Successful B-52 Compromises

The B-52 Stratofortress appeared in 1951, during the jet’s awkward age. However, the compromises made by Boeing Company engineers to get around the period’s (well – deserved) lack of confidence in flight control hydraulics and electronics were so successful that this airplane continues to have an active service life nearly 50 years later. These com­promises are suited to the B-52’s mission in that required maneuvers are modest and spin recovery is not required.

7.6.1 The B-52 Rudder Has Limited Control Authority

The B-52’s rudder has an exceptionally narrow chord, just 10 percent of the fin chord (Figure 7.4). For a given control surface span or length, control hinge moments are proportional to the chord length squared. This gives the B-52 rudder small operating hinge moments for an airplane of its size, making feasible manual operation through a spring tab. But how about rudder power or effectiveness? How can asymmetric thrust effects and cross-wind takeoffs and landings be made with that exceedingly small rudder?

George S. Schairer explained that the original Boeing design called for an all-moving vertical tail. This was abandoned because of doubts as to the reliability of the hydraulic actuators. Instead, the solution was to incorporate a yaw-adjustable cross-wind landing gear. The yaw-adjustable cross-wind landing gear is preset by the flight crew before takeoff or

Successful B-52 Compromises

Figure 7.4 B-52G Stratofortress. A seventh wing spoiler segment has been added, the feeler ailerons

eliminated. Note the extremely narrow (10-percent chord) rudder and elevators. (From Loftin, NASA SP-468, 1985)

on a landing approach, through a range of 20 degrees to either side of neutral (Figure 7.5). Ground rolls can be made at zero sideslip and bank, the airplane crabbed into the relative wind. The preset landing gear angle is based on the reported wind direction and velocity relative to runway orientation.

Since the airplane has eight engines, asymmetric thrust conditions set up by shutting down an engine are low enough to be handled by the narrow rudder.