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From London to Salonica five men were carried. In addition was their luggage, bedding, two tool boxes, spare parts equivalent in weight to one engine, and two 11'-6" spare propellers. Complete, the machine weighed over 6 tons, with a useful load of about 6,000 pounds. In crossing the Albanian Alps the machine frequently was at an altitude of 10,000 feet. The power plant consisted of two 275 horsepower Rolls-Royce motors, and even at this high altitude, and with the heavy loading, no trouble was experienced. During the bombing, only three men were carried, the remainder of the useful weight being made up of bombs and other ammunition. While this record will probably be beaten before this book goes to press, it will at least give an idea as to the requirements and capabilities of the bombing type aeroplane.

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Definition

Properties of Air

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Every existing fluid resists the motion of a body, the opposition to the motion being commonly known as "resistance." This is due to the cohesion between the fluid particles and the resistance is the actual force required to break them apart and make room for the moving body. Fluids exhibiting resistance are said to have "viscosity." In early aerodynamic researches, and in the study of hydrodynamics, the mathematical theory is based on a "perfect fluid," that is, on a theoretical fluid possessing no viscosity, and while this conception is an aid in studying the reactions, the actual laboratory results are far from the computed values. Such theory would assume that a body could move in a fluid without encountering resistance, which in practice is, of course, impossible.