Now what is efficiency? Now, the Propeller efficiency will be equal to output by input which we can write as d T into V A divided by d Q into omega which also we can simplify from the previous derivations we have already done as omega minus omega 1 into V A divided by 1 plus V 1 by V A and this can be shown to be 1 minus a dash divided by 1 minus a, where a dash is equal to omega 1 by omega which is called the rotational flow factor.