flightgear

A flightgear library originally written for the London Clojure Dojo, now being used to turn people on to Clojure at Clojure Dojos the world over.

Usage

FlightGear

1. Download FlightGear for your platform from http://www.flightgear.org/download/ If you're at a meetup group and wifi is saturated, go the BitTorrent route. The mirrors are good, but sometimes timeout. In general, it's a good idea to have a USB stick handy to pass around in case the wifi situation is really bad.

2. Run with the parameter --telnet=5401. Assuming you've downloaded the binary, the way you add this option is by opening the FlightGear GUI application, clicking Advanced Features, then under the Others tab enter --telnet=5401. Once you've done that, you can click Start Flight, and you're off to the races.

Leinigen

Add to your project.clj:

  :dependencies [[org.clojars.dalethatcher/flightgear "0.1.0-SNAPSHOT"]]

API

Quick Start

> (use 'flightgear.api)
> (connect "localhost" 5401) ;; => true
> (starter! true) ;; wait until engine started, 'engine-running?' can be used to query
> (starter! false)
> (flaps! 0.5)
> (throttle! 1)  ;; wait for a little while and you should be airbourne
> (rudder! 0.1) ;; steer a bit to the right (single props tend to veer to one side)

You'll briefly have the elation of flying, most likely followed by a nice crash.

Instruments

Remember these values will have lag and some inaccuracy, depending on local conditions. Note that the inaccuracy is normal: These are analog instruments.

> (indicated-airspeed-kt)
76.08771873
> (indicated-altitude-ft)
2271.735558
> (indicated-attitude)
{:indicated-roll-deg -26.59438056, :indicated-pitch-deg 1.811541719}
> (indicated-heading-deg)
110.7191063
> (engine-running?)
true

If you're wondering whether or not you're in a sane starting gamestate after a reset and/or crash, you can run the following from the REPL (assuming you've successfully connected) to peek at the values after doing a File > Reset:

(println {:airspeed (indicated-airspeed-kt)
          :altitude (indicated-altitude-ft)
          :attitude (indicated-attitude)
          :position (position)
          :orientation (orientation)
          :heading (indicated-heading-deg)})

My starting values with a "Cessna 172P - Canvas Demo" aircraft from San Francisco International airport are as follows:

{:airspeed 2.136604309,
 :altitude -41.86214963,
 :attitude {:indicated-roll-deg 40,
            :indicated-pitch-deg 12},
 :position {:sea-level-radius-ft 2.089963105E7,
            :ground-elev-ft 1.591905672,
 :ground-elev-m 0.4852128489,
 :altitude-ft 6.006853687,
 :latitude-deg 37.62870959,
 :longitude-deg -122.3933424},
 :orientation {:roll-deg -0.2522372877,
               :heading-deg 117.8880022,
               :pitch-deg 2.786319015},
 :heading 108.2690857}

Controls

See http://www.aerospaceweb.org/question/design/q0101.shtml for a description of aircraft control surfaces.

(starter! true|false) ; Turn the starter key, don't forget to turn off!
(throttle! 0..1)      ; Power to the engine.
(flaps! 0..1)         ; Sort of a fixed up and down mostly used for take off and landing.
(rudder! -1..1)       ; Steer left and right (yaw).
(elevator! -1..1)     ; Up and down (pitch).
(aileron! -1..1)      ; Left and right with rotate (roll).

Telemetry

These are direct values from the flight simulator, aka cheating! :)

> (position)
{:ground-elev-ft 1.602206714, :ground-elev-m 0.4883526066, :altitude-ft 6.017082775, :latitude-deg 37.62871089, :longitude-deg -122.3933408}
> (orientation)
{:roll-deg -0.2482645472, :heading-deg 117.8881856, :pitch-deg 2.792487719}
> (velocities)
{:wBody-fps 1.462199396E-8, :vBody-fps 1.285159097E-10, :uBody-fps -2.054781393E-9}

Resetting Your Plane and Other Tips

You're going to crash. It's only a matter of time. When you do, there can be some issues getting the game state, repl, and your instrumentation back to where it ought to be. With the FlightGear window (the one you just saw your plane crash in) focused, click File > Reset to get back to where you started.

You don't have to "cheat" if you don't want to, but under Advanced Features > Features, I suggest turning off Real weather fetch, Horizon effect, Clouds, and 3D Clouds. It'll make things run smoother, and the last thing you need on your maiden voyage is annoying doses of reality. This is programming. You have the option of turning off physics. Take advantage.

Is it really dark where you're flying? Click Environment > Time Settings and change it to morning if that's easier for everyone to see.

Finally, there are lots of reasons why things behave the way they do in FlightGear. It tries to be a first-class simulator. There is documentation worth reading: [http://www.flightgear.org/Docs/getstart/getstart.html#getstartpa1.html](FlightGear Documentation)

License

Copyright © 2013 Dale Thatcher

Distributed under the Eclipse Public License, the same as Clojure.