The purpose of this document is to illustrate some of the ways with which you can navigate between airfields using ground-based Non-Directional radio Beacons (NDB) and airborne Automatic Direction Finder (ADF) equipment, in conjunction with the magnetic compass and Directional Gyro (DG), within the Combat Flight Simulator environment. In the illustrations that follow, be advised that the instruments will always be coupled in the following order: DG and ADF.
To begin, fire up CFS, select “free flight”, and choose an airplane. Select Duxford from the airfield menu. Next, enter the scenario.
Once inside your cockpit, look off the left wing. Unless blocked by the particular type of airplane you selected, you will see the Duxford NDB tower in the distance. Next, ascertain that your airplane is ADF equipped; usually, hitting the SHIFT+2 keys will bring up your NavCom stack. If your plane is ADF equipped, it will usually have one of two kinds of ADF Indicators on the instrument panel: A Fixed Card ADF, or a Rotating Card ADF. They are essentially the same, except the Rotating version allows the pilot to rotate the compass card around the circumference of the instrument. If you have a Rotating ADF, be sure the compass card is rotated so that 000 is at the top of the instrument, and then leave it alone. (If you are not experienced with using ADF’s, you will find that the Fixed Card ADF is easier to use; since you will essentially be using the ADF to figure out angles, you avoid excessive mathematical computations.) Next, adjust the time of day to “Dusk”. Ideally, you should fly this scenario at night; however, for instructional purposes, it may be beneficial for you to be able to see the airfields so you can relate the infor-mation you visually acquire outside the airplane with the information you acquire from the ADF inside the airplane. However, this document will address the scenario as though the only outside visual references you may have are celestial, for the purpose of getting you used to using the ADF.
Start your engine(s). While waiting for the oil pressure to come up into the green arc, set up the ADF. Since you are going to be flying to Martlesham (MTL), dial in the MTL frequency of 252, then hit the IDENT button. After a brief pause, you will begin to hear MTL’s Morse Code identifier (-- - .-..) over the speaker. Leave the ident on. Remember, it is the only way you can be sure that the station is broadcasting reliable navigational signals. Next, look at the ADF needle; it should be pointing towards the MTL NDB.
Takeoff normally, and initiate a climbing right turn towards the head of the ADF needle. Upon rollout to wings-level, the head of the needle should be pointing straight off the nose and you should be flying a magnetic heading of roughly 095. This heading may differ slightly from the heading you see when you actually fly the scenario, as it depends upon when you initiate your own turn-on-course, but it should not be drastically different if you takeoff normally. Level off at 2,000 feet. Congratulations! You are now homing to the MTL NDB.
As you fly towards MTL, you may notice that you are slightly off course (must’ve strayed while rubbernecking for bandits) by seeing the head of the ADF needle slightly off straight-up 000. Simply turn towards the needle and get back on course; if you are vigilant, you will only be a degree or two off anyway, so very shallow banks are in order here to avoid over-correcting. As you near MTL, back on course with the ADF needle off the nose, you will notice the needle begin to swing. Since you know that the needle always points to the station, and you are aware that you are very close to the station, logic dictates that you must be close to flying past the MTL NDB. Don’t chase the needle! Let it fall. Once the ADF needle swings from the nose to the tail (from straight up to straight down), you have a positive indication that you have reached Station Passage. (See below.)
Since you are now past the MTL NDB and flying away from it, and knowing that the needle always points to the station, you must now endeavor to keep the needle off the tail of the plane (straight down on the ADF), since the station is at a 180 degree angle from the nose of the airplane. Once you are on course, note your magnetic heading and fly that heading outbound for two minutes. After the second minute elapses, make a 45 degree left turn and fly that heading for one minute. (See below.)
(You are flying outbound on a heading of 095. You need to make a 45 degree left turn. Subtract 045 from 095 and you can see that you will need to turn to a heading of 050. You will now see the head of the ADF needle approximately 45 degrees off the tail after you rollout to wings-level. However, since you will travel away from the 095 bearing during your turn, you will not see a 45 degree angle [in this case from 180 to 225] from the tail of the plane, nor are you looking for one.
The approximate angle is being included to help you increase your situational awareness and to illustrate how the ADF needle reacts when you turn the airplane in a prescribed manner.)
Fly 050 for one minute. During this minute, mathematically calculate the reciprocal of 050, which is 230 (add 050 to180) . At the expiration of one minute, make a right turn to your calc-ulated heading. You are now flying a leg that will lead you to intercept your desired bearing back to the MTL NDB. (See below.)
Since you flew outbound from the MTL NDB on 095, it should be simple to deduce the desired reciprocal inbound, 275 (add 095 to 180). Note that you are currently flying 230, which will give you a 45 degree intercept angle for the 275 bearing back to the MTL NDB. (Subtract 230 from 275). Knowing this, you are now simply looking for a 45 degree angle on the ADF Indicator. As you approach the 275 bearing, you will see the ADF needle slowly begin to swing toward 045. As long as you stay on your magnetic heading of 230, once that ADF needle hits 045 on the ADF, you are on the 275 bearing. Turn right. Upon rollout to wings-level, you should be flying level at 2,000 feet, with a magnetic heading of 275, and the ADF needle pointing back off the nose. (See below.)
Since you are relatively close to the station, within a few minutes you will again pass over the MTL NDB, and the needle will once again swing 180 degrees, falling from straight up to straight down. With the ADF pointing at the tail, navigate away from MTL.
Once established outbound, go ahead and bring up your NavCom stack (SHIFT+2). On the ADF, tune in the Duxford (DUX) frequency of 227. Since the IDENT should already be on (you did leave it on to ensure you were receiving reliable signals for navigation, didn’t you?), you will begin to hear the Morse Code identifier for Duxford (-.. ..- -..-) over the speaker. Once you are certain that the signal is correct and indeed reliable for navigation, look at the ADF Indicator; the needle will have swung from straight down to nearly straight up. Expect that it will not be perfectly off the nose! Remember, you are flying the reciprocal of the bearing that brought you to MTL, not the reciprocal of the bearing between the MTL and DUX NDB towers. The bearing you used was initially intercepted shortly after takeoff at some altitude, on some heading, some-where off the departure end of the runway at DUX. Your ADF equipment has no idea where this point is, nor does it care. It will only point to a selected station, which will not be aligned with some random point in the atmosphere somewhere near the departure airport. Consequently, you will have to adjust your course slightly to center the ADF needle back off the nose.
At this point, simply home back towards Duxford. Upon landing, congratulate yourself on your superb navigation/orientation skills, and enjoy a few “medicinal” brandies for a job well done!
(Special thanks to C&CC, AutoCAD/Photo Editors for the illustrations.)