Development of the H-19 was initiated privately by Sikorsky without government sponsorship. The helicopter was initially designed as a testbed for several novel design concepts intended to provide greater load-carrying ability in combination with easy maintenance. Under

648-503: A patrol over MiG Alley . McConnell was able to turn and shoot down the attacking MiG, but his F-86 was badly damaged and began losing engine power. Realizing he could not make it back to base, McConnell headed for the USAF rescue base at Cho-do , spotting an H-19 below him. H-19 pilots Joe Sullivan and Don Crabb, alerted that two damaged Sabres were headed towards them, saw McConnell's F-86 and changed course to parallel it. McConnell ejected over

729-483: A remote hilltop in the same area. Their performance continued to improve and in Operation Haylift II on 23–27 February 1953, HMR-161 lifted 1.6 million pounds (730 t) of cargo to resupply two regiments. Although HMR-161 helicopters were operating in "hot" landing zones near enemy troops, they did not lose any helicopters to enemy fire. HRS-1 helicopters were also used to relocate rocket launcher batteries;

810-410: A rocket nozzle at the tip of each rotor blade with the fuel tank located in the center above the rotor blade hub. Enough fuel was provided for seven minutes of operation. Although tests of the system were considered successful, it was never adopted operationally. Major innovations implemented on the H-19 were the forward placement of the engine below the crew compartment and in front of the main cabin,

891-500: A severe nose down attitude and uncontrolled contact with the ground. Compounding the accident was the failure of both hydraulic systems due to the loss of the tail rotor gear box, which rendered the aircraft virtually uncontrollable. There were three fatalities and thirteen serious injuries. The airline ceased flying that day and never resumed operations, filing for bankruptcy the following month. Sikorsky H-19 Chickasaw The Sikorsky H-19 Chickasaw (company model number S-55 )

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972-442: A single wingtip vortex , less than one wing chord downstream of that edge. This phenomenon also occurs with other active airfoils , such as propeller blades. On the other hand, two parallel vortices with opposite circulations (such as the two wingtip vortices of an airplane) tend to remain separate. Vortices contain substantial energy in the circular motion of the fluid. In an ideal fluid this energy can never be dissipated and

1053-484: A transparent Plexiglas floor. Five aircraft were built in 1999 to comply with strict National Park Service noise limits for Grand Canyon aerial tours; however, the aircraft were only used in this role for two years because it was difficult for pilots in the high-mounted cockpit to communicate with tourists in the main cabin. After being retired from sightseeing, the helicopters were used in utility and lift roles. See Westland Whirlwind museum examples for examples of

1134-539: A tree. HMR-161 reported 90% aircraft availability. The success of helicopter operations with the USMC prompted the service to seek a military light utility vehicle that the HRS could lift, leading to the development of the aluminum-bodied, 1,700 lb (770 kg) M422 Mighty Mite in the early 1950s. However, developmental issues delayed deployment of the M422 until 1959, by which time

1215-720: Is a multi-purpose piston-engined helicopter that was used by the United States Army and United States Air Force . It was also license-built by Westland Aircraft as the Westland Whirlwind in the United Kingdom. United States Navy and United States Coast Guard models were designated HO4S , while those of the U.S. Marine Corps were designated HRS . In 1962, the U.S. Navy, U.S. Coast Guard and U.S. Marine Corps versions were all redesignated as H-19s like their U.S. Army and U.S. Air Force counterparts. The H-19 pioneered

1296-402: Is called a vortex tube . In general, vortex tubes are nested around the axis of rotation. The axis itself is one of the vortex lines, a limiting case of a vortex tube with zero diameter. According to Helmholtz's theorems , a vortex line cannot start or end in the fluid – except momentarily, in non-steady flow, while the vortex is forming or dissipating. In general, vortex lines (in particular,

1377-471: Is demonstrated by smoke rings and exploited in vortex ring toys and guns . Two or more vortices that are approximately parallel and circulating in the same direction will attract and eventually merge to form a single vortex, whose circulation will equal the sum of the circulations of the constituent vortices. For example, an airplane wing that is developing lift will create a sheet of small vortices at its trailing edge. These small vortices merge to form

1458-460: Is never removed, it would consist of circular motion forever. A key concept in the dynamics of vortices is the vorticity , a vector that describes the local rotary motion at a point in the fluid, as would be perceived by an observer that moves along with it. Conceptually, the vorticity could be observed by placing a tiny rough ball at the point in question, free to move with the fluid, and observing how it rotates about its center. The direction of

1539-559: Is not well documented, but is estimated at only six or seven of the S-55 and S-58 versions combined. In the mid-1980s, the U.S. Army sought an economical helicopter to simulate the sound and radar signature of the Soviet Mil Mi-24 during exercises. OHA sold the Army fifteen modified S-55/Mi-24 s with a new five-bladed rotor system, which was quieter than the original three-bladed rotor and made

1620-444: Is spun at constant angular speed w about its vertical axis, the water will eventually rotate in rigid-body fashion. The particles will then move along circles, with velocity u equal to wr . In that case, the free surface of the water will assume a parabolic shape. In this situation, the rigid rotating enclosure provides an extra force, namely an extra pressure gradient in the water, directed inwards, that prevents transition of

1701-399: Is started, a vortex usually forms ahead of each propeller , or the turbofan of each jet engine . One end of the vortex line is attached to the engine, while the other end usually stretches out and bends until it reaches the ground. When vortices are made visible by smoke or ink trails, they may seem to have spiral pathlines or streamlines. However, this appearance is often an illusion and

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1782-610: Is the case in tornadoes and in drain whirlpools. A vortex with helical streamlines is said to be solenoidal . As long as the effects of viscosity and diffusion are negligible, the fluid in a moving vortex is carried along with it. In particular, the fluid in the core (and matter trapped by it) tends to remain in the core as the vortex moves about. This is a consequence of Helmholtz's second theorem . Thus vortices (unlike surface waves and pressure waves ) can transport mass, energy and momentum over considerable distances compared to their size, with surprisingly little dispersion. This effect

1863-585: Is the highest flying time helicopter in the world, with more than 82,000 flight hours since its construction in 1962. N6682D is in the 1968 film Coogan's Bluff , starring Clint Eastwood , taking off atop the Pan Am Building. N108PA is the helicopter arriving with Eastwood. N6676D is shown taking off from the Downtown Manhattan/Wall St. Heliport in the last of the Secret Agent 077 trilogy of films, 1966's Special Mission Lady Chaplin. It appears in

1944-552: The Yellow Sea near the helicopter and was pulled from the water within two minutes by H-19 medic Arthur Gillespie; McConnell later told his sister "I barely got wet." Seeking favorable publicity for its ace pilots in Korea, the USAF circulated a rescue photo which was widely published in U.S. newspapers; however, Sullivan, Crabb, and Gillespie were flying a different H-19 without rescue markings that day. Historian Kenneth P. Werrell writes that

2025-566: The transmission and rotors. Early civilian and military S-55 models offered a folding 400-pound (180 kg) capacity hoist above the starboard main cabin door, while later models could be equipped with a more capable and reliable 600-pound (270 kg) capacity unit. Starting with the introduction of the S-55C in October 1956, the tailboom was inclined three degrees downward to provide more main rotor clearance during hard landings; models equipped with

2106-414: The vector analysis formula ∇ × u → {\displaystyle \nabla \times {\vec {\mathit {u}}}} , where ∇ {\displaystyle \nabla } is the nabla operator and u → {\displaystyle {\vec {\mathit {u}}}} is the local flow velocity. The local rotation measured by

2187-413: The wake of a boat, and the winds surrounding a tropical cyclone , tornado or dust devil . Vortices are a major component of turbulent flow . The distribution of velocity, vorticity (the curl of the flow velocity), as well as the concept of circulation are used to characterise vortices. In most vortices, the fluid flow velocity is greatest next to its axis and decreases in inverse proportion to

2268-528: The 1967 spy thriller Matchless , arriving and taking off from the Pan Am Building. On October 14, 1963, New York Airways Flight 600, a Boeing Vertol 107, registration N6673D, crashed shortly after takeoff from Idlewild Airport (now JFK) en route to Newark via Wall Street. All three passengers and all three crew members died. The accident was caused by mechanical failure due to contaminated lubricants. On July 15, 1969, de Havilland Canada DHC-6 Twin Otter 200 N558MA

2349-556: The British license-built S-55. Data from U.S. Army Aircraft Since 1947 General characteristics Performance Related development Aircraft of comparable role, configuration, and era Related lists Vortex In fluid dynamics , a vortex ( pl. : vortices or vortexes ) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings , whirlpools in

2430-543: The CH-19E was retired by U.S. Navy squadron HC-5 on 26 February 1969. Surplus H-19s were sold on the open market, and civil interest was sufficient that Sikorsky (and later Orlando Helicopter Airways or OHA) offered conversion kits allowing a military surplus H-19 to be commercially operated under a standard Federal Aviation Administration type certificate as an S-55B. Turboshaft conversions were also offered by aftermarket modification companies. A novel civil conversion of

2511-880: The H-19 by OHA was the Heli-Camper , a campervan -like conversion—featuring a built-in mini-kitchen and sleeping accommodations for four. In the late 1970s, OHA participated in a joint effort with popular American recreational vehicle (RV) manufacturer Winnebago Industries to market the aircraft, now renamed the Winnebago Heli-Home . A larger version based on the Sikorsky S-58 was also developed, and optional floats were offered for amphibious operations. The aircraft were featured in several American popular magazines and reportedly drew large crowds at RV shows and dealerships, but their high purchase price together with rising 1970s fuel prices resulted in very limited sales; production

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2592-589: The H-19 in the Korean War. It was designated as the HRS in USMC service. Marine Squadron HMR-161 arrived in Korea on 2 September 1951 with 15 HRS-1 helicopters. The new helicopter squadron started operations upon arrival. On 13 September 1951, during Operation Windmill I, HMR-161 transported 18,848 pounds (8.5 t) of gear and 74 Marines onto a ridge in the Punchbowl area. A week later HMR-161 shuttled 224 recon company marines and 17,772 pounds (8.1 t) of supplies to

2673-431: The HRS was being replaced by utility helicopters capable of lifting standard U.S. light utility vehicles, rendering the M422 unnecessary and – due to its unique design – a supply chain liability. The Mighty Mite was only produced in small numbers and was mostly withdrawn from service by the late 1960s. The U.S. Air Force (USAF) ordered 50 H-19A's for rescue duties in 1951. These aircraft were

2754-512: The Pan Am Building 40 minutes before their scheduled departure out of JFK. The downtown heliport had 13 flights a day to Newark, 5 nonstops to TWA's terminal at JFK and 12 to LGA, all of which continued to JFK. (Downtown had no weekend flights.) Soon after Pan Am Building flights resumed the March 1977 Official Airline Guide (OAG) showed 48 weekday S-61 departures from there: 12 to EWR, 14 to LGA then JFK, and 22 nonstops to JFK. New York Airways employed

2835-506: The Pan Am Building. The aircraft fell onto its side. Its spinning principal rotor blades killed four passengers waiting to board (including movie director Michael Findlay ) and injured a fifth. Parts of a broken blade fell into the streets below, killing one pedestrian and injuring another. The accident precipitated the permanent closure of the heliport. The Cinema Museum in London holds film of this helicopter from summer 1963. On April 18, 1979,

2916-476: The U.S. Navy found to be adequate in an air–sea rescue role; the H-19B, HO4S-3, HRS-3, and subsequent models would use this powerplant. The R-1300 models also used a single horizontal tailplane in place of the early inverted "V" style, and a new hydro-mechanical clutch gave smoother and more rapid rotor acceleration during clutch engagement and allowed the engine to be started and operated at any speed while disengaged from

2997-587: The United States. An additional 447 were manufactured by licensees of the helicopter including Westland Aircraft, SNCASE in France and Mitsubishi in Japan. The helicopter was widely exported, used by many other nations, including Portugal, Greece, Israel, Chile, South Africa, Denmark and Turkey. In 1954 the U.S. Marine Corps tested an idea to enhance lift in hot-and-high and/or heavily loaded conditions by installing

3078-603: The Vertol flights. Fuel prices soared after the 1973 oil crisis , damaging profitability. The airline could not recover after the 1977 Pan Am Building accident and the 1979 oil crisis , and New York Airways filed for bankruptcy on May 18, 1979. The number of passengers boarded, in thousands, scheduled flights only were 68 in 1957, 144 in 1960, 537 in 1967, 268 in 1970. All surviving New York Airways Boeing Vertol 107s are now operated by Columbia Helicopters , based in Aurora, Oregon : N6674D

3159-654: The aircraft sound similar to an Mi-24. The piston engines and original Sikorsky tail rotors were retained. OHA also produced the S-55QT Whisper Jet , an extra-quiet civil conversion based on the five-bladed S-55/Mi-24, but using an 840 horsepower (630 kW) Garrett TPE331 derated to 650 horsepower (480 kW) from the S-55T, which lowered the aircraft's empty weight by 900 pounds (410 kg). The aircraft were also outfitted with special intake and exhaust silencers, carbon fiber noise-absorbing engine compartment doors, and

3240-417: The axis line) are either closed loops or end at the boundary of the fluid. A whirlpool is an example of the latter, namely a vortex in a body of water whose axis ends at the free surface. A vortex tube whose vortex lines are all closed will be a closed torus -like surface. A newly created vortex will promptly extend and bend so as to eliminate any open-ended vortex lines. For example, when an airplane engine

3321-406: The axis line, with depth inversely proportional to r . The shape formed by the free surface is called a hyperboloid , or " Gabriel's Horn " (by Evangelista Torricelli ). The core of a vortex in air is sometimes visible because water vapor condenses as the low pressure of the core causes adiabatic cooling ; the funnel of a tornado is an example. When a vortex line ends at a boundary surface,

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3402-416: The axis, and increases as one moves away from it, in accordance with Bernoulli's principle . One can say that it is the gradient of this pressure that forces the fluid to follow a curved path around the axis. In a rigid-body vortex flow of a fluid with constant density , the dynamic pressure is proportional to the square of the distance r from the axis. In a constant gravity field, the free surface of

3483-406: The boundary layer separates and forms a toroidal vortex ring. In a stationary vortex, the typical streamline (a line that is everywhere tangent to the flow velocity vector) is a closed loop surrounding the axis; and each vortex line (a line that is everywhere tangent to the vorticity vector) is roughly parallel to the axis. A surface that is everywhere tangent to both flow velocity and vorticity

3564-423: The boundary layer will not separate and vortices will not form. However, when the boundary layer does grow beyond this critical boundary layer thickness then separation will occur which will generate vortices. This boundary layer separation can also occur in the presence of combatting pressure gradients (i.e. a pressure that develops downstream). This is present in curved surfaces and general geometry changes like

3645-561: The cabin windows, but this load proved far too heavy, and even lightly armed H-19 gunships fitted with flexible machine guns for self-defense proved underpowered. The H-19 was also used by the French forces in the First Indochina War . A small number of war-worn H-19s were given to the Republic of Vietnam Air Force in 1958, when the French military departed. These saw very limited service in

3726-453: The cases of the absence of forces, the liquid settles. This makes the water stay still instead of moving. When they are created, vortices can move, stretch, twist and interact in complicated ways. When a vortex is moving, sometimes, it can affect an angular position. For an example, if a water bucket is rotated or spun constantly, it will rotate around an invisible line called the axis line. The rotation moves around in circles. In this example

3807-437: The core (for example, by steadily turning a cylinder at the core). In free space there is no energy input at the core, and thus the compact vorticity held in the core will naturally diffuse outwards, converting the core to a gradually-slowing and gradually-growing rigid-body flow, surrounded by the original irrotational flow. Such a decaying irrotational vortex has an exact solution of the viscous Navier–Stokes equations , known as

3888-407: The core and then into the engine. Vortices need not be steady-state features; they can move and change shape. In a moving vortex, the particle paths are not closed, but are open, loopy curves like helices and cycloids . A vortex flow might also be combined with a radial or axial flow pattern. In that case the streamlines and pathlines are not closed curves but spirals or helices, respectively. This

3969-537: The distance r . Irrotational vortices are also called free vortices . For an irrotational vortex, the circulation is zero along any closed contour that does not enclose the vortex axis; and has a fixed value, Γ , for any contour that does enclose the axis once. The tangential component of the particle velocity is then u θ = Γ 2 π r {\displaystyle u_{\theta }={\tfrac {\Gamma }{2\pi r}}} . The angular momentum per unit mass relative to

4050-419: The distance from the axis. In the absence of external forces, viscous friction within the fluid tends to organise the flow into a collection of irrotational vortices, possibly superimposed to larger-scale flows, including larger-scale vortices. Once formed, vortices can move, stretch, twist, and interact in complex ways. A moving vortex carries some angular and linear momentum, energy, and mass, with it. In

4131-400: The dynamics of fluid, a vortex is fluid that revolves around the axis line. This fluid might be curved or straight. Vortices form from stirred fluids: they might be observed in smoke rings , whirlpools , in the wake of a boat or the winds around a tornado or dust devil . Vortices are an important part of turbulent flow . Vortices can otherwise be known as a circular motion of a liquid. In

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4212-605: The early days of the Vietnam War , before being supplanted by the more capable H-34. Pakistan ordered eight S-55s in 1956 to equip search and rescue squadrons of the Pakistan Air Force . They saw service during the 1965 Indo-Pakistani War , flying various missions including counterintelligence operations at Karachi in co-operation with the Army . They were retired from service in 1971. The H-19 left U.S. military service when

4293-420: The engine could be readily accessed at ground level through dual clamshell-style doors; the entire engine could be changed in only two hours, and the radial engine was oriented backwards relative to a typical airplane installation, allowing more convenient access to engine accessories. The offset flapping hinges and hydraulic servos gave more positive flight control under differing loading conditions, isolated

4374-641: The first African American airline pilot. Perry H. Young made his historic first flight on February 5, 1957. Young had previously made history as the first African American flight instructor for the United States Army Air Corps. At its peak the airline partnered with 24 international and domestic airlines. At various times it served: In 1969 the Official Airline Guide (OAG) listed some inter-airport flights using STOL Twin Otters along with

4455-455: The first HO4S-1 helicopter to the U. S. Navy on 31 August 1950. A U.S. Air Force YH-19 was sent to Korea for service trials in March 1951, where it was joined by a second YH-19 in September 1951. On 27 April 1951, the first HRS-1 was delivered to the U.S. Marine Corps, and on 2 May 1951, the first S-55 was delivered to Westland Aircraft. 1,281 of the helicopters were manufactured by Sikorsky in

4536-424: The flight controls from vibration, and lessened control forces; the H-19 could be flown with only two fingers on the cyclic control . The YH-19 prototypes featured a blunt aft fuselage and a single starboard-mounted horizontal tailplane with a small vertical fin at its outboard end. Initial production models added a large fillet-like fin behind the fuselage and under the tailboom, and the tailplane configuration

4617-419: The fluid particles are moving in closed paths. The spiral streaks that are taken to be streamlines are in fact clouds of the marker fluid that originally spanned several vortex tubes and were stretched into spiral shapes by the non-uniform flow velocity distribution. The fluid motion in a vortex creates a dynamic pressure (in addition to any hydrostatic pressure) that is lowest in the core region, closest to

4698-409: The fluid relative to the vortex's axis. In theory, the speed u of the particles (and, therefore, the vorticity) in a vortex may vary with the distance r from the axis in many ways. There are two important special cases, however: In the absence of external forces, a vortex usually evolves fairly quickly toward the irrotational flow pattern , where the flow velocity u is inversely proportional to

4779-516: The hands of the 6th Transportation Company, during the Korean War beginning in 1951 as an unarmed transport helicopter. Undergoing tests such as medical evacuation , tactical control and frontline cargo support, the helicopter succeeded admirably in surpassing the capabilities of the H-5 Dragonfly which had been used throughout the war by the Army. The U.S. Marine Corps (USMC) made extensive use of

4860-439: The inclined tail also used an 8-foot-9-inch (2.67 m) tail rotor in place of the earlier 8-foot-8-inch (2.64 m) unit. The H-19 Chickasaw holds the distinction of being the U.S. Army's first true transport helicopter and, as such, played an important role in the initial formulation of Army doctrine regarding air mobility and the battlefield employment of troop-carrying helicopters. The H-19 underwent live service tests in

4941-530: The leadership of designer Edward F. Katzenberger, a mockup was designed and fabricated in less than one year. The first customer was the United States Air Force, which ordered five YH-19 aircraft for evaluation; the YH-19's first flight was on 10 November 1949, less than a year after the program start date. This was followed by delivery of the first YH-19 to the U.S. Air Force on 16 April 1950 and delivery of

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5022-444: The liquid, if present, is a concave paraboloid . In an irrotational vortex flow with constant fluid density and cylindrical symmetry, the dynamic pressure varies as P ∞ − ⁠ K / r ⁠ , where P ∞ is the limiting pressure infinitely far from the axis. This formula provides another constraint for the extent of the core, since the pressure cannot be negative. The free surface (if present) dips sharply near

5103-862: The misleading, staged photo was likely a ruse to conceal the fact that the H-19 was not originally on an air rescue mission but was instead supporting special operations in the Cho-do area. On 1 September 1953, Sabena used the S-55 to inaugurate the first commercial helicopter service in Europe, with routes between Rotterdam and Maastricht in the Netherlands and Cologne and Bonn in West Germany . France made aggressive use of helicopters in Algeria, both as troop transports and gunships. Piasecki H-21 and Sud -built Sikorsky H-34 helicopters rapidly displaced fixed-wing aircraft for

5184-556: The one-way fare from LaGuardia to Idlewild was $ 4.50 ($ 51 in 2023 dollars). The aircraft was a Sikorsky H-19, registration number N418A. The trip took ten minutes and their phone number was DEfender 5-6600 . The first scheduled passenger flights to Manhattan arrived in December 1956 at the West 30th Street Heliport . The downtown heliport on East River Pier 6 opened in 1960 and New York Airways moved all its Manhattan passenger flights down there around December 1960. Due to route restrictions on

5265-416: The primary rescue and medical evacuation helicopters for the USAF during the Korean War. The Air Force continued to use the H-19 through the 1960s, ultimately acquiring 270 of the H-19B model. A notable rescue involving a USAF H-19 occurred on 12 April 1953 when a North American F-86 Sabre flown by leading American flying ace Joseph C. McConnell was riddled with cannon fire from an enemy MiG-15 during

5346-445: The reduced pressure may also draw matter from that surface into the core. For example, a dust devil is a column of dust picked up by the core of an air vortex attached to the ground. A vortex that ends at the free surface of a body of water (like the whirlpool that often forms over a bathtub drain) may draw a column of air down the core. The forward vortex extending from a jet engine of a parked airplane can suck water and small stones into

5427-413: The rigid-body flow to the irrotational state. Vortex structures are defined by their vorticity , the local rotation rate of fluid particles. They can be formed via the phenomenon known as boundary layer separation which can occur when a fluid moves over a surface and experiences a rapid acceleration from the fluid velocity to zero due to the no-slip condition . This rapid negative acceleration creates

5508-473: The rockets created a dust cloud when fired, making the launcher a target for counter-battery fire , so launchers and crews were moved twice a day. Each HRS-1 helicopter carried four rocket launchers and extra rockets as external cargo, with the crew in the cabin. The HRS-1 helicopter proved to be durable and reliable in Korean service. One reportedly flew home after losing 18 in (46 cm) of main rotor blade to

5589-400: The rotation of the bucket creates extra force. The reason that the vortices can change shape is the fact that they have open particle paths. This can create a moving vortex. Examples of this fact are the shapes of tornadoes and drain whirlpools . When two or more vortices are close together they can merge to make a vortex. Vortices also hold energy in its rotation of the fluid. If the energy

5670-419: The single-engine Vertol 44, nonstop flights from Manhattan to Idlewild had to await the twin-engine Boeing Vertol 107. Moody's says in 1962 the "operating revenue" of $ 3.9 million included $ 2.2 million federal subsidy. In June 1964 they had 32 daily flights from JFK to Newark Airport and 33 returning; all flights each way between about 0900 and 1930 stopped at Wall Street. The only other flights were 15 round trips

5751-487: The transport of paras and quick-reaction commando teams. In Indochina, a small number of Hiller H-23s and H-19s were available for casualty evacuation. In 1956, the French Air Force experimented with arming the H-19, then being superseded in service by the more capable H-21 and H-34. The H-19 was originally fitted with a 20mm cannon, two rocket launchers, two 12.7mm machine guns, and a 7.5mm light machine gun firing from

5832-462: The use of a nose-mounted radial engine powering a single fully articulated main rotor located above the cabin, which helped maintain a proper center of gravity under varying loading conditions without requiring ballast to maintain longitudinal stability as with prior Sikorsky designs. This layout gave the H-19 series a characteristic bulbous-nosed appearance and made it one of the first truly successful single-rotor utility helicopters , leading to

5913-561: The use of offset flapping hinges located nine inches (230 mm) from the center of the rotor, and the use of hydraulic servos for the main rotor controls. These features yielded an aircraft that was far more capable in a transport role than previous Sikorsky designs. The forward engine location placed the main cabin essentially in line with the main rotor's rotational axis and close to the aircraft center of gravity , making it easier to maintain proper weight and balance under differing loading conditions. The impetus for this design choice

5994-440: The vortex axis is therefore constant, r u θ = Γ 2 π {\displaystyle ru_{\theta }={\tfrac {\Gamma }{2\pi }}} . The ideal irrotational vortex flow in free space is not physically realizable, since it would imply that the particle speed (and hence the force needed to keep particles in their circular paths) would grow without bound as one approaches

6075-402: The vortex axis. Indeed, in real vortices there is always a core region surrounding the axis where the particle velocity stops increasing and then decreases to zero as r goes to zero. Within that region, the flow is no longer irrotational: the vorticity ω → {\displaystyle {\vec {\omega }}} becomes non-zero, with direction roughly parallel to

6156-450: The vortex axis. The Rankine vortex is a model that assumes a rigid-body rotational flow where r is less than a fixed distance r 0 , and irrotational flow outside that core regions. In a viscous fluid, irrotational flow contains viscous dissipation everywhere, yet there are no net viscous forces, only viscous stresses. Due to the dissipation, this means that sustaining an irrotational viscous vortex requires continuous input of work at

6237-430: The vorticity ω → {\displaystyle {\vec {\omega }}} must not be confused with the angular velocity vector of that portion of the fluid with respect to the external environment or to any fixed axis. In a vortex, in particular, ω → {\displaystyle {\vec {\omega }}} may be opposite to the mean angular velocity vector of

6318-429: The vorticity vector is defined to be the direction of the axis of rotation of this imaginary ball (according to the right-hand rule ) while its length is twice the ball's angular velocity . Mathematically, the vorticity is defined as the curl (or rotational) of the velocity field of the fluid, usually denoted by ω → {\displaystyle {\vec {\omega }}} and expressed by

6399-400: Was 12 minutes behind schedule on a flight from New York to Newark, so the pilot decided to take off from a runway intersection. During initial climb the plane was caught in the wake vortex of a departing jet and crashed, killing 3 (2 crew and 1 passenger) of the 14 occupants. On May 16, 1977, the landing gear failed on a Sikorsky S-61L (N619PA) while it was taking on passengers on the roof of

6480-502: Was changed to an inverted "V" shape. Early H-19 and HO4S variants were powered by a Pratt & Whitney R-1340-57 radial rated at 600 hp (450 kW) and used a centrifugal clutch that automatically engaged the main rotor when a preset engine speed was reached. However, the HO4S was deemed underpowered in U.S. Navy service with this powerplant, so the aircraft was re-engined with a 700 hp (520 kW) Wright R-1300-3 radial which

6561-511: Was the recent rejection of the Sikorsky XHJS by the U.S. Navy in favor of the tandem rotor Piasecki HUP Retriever ; the Navy had strongly objected to the necessity to use ballast in the cabin-forward XHJS to maintain proper weight and balance, prompting Sikorsky to seek single-rotor design alternatives that did not require this. Another benefit of this engine location was ease of maintenance, as

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