Joined-Wing Wind-Tunnel Test for Longitudinal Control via Aftwing Twist

Wind-tunnel tests were conducted to assess the use of aftwing twist for longitudinal control in a joined-wing aircraft. Forces and moments required for pitch control were measured experimentally, along with limited chordwise pressure measurements. Comparisons of aerodynamic panel model predictions with experimental data were used to calculate camber and center-of-pressure corrections. The lift-curve slope measured at four flow speeds compared favorably to linear predictions over the range of 20° angles of attack. The pitching moment coefficient was linear at the three lower flow speeds for untwisted and twist-down aft wings over a narrower range of about 10° angles of attack. The pressure exhibited shifts in the chordwise distribution at angles of attack coinciding with the change in the moment curve slope. The large spread in the twist-up aftwing configuration drag and pitching-moment coefficients indicated flow separation on the aft wing, even at small angles of attack, deterring the twist effectiveness. Independent forward and aftwing measurements and more extensive use of pressure sensors are recommended in future experiments to confirm the apparent separation and interference effects that must be avoided if aftwing twist is to be used for pitch control on a joined wing.