IEC/TR 62131 2 Edition 1 0 2011 02 TECHNICAL REPORT Environmental conditions – Vibration and shock of electrotechnical equipment – Part 2 Equipment transported in fixed wing jet aircraft IE C /T R 6 2[.]
Lockheed Tristar KC Mk 1
Vibration data for the Lockheed Tristar KC Mk 1 aircraft were obtained from a Lockheed report on a flight test conducted for a US DoD program This report details a single flight of a Lockheed Tristar L-1011 wide-body commercial aircraft, during which vibration measurements were taken at two positions within the aircraft across a comprehensive range of flight conditions, as outlined in Table 1.
The trial aircraft was completely equipped, as suggested by low-quality photographic evidence showing seating and internal fixtures, indicating it was not just a bare shell The gross weight of the aircraft during the data flight was within a specific range.
190 000 Kg (at take-off) and 165 000 Kg (on landing)
Measurements were made at two positions on the Lockheed aircraft as illustrated in Figure 1
The transducer positions are located near the aircraft's centerline at fuselage stations 804 and 1218 The center of gravity (c of g) transducers are mounted on the structure that supports the cargo bay floor, while the forward transducers are attached to the cabin roof using a bracket connected to the aircraft structure.
The data in reference [1] is of good quality, but the poor photocopy of the original report has led to some spectra being poorly defined The electrical noise from the aircraft systems was recorded at an acceptably low level Additionally, reference [1] indicates that various no signal data were collected to assess the noise floor of the entire instrumentation system The noise measurements, depicted in Figure 2, were conducted with the aircraft powered solely by the auxiliary power unit.
For several flight conditions (specifically numbers 2, 3, 7, 9, and 10 in Table 1), up to four distinct recordings were collected The resulting Power Spectral Densities (PSDs) were averaged and plotted to illustrate that the variation in vibration response across the different flight recordings is minimal The computed root mean square (r.m.s.) values for these cases align with the maximum PSD curve.
According to bibliographic reference [1], the analysis time for each power spectral density (PSD) was a minimum of 45 seconds, with an analysis bandwidth of 1,275 Hz, resulting in a normalized random error of 13, which is considered generally satisfactory Additionally, it was noted that all instrumentation underwent calibration.
To overlay the vibration responses on a single figure, the original data plots were manually digitized using up to 80 points In cases where the plot copies were poorly defined, they were enveloped to ensure that all major peak responses were included in the digitized version.
The flight conditions were categorized into two main groups: take-off and landing, and cruise The take-off and landing environment encompasses flight conditions 2, 3, 9, and 10, which include take-off, power and roll, low altitude climb, low altitude descent, and touchdown In contrast, the cruise environment is represented by flight condition 7, which pertains to high altitude cruise.
BAe VC10 K
In April 1985, a flight trial was conducted to assess vibration and shock data from the transport of two container assemblies within a VC10 aircraft The gathered data during this trial provides valuable insights into the performance and safety of cargo transport in aviation.
2 References in square brackets refer to the bibliography measurements made at the base of the containers The flight trial requirements and its analysis are presented in [1], [1], [5] and [6]
The trials encompassed standard benign conditions like cruising at altitude, as well as various emergency scenarios, including engine failure and firm landings However, the VC10 has limited capacity for handling such emergency situations.
The full list of the various flight conditions covered during the flight is presented in Table 2
The flight's load configuration is illustrated in Figure 16, featuring two 1,800 kg container assemblies The payload was secured following standard procedures, which included lashing the load containers to the designated tie-down points on the aircraft.
The flight instrumentation included 11 accelerometers to assess cargo hold vibrations, strategically placed both near the airframe and at the bases of the transported containers Measurements on the airframe were taken at cargo floor tie-down fixtures, which are firm mounting locations positioned at critical points in the cargo bay For the containers, measurements were conducted at rigid locations around their bases to effectively capture vibration input.
The nature of the vibration environment is, in general, broad band random The maximum vibration amplitudes measured at the cargo hold floor tend to occur within the 200 Hz to
The flight data has been generated with a bandwidth of 600 Hz, resulting in acceleration power spectral density (APSD) and acceleration-time history formats APSD plots cover a frequency range from 3.25 Hz to 2000 Hz, with amplitudes derived from averaging under specific flight conditions These results are applicable when the average properties of the data remain constant over time, such as during straight and level flight Detailed findings from the data processing are documented in references [2], [1], and [1].
The airframe/container measuring instrumentation has an overall accuracy tolerance of ±5.9%, with a typical value around ±4.0% The analysis features a resolution bandwidth of 3.25 Hz, and the variance error ranges from 3% to 12%.
The original data plots were hand digitized with up to 80 points to overlay the vibration responses on a single figure In cases where the plots were poorly defined, the unclear sections were enveloped to ensure that all significant peak responses were captured in the digitized version.
No discernible shocks were observed during either normal or ‘touch-and-go' landings ([1] contains a figure demonstrating this but it is not reproducible)
Although the VC10 was originally designed and operated as a commercial passenger and freight aircraft, it is no longer operated commercially The only known current operator is the
UK military Vibration information for this aircraft is included in this assessment because it has the potential to support the validity of data from other sources.
Boeing 747 Combi (freight and passengers)
A field study was performed on a Boeing 747 Combi aircraft traveling from Stockholm to New York and back, focusing on the measurement and analysis of shock and vibration effects on cargo during air transportation.
The study examined all flight phases, including taxiing, climbing, cruising in both calm and turbulent conditions, descent, and landing Key phases analyzed for cargo-influencing vibrations were: taxiing, take-off, initial climb, cruising under normal conditions, cruising during gusts or air pockets, descent and approach, landing (including touchdown, braking, and roll-out), and taxiing to the apron.
The field data analyzed through conventional frequency analysis and modeling techniques, as reported in [7], were supplemented with flight recorder data from both the field trial and additional flights to enhance the generalizability of the results.
The tri-axial accelerometer test setup was securely mounted on the pallet using double-sided tape, positioned approximately 0.5 m from the edge A separate vertical accelerometer was installed near the pallet's end, also about 0.5 m from the corner This configuration allowed for the recording of accelerations experienced by the pallet, reflecting the input to the cargo, rather than the accelerations dependent on the type of cargo itself It is important to note that the products and their weight do affect the recorded signals, influencing the choice of pallet loads for the test.
'typical' In field trial number 1 the weight of the test pallet was 1 470 kg and in field trial number 2 the weight was 2 550 kg
The Boeing 747, known for its widespread use in freight and passenger transportation, was the aircraft utilized in the field trials Specifically, the plane involved was named Dan Viking.
The 500 in the 747 series, a Combi version delivered in 1981, had the pallet positioned on the main deck, near the center of gravity.
The field data collected during the trip underwent computer analysis in both time and frequency domains Frequency domain analysis utilized conventional spectral analysis and autoregressive modeling techniques, with a sampling frequency of 100 Hz and a low-pass filter set at 31.5 Hz Due to a favorable signal-to-noise ratio, post-analysis adjustments allowed for estimates up to 50 Hz by compensating for filtering effects The number of records, each consisting of 256 samples, varied based on the flight phase duration, with a maximum of 350 records (approximately 15 minutes) for the cruise phase The Blackman window was primarily employed for frequency analysis, while the Hamming window was used for autoregressive modeling in spectral estimation.
Table 5 summarizes the recorded extreme values and root mean square (r.m.s.) values from the experiment The transducers include V2, a vertical accelerometer positioned at the pallet corner, V1, located near the pallet center, T, the transversal accelerometer, and L, the longitudinal accelerometer; V1, T, and L are part of the tri-axial test setup Due to the absence of clear boundaries between different flight phases, signal characteristics and the test protocol were utilized for separation The first four records of the landing phase in Table 5 represent the touchdown event.
Table 6 presents the expected acceleration levels that may be exceeded for over 1% of the test duration, assuming a normal distribution To calculate these levels, the standard deviation is multiplied by a factor of 2.576, indicating that 0.5% of the values will exceed this threshold in both positive and negative directions Consequently, Table 6 illustrates the distribution of instantaneous values.
Supplementary data
Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-
The data collection exercise identified some additional relevant sets of information, which come from reputable sources, but for which the data quality could not be adequately verified
They are included here to facilitate validation of data from other sources Care should be taken when utilizing information in this category
The French military specification GAM EG 13 provides detailed information regarding the cargo hold of a DC8 cargo aircraft, focusing on three transducers across eight different flight conditions A summary of the severity levels for these eight flight conditions is also included.
Table 7 Spectra for the most severe flight conditions are presented in Figures 24, 25 and 26
For the most part the data presented in [1] are of low level to the extent that the measurements appear close to the measurement system noise floor (see Figure 26)
3.4.3 Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-135 (707)
In the early 1970s, J.T Foley at Sandia National Laboratories conducted a significant study to validate transportation severities for the US military specification Mil Std 810, focusing on jet aircraft This research involved three transport aircraft: C5A, C-141, and NC-135, but the methodology used does not allow for the identification of data from individual aircraft Foley's unique analysis process is not directly compatible with other assessments; however, he produced test spectra that can be effectively compared with data from alternative methods and sources, as illustrated in Figures 27 to 30 and Tables 8 and 9.
General remark
The purpose of the following paragraphs is to review each data source for self consistency
The evaluation of vibration data considers variations caused by operational usage and aircraft characteristics The confidence levels obtained from this analysis significantly impact the factoring and enveloping methods employed to determine environmental levels.
Lockheed Tristar KC Mk 1
Relative severity of flight conditions
Take-off, maximum power, and roll conditions generate the highest vibration levels due to the engines' increased power demands Additionally, climb and acceleration phases produce higher APSD levels compared to cruising Landing, particularly during touchdown in the fore and aft direction, also shows significant vibration levels, primarily attributed to the use of reverse thrust after the aircraft has touched down.
Position within the cargo hold
Vibration levels at the forward transducers are generally higher than those at the center of gravity (c of g) under the same flight conditions, especially in lateral responses, which can be up to four times greater The only exception occurs during touchdown, where c of g levels exceed due to reverse thrust, resulting in increased engine-induced responses in the 200 Hz to 600 Hz range The spectral characteristics differ significantly between the forward and c of g positions, with forward measurements showing consistent peaks at 35 Hz, 100 Hz, 130 Hz, and 180 Hz to 250 Hz, while c of g responses are mostly flat with peaks between 400 Hz and 600 Hz Typical vibration responses for take-off and landing are illustrated in Figures 8, 9, 12, and 13, and Figures 10 and 11 depict responses during cruise.
Relative severity of measurement axes
At the center of gravity (c of g), the fore and aft direction shows the highest vibration levels, likely due to the proximity and alignment of the transducers to the engines The vertical and lateral responses at the c of g are generally similar In contrast, the forward group measurements reveal that the longitudinal and transverse directions yield an equal number of peak responses, while the vertical responses are typically lower than those in other directions.
BAe VC10 K
Relative severity of measurement axes
To ensure maximum consistency, the relative severity of vibration across three measurement axes was analyzed using data from triaxial accelerometers The findings reveal that the vibration levels in the vertical, transverse, and fore/aft axes are typically in the ratio of 1:0.8:0.3, respectively.
Data from the forward container exhibit a distinct pattern due to power supply noise affecting low vibration levels This is evidenced by the comparison of Acceleration Power Spectral Densities (APSDs) between forward and rear-mounted containers, illustrated in Figures 19 and 20 Additionally, the analysis of acceleration (g) root mean square (r.m.s.) in the frequency range of 3.25 Hz to 399 Hz, as detailed in Table 4, aligns with expectations concerning the relative severity of the axes when noise components are excluded.
Boeing 747 Combi (freight and passengers)
Relative severity of flight conditions
The rear of the aircraft experiences more severe conditions than the forward locations, primarily due to thicker boundary layers, the proximity of the engines, and the influence of engine jet flow.
Most data sources have employed acceleration power spectral density to analyze vibration data, which is effective for cruise vibrations due to their broad band random characteristics and relative stationarity However, this method is less suitable for take-off and landing conditions, where responses fluctuate rapidly and peak for only a few seconds While most data for these phases, except for Foley's, is presented as acceleration power spectral densities, the analysis periods differ significantly.
Lockheed Tristar KC Mk 1
The data consistently reveals distinct dynamic characteristics in the vibration environment during take-off and landing compared to cruising Consequently, the descriptions of these environments are provided separately for take-off and landing, as well as for cruise.
The descriptions compile all digitized vibration spectra from various measurement sites and directions under relevant flight conditions, representing the worst-case measured data for the environment.
The environment vibration description for cruise is given in Figure 14 It includes all the spectra produced from the data recorded during flight condition 7
The environmental vibration descriptions for take-off and landing are given in Figure 15 It includes all the spectra produced from the data recorded during flight conditions 2, 3, 9 and
The data encompasses measurements from both the forward and center of gravity (c of g) sites, highlighting peak responses at frequencies of 35 Hz, 100 Hz, 130 Hz, and 180 Hz to 250 Hz from the forward position, as well as significant responses in the frequency range of 400 Hz to 600 Hz from the c of g measurements.
BAe VC10 K
Environment descriptions, in terms of a set of worst case vibration spectra, have been compiled by overlaying APSDs during all flight conditions The resulting spectra are shown in
Figure 21 No environment description for shock conditions are presented as there was none perceivable in the measurements.
Boeing 747 Combi (freight and passengers)
No vibration or shock environmental descriptions were derived or presented in [1]
The data collection process has revealed two pertinent information sets from reputable sources; however, the quality of this data remains unverified These sets are included to assist in validating data from alternative sources, but caution is advised when using this information.
No environmental descriptions were derived or presented in [8]
7.3 Lockheed C5A (Galaxy), Lockheed C-141 (Starlifter) and Boeing NC-135 (707)
The environmental descriptions for these aircraft, based on vibration analysis, differ from those in this assessment Figure 27 illustrates Foley’s environmental description for vibration, showcasing the one standard deviation level of response after applying various band pass filters For a comprehensive discussion on Foley's methodology, refer to source [9] Additionally, a landing shock has been identified.
Foley is shown in Figure 28 From the environmental description Foley derived test severities for take-off and landing (Figure 29 and Table 3 as well as cruise (Figure 30 and Table 10)
The test descriptions involve a broadband random test with several discrete sine components superimposed The reasoning behind this approach is not well understood, and the frequencies of these components seem to correspond to the harmonics of aircraft power supplies.
Broadly the identified data sources indicate a maximum spectral value during cruise of
The vibration levels measured on the aircraft floor ranged from 0.001 g²/Hz to 0.005 g²/Hz during take-off and landing The maximum root mean square (r.m.s.) value recorded was 0.67 g, which occurred near the engines while reverse thrust was applied Typically, the highest r.m.s value observed on the aircraft floor was lower than this peak.
The aircraft floor responses typically exhibit a broad band spectrum ranging from approximately 10 Hz to 1,000 Hz, while the spectral content may vary by source and location In contrast, the responses on packages are predominantly below 100 Hz, with the specific frequency likely influenced by the dynamic characteristics of each individual package.
IEC 60721-3-2:1997 outlines environmental categories for stationary and non-stationary vibrations, specifically categories b) and c), which cover various transportation conditions, including those experienced during jet aircraft transport These categories are represented in Figures 29 and 30 and include all three dynamic classification groups defined in the standard.
The data analysis for this exercise shows that IEC 60721-3-2 accurately classifies jet air transport as stationary vibration random Additionally, the observed severities in real-world scenarios fall within the vibration severities outlined in the standard.
According to IEC 60721-3-2:1997, Table 5, environmental category b) classes 2M1, 2M2, and 2M3, the acceleration power spectral density values are significantly higher than those recorded for jet air transport Specifically, the values in this standard are between 10 and 100 times greater than the worst-case scenarios previously observed.
The data reviewed did not reveal any significant shocks, particularly not those comparable to the standards set by IEC 60721-3-2:1997, Table 5, for environmental category c) concerning non-stationary vibration and shock This aligns with findings from [7], which indicated that the most severe stress levels occur during ground handling and transport phases of air transport, while take-off and landing are less severe, and airborne phases experience even lower accelerations.
An argument could be made that IEC 60721-3-2:1997, Table 5, environmental category c)
Non-stationary vibration, which includes shock, is particularly relevant during take-off and landing phases However, the test severities depicted in Figure 30 do not adequately represent these conditions Despite being transitory, take-off and landing generate substantial vibration This contradicts the classification in IEC 60721-3-2:1997, Table 5, environmental category c), where the severities are characterized as a simple shock pulse rather than true non-stationary vibration.
In addition to IEC 60721-3-2, various environmental test severities for equipment transported in jet aircraft can be compared with identified data sources The test severities from Foley are illustrated in Figures 27 and 28, along with those from ASTM D 4728-91 and Mil.
Figures 33 and 36 illustrate Std 810 issue F and G, AECTP 400, and Def Stan 00-35, highlighting significant variations in test severities The test spectra primarily reflect conditions on the aircraft floor, while one AECTP severity and the ASTM D 4728-91 test severity correspond to responses observed on packages Among the reviewed test specifications, only a few stand out.
ASTM D 4728-91 is designed for non-military applications and serves as a reasonable test severity for packaging However, its limited frequency range renders it insufficient to accurately represent conditions found on the aircraft floor.
The significant variation in test specifications remains unexplained, although most test severities incorporate a conservatism factor to address measurement discrepancies However, the specific sizes of these factors are not disclosed One possible explanation for the large variations is that the severities primarily rely on take-off and landing measurements, which are challenging to determine accurately due to their brief durations.
In the case of Def Stan 00-35 severity, the test duration is linked to usage, with a 1-hour test representing 6 hours of flight The most intense vibrations occur briefly during take-off and landing, while vibrations during cruise are generally less than one-fifth of those experienced during take-off and landing.
00-35 test duration appears extremely conservative