Design of wood aircraft structures

260 Pages·2014·17.26 MB·English

M
The contents uf th1> letin shall not
ia part without tpei authorization of the Aeronautical Board*

ANC—
18
June, 1944
ANC BULLETIN
WOOD
DESIGN OF
AIRCRAFT STRUCTURES
WAR DEPARTMENT
ARMY AIR FORCES
NAVY DEPARTMENT
BUREAU OF AERONAUTICS
DEPARTMENT OF COMMERCE
CIVIL AERONAUTICS ADMINISTRATION
Issued by the
ARMY-NAVY-CIVIL COMMITTEE
» on
AIRCRAFT DESIGN CRITERIA
Under the supervision ofthe
AERONAUTICAL BOARD
The contents of this bulletin shall not be reproduced in whole or
in part without specific authorization of the Aeronautical Board.
UNITED STATES GOVERNMENT PRINTING OFFICE
WASHINGTON: 1944
This Bulletin
by
FOREST PRODUCTS LABORATORY
FOREST SERVICE
UNITED STATES DEPARTMENT OF AGRICULTURE
and
ARMY-NAVY-CIVIL COMMITTEE
on
AIRCRAFT DESIGN CRITERIA
I]
NOTICE
Thereaderisherebynotifiedthat thisbulletin issubjecttorevisionandamend-
ment when and where such revision or amendment is necessary to effect
agreement with the latest approved information on aircraft design criteria.
When using this bulletin, the reader should therefore make certain that it is
thelatest revision and thatall issued amendments, ifany, areknown.
Ill
TABLE OF CONTENTS
Page
CHAPTER GENERAL
1. 1
1.0. Purpose and Use of Bulletin 1
1.1. Nomenclature 1
,
CHAPTER 2. STRENGTH OF WOOD AND PLYWOOD ELEMENTS 9
2.0. Physical Characteristics of Wood 13
2.1. Basic Strength and Elastic Properties of Wood- .., 16
2.2. Columns 28
2.3. Beams 30
2.4. Torsion 36
2.5. Basic Strength and Elastic Properties of Plywood 37
2.6. Plywood Structural Elements 59
2.7. Flat Rectangular Plywood Panels 76
2.8. Curved Plywood Panels 109
2.9. Joints 114
CHAPTER 3. METHODS OF STRUCTURAL ANALYSIS 131
3.0. General 133
3.1. Wings 135
3.2. Fixed TailSurfaces 185
3.3. Movable Control Surfaces 185
3.4. Fuselages 185
3.5. Hulls and Floats • 199
3.6. Miscellaneous 201
CHAPTER 4. DETAIL STRUCTURAL DESIGN 204
4.0. General 205
4.1. Plywood Covering 205
4.2. Beams 210
4.3. Ribs 216
4.4. Frames and Bulkheads 220
4.5. Stiffeners 220
4.6. Glue Joints 222
4.7. MechanicalJoints 224
4.8. Miscellaneous Design Details 227
4.9. ExamplesofActualDesign Details 233
IV
CHAPTER GENERAL
1.
1.0. PURPOSE AND USE OF BULLETIN.
1.00. Introduction. This bulletin has been prepared for use in the design of both
militaryand commercial aircraft, and contains material which is acceptable to the Army
Air Forces, Navy Bureau of Aeronautics, and the Civil Aeronautics Administration.
It should, of course, be understood that methods and procedures other than those out-
lined herein are also acceptable, provided they are properly substantiated and approved
by the appropriate agency. The applicability and interpretation of the provisions of
this bulletin as contract or certification requirements will in each case be defined
by the procuring or certificating agency.
1.01. Scope ofBulletin. The technical material in this bulletin is contained in
chapters 2, 3, and 4, and pertains to three related phases of the structural design of
wood aircraft.
Chapter 2 presents information on the strength and elastic properties of structural
elements constructed of wood and plywood. This information supersedes that contained
in the October 1940 edition of ANC-5, "Strength of Aircraft Elements."
Those sections of chapter 2, which are based on incomplete data or theoretical
analysis, that have not been fully verified by test have been, as a caution, marked with
a double asterisk. Those sections that are based on reasonably complete information
but require further substantiating tests are marked with a single asterisk. The use of
the various formulas and data in these sections should, therefore, be commensurate
with the limitations noted. Since further research on the strength and elastic properties
of wood and plywood structural elements is being actively carried on by the Forest
Products Laboratory, it is anticipated that revisions to chapter 2 will be made from
time to time as this work progresses.
Chapter3 containssuggested methods ofstructural analysisforthe design of various
aircraft components. Although these methods are in many cases the same as those
used for metal structures, special considerations have been introduced which take into
account the orthotropic properties of wood.
Chapter 4 presents recommendations on the detail structural design of wood air-
craft and contains some examples of how various manufacturers have treated the solu-
tion of specific detail design problems.
1.02. Acknowledgement. The ANC Committee on Aircraft Design Criteria and
the Forest Products Laboratory express their appreciation to aircraft manufacturers
and others for the valuable assistance given in connection with various parts of this
bulletin.
1.1. NOMENCLATURE.Thissection presentsthe definitionsofstandardstructural
symbols whichareused inthebulletin. In addition, sections 1.10 and 1.11 are presented
to clarify the differentiation between the definitions for strength and elastic properties
of plywood elements and those for like properties of plywood panels. These sections
also outline the use of table 2-9.
1
2 ANC BULLETIN—DESIGN OF WOOD AIRCRAFT STRUCTURES
—
1.10. Definitions for Plywood Elements Beams, Prisms and Columns in Com-
pression, Strips in Tension. A plywood element is any rectangular piece of plywood
that is supported, loaded, or restrained on two opposite edges only. In defining the
various strength and elastic property terms for plywood elements; the face grain direc-
tion has been used as a reference; for example, the subscript w denotes a direction
parallel to (with) the face grain, while the subscript x denotes a direction perpendicular
to (across) the face grain. This is illustrated by figure 1-1. The strength and elastic
properties given in table 2-9 of the bulletin are for plywood elements.
TABLE Z-3 TABLE 2-9
—
Figure 1-1. Plywood element (supported, loaded, or restrained on two opposite edges only).
1.11. Definitions for Plywood Panels1. A plywood panel is any rectangular piece
of plywood that is supported, loaded, or restrained on more than two edges. In defining
the various strength and related property terms for plywood panels, the side of length a
ratherthantheface grain directionhasbeenused asthereference. For anypanel having
tension or compression loads (either alone or accompanied by shear) the side of length a
is the loaded side. For panels having only shear loads (with no tension or compression),
the side a may be taken as either side. (Sec. 2.701). For panels having normal loads,
side a is the shorter side. The subscripts a and 1 denote a direction parallel to the side
of length a, and the subscripts b and 2 denote a direction perpendicular to the side of
length a. This is illustrated by figure 1-2. Since, in panels, the directions in which
Ea, Eb, Ei, E2, etc., aretobe measured are relatedtothe directionsofthe sidesoflengths
a and b, it is necessary to relate these directions to the face grain direction before the
terms can be evaluated from table 2-9. It may be stated, therefore, that:
b
L
E E ETC—CANNOTBE E ,E ETC—CANNOTBE
a. f, i) 2,
EVALUATED UNTIL EACE EVALUATED UNTIL FACE
GRAIN DIRECTION15 KNOWN GRAIN DIRECTION15 IfNOINN
—
Figure 1-2. Plywood panel (supported, loaded, or restrained on more than two edges).
1 The designationsforsidesaand basusedhereinaredifferentfromthose usedinANC-5, in which
thesideof length h is defined as the loaded sidein tension orcompression and astheshortsidein shear
GENERAL 3
a, the(1v)aWluheesnofthEeaf,aEceh,gErahinE>d,ireetcc,timonayofbaeptlaykweonofdrpoamnetlheiscpoalruamllneslftoortEhew,sEidTe,oEffwl,enEgftxh,
etc., respectively, in table 2 9. This is illustrated by figure 1-3.
E^
E^.E,,ETC.-VALUES FROM ETC.- VALUES FROM
COLUMNS FOR EWtEfw,ETC. COLUMNS FOR EXtEfx,ETC.}
RESPECTIVELY IN TABLE RE5PECTIVEL IN TABLE
Y,
t
Z-9 2-9
—
Figure 1-3. Plywood panel (face grain direction parallel to side of length a).
(2) When the face grain direction of a plywood panel is perpendicular to the side
oEfwl,eEnfgxt,hEaf,wt, heetc.v,alrueesspecotfiEveal,y,Eib,nEt,a,blEeg,2-e9t.c.,Thmiasyisbeiltluaskternatefdrobmytfhieg'ucreol1u-m4.ns for Ex,
////////////////////////////
T
FACE GRAIN
' DIRECTION
a
1
V77777777, 7Z
E„ E ETC-VALUES FROM E ,E ETC -VALUES FROM
b z>
COLUMAI5 FORE E ETC, COLUMNS E„ E ,ETC,
RESPECTIVELY,x,IfNx,TABLE RESPECTIVELYt,f7wnTABLE
2.-3 2-9
—
Figure 1-4. Plywood panel (face grain direction perpendicular to side of length a).
1.12. STANDARD STRUCTURAL SYMBOLS FOR CHAPTER TWO. In
general, symbols that areusedonlyin the section where theyare defined are not included
in this nomenclature. »
-area of cross section, square inches -The length of the loaded side of a ply-
(total). wood panel for compression or tension
loads, and the length of either side for
shear loads (Sec. 2.701); subscript de-
noting parallel to side of length a for
plywood panels.
-areaofplieswithgraindirection parallel
tothedirectionofappliedstress.
ANC BULLETIN—DESIGN OF WOOD AIRCRAFT STRUCTURES
-area of plies with grain direction per-
pendicular to the direction of applied
stress (surfaces of plies parallel to plane
of glue joint tangential to the annual
growth rings, as for rotary-cut or flat-
sliced veneer, flat-sawn lumber).
-area of plies with grain direction per-
pendicular to the direction of applied
stress (surfaces of plies parallel to plane
ofgluejoint radialtotheannualgrowth
rings, as for quarter-sliced veneer,
quarter-sawn lumber).
—
b the length ofthe unloadedside ofa ply-
wood panel for compression or tension
loads, and the length of either side for
shear loads (Sec. 2.701); subscript de-
noting parallel to side of length b for
plywood panels; subscript denoting
"bending"forsolidwood.
—
br subscriptdenoting "bearing."
—
circumference c end-fixity coefficient for columns; sub-
scriptdenoting "compression '; distance
—from neutral axis to extreme fiber.
c' distancefromneutralaxistotheextreme
fiber having grain direction parallel to
the applied stress (plywood).
—
cr subscriptdenoting "critical."
-diameter d —depth orheight
—
-modulus of elasticity of wood in the cz, unit strain (tension or compression) in
direction parallel to the grain, as de- the L direction.
termined from a static, bending test.
(This value is listed in table 2-4.)
—
-modulus of elasticity of wood in the cr unit strain (tension or compression) in
direction radial to the annual growth the R direction.
rings.
—
modulus of elasticity of wood in the ct unit strain (tension or compression) in
directiontangentialtotheannualgrowth the T direction.
rings.
modulus of elasticity of wood in the
direction parallel to the grain, as de-
termined from a compression test
(value not listed in table 2-4, but ap-
proximatelyequalto1.1 El).
-unit strain (shear) or the change in
angle between lines originally drawn in
the L and T directions,
(Lit -unit strain (shear) or the change in
angle between lines originally drawn in
the L and R directions,
-unit strain (shear) or the change in
angle between lines originally drawn in
-effective modulus of elasticity of ply- the T and R directions.
woodintensionorcompressionmeasured
parallel to the side of length a of ply-
wood panels.