AC 43 - 204 8/14/97 lection according to the application. They generally have a 55- degree field of view although fields of view can range from 10 to 90 degrees. The distal tips are generally not interchangeable, bility to rotate the optical shaft from 120 to 370 degrees for scanning purposes, and others have movable prisms at the tip for longitudinal scanning.
(1) Basic Design. The rigid borescope typically has a series of achromatic relay lenses in the optical tube.
lenses preserve the resolution of the image as it travels from the objective lens to the eyepiece. The tube diameter of these borescopes ranges from 0.035 to 2.75 inches. The illumination system can be either a distal lamp or a light-guide bundle, and the various features may include rotating optical shait, various viewing heads, and adjustable focusing of the objective lens.
(2) Micro-borescopes. Micro-borescopes are smalldiameter borescopes having an integral light-guide bundle and a one-piece rod lens for maximum resolution with a minimum diameter. Some typical uses for micro-borescopes in aircraft maintenance are inspection for damage within fuel nozzles, electronic components, instruments, hydraulic components, castings, and other miniature equipment. The lengths of micro borescopes range from 2 to 32 inches, and the diameters range from 0.020 to 0.125 inch. They are available with forward, forward oblique, and right angle views; support stands with micrometer adjustable fixturing; photo and video adapters; up to 30-power magnification;
and fixed or ocular focus. Figure 4-10 shows a typical microborescope.
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FIGURE 4-10. TYPICAL MICRO-BORESCOPE (Courtesy of Industry Technology, Inc.)
(3) Extendible Borescopes. Extendible borescopes allow the user to vary the length of the borescope tube by inserting extension tubes. Some typical uses for rigid extendible borescopes in aircraft maintenance are inspection for damage within turbine engine combustion cases and inspection for cracks in aircraft rear pressure bulkheads. Extendible borescopes are available with either a fiber-optic light guide or an incandescent lamp at the distal end. Extendible borescopes with an integral lamp have a maximum length of about 100 feet.
borescopes with a light-guide bundle are available with smaller tube diameters, but have shorter maximum lengths (approximately 30 feet).
work of several different borescopes. Therefore, when feasible for the inspection tasks involved, they can have the advantage of economy, adaptability, and less bulk and weight for easy transportation and use over the purchase and use of a different borescope for each inspection task. Interchangeable viewing heads are available for extendible borescopes. Figure 4-11 shows a typical extendible borescope.
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FIGURE 4-11. TYPICAL EXTENDIBLE BORESCOPE (Courtesy of Titan Tool Supply Company, Inc.)
Endoscopes. The endoscope is much like a borescope with a high-intensity light source, except that it has a superior optical system which remains constantly in focus from about 4 mm
(0.16 inch) to infinity. Actually, when the tip is about 4 mm rom the suriace, a magniiication oi about lux is achleved.
doscopes are available in diameters down to 1.7 mm (0.07 inch) and in lengths from 100 to 150 mm (4 to 6 inches).
(5) Mirror Adapters. Mirror adapters can be used to convert a direct-viewing borescope into a side-viewing borescope.
A mirror adapter is designed to fit over the tip of the borescope and reflect an image from the side of the borescope. However, there is some reduction in resolution and image contrast; therefore, not all applications are suitable for this device. A side, forward oblique, or retrospective viewing head provides better resolution and a higher degree of image contrast than a directviewing borescope with a mirror adapter. A mirror adapter also produces an inverse image and can produce unwanted reflections from the shaft.
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8/14/97 10 43-204
(6) Scanning. Some rigid borescopes have the ability to scan longitudinally along the axis of the shaft. A movable prism with a control at the handle accomplishes this scanning. Typically, the prism can shift the direction of view through an arc of 120 degrees. Figure 4-12 shows a typical scanning borescope.
lupus toscope Prem contro Abortiont connector FIGURE 4-12. TYPICAL SCANNING BORESCOPE (Courtesy of Richard Wolf Medical Instruments Corporation) Zooming Borescopes. This instrument does not entirely fit the definition of a rigid borescope; however, it is used for inspection of bores and cavities. The zooming borescope (see Figure 4-13) can be used in aircraft maintenance for checking the whole interior surface of tubing and bores for surface -inish, cracks, dirt, weld cracks, porosity, etc. It can also be ised for checking the finish and chamfer on interior "O" ring grooves and keyways. It is 3/4 inch in diameter and 4 inches long when fully extended and contains an objective lens that magnifies outward in a "v" shape configuration (fisheye lens). It can be used on holes from 3/16 to 5 inch diameter. The whole in- Chap 4 Par 404 Page 135
terior diameter will be in focus at all times. On larger diameters, the instrument would have to be tipped slightly to focus on a specific area of sidewall. The instrument is suitable for viewing parts from 1 inch to 20 feet in length. The focus can be adjusted by holding the instrument in one hand and turning the zoom with the other hand for sharper definition of any depth of field. The area is sharp and in focus at any given focal plane and will vary from about 6 inches to 5 feet, depending on the length of the part and distance from the instrument. For more detail beyond 5 feet, a magnification booster is available. The zooming borescope does not have its own light source, but relies on existing ambient light. Unless the part is very small in diameter, or standard room illumination is poor, no additional light source is necessary. should additional light be necessary, an inspection flashlight (see Table 3-8) can be held against the other end of the part.
FIGURE 4-13. ZOOM-A-BORE INSPECTION INSTRUMENT WITH
MAGNIFICATION BOOSTER ATTACHED (Courtesy of Titan Tool Supply Company, Inc.)
(8) Micro-Bore Viewing System. Small area borescope viewing systems exist for optical checking of bores and cavities (see Figure 4-14). This system does not fit the definition of a rigid borescope; however, it is used for inspection of bores and cavities. The system was designed to overcome the lighting limichap 4 Page 136 Par 404
tations of some of the micro-borescopes and will not break as easily as the small-diameter borescope probes. This optical device in the illustration comprises 17 different lenses on a rotary system, each with a predetermined focal length (minimum of
0.020 inch to a maximum of 10 inches). It can be used for the internal viewing of micro-bores, tubes, and cavities from 0.039 to 0.315 inch diameter, with depths up to 10 inches. The illumination system is adjustable and contains a 2.5 volt Halogen light bulb. For deep cavities, additional illumination may be necessary, which can be provided by a small diameter inspection light.
FIGURE 4-14. MICRO-BORE VIEWING SYSTEM (Courtesy of Titan Tool Supply Company, Inc.)
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The micro-bore viewing system can be used in aircraft maintenance for checking the inside of small tubes, miniature drilled, bored, and ground holes for surface finish, cracks, dirt, weld cracks, porosity, etc. It can also be used for inspecting the inside of miniature holes in turbine blades and valve bodies.
(9) Mirror Tube Viewing Systens. These systems allow the viewing of small holes and cavities and are meant to be inexpensive alternatives to a rigid borescope for some applications.
The system shown in Figure 4-15 allows the viewing of holes and cavities to a depth of 2 inches with 5-power magnification without any attachments. Included with the unit are two separate twist-on mirror tubes, a 0.196 inch diameter, with a viewing depth of 1 inch, and 0.236 inch diameter, which allows a viewing depth of 1.2 inches. Illumination is provided by a miniature Halogen light bulb projecting the illumination directly on the axis down the hole. Powered by two AA batteries.
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90° Viewing FIGURE 4-12' (courtesy of Titan Tool Supply MIRROR TUBE VIEWING SYSTEM Company, Inc.)
The mirror viewing system shown in Figure 4-16 is for viewing holes up to 68 inches in depth. The main probe can be 4 to 20 mm in diameter. The field of view is 30 to 70 degrees.
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AC 43—204 8/14/97 FIGURE 4-16. DEEP-HOLE MIRROR VIEWING SYSTEM (Courtesy of Instrument Technology, Inc.)
Flexible Borescopes. Flexible borescopes are generally used in applications that do not have a straight line access path to the area to be inspected. Some typical uses of flexible borescopes in aircraft maintenance are inspection of corrosion, Chap 4 Page 140 Par 404
cracks, and scratches on bore walls of castings; inspection for corrosion and cracks of wing stringers, wing attachment fittings, spars, and other aircraft structural members; inspection of engine cylinder sleeves, pistons, and valves for damage; and inspection of aircraft turbines for cracks, corrosion, damage by foreign objects, and erosion. The two types of flexible borescopes are flexible fiberscopes and flexible videoscopes.
Figure 4-17 shows some typical flaws seen through a flexible fiberscope D FIGURE 4-17. TYPICAL FLAWS SEEN THROUGH A FLEXIBLE FIBERSCOPE (Courtesy of Olympus Corporation) Chap 4 Par 404 Page 141
Flexible Fiberscopes. A typical flexible fiberscope consists of a fiber-optic light-guide bundle, a fiber-optic image-guide bundle, an objective lens, interchangeable viewing heads, and remote controls for articulation of the distal tip.
Flexible fiberscopes are available in diameters from 0.055 to 0.5 inch and in lengths of over 300 feet. The light-guide bundle is used to carry illumination from a remote source to the distal Since each fiber in the light-guide bundle transmits only illumination and not an image, the fibers do not have to be precisely aligned and are generally larger than those in the imageguide bundle. The image-guide bundle is used to carry the image formed by the objective lens back to the eyepiece, and the fibers in the image guide are precisely aligned so that they are in an identical relative position to each other at their terminations for proper image resolution. The diameter of the fibers in the image guide is a factor in obtaining good image resolution.
large number of small-diameter fibers in the image-guide will provide a bright image with high resolution (see Figure 4-18).
lich resolution allows the use of an obiective lens with a wider field of view and also allows magnification of the image at the eyepiece for better viewing of objects at the periphery of the image (see Figure 4-19). Interchangeable distal tips provide various directions and fields of view on a single fiberscope;
however, because the tip can be articulated for scanning purposes, distal tips with either a forward or side viewing direction are usually sufficient. Fields of view are typically 40 to 60 degrees, although they can range from 10 to 120 degrees. Most fiberscopes provide adjustable focusing of the objective lens.
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8/14/97 AC 43-204 Two views down a combustar con with the datal tip in the some pastion. A fiberscope with smaller diameter fibers and 40% more fibers in the image bundle provides better resolution (a) than a fiberscope Riben (b). Courtesy of Olympus Corporation FIGURE 4-18. COMPARISON VIEWS WITH DIFFERENT QUANTITIES OF
FIBERS IN THE FIBERSCOPE IMAGE BUNDLE (Courtesy of Olympus Corporation) chap 4 Par 404 Page 143