General (2-1)

 

The exchange of ideas is essential to everyone, regardless of his or her vocation or position. Usually, this exchange is carried on by the oral or written word; but under some conditions, the use of these alone is impractical. 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; the meaning of an oral description can be completely changed by the use of a wrong word. To avoid these possible errors, industry uses drawings to describe objects. For this reason, drawing is the draftsman’s language. Drawing, as we use it, 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 very important that the aviation mechanic who is to make or assemble the object understand the meaning of the different lines, notes, abbreviations, and symbols that are used in a drawing.
(See especially 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 20th century, drawings were created on a drawing “board” with pen or pencil and paper. However, with the introduction and advancement of computers in the later decades of the 20th 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 saw computer software programs with the capability of assembling 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 literally became possible to design a part and have it precisely manufactured without ever having it shown 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 Drafting (CADD) — where a computer is used in the design and drafting process,
• Computer Aided Design (CAD) — where a computer is used in the design of a product,
• Computer Aided Manufacturing (CAM) — where a computer is used in the manufacturing of a product, and
• Computer Aided Engineering (CAE) — where a computer is used in the engineering of a product.

As computer hardware and software continue to evolve, there continues to be a greater amount of CAE done 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 2-1]

 

 

Purpose and 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. Other types of sensitized paper have been developed; prints may have a white background with colored lines or a colored background with white lines.
Drawings created using computers may be viewed as they appear on the computer monitor, or they may be printed out in “hard copy” by use of an 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 2-2]

 

 

 

 

Care and Use of Drawings
Drawings are both expensive and valuable; consequently, they should be handled carefully. Open drawings slowly and carefully to prevent tearing 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 other persons and lead to incorrect work. only authorized persons 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 a proper size for filing, and care should be taken so that the original folds are always used.

 

 

Types of Drawings

Drawings must give such information as size and shape of the object and all of 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 particular object.

Drawings may be divided into three classes: (1) detail, (2) assembly, and (3) installation. [Figure 2-3]

 

 

Detail Drawing
A detail drawing is a description of a single part, describing by lines, 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; and, when single parts are small, several detail drawings may be shown on the same sheet or print. (See detail drawing at the top of Figure 2-3.)

 

Assembly Drawing
An assembly drawing is a description of an object made up of two or more parts. Examine the assembly drawing in the center of Figure 2-3. It describes the object by stating, in a general way, 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 which 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. (See installation drawing at the bottom of Figure 2-3.)

 

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 the use of 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 2-4, a sectional view of a coaxial cable connector, 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 to advantage with symmetrical objects to show both the interior and exterior.
Figure 2-5 is a half sectional view of a quick disconnect used in aircraft fluid systems.

 

 

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 Figure 2-6.

 

 

 

Removed Section
A removed section illustrates particular parts of an object. It is drawn like revolved sections, except it is placed at one side and, to bring out pertinent details, often drawn to a larger scale than the view on which it is indicated.
Figure 2-7 is an illustration of removed sections. Section 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. Note that they are often drawn to a larger scale to bring out pertinent details.

 

 

 

 

Title Blocks
Every print must have some means of identification. This is provided by a title block. [Figure 2-8] 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 insofar 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 scale to which it is drawn.
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, which appears in a number block in the lower right-hand corner of the title block. It may also be shown in other places—such as near the top border line, in the upper right-hand corner, or on the reverse side of the print at both ends—so that the number will show 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.

 

 

Reference and Dash Numbers
Reference numbers that appear in the title block refer you to the numbers of other prints. When more than onedetail 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.