ASTM F3409-19e1

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
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Designation:F3409 −19
Standard Practice for
Simplified Aircraft Loads Determination
This standard is issued under the fixed designation F3409; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
ε NOTE—The images in Figs. 1 and 2 were interchanged editorially in October 2022.
1. Scope 2. Referenced Documents
1.1 This practice provides an acceptable, and simplified, 2.1 ASTM Standards:
means of determining certain design loads criteria and condi- F2245 Specification for Design and Performance of a Light
tions for fixed wing aircraft. In particular, the practice provides Sport Airplane
F3060 Terminology for Aircraft
overall aircraft flight loads and flight conditions as well as
control surface loads, wing loads, gust load factors, and gust F3116/F3116M Specification for Design Loads and Condi-
tions
loads on stabilizing surfaces.
1.2 This practice is intended to be referenced by other
3. Terminology
standards that define requirements for comprehensive aircraft
3.1 Definitions:
loads. This practice does not provide all aircraft loads required
3.1.1 A listing of terms, abbreviations, acronyms, and sym-
for structural compliance. In addition, each load or condition
bols related to aircraft can be found in Terminology F3060.
determined through this practice has limitations on its use
Items listed in 3.2 are more specific to this standard.
within the relevant section to which it must adhere.
3.2 Abbreviations:
1.3 Units—The values given in this standard are in SI units
n = airplane positive maneuvering limit load factor
and are to be regarded as standard. Any values given in 1
n = airplane negative maneuvering limit load factor
parentheses are mathematical conversions to inch-pound (or 2
n = airplane positive gust limit load factor at V
3 C
other) units that are provided for information only and are not
n = airplane negative gust limit load factor at V
4 C
considered standard. The values stated in each system may not
n = airplane positive limit load factor with flaps fully
flap
be exact equivalents. Where it may not be clear, some
extended at V
F
equations provide the units of the result directly following the
V = minimum design flap speed =
Fmin
equation.
0.818 5 =n W ⁄ S
~ !
1.4 This standard does not purport to address all of the 1
safety concerns, if any, associated with its use. It is the
V = design maneuvering speed =
A
responsibility of the user of this standard to establish appro-
priate safety, health, and environmental practices and deter-
W
V =n □where□V 5
mine the applicability of regulatory limitations prior to use. S 1 S
S D
ρ C S
1.5 This international standard was developed in accor- ! S D
Lmax
dance with internationally recognized principles on standard-
ization established in the Decision on Principles for the
V = minimum design cruising speed
Cmin
Development of International Standards, Guides and Recom-
1.27 5 =n ~W ⁄ S!
mendations issued by the World Trade Organization Technical
Barriers to Trade (TBT) Committee.
but need not exceed 0.9 V
H
1 2
This practice is under the jurisdiction ofASTM Committee F37 on Light Sport For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Aircraft and is the direct responsibility of Subcommittee F37.20 on Airplane. contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Current edition approved Nov. 1, 2019. Published March 2020. DOI: 10.1520/ Standards volume information, refer to the standard’s Document Summary page on
F3409-19E01. the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
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F3409−19
and n , corresponding to the maximum design weights.
V = minimum design dive speed
Dmin
4.2.2 Each flight load may be considered independent of
1.79 5 =n ~W ⁄ S!
altitude and, except for the local supporting structure for dead
weight items, only the maximum design weight conditions
but need not exceed
must be investigated.
1.4□V =n ⁄3.8
Cmin 1 4.2.3 Figs. 1 and 2 must be used to determine values of n
See 4.2.5.2.
and n , corresponding to the minimum flying weights, and if
V = design cruising speed (if greater than V )
Csel Cmin
these load factors are greater than the load factors at the design
weight, the supporting structure for dead weight items must be
4. Simplified Design Load Criteria
substantiated for the resulting higher load factors.
4.1 Limitations:
4.2.4 Each specified wing and tail loading is independent of
4.1.1 Methods provided in this section provide one possible
thecenterofgravityrange.Theapplicant,however,mustselect
means (but not the only possible means) of compliance. These
a CG range, and the basic fuselage structure must be investi-
requirements may be applied to airplanes meeting the follow-
gated for the most adverse dead weight loading conditions for
ing limitations without further justification.
the CG range selected.
4.1.1.1 A main wing located closer to the airplane’s center
4.2.5 The following loads and loading conditions are the
of gravity than to the aft, fuselage-mounted empennage.
minimums for which strength must be provided in the struc-
4.1.1.2 A main wing that contains a quarter chord sweep
ture:
angle of not more than 15° fore or aft.
4.2.5.1 Airplane Equilibrium—The aerodynamic wing loads
4.1.1.3 A main wing that is equipped with trailing-edge
may be considered to act normal to the relative wind and to
controls (ailerons or flaps, or both).
have a magnitude of 1.05 times the airplane normal loads (as
4.1.1.4 A main wing aspect ratio not greater than 7.0.
determined from 4.3.2 and 4.3.3) for the positive flight
4.1.1.5 A horizontal tail aspect ratio not greater than 4.0.
conditions and magnitude equal to the airplane normal loads
4.1.1.6 A horizontal tail volume coefficient not less than
for the negative conditions. Each chord-wise and normal
0.34.
component of this wing load must be considered.
4.1.1.7 A vertical tail aspect ratio not greater than 2.0.
4.2.5.2 Minimum Design Airspeeds—The minimum design
4.1.1.8 Averticaltailplanformareanotgreaterthan10%of
airspeeds may be chosen by the applicant except that they may
the wing planform area.
not be less than the minimum speeds found in 3.2. In addition,
4.1.1.9 Horizontalandverticaltailairfoilsectionsmustboth
V min need not exceed values of 0.9 V actually obtained at
be symmetrical. C H
sea level for the lowest design weight category for which
4.1.1.10 Amain wing that does not have winglets, outboard
certification is desired. In computing these minimum design
fins, or other wing tip devices.
airspeeds, n may not be less than 4.0.
4.1.2 This section may be used outside of the limitations in
4.2.5.3 Flight Load Factor—The limit flight load factors
4.1.1 when evidence can be provided that the method provides
safe and reliable results. specified in Table 1 represent the ratio of the aerodynamic
force component (acting normal to the assumed longitudinal
4.1.3 Airplanes with any of the following design features
shall not use this section. axis of the airplane) to the weight of the airplane. A positive
flight load factor is an aerodynamic force acting upward, with
4.1.3.1 Canard, tandem-wing, or tailless arrangements of
the lifting surfaces. respect to the airplane.
4.1.3.2 Biplane or multiplane wing arrangements.
4.3 Flight Conditions:
4.1.3.3 V-tail or any tail arrangement where the horizontal
4.3.1 General—Each design condition in 4.3.2 – 4.3.4 must
stabilizer is supported by the vertical stabilizer (T-tail, cruci-
be used to assure sufficient strength for each condition of speed
form (+), etc.).
and load factor on or within the boundary of a flight loads
4.1.3.4 Wings with delta planforms.
envelopediagramfortheairplanesimilartothediagraminFig.
4.1.3.5 Wings with slatted lifting surfaces.
3. This diagram must also be used to determine the airplane
4.1.3.6 Full-flying stabilizing surfaces (horizontal and ver-
structural operating limitations.
tical).
4.3.2 Symmetrical Flight Conditions—The airplane must be
4.2 Flight Loads:
designed for symmetrical flight conditions as follows:
4.2.1 Table 1 must be used to determine values of n , n , n ,
1 2 3
4.3.2.1 The airplane must be designed for at least the four
basic flight conditions, “A,” “D,” “E,” and “G” as noted on the
TABLE 1 Minimum Design Limit Flight Load Factors
flight loads envelope of Fig. 3. In addition, the following
Flaps Up n =4.0
requirements apply:
n = –0.5n
2 1
(1) The design limit flight load factors corresponding to
n from Fig. 1
n from Fig. 2
Conditions “D” and “E” of Fig. 3 must be at least as great as
Flaps Down n =0.5n
f 1
those specified in Table 1, and the design speed for these
A
n =0
f
conditionsmustbeatleastequaltothevalueof V from3.2.
Dmin
A
Vertical wing load may be assumed equal to zero and only the flap part of the
(2) For conditions “A” and “G” of Fig. 3, the load factors
wing need be checked for this condition.
must correspond to those specified in Table 1, and the design
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F3409−19
FIG. 1Chart for Finding n Factor at Speed V
3 C
FIG. 2Chart for Finding n Factor at Speed V
4 C
speeds must be computed using these load factors with the 4.3.2.2 If the flaps or other high-lift devices intended for use
maximum static lift coefficient C determined by the appli- at the relatively low airspeed of approach, landing, and takeoff
NA
cant. are installed, the airplane must be designed for the two flight
(3) Conditions “C” and “F” of Fig. 3 need only be conditions corresponding to the values of limit flap-down
investigated when n W/S or n W/S is greater than n W/S and factors specified in Table 1 with the flaps fully extended at not
3 4 1
n W/S, respectively. less than the design flap speed V from 3.2.
2 Fmin
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F3409−19
FIG. 3Generalized Flight Loads Envelope
4.3.3 Unsymmetrical Flight Conditions—Each affected ~C 2 0.01 δ !V
m b D
K 5 (3)
C 2 0.01 δ V
structure must be designed for unsymmetrical loadings as ~ !
m a C
follows:
where:
4.3.3.1 The aft fuselage-to-wing attachment must be de-
δ = down aileron deflection corresponding to ∆ , and
a a
signed for the critical vertical surface load determined in
δ = down aileron deflection corresponding to ∆ as com-
b b
accordance with 5.2.3.
puted in 4.3.3.4(1).
4.3.3.2 The wing and wing carry-through structures must be
(3) If K is less than 1.0, ∆ is ∆ and must be used to
a critical
designed for 100 % of Condition “A” loading on one side of
determine δ and δ . In this case, V is the critical speed that
u d C
the airplane’s plane of symmetry and 70 % on the opposite
must be used in computing the wing torsion loads over the
side.
aileron span.
4.3.3.3 The wing and wing carry-through structures must be
(4) If K is equal to or greater than 1.0, ∆ is ∆ and
b critical
designed for the loads resulting from a combination 75 % of
mustbeusedtodetermineδ +δ .Inthiscase, V isthecritical
u d D
the positive maneuvering wing loading on both sides of the
speed that must be used in computing the wing torsion loads
plane of symmetry and the maximum wing torsion resulting
over
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