Find the ViewportHandling.lua file and comment out the render_purpose.general string with -- so it looks like this.Look in here:
Program Files\Eagle Dynamics\DCS World\Scripts\Aircrafts\_Common\Cockpit
function set_full_viewport_coverage(viewport)
dedicated_viewport = {viewport.x,
viewport.y,
viewport.width,
viewport.height}
dedicated_viewport_arcade = dedicated_viewport
purposes = {--render_purpose.GENERAL,
render_purpose.HUD_ONLY_VIEW,
render_purpose.SCREENSPACE_OUTSIDE_COCKPIT,
render_purpose.SCREENSPACE_INSIDE_COCKPIT} -- set purposes to draw it always
render_target_always = true
end