Now I'm trying every way that I know to increase the fps for recorded images(1280x800, cannot be changed). Now the fastest I can get is about 10hz. First I will list out all changes that I made:

1. Set "ViewMode" : "NoDisplay"
2. Only record scene images which means that I turned off my depth view and Segmentation view sub-windows.
3. Change compressed image format to JPEG(default is png)
4. render_target->InitAutoFormat(settings.width, settings.height); changed to
   render_target->InitCustomFormat(settings.width, settings.height, PF_B8G8R8A8, true);

Now I know most of the time cost is coming from RHICmdList.ReadSurfaceData(), but just have no idea how to solve it. And from the materials that I've collect I know in the previous version of Airsim and UE doesn't go this slow, right? Since it's not proper to downgrade any one of them, Is there any other way to achieve 50+FPS?
My setup:
Windows10, Nvidia Quadro K1100M, UE4.18, Airsim latest version