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 On The Vertical Horizon:
The Integrated High Performance Turbine Engine Technology - IHPTET (pronounced "IP-tet") - initiative is a joint DoD/NASA/Industry effort, with the objective of developing and demonstrating advanced engine technologies capable of more than doubling turbine engine power-to-weight ratio and reducing specific fuel consumption (SFC) by 40% over modern production engines. The specific top-level goals for turboshaft and turboprop engines, as well as for turbofan/turbojet and expendable engines, are shown in figure 1. These goals are to be achieved with no compromise in life and durability levels relative to the 1987 state-of-the-art. For the turboshaft/turboprop class this means 6,000 hours for creep/stress rupture, 15,000 cycles for low cycle fatigue in the compression system, and 7,500 cycles for low cycle fatigue in the hot section (combustor, turbines, and exhaust systems).
Figure 1: Top-Level IHPTET Goals The primary technical challenges are in increasing the engine overall pressure ratio, operating at higher maximum cycle temperatures, increasing component efficiencies, developing advanced durable high temperature materials, and reducing component weight. The IHPTET program was initiated in 1988, and brought together in a coordinated program a number of turbine engine technology efforts that had been ongoing since the 1960s. The first task for the program was to develop the goals, a rigorous process that culminated after two years of effort with highly detailed targets for each engine component. In response to growing system affordability concerns, the IHPTET community began investigating the addition of acquisition- and maintenance-related cost goals in FY93. These goals were instituted in FY95. IHPTET is funded jointly by industry and government. The Army is the lead agency for the turboshaft/turboprop class of IHPTET, which averages about $19M per year including contractor cost shares (typically 25-50%). The total government investment (in all engine classes of IHPTET) is less than 2% of the total DoD Science & Technology budget, while the combined government and industry investment is less than 2% of domestic engine sales revenue. Despite this modest investment, the payoff is critical for the US to maintain its lead in turbine engine technology. The program is not just for military engines, but contributes greatly to the improvement of commercial engine performance as well. This is part of the incentive for the industry contribution, since the US share of the engine industry world market decreased from over 80% in 1970 to less than 60% by 1990. The engine cores (high pressure compressor/combustor/turbine) used to demonstrate the IHPTET goals are developed under the Joint Turbine Advanced Gas Generator (JTAGG) component of the IHPTET program. These JTAGG cores are used to demonstrate and integrate the advanced component technologies, such as advanced materials, innovative structural designs, improved aerothermodynamics, and advanced computational methods. Progress So Far Phase I JTAGG turboshaft contracts were awarded to both General Electric (with AlliedSignal Engines - now part of Honeywell - as a partner) and Textron Lycoming (later part of AlliedSignal) in 1989. The Phase I goals were demonstrated by both contractors in 1995 (see figure 2). In fact, the Lycoming JTAGG I gas generator was the first - on July 28, 1995 - of the IHPTET demonstrators to achieve the performance objectives and thereby demonstrate the feasibility of achieving the overall IHPTET program goals. To date, technological improvements in the compression systems, combustion systems, turbine systems, controls and accessories, and mechanical systems of a gas turbine engine have been demonstrated in JTAGG, providing a 22% reduction in SFC and a 63% increase in shaft horsepower-to-weight ratio, while maintaining the durability requirements.
Figure 2: AlliedSignal (left) and Lycoming (right) JTAGG I demonstrators A Phase II JTAGG contract was awarded in 1994 to Lycoming (now Honeywell). AlliedSignal (in partnership with General Electric) had also bid for the JTAGG II program, but due to funding constraints, that program was not funded. Some of the specific advanced technologies to be demonstrated on the Honeywell JTAGG II engine include: a splittered rotor (see figure 3), high tip speed impeller, rich-quench-lean (RQL) Lycolite(tm) combustor liner, monolithic ceramic low pressure turbine vanes, High Effectiveness Advanced Turbine (HEAT(tm)) blades, high speed hybrid ceramic bearings, and brush seals. These technologies are intended to allow higher temperatures at combustion initiation, a higher maximum cycle temperature, reduced specific weight, increased component efficiencies, effective control of cooling air in the small blades and vanes, improved centrifugal impeller aerodynamics, and operation at higher rotor speeds.
Figure 3: Splittered Rotor
Figure 4: RQL Lycolite(tm) combustor The JTAGG II demonstrator (see figure 5) has completed initial design, fabrication and component testing. The initial gas generator demonstrator tests are set to begin in April 2000, with the final build to demonstrate the Phase II goals expected in the January 2001 timeframe. After the completion of the demonstration test program, the Honeywell JTAGG II gas generator will go on to be the core engine for the Joint Expendable Turbine Engine Concept (JETEC) turbofan now being developed by Honeywell.
Figure 4: Honeywell JTAGG II demonstrator In late 1997, AlliedSignal (with GE as a partner) was awarded the Phase III demonstrator contract. The key technologies to be demonstrated on the JTAGG III core include: a forward swept splittered rotor, a forward swept split inducer impeller, a ceramic matrix composite (CMC) combustor liner, a cooled CMC turbine nozzle, cooled and uncooled monolithic ceramic turbine blades, magnetic bearings, and finger seals. Initial design is essentially complete and component fabrication is underway. Component rig testing is planned for 2000 and 2001. Gas generator tests are scheduled for mid-2001 to late-2003. Planned Applications In addition to developing technologies that can provide near term improvements to existing engines, the IHPTET technologies are also being targeted for new engine developments. JTAGG I and II-derived engines are being planned for development under the Common Engine Program (CEP) for Black Hawk/ Apache upgrades, while JTAGG III-derived engines would most likely be required for the Future Transport Rotorcraft (FTR - previously known as the Joint Transport Rotorcraft, or JTR). The CEP, if funded, will develop a new centerline engine applicable to Black Hawks and Apaches that will enable achievement of future payload and range requirements. The CEP goals include a 25-30% reduction in SFC, a 60% improvement in power-to-weight and a minimum of 20% reduction in acquisition and maintenance costs. It is expected that the CEP development program will be funded from FY01 thru FY07 to qualify a production engine of roughly 3,000 shp. These goals would enable a 60% improvement in range or 70% increase in payload for a 9,000 lb (versus current 5,100 lb) UH-60X external lift mission, as well as reduce the logistics and maintenance burdens. The CEP will enable the Black Hawk to meet the increased lift and range requirements called out in the Operational Requirements Document (ORD) for Modernization of the UH-60 Black Hawk Utility Helicopter Fleet. In addition to the possibility of the Honeywell JTAGG-derived engine for the CEP, GE and Pratt & Whitney recently announced that they are negotiating a 60/40 joint venture to compete for the CEP development (see figure 5). The team expects to commence pre-development work this year, incorporating JTAGG/IHPTET technologies.
Figure 5. Honeywell (left) and GE (right) CEP mock-ups Concurrent with the CEP program, high power-to-weight engines must also be developed for the FTR. To meet the timeline for the FTR that is currently envisioned, an engine demonstrator program could begin in FY04, using IHPTET Phase II and III JTAGG technologies. Engineering and Manufacturing Development (EMD) for the engine could be conducted from FY08-10 to be available for the FTR EMD in FY11, and FTR production in FY14. This engine, in the 10,000 shp class, would enable the four-fold increase in range, and the doubling of payload capability over today's heavy lift rotorcraft, envisioned for the FTR. Summary The IHPTET Program is conducting a systematic development and demonstration of advanced turbine engine technologies to help maintain US technological superiority in gas turbine engines. Substantial progress has been made over the past 12 years. With the planned testing of the JTAGG II and III demonstrators over the next three years, the US defense services are well poised to reap the benefits of revolutionary improvements in turboshaft engine capabilities for future combat rotorcraft.
About the Author: Mike Hirschberg is an aerospace engineer at ANSER, Inc. He currently supports the Joint Strike Fighter propulsion system development and serves as the managing editor of Vertiflite. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
