Improving Airplane Touchdown Control by Utilizing the Adverse Elevator Effect

The main objective of this original research article is to understand the short-term dynamic behavior of the transport-category airplane during landing flare elevator control application. Increasing the pitch angle to arrest the sink rate, the elevator will have to produce negative lift to rotate the airplane’s nose upward. This has an immediate adverse effect of initially accelerating airplane downward. A mathematical model of landing flare based on the flat-Earth longitudinal dynamics of rigid airplane was developed which is realistic only on very short time-scales as pitch stiffness and damping were neglected. Pilot control scenarios using impulse and step elevator pull-up and push-over were used. Laplace integral transforms were used to transform ordinary differential equations into algebraic ones in complex domain. Transfer functions were defined for airplane response in pitch, angle of attack (AOA) and height. Based on the understanding and utilization of the adverse elevator effect a new landing flare technique is suggested which can substantially reduce scatter of touchdown points and increase consistency of landings. The new pull-push landing touchdown technique could reduce the probability of runway overruns and increase airframe life-time and is especially useful when landing on contaminated runways and/or during Land and Hold Short (LAHSO) operations