The E6B Flight Computer, or simply the "whiz wheel", is a form of circular slide rule used in aviation. They are mostly used in flight training, but many professional and even airline pilots still carry and use these flight computers. These flight computers are used during flight planning to aid in calculating fuel burn, wind correction, time en route, and other items. In the air, the flight computer can be used to calculate ground speed as well. The back is designed for wind correction calculations, i.e., determining how much the wind is affecting one's speed and course.
Basic Details and explanation of "How to use an E6B Calculator".....
The front side of the flight computer is a logarithmic slide rule that performs multiplication, division, addition and subtraction. Throughout the wheel, unit names are marked (such as gallons, miles, kilometers, pounds, minutes, seconds, etc.) at locations that correspond to the constants that are used when going from one unit to another in various calculations. Once the wheel is positioned to represent a certain fixed ratio (for example, pounds of fuel per hour), the rest of the wheel can be consulted to utilize that same ratio in a problem (for example, how many pounds of fuel for a 2.5-hour cruise?) This is one area where the E6B and CRP-1 are different. Since the CRP-1s are made for the UK market, they can be used to perform the added conversions of Imperial to Metric units.
The wheel on the back of the calculator is used for calculating the effects of wind on cruise flight. This part of the calculator consists of a rotatable semi-transparent wheel with a hole in the middle, and a slide on which a grid is printed, that moves up and down underneath the wheel. The grid is visible through the transparent part of the wheel.
To solve this problem with a flight computer, first the wheel is turned so the wind direction is at the top of the wheel. Then a pencil mark is made just above the hole, at a distance representing the wind speed away from the hole. After the mark is made, the wheel is turned so that the course is now selected at the top of the wheel. The ruler then is slid so that the pencil mark is aligned with the true airspeed seen through the transparent part of the wheel. The wind correction angle is determined by matching how far right or left the pencil mark is from the hole, to the wind correction angle portion of the slide's grid. The true ground speed is determined by matching the center hole to the speed portion of the grid.