The queen of the skies - part I

The Boeing 747 is the very airplane that revolutionized air transportation. It was the first wide body civilian aircraft, it opened the wide body era in carrying twice as many passengers than previous jets could carry.

The studies of the Boeing 747 go back to the middle of the 1960's when the United States Air Force asked the manufacturers to design a high capacity transport aircraft, the big three aircraft manufacturers in the United States were at that time Boeing, Mc Donnell Douglas and Lockheed. Lockheed won the contract and pursued the development of the C-5 Galaxy, a giant aircraft designed for heavy military transport but never made in passenger version. Only the US Air Force has operated the C-5 Galaxy which first flew in 1968.
Boeing was for a long time working with Pan American World Airways in designing passenger aircraft. Pan Am which introduced the Boeing 707 in 1958 (that was when the United States entered the jet age) on intercontinental routes saw how rapidly air travel was growing and thus requested Boeing to design a new aircraft able to carry twice as many passengers.
Joe Sutter, a Boeing engineer from Seattle WA, who had been working on the 737 at the time, was assigned in the development of the new 747. He wrote a book about the history of the 747 and how he worked on it during all phases of negotiations, design, testing and entry in service. He tells about his whole life at Boeing. The Boeing company was put at financial risk because the cost of the project was tremendously high and there was doubt it would be successful in sales to most commercial airlines, but Pan Am really wanted such an aircraft for future expansion.
Pan Am had first thought of a double decker jet, but at that time the Federal Aviation Administration (FAA) would not approve such project for safety reasons, all passengers would have to be evacuated within 90 seconds in the event of an incident. Pan Am engineers then came with a new idea: how about carrying the same amount of passengers on one single deck? The FAA regulations at the time could be met in this concept. This was the invention of the wide body airplane: two aisles on one deck.
Boeing wasn't very convinced that the airplane would be profitable to the airlines in carrying only passengers, so it decided to pursue designing the 747 also in freighter version. But how could a 747 freighter be loaded with over 100 tons of freight in as little time as possible? The solution was to put a door on the nose so that all the freight could be loaded more efficiently, the nose door would swing upwards. By meeting this concept, the cockpit which was originally on the main deck was moved upwards, this was how the hump on the 747 came. The design was finally frozen and in 1966 Pan Am signed the first contract with Boeing for the purchase of 25 units. It was at that time the new facility in Everett WA was built, to build large aircrafts, because those could not be accommodated in the Renton plant where all previous models had been built. Renton and Everett are the two main facilities of Boeing located in the Seattle area.

The first Boeing 747 was ready to roll out of the Everett plant in late 1968. It was designed with four redundant hydraulic systems, plus triple slotted flaps like the 727 had, so that it would be able to land on airports with not so long runways, and it was also designed with four set of four wheels so that the weight of the aircraft would be better spread out to each landing gear, thus reducing the pressure applied by each tire on the ground. I believe that the tire of a 747 is inflated to a pressure of about 200 psi (12 bars, or 12 times the atmospheric pressure).

The 747 made its maiden flight on February 9, 1969, out of Everett WA. Since then, several tests were conducted in various conditions, before the FAA would approve delivery to the airlines. Boeing was working with Pratt & Whitney, an company supplying jet engines to airplanes, in designing a high bypass ratio engine for the 747. High bypass ratio means that more air enters the engine for less air being mixed with the fuel, the remaining volume of air would flow around the main core of the engine, thus reducing shear stress and fuel consumption for more power generated. I believe that 5 to 1 is the bypass ratio for the jet engines designed by Rolls Royce, General Electric and Pratt & Whitney, to equip the wide bodies then new at the time. It means that for five units of air volume, one is compressed and mixed with the fuel, and the other four bypass the engine after entering the first fan mounted on the shaft. Anyway, I won't go into too much technical detail, this was just to explain how efficient the 747 was compared to what the 707 was.

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