1、_SAE Technical Standards Board Rules provide that: “This report is published by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising theref
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3、y be reproduced, stored in a retrieval system or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. TO PLACE A DOCUMENT ORDER: Tel: 877-606-7323 (inside USA and Canada) Tel: +1 724-776-4970 (outside US
4、A) Fax: 724-776-0790 Email: CustomerServicesae.org SAE WEB ADDRESS: http:/www.sae.orgSAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/ARP5644AEROSPACERECOMMENDEDPRACTICEARP5644 Issued 2013-04 Landing Gear Shock Absorption Testing
5、 of Civil Aircraft RATIONALEThis SAE Aerospace Recommended Practice (ARP) has been developed to document the requirements for jig drop testing of civil aircraft landing gear. It details the requirements of the FAA Code of Federal Regulations and EASA Certification Specifications. It provides recomme
6、ndations for drop test procedures, data collection, test conditions, post-test inspections, and test reporting. It also provides guidance for analytical test correlation. TABLE OF CONTENTS 1. SCOPE 31.1 Purpose . 32. REFERENCES 33. BACKGROUND 44. DEFINITIONS . 45. TEST OBJECTIVES 56. GENERAL REQUIRE
7、MENTS . 56.1 Part 25 Aircraft - Transport Category Airplanes 56.2 Part 23 Aircraft - Normal, Utility, Acrobatic, and Commuter Category Airplanes . 66.3 Part 27 Aircraft - Normal Category Rotorcraft . 66.4 Part 29 Aircraft - Transport Category Rotorcraft . 77. TEST SPECIFICATION REPORT 78. TEST WITNE
8、SSING . 79. TEST CONFORMITY 710. TEST EQUIPMENT . 710.1 Tower 710.2 Carriage 910.3 Lift Cylinders . 910.4 Load Platform 910.5 Wheel Spin Device 910.6 Landing Gear Test Article . 910.7 Data Acquisition System . 910.8 Video Recording 1011. INSTRUMENTATION . 10SAE ARP5644 Page 2 of 24 12. DATA REDUCTIO
9、N AND COMPUTATIONS . 1112.1 Drop Height and Sink Rate . 1112.2 Lift and Weight 1112.3 Energy . 1312.4 Wheel Speed . 1312.5 Load Factor . 1312.6 Stroke Rate and Discharge Coefficient . 1413. TEST CONDITIONS PRIOR TO DROP TESTING . 1413.1 Static “Air Curve” Test . 1413.2 Gas Entrainment Test . 1413.3
10、Rebound Snubbing Test . 1514. DROP TEST CONDITIONS 1614.1 Aircraft Attitude 1714.2 Weight Requirements . 1714.3 Lift Requirements 1714.4 Wheel Speed at Tire Contact 1714.5 Development Drops 1714.6 Limit Energy Drops 1814.7 Reserve Energy Drops 1814.8 System Failure Drops . 1914.9 Growth Drops 1914.1
11、0 Miscellaneous Drops . 1914.11 Summary of Drop Test Conditions 1915. GEAR TEAR DOWN INSPECTION 1916. TEST REPORTING . 2017. CERTIFICATION BY ANALYSIS 2218. ANALYTICAL CORRELATION . 2218.1 Static “Air Curve” Test . 2218.2 Rebound Snubbing Test . 2218.3 Drop Tests . 2318.4 Effect on Certification Loa
12、ds . 2419. NOTES 24FIGURE 1 DROP TEST EQUIPMENT SCHEMATIC . 8FIGURE 2 FREE DROP HEIGHT VERSUS SINK RATE 11TABLE 1 SUMMARY OF PART 25 MAIN GEAR DROP TEST CONDITIONS . 20SAE ARP5644 Page 3 of 24 1. SCOPE The intent of this document is to provide recommended practices for conducting shock absorption te
13、sting of civil aircraft landing gear equipped with oleo-pneumatic shock absorbers. The primary focus is for Part 25 aircraft, but differences for Part 23, 27, and 29 aircraft are provided where appropriate. 1.1 Purpose The purpose of this document is to provide landing gear shock absorber impact tes
14、t requirements and recommendations for civil aircraft. Guidance on test analytical correlation is also provided. Test data acquisition is defined which allow forthe evaluation of the landing gear performance in regards to energy absorption requirements and validation of the analytical model used to
15、determine design landing loads on the aircraft. The requirements and recommendations provided herein are intended to be used in the test specification report provided to the testing facility. 2. REFERENCES Landing gear impact testing of civil aircraft is governed by the following Parts of the Code o
16、f Federal Regulations for U.S. certification.14 CFR Part 23: Normal, Utility, Acrobatic, and Commuter Category Airplanes 23.723, Amendment 23-49, Feb 9, 1996 23.725, Amendment 23-48, Feb 9, 1996 23.726, Amendment 23-7, Aug 13, 1969 23.727, Amendment 23-7, Aug 13, 1969 14 CFR Part 25: Transport Categ
17、ory Airplanes25.723, Amendment 25-103, May 16, 2001 AC 25.723-1, “Shock Absorption Tests”, May 25, 2001 Draft revision to AC 25.723-1, ARAC LDHWG Report, March 26, 2003 14 CFR Part 27: Normal Category Rotorcraft 27.723, original release 27.725, original release 27.727, Amendment 27-26, May 6, 1990 1
18、4 CFR Part 29: Transport Category Rotorcraft 29.723, original release 29.725, Amendment 29-3, Jan 26, 1968 29.727, Amendment 29-30, April 5, 1990 For European certification, the regulations are provided in the following Certification Specifications (CS): CS-23: Normal, Utility, Aerobatic, and Commut
19、er Category Aeroplanes23.723, Initial Issue, November 14, 2003 23.725, Initial Issue, November 14, 2003 23.726, Initial Issue, November 14, 2003 23.727, Initial Issue, November 14, 2003 CS-25: Large Aeroplanes25.723, Initial Issue, October 17, 2003 AMC 25.723, Initial Issue, October 17, 2003 SAE ARP
20、5644 Page 4 of 24 CS-27: Small Rotorcraft 27.723, Initial Issue, November 14, 2003 27.725, Initial Issue, November 14, 2003 27.727, Initial Issue, November 14, 2003 CS-29: Large Rotorcraft 29.723, Initial Issue, November 14, 2003 29.725, Initial Issue, November 14, 2003 29.727, Initial Issue, Novemb
21、er 14, 2003 3. BACKGROUND The shock absorption test requirements for civil aircraft are based on 14 CFR Parts 23, 25, 27, and 29, and on Advisory Circular (AC) 25.723-1. These requirements are essentially the same as those in European Aviation Safety Agency (EASA) Certification Specifications. For P
22、arts 23, 27, and 29 aircraft (and until 2001 for Part 25 aircraft), the primary objectives of the drop test are to validate the limit design landing load factor, and to demonstrate energy absorption capability for limit and reserve energy levels. For Part 25 aircraft, the regulations changed signifi
23、cantly at Amendment 25-103. For this amendment, the primary purpose of the test changed from validation of limit load factor to validation of the dynamic analysis used to determine design landing loads. In addition, the revised requirements and accompanying Advisory Circular provide guidance on the
24、use of analysis for certification of growth versions of the aircraft in lieu of testing.4. DEFINITIONS AIR CURVE (OR “SPRING CURVE”): The shock strut gas pressure as a function of stroke (the gas is typically nitrogen, not air). ARAC: Aviation Rulemaking Advisory Committee. FREE DROP HEIGHT: Distanc
25、e the carriage drops prior to contacting the lift cylinders - this height determines the sink rate.LDHWG: Loads and Dynamics Harmonization Working Group (ARAC). LIMIT DESIGN ENERGY: The maximum kinetic energy associated with the design limit descent rates and weights. LOAD PLATFORM: The surface that
26、 the tires contact during the test, which includes load measurement instrumentation. MLW: The maximum structural design landing weight corresponding to the limit design sink rate. MTOW: The maximum structural design takeoff weight. MASS TRAVEL: The vertical distance travelled by the carriage after r
27、elease. MAXIMUM VERTICAL REACTION (MVR): The maximum vertical ground load achieved during the landing event for the limit design landing energy condition. This parameter is provided by the airframe manufacturer. METERING PIN: A shaft passing through the main orifice plate which provides a variable o
28、rifice area versus strut compression by means of a varying diameter; other examples are fluted or grooved pins. This device provides the desired strut load versus stroke as prescribed by the airplane manufacturer. OLEO-PNEUMATIC: Refers to hydraulic fluid damping/gas spring type of shock strut confi
29、guration. RESERVE ENERGY: The kinetic energy associated with 1.2 times the design limit sink rate at MLW. SAE ARP5644 Page 5 of 24 SINK SPEED OR SINK RATE: The vertical downward component of the landing speed at touchdown. STROKE: The amount of shock strut compression with respect to the fully exten
30、ded position. TEST SPECIFICATION REPORT (TSR): A report issued by the airframe manufacturer providing the test requirements for the test article, test conditions, instrumentation, conformity requirements, schedule, and post-test tear down inspection instructions. UNSPRUNG MASS: The moving portion of
31、 the gear below the gas spring (inner cylinder, truck, rolling stock, etc.). 5. TEST OBJECTIVES For Part 25 aircraft, until the changes in 14 CFR 25.723 at Amendment 25-103 (2001), the objectives of a jig drop test were to demonstrate that the design limit load factor was not exceeded and that the g
32、ear would not fail in a reserve energy test. Due to advancements in dynamic analysis capabilities, dynamic landing analyses have progressed to the point where accurate drop test simulation is now routinely performed. In addition, 14CFR 25.473 now requires that airframe flexibility and the dynamic ch
33、aracteristics of the landing gear be taken into account in the development of certification design loads, and further requires that this model be validated by drop tests. Therefore, in addition to demonstration of energy requirements, the objectives of a jig drop test with the amended Part 25 regula
34、tions include validation of the analytical model used to determine certification landing loads on the aircraft. Once validated, these models may be used to certify landing gear for derivative airplane models in lieu of drop testing. However, the drop test requirements remain in effect for new landin
35、g gear designs.For Parts 23, 27, and 29 aircraft, the regulations were not revised in the same manner as stated above for Part 25 aircraft, thus the objectives remain the validation of the limit landing load factor used for airframe design, and the demonstration of the limit and reserve energy requi
36、rements. 6. GENERAL REQUIREMENTS The requirements discussed in this section are based on Title 14 of the FAA Code of Federal Regulations (CFR) and EASA Certification Specifications (CS), at the Amendment levels specified in the references above. The FAA and EASA regulations are harmonized for drop t
37、est requirements, thus references to paragraph numbers in this report may be taken as referring to both agencies. The symbol “” refers to section number. When specifying required sink rates and drop heights in this and following sections, FAA values in English units are followed by EASA values in SI
38、 units. 6.1 Part 25 Aircraft - Transport Category Airplanes The limit energy test requirements for Part 25 Transport Category aircraft are given in 25.723, with further guidance provided in AC 25.723-1 and AMC 25.723. During the Aviation Rulemaking Advisory Committee (ARAC) harmonization effort from
39、 2001 to 2003, the Loads and Dynamics Harmonization Working Group (LDHWG) proposed to revise the drop test requirements and associated AC in an effort to incorporate the special conditions levied upon airplanes with more than two main landing gear units, such as the 747, DC-10, MD-11, A-340 and A-38
40、0. (All ground load loads requirements with the exception of towing were revised at the same time.) The committee released a Working Group Report (WGR) along with the revised rules and ACs. It is expected that the proposed revised rules will be released at some time in the future. However, since the
41、y have been released as part of the WGR, they may be used as an acceptable means of compliance (subject to agreement of the certifying agencies), and are thus provided in this report. 14 CFR 25.723(a) states: “The analytical representation of the landing gear dynamic characteristics that is used in
42、determining the landing loads must be validated by energy absorption tests. A range of tests must be conducted to ensure that the analytical representation is valid for the design conditions specified in Sec. 25.473.” A similar statement isfound in AC 25.723-1: “Shock absorption tests are necessary
43、to validate the analytical representation of the dynamic characteristics of the landing gear unit that will be used to determine the landing loads. A range of tests should be conducted to ensure that the analytical model is valid for all design conditions. In addition, consideration should be given
44、to ensuring that the range of test configurations is sufficient for justifying the use of the analytical model for foreseeable future growth versions of the airplane.”SAE ARP5644 Page 6 of 24 Limit energy requirements are given in 25.723(a)(1): “The configurations subjected to energy absorption test
45、s at limit design conditions must include at least the design landing weight or the design takeoff weight, whichever produces the greater value of landing impact energy.” This is a difference from past regulations, which required tests at both MLW and MTOW.14 CFR 25.723(a)(2) gives the requirements
46、for test attitudes and drag loads: “The test attitude of the landing gear unit and the application of appropriate drag loads during the test must simulate the airplane landing conditions in a manner consistent with the development of rational or conservative limit loads.” Thus the test must cover th
47、e range from level to maximum tail down attitudes. The drag load requirement drives the type of platform used in the test to ensure that a sufficiently high friction coefficient is achieved to validate the fore-aft dynamic characteristics of the gear. The requirements for the reserve energy test are
48、 provided in 25.723(b): “The landing gear may not fail in a test, demonstrating its reserve energy absorption capacity, simulating a descent velocity of 12 f.p.s. at design landing weight, assuming airplane lift not greater than airplane weight acting during the landing impact.” The requirements sta
49、ted above are intended for new landing gear designs. The regulations allow the use of analysis for certification of landing gear test requirements for growth versions of the aircraft. This is stated in 25.723(c) as follows: “In lieu of the tests prescribed in this section, changes in previously approved design weights and minor changes in design may be substantiated by analyses based on previous tests conducted on the
