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Using a flightcomputer

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A flight computer can be a good thing to bring with you in the plane. Maybe you meet weather you want to fly around, or there is other reasons you need to alter your course.

Navigation plans are set when you still is on the ground, and you use the available information you have at hand to make it. It is normal to create the plan in shorter distances, which is called legs, before you reach your final destination. You also plane stops for refueling, so you never have to pass minimum fuel level with a good safety margin.

Despite this, unforeseen things can happen, so you need to alter your flight plan after started trip. What if you meet weather which gives you poor minima and you need to fly around? Do you have enough fuel to do this? Maybe you meet a large showe of rain you wish to avoid, which direction do you need to keep to correct for this wind?

It is never a good strategy to do this on the "gefûhl", even it if often is done so. If you have made a plan for how you want to fly around, and know the direction of the wind, and remaining fuel on the tank, you need to know the remaining distance on the leg, you can calculate if it is possible to get around and still be withing safetymargins.

This is why we have written this article for how to use such a flight computer. We will not cover all the ares you can use this magnificient toor, but you will learn abour some possibilities. There are electronic fligth computers which can be easier to use, but these need batterues which can be empty.

If you are in your airplane on your way, it is rarely possible to use pen and paper and a calculator to do calculations. But with a flight computer you can within a minutes, do qualified calculations if a change in the flightplan can be done. Mechanical flight computers comes in aluminimum and plastic. We like the plastic one which does not so easy break apart. 

A flightcomputer have two sides, one side which is called the wind side, and one which is called the computer side. 

 

On the computer side you can do multiplication, divisions, calculate time usage, speed, distance, fuel usage, ground speed and pressure altitude.

On the windside there is a rotating disc which is called the Azimuth disk. It is marked with a 360 degrees set of compass markes. In addition there is a movable coordinatesystem wih speed and angle marks in order to find correction angles, groundspeed, true direction and so on.

Flight computer

First in this article we will step through how to use the windside in order to calculate groundspeed and true heading. In order to calculate theis you need to know windspeed and wind direction, wanted course and measured airspeed (the speed you plan to have as cruising speed)

 

1. Align the wind direction under the "True Index" mark by rotating the azimuth plate. If the winds are from 330° at 20 knots, align 330 under the true index.

2. Align the grid so the center grommet is over one of the heavy lines. It doesn't matter which line is used at this point.;

3. Mark the wind speed by counting up from the center grommet. Each light line represents two knots. Mark a dot or an X in pencil on the 20 knot line (two heavy lines above the center grommet). This is the wind dot.

 

 

 

 

 

 

FlightComputer

4. Rotate the azimuth plate until your desired course (true course) is aligned under the True Index mark. Use 175° for this example.

5. Slide the grid until the wind dot is over your true airspeed. In this example, the true airspeed is 120 knots.

6. Read ground speed under the grommet. Ground speed is the speed of the aircraft over the ground and in this example is 138 knots.

 

 

 

 

 

 

 

FlightComputer

7. Find the wind correction angle (WCA) by checking the number of degrees to the right or left between the center grommet and the wind dot. If the wind dot is to the right, the WCA is positive. If it is to the left, the WCA is negative. In the example, the wind correction angle is +4°.

8. Add or subtract the wind correction angle from the true course to find true heading. Adding 4° to 175 equals 179° for the true heading.

9. Add (or subtract) magnetic variation and compass deviation to find the compass heading to be flown. The variation is the difference between true north and magnetic north and can be found on a VFR or IFR chart. Easterly variations are subtracted and westerly variations are added. Compass deviation is printed on a placard under the magnetic compass in the airplane

The variation changes all the time, since the magnetic north strength is not constand. (In the greater part of th the 19th century, the variation in most of southern Norway was about -20 degrees. UNderneath are some curent examples for the largest towns in Norway:

Variation Table:

Bergen -2 degrees

Stavanger -1 degrees

Kristiansand 0 degrees

Oslo +1 degrees

Trondheim +1 degrees

Tromsø +6 degrees.

TIP:

 If you know ground speed between checkpoints and the wind correction angle, the process can be followed backwards to find actual wind speed and direction while flying. 

If the wind dot is below the grommet, you have a tailwind; if it is above the grommet, you have a headwind. 

 

 

Innherred Mikrofly Klubb,  , Henning Flyplass,  Pb. 2117,  7701 Steinkjer
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