Unformatted text preview: AC65-15A Airframe Or Powerplant MECHANICS AIRFRAME HANDBOOK U.S. DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION AIRFRAME A N D POWERPLANT
AIRFRAME H A N D B O O K US. DEPARTMENT O F TRANSPORTATION
FEDERAL AVlATiON ADMINISTRATION
FLIGHT STANDARDS SERVICE First Edition 1972
First Revision 1976 PREFACE
This handbook was developed and first printed in 1972 as one of a series of
three handbooks for persons preparing for certification as an airframe or powerplant
mechanic. It is intended that this handbook will provide basic information on principles, furdamentals and technical procedures in the subject matter areas relating
to the airframe rating. It is designed to aid students enrolled in a formal course of
instruction as well as the individual who is studying on his own. Since the knowledge requirements for the airframe and powerplant ratings closely parallel each
other in some subject areas, the chapters which discuss fire protection systems and
electrical systems contain some material which is also duplicated in the Airframe
and Powerplant Mechanics Powerplant Handbook, AC 65-12A.
This volume contains information on airframe construction features assembly
and rigging, fabric covering, structural repairs, and aircraft welding. The handhook also contains an explanation of the units which make up the various airframe
Because there are so many different types of aircraft in use today, it is reasonable to expect that differences exist in airframe components and systems. To avoid
undue repetition, the practice of using representative systems and units is carried
out throughout the handbook. Subject matter treatment is from a generalized point
of view. and should be supplemented by reference to manufacturers' manuals or
other textbooks if more detail is desired. This handbook is not intended to replace,
substitute for, or supersede official regulations or the manufacturers' instructions.
Grateful acknowledgement is extended to the manufacturers of engines. propellers and powerplant accessories for their cooperation in making material available for inclusion in this handbook.
Copyright material is used by special permission of the following organizations
and may not be extracted or reproduced without permission of the copyright owner. Monsanto Chemicals Co.
Townsend Corporation J. 0. King, Inc.
DuPont De Nemours
National Fire Protection Association
National Association of Fire
Flight Safety Foundation
4merican Petroleum Institute
Goodyear Tire and Rubber Co.
Skydrol CE3 Fluids
Fire Extinguisher and
Aircraft Tires Bendix Energy Controls Aircraft Wheels
Portable Oxygen Generators
in the D C l O
Portable Oxygen Generators Rohm and Haas
Douglas Aircraft Company
Aviation Maintenance Foundation, Inc.
Puritan Equipment, Inc. The advancements in aeronautical technology dictate that an instructional handbook must be under continuous review and brought up to date periodically to be
valid. Flight Standards requested comments, from the certificated mechanic schools
on the three handbooks. As a result, the handbooks have been updated to this extent:
indicated errors have been corrected, new material has been added in the areas which
were indicated as being deficient, and some material has becia rearranged to improve
the usefulness of the handbooks.
We would appreciate having errors brought to our attention, as well as receiving suggestions for improving the usefulness of the handbooks. Your comments and
suggestions will be retained in our files until such time as the next revision will be
Address all correspondence relating to these handbooks to:
US. Department of Transportation
Federal Aviation Administration
Flight Standards National Field Office
P.O. Box 25082
Oklahoma City, Oklahoma 73125
The companion handbooks to AC 65-15A are the Airframe and Powerplant
Mechanics General Handbook, AC 65-9A and the Airframe and Powerplant Me.
chanics Powerplant Handbook, AC 65-12A. iv CONTENTS
PREFACE _________.______________________________---------------- iii CONTENTS - _____ -__- _____ - _________ -__-__- ________________ - _____ - ” CHAPTER 1. AIRCRAFT STRUCTURES
G eneral ___-_-__-__--__-__-_____________________--------------Major
Fixed-Wing Aircraft ________________________________________---Fuselage ________________._______________________-------------Wing Structure _____._________________________________
Nacelles or Pods ______________._________________________------Empennage ________________________________________-----------Flight Control Surfaces ________________________________________-Landing Gear ________-_______________________________---------Skin and Fairing __-__-_________-________________________------Access and Inspectmn Doors ______ - _________________ - _____ -___-__
Helicopter Structures _-- _____ -__-__-__-- ___________ -__-___-__-___ 1
24 CHAPTER 2. ASSEMBLY AND RIGGING
General -__-__-__-______-__-____________________--------------Theory of Flight _--__-__-_________-_____________________------Aerodynamics ________________________________________---------The Atmosphere ________________________________________-------Pressure -__-__-__-______-__-____________________-------------Density -__-__-__--__-__-__-____________________-----~---~----Humidity., ________________________________________------------. .
Bernoulb s Prmc~ple and Subsomc Flow ____________________________
Motion _-.___________-_________________________--------------A’*r f 01s
‘I __-_________-__-__-_----------------------------------Center of Gravity ___- ________________________________________--Thrust and Drag ________________________________________------Axes of an Ancraft ________________________________________----Stability and Control -__- _________ -__- ___________________________
Control _-______-__-__-__-______________________--------------Flight Control Surfaces -__--__- ______ -__- ______ -__- ______________
Control Around the Longitudinal Axis _-__- ______ - _________________
Control Around the Vertical Axis _-- _________ - ____________________
Control Around the Lateral Axis ______ -__-___- _____ - ______________
Tabs __._____________________________________----------------Boundary Layer Control Devices’ __________________________________
Forces Acting on a Helicopter __-__- ______________________________
Helicopter Axes of Flight ________________________________________
High-Speed Aend ynamics .______________________________________
Typical Supersonic, Flow Patterns ______ -__-__- _________ - __________
Aerodynamic Heating __-__--__-__-__- _______________ -- __________
Flight Control Systems ________________________________________-Hydraulic Operated Control Systems ______________________________
Cable Guides ________________________________________---------Mechanical Linkage ________________________________________---- 27
vi CHAPTER 4. AIRCRAFT PAINTING AND FINISHING-(Cont.)
430 ... ~~ 433
46% I. ,... %9
51 3 519
600 . xi . CHAPTER 1
The airframe of a fixed-wing aircraft is generally
considered to consist of five principal units, the
fuselage, wings, stabilizers, fight control surfaces,
and landing gear. Helicopter airframes consist of
the fuselage, main rotor and related gearbox, tail
rotor (on helicopters with a single main rotor), and
the landing gear.
The airframe components are constructed from a
wide variety of materials and are joined by rivets,
bolts, screws, and welding or adhesives. The air.
craft components are composed of various parts
called structural members (;.e., stringers, longerons,
ribs, bulkheads, etc.). Aircraft structural members
are designed to carry a load or to resist stress. A
single member of the structure may be subjected to
a combination of stresses. In most c a m the struo
tural members are designed to carry end loads
rather than side loads: that is, to be subjected to
tension or compression rather than bending.
Strength may be the principal requirement in Certain structures, while others need entirely different
qualities. For example, cowling, fairing, and similar parts usually are not required to carry the
stresses imposed by flight or the landing loads.
However, these parts must have such properties as
neat appearance and streamlined shapes. (1) Tension.
( 5 ) Bending.
The term “stress” is o h used intemhangeably
with the word “strain.” Stress is an internal force
of a substance which oppow or resists deformation. Strain is the deformation of a material or
substance. Stress, the internal force, can cause
Strali. Tension (figure 1-la) is the stress that resists a
force that tends to pull apart. The engine pulls the
aircraft forward, but air resistance tries to hold it
back. The result is tension, which tries to stretch
the aircraft. The tensile strength of a material is
measured in p.s.i. (pounds per square inch) and is
calculated by dividing the load (in pounds) required to puil the material apart by its croea-8dctional area (in square inches).
Compression (figure I-lb) is the stress that re5
ists a crushing force. The compressive strength of a
material is also measured in p.8.i. Compression is
the stress that tends to shorten or squeze aireraft
Torsion is the stress that produces twisting (figure
1-lc). While moving the aircraft forward, the engine also tends to twist it to one side, but other
aircraft components bold it on course. Thus, torsion
is created. The torsional strength of a material is iia
resistance to twisting or torque.
Shear is the stress that resists the force tendmg
to cause one layer of a material to slide over an
adjacent layer. Two riveted plates in tension (figure
1-Id) subject the riveta to a shearing force.
Usually, the shearing strengtb of a material is either
equal to or lesa than its tens& or compressive
strength. Aircraft parts, especially screws, bolts, and
rivets, are often subject to a shearing force.
Bending stress is a combination of compression
and tension. The rod in figure I-le has been shortened (comprawred) on the inside of the bend and
stretched on the outside of the bend. MAJOR STRUCTURAL STRESSES In designing an aircraft, every square inch of
wing and fuselage, every rib, spar, and even each
metal fitting must be considered in relation to the
physical characteristiui of the metal of which it is
made. Every part of the aircraft must be planned to
carry the load to be imposed upon it. The determination of such loa& is cailed stress analysis. Although planning the design is not the function of
the aviation mechanic, it is, nevertheless, important
that he understand and appreciate the stresees involved in order to avoid changes in the original
design through improper repairs.
There are five major strcsses to which ail aircraft
are subjected (figure 1-1) :
P 0 fc) Torsiod (e) FIGURE
1-1. Banding (the c5ubhuöon S t W Y )
Five atrasses acting on an aircrah. FIXED-WING AIRCRAFT
The principal components of a single-engine, propeller-driven aircraft are shown in figure 1-2.
Figure 1-3 illustrates the structural Components
of a typical turbine powered aircraft. One wing and
the empennage assemblies are shown exploded into
the many components which, when assembled, form
major structural units. multi-engine aircraft the engines may either be in
the fuselage, attached to the fuselage, or suspended
from the wing structure. They vary principally in
&e and arrangement of the different compartments.
There are two general types of fuselage constmction, the truss type, and the monocoque type. A
truss is a rigid framework made up of members
such as beams, struts, and bars to resist deformation by applied loads. The truss-framed fuselage is
generally covered with fabric. FUSELAGE
The fuselage ia the main structure or body of the
aircrait. It provides space for cargo, controls, accessories, passengers, and other equipment In singleengine aircraft, it also houses the powerplant. In Truss Type The truss type fuselage frame (figure 1-4) is
usually constructed of steel tubing welded together
in such a manner that all members of the tmas can
carry both tension and compression loads. In some
2 Frcoul-E Ainmftarontrralwmponcma In addition to formem, frame assemblieu, and
bulkheads, the semimonocoque construction has the
skin reinforced by longitudinal memhera. The reinforced shell bae the skin reinforced by a compi.te
framework of structural members. Different pop
tions of the same fuselage may belong to my one of
the three classee, but moot aircraft are considered to
be of semimonocope type consmc~on. aircraft, principally the light, singloengine mod&
trues fuselage frames are constructed of alminum
d o y and may be riveted or bolted into one piece,
with cross-bracing achieved by using solid rods or
tubes. Monocoque Type
The monocoque (single shell) fuaelsge relies
largely on the strength of the skin or covering to
carry the primary stresses. The design may be divided into three cineses: (1) Monocoque, (2) semi.
monocoque, or (3) reinforced shell. The true monoformers,
coque construction (figure 1-5)
frame assemblies, and bulkheads to give shape to
the fuselage, but the &in cania, the primary
stresses. Since no bracing memhera are preseia, the
skin mnst be strong enongh to keep the W a g e
rigid. Thus, the biggest problem involved in monocoque construction is maintaining enough strength
while keeping the weight within allowable limits.
To overcome the strength/weight problan of
monocoque construction, a modification Caned semimonocoque construction (figure 1-6) was deveiOped SemimonOcWJe TYPe
The eemimonocoque W a g e is constructed psmarily of the d o y s of aluminum and magn&~m,
although steel and titanium are found in areas of
high tsmperatuies. Primary bending loads are taken
by the bngerom, which usually extend acroen emerd points of support The longuons are supple
mented by other longitudinal membels, called
stringers. Stringers are more nUmCIOüü and lighter
in weight than longerons. The vertical structnral
memhera ere referred to ae bulkheads, h
formers. The heaviest of theae vertical d e m are
located at intervals to carry concentrated loads and
at points where fittings are used to attach other
units, such as the win& powerphts, and stabilis.
3 Wing center section or. strut edge Powerplant FIGURE
1-3, Typid anicturai mmponuita of a turbine powered eimdt, Longeron (tnbular steel) rons and serve as fin-ins. They have some rigidity,
but are chiefly used for giving shape and for attachment of the skin. The strong, heavy longerons hold
the bulkheads and formers, and these, in turn, hold
the stringers. All of these joined together form a
rigid fuselage framework.
There is often little differenee between some
rings, frames, and formers. One manufacturer may
call a brace a former, whereas another may call the
same type of brace a ring or frame. Manufacturers’
instructions and specifications for a specific aircraft
are the best guides.
Stringers and longerons prevent tension and compression from bending &e fuselage. Stringers are
usually of a one-piece aluminum alloy coiistruction,
and are manufactured in a variety of shapes by
casiing, extrusion, or forming. Longerons, like
stringers, are usually made of aluminum alloy; how- Diagonal web members
(tubuiar steei) hcvag 1 4 W m m irues of welded tub& steel e m Figure 1-7 shows one form of the semimonocoque design now in use.
The stringers are smaller and lighter than longe4 . . . ..>.- , . . 1
_ . o . . . . ...,, ,.----- :7 , . ~ I ’.,. doea not depend on a few members for strength and
rigidity. ”his means that a ssmimonocoque fiwelnge,
because of its stressed-skin construction, may withstand considerable damage and stili be shong
enough to bold together.
Fuselages are generaily constructed in two or
more sections. On small aircraft, they are p e r a l l y
made in two or three sections, while larger aircraft
may be made up of aa many aa six d o n s .
Quick a m to the accessories and other equip
ment carried in the fuselage is provided for by
numerous acceaa doom, inspection platea, landing
wheel wells, and other openings. Servicing diagrams
showing the arrangement of equipment and loeation
of a m doom are supplied by the manufachurr in
the aircraft maintenance manual. ever, they may be of either a one-piece or a built-up
By themselves, the structural members discussed
do not give strength to a fuselage. They must first
be joined together by such connective devicea aa
[email protected] nuts and bolts, or metal screws. A
gusset (figure 1-7) is a type of connecting bracket.
The bracing between longerons is often referred to
as web members. They may be installed verticaily or
The metal sün or covering is riveted to the longerons, buikhads, and other structural membera
and carries part of the load. The fusdage skin
thicknees wiii vary with the load carried and the
stresses sustained at a particular location.
There are a number of advantages in the use of
the semimonocoque fuselage. The bulkhads,
frameu, stringers, and longerons facilitate the d e
sign and construction of a stnamüned fuselage, and
add to the strength and rigidity of the structure.
The main advantage, however, iim in the fact that it Loca?ionNumbering Systems There are various numbering systems in ww to
facilitate location of specific wing frames fuselegs
bulkheads, or any other structural m&rs
aircraft. Most manufacturers use some s
station marking; for example, the no88 of the allcraft may be designated zero station, and all other
stations are located at measured ditanoes in inchss
behiid the zero station. Thns, when a blueprint
reads “fuselage frame station 137,” that p d &
frame station can be located 137 in. behmd the no88
of the aircraft. A typical station diagram is shown
in figure 1-8.
To locate structured to the right or left of the
center line of an aircraft, many manufachinrs consider the center iine as a zero station for stniehuil
member location to its right or I& With such a
5 dicuiar to the rear beam of the wing and
parsllel to, and outboard from, the inboard edge of the flap.
( 6 ) Nacelle siation (N.C. or Nac. Sui.) ie
measured either forward of or bebind
the front spar of the wing and perpeudicular to a designated water line.
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