#2602 Aircraft Center: Missing default aircraft and custrom folders

[Bjoern K]

When opening the Aircraft Center from "File" --> "Aircraft Center", default aircraft (C172p and the UFO) and aircraft from folders defined in "AddOns" --> "Additional aircraft folders" (Launcher) are not listed as "Installed Aircraft".
The list only contains aircraft downloaded with the Launcher from FGAddon.

See screenshot:

[Bjoern K]

The top of my "installed aircraft" list when using the normal launcher:

[Bjoern K]

OS: Arch Linux

SG HEAD: a49619fa6c23bf7ad8839de63d8454291cb29cf3
FG HEAD: 083d364f9c2e809716f4cceb634ed41b836ac725

[Gijs]

The experimental aircraft center has been removed from the menu as of [b0cfcd].