For constant energy transfer over the entire span of the blade, the above equation should be constant for all values of r {\displaystyle r} . But, U 2 {\displaystyle U^{2}} will increase with an increase in radius r {\displaystyle r} , therefore to maintain a constant value an equal increase in U V f cot ⁡ β 2 {\displaystyle UV_{\rm {f}}\cot \beta _{\rm {2}}} must take place. Since, V f {\displaystyle V_{\rm {f}}} is constant, therefore cot ⁡ β 2 {\displaystyle \cot \beta _{\rm {2}}} must increase on increasing r {\displaystyle r} .