Flightgear IFR radio navigation basics
For those of you who want to start flying right away and don't have the patience to understand long articles with loads of theory, here's a run-down, straight-to-the-point guide for radio navigation/IFR flying.
IFR or Instrument Flight Rules, simply defines methods by which you can get from one place to another in the aircraft using only your instruments for reference. The reason you want to use instruments to do this and not your eyes(i.e. visual flight rules) is because it doesn't work, plain and simple. Try it with a flight longer than the ones in which you just take-off and land, and you'll get what I mean.
There are two ways to radio navigate.
1. Simply follow a radio signal until you hit the radio beacon. The aircraft's ADF Gauge helps you do that. It simply points to the direction at which the radio beacon is from the plane. Turn your plane in that direction and you'll head straight to it. You'll know when you reach. The aircraft makes a particular beeping sound near the beacon. This method has one major disadvantage. It cannot help you find and stay on a path. This is very important for an aviator for many reasons, but as a novice flight simmer, the biggest disadvantage you'll face is the difficulty in aligning with the runway when you land. Again I urge you to try this out to figure out what I mean. Trying and practice is everything when it comes to flying.
2. To overcome the above disadvantage, an interesting kind of radio beacon was installed. It could tell you if you are heading in a particular direction from the point where the radio beacon is located. The VOR gauge helps you deal with this kind of a radio beacon. It simply tells you whether you need to turn left to get to the path, or turn right. And it stays on the dead center when you're on the path.
Lets look at these navigation methods in more detail
ADF based navigation
Here's an ADF gauge. The yellow arrow points to the direction of the beacon. In this case, we're heading straight towards the beacon. If the arrow is in another direction, just turn your airplane till the needle points straight up. Remember to align yourself well before the beacon. If you try to do this when you're too close to the beacon, you'll be flying around like a dog trying to catch its tail!
One more thing, if that needle stays horizontal regardless of your turning, then you're too far away from the beacon. Head in the general direction of the beacon till the ADF indicator springs to life.
How do you know which beacon you are following? Details coming up below!
VOR Based Navigation
This is a VOR gauge. The slanted indicator on the right is telling you to turn the aircraft right to get on to the flight path. Remember that this is a path. Your aircraft will keep turning a little due to air currents, so you'll have to adjust the heading now and then to stay on the path. Don't get panicky about this. Just note the deviation for some time and then compensate. You don't want your passengers throwing up in your cabin do you? ;). Same deal with VORs about distance…align much earlier.
Sometimes it can get a little frustrating when you try to lock on to a flightpath.This is because once you hit the spot the gauge turns to the other direction. You then turn and its already too late, so you turn beyond the heading to compensate, and the process repeats. To avoid this cat and mouse game, as a general rule, when you are close to the path, or after it has crossed and you are turning, turn 30 degrees more/less along the heading you are turning towards, and stay on this heading till your gauge is almost at the center, then turn 30 degrees back to align with the path.
Setting the gauges
Ok, so how do we set the beacons which we want to track? That's simple…look at the Atlas in flightgear. The ADF gauge beacons are called NDBs and they are violet circle made up of a lots of dots. A rectangle near the beacon gives you the name of the beacon and the radio frequency of the beacon. Go to Equipment -> Radio Settings in Flightgear and set the ADF frequency to this frequency.
VORs are easier to spot. You'll see a huge circle with direction markings all around the VOR. This is because with the VOR you not only have to set the frequency, you also need to set the direction in which you want to fly into or out of the VOR. The direction is called OBS. The rectangle near the center of the VOR will give you the frequency of the VOR. VOR settings can be made in Equipment -> Radio Settings -> NAV1 or NAV2. Planes that have gauges for NAV1 and NAV2 can track two VORs.
Check the image to see if you can spot the VOR and NDB beacons.
Once you get the hang of this, try out this practice flight just to get acquainted with radio navigation. All practice flights require the use of both VORs and NDBs so be prepared to keep your eyes on both the indicators!
A few final words...
Radio navigation is a complex topic, but I've tried my best to explain the concepts with simple terminology. Unfortunately, since I've already been simming for over a month, and know a lot about flying, I'm not sure if this article is helpful for people learning to fly with Flightgear. If you feel that you don't understand something, please write me a comment and I'll do my best to explain things to you. I may even write another article to help you out! Suggestions and constructive criticisms are also very welcome!
If this article helped you make your first flight successful, do let me know…I'd love to hear about your experience and how it felt.
Take care…and happy flying!