MODULE 7
SUB MODULE 7.5
ENGINEERING DRAWINGS,
DIAGRAMS & STANDARDS
1
OVERVIEW
• Introduction
• Types of drawings
• Symbols and Abbreviations
• Drawing Practices
• Dimensions
• Tolerance Dimensions
• Geometrical Tolerance
• Projections
• Methods of Graphic Representation
• Title Blocks and Numbering Systems
2
INTRODUCTION
• Drawings and prints (copies of drawings) are essential
tool in the design and manufacture of aircraft and all
other manufactured devices and machines.
• A drawing is used to describe an object by means of
lines and symbols.
• The purpose of an engineering drawing is to record
and convey the designer’s requirements to other,
interested, people.
• Therefore, include sufficient information to enable
production planning, manufacture, assembly, testing,
inspection and subsequent maintenance of the
particular component or assembly to be achieved in
the most cost-effective manner.
3
TYPES OF DRAWINGS
• working drawing:
– detail drawing
– assembly drawing
– installation drawing
Other types of drawings include:
electrical wiring diagrams
 sectional drawings
 exploded view drawings pictorial diagrams
schematic diagrams
 block diagrams
 logic flowcharts
4
DETAIL DRAWINGS
• When an aircraft is designed, a detail drawing is
made for every part.
• A detail drawing supplies all the information
required to construct a part, including all
dimensions, materials, and type of finish.
• When needed, an enlarged section or a drawing
of another view.
• When a detail drawing is made, it is carefully and
accurately drawn to scale and dimensioned.
5
6
ASSEMBLY DRAWINGS
• After individual parts are fabricated, they are
assembled into various subassemblies with the
aid of an assembly drawing.
• An assembly drawing depicts the relationship
between two or more parts.
• These drawings reference individual parts by their
part number and specify the type and number of
fasteners needed to join them.
7
8
INSTALLATION DRAWINGS
• All sub-assemblies are brought together in an
installation drawing.
• This type of drawing shows the general
arrangement or position of parts with respect to
an aircraft and provides the information needed
to install them.
9
10
SECTIONAL DRAWINGS
• When it is necessary to show the internal
construction or shape of a part a sectional
drawing is used.
• There are four types of sectional drawings:
– Revolved section
– Removed section
– Complete section
– Half section
11
REVOLVED SECTION
• A portion of an object is turned or revolved to
show a different view.
• The revolved section drawing is often used to
illustrate simple items with no interior parts.
• Basically, this drawing shows how a part is
sectioned and revolved to illustrate it from a
different view.
12
REMOVED SECTION
• Is used to illustrate simple objects. However,
to do this, the object is cut by a cutting plane
line and a section is removed to illustrate
another angle.
13
COMPLETE SECTIONS
• Complex assemblies like cable connectors are
typically shown in complete sections.
• It is easy to identify individual parts within a
complex assembly. This feature is further
enhanced through the proper use of section
lines.
14
HALF-SECTIONS
• With this type of drawing, typically the upper half
of a drawing shows the internal construction of
the assembly, while the lower half shows the
entire assembly as it appears from the outside.
• The half-sectional view allows the inside and
outside of a part to be seen at the same time.
15
EXPLODED- VIEW DRAWING
• Illustrated parts drawings often make use of
exploded view drawings to show every part in an
assembly.
• In this type of drawing, all parts are typically in
their relative positions and expanded outward.
• Both its physical appearance and its reference
number, which is used on the parts list, identify
each part.
16
BLOCK DIAGRAMS
• With electrical systems and electronic
components
becoming
more
complex,
procedures and graphical aids have been
developed. One such aid is the block diagram.
• A block diagram consists of individual blocks
that represent several components such as a
printed circuit board or some other type of
replaceable module.
17
18
LOGIC FLOWCHARTS
• Logic flowcharts are another aid used in
troubleshooting. A logic flowchart represents the
mechanical, electrical, or electronic action of a
system without expressing construction or
engineering information.
• When using a logic flowchart, go to the oblong
START symbol and follow the arrows through the
logical testing sequence.
19
20
21
22
23
LOGIC FLOWCHARTS
• On most flow charts rectangular boxes explain a
procedure, while diamonds identify questions
that require a specific answer.
• After using a rectangular box to test something,
you must match the existing condition before
proceeding to the next course of action.
• Each diamond has one input and at least two
outputs. In order to assure that all
discrepancies are addressed, you must follow a
flow chart to the oblong END.OF TEST symbol.
24
ELECTRICAL WIRING DIAGRAMS
• Wiring diagrams typically identify each
component within a system by its part
number and its serial number, including any
changes that were made during the
production run of an aircraft.
• Because of this, wiring diagrams are extremely
valuable for troubleshooting.
25
26
PICTORIAL DIAGRAMS
• Pilot's handbooks and some training manuals
often use pictorial diagrams of electrical and
hydraulic systems.
• In a pictorial diagram pictures of components are
used instead of the conventional electrical
symbols found in schematic diagrams.
• In most cases, pictorial diagrams help a person
visualize the operation of a specific system.
27
28
SCHEMATIC DIAGRAMS
• A schematic diagram is used to illustrate a
principle of operation and, therefore, does not
show parts as they actually appear or function.
• However, schematic diagrams do indicate the
location of components with respect to each
other and in the case of a hydraulic system, the
direction of fluid flow.
• Because of this, schematic diagrams are best
utilized for troubleshooting.
29
30
31
SYMBOLS AND ABBREVIATIONS
32
Purpose:
• A symbol is a visible sign used instead of a word
or words to represent ideas, operations,
quantities, qualities, relations, or positions.
MATERIAL SYMBOLS
• A symbol is a visible sign used instead of a word
or words to represent ideas, operations,
quantities, qualities, relations, or positions.
33
MATERIAL SYMBOLS
34
FINISH AND SURFACE-ROUGHNESS
SYMBOLS
• The surface of a metal part is "finished" by
performing a machining, coating, or handfinishing operation on that surface. Scraping, filefitting, reaming, lathe turning, shaping, and
grinding are some finishing operations.
• On many existing blueprints the symbol for a
finished surface is a letter V with its point
touching the surface to be finished, drawn with
an angle of 60 between the sides of the V.
35
FINISH AND SURFACE-ROUGHNESS
SYMBOLS
• Numbers may be placed within the angle formed
by the sides of the V to represent the type of
finish to be applied to that particular surface.
When a part is to be finished on all surfaces, the
abbreviation F.A.O. is sometimes used to
represent "finish all over.“
• Many manufacturers in the aerospace industry
have adopted the root-mean-square (rms) microinch system of surface-roughness designation.
36
• The NAS Committee has selected a series of
preferred roughness numbers that cover the
range of aircraft requirements. These numbers are
2, 5, 10, 20, 40, 100, 250, and 500. They indicate
maximum allowable or acceptable roughness of
the surface on which they are specified in rms
micro-inches.
• Rms 500. This is a very rough, low-grade machine
surface resulting from heavy cuts.
• The extremely smooth finishes are indicated by
rms 10, 5 & 2.
37
500
250
100
40
20
10
5
2
38
ELECTRICAL SYMBOLS
39
40
41
42
43
44
45
46
47
48
ABBREVIATIONS
• The use of abbreviations is not encouraged in the
aerospace industry except where a saving of
space is necessary. Use of capital letters is
preferred on drawings and generally restricts the
use of small (lowercase) letters to reports,
manuals and other technical publications, where
they are used along with capital letters.
• The period (.) is used after an abbreviation only
when the abbreviation spells an English word. For
example ADD. for additional, and AIL. for aileron
are used with periods because the words add and
ail are common English words.
49
50
DRAWING
PRACTICES
51
Types of Lines
• Visible lines : A visible line consists of a mediumweight solid line and is the most common type of
line used on most drawings.
• Hidden lines indicate invisible edges or contours.
Hidden lines consist of a dashed line of medium
weight.
• Centerlines are made up of alternating long and
short dashes and are used to show the middle of a
symmetrical part. In the case of a hole, the exact
center is marked by the intersection of two short
dashes.
52
• Extension lines are light lines that extend from the
point where a measurement is made. These lines
do not actually touch the visible lines of an object,
but are approximately 1/16 inch from a part's edge.
• Dimension lines are light lines that are broken in
the center so a dimension can be inserted.
• Cutting-plane lines consist of medium or heavy
alternating long dashes and two short dashes with
an arrowhead at each end. A cutting-plane line is
used to indicate the plane in which a sectional view
of an object is taken.
53
• Phantom lines are light lines made of alternating
long dashes and two short dashes. These lines
indicate the presence of another part and are
included for reference or to indicate a part's
alternate position.
• Short break lines are used across small dimensions
to show that a part continues. Break lines are
medium weight lines that are often drawn
freehand.
• Long break lines are used across a large part and
consist of a light line with a series of irregular
breaks or zigzags. Long break lines usually extend
beyond the solid lines indicating the edges of the
part.
54
• Leader lines are light lines with arrowheads that
extend from a note, number, or information box
to a part. To minimize confusion, leader lines
should never cross a dimension line, an extension
line, or another leader line.
• Section lines are used to show differences in
types of materials or exposed surfaces. Although
different section lines can illustrate various
materials, if the materials used are listed in the
bill of materials, the symbol for cast iron is
frequently used to represent all metals
55
56
LETTERING
57
• For an aircraft drawing: accurately portrays
information. Therefore, lettering is often used to
help identify some items.
• For legibility, ease of reading, and speed, all
lettering is done freehand, using single-stroke
Gothic upper-case letters.
• When it comes to placing letters on a diagram it is
common practice to draw very light guidelines and
to space letters so there is approximately the same
distance between them for uniformity. Fractions
are always made with a horizontal division line and
numbers should be two thirds as high as whole
numbers.
58
• The letters on a drawing are normally in a range of
⅛ inch to as large as one inch high and may be
drawn vertically or on a slant. Slanted letters make
an angle of 68º from the horizontal.
• The spacing of letters and words is important so
that each word and figure will be clear and distinct
from the others.
59
60
61
DIMENSIONS
62
• Dimension figures must be written clearly and
neatly to avoid confusion and possible errors.
They should be written above and parallel to the
dimension line and as close to its center as
possible.
• Arrowheads terminating the dimension lines must
just touch the corresponding outlines, or
centerlines, or extension lines. The size of
arrowheads depends on the thickness of visible
outlines and must be one and the same for all
dimension lines of a given drawing. Extension
lines must extend 2 to 5 mm beyond the ends of
the arrowheads.
63
• When dimensioning very narrow spaces do as
shown in figure (b). As is seen from the figure (b),
if there is no room for arrowheads at the ends of
dimension lines, arrange in a continuous chain,
draw a leader line and place the dimension next.
• On half-sectioned views with an axis of symmetry
it is permissible to dimension as in figure (c). In
this case the dimension line must extend
somewhat beyond the axis of symmetry.
64
65
66
67
68
TOLERANCE DIMENSIONS
• A toleranced dimension defines limits of size of a
feature, and also has bearing on the geometrical
form of the feature.
69
PROCESS AND IDENTIFICATION
MARKINGS
• Drawings will often call for identification
markings on parts, and will indicate both the
position of the markings and the method of
application, e.g. rubber stamp. In addition, it
is sometimes necessary to mark the
component to show that a particular process
has been carried out, and this will also be
specified on the drawing.
70
71
72
PROJECTIONS
73
PROJECTIONS
• Engineering drawing is based on projection
drawing, which studies practical methods of
representation of geometrical solids and their
combinations, various objects, parts of machines,
instruments, and apparatus.
• Projection drawing is especially important for
developing three-dimensional visualization and
habits of logical reasoning.
74
METHODS OF GRAPHIC REPRFSENTATION
• The projection is a view of an object "thrown' onto
a plane by means of straight lines or rays which are
usually drawn through definitive or significant
points of the object up to where they pierce the
plane.
• The points at which the rays intersect with the
plane are called the projections of the points and
the plane is called the plane of projection.
• If all the rays called the projecting lines, or
projectors, issue from one point O, then the
projection of the object on the plane of projection
is called the central projection of this object.
75
76
AXONOMETRIC PROJECTION
• An axonometric projection of an object by placing
the file in front of the plane and drawing a series
of projecting lines, but this time parallel to each
other, as if the center of projection is removed to
infinity from the plane of projection.
• Axonometric projection provides a clear but
distorted representation. Right angles in actual
object are seen as acute and obtuse angles,
circles are projected as ellipses, etc.
77
78
ORTHOGRAPHIC PROJECTION.
• All working drawings of individual parts of
machines units, devices, instruments etc. are
made using orthographic projections with all
projecting rays parallel to each other.
• In orthographic projection it is customary to place
the principal edges and faces of the object parallel
to the plane of projection
• In orthographic projection faces, corners, and
edges will be projected on the plane undistorted,
also in true size.
79
• In orthographic projection there are six possible
views from which an object can be drawn: the
front, rear, top, bottom, left side, and right side.
• Each view is drawn as if you put an object in a
transparent box and viewed it from one of the box
faces. All rays extending from the part are parallel
and perpendicular to the side they are viewed
from.
• Most common, in a three-view drawing the front,
right side, and top views are illustrated.
80
81
82
1st Angle Projection or 3rd Angle
Projection
• In 1st angle projections, each view shows what
would be seen by looking on the far side of an
adjacent view.
• But in 3rd angle projections, each view shows
what would be seen by looking on the near
side of an adjacent view.
83
84
AXONOMETRIC PROJECTIONS
• Axonometric projections differ from orthographic
projections in that in axonometry an object is
projected only onto one plane of projection called
the axonometric {or picture) plane.
• The drawing of the object is placed on the picture
plane so as to expose three sides.
• In mechanical engineering axonometric projections
are used as an auxiliary to orthographic projections
of a mechanical part when the necessity is felt to
give a clearer picture of its shapes, which are
difficult to visualize from the orthographic
projections.
85
86
87
AXONOMETRIC PROJECTIONS
• There are two such axonometric projections
largely in use. They are
– Isometric Drawings
Projections)
– Oblique
Drawings
Projections).
(Rectangular
Isometric
(Rectangular
Dimetric
88
Isometric Drawings
• With Isometric Drawings, the object is rotated
so three sides are visible.
• In other words, to make an isometric drawing,
an object is rotated so that three views are
visible and touching the drawing plane.
• Also note that the three sides of the object
are drawn at an angle of 120º.
89
90
OBLIQUE DRAWINGS
• An oblique drawing is a drawing with one
object face parallel to the drawing plane.
• In other words, two axes are perpendicular to
each other, with the front of the object
identical to the front view of an orthographic
drawing.
• The depth axis of the oblique drawing is
typically 45 degrees.
91
92
OBLIQUE DRAWINGS
• There are two special types of oblique drawings.
• They are :
– The cabinet drawing, and
– The cavalier drawing
93
Cabinet drawing
• A cabinet drawing gets its name from
drawings used for cabinetwork.
• In these drawings, the oblique side is at a 45
degree angle to the front side and is 1/2 the
scale.
• This allows for an accurate and undistorted
front view. The remainder of the drawing is
present only to illustrate depth.
94
Cavalier drawings
• Use the same scale for the front view as the
oblique side lines.
• However, the oblique sides are still set at a 45
degree angle to the front view.
• This creates a distorted picture of an object's
true proportions.
• These drawings are primarily used when
detailing is required on the oblique side.
95
PERSPECTIVE DRAWINGS
• A perspective drawing is used when you need
to see an object similar to the way the human
eye sees it.
• The basic difference between a perspective
drawing and an oblique or isometric drawing
is that on a perspective drawing the lines, or
rays of an object meet at a distant point on
the horizon.
• This point is referred to as the vanishing point.
96
97
98
TITLE BLOCKS AND NUMBERING
SYSTEMS
99
100
101
102
• TITLE BLOCKS
– The title block is the index to the drawing, it
provides all necessary information that is not
shown in or near the actual drawing.
• THE DRAWING, OR PRINT NUMBER
– It is customarily printed in large numerals.
When a drawing consists of more than one
sheet, the basic drawing number and the sheet
number identify each sheet.
103
• THE DRAWING SIZE
– In general, drawing sizes are established according to
MIL-STD-2A.
FLAT SIZES
ROLL SIZES
SIZE WIDTH LENGTH
(inch)
(inch)
A
8½
11
B
11
17
C
17
22
D
22
34
SIZE
E
34
44
K
F
28
40
T
G
H
J
WIDTH LENGTH
(inch) (inch)
11
34
11
42
28
50
34
50
40
50
104
• ZONE NUMBER
– Roll-size drawings are usually divided into
zones to make it easy to find what the
blueprint reader is looking for.
– The zoning is identified by alphabetical and
numerical entries in the margin and by
subdivision of the margin.
– The size of the zone spacing is designed to suit
the type and scope of' the drawing.
– Zoning can also be employed on flat sheet
drawings if necessary to clarify locations.
105
• NAME OF PART, UNIT OR ASSEMBLY
– The name of the part, unit, or assembly is given
first followed by descriptive terms: , the name of a
carburetor air intake flange would read: "FLANGE,
CARBURETOR AIR INTAKE.
• REVISION
– It will be noted here whether any revisions have
been made in the drawing, the disposition and
date of the revision, the name or initial of the
person making it, an indication of approval, and
the serial number on which it is to be effective.
– The disposition of previously made parts may also
be indicated.
106
• DIMENSIONS AND LIMITS
– Limits and tolerances are shown in a
supplementary block adjacent to the basic title
block.
• PART NUMBER
– Each part of an aerospace vehicle always has a
number of its own. The part numbers of the
material or items are shown in the title block.
– Some manufacturers, when they make
drawings of parts, make their item part number
and the drawing number the same.
107
• RIGHT-HAND AND LEFT-HAND PARTS
– The usual practice in drawing a part for one
side only is to show the left-hand part and lefthand part number and also gives the righthand part number, which is the same as the
basic number with –2 added.
– For example, the title block might read
"135795-1, LH SHOWN; 135795-2, RH
OPPOSITE."
108
• STATION NUMBERS
– A station numbering system can be used to
help the print reader find such things as
fuselage frames, wing frames, and stabilizer
frames.
– When a print reads "FUSELAGE FRAME-STA.
182," that means that the frame is 182 in back
of station zero.
109
110
THANK YOU!!!
111