To officially confirm what @asj5547 correctly said: The definitive answer is that RealFlight Evolution now uses DirectX 11, which is what you need in order to run using that graphics device.
Earlier full versions of RealFlight (e.g., RF9, RF8) do not and will not support DX11.
RealFlight Trainer Edition will receive a DX11 update down the road, but that's still a little ways away.