The E6B computer has been used by aviators for many years. It's not an electronic computer but a type of slide ruler, although electronic calculator versions are available, too. It's used to calculate true airspeed, density altitude, ETA, wind correction, and fuel consumption, and to convert temperatures. It originally was designed for the U.S. military but is now available from pilot shops and other aviation retailers. The aluminum slide-ruler version is under $35, the cardboard and plastic versions are under $20, and the electronic calculator versions are under $100. Regardless which type you buy, they’re all referred to as E6B "computers" because they help you compute.
Density altitude is the altitude your plane thinks it's flying at, also known as performance altitude. It is the pressure altitude (set your altimeter to 29.92 to read your pressure altitude) adjusted for nonstandard conditions, such as a hot day. Your plane could be flying at 5,000 ft. MSL (mean sea level), for example, but perform like it's really at 7,000 ft. because of warmer, thinner air. Density altitude is important to know because it can mean you need more runway length on a low-density day than on a standard day. Your flight computer can help you calculate density altitude and the operating handbook will tell you how much runway the plane needs to take off and land.
Rather than bore you with instructions on how to use your E6B computer during a cross-country trip, decide which type you want (slide-rule type or electronic calculator type), buy it and read the instructions. It can easily help you solve many flight problems.
Though the aluminum slide-ruler model has been the mainstay of aviation for more than half a century, the electronic calculator version is becoming increasingly popular. In fact, you can use an electronic E6B during your FAA knowledge test if you wish (with some restrictions). It has an advantage over the slide-rule version because it steps you through numerous problems, prompting you for the information you need. You can use it to calculate solutions to navigational, weight and balance, fuel, and conversion problems. The mo
st popular model includes 19 aviation functions and 14 conversions at under $100.
What kinds of calculations will you need to solve for your cross-country flight?
- Calculating the effects of wind and magnetic variation on your flight path
- Calculating estimated time en route in hours and minutes
- Calculating fuel consumption in gallons or time
- Calculating your estimated time of arrival
- Calculating the weight of fuel onboard
- Converting minutes into hours, temperatures from Celsius to Fahrenheit, and knots to mph
Remember that the course is the intended path of your aircraft to reach a specific destination, the heading is the direction in which you must point the aircraft nose, and the track is the plane's actual path over ground. The difference between the course and the heading is the wind-correction angle. This is also called the crab angle. The difference between the heading and the track is called the drift angle.
The formulas you need for your FAA knowledge test (and future flying) are:
TH = TC [±] WCA
MH = TH [±] VAR
CH = MH [±] DEV
Where TH = true heading, TC = true course, WCA = wind correction angle, MH = magnetic heading, VAR = magnetic variation, CH = course heading, and DEV = deviation (compass error). Your E6B computer will help you solve these problems.
The ground-school or knowledge-test preparation course you select will help you develop memory aids that can step you through various problems you will face as you plan your cross-country trip.
Another useful tool you'll need in planning your trip is a plotter. It's simply a ruler marked out in statute and nautical miles plus a protractor or half circle with degrees. You use it to mark a straight path on a sectional or WAC (world aeronautical chart), and then determine your course. You can buy a basic plotter for less than $20 for the fancier models, or half that for the simple ones. Better ones have rotating protractors and scales for both sectional and WACs.