There are, however, a number of factors which tend to decrease the progress of a machine through the air: the head resistance of the fuselage, the motor, the struts, the wires, the landing-gear, etc. These things do not add to the lift and are described as “dead-head” resistance. Stream-line, or the tapering of all surfaces which resist the air, helps reduce this resistance, so that the design of the plane has much to do with its speed, also as to whether the plane can climb faster than fly straight ahead. Naturally the horse-power of the motor determines the flying speed of the aeroplane as much as any other factor. To lift a plane off the ground it must be travelling at least 35 miles an hour with respect to the air, as we have pointed out before. So if a gale is blowing 20 miles an hour the aeroplane may be lifted off the ground when moving no faster than 15 miles an hour with respect to the earth. Likewise unless a machine is moving 35 miles an hour it will lose flying speed and fall to the ground. Machines do not all land at the same speed. The famous Morane monoplane skimmed along the ground at anywhere from 45 to 90 miles an hour. It is manifestly impossible to do more than suggest the fundamental principles of aeroplane flight here. To be sure, the type of aircraft has, as we have indicated, much to do with why and how it flies. Because of its similarity to the bird and owing to the lack of struts, etc., to increase the head resistance the monoplane or single-wing plane is the fastest machine. The absence of struts and the few bracing wires brings a greater strain on the wings and increases its chances of breaking. The biplane, with its two parallel wings separated by struts, is more easily braced and proportionately stronger. The lift is also greater, due to the additional wing surface. The vacuum made over the lower wing is interfered with by the upper plane, and thus neutralizes somewhat the lifting and flying efficiency of the upper wing. Since a plane must reverse all its stresses when looping, the double supports of the biplane make it less susceptible to doubling up and falling. These are some of the reasons for the popularity of the biplane. The triplane is so called because it has three tiers of wing surfaces set one above the other. This allows for even greater strength in construction, and despite the resistance several very fast-climbing triplanes have been built. The famous Caproni triplanes with three motors have a wing spread of 127 feet. Many biplanes and flying-boats also have approximately 126-foot wing spread. The well-known Handley Page bomber and the NC-1, NC-2, NC-3, NC-4 Naval Flying Boats, which tried the Atlantic flight, had a similar wing spread.