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Topic: Tilt rotors

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	Rotary Aerodynamics, Rotorcraft, Helicopters, Tilt Rotors
		In the latter case the two rotors can be in tandem on two different shafts (CH-47 Chinook), co-axial and counter-rotating (Kamov Ka 52), or inter-meshing (Kaman K-1200), with number of blades variable ranging from 2 (most Bell helicopters) to 8 (heavy lift Mil 26).
		The tilt rotor performs a conversion of VTOL aircraft into a more ordinary aircraft by tilting the propeller from vertical to horizontal to achieve horizontal flight.
		The compound thrust would alleviate the rotor loading, would decrease its rotational speed, and with it all the problems associated to the extreme tip speeds (transonic and supersonic Mach numbers, dynamic stall effects, fatigue, structural vibrations, noise generation, etc.).
	www.aerodyn.org /Rotors/rcraft-concepts.html (521 words)

	Tiltrotor - Wikipedia, the free encyclopedia
		As the craft gains speed, the proprotors are slowly tilted forward, eventually becoming perpendicular to the ground.
		Vertical motion is controlled with conventional rotor blade pitch and either a conventional helicopter collective control lever (as in the Bell-Agusta BA-609) or a unique control similar to a fixed wing engine control called a thrust control lever (TCL) (as in the Bell-Boeing V-22 Osprey).
		In a helicopter the maximum forward speed is defined by the speed that the rotor turns at; at some point the helicopter will be moving forward at the same speed as the spinning of the backwards-moving side of the rotor, so that side of the rotor sees zero or negative airspeed, and begins to stall.
	en.wikipedia.org /wiki/Tilt-rotor (930 words)

	Optimum Speed Tilt Rotor OSTR
		Tilt rotor type rotorcraft incorporate wings which produce lift in forward flight, and, at forward speeds which is adequate to support the weight of the rotorcraft.
		The rotors (usually 2 or 4) are "tilted" from a first position where their axis of rotation is vertical and where the rotors act as a regular helicopter rotors to a second position where their axis of the rotation is relatively horizontal and the rotors act as propellers producing forward thrust.
		The best-known tilt rotor rotorcraft is the V-22 Osprey.
	www.globalsecurity.org /military/systems/aircraft/ostr.htm (982 words)

	Bell XV-15 - Wikipedia, the free encyclopedia
		The tilting engine concept introduced complexities in the design of the engine pods themselves, and the design of the engines to be able to shift from operating horizontally to operating vertically.
		The focus was on tilt rotor pods and integration of the tilting rotors with the wings and fuselage of the aircraft, and studying the airflow as the rotors tilted.
		Tilt rotors with fixed rotors and with folding rotors were investigated.
	en.wikipedia.org /wiki/XV-15 (1299 words)

	Tiltrotor (Nick Lappos)
		Tilt rotors must have small highly loaded disks, unlike multi rotor helicopters whose disks stay above the aircraft, and don't have to swing past the fuselage.
		For the rotors to be at the ends of the wings, and then convert to props, the rotors must not come too close to the cabin.
		Generally, a tilt rotor must have only about 40% of the rotor disk area of an equivilent helicopter, which means that ot will need about 50% more power for the same payload (or that it will have much less payload for the same power).
	yarchive.net /air/tiltrotor.html (3977 words)

	Rotors Aerodynamics, Modes of Operation
		The modes of operation of an open airscrew (propeller, helicopter rotor, wind turbine, auto-gyro) depend essentially on the direction of the thrust and on the movement of the airscrew with respect to the undisturbed fluid.
		A rotor in hover is a propeller at zero advance ratio; a rotor in ascent/ descent has a positive or negative advance ratio; a rotor in forward flight is intrinsically unbalanced due to a rolling moment created by the asymmetry of the loading.
		Rotors of high solidity are slow, rotors of small solidity (having a few blades) are fast.
	aerodyn.org /Rotors/modes.html (679 words)

	DLR Portal - Helicopter research: Major EU measurement programme with tilt rotors successfully concluded
		Hundreds of pressure sensors were fitted on the rotor blades, the engine nacelle and the wings to record the often very unsteady distribution of lift on the components.
		DLR's many years of experience in controlling rotors in the wind tunnel came into its own in critical situations where a sensor malfunction meant that the test run had to be terminated by 'flying blind': the model was brought back to a secure operating status and safely shut off every time, without sustaining any damage.
		This rotor is a spin-off of the DLR/ONERA partnership, which has already given rise to the development of the patented quiet ERATO rotor for helicopters.
	www.dlr.de /en/DesktopDefault.aspx/tabid-10/60_read-2954 (583 words)

	Rotary Aerodynamics, Rotorcraft, Helicopters, Tilt Rotors
		In the latter case the two rotors can be in tandem on two different shafts (CH-47 Chinook), co-axial and counter-rotating (Kamov Ka 52), or inter-meshing (Kaman K-1200), with number of blades variable ranging from 2 (most Bell helicopters) to 8 (heavy lift Mil 26).
		The tilt rotor performs a conversion of VTOL aircraft into a more ordinary aircraft by tilting the propeller from vertical to horizontal to achieve horizontal flight.
		The compound thrust would alleviate the rotor loading, would decrease its rotational speed, and with it all the problems associated to the extreme tip speeds (transonic and supersonic Mach numbers, dynamic stall effects, fatigue, structural vibrations, noise generation, etc.).
	aerodyn.org /Rotors/rcraft-concepts.html (521 words)

	NASA - Tilt Rotor Aircraft Joins National Air And Space Museum Collection
		The XV-15 tilt rotor aircraft today took its place in what could be called "aviation's hall of fame," when NASA and the U.S. Army transferred the vehicle to the National Air and Space Museum's new Steven F. Udvar-Hazy Center near Washington Dulles International Airport in Virginia.
		Tilt rotors are a unique type of aircraft that possess the take-off, hover and landing capabilities of a conventional helicopter with the range and speed of a turboprop aircraft.
		Tilt rotor flight research began in the 1950s with the Bell XV-3 convertiplane.
	www.nasa.gov /home/hqnews/2003/sep/HQ_03295_tilt_rotor.html (591 words)

	1505
		On the Interleaving, the spar, which connects the rotors to the fuselage, will be sheathed in an airfoil.
		A single rotor and a comperable Intermeshing configuration are also added for interest.
		The inability to fold the rotor blades due to the extreme rigidity of the rotors.
	www.unicopter.com /1505.html (633 words)

	NASA Quest > Aerospace Team Online (Site not responding. Last check: 2007-11-03)
		Tilt rotors are currently being manufactured for the Navy; their designation is the V-22 Osprey.Tilt rotors don't need runways since they can land like a helicopter.
		Because the rotor blade is rotating, the wake is like a helix and the blades intersect the helix under certain operating conditions (like when the helicopter is descending for a landing).
		Tilt rotors can fly helicopter-like conditions, that is, they can hover and fly at low speeds.
	quest.arc.nasa.gov /aero/chats/11-10-98gy.html (1855 words)

	V/STOL: The First Half-Century - Part 2
		Rotor instability concerns led to a change from 23 ft three-bladed full-articulated rotors to 24 ft two-bladed semi-rigid rotors.
		Tilting the entire wing, instead of just the rotor or propeller, provides the benefit of increasing aerodynamic flow over the lifting and control surfaces during transition, and minimizes the lift loss due to downwash in hover.
		The tail rotor folded to the port side to reduce the stowage length and to protect against accidental damage during loading.
	www.aiaa.org /tc/vstol/same.html (5475 words)

	A History of Helicopter Flight
		For rotor control, Hafner's machine in notable in that it used a swashplate for blade pitch, which was a very early application of the final mechanism that was to become the standard means of providing pitch control on the modern helicopter.
		It was found that when the rotor disk was inclined backward at a small angle of attack and as the machine was pulled forward by a propeller, the rotor was turned by the action of the airflow on the blades.
		Because the rotors of a tilt-rotor are not large, the hovering efficiency of the tilt-rotor is not as high as that of a helicopter.
	www.glue.umd.edu /~leishman/Aero/history.html (13692 words)

	Vortex Ring State
		For rotor operations in the VRS, an inherent unsteadiness (aperiodicity) is a characteristic of the flow state, which is reflected by the waves and knots produced on the tip vortex filaments.
		The rotor then transitions through the vortex ring state where there is a large recirculation of flow in the plane of the rotor, into autorotational flight and into the windmill brake state where the wake flow returns to a well-behaved periodic solution.
		Near the rotors, note that in this case the tip vortices are convected slightly above the tip-path-planes, and in this case it is the resulting interactions of blades and tip vortices that is the source of the disturbances that initiate the wake dynamics.
	www.glue.umd.edu /~leishman/Aero/vring.html (6915 words)

	CNN.com - The full-tilt flying machine - Mar 24, 2006
		To accelerate the MV-22 into airplane-like flight, the nacelles rotate forward, and the prop-rotors transition from generating lift and controlling the direction of the aircraft to simply creating forward thrust.
		VRS is so dangerous to tilt-rotors because the effect can be asymmetrical: If only one rotor experiences VRS, the aircraft will quickly roll out of control instead of merely sinking more quickly.
		The Osprey now has a VRS warning system and its pilots are trained to recognize the signs of VRS and to escape by simply easing the Osprey forward.
	www.cnn.com /2006/TECH/space/03/24/osprey (603 words)

	National Defense Magazine
		With the speed and range of a turboprop and the vertical takeoff and landing performance of a helicopter, the tilt rotor promises to infiltrate, exfiltrate and resupply SOF over long distances in a single night.
		Original requirements for the special operations tilt rotor were shaped by the 1980 aborted mission to rescue U.S. hostages in Iran.
		The tilt rotor covered flat terrain in both helicopter and airplane modes and at altitudes down to 100 feet.
	www.nationaldefensemagazine.org /issues/2003/Nov/Air_Force_Tilt.htm (2280 words)

	Vertol VZ-2A
		A number of experimental projects appeared throughout the late 1950s and early 1960s with a variety of propulsion and lift devices to achieve vertical flight, including tilt rotors, tilt propellers, tilt jets, tilt wings, tilt ducts, lift fans and deflected thrust systems.
		The Vertol VZ-2 was the first tilt wing aircraft to successfully transition from vertical to horizontal flight.
		Another similarly sized rotor, mounted vertically on the lower right side of the vertical stabilizer, provided yaw control during slow speed flight and hovering.
	www.nasm.si.edu /research/aero/aircraft/boeing_vertol.htm (1180 words)

	SignOnSanDiego.com > News > Military -- Pilots test Osprey in rapid descent
		WASHINGTON – In a flight over southern Maryland recently, test pilots rolled the huge twin rotors of an MV-22 Osprey from horizontal to helicopter position and slowed the aircraft to 40 knots airspeed.
		The rapid-descent tests are done to address concerns that the Osprey is prone to encounter a dangerous flight condition known as vortex ring state, or VRS.
		Helicopter-type aircraft are susceptible to that when they descend extremely rapidly at a very slow airspeed, causing the rotors to lose lift when they encounter turbulence.
	www.signonsandiego.com /news/military/20030125-9999_1n25osprey.html (598 words)

	Dallas Morning News \| News for Dallas, Texas \| Business
		A technician controls the rotors on a half-model of the aircraft during wind tunnel testing at the NASA Langley Research Center.
		The two Sikorsky entries are variations of a big helicopter with two rotors, one atop the other, whose blades turn in opposite directions.
		The half-model quad tilt-rotor is 20 percent the size of the aircraft Bell-Boeing intends to build, but its wings have the same strength and flexibility as real ones and the rotors on their tips spin and tilt the same way as the V-22's.
	www.dallasnews.com /sharedcontent/dws/bus/stories/082406dnbusquadtiltrotor.2f76857.html (1043 words)

	SignOnSanDiego.com > News > Military -- Osprey tests pilots seek to prove tilt-rotor's safety
		The rapid-descent tests are to address the critics' concern that the Osprey is too prone to encounter a dangerous flight condition known as vortex ring state.
		The first phase of the tests, which are expected to run into February, have shown that the Osprey can safely descend faster than the accepted limit of 800 fpm at 40 knots, Navy spokesman Ward Carroll said.
		But all of the tests so far have been straight ahead, while the Osprey that crashed at Marana was turning, causing one rotor to stall first.
	www.signonsandiego.com /news/military/20030124-1551-cnsosprey.html (684 words)

	THAT VEXING VORTEX RING
		Converting rapidly from the helicopter mode to the airplane mode is accomplished by continuous rotation (tilt) of the prop-rotors’ nacelles from the helicopter rotor position to the conventional airplane propeller position.
		During the twelve second conversion period, the aircraft speed increases and lift is transferred from the rotors to the wing.
		This ring, once formed, is quite "sticky" and requires a rapid tilt of the rotor to gain forward speed and thereby "shed" the vortex.
	www.angelfire.com /me/swissair111memorial/modded/ThatVexingVortexRing.html (3946 words)

	Image of the Day
		The XV-15 tilt rotor aircraft today took its place in what could be called "aviation's hall of fame," when NASA and the U
		The XV-15 tilt rotor aircraft Tuesday took its place in what could be called "aviation's hall of fame," when NASA and the U.S. Army transferred the vehicle to the National Air and Space Museum's new Steven F. Udvar-Hazy Center near Washington Dulles International Airport in Virginia.
		Using lessons learned from the XV-3, NASA's Ames Research Center, Moffett Field, Calif., in partnership with the U.S. Army, developed design specifications for a new aircraft to demonstrate the viability of the tilt rotor concept.
	www.space.com /imageoftheday/image_of_day_030917.html (248 words)

	Tilt rotor - Planenews Aviation News Portal - Tilt Rotor Aircraft Joins (Site not responding. Last check: 2007-11-03)
		The scale wind tunnel semispan model of the V tiltrotor aircraft is considered.
		The aircraft tilted the rotors for transition from vertical to horizontal flight.
		The Osprey is a tiltrotor aircraft with a 38-foot rotor system and engine/transmission The V-22 is the world's first production tiltrotor aircraft.
	newinfoseek.com /nwis/tilt-rotor.html (452 words)

	Science Chat Forum
		As the Osprey lifts off in helicopter mode, the onboard computers, commanded by the pilot, control it by changing the pitch of the rotor blades—the angle at which they bite into the air as they spin around the hub.
		If either of the two Allison AE 1107C turboshaft engines fail, a central driveshaft inside the wing diverts power from the working engine to spin the prop-rotor of the disabled one.
		To support powerful engines and big whirling rotors at the tips, the wings are made almost entirely of superstrong and expensive carbon-fiber composite material, which also helps suppress vibrations.
	www.sciencechatforum.com /Web/article.php?id=493 (568 words)

	Technology: Tilt-Body
		They are sensitive to turbulence due to their large prop discs, and the exposed rotor blades are seen as a danger to personnel on the ground or deck.
		Its two wingtip rotors tilt forward for level flight and upward for vertical or near-vertical flight.
		The tip rotor assemblies themselves must be geared to tilt 90 to effect transitions into and out of horizontal flight.
	www.freewing.com /advantages.html (2383 words)

	THE CL-84 DYNAVERT
		When the pilot pushed the wing tilt lever left (wing in horizontal or conventional position) and moved the control stick lever left or right, the ailerons moved.
		When the pilot pushed the wing tilt lever right (wing in vertical position) and moved the rudder pedal lever left or right (which usually moves the rudder), the ailerons moved fully.
		The control of the flaps/ailerons were being shared by the control stick and the rudder pedals, causing the aircraft to partially roll and partially yaw.
	www.aafo.com /news/old/dynavert.htm (851 words)

	BellTiltrotors
		The QTR would use V-22 propulsion and support systems: engines, rotor systems, drive train, transmission, hydraulics, electronics, and generators, except that QTR would have four engines, instead of two, mounted on fore and aft wings.
		Water tunnel tests indicate that the rotor wake from the front rotors in forward flight flow down and inboard, below and inboard the rear rotors.
		With advanced engine technologies, wing download reductions, higher transmission torque, and 30% additional rotor area, a QTR capable of lifting 22 tons on a hot day could be available for production by 2015.
	www.vtol.org /vertiflite/BellTiltrotors.htm (2183 words)

	USATODAY.com - Civilian helicopter-plane readies for takeoff (Site not responding. Last check: 2007-11-03)
		Curtis added there will be a learning curve for pilots of civilian tilt rotors, who will have to master the difficulties of flying an aircraft that has two turboprops that can rotate 90 degrees.
		He also said there is a higher tolerance among the users of smaller aircraft for crashes than there is for commercial passenger planes or military aircraft.
		Aviation safety experts have said VRS will not be a major concern for civilian tilt rotors because they will not be used like the Osprey in dropping troops into war zones.
	www.usatoday.com /tech/news/techinnovations/2003-02-27-tilt-rotor_x.htm (899 words)

	Jack Kelly: Bag this boondoggle
		The vortex ring state is a wing-induced rotor stall unique to tilt-rotors.
		There are no door gunners, because the tilt rotors on the end of the wings would block much of a gunner's view and his field of fire.
		And the V-22's small rotors kick up substantial "downwash," kicking up clouds of dust thick enough to impair a pilot's vision, and forcing dismounting Marines to lie flat on the deck until the Osprey has departed the landing zone.
	www.post-gazette.com /forum/col/20030105edkell05p3.asp (762 words)

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