Advisory U.S. Department of Transportation Federal Aviation Circular Administration Subject: AIRFRAME GUIDE FOR Date: 4/30/07 AC No: 23-19A CERTIFICATION OF PART 23
AIRPLANES Initiated by: ACE-100
FOREWORD This Advisory Circular (AC) sets forth an acceptable means of showing compliance with Title 14 Code of Federal Regulations (14 CFR), part 23, for certification of the airframe (Subpart C and portions of Subpart D) of normal, utility, acrobatic, and commuter category airplanes and airships. The policy in this AC applies to airs hip projects; however, the certifying office should only use specific applicability and requirements if they are reasonable, applicable, and relevant to the airship project. This AC both consolidates existing policy documents, and certain ACs that cover specific paragraphs of the regulations, into a single document and adds new guidance.
This document provides guidance for the original issue of part 23 and the various amendments.
This version of the AC covers policy available through January 1, 2007. Policy that became available after January 1, 2007, will be covered in future revisions to the AC.
s/ Charles L. Smalley Acting Manager, Small Airplane Directorate Aircraft Certification Service
CONTENTS
Section PAGE
SUBPART C−−STRUCTURE4
GENERAL4
23.301 Loads4
FIGURE 18
SPANWISE WING-LOADING METHODOLOGIES8
23.302 Canard or tandem wing configurations10
23.303 Factor of safety10
23.305 Strength and deformation10
23.307 Proof of structure16
FLIGHT LOADS23
23.321 General23
FIGURE 224
FLIGHT LOADS24
FIGURE 325
23.331 Symmetrical flight controls26
23.333 Flight envelope26
23.335 Design airspeeds26
23.337 Limit maneuvering load factors27
23.341 Gust load factors27
23.343 Design fuel loads28
23.345 High lift devices28
23.347 Unsymmetrical flight conditions28
23.349 Rolling conditions28
23.351 Yawing conditions28
23.361 Engine torque28
FIGURE 429
LIMIT ENGINE TORQUE DEFINITION29
FIGURE 530
23.363 Side load on engine mount31
23.365 Pressurized Cabin Loads31
23.367 Unsymmetrical loads due to engine failure32
23.369 Rear lift truss32
23.371 Gyroscopic and aerodynamic loads32
23.373 Speed control devices33
CONTROL SURFACE AND SYSTEM LOADS34
23.391 Control surface loads34
23.393 Loads parallel to hinge line34
23.395 Control system loads34
FIGURE 635
CONTROL SYSTEM LOADS35
23.397 Limit control forces and torques36
23.399 Dual control system36
23.405 Secondary control system36
23.407 Trim tab effects37
i
23.409 Tabs37
23.415 Ground gust conditions37
HORIZONTAL STABILIZING AND BALANCING SURFACES38
23.421 Balancing loads38
23.423 Maneuvering loads38
23.425 Gust loads39
23.427 Unsymmetrical loads39
VERTICAL SURFACES42
23.441 Maneuvering loads42
23.443 Gust loads42
23.445 Outboard fins or winglets42
AILERONS AND SPECIAL DEVICES43
23.455 Ailerons43
23.457 Wing flaps43
23.459 Special Devices43
GROUND LOADS44
23.471 General44
FIGURE 745
23.473 Ground load conditions and assumptions46
23.477 Landing gear arrangement49
23.479 Level landing conditions49
23.481 Tail down landing conditions49
23.483 One-wheel landing conditions51
23.485 Side load conditions51
23.493 Braked roll conditions51
23.497 Supplementary conditions for tail wheels51
23.499 Supplementary conditions for nose wheels51
23.505 Supplementary conditions for skiplanes51
23.507 Jacking loads52
23.509 Towing loads52
23.511 Ground load; unsymmetrical loads on multiple-wheel units52
WATER LOADS53
23.521 Water load conditions53
23.523 Design weights and center of gravity positions53
23.525 Application of loads53
23.527 Hull and main float load factors53
23.529 Hull and main float landing conditions53
23.531 Hull and main float takeoff condition53
23.533 Hull and main float bottom pressures54
23.535 Auxiliary float loads54
23.537 Seawing loads54
EMERGENCY LANDING CONDITIONS55
23.561 General55
FIGURE 857
RELATIONAL VIEW OF TURNOVER PROTECTION57
23.562 Emergency landing dynamic conditions59
FATIGUE EVALUATION64
23.571 Metallic pressurized cabin structures64
23.572 Metallic wing, empennage, and associated structures64
ii
23.573 Damage tolerance and fatigue evaluation of structure67
23.574 Metallic damage tolerance and fatigue evaluation of commuter category
airplanes68
23.575 Inspections and other procedures68
SUBPART D—DESIGN AND CONSTRUCTION69
23.601 General69
23.603 Materials and workmanship69
23.605 Fabrication methods73
23.607 Fasteners75
23.609 Protection of structure75
23.611 Accessibility76
23.613 Material strength properties and design values76
23.615 Design properties77
23.619 Special factors77
FIGURE 978
23.621 Casting factors79
FIGURE 1080
23.623 Bearing factors81
23.625 Fitting factors81
23.627 Fatigue strength81
23.629 Flutter81
WINGS85
23.641 Proof of strength85
CONTROL SURFACES86
23.651 Proof of strength86
23.655 Installation86
23.657 Hinges86
23.659 Mass balance86
APPENDIX A TO PART 23—Simplified Design Load Criteria87
iii (and iv)
1. What is the purpose of this advisory circular (AC)? This advisory circular (AC) provides information and guidance on an acceptable means, but not the only means, to comply with Title 14 of the Code of Federal Regulations (14 CFR) part 23, Subpart C, and portions of Subpart D. However, if you use the means de scribed in the AC, you must follow it in all important respects. This AC consolidates the substance of existing Civil Aeronautics Administration (CAA) and Federal Aviation Administration (FAA) letters into a single reference. It also presents information from certain existing AC's that cover general topics and specific airworthiness standards. This AC is not mandatory and does not constitute a regulation.
2. Who does this AC apply to?
a. This AC applies to any interested party that wants to certify an airplane to part 23 regulations.
b. This material has no legal status. However, to encourage standardization during the certification process, the FAA recommends that the applicant consider this guidance during each small airplane type certificate and supplemental type certificate project.
3. Does this AC cancel any previous AC’s? Yes. The following AC is cancelled:
AC 23-19, Airframe Guide for Certification of Part 23 Airplanes.
4. What is the background of this guidance material? This AC is current with the airworthiness standards that appear in part 23 through Amendment 23-51, effective March 11, 1996, and policy issued through January 1, 2007. This information spans approximately 30 years of FAA and CAA letter-written aviation guidance. It includes some historical guidance that dates from Civil Air Regulations (CAR) 3 and the earlier CAR 04.
5. How is this advisory circular organized?
a. The paragraph headings are keyed to part 23. This AC includes all the regulatory topics found in part 23 Subpart C, and in Subpart D through CONTROL SURFACES.
b. Each AC paragraph matches with the applicable part 23 section for the corresponding amendment shown in the title.
c. Reference to AC information appears without the section “§” symbol, for example, "23.301."
d. Any reference to the like-numbered airworthiness standard is shown with a section symbol, for example, “§ 23.301.”
e. When “Original” appears as the amendment number applicable to a specified section, it specifies that part 23 of the 14 CFR effective February 1, 1965, unchanged by any later amendment, applies to that section. As part 23 changes are introduced by new amendments, the FAA will make appropriate revisions to this AC.
6. Are there any related publications, and where can they be found?
a. Yes. You may get copies of current edit ions of the following publications free from:
U.S. Department of Transportation Subsequent Distribution Office Ardmore East Business Center 3341 Q 75th Avenue Landover, MD 20785
b. Some of these publications are also available on the Internet at http://www.faa.gov.
The related publications include:
(1) AC 20-33B, Technical Information Regarding Civil Aeronautics Manuals 1, 3, 4a, 4b, 5, 6, 7, 8, 9, 13, and 14;
(2) AC 20-44, Glass Fiber Fabric for Aircraft Covering;
(3) AC 20-71, Dual Locking Devices on Fasteners;
(4) AC 20-107A, Composite Aircraft Structure;
(5) AC 20-146, Methodology for Dynamic Seat Certification by Analysis for Use in Parts 23, 25, 27, and 29 Airplanes and Rotorcraft;
(6) AC 21.25-1, Issuance of Type Certificate: Restricted Category Agricultural Airplanes;
(7) AC 23-9, Evaluation of Flight Loads on Small Airplanes with T, V, +, or Y Empennage Configurations;
(8) AC 23-13, Fatigue and Fail-Safe Evaluation of Flight Structure and Pressurized Cabin for Part 23 Airplanes;
(9) AC 23-15A, Small Airplane Certification Compliance Program;
(10) Advisory Circular 23-20, Acceptance Guidance on Material Procurement and Process Specifications for Polymer Matrix Composite Systems;
(11) AC 23.562-1, Dynamic Testing of Part 23 Airplane Seat/Restraint Systems and Occupant Protection;
(12) AC 23.629-1A, Means of Compliance with Section 23.629, Flutter;
(13) AC 25.571-1C, Damage Tolerance and Fatigue Evaluation of Structure;
(14) AC 183.29-1 (latest revision), Designated Engineering Representatives Consultant Directory;
(15) Policy Statement PS-ACE100-2001-006, “Static Strength Substantiation of Composite Airplane Structure”
(16) Policy Statement PS-ACE100-2002-006, “Material Qualification and Equivalency for Polymer Matrix Composite Material Systems”
(17) Policy Statement PS-ACE100-2004-10030, “Substantiation of Secondary Composite Structures”
(18) Policy Statement PS-ACE100-2005-10038, “Bonded Joints and Structures – Technical Issues and Certification Considerations”
(19) FAA Order 8110.4C, Type Certification;
(20) FAA Order 8100.5A, Aircraft Certification Service Mission, Responsibilities, and Relationships, and Programs;
(21) TSO-C27, Twin Seaplane Floats.
(22) Civil Aeronautics Manual 04 (CAM 04) – Available on the Internet at:
http://dotlibrary.specialcollection.net/
(23) Civil Aeronautics Manual 08 (CAM 08) – Available on the Internet at:
http://dotlibrary.specialcollection.net/
c. In addition, copies of the following publications are available on request from:
Small Airplane Directorate Standards Office Federal Aviation Administration DOT Building 901 Locust Street, Room 301 Kansas City, Missouri 64106
(1) ANC-1(1), Spanwise Air-Load Distribution, Army-Navy-Commerce Committee on Aircraft Requirements, 1938
(2) ANC-1(2), Chordwise Air-Load Distribution, Army-Navy-Civil Committee on Aircraft Design Criteria, Amendment –1 dated 3 January 1944
7. Where can I get engineering advice? See AC 183.29-1 for a list of engineers who are appointed by the FAA to do certain kinds of FAA approval work, and are familiar with the certification process.
8. Should I Confer with the FAA Aircraft Certification Office Project Engineer? Yes.
An FAA project engineer can be an invaluable guide to the FAA Certification Process and the particular airworthiness standards for airplane design or modification.
Airframe Guidance for Certification of Part 23 Airplanes SUBPART C−−STRUCTURE
GENERAL
23.301 Loads (Amendment 23-48)
9. Should references be included in the loads calculations? Yes. Each Basic Loads calculation should be annotated with the airworthiness standard section for which compliance is shown, for example, use part 23, § 23.301(a); they may also be shown in Design Criteria, Test Plans, Test Reports, and Software Documents.
10. What effect do cutouts have in structure? Doors, windows, access holes, etc., in aircraft structure causes redistribution of axial and shear loads, pressure loads, and stiffness changes. Fatigue capabilities may be affected. Damage tolerance capabilities may be affected. Account for all such design changes.
11. Do Biplane designs require any special aerodynamic load criteria?
a. Yes. A previously used typical approach includes:
(1) Developing an equivalent single wing (cellule), which aerodynamically represents the biplane wings. Civil Aeronautics Manual 04 (CAM 04), paragraph 217, provides an acceptable method unless the biplane has an unusual amount of stagger or decalage. Also, see CAM 04, Appendix III.
(2) Defining wing and tail loads from part 23 load conditions using the equivalent single wing.
(3) Distributing the equivalent single wing load between the upper and lower biplane wings. CAM 8, paragraph 212, pr ovides an acceptable method for biplanes with no decalage.
(4) Distributing the individual wing-loads spanwise using a method such as Schrenk or ANC-1. (See Figure 1.)
b. Other acceptable methods for obtaining aerodynamic parameters for biplanes and other unique configurations include computational fluid dynamic (CFD) codes, including VS-Aero, MG-Aero, and TRANAIR. Applicants should validate the suitability of these codes for their particular configuration. Wind tunnel and flight tests are also acceptable methods of measuring load intensities.
12. What is the effect of increased engine power? An increase in engine power causes larger loads on, and in, several aircraft structures. A different engine, with different weight, center of gravity (c.g.) and horsepower, will change the inertial, gyroscopic, and aerodynamic loads from those of the previous engine. A changed propeller imparts similar effects on inertial, aerodynamic and gyroscopic loads, which are imposed on airplane structures.
13. Can ultimate load flight tests be used?
a. The FAA discourages attempting ultimate load flight tests unless the applicant understands fully the risks involved, and then the FAA advises caution.
b. See “Note” in 23.305, paragraph 22b, of this AC concerning flight tests.
14. Can I use wind tunnel data?
a. Wind tunnel tests may be used to measure several parameters used in determining airplane loads. Force models can be used to measure the tail-off and tail-on airplane lift, pitching moment and drag curves, downwash at the tail, and stability and control parameters. Pressure models can be used to obtain the wingspan loading and the pressure distributions on airplane components. Measured pressure distributions are particularly useful in determining loads on secondary structure, including nacelles, canopies, and fairings.
b. Lower performance conventional airplanes are commonly designed without the benefit of wind tunnel testing. Conventiona l, as used here, means an airplane having a main wing at or near the c.g. and an empennage aft of the airplane c.g. Wind tunnel tests are more likely to be useful for airplanes with unconventional configurations, unusual aerodynamic features, or high performance airplanes where compressibility effects cannot be neglected.
c. Scaling of test results to full-scale airplane values requires similarity of geometry, Mach Number and Reynolds Number. Similarity of Reynolds Number is the most difficult of these to achieve. Test da ta acquired at Reynolds Numbers significantly lower than flight may be of little use for certification purposes due to the large corrections that must be applied to the test data. Reynolds Number similarity can be achieved by using large-scale models or pressurized wind tunnels. Boundary layer transition strips or dots are frequently used to model flight scale Reynolds Number effects on a model tested at lower Reynolds Numbers.
15. How can I determine the span-wise lift distribution? The span-wise distribution of lift on the wing may be obtained from wind tunnel test, flight test, analysis, or a combination of analysis and test. Figure 1 lists some commonly used span-wise lift distribution analysis methods. In addition to the methods listed in Figure 1, there are 5
various computer codes available that use computation fluid dynamics (CFD), such as, VS-Aero, MG-Aero, and TRANAIR.
a. The National Advisory Committee for Aeronautics (NACA) Technical Report 572 reports on the Anderson method. The wings under consideration covered a complete range of taper ratios and aspect ratios from 2 to 20. It does not say that 20 is a limit.
b. Reference 1 (page 228) states that NACA Technical Report 585 contains an exact method.
c. The “Fourier Series Method” is described in Reference 1 on pages 233 to 242.
This is the method in ANC-1 (which has tabular forms for ease of calculation). This method uses lifting line theory, which is good for conventional unswept wings with aspect ratios greater than 5 or 6 (see Reference 1, page 247).
d. Weissenger's “Method” (Reference 2) is applicable to straight or swept wings of low or high aspect ratio. This is a modified lifting theory method.
e. Schrenk's “Approximation” basically averages the lift forces obtained from an elliptical lift distribution with those obtained from a planform lift distribution. This approximation is accurate for wings that approach an elliptical planform (Reference 1, page 224). This method is contained in Civil Aeronautics Manual (CAM) 04, Appendix IV. The Limitations, in Section 6, state that it applies to the normal range of aspect ratios (from 5 to 12).
f. Reference 3 (page 14) lists NACA Technical Reports 572, 585, and 606. The first two of these technical reports are discussed in Items a and b above. Technical Report 606 is titled “Empirical Corrections to the Span Load Distribution at the Tip.”
Correction is only necessary if the wing is tapered less than 2:1 and has a blunt tip.
g. Reference 4 lists several references: 3.5 through 3.12 (see Enclosure 3).
h. In the paper titled “Application of Microcomputer Software to the Aerodynamic Design of a Motorglider” Technical Soaring, October 1993, the lifting line theory FORTRAN program in Reference 5 (pages 159-164) was used (on an Apple Macintosh Plus computer) to calculate the lift distribution of a 17-meter (55.76 foot) wing (aspect ratio unstated). A comparison wa s made of the lift distribution calculated by Schrenk's approximation.
i. Reference 6 contains a vortex lattice FORTRAN program.
j. Reference 7 is an aeroelastic supplement for the NASTRAN finite element program.
k. NACA TN 3030 titled, “A Method for Calculating the Subsonic Steady-state Loading on an Airplane with a Wing of Arbitrary Planform and Stiffness” includes both 6
the aeroelastic effects and the ability to base the span loading on linearized wind tunnel wing section data. It also allows for correc ting wind tunnel model elastics and jig twist.
FIGURE 1
SPANWISE WING-LOADING METHODOLOGIES
METHOD APPROACH TO SOLUTION LIMITATIONS ON
APPLICATION
COMMENTS ANC-1 Fourier Solution. Based on lifting line theory. Basic and additional lift.
Conventional unswept wings with aspect ratios greater than 5 to
6.
Exact Solution despite limitations of lifting line theory. Similar Methods:
LOTZ GLAUERT (Elements of Aerofoil and Airscrew Theory) ANDERSON (Theory of Wing Sections) SHRENK’S Approximate Conventional Accuracy approaches NACA TM- Solution. Based on unswept wings ANC-1. Small 948 lifting line theory.
Basic and additional lift.
with aspect ratios greater than 5 to
6.
inaccuracies overshadowed by original assumptions. Much easier to apply.
SHERMAN’S Successive Applicable to any Accuracy compares with NACA TN-732 approximations to straight wing ANC-1 but unsatisfactory match chord without high lift due to separate calculation distribution. Each devices. for each angle of attack.
angle of attack requires separate calculation.
PLANFORM Air load Untwisted high Unconservative for Taper (Often used for distribution directly taper ratio wings. Ratios < 0.25.
horizontal tail) proportional to chord variation.
Conservative for Taper Ratios > 0.35.
WEISSINGER Iteration process Applicable to Lifting surface method NACA TM based on modified straight or swept also presented as 1120 lifting line theory.
Basic and additional lift.
wings of low or high aspect ratio.
applicable to straight wings.
DeYOUNG & Based on simplified Applicable to Extension of Weissinger HARPER lifting surface straight or swept Method. Can account for NACA TR 921 theory. Basic and additional lift.
wings of low or high taper ratio.
compressibility M > 0.5 @ S.L.
DIEDERICH Matrix Iteration No planform Considers loading and NACA TR process utilizing limitations. divergence speed.
1000 aero-elastic matrix determined from aerodynamic and structural properties of wing.
NOTE: See NACA TN 606 for Empirical Tip Corrections, and RM L53B18 for Tip Tank Effects on Load Distribution.