The B-1B 'Lancer' has a blended wing body configuration, with variable-sweep wings (15 to 67.5 degrees), four turbofan engines, triangular fin control surfaces and cruciform tail. The length of the aircraft presented a flexing problem due to air turbulence at low altitude. To alleviate this, Rockwell included small triangular fin control surfaces or vanes near the nose on the B-1B. The B-1B's Structural Mode Control System rotates the vanes automatically to counteract turbulence and smooth out the ride. The B-1B uses serpentine air intake ducts and fixed intake ramps, which limit its speed compared to the B-1A. Vanes in the intake ducts serve to deflect and shield radar emissions from the highly reflective engine compressor blades.