Rolls-Royce LiftSystem

Requirement

The F-35B STOVL variant of the Joint Strike Fighter (JSF) aircraft was intended to replace the McDonnell Douglas AV-8B Harrier II and the McDonnell Douglas F/A-18 Hornet used by the United States Marine Corps. It would also replace the British Aerospace Harrier II and the British Aerospace Sea Harrier used by Royal Air Force and Royal Navy. The aircraft had to have a supersonic capability, and a suitable vertical lift system that would not compromise this capability was needed for the STOVL variant. This requirement was met by the Rolls-Royce LiftSystem, developed through a $1.3 billion System Development and Demonstration (SDD) contract from Pratt & Whitney. This requirement was met on 20 July 2001.

Design and development

Instead of using separate lift engines, like the Yakovlev Yak-38, or rotating nozzles for engine bypass air, like the Harrier, the "LiftSystem" has a shaft-driven LiftFan, designed by Lockheed Martin and developed by Rolls-Royce,

The team responsible for developing the propulsion system included Lockheed Martin, Northrop Grumman, BAE Systems, Pratt & Whitney and Rolls-Royce, under the leadership of the United States Department of Defense Joint Strike Fighter Program Office. Paul Bevilaqua, Chief Engineer of Lockheed Martin Advanced Development Projects (Skunk Works), invented the lift fan propulsion system. The concept of a shaft-driven lift-fan dates back to the mid-1950s. The lift fan was demonstrated by the Allison Engine Company in 1995–97.

The U.S. Department of Defense (DOD) awarded General Electric and Rolls-Royce a $2.1 billion contract to jointly develop the F136 engine as an alternative to the F135. The LiftSystem was designed to be used with either engine.

Rolls-Royce managed the overall development and integration program in Bristol, UK, and was also responsible for the LiftFan turbomachinery, 3BSM and Roll Post designs. Rolls-Royce in Indianapolis provided the gearbox, clutch, driveshaft and nozzle and conducted the build and verification testing of the LiftFan.

Operation

The Rolls-Royce LiftSystem comprises four major components:

• LiftFan
• Engine to fan driveshaft
• Three-bearing swivel module (3BSM)
• Roll posts (two)

The three-bearing swivel module (3BSM) is a thrust vectoring nozzle at the rear of the aircraft which directs engine exhaust to pass either straight through with reheat capability for forward flight, or to be deflected downward to provide lift.

For vertical flight, 29,000 hp is transferred by an extension shaft on the engine fan using a clutch and bevel-gearbox to a contra-rotating lift-fan located forward of the engine. The fan airflow (low-velocity unheated air) leaves through thrust-vectoring vanes on the underside of the aircraft, and balances the lift from the rear nozzle. For lateral stability and roll control, bypass air from the engine is used in a roll-post nozzle in each wing. For pitch control, the areas of exhaust nozzle and LiftFan inlet are varied while keeping the total lift constant. Yaw control is achieved by yawing the 3BSM. Forward, and also backward, motion is controlled by tilting the 3BSM and vanes in the LiftFan variable area vane box nozzle.

The following are the component thrust values of the system in lift mode:

In comparison, the maximum thrust of the Rolls-Royce Pegasus 11-61/F402-RR-408, the most powerful version which is used in the AV-8B, is 23800 lbf. The weight of the AV-8B is about 46% of the weight of the F-35B.

Like lift engines, the added LiftSystem components are dead weight during flight, but the advantage of employing the LiftSystem is that its greater lift thrust increases takeoff payload by an even larger amount.

Engineering challenges

While developing the LiftSystem many engineering difficulties had to be overcome, and new technologies exploited.

The LiftFan uses hollow-bladed titanium blisks (a bladed disk or "blisk" achieved by super-plastic forming of the blades and linear friction welding to the blisk hub). Organic matrix composites are used for the interstage vanes. The LiftFan is cleared for flight up to 250 kn This condition appears as a crosswind to the horizontal intake and occurs when the aircraft transitions between forward flight and hover.

The clutch mechanism uses dry plate carbon–carbon technology originally derived from aircraft brakes. Friction is only used to engage the lift fan at low engine speeds. A mechanical lock-up is engaged before increasing to full power.

The gearbox has to be able to operate with interruptions to its oil supply of up to a minute while transferring full power through 90 degrees to the LiftFan.

The Three-Bearing Swivel Module has to both support the final hot thrust vectoring nozzle and transmit its thrust loads back to the engine mounts. The "fueldraulic" actuators for the 3BSM use fuel pressurised to 3500 lbf/in2, rather than hydraulic fluid, to reduce weight and complexity. One actuator travels with the swivel nozzle, moving through 95 degrees while subject to intense heat and vibration.

Testing

During concept definition of the Joint Strike Fighter, two Lockheed airframes were flight-tested: the Lockheed X-35A (which was later converted into the X-35B), and the larger-winged X-35C, with the STOVL variant incorporating the Rolls-Royce LiftFan module.

LiftSystem flight testing commenced in June 2001, and on 20 July that year the X-35B became the first aircraft in history to perform a short takeoff, a level supersonic dash and vertical landing in a single flight. By the time testing had been completed in August, the aircraft had achieved 17 vertical takeoffs, 14 short takeoffs, 27 vertical landings and five supersonic flights. During the final qualifying Joint Strike Fighter flight trials, the X-35B took off in less than 500 ft, transitioned to supersonic flight, then landed vertically.

Ground tests of the F136/LiftSystem combination were carried out at the General Electric facility in Peebles, Ohio in July 2008. On 18 March 2010, a STOVL equipped F-35B performed a vertical hover and landing demonstration at Patuxent River Naval Air Station in Lexington Park, MD.

Collier Trophy award

In 2001, the LiftSystem propulsion system was awarded the Collier Trophy, in recognition of "the greatest achievement in aeronautics or astronautics in America", specifically for "improving the performance, efficiency and safety of air or space vehicles, the value of which has been thoroughly demonstrated by actual use during the preceding year."

Specifications (LiftSystem)

;Main engine: ;Pratt & Whitney F135 : 17600 lbf dry thrust

Components: ;LiftFan :Two-stage contra-rotating hollow titanium blisk fan of 50 in diameter. Uppermost fan fitted with variable inlet guide vanes. Capable of generating more than 20000 lbf cold thrust ;Three-bearing swivel module :Able to rotate through 95 degrees in 2.5 seconds and vector 18000 lbf dry thrust in lift mode, with reheat capability in normal horizontal attitude ;Roll posts :Two: hydraulically actuated

Gallery

File:F-35 compilation.ogg|X-35/LiftSystem flight demonstration of transition to VTOL configuration, hover, take off in STOVL configuration, in-flight re-fuelling, vertical hover and landing. File:F-35_vertical_landing.ogg|Vertical landing demonstration showing operation of the 3BSM. File:F-35B_STOVL_Engine_and_Lift_Fan.JPG|Turbine and lift fan assembly on display at the National Air and Space Museum, Steven F. Udvar-Hazy Center

References

References

1. "Integrated Lift Fan Gets Nod for Collier Trophy".
2. "Background - Joint Strike Fighter".
3. [http://www.rolls-royce.com/products-and-services/defence-aerospace/products/combat-jets/rolls-royce-liftsystem.aspx LiftSystem] Rolls-Royce website. Retrieved: July 2017
4. [http://www.lockheedmartin.com/news/press_releases/2003/PropulsionSystemInLockheedMartinJoi.html Propulsion System in Lockheed Martin Joint Strike Fighter wins Collier Trophy] {{webarchive. link. (25 May 2011 . Lockheed Martin press release, 28 February 2003. Retrieved: 3 November 2008)
5. [http://www.space.com/businesstechnology/071221-how-f-35b-stovl-propulsion-system-works.html From Supersonic to Hover: How the F-35 Flies] By Chris Kjelgaard Senior Editor posted: 21 December 2007
6. "F-35B Lightning II Three-Bearing Swivel Nozzle | Code One Magazine".
7. [http://www.lockheedmartin.com/how/stories/f35_player.html Undated Lockheed Martin video.]{{dead link. (March 2018)
8. [http://www.freepatentsonline.com/5209428.html "Propulsion system for a vertical and short takeoff and landing aircraft"], United States Patent 5209428
9. [http://www.janes.com/extracts/extract/jae/jae_1071.html Rolls-Royce LiftSystem (United States), AERO-ENGINES - LIFTFAN] Jane's Aero-Engines. Retrieved: 4 November 2008 {{dead link. (April 2010)
10. "[http://www.flightglobal.com/articles/1997/05/21/3890/as-allison-begins-jsf-lift-fan-tests.html -as Allison begins JSF lift-fan tests]" ''Flight International'', 21 May 1997. Retrieved: 19 September 2010. [https://web.archive.org/web/20121102194745/http://www.flightglobal.com/news/articles/as-allison-begins-jsf-lift-fan-tests-3890/ Archived] on 2 November 2012.
11. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
12. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
13. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
14. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
15. [http://www.vtol.org/Lockheed.htm Lockheed Propulsion System] {{webarchive. link. (20 June 2010 ''VTOL.org''. Retrieved: 19 September 2010.)
16. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
17. link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
18. [http://www.rolls-royce.com/defence_aerospace/technology/stovl.jsp STOVL pedigree gives Rolls-Royce key technology edge.] {{Webarchive. link. (15 November 2008 Rolls-Royce: Defence Aerospace. Retrieved: 5 November 2008)
19. [http://www.ingenia.org.uk/ingenia/issues/issue20/hutchinson.pdf Going vertical – developing a short take-off, vertical landing system.] {{Webarchive. link. (20 July 2015 Ingenia Online (PDF) August 2004. Retrieved: December 2009.)
20. "Going vertical – developing a short take-off, vertical landing system".
21. link. (13 April 2014 [http://www.aviationweek.com/Blogs.aspx?plckBlogId=Blog:a68cb417-3364-4fbf-a9dd-4feda680ec9c&plckPostId=Blog:a68cb417-3364-4fbf-a9dd-4feda680ec9cPost:41e6d676-ad38-4c26-a670-b72068fabeae Doors 2] {{Webarchive). link. (13 April 2014 " ''[[Aviation Week & Space Technology]]'', 9 December 2011. Accessed: 10 April 2014.)
22. Zolfagharifard, Ellie. "[http://www.theengineer.co.uk/in-depth/rolls-royces-liftsystem-for-the-joint-strike-fighter/1008008.article Rolls-Royce's LiftSystem for the Joint Strike Fighter]" ''[[The Engineer (UK magazine)]]'', 28 March 2011. [https://web.archive.org/web/20131219050153/http://www.theengineer.co.uk/in-depth/rolls-royces-liftsystem-for-the-joint-strike-fighter/1008008.article Archived] on 19 December 2013]
23. "The Shaft Driven Lift Fan Propulsion System for the Joint Strike Fighter" P. Bevilaqua, Presented at the American Helicopter Society 53rd annual forum, Virginia Beach, Virginia, 29 April – 1 May 1997
24. "Joint Strike Fighter official site - History page".
25. PBS: [https://www.pbs.org/wgbh/nova/transcripts/3004_xplanes.html Nova transcript "X-planes"]
26. [http://www.lockheedmartin.com/news/press_releases/2010/100318ae_f35b-vertical-landing.html Lockheed Martin press release] {{Webarchive. link. (22 March 2010 Retrieved: 18 March 2010)
27. link. (31 May 2011 National Aeronautic Association. Retrieved: 10 November 2008)
28. [http://www.theengineer.co.uk/in-depth/rolls-royces-liftsystem-for-the-joint-strike-fighter/1008008.article "Rolls-Royce's LiftSystem for the Joint Strike Fighter"] {{Webarchive. link. (19 December 2013 By Ellie Zolfagharifard, [[The Engineer (UK magazine)). The Engineer]] 28 March 2011