The U.S. Air Force says the Boeing B-52H bomber’s 1960s-vintage Pratt & Whitney TF33-103 engine is “not sustainable past 2030” and must be replaced to keep the Stratofortress flying for another two decades, and the first two test aircraft could start undergoing modification by fiscal 2022.
Seventy-six of the Strangelovian Cold War bombers remain in the service’s arsenal and the fleet has been tapped to carry the new nuclear Long-Range Standoff (LRSO) cruise missile.
To keep the colossal aircraft flying beyond 2050 and meet the high power demands for next-generation weapons, a fire control radar and other electrical systems, the Air Force wants an eight-for-eight swap of the original TF33 with a similarly sized, but far more efficient, commercial replacement.
The service is specifically targeting a 20-40% improvement in fuel consumption compared to the TF33 and enough power-generation capacity to support a peak electrical load of 400-500 kVA. The old bomber will require substantial modification, including a new power architecture and full authority digital engine controls. But the service still wants to minimize any impact to the airframe and onboard systems, while maintaining the gross takeoff weight of 488,000 lb.
These and other details were provided to potential engine manufacturers and prime integrators at an industry event Dec. 12-13, 2017, at Barksdale AFB in Louisiana.
All of the big engine manufacturers attended the forum, including GE Aviation, Pratt & Whitney, Rolls-Royce and Safran. Other attendees included Boeing, Rohr of United Technologies Corporation, Northrop Grumman, L3 Technologies, Omega Air, D-J Engineering, Honeywell, Spirit Aerosystems and McGill Aircraft Parts.
“The B-52 has a long past and a long future (2050+), but the TF33 is not sustainable past 2030 due to age, obsolescence and diminishing manufacturing sources,” the government says in an industry day slide presentation released Dec. 15.
The document notes that the Air Force is considering the potential purchase of 650 engines, enough to upgrade 76 aircraft, with another 42 units kept as spares. The service will seek 20 engines initially to modify the first two bombers for testing.
To avoid the expense of completely recertifying the aircraft and all of its weapons, aerodynamic changes must be minimized at all costs. The aircraft’s center of gravity also must remain unchanged.
The program plan remains in flux, but seed funding to get started has been provided in the Air Force’s budget for fiscal 2018. There likely will be multiple contracts for preliminary designs and studies, followed by single awards to prime contractors for integration and engine manufacturers for engineering and manufacturing development, and production and deployment.
The service has for the first time released a draft or “notional” acquisition schedule. Depending on which course of action the government decides to take, it will likely select one contractor for the engine and one for aircraft integration, with downselects for both anticipated by mid-2020.
Following an extensive development and testing period with the first two modified aircraft, engine upgrades for the first 10 operational aircraft could start in fiscal 2026, followed by full-rate production for the remaining 64 through fiscal 2028-34. If initiated, this would be the most extensive upgrade in the bomber’s storied history.
The Air Force has been studying engine upgrades for the B-52G/H-series Stratofortress since 1971, starting with “Project Seek Four,” which would have swapped eight TF33s for four larger turbofan engines.
There have been no fewer than nine studies and proposals since then, with interest picking up in the late-1990s and mid-2000s. So far, the Defense Department has nothing to show for its efforts except reams of paper. But with the return to larger-power competition from Russia and China and the planned introduction of the LRSO cruise missile, the Air Force appears to be getting serious.
The leading candidates are Rolls-Royce’s 16,000 lb.-thrust BR725 and GE Aviation’s 18,000-lb.-thrust CF34-10. Pratt & Whitney has previously offered upgrades.