Dead Reckoning and Pilotage

Dead Reckoning and Pilotage

by Kyle Ramsey

Purpose 
To explain the two most basic VFR navigation techniques and demonstrate their use in VATSIM.

Objective
While not used extensively in the FS world, all new pilots begin learning how to navigate using Ded Reckoning and Pilotage. This lesson will give the student a brief explanation of these two techniques, show some examples, and provide further references.

Prerequisites
To solve Ded Reckoning problems you will need a plotter that measures distance and courses on aviation maps. You will also need an analog computer (no batteries required) called an E6B. These can be purchased at pilot shops or the internet. Below you will find web pages that also do the calculations the E6B is capable of making. These instruments do require practice to become accurate.

Procedure or Discussion


Pilotage
The most basic of all VFR navigation is Pilotage. Pilotage means look out the cockpit window and see with your eyes where you are. VFR maps are marked with lots of symbols that help find things on the ground and matching them with the map. In FS the terrain and ground objects are not exactly just like real life, even with some of the photo-real scenery. But they are getting closer. You can still fly Pilotage flights by following major landmarks such as rivers, canyons, shorelines, and roads (IFR = I Fly by Roadways).

Pilotage is free flight in its most pure, going where the landscape takes you to see what wonders lie ahead. This does not relieve the pilot from knowing how much gas to take on board and monitoring it while up boring holes in the sky. You are welcome to fly Pilotage flights in VATSIM. In the route section of the flight plan put a statement that lets the controllers know what you're up to like "Hong Kong Harbor Patrol", or "South down the Rhine River".

Ded Reckoning
Ded Reckoning, from Deductive Reckoning (or Dead, from "exactly on", see link #2 below and you decide), is using some simple tools and math to figure out a few valuable parameters on our flight. Navigators using Ded Reckoning take factors about the aircraft; altitude, airspeed, heading, fuel burn rate, compass deviation, and combine them with factors related to the environment; wind speed and direction, air temperature, magnetic variation. From these computations the pilot is able to calculate how long it will take to reach each waypoint flying a course corrected for the predicted winds aloft and the local magnetic deviation. 

In real airplanes the compass deviations are also factored in; these are errors in the wet compass due to magnetic interference of the aircraft and avionics installed and is found on a small card near the mag compass. However FS mag compasses have no such errors so this is omitted.

Once in the air the pilot flies solely using his compass and a watch for timing. Using gyro instruments built by mechanical genius and founder of the Mile High Club Lawrence "Gyro" Sperry, pilot Jimmy Doolittle used ded reckoning under a hood to fly several thousand miles in 1922 from Pablo Beach, Florida, to San Diego, California in a DeHavilland DH-4 to demonstrate the new technology and capability.

Let's do an example. We're flying a Cessna 421 Golden Eagle: 
- On a straight-line leg of 73 NM between two points with a course of 215 degrees as measured using a map and plotter. 
- The local magnetic deviation is 11 East (or -11) that is shown on maps or airport facility directories. 
- Our 421 will fly at 12000 ft with a true airspeed of 165 knots that we looked up in the Aircraft manual performance tables. 
- In air that has wind from 350 at 25 knots and a temp of +7 C which we found in the winds aloft table on the weather web site.
- And burn 44 gph of fuel.

Our first calculation is to convert the Course into a True Course by figuring out how much we'll need to correct for the wind so it does'?t push us off course, called the Wind Correction Angle; we'll use the E6B for this:

TC = Course + WCA
TC = 215 + 6
TC = 221 degrees

Next we calculate into a True Heading by adjusting for the magnetic variation where you add if it is West deviation and subtract if it is East deviation (East is Least):

TH = TC + VAR
TH = 221 + (-11)
TH = 210 degrees

We will set 210 degrees into our cockpit compass to fly this leg. So how long will it take us?

We next calculate the Ground Speed, which is true airspeed corrected for wind and done on the E6B which for this example yields a GS of 182 knots. Using this to calculate the time to fly the 72 NM yields a time between the points of 23 min 44 sec.

Using this time and the fuel burn we looked up in the aircraft's book we find we'll burn just less than 18 gal on this leg [(23.75/60)*182].

This is all the information you need for this leg. If there are other legs you simply do the same calculations as above for each leg.


Extensions 
1. Fly a small light aircraft or helicopter from Luxor, Egypt (HELX) to Cairo, Egypt (HECA) following the Nile River. Find an atlas with this river and follow your progress up the river on the map.
2. You are flying a Beech King Air 200 at 18000 ft and a True Airspeed of 225 knots between the INN and BZO NDBs, distance is 46 NM and course is 184 degrees. Mag Var is Zero, winds aloft are 260 at 35 knots. This Beech burns 115 GPH. Calculate the compass heading you will use to fly between these stations, the ground speed, the elapsed time, and the fuel required for this leg of your flight.

References 
1. http://www.navfltsm.addr.com/basic-nav-general.htm
2. http://www.straightdope.com/mailbag/mdeadreckoning.html
3. http://www.lowapproach.com/e6b.html
4. http://www.flightplan.za.net/navLog.pdf
5. http://www.gazza.co.nz/distance.html
6. http://www.privatejetcharters.com/History.html