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The effect of size on the optimal shapes of gliding insects and seeds
Author(s) -
Ennos A. Roland
Publication year - 1989
Publication title -
journal of zoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.915
H-Index - 96
eISSN - 1469-7998
pISSN - 0952-8369
DOI - 10.1111/j.1469-7998.1989.tb02565.x
Subject(s) - stall (fluid mechanics) , aspect ratio (aeronautics) , glider , drag , lift to drag ratio , wing , reynolds number , lift induced drag , mechanics , mass ratio , drag coefficient , lift (data mining) , wing loading , diameter ratio , aerodynamics , materials science , aerospace engineering , angle of attack , physics , computer science , marine engineering , engineering , composite material , turbulence , data mining
Conventional aerodynamic arguments suggest that possession of high aspect ratio wings will always improve the flight performance of glides. Drag and power will be minimized at intermediate flight speeds. It is shown, however, that as the aspect ratio increases, these minimum drag speeds are reduced, and will fall below the stall speed of the glider. This will happen at lower aspect ratios in small gliders, which operate at higher profile drag coefficients. Increasing the aspect ratio further will improve performance less than this analysis suggests. A detailed analysis is developed to calculate the optimum shape of small gliders. Profile drag increases with aspect ratio, owing to the fall in the Reynolds number, while induced drag falls with increasing aspect ratio. Minimum drag will be encountered and hence the glide angle will be minimized at intermediate values of aspect ratio. Best glide angles are achieved at low speeds (high lift coefficients) and the optimum aspect ratio increases with the mass of the glider. Small natural gliders possess large, low aspect ratio wings. The aspect ratios are generally somewhat below those which would produce the best glide angle at stall speed, but should give a reasonable performance over a range of speeds.