3 ms·

As a non airforce/aeroengineer, can someone explain why the smaller dual engine nacelles haven't been replaced with a larger turbofan engine? surely its more e

As a non airforce/aeroengineer, can someone explain why the smaller dual engine nacelles haven't been replaced with a larger turbofan engine? surely its more efficient and lower maintenance? is it that it would alter the centre of drag/gravity/thrust too much and would require too much engineering?

devman0 4y ago
Someone else mentioned in another thread that it's for resiliency. I guess if you're carrying 70,000 lbs of ordnance you don't want an engine failure messing with your thrust too much during critical flight phases.
buildsjets 4y ago
Because the rudder on the B-52 is too small to maintain lateral directional control with an inoperative outboard engine in a 4-engine configuration at takeoff power/airspeed. Go google for some pictures, on a B-52 it is less than 10% of the span of the vertical stabilizer, compared to more than 25% on a 747. And if the rudder were made large enough to maintain directional control, the loads in the aft fuselage would be large enough that the aft fuselage would need to be re-designed.
colechristensen 4y ago
They thought about it but decided it would be a waste of money. Lots of considerations go into engine choice and making changes is quite expensive. >In 1996, Rolls-Royce and Boeing jointly proposed fitting each B-52 with four leased Rolls-Royce RB211-535 engines. This would have involved replacing the eight Pratt & Whitney TF33 engines (total thrust 136,000 lbf (600 kN)) with four RB211 engines (total thrust 148,000 lbf (660 kN)), which would increase range and reduce fuel consumption, at a cost of approximately US$2.56 billion for the whole fleet. However, a USAF analysis in 1997 concluded that Boeing's estimated savings of US$4.7 billion would not be realized and that re-engining would instead cost US$1.3 billion more than keeping the existing engines, citing significant up-front procurement and re-tooling expenditure.

devman0 4y ago

Someone else mentioned in another thread that it's for resiliency. I guess if you're carrying 70,000 lbs of ordnance you don't want an engine failure messing with your thrust too much during critical flight phases.

buildsjets 4y ago

Because the rudder on the B-52 is too small to maintain lateral directional control with an inoperative outboard engine in a 4-engine configuration at takeoff power/airspeed. Go google for some pictures, on a B-52 it is less than 10% of the span of the vertical stabilizer, compared to more than 25% on a 747. And if the rudder were made large enough to maintain directional control, the loads in the aft fuselage would be large enough that the aft fuselage would need to be re-designed.

colechristensen 4y ago

They thought about it but decided it would be a waste of money. Lots of considerations go into engine choice and making changes is quite expensive. >In 1996, Rolls-Royce and Boeing jointly proposed fitting each B-52 with four leased Rolls-Royce RB211-535 engines. This would have involved replacing the eight Pratt & Whitney TF33 engines (total thrust 136,000 lbf (600 kN)) with four RB211 engines (total thrust 148,000 lbf (660 kN)), which would increase range and reduce fuel consumption, at a cost of approximately US$2.56 billion for the whole fleet. However, a USAF analysis in 1997 concluded that Boeing's estimated savings of US$4.7 billion would not be realized and that re-engining would instead cost US$1.3 billion more than keeping the existing engines, citing significant up-front procurement and re-tooling expenditure.