I don't remember what key was used with XAR, but I finally got some time to mess around with Redline and figured it out:
The backslash ("\") key acts as the brakes.
Hold it down and the red brake bar will rise.
Hold it down too long and the aircraft will nose over. Hold the key down briefly, then let it up, and repeat as necessary to brake.
Alternatively, you can separately map the left and right wheel brakes to their own analog control axis (preferably rudder pedal toe brakes), and get much better control.
The backslash ("\") key acts as the brakes.
Hold it down and the red brake bar will rise.
Hold it down too long and the aircraft will nose over. Hold the key down briefly, then let it up, and repeat as necessary to brake.
Alternatively, you can separately map the left and right wheel brakes to their own analog control axis (preferably rudder pedal toe brakes), and get much better control.