Drawing Types and Document Control

4-1

Aircraft Drawings

Chapter 4

Introduction

The exchange of ideas is essential to everyone, regardless of their vocation or position. This exchange is usually carried on by oral or written word; but under some conditions, the use of these alone is impractical. The aviation industry discovered that it could not depend entirely upon written or spoken words for the exchange of ideas, because misunderstanding and misinterpretation arose frequently. A written description of an object can be changed in meaning just by misplacing a comma, and the meaning of an oral description can be completely changed by using a wrong word. To avoid these possible errors, drawings are used to describe objects. For this reason, drawing is the draftsman’s language.

Drawing, in the aviation industry, is a method of conveying ideas concerning the construction or assembly of objects. This is done with the help of lines, notes, abbreviations, and symbols. It is important that the aviation mechanic who is to make or assemble the object understands the meaning of the different lines, notes, abbreviations, and symbols that are used in a drawing. (See the “Lines and Their Meanings” section of this chapter.) Computer Graphics From the early days of aviation, development of aircraft, aircraft engines, and other components relied heavily on aircraft drawings. For most of the 20 th century, drawings were created on a drawing “board” with pen or pencil and paper. With the introduction and advancement of computers in the later decades of the 20 th century, the way drawings are created changed dramatically. Computers were used not only to create drawings, but they were being used to show items in “virtual reality,” from any possible viewing angle. Further development of computer software programs allowed for assembling of separately created parts to check for proper fit and possible interferences. Additionally, with nearly instantaneous information sharing capability through computer networking and the Internet, it became much easier for designers to share their work with other designers and manufacturers virtually anytime, anywhere in the world.

Using new computer-controlled manufacturing techniques, it became possible to design a part and have it precisely manufactured without ever having shown it on paper. New terms and acronyms became commonplace. The more common of these terms are: • Computer Graphics—drawing with the use of a computer • Computer Aided Design (CAD)—where a computer is used in the design of a part or product • Computer Aided Design Drafting (CADD)—where a computer is used in the design and drafting process • Computer Aided Manufacturing (CAM)—where a computer is used in the manufacturing of a part or product • Computer Aided Engineering (CAE)—where a computer is used in the engineering of a part or product As computer hardware and software continue to evolve, a greater amount of CAE is completed in less time, at lower cost. In addition to product design, some of the other uses of CAE are product analysis, assembly, simulations, and maintenance information. [Figure 4-1] CATIA, ProEngineer, Solid Works, and Unigraphics are some of the more popular CAD software packages used for aircraft design and manufacturing. Most airframe manufacturers use CATIA software to design their aircraft. The complete aircraft is designed and assembled in the software package before it is manufactured. Drawings of all parts of the aircraft are available and can be accessed using the computer software.

Drawings are no longer limited to 1, 2, or 3 views. Drawings from every angle can easily be accessed by using the computer model of the part or product. Technicians can access drawings and aircraft manuals on laptops or even mobile devices when performing maintenance on the shop floor.

Purpose & Function of Aircraft Drawings

Drawings and prints are the link between the engineers who design an aircraft and the workers who build, maintain, and repair it. A print may be a copy of a working drawing for an aircraft part or group of parts, or for a design of a system or group of systems. They are made by placing a tracing of the drawing over a sheet of chemically-treated paper and exposing it to a strong light for a short period of time. When the exposed paper is developed, it turns blue where the light has penetrated the transparent tracing. The inked lines of the tracing, having blocked out the light, show as white lines on a blue background. With other types of sensitized paper, prints may have a white background with colored lines or a colored background with white lines.

Drawings created using computers may be viewed on the computer monitor or printed out in “hard copy” by use of an 4-2 ink jet or laser printer. Larger drawings may be printed by use of a plotter or large format printer. Large printers can print drawings up to 42 inches high with widths up to 600 inches by use of continuous roll paper. [Figure 4-2]

Care & Use of Drawings

Drawings should be handled carefully as they are both expensive and valuable. Open drawings slowly and carefully to prevent tearing of the paper. When the drawing is open, smooth out the fold lines instead of bending them backward. To protect drawings from damage, never spread them on the floor or lay them on a surface covered with tools or other objects that may make holes in the paper. Hands should be free of oil, grease, or other unclean matter that can soil or smudge the print. Never make notes or marks on a print, as they may confuse others and lead to incorrect work. Only authorized individuals are permitted to make notes or changes on prints, and they must sign and date any changes they make.

When finished with a drawing, fold and return it to its proper place. Prints are folded originally in an appropriate size for filing. Care should be taken so that the original folds are always used.

Types of Drawings

Drawings must give information such as size and shape of the object and all its parts, specifications for material to be used, how the material is to be finished, how the parts are to be assembled, and any other information essential to making and assembling the object. Drawings may be divided into three classes: detail, assembly, and installation. Detail Drawing A detail drawing is a description of a single part, describing bylines, notes, and symbols the specifications for size, shape, material, and methods of manufacture to be used in making the part. Detail drawings are usually rather simple. When single parts are small, several detail drawings may be shown on the same sheet or print. [Figure 4-3] Assembly Drawing An assembly drawing is a description of an object made up of two or more parts. [Figure 4-4] It describes the object’s size and shape. Its primary purpose is to show the relationship of the various parts. An assembly drawing is usually more complex than a detail drawing and is often accompanied by detail drawings of various parts.

Installation Drawing An installation drawing is one that includes all necessary information for a part or an assembly in the final installed position in the aircraft. It shows the dimensions necessary for the location of specific parts with relation to the other parts and reference dimensions that are helpful in later work in the shop. [Figure 4-5] Sectional View Drawings A section or sectional view is obtained by cutting away part of an object to show the shape and construction at the cutting plane. The part or parts cut away are shown by using section (crosshatching) lines. Types of sections are described in the following paragraphs.

Full Section A full section view is used when the interior construction or hidden features of an object cannot be shown clearly by exterior views. For example, Figure 4-6 is a sectional view of a cable connector and shows the internal construction of the connector. Half Section In a half section, the cutting plane extends only halfway across the object, leaving the other half of the object as an exterior view. Half sections are used with symmetrical objects to show both the interior and exterior. Figure 4-7 is a half sectional view of a Capstan servo. Revolved Section A revolved section drawn directly on the exterior view shows the shape of the cross section of a part, such as the spoke of a wheel. An example of a revolved section is shown in 4-3 Removed Section A removed section illustrates parts of an object. It is drawn like revolved sections, except it is placed at one side and often drawn to a larger scale than the view indicated to bring out pertinent details.

A-A shows the cross-sectional shape of the object at cutting plane line A-A. Section B-B shows the cross-sectional shape at cutting plane line B-B. These sectional views are drawn to the same scale as the principal view.

Title Blocks

Every print must have some means of identification. This is provided by a title block. [Figure 4-4A] The title block consists of a drawing number and certain other data concerning the drawing and the object it represents. This information is grouped in a prominent place on the print, usually in the lower right-hand corner. Sometimes the title block is in the form of a strip extending almost the entire distance across the bottom of the sheet. Although title blocks do not follow a standard form as far as layout is concerned, all of them present essentially the following information: 1. A drawing number to identify the print for filing purposes and to prevent confusing it with any other print.

2. The name of the part or assembly 3. The drawing scale 4. The date 5. The name of the firm 6. The name of the draftsmen, the checker, and the person approving the drawing Drawing or Print Numbers All prints are identified by a number that appears in a number block in the lower right corner of the title block. It may also be shown in other places—such as near the top border line, in the upper right corner, or on the reverse side of the print at both ends—so that the number shows when the print is folded or rolled. The purpose of the number is quick identification of a print. If a print has more than one sheet and each sheet has the same number, this information is included in the number block, indicating the sheet number and the number of sheets in the series. [Figure 4-4B] Reference and Dash Numbers Reference numbers that appear in the title block refer you to the numbers of other prints. When more than one detail is shown on a drawing, dash numbers are used. Both parts would have the same drawing number plus an individual number, such as 40267-1 and 40267-2.

In addition to appearing in the title block, dash numbers may appear on the face of the drawing near the parts they identify. Dash numbers are also used to identify right-hand and left-hand parts. In aircraft, many parts on the left side are like the corresponding parts on the right side but in reverse. The left- hand part is always shown in the drawing. The right-hand part is called for in the title block. Above the title block a notation is found, such as: 470204-1LH shown; 470204-2RH opposite. Both parts carry the same number, but the part called for is distinguished by a dash number. Some prints have odd numbers for left-hand parts and even numbers for right-hand parts.

Universal Numbering System The universal numbering system provides a means of identifying standard drawing sizes. In the universal numbering system, each drawing number consists of six or seven digits. The first digit is always 1, 2, 4, or 5 and indicates the size of the drawing. The number 1 indicates a drawing of 8½" × 11"; number 2 indicates an 11" × 17" drawing; number 4 represents a drawing of 17" × 22"; and 5 indicates a width of between 17 and 36 inches but on a continuous roll. Letters are also used (and becoming more prevalent) with the most common letters being A through E. The letter A is 8½" × 11", B is 11" × 17", C is 17" × 22", D is 22" × 34" and E is 34" × 44". There are additional letters, such as D1 at 24" × 36", E1 at 30" × 42" and additional sizes unique to even larger formats but generally reserved for inter-company operations.

The remaining digits identify the drawing. Many firms have modified this basic system to conform to their needs. The letter or number depicting the standard drawing size may be 4-4 FLAT PATTERN FOR REFERENCE ONLY -03 D C B AA B C D 12345678 8 7 6 5 4 3 2 1 REVISIONS FOR REVISION HISTORY SEE SHEET 1 SHEET 3 OF 3 SWorks Drawing No.:SIZE 4-5 3 6 5 2 -01 REVISIONS - ITEM 8 6 S-TEC 5 S-TEC 12 S-TEC 1 3 -03 S-TEC 1 2 -02 S-TEC 1 -01 S-TEC D C AA B C D 12345678 8 7 6 5 4 3 2 1 TITLE: SIZE Drawing No.: SHEET 1 OF 3 EC130T2 125 B CWHITWORTH FORM (SWorks) 86359 REV - Zone Numbers F Allowances and ToleranceG C. Bill of MaterialsC Title BlockA ScaleH Drawing NumberB Revision BlockD NotesE 4-6 REF 1 2 C 2 8 (REF) 9 5 2 REF 8 11 10 11 12 2 REF 1 REF 3 6 D C B AA B C D 12345678 8 7 6 5 4 3 2 1 REVISIONS FOR REVISION HISTORY SEE SHEET 1 SHEET 3 OF 3 SWorks Drawing No.:SIZE FORM 86359 REV - REV 4-7 prefixed to the number, separated from it by a dash. Other numbering systems provide a separate box preceding the drawing number for the drawing size identifier. In another modification of this system, the part number of the depicted assembly is assigned as the drawing number.

Drawing Standards

Drawing standards cover such items as paper sizes, notes, numbering systems, geometric dimensions and tolerances, abbreviations, welding symbols, roughness symbols, and electrical symbols. These standards cover metric and inch measurements, as well as computer-drafting standards. Different standards for drawings are used in industry and some of the more common ones are published by the International Organization for Standardization (ISO) and the American National Standards Institute (ANSI). Bill of Material A list of the materials and parts necessary for the fabrication or assembly of a component or system is often included on the drawing. The list is usually in ruled columns that 4-8 AA BB SECTION A-A SECTION B-B provide the part number, name of the part, material the part is to be constructed of, the quantity required, and the source of the part or material. A typical bill of material is shown in Figure 4-4C . On drawings that do not have a bill of material, the data may be indicated directly on the drawing.

On assembly drawings, each item is identified by a number in a circle or square. An arrow connecting the number with the item assists in locating it in the bill of material. Other Drawing Data Revision Block Revisions to a drawing are necessitated by changes in dimensions, design, or materials. The changes are usually listed in ruled columns either adjacent to the title block or at one corner of the drawing. All changes to approved drawings must be carefully noted on all existing prints of the drawing. When drawings contain such corrections, attention is directed to the changes by lettering or numbering them and listing those changes against the symbol in a revision block. [Figure 4-4D] The revision block contains the identification symbol, the date, the nature of the revision, the authority for the change, and the name of the draftsman who made the change.

To distinguish the corrected drawing from its previous version, many firms are including, as part of the title block, a space for entering the appropriate symbol to designate that the drawing has been changed or revised. Notes Notes are added to drawings for various reasons. Some of these notes refer to methods of attachment or construction. Others give alternatives, so that the drawing can be used for different styles of the same object. Still others list modifications that are available. Notes may be found alongside the item that they refer to. If the notes are lengthy, they may be placed elsewhere on the drawing and identified by letters or numbers.

Notes are used only when the information cannot be conveyed in the conventional manner or when it is desirable to avoid crowding the drawing. Figure 4-4E illustrates one method of depicting notes. When the note refers to a specific part, a light line with an arrowhead leads from the note to the part. If it applies to more than one part, the note is worded to eliminate ambiguity as to the parts it pertains to. If there are several notes, they are generally grouped together and numbered consecutively. Zone Numbers Zone numbers on drawings are like the numbers and letters printed on the borders of a map. They help locate a point.

To find a point, mentally draw horizontal and vertical lines from the letters and numerals specified; the point where these lines intersect is the area sought. Figure 4-4F shows the zone numbers on a drawing. Use the same method to locate parts, sections, and views on large drawings, particularly assembly drawings. Parts numbered in the title block can be located on the drawing by finding the numbers in squares along the lower border. Zone numbers read from right to left. Station Numbers & Location Identification on Aircraft A numbering system is used on large assemblies for aircraft to locate stations, such as fuselage frames. Fuselage station 185 indicates a location that is 185 inches from the datum of the aircraft. The measurement is usually taken from the nose or zero station, but in some instances, it may be taken from the firewall or some other point chosen by the manufacturer.

Just as forward and aft locations on aircraft are made by