Chapter 5
Features

FlightGear contains many special features, some of which are not obvious to the new user. This section describes how to enable and make use of some of the more advanced features.

Many of the features are under constant development, so the information here may not be completely up-to-date. For the very latest information (and new features), see the FlightGear Wiki, available from http://wiki.flightgear.org/

5.1 Aircraft Carrier

FlightGear supports carrier operations on the Nimitz, (located near San Fransisco) and Eisenhower. The carriers are equipped with working catapult, arrester wires, elevators, TACAN and FLOLS and are currently available for aircraft using the YASim FDM (in particular the Seahawk, Seafire and A4F.)

To enable the carrier, you must edit your preferences.xml file in $FG_ROOT using a text editor (e.g. Notepad under Windows). Search for the word “nimitz”. You ought to find something that looks like this;

You should remove the “comment” marks so that it looks like this;

Also ensure that the line above that referring to ai being enabled is set to "true"

Save the file and quit the text editor.

5.1.1 Starting on the Carrier

You are now ready to start FlightGear. To position your aircraft on the carrier at startup, use the following command line options (noting the upper-case "N");

Note that several FG aircraft are carrier capable, but the seahawk is possibly the easiest to fly to begin with.

If you are using the Windows or OSX launcher to run FG, you should find a text entry box in the gui that allows you to specify command line options, add the above options there. Linux or Cygwin users can just add them to their usual startup command:

Please note the uppercase “N’ in “Nimitz’.

5.1.2 Launching from the Catapult

Once FlightGear has started, you should ensure that the parking brakes are off and press and hold “L” to engage the launchbar. You must hold down “L” until you have successfully launched. You should notice the aircraft being pulled into alignment with the catapult and see the strops appear and hold down the aircraft. This will only happen if your aircraft is close enough to the correct spot on the catapult; as a rough guide, for the default parking position the seahawk’s nose should be rougly level with the deck observation bubble.

To get the carrier into as good a position as possible for launch, select the “ATC/AI” menu, then check the "Turn into wind" box under the “AI Carrier” section. You should now notice the carrier begin to pick up speed and turn into the wind, and naturally the deck may tilt somewhat as it turns. You should wait for this maneuver to finish and the deck to return to level before moving on to the next stage.

Being engaged to the catapult, you should spool up the engines to full power, ensure the brakes are off and that all flight controls are in a suitable position for launch (stick held right back with the seahawk.) When ready, press “C” to release the catapult. Your aircraft will be hurled forward off the deck, and you should be able to raise the undercarriage and climb slowly away, being careful to avoid stalling.

5.1.3 Finding the Carrier - TACAN

Actually finding the carrier in a vast expanse of open water can be very difficult, especially if visibility is poor. To assist with this task, Nimitz is equipped with TACAN, which allows a suitably-equipped aircraft (Seahawk at present) to obtain a range and bearing to the carrier. First, you must set the appropriate TACAN channel, 029Y in this case, in the radios dialogue (ctrl-r or choose Equipment/Radio Settings from the FG menubar). You should, if within range, notice the DME instrument show your distance from the carrier, and the ADF instrument (next to the DME in the seahawk) should indicate a bearing to the carrier. Turn to the indicated heading and you should see the DME dial indicate your closing in on the carrier.

5.1.4 Landing on the Carrier

This is the most difficult part of the operation, as in real life. You might well find Andy Ross’ tutorial on operating the A4 Skyhawk useful here. It is available from here:

http://wiki.flightgear.org/flightgear_wiki/index.php?title=A-4F_Skyhawk_Operations_Manual

Basically you should use the TACAN to locate the carrier, and line up with the rear of the deck. As this part of the deck is at an angle to the course of the vessel, you may need to correct your alignment often. Ensure that the aircraft is in the correct configuration for approach (the Help/Aircraft Help menu should contain useful data for your aircraft) and that the gear and the arrestor hook are down.

As you approach you should see, on the left hand side of the deck, a set of brightly coloured lights - called the Fresnel Lens Optical landing System (FLOLS). This indicates your position on the landing glideslope. You will see a horizontal row of green lights, and when approximately on the glideslope, an orange light (known in some circles as the “meatball”) approximately in line with the green lights. When approaching correctly, the meatball appears in line with the green lights. If you are high it is above, and when low it is below. If you are very low the meatball turns red. If you fly to keep the meatball aligned you should catch number 3 wire.

Carrier landings are often described as “controlled crashes” and you shouldn’t waste your time attempting to flare and place the aircraft gently on the deck like you would with a conventional landing - ensuring that you catch the wires is the main thing.

Immediately your wheels touch the deck, you should open the throttles to full power, in case you have missed the wires and need to “go around” again; the wires will hold the aircraft if you have caught them, even at full power.

If you wish, you can then raise the elevators from the ATC/AI menu, taxi onto one of the elevators, lower it (uncheck the box on the menu) and taxi off into the hangar.

Don’t be discouraged if you don’t succeed at first - it’s not an easy maneouver to master. If after a little practice you find the Seahawk too easy, you could move on to the Seafire for more of a challenge!

5.2 Atlas

Atlas is a "moving map" application for FlightGear. It displays the aircraft in relation to the terrain below, along with airports, navigation aids and radio frequencies.

Further details can be found on the Atlas website:

http://atlas.sourceforge.net

5.3 Multiplayer

FlightGear supports a multiplayer environment, allowing you to share the air with other flight-simmers. For server details and to see who is online (and where they are flying), have a look at the excellent multiplayer map, available from

http://mpmap02.flightgear.org

Click on the ‘server’ tab to see a list of multiplayer servers. At time of writing there are two sets - one for official FlightGear releases, and one for the current development stream (CVS). The servers within each set are connected.

5.3.1 Quick Start

To connect to a server, note down the server name (usually mpserver0?.flightgear,org) and port number (usually 5000) for the appropriate server closest to you, and start FlightGear as follows.

Using the FlightGear Launcher

The final screen of the FlightGear Launcher has a section for Multiplayer. Simply select the checkbox, enter the hostname and port number you noted above and choose a callsign to identify yourself. Your callsign can be up to 7 characters in length. You must also check The AI models checkbox under Features to make other aircraft visible.

Using the Command Line

The basic arguments to pass to fgfs for multiplayer are these:

Where

1. <portnumber> is the port number of the server e.g. 5000.
2. <server> is the name of the multiplayer server e.g. mpserver01.flightgear.org.
3. <client> is the name of your computer, or the IP address ip address of the network interface being used by FG to connect to the server - even if that’s a local 192.168 type address. e.g. 192.168.0.1
4. <callsign> is the call sign to identify yourself, up to 7 characters, e.g. N-FGFS.

Once the simulator has loaded, you should see yourself displayed on the map. If you don’t, check the console for error messages and see the Troubleshooting section below.

5.3.2 Troubleshooting

To get multiplayer to work, we need information about the IP address of our computer and the ability to communicate with the server. How to get this information depends on your configuration and is described below.

Those using a USB modem to connect to the Internet

First of all, you need to know the IP address of the network interface you’re going to be running FG multiplayer over. If your Internet connection is via an ADSL modem that plugs directly into your computer with a USB connection, you should be able to find your IP address by visiting http://www.whatismyip.com . Please note that this address may very well change every now and again - if MP stops working, check this first.

Those using some kind of Ethernet router to connect to the Internet

Otherwise, your connection is likely via some kind of router that connects to your computer via an RJ-45, or "Ethernet" connector (similar shape to most Western telephone plugs), or by a wireless link. You need to find the IP address of that network interface.

Under linux, this can be found by logging in as root and typing "ifconfig". You may find more than one interface listed, beginning with "lo" - ignore that one. You should have something like "eth0" or "wlan0" also listed - look through this block of text for "inet addr". This will be followed directly by the number you’re looking for, e.g. "inet addr:192.168.0.150"

Under Windows XP, click start, run, and type "cmd". In the terminal window which appears, type "ipconfig" This should show you your IP address - note it down.

With Windows 98, click start, run, and type "winipcfg" to get information about your IP address.

Configuring your router

This section ought to be unnecessary now with recent versions of the FG server. If you have problems though, it won’t hurt to follow through.

Now, all(!) that remains is to configure your router to forward UDP port 5000 to the IP address you’ve just found. This is not something that can be described in step-by-step detail, because each manufacturer’s configuration interfaces differ greatly. Some tips are given here - if you get stuck, ask nicely on the FlightGear IRC channel for help (details on the flightgear website).

You should know how to log on to your router’s configuration page, usually via a web browser. You are looking for settings pertaining to "port forwarding" "virtual server" "Forwarding Rules" or similar. When you have found the relevant settings, you need to add a rule that forwards port 5000 to the IP address you discovered earlier. If there is a choice given, ensure it is UDP ports that are forwarded. If there is no choice, you may assume that both TCP and UDP are being forwarded. Save your configuration, and most routers will probably then need to be rebooted to apply the changes.

Note: (for BSD users) If you are using a ADSL modem, you might have to put the port forward command into the ppp.conf file rather than firewall. This is because the firewall script will only run each time the machine is booted rather than the ppp line coming back online.

Starting Multiplayer FlightGear

Finally, start FG using the command line given right at the start (if you’re using the windows launcher you will find entry boxes for Multiplayer arguments - insert the relevant details there). You will end up with something like this;

The current server IP address (in the "out" section) can be found by asking on the IRC channel, and likewise the relevant port number; 5000 is the default. Choose your own callsign - this is currently limited to seven characters.

Once you have started FG, you should, if others are flying, see messages in the terminal from which FG was started, similar to the following;

The MultiPlayer Map is available at http://mpmap02.flightgear.org - this should show you if anyone else is currently flying, and where.

If It Still Doesn’t Work

You MUST give your local, behind-the-router IP address for MultiPlayer to work. Trust me on this one!

You should check that your firewall is not causing problems - either turn it off temporarily or add an exception to allow incoming connections on port 5000.

If it’s still just not working for you, ask nicely on the FlightGear IRC channel and someone should be able to assist.

5.4 Multiple Displays

FlightGear allows you to connect multiple instances of the program together to display different views of the simulation though a highly flexible I/O subsystem.

For example, you may want to have the aircraft panel displayed on a screen right infront of you, while the view forward is displayed on a separate screen or using a projector. Using multiple displays can vastly improve the realism of the simulation.

Given enough hardware, you can create sophisticated simulation environments with mock-up cockpits, panels, multiple views, and even a separate control station allowing an instructor to fail instruments, change the weather etc. An example of this is the 747 cockpit project.

http://www.flightgear.org/Projects/747-JW/

5.4.1 Hardware

Each instance of FlightGear can support a single display. Due to the complexity of the FDM and graphics, FlightGear is very processor-intensive, so running multiple instances of FlightGear on a single machine is not recommended.

You will therefore need a computer for each view of the simulation you wish to display, including the panel. The computers obviously must be networked and for simplicity should be on the same subnet.

One computer is designated as the master. This computer will run the FDM and be connected to controls such as yokes, joysticks and pedals. As the machine is running the FDM, it usually only displays a simple view, typically the main panel, to maximize performance.

All other computers are designated as slaves. They are purely used for display purposes and receive FDM information from the master.

5.4.2 Basic Configuration

Creating a basic configuration for multiple displays is straightforward. The master computer needs to broadcast the FDM and control information to the slaves. This is done using the following command line options:

The slave computers need to listen for the information, and also need to have their own FDMs switched off:

5.4.3 Advanced Configuration

The options listed above will simply show the same view on both machines. You will probably also want to set the following command-line options on both master and slave computers.

If using the master computer to display a panel only, you may wish to create a full-screen panel for the aircraft you wish to fly (one is already available for the Cessna 172), and use the following options.

For slave computers displaying side-views, use the following options.

5.5 Recording and Playback

Another feature of the I/O system is the ability to record your flight for later analysis or playback. Technical details of how to record specific FDM information can be found in the $FG_ROOT/protocol/README.protocol file.

To record a flight, use the following command line options:

This will record the FDM state at 20Hz (20 times per second), using the playback protocol and write it to a file flight.out.

To play it back later, use the following command line options:

The playback.xml protocol file does not include information such as plane type, time of day, so you should use the same set of command line options as you did when recording.

5.6 Text to Speech with Festival

FlightGear supports Text To Speech (TTS) for ATC and tutorial messages through the festival TTS engine (http://www.cstr.ed.ac.uk/projects/festival/). This is available on many Linux distros, and can also be installed easily on a Cygwin Windows system. At time of writing, support on other platforms is unknown.

5.6.1 Installing the Festival system

1. Install festival from http://www.cstr.ed.ac.uk/projects/festival/
2. Check if Festival works. Festival provides a direct console interface. Only the relevant lines are shown here. Note the parentheses!

   $ festival   festival> (SayText ~FlightGear~)   festival> (quit)

3. Check if MBROLA is installed, or download it from here:

   http://tcts.fpms.ac.be/synthesis/mbrola/

   See under "Downloads"m "MBROLA binary and voices" (link at the bottom; hard to find). Choose the binary for your platform. Unfortunately, there’s no source code available. If you don’t like that, then you can skip the whole MBROLA setup. But then you can’t use the more realistic voices. See below for details of more voices. Run MBROLA and marvel at the help screen. That’s just to check if it’s in the path and executable.

   $ mbrola -h

5.6.2 Running FlightGear with Voice Support

First start the festival server:

Now, start FlightGear with voice support enabled. This is set through the /sim/sound/voices/enabled property. You can do this through the command line as follows.

Of course, you can put this option into your personal configuration file. This doesn’t mean that you then always have to use FlightGear together with Festival. You’ll just get a few error messages in the terminal window, but that’s it. You cannot enable the voice subsystem when FlightGear is running.

To test it is all working, contact the KSFO ATC using the ’ key. You should hear "your" voice first (and see the text in yellow color on top of the screen), then you should hear ATC answer with a different voice (and see it in light-green color).

ou can edit the voice parameters in the preferences.xml file, and select different screen colors and voice assignments in $FG_ROOT/Nasal/voice.nas. The messages aren’t written to the respective /sim/sound/voices/voice[*]/text properties directly, but rather to aliases /sim/sound/voices/atc,approach,ground,pilot,ai-plane.

5.6.3 Troubleshooting

On some Linux distros, festival access is restricted, and you will get message like the following.

Details on this can be found from:

http://www.cstr.ed.ac.uk/projects/festival/manual/festival_28.html#SEC130.

You can disable access restrictions from localhost and localhost.localdomain by adding the following to a .festivalrc file in $HOME:

Or, you can just disable the access list altogether:

This will allow connections from anywhere, but should be OK if your machine is behind a firewall.

5.6.4 Installing more voices

I’m afraid this is a bit tedious. You can skip it if you are happy with the default voice. First find the Festival data directory. All Festival data goes to a common file tree, like in FlightGear. This can be /usr/local/share/festival/ on Unices. We’ll call that directory $FESTIVAL for now.

1. Check which voices are available. You can test them by prepending "voice_":

   $ festival   festival> (print (mapcar (lambda (pair) (car pair)) \                                       voice-locations))   (kal_diphone rab_diphone don_diphone us1_mbrola \                      us2_mbrola us3_mbrola en1_mbrola)   nil   festival> (voice_us3_mbrola)   festival> (SayText ~I’ve got a nice voice.~)   festival> (quit)

2. Festival voices and MBROLA wrappers can be downloaded here:

   http://festvox.org/packed/festival/1.95/

   The "don_diphone" voice isn’t the best, but it’s comparatively small and well suited for "ai-planes". If you install it, it should end up as directory $FESTIVAL/voices/english/don_diphone/. You also need to install "festlex_OALD.tar.gz" for it as $FESTIVAL/dicts/oald/ and run the Makefile in this directory. (You may have to add "–heap 10000000" to the festival command arguments in the Makefile.)

3. Quite good voices are "us2_mbrola", "us3_mbrola", and "en1_mbrola". For these you need to install MBROLA (see above) as well as these wrappers: festvox_us2.tar.gz, festvox_us3.tar.gz, and festvox_en1.tar.gz. They create directories $FESTIVAL/voices/english/us2_mbrola/ etc. The voice data, however, has to be downloaded separately from another site:
4. MBROLA voices can be downloaded from the MBROLA download page (see above). You want the voices labeled "us2" and "us3". Unpack them in the directories that the wrappers have created: $FESTIVAL/voices/english/us2_mbrola/ and likewise for "us3" and "en1".

5.7 Air-Air Refuelling

5.7.1 What’s possible

At present, there are two tanker aircraft (KC135-E and KA6-D) and three receiving aircraft (A4F, Lightning and T38) capable of in-air refuelling. When flying one of these aircraft in the default scenery area, one can locate the tanker aircraft using air-air TACAN and/or radar and then receive a full or partial load of fuel by flying in close formation behind the tanker. Refuelling is also possible between aircraft in a MultiPlayer session. The KC135 is a boom refueller, while the KA6 has a hose. The A4F and Lightning are both fitted with a probe for hose refuelling while the T38 is fitted with a boom receiver. At the moment, either type can refuel from any tanker, but in the future it is likely that the correct type will have to be used.

5.7.2 Necessary preparations

Like the aircraft carriers, AAR is implemented as an "AI scenario". Selecting these normally requires editing the "preferences.xml" file in the flightgear data directory.

There is a shortcut in this case though; simply selecting the Lightning, A4F or T38 should automatically load a scenario containing a tanker, assuming you haven’t changed anything in your preferences.xml file.

Assuming this is the case, choose one of the aforementioned aircraft, make sure that "AI models" are enabled and start at KSFO (the default airport.)

Depending on the scenario, you might see the tanker crossing overhead when the sim starts; if not, don’t worry.

5.7.3 In the cockpit

Perhaps the first thing to do after starting the engines if necessary is to select the appropriate TACAN channel if your aircraft is so equipped (the A4F and Lightning both are). For the KC135 (by default used by the Lightning and T37) this is currently "040X", and for the KA6D (used by the A4F) it is "050X". Enter this channel using the relevant dropdown boxes in the "radios" dialogue (from the menus, "equipment/radios" or press control-r).

You should now see the current bearing to the tanker indicated in the nav display of the A4 or the TACAN indicator (green needle) in the Lightning. If the tanker is within range, it will also appear on the radar display of the T38 or Lightning. Take off...

5.7.4 In the Air

Turn to an appropriate heading, guided by the TACAN bearing (you should try a "leading" approach to close in on the tanker) and look for the tanker on the radar or nav. screen. Around 5nm away, you should reduce your speed to around 20kts faster than the tanker (these fly at 280 kts TAS) - a "slow overtake". The KC135 will be visible from about 10nm, the KA6-D, being smaller, just over 1 nm. You should use airbrakes as necessary to keep control of your speed should you find yourself overshooting.

Close to within 50ft of the tanker (don’t get too close, or visual artifacts might hide the boom from view). You should see indication in the cockpit that you are receiving fuel - there is a green light in the A4 fuel gauge, and you should see the indicated tank load increase.

Getting to this stage is not necessarily easy - it can take a lot of practice. As with carrier landings, this is not an easy manoeuver in real life either and there are additional complications in the sim; the tanker, being an AI model, is unaffected by the wind and flies TAS (True Air Speed), while you are flying IAS (Indicated Air Speed) and are affected by the environment. As in real life, your aircraft will also steadily increase in weight as the tanks fill which will affect the trim of the aircraft. (You might find it helpful to use the autothrottle to help control your speed - ctrl-a then Page Up/Down to increase and decrease the set speed.)

Once your tanks are full, or you have taken as much fuel as you wish, close the throttle a little, back away from the tanker and continue your intended flight.

5.7.5 More advanced topics

1. Multiplayer Refuelling

   Refuelling is possible within a MultiPlayer session given certain conditions. A basic flyable KC135 model is available - the pilot of this aircraft should use the callsign "MOBIL1", "MOBIL2" or "MOBIL3". Other numbers are acceptable, but only these three have A-A TACAN channels assigned. These are 060X, 061X and 062X respectively.

   If the receiving aircraft uses a YASim FDM, there are no further complications. Should the receiving aircraft be JSBSim based, the user must make sure that there are no AI tankers in their configuration. This means disabling (commenting out) all refuelling "scenarios" in the relevant aircraft-set.xml and in preferences.xml.

   MP refuelling works in exactly the same way as AI refuelling and is a fun challenge. It is best to ensure that your network connection is as free from interruptions as possible; the MP code does a degree of prediction if there is a "blip" in the stream of packets and this can make close formation flight very difficult or even impossible.

2. Selecting Different Scenarios

   There are several AAR scenarios available in the AI directory:

   1. refueling_demo.xml has a KC135 circling near KSFO at 3000ft,
   2. refueling_demo_1.xml the KC135 on a North/South towline at 8000ft and
   3. refueling_demo_2.xml the KA6D on a similar N/S path but at 8500ft.

   These can be selected by editing preferences.xml (use your operating system’s search facility to locate this if you don’t know where it is). Open preferences.xml in a text editor (e.g. notepad if on windows) and search for the <ai> </ai> tags. Place a line like

   <scenario>refueling\_demo</scenario>

   somewhere within the <ai> tags; you should see other scenarios already there too, perhaps commented out (i.e. with <!– –>).