|Bell QTR Quad Tiltrotor|
Bell announced in early 1999 that it was studying a proposed Quad TiltRotor (QTR) to meet Future Transport Rotorcraft (FTR) requirements. As projected, the aircraft would feature a fuselage approximately the size of that of a Lockheed-Martin C-130-30, mated to two sets of wings, engines and tiltrotors from the Bell Boeing V-22 Osprey, the rear units mounted on stub wings to extend span and ensure adequate fuselage clearance. Rear tiltrotors could fold in cruising flight, with their engines providing supplemental thrust. The Quad TiltRotor would be able to accommodate up to 90 passengers, or an AH-64, AH-1Z, RAH-66, UH-1Y or UH-60 helicopter, or three HMMWVs, or up to eight 463L pallets.
Provisional specifications include VTOL maximum T-0 weight 45,360kg; STOL maximum T-0 weight 63,505kg; and a payload up to 18,144kg. The Quad TiltRotor was in the conceptual design phase in mid-2000, with water tunnel testing of a 1/48th scale model to visualise complex airflow patterns around the tandem wings and four tiltrotors completed.
In mid-2000 DARPA awarded Bell a US$400,000 phase 1 contract as part of a three-phase, US$6 million cost-sharing programme to study the feasibility of the QTR concept. Phase 1 involved a detailed technology study. In phase 2, a 1/14th scale hovering model of the QTR was test-flown. Phase 3 comprised wind tunnel tests to determine loads and aerodynamic performance of the full-size aircraft.
The first of two demonstrators could be flown by 2006, with production deliveries starting in 2010. Potential customers include the US Marine Corps (to replace Sikorsky CH-53E helicopters and KC-130 Hercules) and USAF (MH-53J combat SAR/special forces helicopters).
Jane's All the World's Aircraft, 2004-2005
With the Quad Tiltrotor concept, Bell seeks to capitalize on V-22 investments to develop a large payload, high speed, Vertical and/or Short Take Off and Landing (V/STOL) capability for the military within 10 years. 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. The wing structure outboard of the flaperons would also be common; however the front wing would have a slightly longer span than the V-22 to accommodate the wider fuselage The rear wing would be longer than the front wing, putting the rear rotors outboard of the front rotors for higher performance and fuel economy in cruise. The front and rear propulsion systems could be interconnected for additional reliability. The glass cockpit, avionics, instruments, and threat warning systems could also be adapted directly from the V-22.
The QTR fuselage would be the size of a Lockheed Martin C-130-30 Hercules transport, and could transport a wide assortment of loads: eight 463L pallets, 90 passengers, 70 stretchers, a helicopter as large as an AH-64 "Apache", a 155mm howitzer, or three HMMWVs. A rear ramp, rollers and rails would facilitate common logistics equipment used for the C-5, C-17, C-130 and C-141 loading. According to Bell, an advanced concept technology demonstrator (ACTD) could fly by 2005, with production deliveries beginning in 2010. Although it would be possible to use a modified C-130 fuselage for a demonstrator, there are very different structural requirements since the QTR has two wings versus the single wing of the Hercules. For production, lower weight and a better match for the expected payloads would be possible with a new fuselage. Although Boeing builds the V-22 fuselage, Dick Spivey, Bell's Director of Advanced Concepts, said Boeing would not necessarily be a partner on the QTR; either Bell or a subcontractor could build the fuselage. Bell has recently determined that it can eliminate the vertical tail entirely, and provide directional stability via differential rotor thrust.
The QTR would be able to deliver cargo from airfields and port facilities directly to ground maneuver units and to ships at sea, needing as little as 1/2 acre to land. The QTR would allow a practical means to transport up to 13500kg externally or 18000kg internally far from shore bases (due to its size, however, it would obviously not be able to be stowed below deck). With twice the propulsion system of the V-22, the QTR could hover at 45000kg and have a maximum weight of 63000kg; internal volume would be 6-8 times that of the V-22. Maximum unrefueled range would be 3700km and it could cruise at 520km/h.
According to Spivey, Bell has flown two V-22s in close proximity to each other, approaching the distance between the fore and aft rotor system, with no difficulties. 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. It should also be noted that from 1966 to 1980, some 200 flight test hours were conducted on two Bell X-22 quad tilt duct demonstrators.
Using common parts with the V-22 would not only reduce the cost of the QTR, but also that of the V-22. It would allow existing support equipment, test equipment and spares pipeline to be used for both aircraft, reducing the logistics footprint. Efficiencies in maintenance and training could also be realized.
Bell is discussing the Quad Tiltrotor with the Services to define potential requirements (e.g., the Joint Transport Rotorcraft/Joint Common Lift mission), and is pursuing possible risk reduction activities with DARPA. With the QTR, the Marine Corps could deliver thousands of tons of supplies per day to forward troops without having to depend on land supply routes. The Navy could deliver of tons of supplies to carriers and even non-aviation ships while underway, without the need for a catapult or arresting gear. The Army is seeking to replace the heavy lift CH-47 Chinook helicopters it uses today with much greater capability, and is currently funding advanced rotors, transmissions and structures science and technology programs. The Air Force could supply its aerospace expeditionary forces directly from forward operating bases. Humanitarian relief, such as was needed for Central America in October 1998 after hurricane Mitch, could be greatly improved with a large heavy lift V/STOL transport. And non-combatant evacuations could be conducted from the continental US to anywhere in the world using the QTR's aerial refueling capability. For example, in a hypothetical rescue mission, a QTR could take off from Quantico Marine Corps Base in Virginia and fly to the American Embassy in Moscow with two refuelings over the North Atlantic. The QTR could then take up to 80 passengers out to a vertical recovery on an American ship in the Baltic.