The infamous glider is usually an indication that the aircraft is not installed and/or that there is no matching AI aircraft model* either.
* FlightGear will load an AI aircraft if there is one with the exact same path to the model/animation XML file (or in rare cases .ac file), apart from that the path to the AI aircraft begins with "AI/Aircraft/<path>" instead of "Aircraft/<path>". See also the wiki section Howto:Animate models#File name of main model and animation XML file (perm).
Low-level flying — It's all fun and games till someone looses an engine. (Paraphrased from a YouTube video) Improving the Dassault Mirage F1 (Wiki, Forum, GitLab. Work in slow progress) Some YouTube videos
Thank you for this reply. I am starting using download AL aircraft from the scenery downloads. It should be helped. Even with my soslow internet lately................