What Is This Thing?
It might look like you need a degree in Rocket Science to have any business trying to figure out an E6B, but you don’t. It’s actually quite simple once you understand how it’s laid out and a couple basics.  There are seemingly limitless functions on a manual E6B, and some I’ve learned and then looked back and thought, “can I even construct a scenario where this would be of any use?”  Perhaps, but some are pretty impossible and hilarious scenarios so don’t sweat knowing every last function.  Let’s look at a few basics of how it works and five of the most common functions you’ll need to know to fly.

Basic 1: The Rotating Slide Rule Side

The A scale is the outer scale, while the B and C scale stick together on the inner disc. The B and C scale must be good friends.

The A scale is the outer scale, while the B and C scale stick together on the inner disc. The B and C scale must be good friends.

This side has three scales that you can line up to calculate things. The A scale (the outermost circle), the B scale (the middle circle), and C scale (the inner circle).  See, that’s not so bad, right?  The general concept to learn is that for most problems to solve, there are three elements: you line up a number on the outer scale (A) with a number on the inner scale (B or C), and then know where to look for your answer.  So in the examples below, it’s simply “line up this with that and look here for the answer.”

Basic 2: It Takes A Little Common Sense (And A Decimal Point)
You’ll be lining up one number with another number to get your answer. You might, for instance, get a ground speed result of “11” as it reads on the E6B. You have to reason if that means 11, 110, or 1100. If your ground speed is 11, you’ve got bigger things to worry about than calculating your ground speed.  If your ground speed is 1100, then call Guiness, speed racer. But 110? Now that’s a reasonable ground speed, my friend.

A little common sense will let you interpret the result properly.

A little common sense will let you interpret the result properly.

Basic 3: The Wind Side
The back side of the E6B is the wind side. Like the flip side, it also has a rotating scale where you match one number against another. But notice the center of the circle is clear. You can mark on it with a pencil and it will erase right off. High tech, huh?  The center of the circle has a small hole that is used as a reference point. Every E6B I’ve seen has the instructions for the wind side right at the top – very handy to jog your memory.

The directions for the most common use of the wind side are printed right at the top. It's kinda like writing the formula on your hand for a test.

The directions for the most common use of the wind side are printed right at the top. It’s kinda like writing the formula on your hand for a test (I don’t endorse that).

Now Let’s Fly Somewhere
Now that you’ve had a basic tour of the E6B, let’s put it to good use. You won’t need anything for this trip (the pictures will guide you), but feel free to follow along on a map with your own E6B if you have access to one. If you’re looking to buy an E6B, you can pick up a standard ASA E6B here.  The one used in this blog is the smaller ASA Micro E6B.  If you don’t have one, you can download this E6B app which mimics a manual E6B. My home airport is Thomson-McDuffie County (KHQU) just outside of Augusta, GA.  Let’s walk through a few questions and how to solve them.

Here we are at Thomson-McDuffie County Airport in Georgia. Where should we fly today?

Here we are at Thomson-McDuffie County Airport in Georgia. Where should we fly today?

1. Time To A Destination
“How long would it take to fly to Nashville?”  To figure out the time to a destination, we need to use the Time-Speed-Distance concept. If you know any two of those values, the third can be found easily. Let’s look at a route from Thomson-McDuffie County (KHQU) to Smyrna (KMQY), right outside Nashville. We’ll make a stop along our route in Athens (KAHN) and then fly over Chattanooga (KCHA) as we make our way there. In this case, by knowing how fast we will be cruising – let’s say 110kts – and how far away your destination is – 248nm – that time can be found as follows:

-On the B scale, you’ll see a “rate” arrow at the 60. Line up this rate arrow with the known airspeed of 110 on the A scale.
-Look for the known distance of 248 on the A scale (this is where that common sense decimal comes in – look between the 24 and 25). The time of 135 minutes reads on the B scale in line with the 248. A simple conversion shows that 135 minutes is 2 hours and 15 minutes.
-Fun fact: if you look at the same place on the C scale, it is between the 2:10 and 2:20 marks (our answer of 2:15). The C scale is known as the time scale.

One you line up your rate arrow, all you have to do is look at the mileage on the A scale.

Once you line up your rate arrow to your speed of 110, all you have to do is look at the mileage of 248 on the A scale (it’s between the 24 and 25 – remember that common sense decimal?).

2. Fuel Burn (Endurance)

We stopped off at Athens for a nice cold Coke. Why? Because we can.

We stopped off at Athens for a nice cold Coke. Why? Because we can.

“Do we have enough gas?”  In aviation, waiting for the gas light to come on before getting gas is just not gonna fly. Literally, you probably won’t be flying. “Fuel is on the watch,” meaning that you calculate how long you can fly for each leg of your flight.  Fuel works a lot like those time-speed-distance problems in that knowing two values gives you a third.  After stopping for a Coke in Athens (KAHN), we determine that we have 32 gallons of gas. Knowing that we plan to burn 9 gallons per hour, we can determine how long you can fly as follows:

-Line up the rate arrow with known per hour value of 9 (the 90 on the E6B).
-Find the known value of 32 on the A scale to fall in between the 21 and 22 on the B scale (again think “gallons over hour” to remember that the gallons are on the top A scale and time on the lower B scale).
-A little common sense tells you that the 21.3 as it reads on the E6B means that you have 213 minutes of fuel (or a little over 3:30 hours as it reads on the C scale). 3 hours 33 minutes to be exact.

When you have a "something per hour" calculation, that rate arrow is used to point at the unit per hour.

When you have a “something per hour” calculation, that rate arrow is used to point at the unit per hour.  In this case, our fuel is 9 gallons per hour.

3. Groundspeed

The "X" pencil mark shows the checkpoint Matthews Private Airport checkpoint 20 miles past Chattanooga.

The “X” pencil mark along our course line shows the Matthews Private Airport checkpoint (the “R” in the circle) 20 miles past Chattanooga.

“Wow, we’re making great time.  How fast are we going?”  When timing from one checkpoint to the next, aircraft performance (airspeed) along with the wind determines just how fast over the ground we are going. In the same concept of Time-Speed-Distance used above, knowing that we flew the 20nm leg from Chattanooga to the next checkpoint of the Matthews Private Airport in 10 minutes,we can figure out the ground speed as follows:

-Line up the known distance of 20 on the A scale with the known time of 10 on the B scale.
-Now the rate arrow (the 60) points to the speed of 120.
-Hint: the A and B scales are used the most. When thinking of what scale to use for what, I just think “miles per hour” (as in miles over hour) so I think the same with the A scale and B scale – “miles (A) over hour (B/C).”

When you know the distance and time (20 miles in 10 minutes), just line the two numbers up. The rate pointer will point to your ground speed.

When you know the distance and time (20 miles in 10 minutes), just line the two numbers up. The rate pointer will point to your ground speed.

4. Wind Correction
“Is that headwind gonna slow us down much?” There is an old physics problem where trying to drive a motor boat directly across a fast flowing river shows that you must angle the boat upstream to travel directly from shore to shore. Pointing straight across the river will cause you to drift downstream. The same concept applies to flying. When flying from one point to another, you are subject to being pushed by the river of air similar to being pushed downstream by water.  We can use the E6B to calculate how far we need to turn our aircraft “upstream” to stop the wind from blowing us off course. Consider that a direct headwind will simply slow us down, and a direct tailwind will speed us up.  However, when we adjust for a wind that has some component coming from the side, our heading must be adjusted to keep the same ground track to your destination. This will affect our ground speed as well as our heading. The course from Thomson (KHQU) towards Chattanooga (KCHA) is 310 degrees.  Our airspeed, like we calculated above, is 110kts.  The weather briefer told us that the wind is from 180 degrees at 20 kts. We can determine the wind correction as follows (hint: follow along with the directions at the top of the E6B):

-Spin the circle to set the known wind direction of 180 under the True Index.
-Slide the circle so that the center hole in the circle is at the 100 mark. It’s just an easy reference point for the next step.
-Now use a pencil to make a little mark (dot or X) at the known wind velocity of 20. In this case, the mark will be at 120 since the 100 was just an easy starting point. You are really just making a 20 unit mark away from the hole.

The wind direction of 180 is under the True Index and the wind speed of 20 is marked up from the center hole.

Step 1: The wind direction of 180 is under the True Index and the wind speed of 20 is marked up from the center hole.

-Now spin the circle to set your known course of 310.  Notice that our pencil mark has moved around some.

Spin around to put your course under the True Index.

Step 2: Spin around to put our course under the True Index.

-Slide the whole circle up until your pencil mark rests on the known airspeed line of 110. Our estimated ground speed of 122 reads under the center hole and the wind correction angle of 8 is the number of units left or right of the center line that the pencil mark rests.
-The reminder key is on most E6Bs, but like book reads from left to right, you add the degrees to the right of the center line and subtract those to the left. In this case, we will subtract 8 degrees from our course of 310 for our wind correction to get 302 (magnetic variation and deviation must then be considered, but that is the topic for another day).

Slide your pencil mark to your airspeed line. The center hole marks your ground speed and your pencil mark shows your left or right wind correction angle in degrees..

Step 3: Slide your pencil mark to your airspeed line. The center hole marks our ground speed and your pencil mark shows our left or right wind correction angle in degrees..

Practical Use
In the field of carpentry, the old saying is “measure twice, cut once.”  A hasty or inaccurate measurement, without double checking yourself, might lead to a wooden board too short for the job.  In aviation, the same concept applies.  Take, for instance, cross country flight planning. The way most pilots initially learn to calculate wind correction, time in route and fuel burn is a manual E6B and a sheet of paper.  Nowadays, it’s easy to plug in some info into a computer or iPad and have a flight plan and calculations done for you.  Which one you use is a personal preference – both are easy and accurate in their own way. I recommend using the manual E6B to calculate and then using an electronic version or computer flight planner to double check your work. That’s a pilot’s version of “measure twice, cut once.”  A short board is one thing, but short on fuel is a problem you don’t want to catch when it’s too late.

Spin The Wheel
In a time where calculators and computers can give us virtually instant information, the manual E6B is still a staple in my flight bag.  Sure, I have an electronic version of the E6B on my phone, but I find it to be quicker to spin the wheel on my trusty metal version than to open an app, find the function I want and type in the values.  Plus, the good old metal one will never get low on batteries.  Tell me what you fly with – do you prefer a manual or electronic flight computer?

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4 Comments

  1. James kephart

    Its been 69 years since I’ve had one in my hands. Used to make fliteplans in Air Force

    Reply
    • Clay

      And the batteries are still ticking, huh? I love that they are still just as useful today. Thanks for reading, James, and for your service in the Air Force!

      Reply
  2. Jody

    Hi Clay. Small problem.

    Can i calculate unknown wind direction and speed with the e6b if i have, oat, pressure altitude, Tas and heading?

    And if my numbers are greater than that of the wind/velocity scale, how can i reduce them or make them smaller ratio wise.

    E.g my e6b max speed shown is 260 and i have a TAS of 300, i am unable to view my drift.

    Reply
    • Clay

      Hi Jody!

      This sort of problem is one I’ve pondered before. To determine the unknown wind speed and direction, you need to have the variables of groundspeed, TAS, true heading and true course. Some E6B computers have a “high speed” wind side. The app “Flight Computer” by Diego Rodrigues has that in a manual E6B format for iPhone and iPad.

      Reply

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