355TH VIRTUAL FIGHTER GROUP
GROUP TRAINING OFFICE
TOPIC : FORMATION FLYING
SUBJECT : INTRODUCTION
NAVIGATION
Several of you have asked how you will navigate in B-17 II. While, like you, I have no firm information of how B-17 II will actually be set up, I am willing to bet that it will be similar to the way things were done in B-17 I only better.
B-17 II did not have a drift meter in it nor did it need it, for I do not believe that wind was a factor in the dash one program. However , we have been told that we will have a drift meter and will have winds at various flight levels in the dash 2 version.
So I am going to build this abbreviated navigation course around B-17 I, then relate it to what I believe we will have in B-17 II. As a beginning I will give you a broad overview of how you get from Point A to Point B and illlustrate with a specific example.
To deliberately use a confusion of terms, in aerial navigation the wind is the constant variable. If there were no wind, or if it were a known constant, navigation would be as simple as aiming the prow of your canoe at a tree across a still pond and touching the far shore at a point that was in line with your tree and starting point.
But now let's cross a river with a current instead of that still pond... Instead of just aiming our nose at that tree we must point it upstream, against the current, enough to cancel out the amount the current will sweep us downstream in the time it takes us to cross the river.
Now, instead of a river lets move out into the ocean where we have tides, and currents that vary in strength and direction, this is more analogous to the varying forces the wind will exert on our plane, but over the centuries, these tides and currents have been charted, thus are predictable.
Now we get in an airplane and find that our wind is only vaguely predictable and is a constantly changing factor. As Shakespeare said "Aye, there's the rub!"
This is what makes aerial navigation an art not a science, though there are some tried and true practices that are used to solve the continually changing situation.
To figure where to head in the first place, we get an aeronautical chart which incoporates the information we need about the physical earth we will be flying over on our way from here to there.
The first thing we use is the coordinate system on that chart... the lines of latitude and longitude which are, in effect a grid system which allows us to pinpoint exactly where something is on our globe, and which locate all such points in relation to each other.
First
you find point A on your Chart. This is your starting point.... Now find Point
B, your destination.. Draw a straight line between them. This is what is known
as the "True Course" (TC) from the one to the other.
Let’s say that the angular measurement between the meridian line and the True course line is 120 degrees. In other words, 120 degrees is our true course from point A to point B.
But what we actually need is a Compass heading (CH) between those two points, in order to point our airplane in the proper direction (at the proper tree).
(A "course" is a direction on the earth between two points; a "heading" is how we point the nose of the plane to cancel out the effect of the wind, as it tries to blow us off of our intended course or "track".) (The True course line is our desired "track", while our "track made good" is our actual track over the ground, which might not be the desired track shown by the true course line.)
In order to find our heading, we must take into account our wind, which will tell us the amount we must offset the nose of the plane upwind to cancel out our drift.
But there are other factors we must consider... our compass has an error in it called deviation, which is caused by changed magnetic influences in the aircraft brought about by iron or steel near the magnetic compass needle or electrical currents that create other magnetic fields that affect that needle.
Deviation errors are found by checking the compass on the plane while pointing it in the cardinal directions and comparing the compass readings with known magnetic North readings. Deviations are recorded on a Deviation card posted in the plane near the compass.
Another factor we must consider in arriving at our final compass heading is "Variation".
Because the True North Pole on our earth is not located in exactly the same place as the "Magnetic North Pole" (they are about 27 nautical miles apart I believe) our compass needle points toward magnetic north, not true north . The difference between where the needle points, from where it should point to show us True north, is what is called variation.
On out chart, the average variations from true North are shown as lines of equal variation and are given in degrees east or west. (A minus or plus correction we apply to change our true course to a compass course or compass heading.)
To give us an easy way to include these factors in our calculations to convert true course to the compass heading we need to fly to get from A to B, we use what is called a "Pre flight Planning Log."
Here we have columns to enter the figures we need to change our true course to the desiredCompass Heading we need to fly to arrive at point B.
The log has spaces to enter True Course(TC); Drift Correction angle(DCA); True heading (TH); deviation(DEV); Magnetic Heading(MH); Variation(VAR) and (at last)Compass heading(CH).
You work across the log from left to right systematically , when working from "True Course" to "Compass Heading".
(TC)(+or- Drift Correction)=(TH)(+/- Dev)= (MH)(+/- VAR)=(CH)
You remember that we have measured and found our TC to be 120 degrees.
We take our reported wind from the weather office, and using an aeronautical computer ( one type is called an "E6B" ) we use a graphic solution that incorporates our planned True Air Speed and the "angle off" of the wind as well as its direction and velocity, to find our drift correction angle (DCA) and calculated ground speed. (GS)
Let’s say that our wind is from the north which puts it on our left, and quartering on our tail if we are pointed at 120 degrees.
This means that we will have to turn left (decrease our heading) into the wind, an amount sufficient to cancel out our drift to the right, otherwise we would end up south of our destination.
Let us say that I discover that my drift correction angle is minus two degrees. Then my TH is(120-2=118 degrees.)
But I find that my compass error(Deviation) at about 120 degrees is a plus 1. Applying that deviation I now have a Magnetic heading (MH) of (118 + 1 = 119 degrees).
Looking at my chart I find that my variation is this area is minus 6. Applying that I now have (119 degrees minus 6 = 113 degrees) which is the heading I will want to put on my compass to get to B.
BUT ( and that "but" is as big as that on an elephant )we figured that compass heading on a basis of the Metro wind, which was an educated guess on the part of a meteorologist. ( who also practices an arcane art not a science, regardless of what he avers.)
The wind, even if correct, is only for the flight level we used to find it, and does not take into account the winds that we were subjected to as we climbed up through them to our cruising altitude. So it is very likely that we have already drifted off of our desired track(the TC line) even if we held a perfect heading on the compass as we climbed out. (something very few of us, if any actually do)
So, as we fly along we must periodically check our Dead Reckoning (DR)Pre flight calculations(For DR is what our calculations are called.) to see where we actually are.
This is called "fixing our position" or " a fix" for short. Fixes of our actual position can be made by actually looking down at the ground and identifying a cultural or terrain feature which is also on our chart, (This is called Pilotage) Fixes are also obtained by various other means, such as radio bearings, radar, celestial observations, or (the latest) by ground positioning via satellite.
Regardless of how obtained, the fix is used to correct our dead reckoning(DR) calculations.
As we have flown along we have noted and recorded our average compass heading, True air speed , and altitude. So when we find our actual position we use those figures to calculate by dead reckoning where we should actually be for the time of the fix. (by working backwards on our INFLIGHT log, from right to left, and reversing all the signs.)
We can then can plot that DR position on our chart, compare it to our actual position and then, calculate our approximate in-flight wind.
Now we use this wind to calculate our correction from our actual position, to head to point B, just as we did when we were doing our Pre flight calculations. Only this time we start from our actual position at the time of the fix;drawing the true course from there to B. By calculating (dead reckoning from that fix), using our new wind) we can find the new heading and the new ground speed, thus figure the time when we will arrive at B (Estimated time of Arrival).
(Estimated because it is an art not a science) And that is what makes navigation fun!. When you arrive exactly over your destination exactly at the time you said you would, it gives you a real sense of satisfaction!.
Navigation techniques based on dead reckoning work the same anywhere in the world. The key is using the best information you have available for your DR calculations and using your navigational judgement to decide how much weight to give to the many approximations. That’s where the navigational judgement or "art" comes in.
A good navigator will sometimes just come up with a "hunch" when he gives a heading correction . This is called "using a hair ball" because in essence, for want of any other information the navigator plucks a hair from his fast thinning scalp; rolls the hair into a ball between his palms, then opens his palms to see which way the hair unrolls.
Hunch headings are a means of buying the navigator time to figure out just where he actually is, and where he should really go from there. (It keeps the pilot and crew quiet and off his back while he thinks.)
Hope this isn't confusing you!
But if it is, not to worry, Navigators are always in a state of at least partial confusion. If you have gotten lost during this dissertation don’t let it worry you.
Navigators get lost frequently! But the test of a good navigator is if he can find himself again before the rest of the crew finds out! So Join the club! But when you get lost, you can get lost scientifically and systematically from now on!
There is much, much more in the way of "How" you do this stuff, in addition to my summary of what you do...I have only "hit the high spots ".
In my next posting I will begin to show how this general knowledge is used to navigate in B17-1 and then apply it to B17-2.
QUESTIONS ANSWERED
Q : To begin with, your earlier postings on this topic led me to a search of where I could get my hands on an E6B, and with a little searching I turned up a few aviation supply houses on the Web that offer them. (Just go to a meta-search site and type in the words and you'll find some). There is a student version of the E6B that sells for somewhat under $10, but I think I'll head out to the local general aviation airport and see what they have available in the "pilot's shop" (the glass case behind the counter), all in my effort to support local industry.
A : The student version is good enough. if you end up wanting to do more navigation, you can always buy a better one. Also buy a Weems Plotter, which is kinda like a transparent plastic protractor with a 10 inch long straight edge on the bottom. You will use it to draw lines and measure courses and bearings on your charts. You will also find a cheap draftsman's divider is handy for measuring distances on paper charts.( a 5 buck divider is plenty good enough. Eventually, if you really get into this you will buy some european charts unless Wayward includes them in the B17-2 box.
Q : The calculations we need to make in order to draw (or plot) a straight line on a map are clear, but apparently these are adjusted by using DR (dead reckoning) to get a fix.
A : Not quite the way it is done. We draw the straight line(true course) between our departure and the next waypoint or destination, then do our dead reckoning calculations on out Pre flight log to see what compass heading we must fly to make our Track over the ground match our true course line.Then, in flight we obtain a fix and using that position, calculate by dead reckoning where our In-flight average instrument readings should have taken us. Then we compare our DR position to our fix position and the difference between them will enable us to use our E6b to figure the actual in flight wind that has been affecting us. We then use this wind to correct our new true course to destination from our fix, using dead reckoning procedures to calculate it.
Whew! Are we there yet???
Q : This requires a fairly clear sky. If we don't have a clear sky, then what other resources would we have had in 1943 - 1945 to assist us. Radio beacons, for example?
A : If you mean that we cannot see the ground and obtain a fix, there is a procedure called a double drift that can be taken when we can see the ground but not identify any features on it. The Double drift (DD) procedure enables us to obtain a wind. without having a fix. We may also have radio bearings available in B17-2 I do not know for sure.
Q : I'm not a pilot, so I was wondering what the "Preflight Planning Log" was/is you mentioned, and how long did it take the navigator to come up with the data?. My guess is that this was both a plan and a record of the calculations he was required to make. Did this have to be ready prior to take off?
A : You are right and he did make this preflight plan prior to take-off.How long it took him to do it depended on how many "legs" or waypoints were in the flight plan. He used a similar In-flight log to keep track of what actually happened in the air... average instrument readings etc.
Q : What other factors, other than wind and compass readings, did the navigator have to take into consideration?
A : Average instrument readings ( Airspeed, Altitude, Free air temperature Compass headings, time of observations, etc.
Q : For example, did some types of aircraft (or pilots) tend to pull one way or the other?
A : Yes...
Q : Did loaded weight have a bearing on this?
A : No, but loaded pilots did!
vMaj. Joe “AC” Worsley
Group Training Officer
355th Virtual Fighter Group