In the “General” tab of the Settings menu there is a strange-looking setting called FLIGHT MODEL:
This is usually left at the default setting for the default Laminar aircraft but some add-on aircraft may well require higher Flight Models per Frame setting particularly if it is a very fast combat aircraft, a very light glider or drone, or a very small aircraft like a Radio-controlled small scale aircraft being flown in a full-scale simulator like X-Plane.
Many X-Pane users have no idea what to do with this setting. However, buried in the X-Plane.org forums there was an interesting discussion about this with contributions from many of the most experienced X-Plane users. It’s well worth a read. You’ll find the thread here
The official manual also has a few things to say about Flight Models per Frame. Go to the on-line Desktop manual and in your browser search for “My Frame Rate is Low” and you’ll get to the right page.