The E6-B
2025-12-09
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Over the last two months, I took a ground training course to become a private pilot. I've been interested in aviation my entire life, but the course taught me many things I didn't know, such as visual flight requirements, estimation of flying conditions base don the weather, and aerial traffic patterns when taking off and landing.
I also love slide rules and other forms of mechanical computation. Aviation involves many kinds of calculation, and to facilitate those calculations, private pilots are trained to use flight computers. The one assigned to us by our instructor was the E6-B mechanical computer.
The E6-B is a circular slide rule that also houses a two-sided panel. One side features the main slide rule that performs conversion operations, while the other side uses a transparent pane over a polar graph which is used to perform vector operations. It was created by Philip Dalton, a member of the US Navy, in the late 1930s. By the time of his death in 1941, it was used across the US Army Air Force, and it soon propagated to commercial and private aviation as well. The E6-B performs a huge variety of calculations, including
- airspeed correction,
- altitude correction,
- fuel burn,
- time and speed conversions,
- gallons to liters conversion,
- ground speed calculation,
- headwind and crosswind components of wind speed,
- miles to kilometers conversion,
- statute miles to nautical miles conversion,
- wind angle correction calculation,
and many more.
I was in a class of 7 students, and I was the only one among them who had ever used a slide rule of any kind. Other students struggled to understand how it worked, and their rote approach to memorizing its functions led to many calculation errors. While they preferred to reach for the calculators on their smartphones--one even asked for answers from ChatGPT--I immediately took to the E6-B, and it became my primary calculation tool. That was a boon to me when we took our final practice exam and I didn't have to figure out whether my calculator would be allowed.
Of course, electronic E6-B computers exist today, but the FAA still encourages pilots to use mechanical flight computers when training and keeping one in the cockpit while flying. It's highly standardized, its widely available for less money than a digital computer, extensive training exists for it, and it's immune to problems like dead batteries or electrical interference.
I love that the E6-B is still in wide use in the 21st century. I worry about modern society's total reliance on digital technology to run the world; I wish we complemented those systems with mechanical, chemical, or even human-powered systems. They provide robustness, redundancy, energy savings, and health benefits that ignored by the world's manic drive for efficiency and profit. In the world of aviation, however, safety is prioritized above all else, so it's necessary to have a tool that can still be used to fly safely when all else fails. The E6-B provides that fail-safe.
Personally, I'd like to see slides rules come back as a form of fallback calculation. It would be interesting to see a slide rule that performs hexadecimal or binary calculations, for example.
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[Last updated: 2025-12-09]