Estimation of lift and drag characteristics of light transport aircraft in the presence of ground effect during landing

Abstract

This paper presents ground effect analysis on lift and drag characteristics of a light transport aircraft during landing phase of flight. It also attempts to provide some insight in to ground effect factor and its dependency on dimensionless height above ground. The ground effect factor determined here through flight data is compared with theoretical values obtained through academically established ground effect factor expression. The basic trend of ground effect factor is expected to be always less than unity and thus ensuring reduction in induced drag during course of flight in proximity to ground during landing. The accuracy and consistency of ground effect factor determined with reducing dimensionless height above ground is also determined for establishing limit of acceptable level of deviation. Below this dimensionless height above ground, deviation from theoretical values shows inconsistency due to higher level of turbulence and measurement limitations of instrument. Ground effect characteristics have been obtained from flight experiments and mathematical modelling in order to enhance perception of ground effect phenomena. Previously various researches were performed using analytical, ground based experiments and flight experiments. This paper focuses on attempt of modelling ground effect using flight data and through MATLAB tool. The aerodynamic characteristics of any object flying close to ground and at far away from ground show phenomenal differences. The attribute of changing aerodynamic characteristics, makes ground effect of paramount importance. The effect on aerodynamic characteristics are in turn effect handling qualities of aircraft during Take-off and Landing. The flight test data was acquired using proper instrumentation measuring control surface deflection, flow angles, engine parameters and other GPS assisted parameters. The ground effect factor responsible for effect on lift dependent drag in the presence of ground is determined with flight test experiments and compared with theoretically accepted values of academic importance. The flight test program is with transient descending flight maneuver from above the screening height till touchdown of aircraft or dynamic ground effect. The intention is to differentiate between outside ground effect characteristics and inside ground effect characteristics. The ground effect is modelled using equations of motion during approach phase of flight. Ground effect is modelled with methodology of maintaining near constant angle of attack during real flight.