what software do i need to create my own fsx addons

Planes or scenery, or both?
The FSX SDK offers a read and some tools and you also get some freeware editors to e. g. design airports without the need to get into 3D model creation. Check http://www.fsdeveloper.com/ if you like, there's a forum for all kind of devs.

Maybe I should do scenery... it sounds easier.

The hardest port about creating Aircraft or even scenery is the lack of information in the SDK documentation

That sums it up.

So maybe try to add some glass to a steam gauge plane or edit some vital flying parameters to check how they influence the experience.
This is the sort of thing I'm often doing a lot of. It isn't quite the same as building your own, but you can learn a lot by doing this sort of thing. Something to remember is this: Adding to a 2D panel is easy. Adding to a 3D VC is not as easy. The reason for this are:
1) The gauges are pasted onto a texture and often that texture is shared by all the other gauges. This is pretty easy because you can move them around as you want. It can take quite a blot of tweaking because the gauges might get distorted because of the texture resolution.
2) The gauges are pasted onto a texture, but each gauge has its own texture. This makes it difficult because you are very restricted with the changes in size. You can't change the location in the VC.
3) The gauges are 3D. This usually meant that the code and the gauge are made during the modelling of the aircraft. You can't change them at all. You get what you get! They also look fantastic if done well. I have noticed that a lot of developers are shifting over to do it this way.

If you are interested. When I change/add gauges to an existing aircraft, I often use FS Panel studio to "confirm" or get the position and size to where and how I want it. I don't always save my work, IU manually write the info into the panel.cfg. FS Panel Studio has a nasty habit of changing the gauges by adding lines that are not originally there. It can make the gauges look funny. It is, however, a useful addition to the FS SDK and I would recommend it.

Mark

boeing247 wrote on Aug 12^th, 2011 at 3:11pm:

Many will say yes. The EULA usually informs you that you get it "AS IT IS" and that changes are NOT allowed. If I make changes that can be seen as that, I keep it to myself. The other side to that is that most don't mind you editing the panel.cfg files to your own likes. Reverse engineering is a BIG NO-NO!

Captain Sim have those conditions in their EULA, which you are supposed to read before accepting and then continuing with the installation.

So you understand my view, I do not open the MDL, GAU or DLL files and make changes to them. I probably shouldn't in the CAB files either - think fuel displaying in pounds and not kilos mod for the 757 and 767.

These were the reasons I wanted to create my own aircraft in the first place. The main one being the default C172 in FS9. It had half a VC/Cabin. You can not see the nose when you raise your view in the VC. I hated that. In the airliners, I want to create my own, with its own interior and call it something like a business jet. I would like to add more fuel tanks to give it extended range and that sort of thing. I do have a freeware add-on that is fantastic for that, I just hate the instrumentation in the VC.

Mark

By the way, Mark, do you have any good tutorials for scenery design? I want to do some some improvements on Catalina Island (First KAVX, then I'll move on to the cities of Avalon and Two Harbors), off the coast of Southern California.

Go to File>Compile Airport, then put the .bgl file in the Addon Scenery folder in the main FSX folder. When you open FSX, go to your scenery library and click "Add Scenery" (I think that's what it says).