Prepar3D v4, Big drop on FPS when changing view at night

[steveli]

I found that in Prepar3D v4, a big drop on FPS when changing the external view at night time. In the day time, there is no FPS drop no matter which external view angles are on. At night time, when the viewing airplane direction is toward to downtown area (downtown area is on the far background), then a significant FPS drop will be observed. For example, airplane take off from runway 16L at KSEA(Seattle-Tacoma), 25 FPS was observed at day time no matter which direction to view the airplane. But at night time, 15 FPS was observed when view the airplane from its back (toward south), and FPS drops to 4 when view the airplane from its front (toward to north, Seattle downtown is on the far background). I have tried several other big city locations, the same FPS drop were observed. This FPS drop is only happened at night time, no FPS drop at day time. I tried to turn off shadows and HDR lighting with no help. Also, all of this is on Prepar3d V4 default scenery without any add-on.

Did anyone else have similar problem? Can any of the LM Prepar3D team member make some experiment as what I described above and see if it's repeatable on your system or not. If it is, can you provide us a solution on it? Thanks!

[Senchay]

THe only problems i have are caused by the dynamic lightning. On airports with it it massivley decerase fps. Othwerwise this doesnt happen to me.

[Chazypax]

I'm getting the exact same problem using Prepar3d v4. During the day FPS are fine, when at night, there is a huge drop.

[steveli]

I have solved this problem by removing Ultimate Terrain X (V1). After removing UTX V1, everything turns back to normal. Flight1 claimed UTX V2 is compatible with P3D V4 but I haven't tried it yet.