GUY NORRIS / LOS ANGELES
Ressurected plan to revamp bomber calls for proposals for eight as well as four powerplants - but costs will be crucial
Engine makers are submitting new proposals for Boeing's resurrected B-52 bomber re-engining plan. The revised bids have been prepared after Boeing asked the manufacturers to look at eight-engined as well as four-engined schemes.
Boeing received a $3 million US Air Force study contract earlier this year. The manufacturer made an unsolicited proposal in 1996 to replace the B-52's eight Pratt & Whitney TF33s with four Rolls-Royce RB211-535E4 turbofans.
A Defense Science Board review of a 1997 Department of Defense analysis found insufficient consideration had been given to savings from fewer mid-air refuellings, or from reduced maintenance costs.
The plan is being considered under a scheme in which the programme would pay for itself through the savings from lower engine operating costs. However, the use of eight engines rather than four is expected to make it harder for the programme to qualify.
Boeing has asked for the eight-engined study to offset potential asymmetry control issues, particularly at take-off, following an outboard engine failure. Smaller engines could also reduce installation and centre-of-gravity concerns, as well as weapons-release clearance issues.
P&W is offering an F117X variant of its Boeing C-17 engine - a military PW2000 - but is offering the PW6000 and the JT8D-200 for the eight-engined option. Speaking at last month's Speednews aerospace and defence industry suppliers conference, P&W tanker and mobility programmes general manager Michael Lombard said: "From a cost perspective, a four-engine solution is the way to go, and we're focusing on that." He said P&W was "working with Boeing on a possible thrust bump on the outboard engine "for its F117X proposal.
The PW2000 option offers a 30% fuel burn improvement compared with the TF33, while the PW6000 would offer a 20% improvement. The JT8D-200 would give only a 10% benefit, says Lombard, but the lowest conversion cost.
Rolls-Royce North America development and defence programme director Ron Riffel says the RB211-535E4 is one offer for the B-52, adding: "We have presented the BR700 as an alternative." The favoured eight-engined option is expected to be a derated BR715 at 18,500-22,000lb thrust (82-98kN).
General Electric is offering the CFM International CFM56-3, but has not revealed whether its bid is based on eight engines or fewer.
Source: Flight International
