Proposed four-rotor derivative of the V-22 Osprey
The Bell Boeing Quad TiltRotor (QTR) is a proposed four-rotor derivative of the Bell Boeing V-22 Osprey developed jointly by Bell Helicopter and Boeing. The concept is a contender in the U.S. Army's Joint Heavy Lift program (a part of Future Vertical Lift program). It would have a cargo capacity roughly equivalent to the C-130 Hercules, cruise at 250 knots, and land at unimproved sites vertically like a helicopter.[1]
Development
Background
Bell developed its model D-322 as a quad tiltrotor concept in 1979. The Bell Boeing team disclosed a Quad TiltRotor design in 1999 which the companies had been investigating during the previous two years. The design was for a C-130-size V/STOL transport for the US Army's Future Transport Rotorcraft program and would have 50% commonality with the V-22. This design was to have a maximum takeoff weight of 100,000 lb (45,000 kg) with a payload of up to 25,000 lb (11,000 kg) in a hover.[2][3] The design was downsized to be more V-22-based and to have a payload of 18,000 to 20,000 lb (8,200 to 9,100 kg). This version was referred to as "V-44".[2][4] Bell received contracts to study related technologies in 2000. Development was not pursued by the US Department of Defense.[2]
From 2000 to 2006, studies of the aerodynamics and performance of a Quad Tilt Rotor were conducted at the University of Maryland, College Park. This effort was initially funded by NASA/AFDD and subsequently by Bell. An experimental investigation in helicopter mode with ground effect found that it was possible to reduce the download on the aircraft from 10% of the total thrust to an upload of 10% of the thrust.[5] A parallel Computational Fluid Dynamics (CFD) study confirmed these findings.[6]
Joint Heavy Lift studies
In September 2005, Bell and Boeing received a cost-sharing contract worth US$3.45 million from the U.S. Army's Aviation Applied Technology Directorate for an 18-month conceptual design and analysis study lasting through March 2007, in conjunction with the Joint Heavy Lift program.[7][8] The contract was awarded to Bell Helicopter, which is teaming with Boeing's Phantom Works. The QTR study is one of five designs; one of the five is also a Boeing program, an advanced version of the CH-47 Chinook.[1]
During the initial baseline design study, Bell's engineers were designing the wing, engine and rotor, while the Boeing team was designing the fuselage and internal systems.[9] A similar arrangement is used on the V-22.
A one-fifth-scale wind tunnel model has undergone testing in the Transonic Dynamics Tunnel (a unique transonic wind tunnel) at NASA's Langley Research Center during summer 2006. The "semi-span" model (representing the starboard half of the aircraft) measured 213 inches in length and had powered 91-inch rotors, operational nacelles, and "dynamically representative" wings.[10]
The primary test objective was to study the aeroelastic effects on the aft wing of the forward wing's rotors and establish a baseline aircraft configuration.[1] Alan Ewing, Bell's QTR program manager, reported that "Testing showed those loads from that vortex on the rear rotor [are the] same as the loads we see on the front [rotors]," and "Aeroelastic stability of the wing looks exactly the same as the conventional tiltrotor". These tests used a model with a three-bladed rotor, future tests will explore the effects of using a four-bladed system.[9]
Besides the research performed jointly under the contract, Bell has funded additional research and wind tunnel testing in cooperation with NASA and the Army.[11] After submission of initial concept study reports, testing of full-scale components and possibly a sub-scale vehicle test program was expected to begin.[1] Pending approval, first flight of a full-scale prototype aircraft was slated for 2012.[9]
The study was completed in May 2007,[12] with the Quad TiltRotor selected for further development. However, additional armor on Future Combat Systems manned ground vehicles caused their weight to increase from 20 tons to 27 tons, requiring a larger aircraft.[13] In mid-2008, the U.S. Army continued the Joint Heavy Lift (JHL) studies with new contracts to the Bell-Boeing and Karem Aircraft/Lockheed Martin teams. The teams were to modify their designs to reach new JHL specifications. JHL became part of the new US Air Force/Army Joint Future Theater Lift (JFTL) program in 2008.[14] In mid-2010, the US DoD was formulating a vertical lift aircraft plan with JFTL as a part.[15] The DoD also requested information from the aerospace industry on technologies for JFTL in October 2010.[16][17][needs update]
Design
The conceptual design featured a large tandem wing aircraft with V-22 type engines and 50-foot (15 m) rotors at each of the four wing tips. The C-130-size fuselage would have a 747-inch (19.0 m) cargo bay with a rear loading ramp that could carry 110 paratroopers or 150 standard-seating passengers. In cargo configuration, it would accommodate eight 463L pallets. This baseline version includes a fully retractable refueling probe and an interconnecting drive system for power redundancy.[9]
In addition, the Bell-Boeing team included eight possible variants, or "excursion designs", including a sea-based variant. The design team planned on payloads ranging from 16 to 26 tons and a range of 420 to 1,000 nautical miles (780 to 1,850 km).[9] One of the design excursions explored, dubbed the "Big Boy", would have 55-foot (17 m) rotors and an 815-inch (20.7 m) cargo bay, making it able to carry one additional 463L pallet and accommodate a Stryker armored combat vehicle.[9]
