A fan is to produce a total pressure rise of 6 in. \(\mathrm{H}_{2} \mathrm{O}\) and a flow of \(4000 \mathrm{ft}^{3} / \mathrm{min}\). Two motors are available, \(3550 \mathrm{rpm}\) and \(1160 \mathrm{rpm}\). For each motor, specify the best (most efficient) type of fan to use and sketch the impeller.