As of 1997 the V-22 escort aircraft was expected to serve in the air-to-air combat mode while escorting the V-22s to shore and back to ship-board base. Additionally, the escort is required to engage in air-to-ground warfarein the vicinity of the landing zone where the V-22 is off-loading troops and/or cargo.
The basic mission requirements and constraints dictate that the vehicle must:
- Be capable of operating from the same class of Navy ships as the V-22 (LHA, LPH, and LHD). I.e. - must be able to fit into the ship elevators and hanger decks.
- Have a two-man crew.
- Have a maximum hover-out-of-ground-effect(HOGE) disc loading of 20 lbs/ft2 at maximum takeoff gross weight (TOGW) to minimize erosion and blowing dust from unpreparedsurfaces during VTOL operations .
- Have a vertical rate of climb (VROC) of at least 1,000 feet per minute at TOGW, standard sea level, maximum rated engine power (MRP).
- Have a dash speed of at least 400 knots at an altitude of 3,000 feet, MRP.
- Be able to sustain a 5.0 g turn at TOGW, flying at 250 knots at an altitude of 3,000 ft.
- Have a weapons load consisting of: internal or turreted 20 millimeter cannon+1500 rounds of ammunition, 4 AIM-9L air-to-air missiles, and 4 AGM-114 air-to-ground missiles.
The two most promising VTOL candidates that can fulfill this mission are the Variable Diameter Tiltrotor (VDTR) and the Stopped Rotor/Wing (SRW). These concepts were selected for comparison in this study based on their potential to meet the dash requirementas well as the military nature of the mission.
The Bell/Agusta 609, made by a commercial joint venture between Bell Helicopter and Agusta, of Italy, is about one-third the size of the V-22. The Bell/Agusta 609 potentially could serve in an armed escort role, assuming that it could be reconfigured as a gunship. An armed 609 also would be considered as a possible replacement for the Marine Corps' Cobra gunship, in the 2015-2020 timeframe.
In 1998 Boeing revived the CRW (canard rotor wing) design for armed V-22 escort duties, as well as unmanned surveillance missions. In 2001 the US Marine Corps considered a new type of hybrid vertical-takeoff and landing rotorcraft, the canard-rotor wing. It can operate out of the same areas, but has much higher speed [up to 400 knots]. The Dragonfly UAV could be a fighter escort for the V-22.
In 2003 the US Marine Corps considered the HV-911 Eagle Eye tiltrotor UAV as the much-discussed V-22 escort. The Eagle Eye would be air transportable inside V-22s on missions, reducing footprint and ending the need to use C-130s. The USCG signed up for the aircraft as one of the primary surveillance assets it's programmed to get as part of the Deepwater project. It is helping the Marines get the new escort proposal in shape.In 2003 Bell continued concept development involving attack and escort versions of the tiltrotor for use with both the V-22 and the QTR. These range from reaping the benefits of commonality by mating the V-22 wing and propulsion systems with a different fuselage and cockpit, which would create an attack tiltrotor with A-10 characteristics, to developing a completely new design for a stealthy attack/escort tiltrotor.
A more radical design that has already seen some wind-tunnel time is our Stop-Fold TiltRotor (SFTR) concept vehicle. If a tiltrotor combines the best characteristics of a helicopter and a turboprop, this aircraft would combine the best aspects of a tiltrotor and a jet. The SFTR's unique design allows it to take-off and land like either a helicopter or a turbofan jet. At low speeds (up to 150 knots), it operates like a conventional tiltrotor, but above that speed its rotors can be feathered, stopped, and folded along the nacelles, and the turbofans would convert from shaft drive to thrust - giving the aircraft a speed range of zero to its power limit. High subsonic, or even supersonic speeds are possible with this design. The SFTR provides jet performance while "up and away" with the easy maneuverability, reasonable downwash and hover efficiency of a tiltrotor during the takeoff and landing portion of flight.
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