The cockpit of the plane might be super detailed and require more computer power than the world scenery does. I see this with the airliners most often. The best you can do is follow these instructions for setting the rendering options. Make sure you base it on the most intensive plane, scenery, weather, etc you want to use. That means if using light scenery areas or clear weather you may have a really high frame rate, but you won't have to adjust it every time you want to use a powerful plane or a lot of clouds.
Welcome to X-Plane Q&A, where you can ask support questions and get answers from members of the community.
This site is for X-Plane support questions only. Please search for existing answers before posting your question. Off-topic questions will be locked.
If you’re new, you’ll need to register before asking your first question.
If your question is answered, click on the check mark to select the best response.