As the title says, CFD just ends at the end of the "tunnel". This may not seem like a problem, who cares about what happens to the air behind the plane.
Well, the air infront of it does. The air from the CFD just hits a wall at the end of the "tunnel", Slowing the air around the tail section of the plane.
The default voxel area is 1.5x the wingspan of the plane. With that, the air on the Tail is affected and slowed down.. did anyone notice how bad castoring wheels are with CFD and the modern prop model???
Here we have my good old modded DA40NG with all the default CFD parameters.
full power, ISA weather, 0 wind
If you look at the tail airspeed box, you can see 15 knots.
Also you can see the air starting to flare out in the back like its hitting a wall. (because it is)
With 2x voxel scale, we see this:
The tail airspeed box now shows 19 knots (borderline 20). This may only be a 1.3x in speed, however, 1.3 x 1.3 = 1.7 - 1.8!
With this we (should) get 1.8x the rudder force. Already this simple config change makes a big difference.
You can also see how the streamlines continue for a longer distance.
Can this be fixed or can the length of the CFD "tunnel" be adjusted? Either make it longer by default or give us a setting.