How is it possible for the E6 slide rule to be used more quickly than a flight computer?

Fiddling with various log scales seems more time consuming than just punching a few flight computer keys.

Re this item E6B Flight Computer

It’s like reading an analog clock. With a digital clock, you read the numbers. With an analog one you intuitively read the angles. It’s often quicker to tell the time by reading the angles. (Especially if you don’t need or want the exact number.)

With an E6B, you know the scales. So the pilot can quickly spin the wheel with his thumb. The answer can then be read directly off the opposing scale. I never used my electronic E6B much, so I’d always have to stop and think about which buttons to push. And the batteries kept dying. It was quicker and more convenient to use the whiz wheel.

if you get good at a circular slide rule you can be amazing fast. you can beat calculators with the limitation on significant figures.

in aviation i suppose the smart thing would to always have known good spare batteries or a manual device.

But you don’t punch “just a few keys”. You have to enter the first number, the operation, wait, and not make any mistypes.

A slide wheel can be used with one hand, as your wiki quote says. You only have to move to one number and get several results at once in the window, whereas with a calculator, you have to punch keys seperately to get from airspeed + wind speed to speed over ground first, then to how long your fuel will last second, to how high you should fly for maximum efficiency third, etc.

I don’t know about flight computers in particular, but in general, an advantage about slide rules is that certain relationships in life - ratios, say - are easy to set on a slide rule. That is, you can have one scale represent numbers that are larger by a factor like 2Pi or 8 or the square root of two, relative to the numbers on another adjacent scale. Then your eye can drift along the seam where the two scales join, looking for a combination that you like. It’s sort of like looking at storage boxes and shelving units that are displayed right next to each other in a store. You glance around looking for relationships that will work for you. Or you might have one scale that represents the squares or the cubes of the numbers on another scale. You might even arrange the scales so one scale represents the size of cubical tanks in inches, and the adjacent scale represents the volume of said tanks in gallons, and you are looking for a simple relationship where an easy to remember number of inches corresponds to a nice round number of gallons.

These are easy and visceral things you can do with a slide rule that are more difficult with a calculator, and even a little difficult to explain, especially to someone who hasn’t used a slide rule like that.

My dad the math genius mentions that back in the day when he used a logarithmic slide rule for multiplication and division, after enough practice he could compute by simply imagining the slides visually in his head.

You certainly can’t do that with a calculator.

Well if it’s good enough for him I guess it’s good enough for anybody.

This may not be true for other sectors of aviation, but in my experience circular slide rules are not commonly used. Everyone HAS one (mine is a Jepesen CR-3 I think), but for actual calculations every pilot I’ve flown with has routinely used a cheap calculator. The last time I used my CR3 regularly was when I did my ATPL exams and it was necessary to use it because it has specific functions such as calculating true air speed, Mach number, density altitude etc, in addition to the ability to quickly do multiplication and division. When I am actually flying it doesn’t get touched. This is partly because modern GPS and flight management systems generally have all the information available already. If I want to know our true airspeed I push the “TAS” button on the glare shield. If I want to know the wind I glance down at the FMS and the wind is displayed on the main navigation page along with crosswind and headwind component. Even when I was flying less sophisticated aircraft everything that needed to be calculated on a day to day basis was done either with a calculator or using rules of thumb and that great aviation technique of “suck it and see.”

I won’t say they’re never used, but it is rare. In 5500 hours I have never used the wind vector side in earnest.

Having said that, they certainly have advantages. Probably the biggest advantage they have over a calculator is the ability to set a ratio and then obtain a series of answers without having to move the slide again. For example, say you’re working out your fuel burn for each leg of a flight you are planning and you know that your aircraft burns 1000 lbs/hour. If you were using a calculator or electronic flight computer you would have to do a separate calculation for each leg of the flight. With a circular slide rule you set the 10 (representing 1000 in this case) on one scale against the 60 minute / 1 hour mark on the other scale and then just go to each time interval on the time scale and read off the fuel used against it. Very quick and easy. Not as quick and easy as using an Excel spreadsheet though so once again it loses out to more modern equipment.

“…an utterly insignificant little blue green planet whose ape-descended life forms are so amazingly primitive that they still think digital watches are a pretty neat idea.”


I agree with Richard Pearse’s post. As a flight instructor, I use them all the time when training students because they are supposed to know how. And it’s true that for certain calculations - like fuel burn or time between waypoints at a certain groundspeed - it’s very quick and easy.

However, I can’t remember the last time I used a whiz wheel in flight that wasn’t for training purposes. Even your basic hand-held GPS gives you groundspeed, which is what half of all the E6-B calculations are ultimately used to derive.

With a calculator, you have to punch in the numbers for each calculation. With a whiz wheel, you can set it once for the ratio, then just read off the answer for any given input.

Suppose I want to check myr ground speed against section lines.
With a single setting of an E6-B I can read MPH for any seconds/mile. With a slightly different setting I can read kt instead. I can double or triple check my speed without shifting the wheels.

Non-aviation example:
If sales tax is 8.5%, you set the 1 of one scale at 1.085 on the other, then you can read the cost with tax of any other price without changing the setting. Maybe a little faster on the first calculation, and LOTS faster on the following ones. And yes, you might be a few cents off on an item costing several hundered dollars.

I learned to fly civilian in the late 60s. I always used both sides of a Jepp CR for flight planning. Once airborne, it came out for leg length & fuel burn confirmation once I had a good groundspeed from timing past landmarks. Other than for curiousity sake I don’t think I’ve ever used the back side inflight in a small aircraft.

USAF issued me an E6B & taught me how to use it. I’ve never used or carried it inflight. No time in a fighter for such niceties.

In 10+years flying big but non-magic jets my CR was always in a shirt pocket. It probably got pulled out every 3rd leg or so to to time/distance/burn calcs. Our computer-generated flight plans were good enough that as long as we were flying the plan the CR wasn’t needed. But once we got rerouted or the wind was much different than planned, the CR was indispensible.

In 5+years of flying magic big jets I don’t think the CR has come out of my pocket in flight. The FMS knows all & tells all. But my CR still rode in my shirt pocket.

And I have never owned, nor seen any use for, an electronic flight computer/calculator. As far as I can see, all they do is hide enough of the details so that you’re highly susceptable to undetectable GIGO errors.

When I used to have to do weight & balance for every leg (don’t ask), a 4-banger calculator was handy for calculating moments & totals. I would not trust a solution from a dedicated pilot calculator unless I could see the whole thing in a spreadsheet-like display. Goofs are too easy, and too readily fatal, to trust to a black hole calculation.

Yeah, I’m a bit of an old-fashioned aviator I guess.

The E6B is what I know as a “flight computer.” Do the make newfangled digital ones nowadays?

You can get electronic flight computers. I’ve never seen anyone use one though.

I got an “electronic E6B” (which is a fancy calculator/dedicated computer) which I found fantastic for *planning *cross country trips, but en route if I had to recalculate anything I used the whiz wheel. Of course, I am also a strictly VFR pilot who flew older planes without the up to date GPS and flight management systems - in other words, the airplanes flown during the E6B heyday.

Really, I tried to make my planning thorough enough a need for en route recalculation was unlikely.

The huge advantage of the slide rule, which a few have pointed out, is the ability to set it at one point and be able to read off the answer to a multitude of calculations, as well as a related inverse calculation. There have definitely been times that I wish I had one when all I had otherwise was a basic four-function calculator and I had to multiply a ton of things by some other number. While a modern computer spreadsheet might generally beat it out in terms of power, the fact that you never have to enter any data other than setting the ratio makes it the absolute best tool to use when faced with certain problems.

I actually really want to get one now - my father had one and showed it to me, but I never used it since calculators were ubiquitous by the time I needed one.

Heh. OK, this thread made me break out my E6Bs. Looking them over, three of them were hand-me-downs from dad.

I have a well-used Aero Products ©1967 one. (Note: the © doesn’t mean it was made then. But I think dad started flying in '68 and he may have bought it early in his career.) Got it from dad. It had been used in a desert environment, so the markings under the windows are pretty much sanded off. Too bad. I like the blue markings.

I have a Jeppesen one that’s probably about the same age as the Aero Products one. The wind ring is really tight. I wonder if there’s a way of loosening it? But the markings under the windows (and the rest of it) are in fine shape. The slider has green markings. I used this one when I started flying.

The SanTech one might have belonged to dad. Or I may have bought it. It’s in nearly-new condition. The wind ring is a little stiff, though. It has a blue slipcase and manual.

Dad gave me his Telex, which still has its brown slipcase. Pretty good shape, though the circular slide rule is a little stiff – as is the wind ring. (What IS it with the bleedin’ wind rings?)

And there’s a pocket-sized ones that I bought. The wheel’s a little stiff, but the wind ring turns easily enough. 'Course, it’s missing a screw.

I’m sure I have another E6B around here somewhere. I remember the blue, folding case and the orange manual. I think that’s the one I used the most, so it’s not with the others.

If anyone is interested, be they curious about how to use an E6B or they already know how to but want to brush off the rust, here’s a manual:

Back in the late '70s, my dad (an electrical engineer) got me a scientific calculator for college. For the fun of it, we set up some problems, and solved them together, me with the calculator, he with his slide rule.

He beat me every time.