All About Engines

112 All About Engines engine we shall have to use a formula. It is only a simple one—not half so difficult as some of those worked by you fifteen-year-old schoolboys, so there is no need to be afraid of it. Here it is : W x v2 g x r where W =- the weight of the body in pounds; v = the velocity of the centre of gravity of the body in feet per second ; r = the distance of centre of gravity of the body from centre of rotation in feet ; and g = the gravitational constant, 32'2. Suppose that in a certain engine the moving parts weigh 100 lb., that r is equal to 1 foot, and that the engine is making 200 revolutions per minute. A point on the circumference of this circle of 1 foot radius will move 2 x 3) x 1 = 6? feet in one revolution, and 6| x 200 = 1,256 feet in one minute, or almost exactly 21 feet in a second. This is the velocity corresponding to v in the above formula. The centri- fugal force due to the rotating parts is, therefore, 100 x 21 x 21 32-2 =“ 1,380 lb. approximately. This means that there would be a force of nearly 1,400 lb., or five-eighths of a ton, pressing the rotat- ing shaft against the bearing, and not only tend- ing to squeeze out the oil and thus to cause over- heating, but exerting a pull, through the bearing, on the bed, now forwards, now backwards, now up, now down. If the bed were not securely bolted down to a heavy foundation it would tend to jump and