The Bell Boeing Quad TiltRotor (QTR) is a proposed four-rotor derivative of the V-22 Osprey tiltrotor being developed jointly by Bell Helicopter Textron and Boeing Integrated Defense Systems. The concept is a contender in the U.S. Army's Joint Heavy 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.
During the initial baseline design study, Bell's engineers are designing the wing, engine and rotor, while the Boeing team is designing the fuselage and internal systems.
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 right half of the aircraft) measured 213 inches in length, and had powered 91-inch rotors, operational nacelles, "dynamically representative" wings.
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. 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.
Besides the research performed jointly under the contract, Bell has funded additional research and wind tunnel testing in cooperation with NASA and the Army. After submission of initial concept study reports, testing of full-scale components and possibly a sub-scale vehicle test program was expected to begin. Pending approval, first flight of a full-scale prototype aircraft was slated for 2012.
The study was completed in May 2007, with the Quad TiltRotor selected for further development. However, additional armor on Future Combat Systems (FCS) vehicles caused their weight to increase from 20 tons to 27 tons which requires a larger aircraft. In mid-2008, the Army continued the Joint Heavy Lift (JHL) studies with new contracts to the Bell-Boeing and Karem Aircraft/Lockheed Martin teams. The teams are 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.
In addition to the baseline configuration, the Bell-Boeing team is including eight possible variants, or "excursion designs", including a sea-based variant. The design team is planning on payloads ranging from 16 to 26 tons and a range of 420 to 1000 nm. The baseline version includes a fully retractable refueling probe and an interconnecting drive system for power redundancy.
One of the design excursions explored by the team, dubbed the "Big Boy", would have 55-foot rotors and an 815-inch-long cargo bay, making it able to carry one additional 463L pallet, and accommodate a Stryker armored combat vehicle.