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Aviation History
1959
1959 - 1654.PDF
799FLIGHT, 12 June1959 Thunderchief 'THE MOST POWERFUL ONE-MAN AIRPLANE IN THE WORLD' PHOTOGRAPHS of the Republic F-105 Thunderchief donot do the aircraft justice, for a mere picture can conveylittle of the capability of this aeroplane. In general, it looks like an ordinary fighter, yet it can carry a heavier bomb loadthan a B-17 and can fly a great variety of military missions. Initially, the 105 was a private venture by Republic AviationCorporation of Farmingdale, Long Island. For many years this company has been one of the foremost manufacturers of fightersand fighter/bombers for the U.S. Air Force and for the Army Air Force and Air Corps before it; few of our readers need anyintroduction to the names Thunderbolt, Thunderjet, Thunder- streak and Thunderflash. During 1951 the fighting in Korea provided proof of the staminaof the first generation of jet combat aircraft. Every force engaged in this battle learnt much from it—albeit "the hard way"—andthe U.S. Air Force in particular determined that the forthcoming "Century series" of supersonic intercepters, fighters and fighter/bombers should mark a tremendous advance over their pre- decessors. Republic's own F-84G Thunderjet bore the bruntof the fighter/bomber load in Korea and proved itself both capable and popular. Nevertheless, its designer, AlexanderKartveli, now Republic's vice-president for research and develop- ment, knew that it would shortly be possible to design a far moreimpressive aeroplane. He and his colleagues were keenly aware of the fact that there were many missions—in particular thoseinvolving delivery of a thermonuclear weapon—which could be accomplished only by the B-47. The logical course of actionseemed to be to take a B-47 bomb bay (figuratively speaking), and perhaps a miniaturized version of its bombing system, and builda smaller, supersonic aeroplane round it. By September 1951 a small team of fifteen engineers sat downto work on the new project, which bore the company number AP-63. It was decided from the outset that the new aeroplanecould be a single-seater and that it should have a single power- plant; and the engine chosen was the 15,000 lb-thrust turbojetthen being planned for the Air Force by Pratt & Whitney Air- craft as the XJ75. By late 1952 enough arithmetic had been doneto show that the AP-63 would work very well indeed, and the company were accordingly awarded a U.S. Air Force develop-ment contract. The project thus became the XF-105, and the engineering team working on it grew steadily to 300. The first XF-105A (U.S.A.F. serial number 54-0098) was flownby the company's chief experimental test pilot, H. G. "Hank" Beaird, at Edwards Air Force Base on October 22, 1955, approxi-mately one month ahead of schedule. The flight lasted 45 minutes, and before Beaird landed he had taken the new aircraft beyondMach 1. The XJ75 was then far from ready to drive a fighter, and, in fact, had only recently started its flight tests slung fromthe bomb bay of a B-45. Accordingly the 105A was powered by a Pratt & Whitney J57, of much lower rating, although it wasotherwise approximately representative of what Republic con- sidered to be the production configuration. However, more than a year previously a flood of new aero-dynamic data on supersonic-aircraft design had begun to flow from the N.A.C.A., universities and aircraft companies. Applica-tion of the new information showed Republic that, provided they made the F-105 a slightly different shape, drag would be less thanthrust up to speeds very much greater than its designers had ever considered. The company therefore had to conduct whatmight be called "an agonizing re-appraisal," which consumed many weeks but produced a better aeroplane. By 1956 this workhad led to the F-105B which, although superficially similar to the A model, was in detail largely redesigned. The B was thefirst aircraft to be powered by the big J75—making it easily the most powerful single-engined aeroplane in the Western worldat that time—and the engine was fed through a completely new duct system which had recorded remarkable efficiencies at highsupersonic Mach numbers during extensive ground testing. In contrast to the A, the B was fully area-ruled and it also had arevised vertical tail surface. The first B model (U.S.A.F. serial number 54-0101) was flownby the same pilot on May 26, 1956. Since that date Republic have never looked back. The 105 has amazed every pilot whohas handled it, and it has shown itself to be the most versatile aeroplane of the entire Century series. It is appropriate at thispoint to examine the design and manufacture of the first produc- tion model, the F-105B, and to conclude this account with a briefreference to the later versions which are following it. The F-105B Thunderchief is a single-seat day fighter/bomber.Powered by a J75-P-5 (the first batch were originally fitted with the P-3 engine), it has an internal weapons bay, four wing pylonsand a fifth external attachment under the bomb bay, an M-61 "Gatling gun," an autopilot, integrated radar fire control andprovision for in-flight refuelling. In general, the structure of the 105B is remarkably conventional.Integrally stiffened skins and honeycombs seem to be conspicuous by their absence, and traditional methods of manufacture areemployed wherever practicable. The ruling material is 75ST aluminium alloy, and steel, titanium and magnesium alloys arerestricted to localized areas where these materials can show dis- tinct advantages. The airframe is sub-divided into major portions,each made in a separate pan of the Farmingdale plant (there is practically no sub-contracting) on what is generally known as the"colony" system. Port and starboard wings, for example, leave their colony in a virtually completed state. The system will bereferred to again as the description of the aircraft proceeds. Although its fine lines and fighter-type canopy belie the fact,the fuselage has a length of over 63ft; this is twice the length of a Vampire and comparable with the body of a Canberra. Forproduction purposes the fuselage is broken down into nose sec- tion, centre fuselage, rear fuselage and aft section, each of whichis manufactured in its own colony. The nose is relatively con- ventional, this portion being built up from approximately circularframes of various sections held together by heavy longerons. Eventually the entire nose is filled with weapon-system equip-ment, so that more than half of its surface consists of dielectric areas and access hatches. At the rear is the roomy cockpit, witha pressure-bearing floor built up from transverse and longitudinal beams. Beneath this floor is the bay for the nose undercarriage,which retracts in a forwards direction. The centre fuselage is built up from partial frames and angle-section stringers, the latter being broken fore and aft of the main frames. On the underside is the weapons bay, with its twinupward-hinging doors. Amidships are the winglets, which form an integral part of the fuselage and intake structure. The heaviestloads in the entire aircraft are accommodated by the main frame and the forward H-frame, both of which are machined frommassive forgings in high-strength steel. Kearney & Trecker three-axis millers are used on these forgings, with Bendix digitaltape control. The root rib along either side is machined on a converted Cincinnati spar mill with rising and falling cutters.This root rib is pierced by the main frame at station 442 and forms the outer boundary of the winglet and duct sub-assembly. The rear fuselage cross section increases from front to rear
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