IEC TR 62131-7:2020

IEC TR 62131-7 ®
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Environmental conditions – Vibration and shock of electrotechnical equipment –
Part 7: Transportation by rotary wing aircraft:
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IEC TR 62131-7 ®
Edition 1.0 2020-04
TECHNICAL
REPORT
colour
inside
Environmental conditions – Vibration and shock of electrotechnical equipment –

Part 7: Transportation by rotary wing aircraft:

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 19.040 ISBN 978-2-8322-8237-3

– 2 – IEC 62131-7:2020 © IEC 2020
CONTENTS
FOREWORD . 5
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 7
4 Data source and quality . 8
4.1 Vibration of Boeing CH-47 rotorcraft . 8
4.2 Set down of underslung cargo from a Boeing CH-47 rotorcraft . 9
4.3 Supplementary data . 10
5 Intra data source comparison . 13
5.1 General . 13
5.2 Vibration of Boeing CH-47 rotorcraft . 13
5.3 Set down of underslung cargo from a Boeing CH-47 rotorcraft . 13
5.4 Supplementary data . 14
6 Inter data source comparison . 14
7 Environmental description . 14
7.1 Physical sources producing mechanical vibrations . 14
7.2 Environmental characteristics and severities . 16
7.3 Derived test severities . 17
8 Comparison with IEC 60721 (all parts) [16] . 18
9 Recommendations . 21
Bibliography . 50

Figure 1 – Typical vibration spectra for CH-47 rotorcraft during straight and level flight at
160 kn [1] . 22
Figure 2 – Typical vibration spectra for CH-47 rotorcraft during hover [1] . 22
Figure 3 – Typical vibration spectra for CH-47 rotorcraft during transition to hover [1] . 23
Figure 4 – Typical vibration spectra for CH-47 rotorcraft during autorotation [1] . 23
Figure 5 – Comparison of CH-47 vibration overall RMS for different flight conditions [1] . 24
Figure 6 – Comparison of CH-47 vibration RMS severities at rotor shaft frequency (r) for
different flight conditions [1] . 25
Figure 7 – Comparison of CH‑47 vibration RMS severities at rotor blade passing
frequency (nr) for different flight conditions [1] . 26
Figure 8 – Comparison of CH‑47 vibration RMS severities at second rotor blade passing
frequency (2nr) for different flight conditions [1] . 27
Figure 9 – Comparison of CH‑47 vibration RMS severities at third rotor blade passing
frequency (3nr) for different flight conditions [1] . 28
Figure 10 – Comparison of CH‑47 vibration RMS severities at fourth rotor blade passing
frequency (4nr) for different flight conditions [1] . 29
Figure 11 – Comparison of CH‑47 vibration RMS severities across cargo bay floor during
hover [1] . 30
Figure 12 – Comparison of CH‑47 vibration RMS severities across cargo bay floor during
transition to hover manoeuvre [1] . 30
Figure 13 – Comparison of CH‑47 vibration RMS severities across cargo bay floor during
a transition to autorotation manoeuvre [1] . 31
Figure 14 – Comparison of CH‑47 vibration RMS severities across cargo bay floor during
straight and level flight [1] . 31

IEC 62131-7:2020 © IEC 2020 – 3 –
Figure 15 – CH‑47 rotorcraft ISO container set down shock severities [2] . 32
Figure 16 – Relative amplitude variations with airspeed for the Lynx rotorcraft [3]. 32
Figure 17 – Relative amplitude variations with airspeed for the Seaking rotorcraft [3] . 33
Figure 18 – Relative amplitude variations with airspeed for the Chinook rotorcraft [3] . 33
Figure 19 – Airframe to airframe relative amplitude variations for the Lynx rotorcraft [3] . 34
Figure 20 – Comparison of fleet vibration statistics [5] . 35
Figure 21 – Super Frelon rotorcraft measurements for X axis [6] . 36
Figure 22 – Super Frelon rotorcraft measurements for Y axis [6] . 36
Figure 23 – Super Frelon rotorcraft measurements for Z axis [6] . 37
Figure 24 – Vibration test severity derived for the CH‑47 rotorcraft using the approach of
Mil Std 810 [9] . 37
Figure 25 – Vibration test severity derived for the transportation of equipment in CH‑47
rotorcraft using the approach of STANAG 4370 AECTP 400 Method 401 Annex D [10] . 38
Figure 26 – Vibration test severity for equipment carried as underslung loads STANAG

4370 AECTP 400 Method 401 Annex D [10] . 38
Figure 27 – Rotorcraft specific vibration test severities for Chinook (CH‑47) from
Def Stan 00‑35 [5]. 39
Figure 28 – Rotorcraft specific vibration test severities for Merlin from Def Stan 00‑35 [5] . 39
Figure 29 – Rotorcraft specific vibration test severities for Lynx/Wildcat from
Def Stan 00‑35 [5]. 40
Figure 30 – Vibration test severities for underslung loads from Def Stan 00‑35 [5] . 40
Figure 31 – Rotorcraft specific vibration test severities for CH‑47 from RTCA/DO‑160 [11]
and EUROCAE/ED‑14 [12] . 41
Figure 32 – IEC 60721‑3‑2:1997 [17] – Stationary vibration random severities . 41
Figure 33 – IEC TR 60721‑4‑2:2001 [18]– Stationary vibration random severities . 42
Figure 34 – IEC 60721‑3‑2:1997 [17] – Stationary vibration sinusoidal severities . 42
Figure 35 – IEC TR 60721‑4‑2:2001 [18] – Stationary vibration sinusoidal severities . 43
Figure 36 – IEC 60721‑3‑2:1997 [17] – Shock severities . 43
Figure 37 – IEC TR 60721‑4‑2:2001 [18] – Shock severities for IEC 60068‑2‑29:1987 [20]
test procedure . 44
Figure 38 – IEC TR 60721‑4‑2:2001 [18] – Shock severities for IEC 60068‑2‑27 [19] test
procedure . 44
Figure 39 – Comparison of CH‑47 rotorcraft vibrations [1] with IEC 60721‑3‑2:1997 [17] . 45
Figure 40 – Comparison of Super Frelon rotorcraft X axis vibrations [6] with
IEC 60721‑3‑2:1997 [17] . 45
Figure 41 – Comparison of Super Frelon rotorcraft Y axis vibrations [6] with
IEC 60721‑3‑2:1997 [17] . 46
Figure 42 – Comparison of Super Frelon rotorcraft Z axis vibrations [6] with

IEC 60721‑3‑2:1997 [17] . 46
Figure 43 – Comparison of Mil Std 810 vibration test severity [9] with
IEC 60721‑3‑2:1997 [17] . 47
Figure 44 – Comparison of AECTP 400 vibration test severity [10] with
IEC 60721‑3‑2:1997 [17] . 47
Figure 45 – Comparison of Def Stan 00‑35 vibration test severity [5] with
IEC 60721‑3‑2:1997 [17] . 48
Figure 46 – Comparison of DO160 vibration test severity [11] with
IEC 60721‑3‑2:1997 [17] . 48

– 4 – IEC 62131-7:2020 © IEC 2020
Figure 47 – Comparison of underslung load vibration test severities [5] and [10] with
IEC 60721‑3‑2:1997 [17] . 49
Figure 48 – Comparison of CH‑47 rotorcraft set down shock severities [2] with
IEC 60721-3-2:1997 [17] . 49

Table 1 – Typical structural dynamic excitation frequencies and their source . 15

IEC 62131-7:2020 © IEC 2020 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ENVIRONMENTAL CONDITIONS – VIBRATION AND
SHOCK OF ELECTROTECHNICAL EQUIPMENT –

Part 7: Transportation by rotary wing aircraft

FOREWORD
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent
rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected data
of a different kind from that which is normally published as an International Standard, for
example "state of the art".
IEC TR 62131-7, which is a Technical Report, has been prepared by IEC technical committee
104: Environmental conditions, classification and methods of test.
The text of this Technical Report is based on the following documents:
Enquiry draft Report on voting
104/839/DTR 104/854/RVDTR
Full information on the voting for the approval of this technical report can be found in the report
on voting indicated in the above table.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.

– 6 – IEC 62131-7:2020 © IEC 2020
A list of all parts in the IEC 62131 series, published under the general title Environmental
conditions – Vibration and shock of electrotechnical equipment, can be found on the IEC
website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
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IEC 62131-7:2020 © IEC 2020 – 7 –
ENVIRONMENTAL CONDITIONS – VIBRATION AND
SHOCK OF ELECTROTECHNICAL EQUIPMENT –

Part 7: Transportation by rotary wing aircraft

1 Scope
This part of IEC 62131, reviews the available dynamic data relating to the transportation of
electrotechnical equipment by rotorcraft (helicopters). The intent is that from all the available
data an environmental description will be generated and compared to that set out in IEC 60721
(all parts) [16] .
For each of the sources identified the quality of the data is reviewed and checked for
self-consistency. The process used to undertake this check of data quality and that used to
intrinsically categorize the various data sources is set out in IEC TR 62131-1 [21].
This document primarily addresses data extracted from a number of different sources for which
reasonable confidence exist in its quality and validity. This document also reviews some data for
which the quality and validity cannot realistically be verified. These data are included to facilitate
validation of information from other sources. This document clearly indicates when utilizing
information in this latter category.
This document addresses data from a number of data gathering exercises. The quantity and
quality of data in these exercises varies considerably as does the range of conditions
encompassed.
Not all of the data reviewed were made available in electronic form. To permit comparison to be
made, in this assessment, a quantity of the original (non-electronic) data has been manually
digitized.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
No terms and definitions are listed in this document.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
___________
Numbers in square brackets refer to the bibliography.

– 8 – IEC 62131-7:2020 © IEC 2020
4 Data source and quality
4.1 Vibration of Boeing CH-47 rotorcraft
A number of measurement exercises have been undertaken on the Boeing CH-47 rotorcraft, of
those the measurements presented in [1] and [2] are typical. Many measurement exercises have
focused on the vibration responses of carried goods, passengers and crew. However, the
measurements of [1] and [2] were made specifically to characterize the vibration responses of
the payload deck area within the rotorcraft.
The Boeing CH-47 rotorcraft is a twin rotor, twin engine heavy lift aircraft which first entered
service in 1961. Although it is designed as a military aircraft, a number of commercial variants
exists and those versions are widely used for the transportation of large or heavy equipment.
They are also typically used to transport items to locations difficult to access by other means.
The CH-47 is known by a number of different names including Chinook, Model 234 and
Model 414. Also different designations arise indicating variants of the original design. The
particular rotorcraft used in the measurement exercise was typical of most Boeing CH-47
variants with twin rotors each comprising three blades. The rotor shaft speed is around 225 rpm
(3,75 Hz) giving a rotor blade passing frequency of 11,25 Hz.
The Boeing CH-47 was one of the fastest rotorcraft available when it first entered service and
even today it is still amongst the fastest rotorcraft in commercial use. As rotorcraft vibration
severities are strongly related to aircraft speed, an aspect which will be discussed later, the
Boeing CH-47 is often used to set rotorcraft vibration severities for the transportation of
equipment.
The cargo bay area of the Boeing CH-47 extends from frame 120 which is located just aft of the
plane of the forward rotor to frame 482 which is located just forward of the plane of the aft rotor
and attachment location of the twin engine. Frame 320 is located approximately in the centre of
the length of the cargo bay area.
Rotorcraft generate a dominant vibration severity which commonly coincides with sensitivity of
the human body to vibration. Indeed prolonged exposure to some rotorcraft vibrations can
exceed recommended daily dosage to such vibrations. As a consequence, many rotorcraft
vibration measurement exercises are aimed at quantifying human body exposure. However, the
sensitivity of the human body to vibrations is predominantly biased towards the low frequencies,
which are well below the frequency range normally considered for the testing of electrotechnical
equipment. As such, measurement exercises made to quantifying human body exposure are
mostly unsuitable for the purpose of this document. Moreover, a rotorcraft of concern from the
viewpoint of human body exposure may not necessarily be of concern from the viewpoint of
electrotechnical equipment. This is because the sensitivity of the human body is biased towards
certain low frequencies.
The measurements of [1] and [2] on the Boeing CH-47 rotorcraft comprised twelve piezo-electric
accelerometers and associated charge amplifiers. The vibration measurements were recorded on
a 14-channel FM recorder. The system provided an effective measurement frequency range of
2,5 Hz to 2 500 Hz. The accelerometers were arranged in four mostly tri-axial groups placed on
the cargo bay floor, along its length on the starboard side. Separate flights vibration
measurements were additionally made on two payloads, each of approximately two tonne,
carried within the cargo bay area. All the transducers were internally mounted on relatively stiff
airframe locations.
Measurements were made during several flights and during a range of different flight conditions.
Typically, vibration measurements on rotorcraft are made during a range of different steady state
conditions. Such steady state conditions include hover and a variety of straight and level flight
speeds at different altitudes. Additionally, vibration measurements are commonly made during a
___________
Boeing CH-47 is the trade name of a product supplied by Boeing. This information is given for the convenience of
users of this document and does not constitute an endorsement by IEC of the product named.

IEC 62131-7:2020 © IEC 2020 – 9 –
variety of transient flight conditions. Such transient conditions include take-off, landing, transition
to hover as well as transition to autorotation. Some of these transient conditions occur at some
time on most flights whereas other conditions (such as transition to autorotation) may only be
used in emergency or training situations. Transient conditions can be difficult to measure but can
give rise to quite severe vibration severities. Steady state and transient vibration conditions can
arise due to a number of mechanisms which are addressed in Clause 7.
The measurements of [1] and [2] on the Boeing CH-47 rotorcraft were analysed mostly in the
form of acceleration power spectral densities (PSDs), although very few of these are presented
in the reports referenced. Neither of the two reports indicates the record duration used for the
power spectral density analysis. However, the analysis durations, typically used by the agency
that made these measurements, is around 30 s for steady state conditions. With that said,
durations will be more limited for the transient flight conditions and usually limited to the duration
of the events, some of which only occur for a few seconds.
The approach used to quantify the vibration amplitudes at the rotor shaft, blade passing
frequency and their harmonics, is a particular data analysis issue encountered when addressing
rotorcraft vibration data. In this case the frequency analysis bandwidth is around 2,5 Hz. Whilst
this is adequate to describe the broadband background vibration induced by rotorcraft, it is
generally regarded as inadequate to quantify, in terms of power spectral density amplitude, the
tones arising from the rotor blade passing frequency and the associated harmonics. For this
reason the tones arising from the rotor blade passing frequency and subsequent associated
harmonics, are quantified in terms of root mean square (RMS) values. The usual approach used
by this measurement agency, was to compute the tonal component root mean square by
integration of the power spectral density amplitudes for each tonal component. Reports [1] and
[2] indicate that peak hold spectra were used (rather than the "average" power spectral density
values) to estimate the amplitudes at rotor and blade passing frequencies.
Reports [1] and [2] present power spectral densities for selected flight conditions only. A number
of these are reproduced in Figure 1 to Figure 4. These include straight and level flight at the
rotorcraft's typical best sustained flight speed, during hover as well as during transient events of
transition to hover and transition to autorotation. The reports mostly present severities in terms
of root mean square values at rotor speed (3,75 Hz), the first harmonic of rotor speed (7,5 Hz),
rotor blade passing frequency (11,25 Hz) and the next seven harmonics of rotor blade passing
frequency (22,5 Hz, 33,75 Hz, 45 Hz, 56,25 Hz, 67,25 Hz, 78,5 Hz, 90 Hz). The reports also present the
overall of root mean square values (2,5 Hz to 2 000 Hz). Some of this information is presented in
this document as Figure 5 to Figure 14.
Compared in Figure 5 to Figure 10 are root mean square values for different flight conditions and
for three locations along the floor of the cargo bay floor. The figures separately illustrate and
compare the values of the overall of root mean square (2,5 Hz to 2 000 Hz), at rotor speed,
blade passing as well as the second, third and fourth harmonic of blade passing. It should be
noted that the overall root mean square value is that with the primary tonal values removed, i.e.
it is a measure of the broadband background vibration.
Compared in Figure 11 to Figure 14 are root mean square values for different cargo bay floor
locations and axes. The comparisons are made for the same four selected flight conditions for
which power spectral densities are presented in Figure 1 to Figure 4.
Although the information in this document is limited, the quality of the information is reasonable
and meets the required validation criteria for data quality (single data item).
4.2 Set down of underslung cargo from a Boeing CH-47 rotorcraft
Although the Boeing CH-47 rotorcraft has a significant sized internal cargo area, it is not
uncommon to transport bulky items as underslung loads. In such cases the load may be attached
by cables or nets to release hooks on the underside of the rotorcraft. Although the Boeing CH-47
rotorcraft has several such release hooks, it is common to utilize a single hook for most single
items.
– 10 – IEC 62131-7:2020 © IEC 2020
It should be noted that when underslung loads are carried by smaller rotorcraft they may use
two, three or even four point attachments. In all cases, it is possible for the dynamic responses
of the cargo and its suspension arrangement to interact with the dynamics of the rotorcraft
inducing increased dynamic loads in the attachment arrangement and hence the cargo/rotorcraft.
It is not unknown for failure of such arrangements to occur during flight.
Following the measurement exercise described in 4.1, further work [2] was undertaken to
establish set down shock conditions of underslung loads. For the purpose of this work an air
portable ISO container was suspended (at its upper attachments) by four cables to a single point
payload release hook under the rotorcraft fuselage. The air portable ISO container was a 10-
foot-(3 m) long unit (i.e. half the length of a standard TFU container) holding a two-tonne
payload. The pilot instructions were to perform representative set downs of the container. It was
set down onto a hard concrete surface, as far as practicable, on its four corner stacking points
using "realistic" rotorcraft decent velocities.
The suspended load was instrumented using the same equipment as described in 4.1. However,
in this case the two trial-axial accelerometers were located at each of the lower four corners of
the air portable ISO container. The system provided an effective measurement frequency range
of 2 Hz to 250 Hz with a subsequent acquisition rate of 1 000 samples per second (sps).
Measurements were made throughout the set down and the specific event subsequently
extracted for shock analysis.
The analysis was in the form of time histories (which are not suitable for reproduction here) and
shock response spectra (SRS). The time histories used for the shock response spectrum
calculations were of approximately 1 s duration and adopted a resonant gain or Q of 16,66 to
facilitate comparison with some historic US data. Although the measurement exercise
encompassed twelve separate set downs of the underslung payload, not all of these provided
data of suitable quality for subsequent analysis.
Figure 15 show the shock response spectra for six set downs. The figure includes the vertical
responses from both instrumented lower corners of the air transportable ISO container. The
shock response spectra for six set downs imply that the set down velocities were in the range of
approximately 0,2 m/s to 1 m/s. This broadly aligns with broader experience of setting down
underslung loads on land or stationary vehicles. The set down velocities would typically be
greater when setting down underslung loads onto ships.
Although the information in this document is limited in quantity and frequency range, the quality
of the information is reasonable and meets the required validation criteria for data quality (single
data item).
4.3 Supplementary data
The supplementary data, detailed below, comprises information arising from reputable sources,
but for which the data quality could not be adequately verified.
A study, [3] and [4], was undertaken to identify parameters and methodologies by which
estimates could be established of the vibration severities experienced by weapons carried on
rotorcraft. Although the objective of this work related to externally carried weapons, it did first
need to consider the vibration severities of the rotorcraft itself. The work did not present
measured rotorcraft data directly, hence its consideration as supplementary data. However, the
work did present information related to parameters which influence vibration severity for several
Figure 16 to Figure 18 show the relative vibration amplitude at blade passing
rotorcraft types.
frequency for different airspeeds (referenced to 100 kn) and for three different rotorcraft i.e. the
Lynx, Seaking and Chinook (CH-47). These are respectively small, medium and large rotorcraft.
This information indicates that whilst the most severe vibrations occur at the highest speed for
the CH-47, that is not necessarily the case for the other types. The study also presented (see
Figure 19) aircraft to aircraft variations that occur between different airframes of the Lynx
rotorcraft.
IEC 62131-7:2020 © IEC 2020 – 11 –
Early editions of UK Defence Standard 00-35 [5] presented some of the information from the
study [3] and [4] addressed in the preceding paragraph. Later editions have replaced the
rotorcraft to rotorcraft information shown here in Figure 19 with more extensive information from
a more modern rotorcraft. The data shown in Figure 20 arises from more than a thousand
measurements made on 36 different airframes of the same rotorcraft type and build standard.
These measurements, made as part of a fleet maintenance activity, are made at the same
aircraft reference location (a hard point on the cockpit floor). Although the original measurements
were made in terms of vibration amplitude at the blade passing frequency, they have been
converted to variations about the average amplitude. The most severe amplitudes are over three
times the average amplitude and six times the most benign observed.
The French military standard GAM-EG-13 [6] includes vibration information from the Aerospatiale
rotorcraft. This is a three-engine heavy lift rotorcraft which is also
SA 321 Super Frelon
produced in China where it is known as the Z-8. Power spectral density measurements are
presented for three axes and nine flight conditions in Figure 21 to Figure 23 for the X, Y and Z
axes respectively. The orientation of the axes and the location of the measurements is unknown
but is presumed to be the cargo bay floor with the Z axis vertical. The duration of the
measurements used in the analysis and the analysis frequency bandwidth are unknown
(although it appears likely that a resolution of better than 1 Hz was adopted). The military
standard indicates the rotorcraft take-off weight to be 12 900 kg, the mass on landing to be
12 100 kg and the unladen mass of the rotorcraft to be 7 925 kg. The ten flight conditions are
indicated to be: on ground rotor not turning, rolling take-off, stationary ground effect, accelerate
to a forward speed of 70 kn, straight and level flight at 85 kn, 110 kn and 130 kn all at a flight
level of 500 ft (150 m), as well as deceleration in forward speed followed by transition to hover.
As part of an exercise, in the early 1970s, to authenticate test severities for the US military
specification Mil Std 810, J.T. Foley [7] at the US Sandia National Laboratories undertook an
extensive exercise to establish transportation severities on a number of platforms including some
information on transportation in an (unknown) rotorcraft. Unfortunately, the analysis process
used by Foley throughout his work is relatively unique and not directly comparable with the
information presented in this document.
The SRETS study (see [8]) was undertaken during 1998 and reviewed both measured data
sources and test severities for a variety of methods of transportation. It contained no measured
data from transportation in rotorcraft although it did refer to rotorcraft test severities. However,
those appear in NATO STANAG 4370 AECTP 400 [10] and as such are already considered
within this document.
A number of environmental test standards include test severities for equipment either
transported or installed in rotorcraft. These test standards adopt differently shaped random or
composite profiles and they are not particularly consistent with respect to amplitude. Moreover,
the difference between measured severities and test severities can be quite marked for
rotorcraft. Test severities for equipment installed in rotorcraft do tend to have a notably higher
amplitude than observed in the measured data. This seems to be because the tests typically
encompass installation for the entire life of the rotorcraft airframe. As a consequence such tests
often incorporate increased amplitudes to facilitate a degree of accelerated testing. The need for
accelerated testing is less important for equipment transported in rotorcraft as exposure to this
environment is generally limited to a few hours. This is a consequence of the limited range of a
rotorcraft as well as the relatively high cost of this method of transport. For these reasons, it is
worthwhile considering the test severities of a number of representative standards.
Over the years the US defence equipment test standard Mil Std 810 [9], has included a number
of different vibration test types and severities for equipment transported and installed in
rotorcraft. The latest version of this standard uses sinusoidal tones on a shaped random
vibration background. The standard sets out separate advice on the vibration severities for
equipment transported by rotorcraft and those for equipment installed in rotorcraft. However, in
___________
SA 321 Super Frelon is the trade name of a product supplied by Aérospatiale. This information is given for the
convenience of users of this document and does not constitute an endorsement by IEC of the product named.

– 12 – IEC 62131-7:2020 © IEC 2020
reality the two sets of severity guidance are essentially identical. Within each set of guidance
four severity levels are provided of which three are very location specific (instrument panel, on or
near drive system elements and external stores). A single severity level is used for all the
remaining airframe locations and is applicable to both transported and installed equipment. The
standard requires that the severities are tailored to a specific rotorcraft type and for that purpose
supplies information on main and tail rotor speeds as well as the number of blades on each.
Figure 24 shows the vibration test severity derived for the CH-47 rotorcraft using the severity
derivation approach set out in Mil Std 810 [9]. It should be noted that for comparison purposes
the tone components in Figure 24 have been converted to narrowbands of frequency bandwidth
±5 % of the narrowband centre frequency.
Guidance for establishing initial vibration test severities for rotorcraft are set out in NATO
STANAG 4370 AECTP 400:2006 [10] Method 401 Annex D. That annex separately addresses
vibration severities for transported equipment and for installed equipment. In this case, the two
test severities are different. Figure 25 shows the vibration test severity derived from the
approach set out in Method 401 Annex D for equipment transported in the CH-47. Method 401
Annex D also contains vibration test severities for equipment carried as underslung loads carried
in both containers and nets (see Figure 26). The vibration test for equipment installed within
rotorcraft uses four harmonically related tones which are swept across frequency bands (of
20 Hz, 40 Hz, 60 Hz and 80 Hz respectively for the tones). The width of each of these swept
bands approximately relates to the range that may be encountered by a wide range of rotorcraft
types. It should be noted that again for comparison purposes the tone components in Figure 36
have been converted to narrowbands of frequency bandwidth ±5 % of the narrowband centre
frequency.
The latest UK Def Stan 00-35 [5] environmental test standard for defence equipment contains
four vibration test severities for transportation of equipment in rotorcraft. Three of these are for
specific rotorcraft types and one is a generic test for underslung loads (although the standard
does not include a shock test specifically for set down of loads). Previous issues of this standard
included a test for multi-rotorcraft types. However, this has been removed in the latest issue as it
was found its severities produced unrealistic test failures. The rotorcraft specific vibration test
severities relate to Chinook (CH-47), Merlin and Lynx/Wildcat rotorcraft and are shown in Figure
27, Figure 28 and Figure 29 respectively. The first two types are both large transports but the
latter is a small rotorcraft which is included only for man portable equipment. Figure 30 shows
the vibration test severity for underslung loads. It should be noted that the standard allows the
use of both tones and narrowbands to replicate the blade passing harmonics. The severities for
the blade passing harmonics are defined in terms of root mean square values from which
narrowband amplitudes may be calculated using multiples of the frequency bandwidth achievable
by the vibration test controller. In this case, the amplitude shown in the figures are based upon a
narrowband frequency bandwidth of 2 Hz (which is reasonably representative).
US standard RTCA/DO-160 [11] and EUROCAE/ED-14 [12], which are identically worded, are
applicable to equipment installed within aircraft and rotorcraft. These standards specify vibration
test severities for five different locations within the rotorcraft (fuselage, instrument panel and
racks, nacelle and pylon, engine and gearbox as well as the empennage and fin tip). Severities
are supplied for both reciprocating and turbo-jet engines rotorcraft. The severities are
constructed to allow rotorcraft specific severities to be used as well as generic severities when
the rotorcraft blade passing frequencies are unknown. Figure 31 shows the test severities for
equipment located in the fuselage of a rotorcraft with known blade passing frequencies, i.e.
those for the CH-47. Two severities are supplied, one is used when the performance of
equipment is evaluated, the other is the endurance severity used to demonstrate the equipment
life. It should be noted that again for comparison purposes the tone components in Figure 31
have been converted to narrowbands of frequency bandwidth ±5 % of the narrowband centre
frequency.
IEC 62131-7:2020 © IEC 2020 – 13 –
5 Intra data source comparison
5.1 General
The pu
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