swilliam@dtoa1.dt.navy.mil (Williams) (02/04/91)
From: swilliam@dtoa1.dt.navy.mil (Williams) The B-52 Engineered To Endure Condensed from an article in the MECHANICAL ENGINEERING issue, January 1990 Part 1 of 3 When the prototype for the B-52 took off from Seattle's Boeing Field on its maiden flight, little was it realized that this giant would become the most venerable and versatile military aircraft ever built. Indeed, Air Force and Boeing personnel have spent entire 20- and 30- careers flying or supporting the B-52. But the B-52's story is far from over, and the aircraft will be flying well into the 21st century. Several factors keep the B-52 flying and make it one of the key elements in the manned bomber leg of the United States' strategic deterrence triad. Most important, the original design was excellent. The B-52's low weight, low drag, substantial wing area, and large airframe meant much growth potential. In addition, the B-52 has been extensively modified and improved through the years. The basic layout of the B-52 was done over a weekend in 1948 in a Dayton, Ohio, hotel room by a small group of Boeing engineers "on the back of an envelope." However, this "back of the envelope" designed was reinforced by lots of experience in designing and building bombers. Boeing had built two of the most successful bombers of World War II, the B-17 and B-29. After the war Boeing developed the six-jet-engined B-47 strategic medium bomber. Many of its features was incorporated into the B-52. Boeing also won a contract for the XB-55, a successor to the B-47, that was soon abandoned by the U.S. Air Force in favor of the B-52. The Monday following that weekend in Dayton, the team's brief proposal was presented to the Air Force where it was enthusiastically received. The backing of the design concept by General Curtis LeMay, the cigar- chomping head of the Strategic Air Command (SAC), played a large part in getting the B-52 development moving at full speed. Approximately three and a half years elapsed between conception and first flight. The XB-52 rolled out of Boeing's Seattle facility in November 1951 covered with tarpaulins for security. The XB-52 and YB-52 were built as secret weapons in a highly classified assembly area. The YB-52 made its maiden flight on April 15, 1952, and the XB-52 first flew in October of that year. The X and Y designations were a budgetary ploy; the two planes were virtually the same aircraft. Boeing had already received the go-ahead to start producing the first 13 B-52As in early 1951. The first production B-52A flew in August 1954. The first operational B-52 was delivered to the 93d Bomb Wing at Castle AFB, California, in June 1955, just over three years after the YB-52's inaugural flight. (Of all the models, only the XB-52 and YB-52 had the "bubble" canopy with tandem seating for pilot and copilot that was a carryover from the B-47 layout.) Different Versions ------------------ While the 13 B-52As were originally ordered, only three were actually built. The other 10 were produced as B-52Bs. The A models were used for development and test work, including a long life of research work not related to the B-52 program per se. The A models were the most expensive, at over $29 million a copy, since their unit cost included amortization of the preproduction costs. After that, the unit cost dropped dramatically. The B-52B was the first of the stratofortresses delivered to SAC. From the outside it looked just like the A model. The main differences were its reconnaissance and bombing/navigation equipment. Of the 50 B models built, 27 were RB-52Bs; the R stood for reconnaissance. The RB-52Bs had a two-man pressurized capsule filled with electronic equipment for weather and photo reconnaissance and countermeasures missions that was installed in the bomb bay. With the B-52C, the gross weight jumped from the 420,000 pounds of the A and B models to 450,000 pounds. The C also had huge 3000-gallon drop fuel tanks on the wings. Fuel capacity was increased from 37,550 to 41,550 gallons, as the earlier models had only 1000-gallon tanks. At the same time, the radius that the plan could fly without refueling increased from 3110 to 3305 nautical miles. Of all the models that went into operational service, the C model was produced in the smallest quantity, a mere 35. The 170 D models were not significantly different than the B-52C. The B-52D was the first B-52 to be produced in Wichita, Kansas, as well as in Seattle. By the mid-1950s, improvements in Soviet air defenses including interceptors, radars, and surface-to-air missiles had reached the point where the B-52 could not penetrate safely at high altitudes. As a result, the B-52E was the first of the series equipped with equipment for penetration at "on-the-deck" altitudes as well as having an improved bombing navigation system. The 100 E models were produced at both Seattle and Wichita. The main improvement on the B-52F was the J57-P-43W engines, which produced 13,570 pounds of thrust, as compared to the 12,100-pound thrust engines used on the B through E models. The B-52F also benefited from more than 1000 minor structural changes. The 89 B-52Fs that were produced were the last of the B-52s to be built at both Seattle and Wichita. The B-52G was essentially a new aircraft, even though externally the only readily apparent changes were a shorter vertical tail and lack of ailerons. While gross weight climbed to 488,000 pounds, the empty weight actually went down. The end result was more capacity for fuel and mission equipment. The B-52G had an unrefueled radius of 3785 nautical miles. Much of the weight savings came with the replacement of the bladder fuel cells with integral fuel tanks, the so-called wet wing. Reduction of tail height and elimination of the ailerons saved much more weight. The tail gunner was moved from his lonely position in the tail of the aircraft up to the front with the rest of the crew. The tail gunner operated the four turret- mounted 50-caliber machine guns using radar and closed-circuit TV. The biggest change, however, was that the B-52G became a missile platform as well as a bomb dropper. Even more changes would come on the B-52H, the last of the series. There were new engines, as the TF33 turbofan replaced the turbojets previously used. Power shot up by 30 percent and fuel consumption decreased by an equal amount. The B-52H has a radius of 4510 nautical miles. The 50-caliber guns in the aircraft's defensive fire control system were replaced by a six-barrel, 20-mm Gatling gun capable of firing 4000 rounds per minute resulting in a significant increase in firepower. Boeing produced 102 B-52H models.