I have installed a bunch of plances the same way I did in Vista and the ones I have added are not showing up within FSX on Windows 7....
Put a checkmark in the box just below the aircraft menu.
The box that says "show all variations".
It is, and was checked.
What have you loaded.
Give us a link or the zip file name and we can check it out.
There are half a dozen... All from https://flyawaysimulation.com/
Are you unzipping it, placing the folder in simobjects/airplanes.
If not, that's your problem.
I can't guess which one I need the link.
Find one, click on "detail" and post that link.
Yes I have done that. I have been using Flight Simulator since it's inception. I know how to add planes and have checked and re-checked.
I asked for a link, what more can I do.