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Aviation History
1957
1957 - 1683.PDF
Boeing B-52 THE STRATEGIC STRATOFORTRESS BY THE TECHNICAL EDITOR A PHILOSOPHER would no doubt condemn the humanrace for the fact that the world's largest aircraft-buildingprogramme (measured in cost, man-hours and airframe weight) should concern a machine designed specifically for causingfearful destruction. From the purely academic viewpoint, how- ever, the Boeing B-52 is an outstanding technical exercise. Sur-rounded as we are with global ballistic missiles, moon rockets and satellites, it is appropriate at this time to sit back and evaluate theworld's mightiest bomber, the like of which we shall not see again. Ten years have passed since the U.S.A.F. Strategic Air Com-mand came into being. As the American instrument of "massive retaliation" it is equipped with some of the largest aeroplanes inthe world. Notwithstanding S.A.C.'s global network of bases and huge establishment of tanker aircraft for in-flight refuelling pur-poses, none of its equipment has a gross weight of less than 200,000 1b. The fact remains that, in the present state of the art,the longer the range of an aeroplane, the bigger that aircraft must be; and in the B-52 the U.S.A.F. asked for longer range than hadever previously been attempted in a jet aircraft. An outline of how the B-52 came to be designed was given in our issue ofDecember 5, 1952, when the prototypes were in the early stages of their flight trials. Now the B-52 is in large-scale service withS.A.C., and it is possible to learn much from its performance and its problems. It is hardly necessary to say that the B-52 was designed by theBoeing Airplane Company, of Seattle, Washington. Its basic con- figuration may at first appear unconventional, but familiarity withit reveals an imaginative simplicity whereby, within the vast frame- work of the airframe, self-contained packages serve the functionsof propulsion, crew accommodation, undercarriage, armament systems, accessory power and so forth, all portions being com-pletely accessible and capable of ready assimilation by the thousands of maintenance engineers in S.A.C. Even the enor- .mous airframe itself is an assemblage of sections built by firms spread throughout the U.S.A. and shipped to Boeing, where theyare assembled with complete interchangeability. It is not proposed to describe the structure in detail, since ageneral indication can be gleaned from our cut-away drawing overleaf. It is, however, worth commenting on the extraordinaryflexibility of the airframe. During static testing the wing tips were moved vertically through 32ft; and, even at rest, the fuselagesags nearly an inch at each end, as the skin-wrinkles testify. Eight thousand hours of tunnel testing preceded the final choiceof wing design, which provides a very high lift/drag ratio for long-range cruising and offers an internal volume so great thatonly part of it is required to accommodate fuel cells. Most of the wing is a giant box formed by two principal spars, joined by ribson which are mounted machined spanwise stringers carrying what are probably the largest pieces of skin used in any aircraft. Thelatter are continuous from the root to the break-joint 84ft away, and they are machined and tapered over their entire area, reachinga maximum thickness of 0.4in at their inner ends. The secondary structure in the rear part of the wing is stabilized by metal honey-comb by such suppliers as Hexcel, Narmco and Kawneer.* Port and starboard wings are attached at their roots to a stub-structure forming a bridge piece of the same width as the fuselage. Major loads are transmitted from the heavy wing-skins throughspanwise bolts arranged around the periphery of each wing root, while the front and rear spars are located by large bolts at themid-depth position. On the front spar these bolts also transmit the weight of the wing and powerplants to the strong framecarrying the front trucks of the landing gear. To a large extent the fuselage is a series of cantilevered sectionshung from the wing stub-structure, which is attached to the front centre fuselage portion. Heavy frames carry the fore and aftlanding-gear units and a horizontal floor-web separates the bomb bay from the fuselage fuel cells. The lower edge of the side panelsterminates at a strong keel member of triangular section which takes fuselage loads past the cut-outs provided for the under-carriage and bomb bay. The long, tapering rear-fuselage sections carry the tail and pressurized gunner's compartment, and thelatter is joined by an unpressurized catwalk along the starboard side of the aircraft to a door in the rear pressure bulkhead of thecrew compartment in the front fuselage. The towering vertical tail can be folded to starboard to allowthe B-52 to enter hangars of normal height. The horizontal tail, which has a root chord not much less than that of the wing, ispivoted aft of mid-chord and is hydraulically moved for trimming purposes. At the front of the central bridge structure of thetailplane are two ball-bearing nuts running in a vertical screw (by Foote Brothers) provided with two threads in opposition.Both the jack-screw and the nuts are driven by hydraulic motors in separate circuits, so that failure of either circuit merely halvesthe drive speed. Maximum jack-screw travel is 43in/min under a 56,000 lb load, and the static limit is 158,000 lb. Completehydraulic failure still leaves the aircraft trimmable, since the gunner can operate the elevator manually via a 200:1 gearbox. Several features of the flying-control system are unusual. Thesurfaces themselves are of exceedingly narrow chord and, except for the spoilers, are operated entirely manually by aerodynamictabs. The elevators and rudder require little comment except to note that the leading edge of the latter surface is of reinforcedplastic by Zenith. Lateral control is provided by small flipper-type ailerons, mounted well inboard and effective only at high indicatedairspeed, together with extremely powerful spoilers arranged in seven sections above the wings (the three-view drawing onpage 774 shows their position and also indicates the "turbulators" ahead of the flipper ailerons). For maximum rate of roll all spoilersections can be opened on one wing only; No. 2 spoiler position can trim out asymmetric loads resulting from engine failure, andopening of all spoiler sections combines very great braking effect with destruction of an appreciable proportion of the lift of thewing, which is most valuable for rapid let-downs and during the landing run. Spoiler operation is hydraulic. The enormous flaps(Continued on p. 774, after double-page drawing of B-52.) *Naming of a sub-contractor or supplier does not imply that thatcompany is the sole producer of the part concerned.
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