Nelson's Weblog: aviation / e6b

Lost computers of our forefathers

One of the fun things about pilot training is learning to do things the old way. I've just learned the art of plotting courses using an E6B, a glorified slide rule. Initially I mocked this old tech, but having learnt it I admire how simple and unmediated it is. And I can do all my calculations on a 65 year old whiz-wheel, my father's Army Air Force issue Computer: Dead Reckoning.

The interesting side of the E6B is the wind correction part. If you've got a 20 knot headwind blowing 50° to your left, what angle do you need to fly straight and how much slower will you be going? It's a simple trigonometric problem, but it's too abstract writing it out and doing the arithmetic. On an E6B you just draw the wind vector, right on the computer, then rotate it to visualize the wind vector vs. your path. Then you read the course correction and speed change off the calibrated graph underneath your drawing. It's like a thousand little vector calculations were done at once and drawn on the paper for you to measure against. Very intuitive.

The other side of the E6B is a simple circular slide rule for doing multiplication and division. It has scales for fuel consumption, distance and rate calculations, converting °F to °C, etc. Initially I used my iPhone for this arithmetic but I kind of prefer rotating the wheels and reading the numbers off the scale. The imprecision of a slide rule reinforces that everything is just an estimate. And I'm constantly sanity checking everything to make sure I'm didn't misread a scale by a factor of 10. That extra work seems to help reinforce the course planning.

I'm pretty sure as soon as I pass my pilot exam I'll never use an E6B again. It's much easier to use map-based flight planning software, or for that matter just to jump in the plane and let the GPS computer figure it out for you. More accurate, too. But the old way's kind of cool.

aviation
2010-01-29 20:16 Z


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