A nonlinear aircraft simulation of ice contaminated tailplane stall

The effects of tailplane icing on the flight dynamics of the NASA Lewis Research Center DHC-6 Twin Otter research aircraft have been analyzed using a specialized nonlinear simulation program. The program performed the integration of standard aircraft equations of motion with aircraft characteristics determined from tables and functions. For this research, a specialized database based on flight test and wind tunnel test data was developed. Unique methods were used to separate the tailplane contribution from the aircraft characteristics to create this database and separately model the wing/body and tailplane aerodynamic characteristics of the DHC-6 Twin Otter aircraft. A pilot model and a reversible control system model tailored for this research were effective in assessing the effects of tailplane icing.; Tailplane angle-of-attack showed trends of decreasing with decreasing airspeed and decreasing pitch rate during pushover maneuvers. At trim flight conditions, tailplane angle-of-attack was shown to decrease with increasing airspeed and increasing flap deflection. All of the pushover maneuvers to zero g load factor with non-zero flap deflections and the iced tailplane model showed a tendency for control difficulties. The simulation responses were shown to be slightly conservative in predicting tailplane stall flight conditions compared to flight test data.; The simulation program responses suggest that a discriminator of susceptibility to ice contaminated tailplane stall for the DHC-6 Twin Otter is a pushover maneuver through a load factor of {dollar}nsb{lcub}rm z{rcub}{dollar} = 0.5g with no significant stick force lightening, no tendency for a divergent load factor or pitch rate, and positive control of the maneuver. The responses showed that tailplane icing causes two distinct stability and control problems; inadequate flying qualities if the tailplane angle-of-attack exceeds that of the hinge moment break, and reduced stability when the tailplane is near the stalling angle-of-attack. A novel V-n diagram limited by tailplane stall angle-of-attack was useful in quantifying these maneuvering limitations caused by tailplane icing across the flight envelope.