1、NASA TECHNICAL NOTEIZk_ZNASA TN D-6124SUMMARY OF CENTER-OF-GRAVITYACCELERATIONS EXPERIENCEDBY COMMERCIAL TRANSPORTAIRPLANES IN LANDING IMPACTAND GROUND OPERATIONSby Paul A. HunterLangley Research CenterHampton, Va. 23365NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. APRIL 1971Ji!/!P
2、rovided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-1. Report No. 2. Government Accession No. 3. Recipients Catalog No.NASA TN D-61244. Title and SubtitleSUM
3、MARY OF CENTER-OF-GRAVITY ACCELERATIONSEXPERIENCED BY COMMERCIAL TRANSPORT AIRPLANESIN LANDING IMPACT AND GROUND OPERATIONS7. Author(s)Paul A. Hunter9. Performing Organization Name end AddressNASA Langley Research CenterHampton, Va. 2336512. Sponsoring Agency Name and AddressNational Aeronautics and
4、 Space AdministrationWashington, D.C. 205465. Report DateApril 19716. Performing Organization Code8. Performing Organization Report No.L-748310. Work Unit No.126-61-11-0111. Contract or Grant No.13. Type of Report and Period CoveredTechnical Note14. Sponsoring Agency Code15. Supplementary Notes16. A
5、bstractData are presented on incremental normal accelerations due to landing impacts andto ground operations associated with taxi, takeoff, and landing. NASA VGH recorders,installed in a totalof 38 turbine-powered airplanes of both foreign and domestic airlines,were used to obtain the data. Limited
6、data on longitudinal deceleration during landing arealso presented.17. Key Words (Suggested by Author(s)Normal accelerationsLanding impactTaxiTakeoffLandingTurbine-powered transports19. Security Cle=if. (of this report)Unclassified18. Distribution StatementUnclassified - Unlimited20. Security Classi
7、f. (of this page) 21. No. of Pages 22. Price“Unclassified 65 $3.00For sale by the National Technical Information Service, Springfield, Virginia 22151f/!j : _Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction
8、or networking permitted without license from IHS-,-,-SUMMARY OF CENTER- OF-GRAVITY ACCELERATIONSEXPERIENCED BY COMMERCIAL TRANSPORT AIRPLANESIN LANDING IMPACT AND GROUND OPERATIONSBy Paul A. HunterLangley Research CenterSUMMARYA summary of landing impact accelerations has shown that for 24 operation
9、s(airline-airplane combination) representing a total of 22 464 landings, the initial positiveincremental landing impact accelerations expected to be exceeded once in 10 000 landingsrange from about 0.79g to about 1.67g (lg = 9.81 m/sec2). These differences among thelanding impact acceleration experi
10、ences of the various operations apparently reflect thecombined effects of differences among the airplane characteristics and landing approachtechniques used by the various airlines. These data were extrapolated by means ofmathematically fitted Pearson curves.In ground operations, only small differen
11、ces in overall normal acceleration experi-ence during taxi, takeoff, and landing exist for the seven operations investigated. Landingrollout contributed most heavily, and taxi contributed the least, to the overall groundacceleration experience. The maximum incremental accelerations recorded ranged f
12、rom0.5g to 0.7g.Longitudinal decelerations measured during 556 landings indicated that maximumvalues ranged from about 0.12g to 0.42g.INTRODUC TIONThe structural loads experienced by commercial transport airplanes during groundoperations (taxiing, takeoff, and landing) have an important bearing on t
13、he design strengthand fatigue requirements. Also, a knowledge of the loads imposed by the airplane on run-ways and taxiways is necessary for the proper design of these surfaces, particularly whennovel design features such as trestles and bridge-type construction are employed. Inas-much as statistica
14、l data on the loads are difficult to acquire, recourse often has been madein the past to deducing the loads from measurements of the center-of-gravity accelera-tions experienced by airplanes during routine operations. Information regarding landingimpact accelerations has been published in references
15、 1 and 7 and small samples ofProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-acceleration data during taxi, takeoff, andlanding for piston and turboprop transports aregiven in references 8 and 3, respectively. A somewhatlarger sample of groundacceler
16、a-tion datais given in reference 7 for a turbojet transport.As part of a continuingprogram to define the operational experiencesand loads ofturbine-powered transports, statistical groundload data havebeencollected on severaladditional types of airplanes operatedby United Statesand foreign airlines.
17、Thedata per-tain to the normal accelerations of the center of gravity during landing impact, taxiing,takeoff, and landing rollout and to the longitudinal decelerations during landing rollout.The frequencydistributions of the measuredaccelerations and some analysesof the dataare presentedin this pape
18、r. In order to provide a convenientsummary of all the groundloads data collected onturbine-powered airplanes, some of thepreviously published dataare also includedherein.AIRPLANESAND SCOPEOF DATASomeof the characteristics of the airplanes from which the datawere collected aregiven in table I. The un
19、its are given in both the International Systemof Units (SI)andU.S. Customary Units. Factors relating the two systems are given in reference 9. Themeasurementsand calculations were madein U.S. Customary Units. The basic airplanetypes are designatedby a Romannumeral anddifferent models of a basic type
20、 are denotedby letter suffixes. The suffix F is used to indicate turbofan-powered versions of twomodels of airplane type I. As shownin table I, data were collected from 18 airplanemodels encompassing12basic airplane types. The airplanes included two-, three-, andfour-engine modelsand rangedin maximu
21、m designtakeoff weight from 166808to1459017newtons (37500to 328000lbf).The scopeof the data is shownin table II for each of the airline operations fromwhich the datawere obtainedand the sample sizes evaluatedfor accelerations experiencedduring landing impact and groundoperations. For purposes of thi
22、s paper, an airline oper-ation is consideredto be one or more airplanes of a given model flown by a single airline.The airline operations are denotedby a letter designationof the airline preceding theRomannumeral and letter suffix designationof the airplane model. Samplesof landingimpact acceleratio
23、n were obtainedfrom 24airline operations involving a total of 38 indi-vidual airplanes. The sizes of the datasamples range from 556to 2445landings andintotal represent 22464landings. Normai accelerations experiencedduring taxi, takeoff,_d landing runout were obtained from sevenairline operations. Th
24、e individual data sam-ples represent from 158to 827flights. Data on the decelerations during landingwereobtainedfrom 556landings of a four-engine turbofan airplane flown in commercial cargooperations by oneairline._ _,-Provided by IHSNot for ResaleNo reproduction or networking permitted without lice
25、nse from IHS-,-,-INSTRUMENTATIONThe data were collected through the use of NASA VGH recorders (ref. 10) whichprovide time-history records of indicated airspeed, normal acceleration, and pressurealtitude on 61-meter (200-foot) rolls of photographic paper. A film transport speed of0.203 millimeter (0.
26、008 inch) per second was used to record landing impact accelerationsand longitudinal decelerations, and a speed of 0.787 millimeter (0.031 inch) per secondwas used to record data during taxi, takeoff, and landing rollout. The remote accelerationsensor was located as close as practicable to the airpl
27、ane center of gravity. In the mostextreme instance, the acceleration sensor was located 1.2 meters (4 feet) aft of the posi-tion equivalent to the 25-percent mean-geometric-chord location. The electrical signalfrom the acceleration sensor is transmitted to a galvanometer in the recorder base.Two typ
28、es of galvanometers having different response characteristics have beenused in the recording program. The response of the accelerometer in combination witheach type of galvanometer is shown in figure 1. As shown in the figure, the frequencyresponse of the recorder with galvanometer A is essentially
29、flat up to frequencies of about6 hertz, whereas that of the recorder with galvanometer B is flat up to about 10 hertz.Above these frequencies, both recorders progressively attenuate the response withincreasing frequency. The center-of-gravity normal acceleration at landing impactgenerally consists o
30、f a low-frequency component associated with the airplane rigid bodyresponse and superimposed high-frequency responses due to the structural modes. Fromspecial investigations of landing impact responses of several types of airplanes, it hasbeen observed that the structural mode responses generally ha
31、ve frequencies betweenabout 1_ hertz to 10 hertz. Also, the magnitude of these responses generally rangebetween 25 to 50 percent of the low-frequency rigid body response. Inasmuch as theslow film speed used in the present investigations does not permit separation of the struc-tural responses from th
32、e rigid body responses, the normal acceleration data obtainedrepresent the peak values of the combined responses. Because two types of recordershaving different response characteristics (fig. 1) have been used, there is a possibilitythat structural responses higher than about 6 hertz may not be refl
33、ected to the sameextent in the data collected with the two recorders. This aspect of the data will be dis-cussed further in the section entitled _Results and Discussion.“EVALUATION OF RECORDSThe evaluation of the records for the landing impact data consisted in reading themaximum positive normal acc
34、eleration increment (from the 1.0g trace position) due toeach initial landing impact. Subsequent accelerations, which may have occurred after theProvided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-initial landing impact, were not includedin the landing i
35、mpact databut were included inthe landing rollout data.The records of normal acceleration during ground operations were edited to denotethe portions of the records corresponding to preflight taxiing, takeoff, landing rollout, andpostflight taxiing. These classifications are definedas follows:Preflig
36、ht taxi - from initiation of taxiing to beginningof takeoff rollTakeoff - from beginningof takeoff roll to lift-offLanding rollout - from immediately after initial landing impactuntil airplane was slowedto taxi speedPostflight taxi - from endof landing rollout to termination of taxiingThe 1.0gpositi
37、on of the acceleration trace wasused as a reference from which to readthe incremental normal acceleration peaks which equaledor exceededselected thresholdvalues. Only the maximum incremental value of the acceleration wasread for eachcrossing of the reference. An incremental threshold value of 0.1gwa
38、s usedfor two ofthe operations, anda value of 0.2gwas usedfor the other five operations. The dataweretabulatedaccording to the four classifications previously discussed. Also, the data duringthe takeoff and landing rollout were further categorized according to intervals of airspeed.The time historie
39、s of deceleration during landing rollout generally exhibited a varia-tion similar to one of the three characteristics curves shownin figure 2. For eachlanding rollout, the maximum deceleration was read in the manner indicated in the figurein terms of inches of trace deflection. The trace deflections
40、 were converted to accelera-tion units and tabulatedin acceleration intervals of 0.01g. The datawere also sortedaccording to whether they camefrom anoperational flight or from an airplane- or pilot-checkflight.RESULTSAND DISCUSSIONLanding Impact AccelerationsThe frequencydistributions of initial pos
41、itive incremental landing impact accelera-tions are given in table III for the 24 operations. For eachoperation, the number oflandings represented, the number of airplanes involved in eachoperation, andthe refer-encesfor thosedatawhich havebeenpreviously publishedare given. In addition, themean valu
42、e and the value of acceleration expectedto be exceeded,on the average, oncein 10000landingsbasedonextrapolation by use of Pearson curves are also given. Thenumber 10000wasarbitrarily chosenas representative of the large amplitudes expectedduring extendedoperations.4Provided by IHSNot for ResaleNo re
43、production or networking permitted without license from IHS-,-,-Effect of galvanometer.- As was discussed in the section entitled _Instrumenta-tion,“ there is some question concerning possible disparity between the acceleration dataobtained by the recorders using the type A galvanometers and those o
44、btained by using thetype B galvanometers. In this connection, the data given in table HI for operation AIAFare particularly of interest inasmuch as part of these were obtained with the type Arecorder and the remainder with the type B recorder. To determine whether there wereany effects of recorder t
45、ype, the data were sorted according to the type of recorder, andthe two samples are shown in figure 3(a) in terms of the probability of equaling orexceeding a given value of acceleration during a landing. The results apparently showan increase in acceleration of about 20 percent by the use of the ty
46、pe B recorder. Becauseonly two rather small samples representing only one operation are involved, the evidenceis not considered conclusive, however. For further analysis, two other large data sam-ples - one from an operation using galvanometer type A and one from an operation usinggalvanometer type
47、B - were randomly divided into a number of smaller samples, compa-rable in size to those shown in figure 3(a). These small samples, presented in figure 3(b,show a variation in probability of exceeding a given landing impact acceleration, say forinstance 0.5g, of the same order for either operation a
48、s that shown in figure 3(a). Conse-quently, the results of figure 3(a) are believed to be attributable to sample size; it is con-cluded that galvanometer type had no appreciable affect on the accelerations measured.Data extrapolation.- In past presentations of landing impact acceleration probability
49、data, the data points have either been connected by straight-line segments or, wheresome extrapolation was desired, have been arbitrarily fitted with a Pearson type III curveusing the method of reference II. For the present data, a brief study was undertaken tofind a curve-fitting method that would predict more reliably the probability of occurrence
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