Introduction: How to Calculate Time and Fuel to a Location Using an E6B
One of the first things that a pilot learns to do is to use an E6B, which is an invaluable tool in quickly calculating your time and fuel to a location. This is important on the ground to make sure we will arrive on time and with enough fuel, but is even more critical in the air should a situation arise in which you need to change your destination. In this Instructable we will learn how to use both sides of the E6B to find these numbers quickly. Note that the numbers used in the sample problems such as airspeed that are given. This is due to the scope of this Intructable only focusing on the use of an E6B.
Things you'll need:
An E6B Flight Computer
A Pencil or Dry Erase Marker
A Piece of Paper to record your results
Time to Complete:
Step 1: Input Wind Direction and Value
There are two sides of an E6B. The side you will need to start on is the side with a movable semi-clear disk. The first step is to rotate the movable disk to the direction the wind is coming from. In the example we will be using for this Instructable, the wind is coming from 150 at a velocity of 10 knots. Headings are based on a typical magnetic compass configuration with headings given in numbers. With the winds set to 150, you then need to move the center circle of the movable disk to 100 knots on the scale behind the plastic. This is simply for ease of use for adding wind velocity, as 100 is a good place to start at. After setting this, make a mark at the 110 knots mark using your pencil or marker. This is because there is 10 knots of wind coming from that direction. Move on to the next step.
Step 2: Input Heading and Find Groundspeed
Now that you have a mark for the wind, rotate the movable disk to the heading to your location. In this example the heading to the destination is 270. With the heading set, move the disk up or down to align that dot over your airspeed, which in this case is 115 knots. Look at the center circle you used earlier. The speed under it is your ground speed of 120 knots, which we will need in the next step to find the time to destination.
Step 3: Input Groundspeed and Find Time
Now that you have your ground speed, you can now find the time to your destination. Flip the E6B to the opposite side. The scale we will be using is on the outside of the movable ring, which can be confusing. For airspeed, values higher than 100 are divided by 10. In the example, because you have 120 knots of ground speed, rotate the ring to move "60 Rate" arrow to 12 (120/10=12). Now, use the same outside scale to find the distance of 70 miles, but do not rotate the ring. The number opposite 70 on the inside scale is the time it will take to reach your destination, which in this example is 35 minutes. Now that we have time, we can find the total fuel burn to the destination.
Step 4: Input GPH and Find Fuel Burn
For the final step, you will need to use a given fuel burn of 9.8 gallons per hour. Rotate the '60 Rate' arrow over to 9.8, which on this scale is actually 98. On the inner time scale, move down to 35, and across from it read the number 57. At 9.8 gallons per hour, it is illogical to think we will burn 57 gallons. This is because the scales on an E6B can be used with small and big numbers, and it takes a little bit of thinking to make sure you are getting the right number. In this case, because we know we burn 9.8 gallons per hour, we should burn less than that travelling for 35 minutes. 5.7 gallons makes much more sense, and is the correct answer. With this you have completed the final step and found time and fuel to your destination.
6 years ago
Does temperature and altitude make any significant difference to the results?
Reply 4 years ago
It most certainly does! What this unstructable misses is that the airspeed you use in step #2 is TRUE airspeed (TAS) and not the airspeed on the airspeed indicator (IAS). True airspeed is the indicated airspeed adjusted for pressure and temperature, which change with altitude and atmospheric conditions. (You have to fly faster to maintain the same IAS at higher altitudes due to the way your airspeed indicator interacts with the lower density air.)
On the dial side of the E6B is the density altitude window. Just align the outside air temperature tick mark for your current altitude (you'd need to either look at your OAT sensor/thermometer or use the Winds Aloft forecast) and align it with your pressure (MSL) altitude. Then look around the inner ring to find your Indicated Airspeed and read the True Airspeed on the outer ring.
For instance if your flying at 8000' MSL and the outside air temp is -1C (standard), with an IAS of 115Kts your True Airspeed is 130Kt TAS.
Note: I use IAS when technically you should use Calibrated Air Speed, but they're almost always with 1-2Kts of one another and CAS is buried in the AFM.
Note2: If you are in flight and want to save a step, and speed is more important than 100% accuracy you can use a rule of thumb to calculate TAS from IAS. Just add 2% per 1000ft to your IAS. In this case, 16% to 115, which is 133Kt TAS.
6 years ago
This would be really useful at my previous job. :) I drove a lot!