Abstract
Induced drag constitutes approximately 40% of the total drag of subsonic civil transport aircraft at cruise conditions. Various types of winglets and several non-planar concepts, such as the C-wing, the joined wings, and the box plane, have been proposed for its reduction. Here, a new approach to induced drag reduction in the form of a combination of an elliptical and an astroid hypocycloid lift distribution is put forward. Lift is mainly generated from high circulation in the center part of the wing and fades away along the semi-span towards the wing tip. Using lifting line theory, the analysis shows that for fixed lift and wingspan the combined lift distribution results in an induced drag reduction of 50% with respect to the elliptical distribution. Due to its wing planform the combined lift distribution leads to a 51.5% higher aspect ratio. If structural constraints are placed, then the higher aspect ratio may affect wing weight. Although any substantial increase of wing weight is not envisaged, further study of the matter is required. Zero-lift drag and lift-dependent drag due to skin friction and viscosity-related pressure remain unaffected. The proposed lift distribution is particularly useful in a blended wing-body design.
Highlights
Fuel costs and greater awareness of the impact of emissions on the atmosphere raise the importance of fuel efficiency for future transport aircraft
As shown in the analysis the use of a combined elliptical and astroid hypocycloid lift distribution results in an induced drag coefficient reduction of 50% (equation(70))
The induced drag coefficient reduction of the combined elliptical and astroid hypocycloid lift distribution is two and a half times the reduction achieved by winglets (Whitcomb, 1976)
Summary
Fuel costs and greater awareness of the impact of emissions on the atmosphere raise the importance of fuel efficiency for future transport aircraft. The other option is to reduce induced drag by increasing wingspan efficiency factor Towards this end several concepts and schemes, such as winglets (Whitcomb, 1976; Chattot, 2006; Demasi et al, 2019) and non-planar lifting surfaces in the. Beyond the classification according to winglet designs and non-planar concepts, publications in the field of induced drag reduction range from reviews (Kroo, 2001) to specific issues (Taylor & Hunsaker, 2020a, 2020b; Phillips et al, 2019; Demasi, 2006). The elliptical lift distribution spans the center part and the astroid hypocycloid the outer parts of the wing This combined distribution reduces wing vortices by smoothly fading away lift towards the wing tip. The proposed lift distribution is examined as to its application to aircraft design
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