Using the E6-B Flight Computer by John Boos

Calculating Temperature conversion, Airspeed Correction, Density Altitude, Fuel consumption, adjusting chart scales, Time en-route, Wind Correction Angle, Ground Speed, and other optional uses like multiplication and division.

The E6-B is a mechanical computer. It has fixed scales for conversions, ands rotating scales on both sides: one for wind calculations, and another for numeric calculations such as fuel consumption and en-route time. Why use the E6-B? It simplifies many calculations that would be difficult and involved on a calculator, such as wind correction angle. Other calculations are easy to read off the dial once it is set, such as: “At 123 knots, how far can I go in 1 hour, 45 minutes, or how long will it take me to go 45 nm? 70 nm?” The E6-B allows you to do those directly, and it never runs out of battery.

Temperature conversion Fahrenheit to Celsius, and Celsius to Fahrenheit The E6-B has a Fahrenheit to Celsius and back conversion scale on the lower part of the slider on the numeric calculation side. Example: What is -20°C in °F? Solution: The scale is labeled °C on the top, and °F on the bottom. Find -20°C on the top, and note that it lines up with -4°F on the bottom. (Better put on a coat, -4°F is cold.) To convert from °F to °C, find the °F on the bottom. The °C number lines up directly above the °F number, so -4°F = -20°C, or 83°F =+30°C.

Airspeed Correction, and Density Altitude The E6-B has built-in scales to convert Pressure Altitude to Density Altitude, and to immediately figure True Airspeed at that Density Altitude from the Calibrated Airspeed. The E6-B includes brief instructions printed on the rotating scale to help you with this calculation. Example: What is the TAS and Density Altitude if the Pressure Altitude is 5,000 feet, the air temperature is -40°C, and my CAS is 140 kts? Solution: Using the instructions on the E6-B, we set 5,000 feet Pressure Altitude opposite -40°C in the window just above the instructions. Then opposite 140 kts CAS on the outer scale, we read TAS of 138 kts on the inner scale. Finally, we read -1,000 feet Density Altitude at the center arrow in the Density Altitude window.

Note that the E6-B built-in reminders. The inner scale has a little CAS printed on the inner scale and a TAS on the outer scale.

Speed, Time, and Distance calculations The E6-B has handy features for speed, time, and distance calculations. On the numeric calculation side, use the outer ring for distance and speed. The inner, rotatable ring is for time. Instructions are on the E6-B, and also reminders that the outer ring is for distance, and the inner ring is for time. Note the scales go from 10 to 99, so you need to multiply or divide your number by 10 until it fits in that range. This will become more clear in the example. Example: Time and Distance known -- finding speed: From my pre-flight planning, I identify two waypoints 18 miles apart. As I fly over them, I find it takes 8 minutes to cover those 18 nm. What is my ground speed? Solution: We use 80 to represent the 8 nm, since 8 is outside the range of 10-99 that is directly on the scales. First, rotate the inner scale until 18 (distance) is above 80 on the inner (time) scale. Next, look above the 60/RATE arrow mark and read 13.5. This must be 135 knots because you know you are flying a little faster than 2 nm per minute, so you expect a number a little faster than 120 knots.

Example: Speed and Distance known, calculating time: Continuing on the same flight, I know I have a ground speed of 135 knots, how long will it take me to fly the next 192 miles to my destination in Minot, ND? It is important for me to know so that I can figure out how much fuel I will need, and whether I will arrive in time for matinee pricing at the Minot Bijou. Time Solution: Leaving the 60/RATE aligned with 135 (13.5), I look under 192 (shown as 19.2) on the outer scale and see it lines up with both 85 and 1:25 on the inner scale. I project 1 hour, 25 minutes remaining to arrive at Minot. Plenty of time for matinee pricing, so I can afford the jumbo popcorn.

Example: Distance Solution: How far will I travel in the next 45 minutes, still going 135 kts? With 60/RATE still aligned with 135 on the fixed outer scale, find 45 on the inner scale and see that the 45 minutes on the inner scale aligns with 102 miles on the fixed outer scale. Solution: 102 miles.

Example: Fuel consumption. From the POH, I know that at my current power setting, the plane consumes 11.4 gph (gallons per hour) of fuel. Knowing that I have 1:25 remaining to Minot, how much fuel will I need? Solution: Use the instructions on the E6-B. Rotate the 60/RATE arrow under the consumption rate of 11.4 gph, look above the 1:25 on the inner scale and read the answer: 16.1 gallons on the fixed outer scale.

Other calculations Adjusting chart scales in the Computer Testing Supplement. The FAA prints standard sectional charts at 8nm per inch, matching your plotter’s “Nautical Sectional” scale, so you can read the distance directly on the plotter. Some charts in the FAA Computer Testing Supplement are printed in a different scale. Before using one of those figures for finding distance, you need to always check the scale (found on one of the edges of the chart) with your plotter. If the scale is different than the FAA sectional charts, you must adjust to accurately measure nm. This adjustment is easy with the E6-B, or you can use your 4-function calculator. Example: On Figure 71, what is the distance from Gnoss (DVO) by (#4), to San Jose Intl (SJC), (#2)? Solution E6-B: Using the plotter, Nautical, Sectional scale, 30 nm on the chart legend scale on the top of Figure 71 measures 26 nm on the plotter. Since the plotter shows 26 nm for 30 nm on the chart, we know that Figure 71 was printed in a scale that is different than a regular FAA paper sectional chart. We will say that Figure 71 has 26 plotter nm for 30 actual nm, and will adjust for this scale difference shortly.

Next, on Figure 71, measure the distance between DVO & SJC, measure 48 “plotter nm.”

Adjusting plotter nm to actual nm. Since 26 plotter nm equals 30 actual nm for Figure 71 on the E6-B, align 26 plotter nm on the inner scale with 30 chart nm on the outer scale. You will now be able to look up any plotter nm on the inner scale and see the actual nm directly opposite on the outer scale.

With 26 plotter nm on the inner scale of the E6-B aligned with 30 actual nm on the outer scale, find 48 plotter nm on the inner scale and read 55.5 chart nm on the outer scale, round up to 56 actual nm. So 56 nm is the actual distance from DVO to SJC.

Wind Correction Angle and Ground Speed Calculations

The E6-B has helpful directions and formulas on the wind calculation side to assist with the Wind Correction Angle (WCA) and Ground Speed (GS) calculation.

Wind Correction Angle and Ground Speed Example: Your cousin, Biff Loman, lives in Findlay, OH and is so fond of the expression, “Holy Toledo,” that you offer to take him to Toledo for the day. You expect: winds 20 knots at 305, and a TAS of 115 knots. Magnetic Deviation in your airplane is 0. Use Figure 60 for more information. What is your Compass Heading and estimated time en-route? We will follow the instructions and formulas on the E6-B.

Next, we need the True Course. On Figure 60, we use our plotter to measure the True Course from Findlay (FDY) to Toledo Suburban (DUH) as 003°.

Step 3: Rotate the scale to put True Course, 003° under the True Index. Step 4: move the slide to put the Wind Velocity pencil dot on the 115 knot TAS line. Step 5: read the Ground Speed of 103 kts under the center. Step 6: Read the WCA between the center line and the Wind Velocity mark as 9° Left.

So you know you will need to fly with a Wind Correction Angle of 9°Left, and expect a Ground Speed of 103 knots.

We now know a lot about our trip, GS = 103 kts, TC = 003°, Dev = 0°. From Figure 60, we find the Magnetic Variation line as 7 deg W for our route. Let’s calculate the Compass Heading, CH, to see where to steer the plane from Findlay to Toledo. Stepping through the formulas on the wind side of the E6-B, we will calculate Magnetic Course, Magnetic Heading and Compass Heading: MC = TC+W var (we don’t even need to use the memory tool of West is Best for variation because the E6-B reminds us in the formula). Magnetic Course: MC = 003° + 7° = 010° MC Magnetic Heading: MH = MC - Left WCA; 010° - 9° = 001° MH Compass Heading: CH = MH +/- Dev; 001° + 0 = 001° CH Wrapping it all up -- En-route time from Findlay (FDH) to Toledo Suburban (DUH). As soon as we know the actual distance, we can calculate en-route time for 103 kts Ground Speed on the E6-B. Using the plotter, we find the Figure 60’s distance scale is 42 plotter nm for 50 actual nm. We then set 42 plotter nm on the E6-B inner scale opposite 50 nm on the outer scale. Next, we measure 36 plotter nm between FDH and DUH. Looking opposite 36 plotter nm on the inner scale, we find the actual distance is 43 nm. On the E6-B, we set the 60/RATE arrow to our Ground Speed of 103, and find 43 nm on the outer scale, we see 25 minutes en-route time on the inner scale. So: steer initially at 001 degrees CH. When you tell your cousin Biff that you expect an en-route time of 25 minutes, he will probably say, “Holy Toledo, only 25 minutes!”

Optional: Straight Multiplication and Division on the E6-B (This is not needed for Private Pilot, but nifty to know how). Generations of cool engineers fondly used straight and circular slide rules for multiplication and division. The E6-B’s two main numeric scales are actually a version of a circular slide rule. So the E6-B is easy to use for multiplication and division: you can do it one-handed and without any batteries. Doing so will impress your friends, thrill your boss, and help you be as cool as those engineers. Multiplication: For A*B=C, find A on the outer scale, put 10 on the inner scale directly under A, then find B on the inner scale, the product C will be directly above the multiplier B. Use approximate calculations in your head to get the right order of magnitude. Division: For C/B=A, Find the dividend C on the outer scale, put the divisor B on the inner scale directly under C, then read the quotient A on the outer scale directly above 10 on the inner scale. Multiplication Example: You are planning to bring in guacamole and chips for the private pilot class to enjoy. From experience in these matters, you estimate that each person will eat 2.4 oz of guacamole. How much guacamole should you plan for a group of 9? (2.4 x 9 =?)

Solution: Align the 10 on the inner scale with 24 on the outer scale, look above 90 on the inner scale and see that you should plan on 21.6 oz of guacamole for the class. Note that calculating the amount of chips is an exercise left for the student.

Division Example: Miles per gallon. I drove my car 315 miles and found it used 8.3 gallons of gas. How many miles per gallon did the car get? (What is 315 / 8.3 = ?) Solution: Find 315 (dividend) on the outer scale, line up 8.3 (divisor) on the inner scale under the 315. Above the 10 on the inner scale, see that the car got 38 mpg (quotient).