The V-22's propulsion system consists of dual counter rotating proprotors attached to gearboxes driven by Allison T406-AD-400 turboshaft engines. The engines, proprotor gearboxes, tilt-axis gearboxes, proprotor controls, and infrared suppressors are all housed in the rotating nacelle on the end of each wing. An interconnecting drive shaft transfers power from each nacelle to the mid-wing gearbox. This is the heart of the tilt-rotor technology.
Under normal, two engine operations, each engine delivers its power to its corresponding proprotor through the proprotor gearboxes. Only a small amount of power (511 hp max) is transferred down the pylon mounted drive shaft, through the tilt-axis gearboxes and down the interconnecting drive shaft to the mid-wing gearbox. The mid-wing gearbox contains the auxiliary power unit (APU), the constant frequency generator and the variable frequency generator. The mid-wing gearbox transmits power between the left and right interconnecting drive shafts without changing speed or direction of rotation. (During single engine operation, power is distributed from the remaining engine to both proprotors through the interconnecting drive shaft.)
The V-22 is equipped with two counterrotating three-bladed proprotors. The blades are constructed primarily of composite material with a metallic leading edge abrasion strip and integral de-ice blanket. These blades are attached to the proprotor hub which transmits drive torque to the proprotor. The proprotor controls respond to cyclic, directional, and thrust lever inputs in both helicopter and conversion modes, and to thrust inputs alone in airplane mode. Vibration reduction has been designed into the entire proprotor assembly including the pendulum dampers used to reduce the vibratory loads generated by the rotation of the proprotors.
The entire rotor, transmission, and engine nacelles tilt through 90 degrees in forward rotation and are directed forwards for forward flight, and through 7 degrees 30' in aft rotation for vertical take-off and landing. Both engines have cross-coupled transmissions so either engine can power the rotors in the event of an engine failure.
Flight Control System
The Osprey has both conventional airplane and conventional tandem-rotor helicopter control surfaces. The primary flight controls consist of cyclic sticks located in front of each pilot, thrust control levers mounted to the left of each seat, and floor-mounted directional pedals. These controls are part of a fully digital, electronic, fly-by-wire system. Because it is completely digital, the V-22's flight control system offers exceptional flexibility to incorporate the actuator control command for both fixed-wing and rotary-wing control surfaces and provides a smooth transition between airplane and helicopter flight modes.
The process of rotating the nacelles to transition between helicopter and airplane modes is called conversion. This process is simple, straight forward, and easy to accomplish. The amount and rate of nacelle tilt can be completely controlled by the pilot or can be performed automatically by the flight control system. The minimum time to accomplish full conversion from hover to airplane flight mode is 12 seconds. A tilt-rotor can fly at any degree of nacelle tilt.
During vertical take-off, conventional helicopter controls are utilized. As the tilt-rotor gains forward speed to between 40 and 80 knots, the wing begins to produce lift and the ailerons, elevators, and rudders become effective. At this point, rotary wing controls are gradually phased out by the flight control system. At approximately 100 to 120 knots the wing is fully effective and cyclic pitch control of the proprotors is locked out.The conversion from airplane flight to a hover simply reverses the process described above. Since the fuselage and wing are free to remain in a level attitude during the conversion, there is no tendency for the wing to stall as speed decreases. Rotor-borne lift fully compensates for the decrease in wing lift.
Because there is great variability available between aircraft and nacelle attitude, the conversion corridor (the range of permissible airspeeds for each angle of nacelle tilt) is very wide (about 100 knots). In both accelerating and decelerating flight this wide corridor means that a tilt-rotor can have a safe and comfortable transition, free of the threat of wing stall.
The V-22's cockpit features side-by-side seating for the pilot and co-pilot. The flight crew have a Pilot's Night Vision System and a Honeywell integrated helmet display. The cockpit is equipped with six night vision goggle compatible displays. The cabin and the cockpit are NBC (nuclear, biological and chemical warfare) protected with a positive pressure filtered air system.
The Marine Corps MV-22 variant has a folding crashworthy jumpseat for a third crew member mounted on the forward face of the cabin/cockpit door. The USAF Special Operations CV-22 variant has a folding, crashworthy jumpseat with an extended seat pan allowing a flight engineer access to the center and overhead consoles.
The U.S. Air Force and U.S. Navy variants are equipped with a terrain following AN/APQ-174 multi-mode radar. They also contain an AN/AAQ-16 FLIR (Forward Looking Infrared) night vision system which is mounted on the nose. This system contains a 3-5 micron indium antimonide staring focal plane array.
The V-22's electronic warfare suite includes an AN/AAR-47 missile warning system which is a passive electro-optical missile warner to protect the aircraft from surface to air missiles. It consists of four electro-optic sensors with photomultipliers, a signal processing unit, and a cockpit display. The aircraft is also equipped with a radar and infra-red threat warning system and chaff and flare dispensers with 60 rounds of dispensables. The CV-22 will have the Suite of Integrated Radio Frequency Measures (SIRFC), being developed by ITT Avionics.The aircraft also has provision for nose and ramp gun mounts.
The V-22 has a cargo compartment, measuring approximately 6 x 6 x 24 feet, with a rear loading ramp that provides easy access. It is fitted with crash-resistant foldaway seats, arranged twelve on each side and inward facing, for 24 fully-equipped combat troops. For the medical evacuation role, the cabin can accommodate 12 litters (stretcher patients) and a team of medical officers.
The internal cargo handling equipment includes a cargo winch and pulley rated at 2,000 lbs, roller rails, and shock absorbing cargo tie down rings fitted on the cabin floor. A cargo door is located on the right of the fuselage immediately behind the cockpit accompanied by a rear loading ramp/door assembly at the back of the fuselage which is hydraulically operated.
The aircraft is also fitted with two external cargo hooks, either of which can support a load of 10,000 lbs and a rescue hoist. If the retractable hooks are used together for stability, the combined capacity can be up to 15,000 lbs.The rescue hoist consists of a hydraulically powered winch mounted on a removable boom and support shaft. The winch holds 250 usable feet of 5.32 in diameter corrosion-resistant steel cable. It has a rated capacity of 600 lbs with a 2.5g limit load factor.
The Osprey's cargo compartment is capable of accepting cargo pallets or containers as large as 68 inches wide, 66 inches high, and 250 inches long, as long as the object is capable of achieving the necessary restraint criteria.
Blade Fold/Wing Stow Sequence
The V-22 is fully shipboard compatible with the world's first complete blade fold and wing stowage system. It is able to operate off all US Navy L-class amphibious ships, the LHA/LHD assault carriers, and can be stowed on full size CV/CVN carriers.
For stowage the wings are rotated to lie above and parallel to the fuselage to create a compact rectangular volume. The automatic wing and rotor folding sequence can be completed in 90 seconds in a 60 knot wind. It can be interrupted or stopped at any point to facilitate maintenance. Manual operation is possible in the event of a system failure.
Once the sequence is initiated, the proprotors turn themselves to a predetermined position. This is called indexing the blades. When complete, one blade on each side is pointing inboard. The remaining four blades automatically fold until all six blades are pointing inward, parallel to the wing. Next, the nacelles begin rotating from the upward, helicopter position to the horizontal, cruise position. Simultaneously, the wing swivels clockwise until the starboard nacelle is positioned in front of the aircraft's nose and the port nacelle is positioned above the fuselage just forward of the vertical tails. This completes the blade fold/wing stow sequence. When folded, the V-22 fits into a space 63 feet long, 18 feet 5 inches wide, and 18 feet high.
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