You want to create your first own aircraft? Great!
But before you you start- some really substantial things!
1. The question of Licence
Do you want it to have completly as Open Source or more protected?
GNU GPL? GNU GPL stands for OpenSource and the licence for the whole FlightGear FlightSimulator Project- if you want to see your aircraft included in FlightGear you have to choose GNU GPL! But beware of, that it may be sold and be changed by other users, and spreaded further under the same licence!
http://en.wikipedia.org/wiki/GNU_GPL
Very important: This means that you can't use things from other aircrafts which aren't under GNU GPL!
Freeware? Fine, but this means it can't be included in FlightGear's Downloads, and you should have at least a place for your work to offer.
http://en.wikipedia.org/wiki/Freeware
Or how about Creative Common Licnence?
http://creativecommons.org/licenses/by-nc-sa/3.0/
This allows different grades of protect- from totally free to totally protected.
At least - to have it finally under GNU GPL is the one of best thing and a win for the whole project!
2. Collect informations as much as possible!
* What is this exactly for an aircraft, how and when was it used?
-> Your favourite searchengine is your friend- use it! There is also wikipedia, and tons of aircraft pages to look for.
At the end you should at least know:
- -some develpement specs of the aircraft
-dimensions and weights, fuel specs
-possible derivates
-specifics
-rough specs about velocities, landing speed, cruise levels...
Use the FG-Wiki: http://wiki.flightgear.org/index.php/Aircraft_Information_Resources
As an example: a 737-800 is not a 737-300 with winglets though it may look like that on the first glance...
*Good Drawings
->Your favourite searchengine is your friend- use it! There is also wikipedia, and tons of aircraft pages to look for.
Just google "aircraftname" 3 views or blue prints- you will find for sure a ot of good drawings!
And have a closer look here in the FG-Wiki: http://wiki.flightgear.org/index.php/Modeling_Resources
Often RC-Aircraft forums offers as well plenty of detailed drawings. You can also find pages there which includes very detailed drawings for a small fee.
*Lots of Photos, Photos, Photos and Images
Even the best and detailed drawing doesn't show you all! Sometimes the fuselage has shapes which can't be seen like that on the drawing!
So collect a large set of photos of Fuselage, Nose, Tail, Wings and Gears!
3. the right Flight Dynamic Model
Choose the right fdm!
We use two important but different fdm's in FGFS: YASim and JSBSim.
-YASim simulates the effect of the airflow on the different parts of an aircraft. It is qite similar to X-Plane's fdm (but no conbversion possible) It should be used if you only have the dimensions of the aircraft and some rough specs. It also provides a quite realistic helicopter fdm, so for helicopters YASim is currently most best at the moment.
This will help you with YASim: http://ltts.crlt.indiana.edu/grn/flightgear/yasim_1.html
-JSBSim is a generic, 6DoF flight dynamics model for simulating the motion of flight vehicles. This is great if you have detailed flight datas like airfoils, windtunnel and perfomance datas.
It comes with a nice tool, which helps to develope a fdm which suits quite good to real aircraft and is the base for a perfect fdm!
http://jsbsim.sourceforge.net/aeromatic2.html. And at least there is Datcom, a tool used be the US-Airforce for developement:
http://www.holycows.net/datcom/
For the beginning you could use a similar aircraft's fdm.
In the direction where you stored FGFS you will find more help about: data/Docs/....README
4. fundamental things on 3d-modelling
First: for modelling aircrafts you need some skill.
You don't have?
No problem! On the web there are hundreds and more tutorials which help to learn 3d-modelling! So practice the most important shapes used like cylinders, Cubes, Quaders, Poly-by-Poly-modelling etc. before you really go on and announce your project! Otherwise you might disappoint other users ....
Some additional tips:
- -for the first make a rough model than add details
-texture mapping should be the last thing you do after finishing the aircrafts fuselage. Only map the aircraft if you are sure you are ready and futher changes won't change the mapping. If not it may upsets Livery makers and make it hard to change all liveries made already.
-to few vertices and polygens? Hey, aircrafts has usually soft edges and round fuselages - and even older computers can manage a lot of polygens so do not save with! As many vertices as needed- not more or less!
-regards the normals- the most 3d-modelling-programs shows the directions of the normals. If you disregard this, don't wonder why some surfaces are unvisible!
-use setsmooth or anything similar in your 3d-modelling program to have smooth curves and surfaces.
5. Animations and configuring
No, there aren't great programming skills needed. All the aircrafts mostly shares the same code snippets!
So first take a look on other aircrafts and at the Model-How-To, which is included in yor FlightGear-Program in data/Docs/Model-How-To.
You want some fancy animations like pushback, lights, weapons etc.? Befor you do that- be sure you have understand how all the animations works and the basic ones on your aircraft works correct.
These are:
-Rudder
-Aileron
-Elevator
-Trim surfaces
-Gear
And be sure that the modell is good positioned- no "hovering" above the ground, or wrong contactpoints.
6. converting from other sims
Some other sims use similar model-formats. Or some can be easily converted to FGFS's format. So it is possible and maybe the easist way to get a new aircraft.
But:
-you can't convert the fdm- it has to be written completly new like animations etc!
-ask the original-author! Without his permission you aren't allowed to convert his work. Include your request and his answer in an extra text-file, so everybody can be sure that you didn't infringed copyrights!
-Be polite when requesting permission and respect when he says no!
Finally- how the get my aircraft on FlightGear.org and available for all?
Public or private spaces like unitedfreeworld, avsim etc. are good place to share for the community while developing and for a first release.
But the best place is still GIT, the developement system of FlightGear Project!
The place for all developement -aircrafts, programmings, graphics...- is the mailing-list and the IRC-Chat!
So if your Aircraft is really GNU GPL ask on the devel-list or in the forum if someone might take quick look at it and upload it! So whenever the next release comes-it will be available for all and easy then!
https://lists.sourceforge.net/lists/listinfo/flightgear-devel
irc.flightgear.org, channel = #flightgear
At least
A good aircraft needs time!
Maybe the fuselage is done in some hours or days. But tuning fdm, programming systems etc. needs a lot more. And making the cockpit needs about 10x more time then the exterior model! So be yourself patience!
You are stucked some where?
Don't hesitate to ask! But give some detailled description where and why it is stucked. Otherwise there won't be much help! And the most developers are already quite good recognizing if you really want help or just want them to make your work!
Happy developing!
Edit: adding set smooth hint
Edit2: added suggestions by GRTux
Edit3: added suggestions by MOJO