As a result of the differences found in this post, Bill Atkinson and I have been going through our detailed models. This has resulted in the correction of my model in two points:
- It is not necessary to define a virtual outboard to calculate the blade force. The blade force is simply given by the , independent of the amount of blade slip.
- I had an extra term in the calculation of the blade effective area which upon closer study of the expressions for lift and drag is not necessary. The coefficients already take into account the area effect of the attack angle.
Bill also provided me with a detailed list of input values and calculated results for his model. This enabled me to improve my input values to more closely match his.
Here’s the current comparison:
Here are Atkinson’s results:
This reduces the difference in blade dissipation to an acceptable 1% error, and the power difference at the oarlock, oarhandle, and power dissipated in drag on the shell are on the order of 5%. Now the biggest discrepancies are in the power dissipation in the rower’s body, and the related question of shell and rower kinetic energy exchange during the stroke.