Slope of Lift Curve

Evaluation of the slope of the lift curve of the horizontal stabilizer, aH, as a function of aspect ratio and sweep of the mid-chord line can be made from Figure 8.6, which has been adapted from reference 8.1. Test data for several stabilizers and wings of Bell helicopters are shown on Figure 8.7, taken from reference 8.2.

Many modern helicopters have end plates on their horizontal stabilizers in the form of small vertical surfaces. End plates tend to block the flow around the tip from bottom to top and thus reduce the tip vortex. The result is that the effective span—or the aspect ratio—is increased, with a corresponding increase in the slope of the lift curve. The increase in effective aspect ratio as a function of the – height-to-span ratio is given in Figure 8.8, which was taken from reference 8.3.