angle of attack

In rail work, angle of attack describes the geometric relationship between a wheelset and the track it runs on through a curve. Specifically, it is the angle between the plane defined by the wheel's rotation and the plane of the outer rail. When a train navigates a curve, the wheelset must be positioned at a precise angle to the track rails, and this angle directly affects how the wheel flange contacts the rail and how much lateral force the wheel experiences.

The angle of attack becomes critical at speed. As a train enters a curve, centrifugal force pushes the wheelset outward. If the angle of attack is too shallow, the wheel flange will dig hard into the rail, creating excessive wear and noise, and potentially derailing under extreme conditions. If the angle is too steep, the wheel may not grip the rail properly and could slip sideways. Modern track design, including superelevation (banking) and rail cant, is engineered to optimize the angle of attack for the expected speeds and wheel profiles of the rolling stock that will use that line.

Different rail systems target different angles of attack depending on their operating characteristics. Freight lines with slower, heavier trains may tolerate steeper angles and sharper wheel flanges, while high-speed passenger lines use gentler curves, shallower angles, and more finely tuned wheel profiles. The angle is not a fixed value set at installation, but rather an emergent property of the track geometry, the wheel profile, and the wheelset's lateral suspension characteristics.

Wheel and rail engineers measure angle of attack using trackside geometry surveys or by instrumenting test vehicles with lateral accelerometers and position sensors. Excessive flange wear, rail corrugation patterns, and noise signatures all indicate that angle of attack is suboptimal for the actual traffic mix using that section of track. Renewal of either the wheel profile or the rail profile can restore the correct angle of attack.