Well I will admit that I was wrong about some of my comments about Rembrandt, at least in version 2.8.3 RC3, it actually works pretty fairly on my machine, even squeaking in an occasional 22 fps at KSFO in MP with a fair amount of activity ongoing. But, I am having serious issues, and I'm wondering if these are RC3 bugs or just my not setting Rembrandt up correctly.
The glass effect fix from the Wiki to convert 2.6 aircraft windows to 2.8 seems to work well, but the alpha channels on all propeller prop disk's have lost all transparency, making them black discs, and unless I missed a crucial instruction, (and I've searched this forum and a lot of associated Rembrandt topics in other forum catagories..) this is enough for me to revert back to 2.6.0.
The other big issue is that for some odd reason, JSBsim IC piston engined aircraft, and especially old time, low compression ratio engines are nearly impossible to start. At least not without some rather strenuous sim magiking like ctr+u up to '8000, point the nose down vertically, and hold the starter on for a half minute while cycling the throttle, and maybe the engine will catch. And for most JSB sim piston engines, they seem to have suffered an noticeable reduction in power, and an inability to hold an idle.
I have no idea what change in the code were implemented that deals with JSBsim FDM's but it's a big step retrograde.