Environmental conditions – Vibration and shock of electrotechnical equipment - Part 7: Transportation by rotary wing aircraft

IEC 62131-7:2020(E), 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).

General Information

Status
Published
Publication Date
27-Apr-2020
Current Stage
PPUB - Publication issued
Completion Date
28-Apr-2020
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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:
IEC TR 62131-7:2020-04 (en)
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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

Warning! Make sure that you obtained this publication from an authorized distributor.

® Registered trademark of the International Electrotechnical Commission
---------------------- Page: 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

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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

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– 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

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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

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising all

national electrotechnical committees (IEC National Committees). The object of IEC is to promote international co-

operation on all questions concerning standardization in the electrical and electronic fields. To this end and in

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arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC Publications.

8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

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.

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– 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

colour printer.
---------------------- Page: 8 ----------------------
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.
---------------------- Page: 9 ----------------------
– 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.

---------------------- Page: 10 ----------------------
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
...

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