The Effect of Variations of the Height to Span Ratio of Box Wing Aircraft on Induced Drag and the Spanwise Lift Distribution

Autor: Maarten Waeterschoot

Datum: 13.07.2012



This project covers the effect of variations of the height to span (h/b) ratio of box wing aircraft on induced drag and the spanwise lift distribution. A box wing aircraft is an unconventional non planar configuration. It is comparable with a joined wing aircraft where the tips of the wings are connected. But for a box wing aircraft the tips are connected with winglets so it forms a rectangular box in the front view. This non planar configuration is known for its low induced drag and hence fuel reduction potential. The investigation is done using IDRAG, a program written by Joel Grasmeyer of Virginia Tech that calculates the distribution of the normal force coefficient, induced drag and span efficiency for non planar wings. The lift distribution of a box wing aircraft consists of a constant and an elliptical part. The magnitude and the variation in the shape of the lift distribution is investigated. Simple equations are derived. Equations from literature are compared with IDRAG results and a proposed new equation to calculate the span efficiency of box wings depending on the h/b ratio. According to this new equation span efficiency of box wings increases with increasing h/b ratio. The limit value for the span efficiency for h/b towards infinity e = 3.7.