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How to use it
Y/Q limit. With the flange angle and the friction coefficient you get the limit ratio according to Nadal. If you also enter the lateral force and the vertical load on the wheel, the calculator gives the utilisation and the margin.
Wheel unloading. From the loads of the two wheels of the axle on level track and the minimum load on twisted track you get ΔQ/Q0, the comparison with the limit and the minimum permitted load.
Formulas used
Limits
The calculator deals with the quantities, not with the test. The values of Y and Q come from tests or simulations: the test twist, the curve, the load conditions and the torsional stiffness of the vehicle are defined by the standard and by the method chosen. For setting up the verification and the report there is the service safety against derailment to EN 14363.
FAQ
Why is the Y/Q limit 1.2?
With a 70° flange and friction 0.36 the Nadal formula gives 1.2: it is the reference value for the twisted-track test. With higher friction the limit drops.
What does ΔQ/Q0 measure?
How much the least loaded wheel unloads when the track is twisted, compared with the mean load on level track. The stiffer the vehicle in torsion, the more the wheel unloads.
How is wheel unloading reduced?
By reducing the torsional stiffness of the frame or of the suspension, by increasing the spring deflection or by correcting the load distribution between the wheels.