B-52 - Motorprogrammet på final approach - AW&ST

Du kan studere "The wrinkled one" på Duxford - Foto: Per Gram U.S. Air Force Looks To Fast-Track B-52 Reengining Guy Norris The enduring effort to reengine the venerable B-52, a saga extending back to the 1970s, is poised to enter its final chapter in September when the U.S. Air Force is expected to approve a program to replace the engines on the long-serving bomber. The move, if sanctioned, is likely to be executed under a recently adopted Pentagon “rapid-prototyping” acquisition policy and follows Air Force warnings in 2017 that the bomber’s obsolescent Pratt & Whitney TF33 engines will not be sustainable beyond 2030. Reengining also would come as the aircraft’s role as a future launch platform for long-range standoff and hypersonic weapons becomes increasingly key to U.S. long-range strike capability. Motor Matrix Go-ahead for U.S. Air Force B-52H reengining expected in late September Engine program may be accelerated under new Section 804 rapid-prototyping process Up to 650 engines, including spares, required for 76-aircraft fleet Engine upgrade to produce extra power for additional systems and weapons capability Combined with the growing urgency over supportability of the TF33, a military variant of Pratt’s late-1950s JT3D turbofan, and recognition that the life of the B-52 would be extended to 2050 and beyond to help counter emerging long-range strike threats, the program has been gathering momentum since 2016. In its fiscal 2019 budget request, the Air Force called for $280 million to update the B-52H fleet, of which $64.5 million is earmarked for the start of the reengining program. Having rejected the results of earlier studies on replacing the B-52H’s eight 17,000-lb.-thrust TF33s with four 35,000-lb.-thrust high-bypass-ratio turbofans, the Air Force has briefed industry on its requirement for modern, fuel-efficient commercial engines that can replace the old units on a one-for-one basis. Under the B-52 Commercial Engine Replacement Program (CERP), the service needs 650 engines, including 42 spares, to upgrade its operational fleet of 76 B-52s. Twenty additional powerplants will be needed initially for the retrofit of two bombers for flight testing. Although the Air Force initially presented a notional schedule in late 2017 that indicated reengining of the first batch of 10 bombers would begin in fiscal 2026, the service now believes the B-52 program is a good candidate for acceleration under the streamlined Section 804 acquisition process introduced in the fiscal 2016 National Defense Authorization Act. Under this act, rapid prototyping of “middle-tier” programs (intended to be completed in 2-5 years) can be accelerated to enable residual operational capability within five years of the finalized requirement. Will Roper, the assistant secretary of the Air Force for acquisition, technology and logistics, says the service is “considering whether it is appropriate to apply that process to the B-52 CERP.” The Air Force confirms that Roper also is scheduled to announce a decision on CERP at the end of September. This is separate from deciding if the reegining should be considered a Section 804 program. Boeing, which was selected earlier this year as the integrator for the reengining program, acknowledges many details of the acquisition strategy remain to be worked out. Boeing B-52 program manager James Kroening says, “The questions being asked over the application of Section 804 to the reengining program are where does the prototyping concept make sense in—firstly—reducing the technical risk of the integration and, secondly, accelerating delivery of the capability to the government and warfighter. Those are the things we are working through now with the government.” Overall it appears that regardless of the Section 804 acquisition process, elements of the CERP likely will remain baselined around the original plan of modifying a pair of test aircraft. The final shape of the test and development effort will reflect the outcome of ongoing discussions over how the streamlined prototyping process might be applied. Kroening says these discussions are focused on, among other areas, “the extent to which one applies a more rapid prototyping approach and doesn’t fully produce a system that’s exactly representative of the production kit, and how much one might use that for early testing for instance, and then evolve it into a production representative test.”

Depending on mission scenario and engine selection, Boeing and the U.S. Air Force hope for up to a 40% range increase from a more fuel-efficient, reengined B-52H. Credit: U.S. Air Force

According to the Mitre Corp., a federally funded research and development center, the rapid-prototyping approach for the B-52 may take the form of a cyberspace fly-off between the contenders, which will compete with “digital-twin” versions of their engines. Using this approach, it estimates, the Air Force could cut up to five years out of the usual time taken to make a fielding decision. The baseline fuel-improvement requirement is 20%—with a stretch goal of 40%—compared to current performance. As currently envisioned, assuming the program gets the go-ahead, requests for proposals (RFP) will be issued to interested engine-makers between October and the end of the year. As program integrator, Boeing will work with each of the engine-maker candidates over a six-month period, evaluating a matrix of propulsion and system designs. This first phase will culminate with Boeing submitting reports to the Air Force. “The second step would be the issuing of the actual RFP and [beginning of] the source-selection process with the knowledge of not only what engine suppliers might offer, but also a concept of the complexity of the integration involved with the various engines,” explains Kroening. The contract then would likely be awarded in the second half of 2019. General Electric is proposing variants of its CF34-10 regional airliner engine and Passport business jet powerplant. Pratt, which also has studied a TF33 upgrade package and previously proposed a PW2000 (F117) variant during the four-engine B-52 powerplant replacement study, is offering a version of its PW800 business jet engine, which incorporates the core of the PW1200G geared turbofan. Rolls-Royce, which in the mid-1990s teamed with Boeing to offer leased RB211-535E4s as an option for the bomber, is proposing the BR725 —a variant of the BR700 already in service with the Air Force as the F130. Rolls also may offer a variant of its recently revealed BR700-derived Pearl engine family. It remains unknown whether other engine-makers such as Safran, which attended industry day events for the B-52 program, or Honeywell, are also in the hunt. Boeing says no “official narrowing of the field has yet occurred.” Despite overall plans to minimize the impact of the engine change on aircraft and airframe systems, Boeing says the program presents a major integration challenge. In addition to the new engines, which will be rigged for quick-start capability, the modifications will involve new cowlings, integrated nacelles and redesigned struts. The struts will incorporate an added precooler as well as new electrical, hydraulic, fuel and pneumatic lines. Additional generators will be added, doubling the current tally of four, necessitating an all-new power systems architecture. Wiring for the full authority digital engine control units in the new powerplants also will be added. Flight deck changes will include replacement of the many current “steam gauge” engine displays with a flat-panel multifunction display. “As this aircraft will be in service well beyond the middle of the century, we want to be smart about how that cockpit display is designed and integrated so it can look forward to future opportunities to have an even more integrated cockpit,” says Kroening. The overall integration task “is a significant endeavor, so we anticipate engaging a large element of the Boeing enterprise to accomplish the program,” he points out. The group, which includes Boeing Commercial Airplanes, will be headquartered at the company’s Oklahoma facility, but will require “significant” engineering and other program support from other Boeing sites. Boeing’s analysis of the engine options also will consider the interactive compatibility effects on the bomber’s weapons and its new, yet-to-selected, radar systems. “It’s not completely obvious, but we will have to consider the power-generation system and what impact a different ‘quality’ of power being generated might have on one radar versus another,” adds Kroening.