The Rolls Royce F402-RR-408 Pegasus is the powerplant for the AV-8B Harrier II. The F402 Pegasus engine holds a unique place in the aviation world. This engine develops the powerful thrust required for vertical lift of the AV-8B aircraft. The variable direction exhaust from these allow the aircraft to take off vertically or in the normal horizontal runway mode.
The Harrier incorporates an innovative swiveling engine-exhaust nozzle design with a lightweight airframe to permit unique maneuvering capabilities unmatched by conventional aircraft. The Pegasus provides the Harrier II with both lift and propulsive thrust through four swiveling exhaust nozzles which vector engine thrust from horizontal, for conventional flight, to vertical, for landing. The thrust of the F402-RR-406 is 21500 pounds, while the more powerful F402-RR-408 has a thrust of 23400 pounds. The F402-RR-406 Pegasus engine is a two-spool design with a low and high pressure compressor and turbine based on materials technology available in the late 1950's.
In July 1992, problems in the F402 were said to be the single biggest reason for a 1986-1991 Harrier accident rate three times that of other Navy aircraft. In February 1991, the Marine Corps grounded AV-8Bs in service because of "development difficulties." The engine was reportedly flaming out at certain flight attitudes; a problem was traced to close tolerance between the compressor fan blades and the stators (fixed blades). The DECS software at times delivered inappropriate commands. Problems with overheating were traced to the F402's inlet guide vanes, which suffered from contamination of the lubrication system. In the opinion of both the Navy and Rolls-Royce, fixing the clearance and guide-vane shortcomings would require "a major redesign."
In 1998 the AV8 Harrier experienced problems between its F402-RR-406 engines and the JP-5/JP-8 fuel supplied by Shell Deer Park. The problem as discovered involved vane burning and excessive combustor coking on engines at MCAS Cherry Point. After intensive testing and investigation of the problem, there appeared to be incompatibility with specification JP-5/JP-8 produced by Shell and the subject engines. No other engines are affected. Shell, working with DESC and the Navy took corrective action to modify the refining process at the Shell Deer Park Refinery. This modification eliminated the engine distress. The deployment of the USS Saipan whose MCAS Cherry Point deployed AV8 Harrier aircraft experienced the same problems as those faced at Cherry Point. In this instance the main culprit was JP-5 fuel procured from NAMSOS Norway Storage Depot. Again the engine affected was the F402-RR-406. After more intensive investigation some of the corrective actions taken were to completely restrict the deployed aircraft from the subject fuel, increasing the boroscope testing frequency of the deployed AV8's engines, and downgrading the suspect JP-5 to F76. The USS Saipan replenished its fuel stocks with modified Shell JP-5 from the USS Kanawah, ridding itself of the suspect fuel. The USS Saipan's aircraft was then supported only from controlled JP-5 sources for the duration of its deployment. As such, no additional engine problems were reported. Shell has requested refinery process changes to increase the amount of jet fuel out of the Deer Park refinery. Initial tests indicate acceptable performance could be anticipated. Shell met with DESC, Navy, and Marines to propose this change on 13 November 1998.
Due to the high engine loads experienced during hovering at high ambient temperatures, second stage high pressure turbine stator vanes in the F402-RR-406 can exceed their temperature capability and fail by cracking or melting at the leading edge, followed by failure at the trailing edge. Once cooling air is lost at the airfoil due to failure, cooling air is also lost to downstream components, e.g., low pressure turbine vane, resulting in reduced life. Catastrophic vane failure can also create component failures downstream as fragments pass through low pressure turbine sections.
Silicon-based ceramics have been proposed as component materials for gas turbine engine hot-sections. When the Navy's Harrier fighter experienced Pegasus F402 engine failure because of leading-edge durability problems on the second-stage high-pressure turbine vane, the Office of Naval Research came to the NASA Glenn Research Center at Lewis Field for test support in evaluating a concept for eliminating the vane-edge degradation. In 1999 the High Pressure Burner Rig (HPBR) was selected for testing since it could provide temperature, pressure, velocity, and combustion gas compositions that closely simulate the engine environment. The study focused on equipping the stationary metal airfoil (Pegasus F402) with a ceramic matrix composite (CMC) leading-edge insert and evaluating the feasibility and benefits of such a configuration.
The engine underwent approximately 72 air-on hours of altitude performance testing at AEDC in the Propulsion Development Test Cell J-1 of the Engine Test Facility. The objectives of the test were to assess the engine's altitude performance and to demonstrate AEDC's capabilities to handle this unique vectored-thrust engine. Previously, the F402, which has been in production in various versions for 25 years, had been tested in the United States exclusively at the Naval Air Warfare Center at Trenton, NJ. However, as a result of the Base Realignment and Closure Commission, the Trenton facility was closed, and testing was transferred to AEDC.
The year 2000 saw the a F402 Harrier engine "red-stripe" that would cripple the community of aircraft powered by -408 engines. Harrier support for the 22nd and 24th MEUs were also suspended. Consequently, Marines had less operational deployment commitments and general military subjects training reached high completion rates relative to times when Marines deployed. The recovery from the "red stripe" was spearheaded by a new management philosophy through the introduction of Theory of Constraints. Using the TOC philosophy of identifying a constraint, leadership reviewed the work practices and determined that it was essential to have components and equipment available to decrease aircraft downtime and cannibalization actions. This in turn would increase aircraft readiness, which is fundamental for developing and maintaining aircrew combat proficiency.
A portion of the Corps' AV-8B Harrier jet fleet was grounded following an 11 July 2000 order suspending flights due to concerns about engine bearing problems. The Marine Corps launched an effort to inspect and test all of its F402-RR-408A/B engines for the AV-8B Harrier jet before returning the aircraft to flying status. By August 28, 2000, about 30 of the Corps' 106 Harriers powered by that engine have returned to flying status. About 10 other engines have been inspected and await installation. The remaining engines were due to undergo vibration-scan testing and, if necessary, be repaired before returning to service.
The AV-8B engine life management program (ELMP) is a comprehensive F402 engine program to improve its safety and reliability, and to increase the mean time between engine removals from 275 hours to 800 hours. The F402 is the single engine installed on all AV-8B aircraft. An increase was required in fiscal year 2004 to allow a third F402 accelerated simulated mission endurance test, to continue engine design improvements, and to provide improvements to the engine monitoring systems. Both the Chief of Naval Operations and the Commandant of the Marine Corps have included the AV-8B ELMP among their unfunded priorities for fiscal year 2004. Funding for the Engine Life Management Program will be placed on a cost type contract to Rolls Royce to address safety of flight issues, top readiness degraders, engine removal and mission failure drivers in order to improve Fleet readiness and cost of ownership. It is also developed to assess life management program issues and design fixes for any service revealed deficiencies.
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