Question: A four-bladed airscrew is required to propel an aircraft at 125 ms-1 at sea level, with a rotational speed of 1200 rpm. The blade element at 1.25-m radius has an absolute incidence of 6 degrees, and the thrust grading is 2800 Nm-1 per blade. Assuming a reasonable value for the sectional lift-curve slope, calculate the blade chord at 1.25-m radius. Neglect rotational interference, sectional drag, and compressibility.