Aerodynamic characteristics were determined of three cylindrical shapes representative of tail boom cross sections of the AH-64, UH-60, and UH-1H helicopters. Forces and pressures were measured in a wind-tunnel investigation. Data was obtained for a flow incidence range from -45 to 90 deg and a dynamic pressure range from 1.5 to 50 psf. These ranges provided data representative of full-scale Reynolds numbers and the full range of flow incidence to which these helicopter tail boom shapes would be subjected at low flight speeds. The effects of protuberances such as tail rotor drive-shaft covers and spoilers were evaluated. The data indicate that significant side loads on tail booms of helicopters can be generated and that the addition of spoilers can beneficially alter the side loads. Although an increase in vertical drag occurs, the net effect through reduction of tail rotor thrust required can be an improvement in helicopter performance. Keywords: Rotorcraft; Aerodynamics; Stability and control; Helicopters; Tail booms.