Lines, Symbols, and Drawing Interpretation

4-16

Lines and Their Meanings

Every drawing is composed of lines. Lines mark the boundaries, edges, and intersection of surfaces. Lines are used to show dimensions and hidden surfaces and to indicate centers. Obviously, if the same kind of line is used to show these variations, a drawing becomes a meaningless collection of lines. For this reason, various kinds of standardized lines are used on aircraft drawings. [Figure 4-24] Examples of correct line uses are shown in Figure 4-25. Most drawings use three widths, or intensities, of lines: thin, medium, or thick. These lines may vary somewhat on different drawings, but there is a noticeable difference between a thin and a thick line, with the width of the medium line somewhere between the two.

Centerlines Centerlines are made up of alternate long and short dashes. They indicate the center of an object or part of an object. Where centerlines cross, the short dashes intersect 4-17 Output Relay AC Input Phase A Phase B Phase C Voltage Selector Comparator Reference Voltage DO PU Power Amplifier Signal Conditioning and Balancing Signal Conditioning and Balancing Signal Conditioning and Balancing symmetrically. In the case of very small circles, the centerlines may be shown unbroken. Dimension Lines A dimension line is a light solid line, broken at the midpoint for insertion of measurement indications, and having opposite pointing arrowheads at each end to show origin and termination of a measurement. They are generally parallel to the line that the dimension is given for, placed outside the outline of the object, and between views if more than one view is shown.

All dimensions and lettering are placed so that they read from left to right. The dimension of an angle is indicated by placing the degree of the angle in its arc. The dimensions of circular parts are always given in terms of the diameter of the circle and are usually marked with the letter D or the abbreviation DIA following the dimension. The dimension of an arc is given in terms of its radius and is marked with the letter R following the dimension. Parallel dimensions are placed so that the longest dimension is farthest from the outline and the shortest dimension is closest to the outline of the object. On a drawing showing several views, the dimensions are placed upon each view to show its details to the best advantage.

In dimensioning distances between holes in an object, dimensions are usually given from center to center rather than from outside to outside of the holes. When several holes of various sizes are shown, the desired diameters are given on a leader followed by notes indicating the machining operations for each hole. If a part is to have three holes of equal size, equally spaced, this information is explicitly stated. For precision work, sizes are given in decimals. Diameters and depths are given for counterbored holes. For countersunk holes, the angle of countersinking and the diameters are given. [Figure 4-26] The dimensions given for tolerances signify the amount of clearance allowable between moving parts. A positive allowance is indicated for a part that is to slide or revolve upon another part. A negative allowance is one given for a force fit. Whenever possible, the tolerance and allowances for desired fits conform to those set up in the American Standard for Tolerances, Allowances, and Gauges for Metal Fits. The classes of fits specified in the standard may be indicated on assembly drawings.

Extension Lines Extensions are used to extend the line showing the side or edge of a figure for placing a dimension to that side or edge. They are very narrow and have a short break where they extend from the object and extend a short distance past the arrow of the dimensioning line. Sectioning Lines Sectioning lines indicate the exposed surfaces of an object in a sectional view. They are generally thin full lines, but may vary with the kind of material shown in section. Phantom Lines Phantom lines indicate the alternate position of parts of the object or the relative position of a missing part. They are composed of one long and two short evenly spaced dashes.

4-18 34 – 25 – 12 34 – 51 – 01 34 – 16 – 12 34 – 24 – 01 WIRING DIAGRAM FLIGHT DIRECTOR BOTH ON 2 BOTH ON 1 93 J3A 33 J1A J1B 33 50 J1A J1B 50 J2A 37 J2A J3A 69 J3A J2A 36 J2A J1 31 J1 J2B 79 J2B J1 33 J1 J2A 37 J2A J3A 69 J3A J4A 45 J4A J1A 45 J1 44 J1 J2A 35 J2A J1 42 J1 J2B 64 J2B 48 J1A J4A 48 J4A 48 J1A J4A 48 J4A 45 J4A J1A 45 J3A 1A 1B 2A 2B J3A 93 J3A DIGITAL FLIGHT GUIDANCE COMPUTER-1 22-01-01 UIO - 212 DIGITAL FLIGHT GUIDANCE COMPUTER-2 22-01-01 UIO - 213 ATTITUDE SWITCHING UNIT 34 - 23 UIO - 228 AIR DATA INST SWITCHING UNIT 34 - 14 UIO - 207 M S1 S2 C E N T R A L P R O C E S O R C E N T R A L P R O C E S O R S1 S2 NORMAL L ON AUX NORMAL BOTH ON 2 BOTH ON 1 NORMAL R ON AUX NORMAL Break Lines Break lines indicate that a portion of the object is not shown on the drawing. Short breaks are made by solid, freehand lines. For long breaks, solid ruled lines with zigzags are used.

Shafts, rods, tubes, and other such parts that have a portion of their length broken out have the ends of the break drawn as indicated in Figure 4-25. Leader Lines Leader lines are solid lines with one arrowhead. They indicate a part or portion that a note, number, or other reference applies. Hidden Lines Hidden lines indicate invisible edges or contours. Hidden lines consist of short dashes evenly spaced and are frequently referred to as dash lines. Outline or Visible Lines The outline or visible line is used for all lines on the drawing representing visible lines on the object. This is a medium-to- wide line that represents edges and surfaces that can be seen when the object is viewed directly.

Stitch Lines Stitch lines are used to indicate the stitching or sewing lines on an article and consists of a series of very short dashes, approximately half the length of dash or hidden lines, evenly spaced. Long lines of stitching may be indicated by a series of stitch lines connected by phantom lines. 4-19 EXCESSIVE QUALITY CHECK / NDT PERMANENT COMPOSITE REPAIR ACCORDING TO APPROVED GUIDELINES RETURN TO SERVICE SUBMIT/ CHECK SCHEME WITH MANUFACTURER /OEM APPROVED TEMPORARY REPAIR IMPROVISE AND RETURN TO REPAIR WORKSHOP TEMPORARY REPAIR TYPE DAMAGE ASSESSMENT SCRAP COMPLEX REPAIR EASY REPAIR Cutting Plane and Viewing Plane Lines Cutting plane lines indicate the plane where a sectional view of the object is taken. In Figure 4-25, plane line A indicates the plane that section AA is taken. Viewing plane lines indicate the plane from where a surface is viewed.

Drawing Symbols

The drawings for a component are composed largely of symbols and conventions representing its shape and material. Symbols are the shorthand of drawing. They graphically portray the characteristics of a component with a minimal amount of drawing. Material Symbols Section line symbols show the kind of material from which the part is to be constructed. The material may not be indicated symbolically if its exact specification is shown elsewhere on the drawing. In this case, the more easily drawn symbol for cast iron is used for the sectioning, and the material specification is listed in the bill of materials or indicated in a note. Figure 4-27 illustrates a few standard material symbols.

Shape Symbols Symbols can be used to excellent advantage when needed to show the shape of an object. Typical shape symbols used on aircraft drawings are shown in Figure 4-28. Shape symbols are usually shown on a drawing as a revolved or removed section. Electrical Symbols Electrical symbols represent various electrical devices rather than an actual drawing of the units. [Figure 4-29] Having learned what the various symbols indicate, it becomes relatively simple to look at an electrical diagram and determine what each unit is, what function it serves, and how it is connected in the system.

Reading and Interpreting Drawings

Aircraft technicians do not necessarily need to be accomplished in making drawings. However, they must have a working knowledge of the information that is to be conveyed to them. They most frequently encounter drawings for construction and assembly of new aircraft and components, during modifications, and for making repairs. A drawing cannot be read all at once any more than a whole page of print can be read at a glance. Both must be read one line at a time. To read a drawing effectively, follow a systematic procedure. Upon opening a drawing, read the drawing number and the description of the article. Next, check the model affected, the latest change letter, and the next assembly listed. Having determined that the drawing is the correct one, proceed to read the illustration(s).

In reading a multiview drawing, first get a general idea of the shape of the object by scanning all the views. Then select one view for a more careful study. By referring back and forth to the adjacent view, it is possible to determine what each line represents. Each line on a view represents a change in the direction of a surface, but another view must be consulted to determine what the change is. For example, a circle on one view may mean either a hole or a protruding boss, as in the top view of the object in Figure 4-30. Looking at the top view, we see two circles. However, the other view must be consulted to 4-20 GEAR DOOR OPEN LEFT NOSE RIGHT PROXIMITY DETECTOR PROXIMITY DETECTOR POWER SUPPLY 27 – 02 27 – 23 27 – 60 27 – 61 27 – 83 27 – 84 31 – 51 32 – 15 32 – 62 32 – 63 52 – 61 52 – 70 OTHER PROXIMITY UNIT SCHEMATICS RETARDED THROTTLE GROUND IS SEE 00 - 04 CLOSE TARGET • LOGIC "1" • LOW VOLTAGE (TEST POINTS ONLY) DOWN B LOCKED DOWN UP 2 1 UP DN LANDING GEAR HANDLE SWITCH S1 - 89 32 - 62 LANDING GEAR WARNING B1 - 187 AUTOSPOILER SWITCHING UNIT B5 - 70 27 - 61 LANDING GEAR POSITION INDICATOR 32 - 61 - 04 CENTRAL AURAL WARNING UNIT B5 - 71 SEE 32 - 63 FDAU UIO-206 31 - 31 B5 - 74 DIM & TEST UNIT-1 33 - 11 B5 - 76 DIM & TEST UNIT 3 33 - 11 ALTERNATE GEAR LEVER SWITCH S1 - 466 32 - 62 TURNS ON RED LIGHT PROXIMITY SWITCH ELECTRONICS UNIT 32 - 61 - OI B5 - 80 NOSE GEAR POS INTLK LEFT SWITCH L2-265 32-61-03 A G R TEST DIM G RUNSAFE DIM B TEST UNIT-2 B5-75 33-11 SAFE R2-262 D HDL HOT ON HDL ON SI-412 32-35 NOSE GEAR WARNED LIKE MAIN PRIOR TO 1,024 GEAR INTERLOCK 32-62 SHIP 1,024 & SUBS OR S832 - 17B L2-632 G R TEST DIMU CC DD G Z B I Y A O F D P S 19 39 40 28 29 26 27 16 17 14 15 6 7 53 54 41 42 5 4 37 J1A R MAIN R GEAR UP & LATCHED 2B VDC - L L GEAR UP & LATCHED NOSE L MAIN A 19 GEAR HDL ON ONE NOT WIRED 36 RIGHT AFT RADIO RACK - SHELF 1 18 11 10 E B C D 9 8 20 28 30 28 30 28 30 34 27 29 27 29 27 29 33 44 51 56 57 61 62 24 1 2 3 50 49 47 34 46 6B 12B A9 43 20 18 2 1 3 1 2 1 2 1 32 – 61 – 00 27 – 61 – 11 WIRING DIAGRAM determine what each circle represents.

A glance at the other view tells us that the smaller circle represents a hole, and the larger circle represents a protruding boss. In the same way, the top view must be consulted to determine the shape of the hole and the protruding boss. It can be seen from this example that one cannot read a print by looking at a single view when more than one view is given. Two views do not always describe an object and when three views are given, all three must be consulted to be sure the shape has been read correctly. After determining the shape of an object, determine its size. Information on dimensions and tolerances is given so that certain design requirements may be met. Dimensions are indicated by figures either with or without the inch mark. If no inch mark is used, the dimension is in inches. It is customary to give part dimensions and an overall dimension that gives the greatest length of the part. If the overall dimension is 4-21 ³⁄16 DRILL 3 HOLES EQUALLY SPACED ¹⁄4 DRILL ⁷⁄16 C’BORE ¹⁄8 DEEP 2 HOLES 80° 0.3125 DRILL 0.3217 REAM ³⁄16 DRILL 80° C’SK TO ⁵⁄16 DIA 0.2560 DRILL ¹⁄4 DRILL, ³⁄6 C’BORE ¹⁄8 DEEP, 3 HOLES A Phantom line Center line Sectioning line Outline Hidden line Break line Cutting plane line Section AA Dimension line Extension line Center line Thin Dimension Thin Extension line Thin Break (long) Thin Break (long) Thick Phantom Thin Sectioning Thin Hidden Medium Stitch line Medium Visible line Thick Datum line Thick Cutting plane Extra thick Complex cutting plane Extra thick missing, it can be determined by adding the separate part dimensions. Many drawings used for new aircraft and components are now using the metric system and millimeter (mm) is the unit used for these drawings.

Drawings may be dimensioned in decimals or fractions. This is especially true about tolerances. Instead of using plus and minus signs for tolerances, many figures give the complete dimension for both tolerances. For example, if a dimension is 2 inches with a plus or minus tolerance of 0.01, the drawing would show the total dimensions as: 2.01 1.99 A print tolerance (usually found in the title block) is a general tolerance that can be applied to parts where the dimensions are noncritical. Where a tolerance is not shown on a dimension line, the print tolerance applies. To complete the reading of a drawing, read the general notes and the content of the material block, find the various changes incorporated, and read the special information given in or 4-22 CAST IRON STEEL BRASS, BRONZE, AND COPPER WOOD— ACROSS GRAIN CORK, FELT, FABRIC, ASBESTOS, LEATHER, AND FIBER RUBBER, PLASTIC ELECTRICAL INSULATION MAGNESIUM, ALUMINUM, AND ALUMINUM ALLOYS WOOD— WITH GRAIN BABBITT, LEAD, ZINC, AND ALLOYS near views and sections.

Drawing Sketches

A sketch is a simple rough drawing that is made rapidly and without much detail. Sketches may take many forms— from a simple pictorial presentation to a multi-view orthographic projection. Just as aircraft technicians need not be highly skilled in creating drawings, they need not be accomplished artists. However, in many situations, they need to prepare a drawing to present an idea for a new design, a modification, or a repair method. The medium of sketching is an excellent way of accomplishing this. The rules and conventional practices for making mechanical drawings are followed to the extent that all views needed to portray an object accurately are shown in their proper relationship. It is also necessary to observe the rules for correct line use and dimensioning. [Figures 4-24 and 4-25] Sketching Techniques To make a sketch, first determine what views are necessary to portray the object. Then block in the views using light construction lines. Next, complete the details, darken the object outline, and sketch extension and dimension lines.

Complete the drawing by adding notes, dimensions, title, date, and when necessary, the sketcher’s name. The steps in making a sketch of an object are illustrated in Figure 4-31. Basic Shapes Depending on the complexity of the sketch, basic shapes may be drawn in freehand or by use of templates. If the sketch is quite complicated or the technician is required to make frequent sketches, use of a variety of templates and other drafting tools is highly recommended. Repair Sketches A sketch is frequently drawn for repairs or for use in manufacturing a replacement part. Such a sketch must provide all necessary information to those who must make the repair or manufacture the part.

The degree that a sketch is complete depends on its intended use. Obviously, a sketch used only to represent an object pictorially need not be dimensioned. If a part is to be manufactured from the sketch, it should show all the necessary construction details. Care of Drafting Instruments Good drawing instruments are expensive precision tools. Reasonable care given to them during their use and storage can prolong their service life. T-squares, triangles, and scales should not be used or placed where their surfaces or edges may be damaged. Use a drawing board only for its intended purpose and not in a manner that can mar the working surface.

Compasses, dividers, and pens provide better results with less annoyance, if they are correctly shaped and sharpened and are not damaged by careless handling. Store drawing instruments in a place where they are not likely to be damaged by contact with other tools or equipment. Protect compass and divider points by inserting them into a piece of soft rubber or similar material. Never store ink pens without first cleaning and drying them thoroughly. 4-23 SQUARE SECTION (METAL) SQUARE SECTION (WOOD) ROUND SECTION (SOLID) ROUND SECTION (TUBULAR) ANGLE SECTION (METAL) CHANNEL SECTION (METAL) I-BEAM (METAL) SQUARE SECTION (TABULAR)

Graphs & Charts

Graphs and charts are frequently used to convey information graphically or information given certain conditions. They often utilize values shown on the “x” and “y” axes that can be projected up and across to arrive at a specific result. Also, when data is entered into a computer database, software programs can create a variety of different bar graphs, pie charts, and so forth, to graphically represent that data. Reading & Interpreting Graphs & Charts When interpreting information shown on graphs and charts, it is extremely important that all the notes and legend information be carefully understood to eliminate any misinterpretation of the information presented.

Nomograms A nomogram is a graph that usually consists of three sets of data. Knowledge of any two sets of data enables the interpreter to obtain the value for the third unknown corresponding value. One type of nomogram consists of three parallel scales graduated for different variables, so that when a straight edge connects any two values, the third can be read directly. Other types may use values on the “x” and “y” axes of a graph with the third corresponding value determined by the intersection of the “x” and “y” values with one of a series of curved lines. Figure 4-32 is an example of a nomogram that shows the relationship between aviation fuels, specific weight, and temperature.

Microfilm & Microfiche The practice of recording drawings, parts catalogs, and maintenance and overhaul manuals on microfilms was utilized extensively in the past. Microfilm is available as regular 16 mm or 35 mm film. Since 35 mm film is larger, it provides a better reproduction of drawings. Microfiche is a card with pages laid out in a grid format. Microfilm and microfiche require use of special devices for both reading and printing the information. Most modern aircraft manufacturers have replaced microfilm and microfiche with digital storage methods utilizing CDs, DVDs, and other data storage devices. A great deal of service and repair information for older aircraft has been transferred to digital storage devices. However, there may still be a need to access information using the old methods. A well-equipped shop should have available, both the old microfilm and microfiche equipment, as well as new computer equipment.

Digital Images Though not a drawing, a digital image created by a digital camera can be extremely helpful to aviation maintenance technicians in evaluating and sharing information concerning the airworthiness or other information about aircraft. Digital images can be rapidly transmitted over the World Wide Web as attachments to e-mail messages. Images of structural fatigue cracks, failed parts, or other flaws, as well as desired design and paint schemes, are just a few examples of the types of digital images that might be shared by any number of users over the Internet. Figure 4-33 is a digital image of damage to a composite structure taken with a simple digital camera.

4-24 CONDENSERS CONDUCTORS SINGLE INTERSECTING ELECTRICALLY CROSSING OVER EACH OTHER RELAYS SPST MOMENTARY ON SPDT NORMAL OR MOMENTARY CONTACTS MPDT NORMAL OR MOMENTARY CONTACTS CIRCUIT BREAKERS AUTOMATIC RESET PUSH RESET PUSH RESET PULL OFF SWITCH TYPE MOMENTARY SWITCH TYPE SWITCHES FUSE SPLICE CONTACTS PUSHBUTTON TYPE POLARITYGROUND 10A BASIC ELECTRICAL DISCONNECT SPST MPST MECHANICAL LINKAGE MOMENTARY POSITION NORMAL POSITION MPDT CENTER OFF SPST MOMENTARY ON SPDT CENTER OFF SPDT MOMENTARY ON SPDT SPDT CENTER OFF NORMAL OR MOMENTARY CONTACTS SPDT NORMAL OR MOMENTARY ON NORMAL ON POSITIVE NEGATIVE NORMAL OR MOMENTARY CONTACTS PRESSURE BIMETALIC THERMAL CUT-OUT MOTORS ACDC GENERATORS ACDC CONNECTORS METERS AMMETERVOLT LAMPS − RED, GREEN, WHITE RHEOSTATRESISTOR BUSBATTERY CURRENT LIMITER SOLENOIDTRANSFORMER A B C D P S FIXEDREMOVABLE P DESIGNATED PINS S DESIGNATED SOCKETS NOT ALL PINS SHOW ALL PINS SHOW S P A B C D E V A M+ − G+ −M GM GOR OR RL G W OR +DC − 4-25 Block in Add Detail Darken Views Add Dimensions 1-27-06 WEDGE RJA 1¼" 1" ¾" 1½" 1¼" 3" To provide information about the extent of the damage, a measurement scale, or other object, such as a coin, can be placed near the area of concern before the picture is taken.

Also, within the text of the e-mail, the technician should state the exact location of the damage, referenced to fuselage station, wing station, and so forth. 4-26 7.5 7.0 6.5 6.0 5.5 −40 −30 −20 −10 0 10 20 30 40 Specific Weight (lb/US gal) Temperature (°C) Aviation Gasoline Grade 100/130 Aviation Kerosene Jet A & Jet A1 Jet B (JP-4) NOTE: The fuel quantity indicator is calibrated for correct indication when using Aviation Kerosene Jet A and Jet A1. When using other fuels, multiply the indicated fuel quantity in pounds by 0.99 for Jet B (JP-4) or by 0.98 for Aviation Gasoline (100/130) to obtain actual fuel quantity in pounds.

Fuel Aviation Kerosene Jet A and Jet A1 Jet B (JP-4) AV Gas Grade 100/130 0.785 0.812 0.703 Average Specific Gravity at 15 °C (59 °F) Density Variation of Aviation Fuel Based on Average Specific Gravity