23.343 Design fuel loads (Amendment 23-48)
53. Is there any policy available on this section as of January 1, 2007? No.
23.345 High lift devices (Amendment 23-48)
54. Is there any policy available on this section as of January 1, 2007? No.
23.347 Unsymmetrical flight conditions (Amendment 23-48)
55. Is there any policy available on this section as of January 1, 2007? No.
23.349 Rolling conditions (Amendment 23-48)
56. Is there any policy available on this section as of January 1, 2007? No.
23.351 Yawing conditions (Amendment 23-42)
57. Is there any policy available on this section as of January 1, 2007? No.
23.361 Engine torque (Amendment 23-45)
58. Is there any policy available on paragraph (a) of this section as of January 1, 2007? No.
59. How do I determine the limit engine torque load imposed by sudden engine stoppage due to malfunction or structural failure (such as compressor jamming) for turbine engines to satisfy the requirements of paragraph (b)(1)? Title 14 Code of Federal Regulations (CFR) part 33, § 33.23 requires the specification of the maximum allowable limit and ultimate loads for engine mounting attachments and related engine structure. Therefore, the maximum engine st ructure loading information, as specified in the engine Manufacturers Installation Manual, satisfies the limit engine torque load imposed by sudden engine stoppage due to malfunction or structural failure (such as compressor jamming).
60. Is there any policy available on paragraph (c) of this section as of January 1, 2007?
a. This rule requires the design of engine mounts and supporting structure to sustain limit torque at takeoff power and at maximum continuous power, with corresponding propeller revolutions per minute (r.p.m.), for two specified flight 28
conditions. The rule defines limit torque equa l to mean torque multiplied by a factor that is a function of the number of cylinders of a reciprocating engine (see Figure 4).
FIGURE 4
LIMIT ENGINE TORQUE DEFINITION Tlim = Fcyl Tmean Engine type Turbopropeller Five or more cylinders Four cylinders Three cylinders Two cylinders Fcyl 1.25 1.33 2 3 4
b. NOTE: The limit engine torque, Tlim, is not an engine limit in the sense of part 33, § 33.7. For structural installation lo ads purposes, treat it as simply a limit load arrived at by the equation and figure shown. Engine mean torque is available from the engine manufacturer. The engine type multiplying factor, Fcyl, is a constant for a given engine without regard to the speed or power at which the engine is operating.
c. The FAA published engine torque requirements incorrectly in Amendment 23-26. Part 23, § 23.361 was corrected with Amendment 23-45. The incorrectly written rule failed to require the multiplying factor for the torque load. The applied (incorrectly written) rule can result in lower structural loads than previously required from torque loads. These loads aff ect the engine mount, and either the fuselage or nacelle and wing designs.
d. Policy: Apply the mean torque factors in the manner that existed in part 23 before Amendment 23-26 and corrected in Amendment 23-45. Determine airplane design loads for two engine limit torques and for two flight-load-conditions. These airworthiness standards for engine torque loads constitute the minimum level of safety required by the FAA for the engine mount, and either the fuselage or the nacelle and wing designs. For airplane designs that have a part 23 certification basis that encompasses Amendments 23-26 through 23-44, apply the intent of the regulation depicted by the amendments before or after these amendments. Figure 5 presents a view of torque, aerodynamic, and inertial loads airworthiness standards.
FIGURE 5
VIEW OF TORQUE, AERODYNAMIC, AND INERTIAL LOADS 30
23.363 Side load on engine mount (Original)
61. Is there any policy available on this section as of January 1, 2007? No.
23.365 Pressurized Cabin Loads (Original)
62. How do I determine the cabin pressure loads and what do I combine them with? Multiply the maximum differential pressure loads by the 1.5 factor of safety (see part 23, § 23.303). The maximum differential pr essure loads should include the high side relief valve tolerance pressure. Combine them with the ultimate loads of both the normal flight inertia and the local external aerodynamic pressure distribution conditions.
63. Is the aerodynamic pressure a constant? The airloads will vary over the length of the fuselage.
64. Is there any policy available on paragraph (c) of this section as of January 1, 2007? No.
65. What pressure should be used as limit load (omitting other loads)? For the limit (pressure only) load condition, airplane fuselage structure should be designed to withstand:
P =(1.33)Plim max .relief .valve
66. What pressure should be used as ultimate load (omitting other loads)?
a. For the ultimate (pressure only) load condition, combine the 1.5 factor of safety with the 1.33 burst pressure factor to get an ultimate load case for the pressure vessel structural design. Part 23 special conditions have imposed a 1.67 burst pressure factor for airplanes with design altitudes that exceed 45,000 feet. This practice is consistent with part 25. Aerodynamic and landing impact loads may be ignored for this load case.
P = 15 133 P..ult ( ) max.relief .valve For altitudes that exceed 45,000 feet, P =(1.67)Plim max .relief .valve ..( )PP = 15 167ult max.relief valve .
b. Note that the regulation for pressurization tests requires a strength test on a fuselage designed for pressure to the ultimate load condition given by the above equation (see § 23.843).
67. What is meant by “external door”? External door means an opening, a doorway, in the external surface of the airplane. Evaluate door failure effects regardless of whether the door is inward or outward opening. For this rule, an emergency exit is a door. Also see 23.305, Strength and deformation, paragraph 22, for guidance about conducting static tests for pressure vessels.
23.367 Unsymmetrical loads due to engine failure (Amendment 23-7)
68. What is meant by “critical engine”? Traditionally, the term “critical engine” is used to describe the engine whose failure to operate results in the largest yawing moment, compared to that caused by failure of the other engine. However, in a more general sense, and for this regulation, the term “critical engine” means the engine that, when failed, results in the highest structural loads on the airplane.
69. Is there any policy available on paragraph (b) of this section as of January 1, 2007? No.
23.369 Rear lift truss (Amendment 23-48)
70. What is the purpose of this regulation? Civil Air Regulation (CAR) 3.194 is considered a special supplementary reversed airflow condition for design of the rear lift truss, which has no direct relationship to any of the points on the V-n envelope. It has been historically considered as a downwind taxi for a "tail-wheel" type airplane. The lift truss is the brace (frequently a “V,” sometimes “parallel” struts—one to each existing spar) running from the bottom of the fuselage to the lower spar cap(s) of the wing. These lift truss struts usually attach to the wing at midspan. “Wing struts” are usually loaded in tension (for positive load factor conditions)—except during negative “g” maneuvers or gusts, inverted flight conditions (aerobatic maneuvers), landing, and taxi. In these latter cases, the struts can be loaded in compression; therefore, they are subject to Euler column buckling phenomena. Even when on the ground, the airplane rear lift truss (or strut) can experience significant compression loads if the airplane has a tail wheel. This is especially true when the airplane is tied down or is taxiing downwind.
71. Is there any policy available on paragraph (b) of this section as of January 1, 2007? No.
23.371 Gyroscopic and aerodynamic loads (Amendment 23-48)
72. Is there any policy available on this section as of January 1, 2007? No.
23.373 Speed control devices (Amendment 23-7)
73. Is there any policy available on paragraph (a) of this section as of January 1, 2007? No.
74. Is there any policy available on paragraph (b) of this section as of January 1, 2007? No.
CONTROL SURFACE AND SYSTEM LOADS
23.391 Control surface loads (Amendment 23-48)
75. What is the background on this regulation? The control surface load criteria that previously appeared in Appendix B of part 23 were removed from part 23 at Amendment
23-42. The Appendix B criteria were shown to give inappropriate surface loadings for certain airplane configurations, including:
a. High-performance part 23 aircraft;
b. Aircraft that have spar configurations located aft of the 25 percent chord length; and
c. Aircraft that have horizontal stabilizer leading edges that are not attached at the fuselage.
23.393 Loads parallel to hinge line (Amendment 23-48)
76. Is there any policy available on this section as of January 1, 2007? No.
23.395 Control system loads (Amendment 23-7)
77. Can you explain this regulation schematically? Yes. Figure 6 presents an overall relational view of control system loads airworthiness standards. Also see “Control Systems” requirements that are contained in part 23, §§ 23.671 through 23.701.
FIGURE 6
CONTROL SYSTEM LOADS
CONTROL SYSTEM LOADS
CALCULATE
HM.
MAX P.E.
MIN P.E.
MAX P.
REFERENCES H.M.
< MAX P.E.
NO§ 23.395(a)(1) § 23.397(b) YES H.M. = 125% HINGE MOMENT A.P. = AUTO PILOT FORCE P.E. = PILOT EFFORT G.G. = GROUND GUST A.P.
< MAX P.E.
YES
NO DESIGN TO MAX A.P.
DESIGN TO
MAX P.E.
§ 23.395(a)(2) YES § 23.397(b) H.M.
< MIN P.E.
NO DESIGN TO H.M.
ARE MIN P.E.
INAPP YES
NO DESIGN TO MIN P.E.
§ 23.415(a)(2)
DETERMINE G.G. LOADS G.G.
< .6 MIN P.E.
DESIGN TO G.G. LOADS
DESIGN TO .6 MIN P.E.
§ 23.397(b) NO YES 35
78. Is there anything else I can review to get more information? Yes. See 23.423, Maneuvering loads, for more guidance about control system loads.
79. Is there any guidance for unconventional multipath control systems? The control system loads, and limit control forces, and torque airworthiness standards require that pilot loads be opposed at the attachment of the control system to the control surface horn. For an unconventional multipath control system, which involves control of separate surfaces (each with its own horn), it would be appropriate to expect the pilot forces to be restrained at the control surface horns. If this allows a portion of the system to be designed for less than the minimum pilot-effort forces, special attention should be given to the design of this portion of the system to ensure the rugged system.
80. Does this regulation apply to wing flap control systems? No. The § 23.395 requirements are not applicable to wing flap systems.
23.397 Limit control forces and torques (Amendment 23-45)
81. Is there any policy available on paragraph (a) of this section as of January 1, 2007? No.
82. For paragraph (b) of this section, where should the loads be applied?
a. Apply the 100-pound load on a single fore-and-aft control wheel anywhere along the periphery or at the tip of the grip-handle on U-type wheels, and in both foreand-aft directions.
b. Part 23, § 23.397(b) presents both a symmetric and asymmetric 100-pound wheel load for elevator control. You should also see the Figure 6, which presents an overall relational view of control system loads airworthiness standards.
23.399 Dual control system (Amendment 23-48)
83. Is there any policy available on this section as of January 1, 2007? No.
23.405 Secondary control system (Original)
84. Is there any policy available on this section as of January 1, 2007? No.
23.407 Trim tab effects (Original)
85. What is the maximum out-of-trim condition one should consider when determining control surface loads?
a. This rule only applies when maximum pilot-effort forces are imposed on the control system (refer to part 23, § 23.397). Th en, the trim tab deflection is limited to the maximum out-of-trim condition that can exist under prolonged pilot-effort forces (refer to § 23.143).
b. This interpretation only applies to a trim tab that is attached to a movable control surface that is further attached to a fixed main-aerodynamic surface (i.e., it excludes a trim tab that is attached to a stabilator).
c. See 23.423, Maneuvering loads, for more guidance about trim tabs.
23.409 Tabs (Original)
86. Is there any policy available on this section as of January 1, 2007? No.
23.415 Ground gust conditions (Amendment 23-48)
87. How do the ground gust loads in paragraph (a) fit in with the other control system loads in the design requirements? Refer to the accompanying graphic to
23.395, Control System Loads (Figure 6), which presents an overall view of control system loads airworthiness standards.
88. Is there any policy available on paragraph (b) or (c) of this section as of January 1, 2007? No.
HORIZONTAL STABILIZING AND BALANCING SURFACES
23.421 Balancing loads (Amendment 23-42)
89. Is there any guidance for stabilator design?
a. Yes. You may find stabil ator chordwise air-load distributions in the Basic Glider Criteria Handbook for both the balancing conditions and the maneuvering and gust conditions. Also, stabilator s have historically developed flutter problems; therefore, carefully consider the flutter effects of a stabilator design.
b. The Basic Glider Criteria Handbook, 1962 Revision, Federal Aviation Agency, Flight Standards Service, Washington, D.C., is now available by mail from:
Manager, Standards Office (ACE-110), Federal Aviation Administration, Small Airplane Directorate, DOT Building, 901 Locust, Room 301, Kansas City, MO 64106.
c. Also, see 23.321, General (flight loads), for more guidance about balancing tail loads.
90. Is there any policy available on paragraph (b) of this section as of January 1, 2007? No.
23.423 Maneuvering loads (Amendment 23-42)
91. The condition described in paragraph (a) of the regulations does not appear to be realistic. What is the reason for this?
a. Part 23, § 23.423(a) addresses an artificial load condition intended to provide adequate tail strength for abrupt, unchecked pitch maneuvers up to the design maneuver speed, VA . The condition is artificial because the airplane will pitch, and the load factor will no longer be 1g, before the elevator reaches full deflection.
b. A 6g maneuver involves significant airplane pitch velocity, which relieves pilot input and results in a lower stick force per unit elevator deflection. One may correlate tail angle of attack and airplane pitch velocity with measured and calculated hinge moments to gain confidence in the load calculations.
c. A flight in which the pilot pulls full-back-stick at design maneuver speed, VA, and 1g, initially, would probably result in higher elevator angles than would be calculated at 1g because of airplane response characteristics. However, the tail loads resulting from an analysis accounting for airplane response characteristics would not likely exceed those calculated from an analysis that assumes 1g conditions.
d. The analytical approach is acceptable with the following suggestions:
(1) For elevator deflecti on, divide calculated hinge moment by 1.25 (reference § 23.395(b)).
(2) For an elevator tab configuration, deflect the tab to assist the pilot, per § 23.407, Trim tab effects.
e. See the guidance in 23.421, Balancing loads, for stabilator loads distributions.
23.425 Gust loads (Amendment 23-42)
92. What gust loads should be used for stabilator-type aerodynamic surfaces? For stabilator-type aerodynamic surfaces, use the Basic Glider Criteria Handbook as the information source for air-load distributions.
93. Is there any policy available on paragraph (b), (c) or (d) of this section as of January 1, 2007? No.
23.427 Unsymmetrical loads (Amendment 23-42)
94. What unsymmetrical loads should I use for trim systems? For guidance related to non-aerodynamic trim system designs, see 23.677(b), “Trim systems.”
95. What is meant by “conventional” in paragraph (b) of this section?
Conventional means the airplane’s center of gravity (c.g.) is located within the boundaries of the wing mean aerodynamic chord with the empennage aft and the engine(s) forward.
96. Do the conventional requirements for unsymmetrical loads apply to V-Tail configuration designs? No. A V-tail configuration is considered unconventional;
therefore, the conventional requirements for unsymmetrical loads do not apply.
97. For a T-tail design, is a maneuver at maximum elevator deflection required in combination with a maneuver at maximum rudder deflection at the design maneuver speed, VA?
a. Simultaneous maximum deflection of both the elevator and rudder control surfaces is not required by the regulations, although an airplane designer may choose to design for the combined loads for other reasons. The horizontal and vertical stabilizer maneuver loads regulations require structural substantiation for sudden maximum displacement of elevator and rudder, at the design maneuver speed, VA, as separate conditions (see part 23, § 23.423(a) and § 23.441(a)(1)). However, the airworthiness standard for unsymmetrical tail loads, in § 23.427(a), requires that horizontal stabilizer surfaces and their supporting structure withstand unsymmetrical loads arising from maneuver and gust loads, and yaw and slipstream effects.
b. If maximum simultaneous rudder and elevator deflection at the design maneuver speed, VA, is a proposed maneuver, then this should be a design load condition.