Wet resistance force in aircraft fuel pipe and its optical measurement

A kind of method by means of laser was suggested and experimental set-up was constructed to study wet resistance in fuel pipe and its measurement. The wet resistance force would be acted on the fluid by the surface of the pip because of the wet effect between the liquid and the pip surface. The expression of wet resistance force was derived under small pip condition based on the liquid principle. A laser measurement set-up was constructed based on the light reflected from curved liquid surface and automatic electron-optics detection. The diameter of the special optics pattern depended on both the aperture diameter and curved degree of liquid surface. The analytic expression of light pattern diameter related with the slope of curved liquid surface and aperture diameter was arrived theoretically. The force depended linearly on the liquid surface tension and cosine of contact angle. A special pattern reflected from curved liquid surface was observed which was circle with clear interference fringes. The slop of liquid surface and contact angle was detected by means of the pattern scale and the experimental value of wet resistance force was archived. It has no-touch, no-damage and automatic properties.