except for wing torsional stiffness criteria that specify indicated airspeed (IAS) be used.
However, at 14,000 feet in altitude, the difference between EAS and IAS is small (about 3½ knots).
239. When did flight flutter tests become a requirement? Amendment 23-48 made flightflutter tests a requirement. Before February 9, 1996, the date of the amendment, freedom from flutter, control reversal, and divergence could be shown by either a rational analysis, by flightflutter tests, or by simplified flutter prevention criteria. For all new type certification projects for which application was made after February 9, 1996, flight flutter tests are required to demonstrate compliance to § 23.629.
240. Where can I get a copy of AEER 45? Airframe and Equipment Engineering Report No.
45, “Simplified Flutter Prevention Criteria for Personal Type Aircraft,” by Robert Rosenbaum, and Civil Aeronautics Manual 3, Supplement No. 11, dated March 28, 1952, may be used for simple airplane designs to show compliance with flutter. Copies may be obtained by mail from the following: Manager, Standards Office (ACE -110), Federal Aviation Administration, Small Airplane Directorate, DOT Building, 901 Locust, Room 301, Kansas City, MO 64106.
241. How can I achieve the objective of paragraph (f) of this section?
a. The objective is to prevent airplane flutter from occurring after the failure, malfunction, or disconnection of any single element in the primary flight-control system, in any tab-control system, or in any flutter damper. Balancing the control systems and then showing that the airplane is free from flutter can achieve this. Alternatively, the objective can also be shown by doing the following:
(1) Incorporating a structural fail-safe design throughout the entire flight-control system and then demonstrating that the airplane is free from flutter; or
(2) Incorporating a combination of structural fail-safe designs and balanced-control system.
b. If a hinge pin single failure would allow the pin to fall out of the hinge, create hinge design features to prevent the pin from separating.
242. Is the fail-safe design criterion of § 23.572(a)(2) an acceptable method of compliance for flutter? No. Section 23.629(f)(2) requires the failu re, malfunction, or disconnection of any single element be considered. Both control-surface balance and dual-load, path-tab-system designs have been judged as meeting the airworthiness requirement for irreversible systems.
243. Why isn’t the fail-safe design criterion of § 23.572(a)(2) an acceptable method of compliance for flutter? The fail-safe criterion in § 23.572(a)(2) imposes a static ultimate-load factor of 75 percent of the critical limit-load factor at design cruise speed, VC. This criterion is inadequate for flutter substantiation of dual-load path primary-control systems, or tab-control systems because of the lower speeds and lower structural loads imposed.
244. Is there any additional guidance available for this section? Yes. See AC 23.629-1B, Means of Compliance with Section 23.629, “Flutter,” for additional information about this airworthiness standard topic.
WINGS
23.641 Proof of strength (Original)
245. Is there any policy available on this section as of January 1, 2007? No.
CONTROL SURFACES
23.651 Proof of strength (Original)
246. Is there any policy available on this section as of January 1, 2007? No.
23.655 Installation (Amendment 23-45)
247. Is there any policy available on this section as of January 1, 2007? No.
23.657 Hinges (Amendment 23-48)
248. Is there any additional guidance available for hinges? See 23.393, Loads parallel to the hinge line, for additional guidance about hinges. Also see 23.651, Proof of strength, for information that may affect hinges.
23.659 Mass balance (Original)
249. Is there any policy available on this section as of January 1, 2007? No.
APPENDIX A TO PART 23—Simplified Design Load Criteria A23.1(a) References:
1. Clousing, Lawrence A. and Turner, William N.: Flight Measurements of Horizontal Tail Loads on a Typical Propeller-Driven Pursuit Airplane During Stalled Pull-Outs at High Speed. RMR (WR A - 81), May 1944.
2. Matheny, Coyce E.: Comparison Between Calculated and Measured Loads on Wing and Horizontal Tail in Pull-Up Maneuvers. ARR L5H11 (WR L-193), Oct.
1945.
3. Garvin, John B.: Flight Measurements of Aerodynamic Loads on the Horizontal Tail Surface of a Fighter-Type Airplane. TN 1483, Nov. 1947.
4. Sadoff, Melvin and Clousing, Lawrence A.: Measurements of the Pressure Distribution on the Horizontal-Tail Surfaces of a Typical Propeller-Driven Pursuit Airplane in Flight. III—Tail Loads in Pull-Up Push-Down Maneuvers. TN 1539, Feb. 1948.
5. NACA Flight Research Maneuvers Section: Flight Studies of the Horizontal-Tail Loads Experienced by a Modern Fighter Airplane in Abrupt Maneuvers. Report 792, 1944.
6. AC 23-15A, Small Airplane Certification Compliance Program The first paragraph of the Reference 1 CONCLUDING REMARKS reads:
“With the test airplane operated within maneuvering limits which were considered safe by design specifications in use at the time the airplane was designed, units loads were measured on the stabilizer which were not only considerably in excess of the design unit loads, but which occurred in a direction opposite to the design loads.”