3
Proposed Engine Modifications and Re-engining

The committee has looked at a number of potential engine modifications as well as concepts for re-engining of current aircraft. In general, at 2006 fuel prices, it was difficult to recommend any modifications or engine changes on the basis of fuel savings alone. Some changes, however, bring significant operational improvements and maintenance benefits and should be considered by the Air Force.

KC-135 R/T AIRCRAFT

Among the options available for reducing the weapons system fuel consumption are the following:

  • Changing the mission,

  • Reducing aircraft drag,

  • Upgrading the propulsion system,

  • Modifying the aerodynamics, and

  • Modifying the operational and maintenance practices.

From the above list of options, upgrades to the propulsion system were considered the most cost-effective approach for the KC-135 R/T fleet. There are currently 420 KC-135 R/T in the Air Force inventory. They are powered by 1,799 F108/CFM56-2 engines (1,744 installed and 55 spare). The fleet averages 400+ hours per year per aircraft. For planning purposes it can be assumed that they fly 500 hours per year. The fuel consumption of the KC-135 R/T fleet accounts for a significant share of the Air Force mobility fleet needs (Figure 3-1).

The F108 engine also makes up a significant portion of the mobility fleet inventory (Figure 3-2). The question before the panel is: Should the modification of F108 to gain improved fuel burn be considered at this time?

Engine modifications have been applied to the CFM56 fleet through the years. The latest modification is the three-dimensional (3D) Aero modification program, which has been introduced on the commercial side (CFM56-2), and the service life extension program (SLEP), which has been introduced on the F110-powered fleet. The 3D Aero program and SLEP are similar modifications of the core engine



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Improving the Efficiency of Engines for Large Nonfighter Aircraft 3 Proposed Engine Modifications and Re-engining The committee has looked at a number of potential engine modifications as well as concepts for re-engining of current aircraft. In general, at 2006 fuel prices, it was difficult to recommend any modifications or engine changes on the basis of fuel savings alone. Some changes, however, bring significant operational improvements and maintenance benefits and should be considered by the Air Force. KC-135 R/T AIRCRAFT Among the options available for reducing the weapons system fuel consumption are the following: Changing the mission, Reducing aircraft drag, Upgrading the propulsion system, Modifying the aerodynamics, and Modifying the operational and maintenance practices. From the above list of options, upgrades to the propulsion system were considered the most cost-effective approach for the KC-135 R/T fleet. There are currently 420 KC-135 R/T in the Air Force inventory. They are powered by 1,799 F108/CFM56-2 engines (1,744 installed and 55 spare). The fleet averages 400+ hours per year per aircraft. For planning purposes it can be assumed that they fly 500 hours per year. The fuel consumption of the KC-135 R/T fleet accounts for a significant share of the Air Force mobility fleet needs (Figure 3-1). The F108 engine also makes up a significant portion of the mobility fleet inventory (Figure 3-2). The question before the panel is: Should the modification of F108 to gain improved fuel burn be considered at this time? Engine modifications have been applied to the CFM56 fleet through the years. The latest modification is the three-dimensional (3D) Aero modification program, which has been introduced on the commercial side (CFM56-2), and the service life extension program (SLEP), which has been introduced on the F110-powered fleet. The 3D Aero program and SLEP are similar modifications of the core engine

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 3-1 Number of aircraft in the Air Force large nonfighter aircraft inventory. SOURCE: DESC (2005). FIGURE 3-2 Number of engines installed in the Air Force large nonfighter aircraft fleet. SOURCE: Amos

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Improving the Efficiency of Engines for Large Nonfighter Aircraft with a new version of compressor blades, a modified combustor, and modified high-pressure turbine vanes and blades to improve the aerodynamics. An engine upgrade has been proposed that involves turbomachinery modifications. This upgrade should yield 2 percent specific fuel consumption (SFC)/fuel burn improvements (see Figure 3-3). The projected improvement is based on data from the incorporation of similar modifications to the F110 engine family. The projected cost for the modifications is $15 million for nonrecurring engine tooling. No nonrecurring work is anticipated for the airframe. A number of upgrades have been and are being introduced in the commercial CFM56 engines. Examples are 3D and tech insertion programs, both of which result in fuel savings and increased reliability. They should be considered by the Air Force for potential upgrade to the F108-powered fleet. The modifications can be incorporated during a shop visit or while the aircraft is in depot for other maintenance reasons. The additional rewiring cost per shop visit is projected to be $1 million. The time interval from program go-ahead to delivery of the first aircraft is estimated at 24 months. The modifications are predicted to reduce maintenance costs by 25 percent for a projected time on wing of 12,000 engine flight hours. Projected fuel savings per airplane vary, from $35,000 per aircraft per year to $81,000 per aircraft per year given fuel costs of $2.14/gal and $5.00/gal, respectively. In addition, slight time on station and range improvement benefits are expected. The KC-135 fleet fuel consumption represents a significant part of the Air Force fuel usage for transport, tanker, and bomber aircraft. The decision to proceed with this modification hinges on weapons system service life considerations, the fuel cost impact, the potential residual value of upgraded engines, and the relative importance of reducing U.S. dependency on foreign oil. FIGURE 3-3 Details of proposed upgrades for the CFM56 engine. IGV, inlet guide vane; HPC, high-pressure compressor; VSV, variable stator vane; L/E, leading edge. SOURCE: CFM International.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft TABLE 3-1 Comparison of Candidate Engine Characteristicsa Engine Model Horsepower Specific Fuel Consumption Dimensions (in.) Weight (lb) SLTOb ALTc Diameter Length T56-A15 4,591 0.540 0.383d 44.6 146.3 1,848 T56-S3.5e 4,591 0.500 0.366d 44.6 146.3 1,894 T56-A427 5,823 0.470 0.356 48.3 146.3 1,940 AE 2100 4,591 0.460 0.342d 33.6 124.0 1,644 PW150 5,071 0.433 0.350 30.2 95.4 1,583 aAviation Week and Space Technology Source Book 2006; pp. 142 and 145. bHorsepower SFC – lb/HP hr; SLTO, Sea Level Take Off, references standard takeoff conditions. Standard for rating an aircraft engine. cThrust SFC lb/lb-hr at 12,000 ft, 220 kt. ALT, Altitude. dValues corrected after release of the January 31, 2007, prepublication version of the report. eEstimate based on Egbert and York (2006). C-130 AIRCRAFT The C-130 fleet is one of the largest currently in U.S. military operations, with over 500 aircraft in the Air Force inventory, and the various models of the Rolls-Royce T56 engines that power the aircraft account for the largest share of engine types in the inventory. Of these aircraft, approximately 250 are H models and have life expectancies beyond the year 2020. The other earlier models do not have adequate service life to be good candidates for re-engining (O’Banion, 2006). In addition, approximately 40 C-130J models are derivatives of the H model and incorporate significant upgrades to the flight decks, engines, and other parts. Because the C-130 aircraft is so ubiquitous and versatile and has such a high utilization rate, it accounts for approximately 10 percent of the total Air Force fuel consumption and has been the subject of many engine upgrade studies and activities. The latest T56 engine model fitted to the aircraft, the T56-A15, is designated Series III. Another example of continuous improvement was a focused propulsion study that resulted in flight test and demonstration on the C-130 of the T56-A100, which was the product of the Air Force Engine Model Derivative Program (EMDP) of the early 1980s. More recently, studies have been conducted for the Special Operations Forces program office, Propulsion Development Systems Office’s Advanced Projects Division (Aeronautical Systems Center/Special Operations Forces (ASC/LU)), addressing improved performance for the gunship version of the aircraft and for both the airframe company and a number of engine companies. Some of the information provided from these studies is included in Appendix G. The C-130J derivative concept aircraft has as its centerpiece a new engine (the AE 2100) and propeller. There are five engine candidates that are available from other military or civil applications or that might be considered only slightly modified derivatives of existing engines and that would therefore require only low levels of qualification testing prior to fleet introduction.1 These are shown in Table 3-1: (1) an evolutionary derivative of the current Series III engine incorporating some features from the 1 The GE38 was not included in this review since it was considered to be in an early development stage and not readily available.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft EMDP, (2) Rolls-Royce engine T56-S3.5, (3) the T56-A427, the current production engine, used on the latest version of the Navy E-2C aircraft, (4) the AE 2100, used on the C-130J, and (5) the Pratt & Whitney Canada PW150, used on a civil turboprop. This table combines information from a public domain source (Aviation Week), from a Rolls-Royce briefing to the committee referenced in the table, and from calculations by the committee and is provided here for general reference. The improved engines benefit the fleet in terms of life-cycle costs in the areas of savings on fuel consumption and maintenance. The estimated costs of fuel are provided in Table 3-2 at two fuel prices. The projected improvements in maintenance actions are shown in Table 3-3. Carrying these through to estimated cost savings is not included here since the related costs involve reductions in operational and depot personnel and is considered beyond the capability of the committee. The introduction of new engines and props provides the opportunity for the C-130H fleet to be moved to modern maintenance and support programs, including active systems to monitor real-time conditions and components and accessories designed to meet contemporary reliability expectations. These result in significant improvements in parameters associated with safety, including the in-flight shutdown rate and the mission abort rate. The modern engines and propellers also provide significant improvements in environmental impacts in the form of noise and emissions. For example, the 70 dBA noise footprint of an aircraft fitted with modern engines and props is reduced from 24.25 to 5.4 square miles. These propulsion changes also offer significant improvements in aircraft operational characteristics—for instance, the length of the landing field can be reduced from 4,000 to 3,100 feet and the cruise altitude increased from 18,000 to more than 22,000 feet for one popular configuration. These improvements can positively impact the aircraft and fleet mix and applications. The first-order financial components of retrofit development, hardware acquisition, and fuel savings are shown in Table 3-4. Note that some of the engine costs were supplied by the contractors and have not been subjected to the rigorous verification of normal procurement practices. TABLE 3-2 Fuel Usage and Costsa   T56-A15 T56-S3.5 T56-A427 AE 2100 PW150 Annual fuel use (million gal)b 171 157 149 123 129 Annual fleet fuel cost (million $)           Fuel at $2.50/gal 428 393 373 308 323 Fuel at $5.00/gal 855 785 745 615 645 aBased on contractor data and estimates. bEgbert and York (2006). TABLE 3-3 Propulsion System Reliability and Maintenance Actions   T56-A15 T56-S3.5 T56-A427 AE 2100 PW150 Reliability in terms of MTBR per houra 1,274 NA 1,500 3,500 4,300 Maintenance actions per hour of flight time × 100 (%)b 100 60 60 50 50 NOTE: MTBR, mean time between repairs. aBased on contractor data and calculations. bEgbert and York (2006).

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Improving the Efficiency of Engines for Large Nonfighter Aircraft TABLE 3-4 Components of Financial Evaluationa Costs T56/S3.5 T56/A427 AE 2100 PW150 Engine costs 0.433 0.753 1.0 0.965 Propeller costs (million $) 0.225 0.225 0.250 0.250 Nonrecurring costs of the re-engining (thousand $) 50 17 30 70 Nonrecurring costs of modifying the airframe (thousand $) 10 15 15 25b Annual fuel savings (%)c 8 13 28 25d aEngine costs for the AE 2100 were provided from an average of contractor-provided data; costs for the other engines were calculated using the percentages in Egbert and York (2006). They are expressed here in relative terms to avoid the use of proprietary data; other costs and the fuel savings are from Egbert and York (2006) or other contractor data. bCommittee estimate. cAnnual fuel savings compared to baseline engine (T56-A15). dValue corrected after release of the January 31, 2007, prepublication version of the report. These benefits are sensitive to nonrecurring costs and future fuel costs and require detailed analysis beyond the scope of a study such as this. However, the payback period was shown to be within the structural life of the C-130H fleet and its projected active use within the force structure. The nonrecurring cost of the re-engining varied somewhat from study to study, probably because of the varying extent to which ancillary features such as advanced next generation propellers and other features from the C-130J were incorporated into the airframe and propulsion system at the time of the re-engining. The referenced reports found in Appendix C, along with a report focused on Special Operations aircraft, demonstrate that re-engined aircraft have a variety of attributes that can be applied in different ways to accomplish a range of Air Force missions. The fuel savings for the aircraft with new engines vary from 12 percent to 28 percent, depending on what proportion of a more efficient engine’s capabilities is used to enhance the performance of the aircraft and what proportion of its efficiency is used to duplicate the existing mission profiles and conserve fuel. These prior studies also highlight the extent to which the improved aircraft performance is used to displace existing aircraft by fully utilizing the increased capability of the reconfigured aircraft. These savings may come from fewer operational aircraft, smaller air crews, and reduced support operations. The quantification of these savings was beyond the purview of this report but should be considered in a comprehensive study of the subject. The T56 engine is currently in use in the C-130, C-2, E-2C, and P3 aircraft by the U.S. military and by the militaries of many of its allies. The AE 2100 is in use in the C-130J aircraft and in the C-27J currently proposed for the Army medium airlift requirements. Both the AE 2100 and the PW150 are in use in civil airline fleets. In addition the AE 2100 core is the basis for the AE 1107 turboshaft engine that powers the V-22 Osprey and the AE 3007 turbofan that powers the Embraer family of regional jets, the Citation X business jet, and the Global Hawk military unmanned aircraft system. These multiple applications provide the opportunity for existing commercial product support organizations to support aircraft re-engined with either the AE 2100 or the PW150. And in the case of the AE 2100 there are currently support contracts in place to provide maintenance for the Marine V-22 and C-130J engines and the Air Force C-130J fleet (Plummer, 2006). These contractor-supplied maintenance approaches need to be evaluated in the context of Air Force force structure and staffing plans and quantified in terms of cost savings in a more detailed study of C-130 re-engining. It has been noted that the Air Force and Navy are already cooperating on maintenance approaches for the AE 2100 engine, but any re-engining study of the C-130 should also examine the possibility of aircraft using the T56 engine—for example, the Navy’s E2-C, C-2, and P3 fleets.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Finding 3-1. The C-130 fleet is one of the largest in the Air Force inventory. Owing to its ubiquity, its versatility of use, and high utilization rate, it accounts for a significant portion of Air Force fuel usage. Finding 3-2. The C-130 has been the subject of a major upgrade that incorporates new engines and new technology in the flight deck, propellers, and systems and is entering the Air Force and Marine fleets as the C-130J. Finding 3-3. There are four near-term candidates engines for improving the fuel efficiency of the C-130: (1) a T56 upgrade, (2) the T56-A427 from the Navy’s E2-C, (3) the AE 2100 from the C-130J program, and (4) the PW150, a civil engine. Finding 3-4. The studies conducted to date have been based on a range of nonrecurring cost depending on the non-engine-related upgrades that are included in the costs. Finding 3-5. The C-130H fleet, consisting of approximately 270 aircraft, has a planned life through the year 2025 and is a candidate for retrofitting with more energy-efficient engines. Finding 3-6. The older C-130E aircraft fleet, which comprises approximately 150 aircraft is not a good candidate for engine upgrade from a financial perspective since the aircraft would require expensive structural life extension programs. Finding 3-7. Several of the candidate engines and propeller systems could provide for significant improvements in terms of positive environmental impact for the C-130H. Finding 3-8. The services have implemented contractor maintenance and support programs for the C-130J AE 2100 engine (and the common core AE 1107 turboshaft from the V-22), and these provide a database for innovative support concepts. Conclusion 3-1. Re-engining the C-130H fleet with derivatives of the existing T56 engine shows the best financial case in terms of payback time from fuel cost savings, but it saves the least fuel. Conclusion 3-2. Re-engining the C-130H fleet with new engines such as the AE 2100 or the PW150 saves the most fuel and has a payback within the useful life of the airframe. Recommendation 3-1. The Air Force should conduct a detailed technical and financial study of the C-130 fleet to select and validate a preferred re-engining plan with fuel savings as the primary figure of merit. The Air Force should generate an implementation plan for financially viable candidates. Recommendation 3-2. The Air Force should conduct a study of C-130 airframe and operational techniques focused on fuel savings needs and generate an implementation plan for financially viable candidates.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Recommendation 3-3. The Air Force should pursue re-engining the C-130H on a priority basis, since this aircraft is one of the largest users of fuel in the Air Force inventory. The Air Force should use a competitive bid procurement process to provide the background for a decision on the C-130H models between the AE 2100 and PW150 engine options, either of which would appear to be acceptable on a technical and performance basis, and it should review the economics of engine efficiency upgrades (engine modifications) to the older models with a shorter remaining service life. B-1 AIRCRAFT There are currently 67 B-1B bombers in the Air Force fleet plus 29 aircraft in mothballs. They fly approximately 275 hours per aircraft per year. The Air Force would like to improve fuel efficiency, mission flexibility, and altitude capability, which could increase the B1-B utilization rate. The increase in altitude capability is needed to minimize their vulnerability to surface-to-air missiles and to 57 mm and anti-aircraft artilleries; also, they need to be refueled at 20,000 feet or less, which could put both the B-1B and the refueling aircraft in harm’s way. There is, in addition, a chronic low-pressure turbine failure problem associated with high-temperature operation, and this leads to high maintenance costs. In 2002, Maj Gen Dan Leaf asked Boeing to find the best way to increase B-1B mission flexibility, specifically by increasing altitude capability (see Summary 9 in Appendix C). Boeing studied many aircraft modifications and subsystem upgrades and concluded that re-engining of the F119 was the best solution. It found that the original B-1A altitude and Mach 2.2 speed (which the B-1B structurally inherited) could be restored by increasing the specific thrust of the production F119 engines. Modification The committee identified one candidate for engine modification: Modify the current F101 through a SLEP. This program would include a thrust increase, maximizing thrust at both midpower and augmentation, along with durability improvement incorporated in the low-pressure turbine. This would improve altitude capability by an additional 5,000 to 10,000 feet. There would be no specific fuel consumption benefits. Figure 3-4 describes the existing F110 (engine used on F-16) SLEP. The F101 engine used by the B-1B uses the same core as the F110. The F101 SLEP would be similar to the F110 SLEP described in the figure. Re-engining The committee identified three re-engining candidates for the B-1B: Proposed SFC upgrade of the F101 (see Figure 3-5), which would incorporate a new two-stage fan, a SLEP F101 core, a modified low-pressure turbine (LPT) new radial augmenter, and a new elliptical nozzle known as an augmented load-balanced exhaust nozzle (ALBEN) (see Figure 3-6), which has a 10 percent better SFC. The recurring cost is $500,000 per engine. An additional 3,000 foot altitude improvement is expected over the F101 engine modification SLEP. A 40 percent reduction in engine maintenance cost is projected with a time on the wing of 1,000 hours. The first aircraft delivery would occur 48 months after go-ahead. A fuel saving cost of $2.9 million per aircraft per year is anticipated.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 3-4 F110 SLEP. SOURCE: General Electric. FIGURE 3-5 Engine comparison of current versus proposed F101 upgrade. SOURCE: General Electric. First, re-engine the B-1B with a production F119 engine (see Figure 3-7). The F119 engine provides survivability to eliminate the need for radar cross section vanes in the aircraft inlet. Then, optimize the robust F119 fan for improved spillage drag. Finally, integrate a new elliptical low-observable exhaust system (see Figure 3-8), which eliminates significant boat tail drag. Lift/drag improvements could allow the F119-powered B-1B to supercruise for sustained rapid response

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Improving the Efficiency of Engines for Large Nonfighter Aircraft FIGURE 3-6 F101 Upgrade-ALBEN. SOURCE: General Electric. FIGURE 3-7 F119 cross section. SOURCE: Pratt & Whitney. FIGURE 3-8 Elliptical nozzle. SOURCE: Pratt &Whitney. ability. This system solution could provide the Air Force with Global Strike/Global Persistence attack and fighter/attack capability equivalent of seven F-18s in a Global Response Bomber size at a 50 percent improvement in propulsion system total cost of ownership. The F119 upgrade could be achieved for a nonrecurring engineering (NRE) cost (propulsion only) of $100 million. Re-engining the B-1B with a derivative F119/F135 fan option could trade performance margin for improved fuel economy and enhance the total system impact to the B-1B range/persistence capability. This derivative configuration could be achieved for an NRE of $450 million.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Fuel Consumption To fulfill the statement of task, which is to reduce fuel consumption for the B-1B, there are two alternatives: EMDP for the F101, which includes a new fan and new nozzle to maximize fuel efficiency for the aircraft. This should decrease fuel consumption by 10 percent at NRE costs of $100 million. An EMDP of the F119 engine, which would include a new fan and a low-observable elliptical nozzle to maximize fuel efficiency for the aircraft. This is estimated at an NRE cost (propulsion system only) of $450 million to $500 million each. KC-10 AIRCRAFT Background The KC-10 aircraft is a derivative of the commercial DC-10, a 1970s vintage wide-body aircraft. The commercial version of this aircraft was powered primarily by the CF6-6 and CF6-50 engines; a few were produced with the Pratt & Whitney JT9 engine. The aircraft has been out of production for nearly 20 years. The KC-10A fleet is equipped with GE F103 and GE F101 engines that were manufactured and certified to the same FAA standards as the CF6-50 commercial engines on DC-10 aircraft. These engines have served the industry and the Air Force well and have a reputation for reasonable maintainability, reliability, and fuel efficiency consistent with state of the art for second-generation, high-bypass-ratio turbofan engines of the era. The KC-10 has one tail-mounted engine and two wing-mounted engines. The tail-mounted configuration is very engine specific. It is physically dimensioned to accommodate specific engines that were in production when it was being designed. It is likely that major redesign would be required for the installation of current state-of-the-art engines. In addition, many of the current engines were optimized for thrust production and may not provide significant fuel consumption benefits for the CF6-50. Although the airframe structure and weapons system service life parameters could make it suitable for re-engining, the committee found no performance, operational, or cost-effectiveness justifications for such a program. Re-engining is driven basically by performance, availability, and cost requirements. Today, the KC-10 fleet meets all airframe requirements, and it is the committee’s assessment that no change is warranted. The CF6-50 engine was widely used on the DC-10, 747, and A300 aircraft. This relatively large commercial industry inventory of CF6-50 engines, parts, and maintenance capability acts as a reserve that can be drawn upon as needed to assure continued availability for the F103 engine. Finally, there are no viable candidate engines that could improve fuel consumption by >10 percent or significantly reduce maintenance costs within reasonable cost/benefit parameters. Technology Infusion Benefits Propulsion system upgrade was considered as a potentially cost-effective approach for improved fuel consumption for the KC-10 fleet. There are currently 59 KC-10A aircraft in the Air Force inventory powered by 177 F103 engines. The Air Force retains 22 F103 engines in a spare capacity for the KC-10A fleet, with the equivalent of five more engines that are retained as modular spares.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft High-Pressure Turbine Upgrades The committee considered engine upgrades as a means to achieve fuel consumption and cost savings for the KC-10 fleet. The candidate upgrades were generated for commercial CF6-50 applications but have relevance for the F103 engine. The time, cost, and material content required to implement the upgrades is dependent on the configuration of the F103 engine to be modified. The committee determined that upgrades would not provide significant fuel consumption reductions. Upgrades do, however, offer reduced maintenance costs, improved exhaust gas temperature (EGT) retention, and the potential for improved residual asset value and reduced cost of ownership due to market value resulting from their commonality with commercial engine configurations. A proposed upgrade for a high-pressure turbine (HPT) flow path would require an investment of about $200,000 per engine, with a projected savings of about $169 million by 2021 and a payback period of 6 years. The savings result from reduced material usage and lower maintenance costs. Commonality Considerations for the Air Force Engine Fleet Fleet commonality was reviewed to determine the potential advantages for reliability, maintainability, and/or performance derived from technology infusion. The E-4 is the only other aircraft in the Air Force stable of large aircraft powered by the F103 engine. No studies have been conducted, and no operational issues have been detected by the Air Force with respect to performance, availability, or operating cost limitations for the E-4 fleet. Commonality Issues for the Commercial Engine Fleet Since the F103 engine is the same as the commercial CF6-50 engine, the committee reviewed current activity within the commercial fleet to determine if benefits derived from such programs might have application in Air Force analyses for re-engining/modification. A number of commercial operators are modifying their CF6-50 fleet with hot-section upgrade kits. The CF6-50 hot-section upgrade kit incorporates advanced HPT materials, coatings, and cooling technology from the latest generation of aircraft engine designs. This modification responds to operational experience, with the frequency of engine removals attributable to HPT components such as nozzles, shrouds, and blades. Incorporation of the hot-section modification results in predicted engine time on wing increasing as much as 25 percent. In addition, the modification provides improved EGT margin retention and a reduction in shop visits, scrap, and repair and material costs. Thus the upgrade kit is predicted to significantly improve engine life, cost of ownership, and long-term residual value for the commercial operator community. The KC-10A fleet could realize minor fuel efficiency benefits, on the order of 0.33 percent, and a projected 15 percent reduction in maintenance costs through a CF6-50 upgrade/technology infusion program for the F103 engine in the form of hot-section modifications. The estimated production rate for engine modification is about 30 engines per year. The payback period at this rate could not be justified solely on the basis of fuel savings. The projected 15 percent reduction in engine maintenance cost yields an annual savings for the KC-10A fleet, with an attendant payback period for any modification program.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft Summary There are no compelling operational performance, fuel consumption, availability, or operating cost issues to support a re-engine program for the KC-10A/F103 fleet. In addition, there are no candidate engines that could provide significant improvement in operational performance, fuel consumption, availability, or operating cost for the KC-10A fleet. The projected fuel savings for the CF6-50 HPT/hot-section modification to the F103 engine for the KC-10A fleet do not meet the objectives of this study pertaining to the reduction in fuel consumption for the large aircraft fleet. However, the opportunity for reducing operating costs and improving mission performance/availability in the form of predicted improved on-wing time, improved EGT margin retention, reduced maintenance and material costs, and an attendant reduction in required maintenance manpower would justify review by appropriate Air Force weapons systems and process managers for these modifications depending on the priorities of these issues relative to overall weapons-systems management objectives. Recommendation 3-4. The Air Force should consider the hot-section modification a priority for the F103 engine to the extent Air Force weapons systems managers, planners, and policy makers consider that commonality with commercial engines has value with respect to maintenance (outsourcing, spares, parts, etc.), availability, improvement implications, and potential residual value. Recommendation 3-5. In general, where commercial engine/airframe counterparts exist (KC-10/ DC-10, F103/CF6-50, KC-135/B-707, TF33/JT3, F108/CFM56, etc.), Air Force engine and weapons systems planners, managers, and policy makers should closely monitor the engine’s original equipment manufacturers’ (OEMs’) and commercial operators’ activities and actions relative to reengining and engine modification as a measure of the cost/benefit for these activities. C-17 AIRCRAFT Finding 3-9. The F117 is a modern, high-bypass, fuel-efficient engine on the C-17; however, it is the largest consumer of fuel in the Air Force’s inventory of large nonfighter aircraft/engine systems. Conclusion 3-3. The F117 engine is a possible candidate for decreasing fuel burn by 1.1-1.7 percent. This could be accomplished by redesigning the high-pressure turbine and re-aeroing the low-pressure turbine. This assessment does not include benefits of integration, which has been shown to improve thrust-specific fuel consumption (TSFC) by 5-8 percent for other legacy systems. These elements include bleedless architecture through an electric vapor cycle, the environmental control system, better thermal management through fuel stabilization unit, and improved electrical power generation through a low spool generator. Recommendation 3-6. Since the C-17/F117 system is the largest consumer of fuel, the Air Force should conduct an engine model derivative program (EMDP) study with Boeing and Pratt & Whitney to determine possible fuel savings, implementation costs, and a schedule that would give the best return on investment for the Air Force. For future planning purposes, the Air Force should track and request from Pratt & Whitney all changes to the commercial PW2037/2040 pertaining to reduced fuel burn and durability issues.

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Improving the Efficiency of Engines for Large Nonfighter Aircraft REFERENCES Published DESC (Defense Energy Support Center). 2005. Fuel Used for Large Non-Fighter Aircraft for Calendar Year 2005. Unpublished Mark Amos, Head, New Engines Division, Agile Combat Support Systems Wing, “United States Air Force large aircraft inventory,” Presentation to the committee on April 26, 2006. Norm Egbert, Vice President for Engineering and Technology, and Ron York, Vice President for Special Projects, Rolls-Royce, “Rolls-Royce presentation,” Presentation to the committee on May 24, 2006. Rafael Garcia, B-52 System Program Office, Tinker Air Force Base, “B-52 re-engine study,” Presentation to the committee on April 26, 2006. Jack O’Banion, Director of Air Mobility Requirements, Lockheed Martin Corporation, “C-130 re-engine discussions,” Presentation to the committee on May 23, 2006. Steve Plummer, Senior Vice President for Defense Relations, Rolls-Royce North America, “Commercial airlines business transactions,” Presentation to the committee on June 14, 2006. James Shuppert, Director of Sales for Tanker, Transport, and ISR Engines, “General Electric presentation,” Presentation to the committee on May 24, 2006.