I also suspect that this paper is using an XB-28 nacelle: Some Lift and Drag Measurements of a Representative Bomber Nacelle on a Low-drag Wing I Wind-Tunnel Tests of a Twin-Engine Model to Determine the Effect of Direction of Propeller Rotation on the Static-Stability Characteristics This one used several combinations of vertical stabilizers, including all-moving surfaces and a twin tail. The Influence of Vertical-tail Design and Direction of Propeller Rotation on Trim Characteristics of a Twin-engine-airplane Model with One Engine Inoperative Effects of Direction of Propeller Rotation on the Longitudinal Stability of the 1/10-Scale Model of the North American XB-28 Airplane with Flaps Neutral, Special Report Wind Tunnel models of the XB-28 have been used on a number of NACA studies.