Whiz wheel savvy

The E-6B solves many problems, sometimes all at once. If your groundspeed is 130 knots (top left), how long will it take to fly 150 nm? Answer: 69 minutes. At the same time, look at the "naut" and "stat" arrows on the A scale; 31 nm is 35 sm. What's your true airspeed at 10 degrees Celsius and 6,000 feet? At a CAS of 120 knots (middle right) on the B scale, see 133 KTAS opposite on the A scale. Going 85 knots down final and want to know how long you'll take to cover the 4 nm from FAF to MAP? Put the B scale's "36" mark opposite 85 on the A scale (bottom left), find "40" on the A scale (for 4 nm), and look opposite it on the B scale: 170 seconds, or 2:50 on the C scale.

In today's world, where electronics rule our daily lives, the lowly E-6B flight computer can seem like a quaint anachronism. Maybe that's why so many pilots-students and old pros alike-ignore the trusty "whiz wheel" in favor of handheld or panel-mount GPS information, computer-driven flight planning software, or electronic flight computers. Some students may never have made peace with the E-6B, even though it was introduced as part of their training program. Maybe one of them was you!

Too bad, because the E-6B has a lot going for it. It's easy to learn, requires no batteries, serves as a trusty backup when your handheld GPS or electronic computer's batteries die, can be operated with no keyboard entries, has good handheld ergonomics, and has great daylight visibility. Perhaps pilots are put off by what they perceive as a bewildering cacophony of numbers-heavy concentric rings. For simplicity's sake, let's call the outermost ring of numbers the A scale, the middle ring the B scale, and the inner ring the C scale.

Whatever the reason for any phobias, let's look at just a few of the many basic calculations that an E-6B can quickly perform-and toss in a trick you may not have known before.

Time-speed-distance

How long will it take you to fly a certain distance at a given groundspeed? If you fly a certain distance in a certain amount of time, what's your groundspeed? These questions are easily answered with the E-6B.

If you know your groundspeed, put the B scale's speed "arrow" (located at the 60 position) on your speed. Then look at the A scale to find the distance in question. Let's say your groundspeed is 130 knots and want to know how long it will take to fly 150 nautical miles. Put the speed arrow on the A scale's 130 mark, then find 150 on the A scale. These numbers will be shown as 13 and 15, respectively, because the E-6B can show changing values. That 15 nautical miles represents 150 nm in this example, but it can also represent 1.5 nm or even 1,500 nm. It all depends on the speeds and distances you're dealing with, so use common sense when working the wheel.

Opposite the A scale's 15/150 mark, you'll see 69 on the B scale, and just under 1 hour, 10 minutes on the C scale. Now you have your answer. At 130 knots, you'll cover 150 nm in 69 minutes, or 1 hour, 9 minutes.

Now let's turn this sort of problem around. Let's say you know you've flown 200 nm in 2 hours, 30 minutes. To learn your groundspeed, put 20 on the A scale opposite 2 hours, 30 minutes on the C scale (or 150 minutes on the B scale). Now look at the speed arrow for your answer: It's a very disappointing 80 knots!

True airspeed and density altitude

To determine true airspeed, use the right internal window of the wheel. Put your air temperature over the pressure altitude value. To get pressure altitude, set 29.92 inches of mercury (in Hg) in your altimeter's Kollsman window and note the altitude, and don't forget to return the value to the actual altimeter setting.

Let's say it's 10 degrees Celsius at a pressure altitude of 6,000 feet. Set those values in the window. Now look on the B scale to find your calibrated airspeed (CAS), which can be found in the limitations section of your pilot's operating handbook (POH). Let's say your CAS is 120 knots. Opposite the "12" mark (which stands for 120 knots in this case) on the B scale, see your true airspeed-133 knots-on the A scale.

Using the right window can also give you density altitude, which appears in the central window. So an airport with an elevation of 1,000 feet and a temperature of 20 degrees Celsius has a density altitude of 2,000 feet, as shown in the central window.

Many E-6Bs have instructions for finding true airspeed and density altitude, as well as true altitude, printed right on the wheel. So you don't need to worry about memorizing the steps.

Short time and distance

Students working toward their instrument rating, as well as seasoned pros, face a problem when trying to determine elapsed time from a final approach fix (FAF) to a missed approach point (MAP). That's a pretty important time, because on many nonprecision approaches it's the only way you know when to break off an approach if the runway or runway environment isn't in sight. In other words, when the time's up and you're not in a position to make a normal approach to a landing, or haven't seen the runway, it's time to climb away on a missed approach procedure.

Chart makers try to make this job simple. At the bottom of an approach plate you'll see some groundspeeds and their associated times to fly from FAF to MAP. But the trouble is that the speeds are groundspeeds, and only a few groundspeeds are published-commonly 60, 90, 120, and 150 knots. But what if your groundspeed is 85 knots? How long will it take to fly down final?

That's where you can use the E-6B's short time and distance feature. For this, use the B scale's 36 mark as a speed arrow, and place it opposite your actual groundspeed. Then look at the A scale to find the distance to be flown.

Let's say the distance from FAF to MAP is 4 nm. Find the 40 mark (which stands for 4 nm in this case) on the A scale, then opposite it on the B and C scales, respectively, you'll see that at 85 knots it will take 170 seconds (B scale) or 2 minutes, 50 seconds (C scale), respectively.

This short time and distance is best used when distances are below six or seven miles, especially when groundspeeds are under 70 to 80 knots. That's because distances longer than that can "lap" groundspeeds and give erroneous answers.

Of course, the E-6B can do much, much more. It can multiply and divide, convert from nautical to statute miles, turn fuel in gallons into fuel in pounds, and can figure out fuel consumption. After all, the E-6B is nothing more than a circular slide rule, one that's stood the test of time since the 1930s.And that's just the computer side! On the flip side, the E-6B can calculate wind correction angles, groundspeeds, and wind components. The ins and outs of this neat flying tool could be the subject of a book, and we'll explore it some more in future issues.

Thomas A. Horne is editor at large of AOPA Flight Training and AOPA Pilot magazines.