Bell Boeing Quad TiltRotor explained

Quad TiltRotor
Status:Study

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 100000abbr=onNaNabbr=on with a payload of up to 25000abbr=onNaNabbr=on in a hover.[2] The design was downsized to be more V-22-based and to have a payload of 18000to. This version was referred to as "V-44".[3] Bell received contracts to study related technologies in 2000. Development was not pursued by the US Department of Defense.[4]

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]

Design

The conceptual design featured a large tandem wing aircraft with V-22 type engines and 50feet rotors at each of the four wing tips. The C-130-size fuselage would have a 747inches 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 420to.[9] One of the design excursions explored, dubbed the "Big Boy", would have 55feet rotors and an 815inches cargo bay, making it able to carry one additional 463L pallet and accommodate a Stryker armored combat vehicle.[9]

References

External links

Notes and References

  1. http://www.boeing.com/news/frontiers/archive/2006/december/i_ids03.pdf "Diversity in Design: Boeing offers 2 of 5 development options in rotorcraft program"
  2. Hirschberg, Mike. "On the Vertical Horizon: Bell Designs Are Accelerating at Full Tilt". vtol.org.
  3. http://www.popularmechanics.com/science/defense/1281266.html V-44: Pentagon's Next Air Transport
  4. Norton 2004, p. 86.
  5. Radhakrishnan, Anand and Fredric Schmitz. "An Experimental Investigation of Ground Effect on a Quad Tilt Rotor in Hover and Low Speed Forward Flight". University of Maryland, 2006.
  6. Gupta, Vinit. "Quad Tilt Rotor Simulations in Helicopter Mode using Computational Fluid Dynamics" . University of Maryland, 2005.
  7. http://www.boeing.com/news/releases/2005/q3/nr_050922p.html "Boeing receives two study contracts from U.S. Army for Joint Heavy Lift"
  8. http://boeing.com/news/releases/2005/photorelease/q3/pr_050923p-1.html "Bell-Boeing's QTR selected for Heavy Lift study"
  9. Fein, Geoff. "Bell-Boeing Quadtiltrotor completes first wind tunnel testing" . Defense Daily, 13 October 2006.
  10. http://www.helis.com/news/2006/quadwindtunnel.htm "Wind Tunnel testing completed on Bell Boeing quad tiltrotor"
  11. http://www.bellhelicopter.com/en/support/pdf/rb/rb_oct06.pdf "Wind Tunnel testing completed on Bell Boeing quad tiltrotor"
  12. http://www.flightglobal.com/articles/2008/01/14/220796/heavy-duty-us-army-backs-tiltrotor-as-future-battlefield.html "Heavy duty: US Army backs tiltrotor as future battlefield airlifter"
  13. Osborn, Kris. "USAF, Army Merge Heavy-Lift Efforts". Defensenews.com, 14 April 2008.
  14. Warwick, Graham. "U.S. Army Extends JHL Concept Studies" . Aviation Week, 1 July 2008.
  15. Brannen, Kate. "Pentagon Sheds Some Light on JFTL Effort". Defense News, 15 July 2010.
  16. https://www.fbo.gov/index?s=opportunity&mode=form&id=abcbe12c3ab214cffa29f23eaf6d9bae&tab=core&_cview=1 Joint Future Theatre Lift (JFTL) Technology Study (JTS) Capability Request for Information (CRFI)
  17. http://www.airforce-magazine.com/SiteCollectionDocuments/Reports/2010/October%202010/Day25/JFTL_CRFI__102210.pdf "Joint Future Theater Lift (JFTL) Technology Study (JTS)"