How exactly does people make their own custom aircraft?

[Alpha-Two]

I woukd like to start making my own aircraft into the flight sim. However I do not know where to start, I presume there is some kind of program used to make theese planes already made for msfs2020 but I don't know where I can find it, or what the name is. (Or if it exists)
I am not searching for a program to make models like blender or something, however I am searching for somewhere to make the actual aircraft, give it an engine that works etc. If anyone knows anything about this, then please share here.

[Alpha-Two]

*Please note* I just found out you can use a program called SDK or something to do exactly this, but if anyone knows more about this, that might be usefull for me to know, then share it here.

[Razamanaz]

SDK is the Software Development Kit. Load the game and go to Options-->General Options-->Developer and turn on Dev Mode. In the top left of screen choose Help and you can download the SDK from there.

[Rever]

I don't know myself, but I think you would be best searching for other forums besides steam. I don't recall specific ones that deal with mods but there are some really good communities of flight simmers that share all kinds of information like this.

I would suggest maybe https://flightsim.to/forums - Forums >> Modding and Creations >>Add-ons Talk

I am sure there are other good ones out there.

[Razamanaz]

You will need to acquire the SDK first and foremost. There are also some tutorials available in the same place. You can get more tutorial help here or from Youtube.
https://www.fsdeveloper.com/forum/threads/making-airplanes-jets-gliders-in-msfs-sdk.450471/

[Manwith Noname]

This is a multi step process and isn't easy to teach / learn everything in a short space of time.

You'll need to learn 3D modelling. As you said, Blender is free and actually quite good. Certainly good enough to achieve this goal. You'll need to understand PBR (physically based rendering) and texture formats, how to make and edit them. You'll need to download the SDK as already discussed. You'll also need to know the plane you're making very well, at least if you want to do a good job of it. Not just the exterior shape and design but the cockpit, avionics and systems. You might even need some programming knowledge.

Above all this, you'll need to be highly motivated and determined to see it through.