Flight dynamics — Vocabulary — Part 8: Dynamic behaviour of aircraft

This document defines terms related to the concepts and quantities characterizing some classes of aircraft motion and their fundamental dynamic characteristics. The aircraft is assumed to be rigid, of constant mass and of constant inertia. It is not equipped with systems modifying its natural dynamic behaviour. However, most of the definitions can be applied to the case of a flexible aircraft, of variable mass and of variable inertia. The general concepts defined in this document are applicable to the atmospheric flight phase.

Titre manque — Partie 8: Titre manque

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Published
Publication Date
17-Nov-2022
Current Stage
6060 - International Standard published
Due Date
25-May-2023
Completion Date
18-Nov-2022
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INTERNATIONAL ISO
STANDARD 1151-8
Second edition
2022-11
Flight dynamics — Vocabulary —
Part 8:
Dynamic behaviour of aircraft
Reference number
ISO 1151-8:2022(E)
© ISO 2022
---------------------- Page: 1 ----------------------
ISO 1151-8:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
© ISO 2022 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 1151-8:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

3.1 General ........................................................................................................................................................................................................... 1

3.2 Types of aircraft motion ................................................................................................................................................................. 2

3.3 Types of aircraft motion and natural modes of aircraft motion ................................................................ 4

3.4 Characteristic parameters of individual modes of motion ............................................................................. 5

3.5 Standard input signals ..................................................................................................................................................................... 7

3.6 Response of aircraft to a step ................................................................................................................................................. 11

Bibliography .............................................................................................................................................................................................................................15

Index .................................................................................................................................................................................................................................................16

iii
© ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO 1151-8:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 8, Aerospace terminology.

This second edition cancels and replaces the first edition (ISO 1151-8:1992), which has been technically

revised.
The main changes are as follows:
— new terms related to types of aircraft motion have been added.
A list of all parts in the ISO 1151 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO 2022 – All rights reserved
---------------------- Page: 4 ----------------------
INTERNATIONAL STANDARD ISO 1151-8:2022(E)
Flight dynamics — Vocabulary —
Part 8:
Dynamic behaviour of aircraft
1 Scope

This document defines terms related to the concepts and quantities characterizing some classes of

aircraft motion and their fundamental dynamic characteristics.

The aircraft is assumed to be rigid, of constant mass and of constant inertia. It is not equipped with

systems modifying its natural dynamic behaviour. However, most of the definitions can be applied to

the case of a flexible aircraft, of variable mass and of variable inertia.

The general concepts defined in this document are applicable to the atmospheric flight phase.

2 Normative references
There are no normative references in this document.
3 Terms and definitions

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General
3.1.1
flight variable

physical quantity, the value of which as a function of time characterizes aircraft motion

3.1.2
flight state
set of values of the flight variables (3.1.1)

Note 1 to entry: This concept should not be confused with that of flight point (ISO 1151-7:1985, 7.5.5).

3.1.3
steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered remain constant with time

3.1.4
quasi-steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered vary so slowly with time that their

variations can be disregarded in the study
3.1.5
unsteady flight state

flight state (3.1.2) in which at least one of the flight variables (3.1.1) considered varies so rapidly with

time that its variations cannot be disregarded in the study
© ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
ISO 1151-8:2022(E)
3.1.6
reference flight state
flight state (3.1.2) chosen as reference in a given study

Note 1 to entry: In most cases, a steady flight state (3.1.3) or a quasi-steady flight state (3.1.4) is chosen as

reference.

Note 2 to entry: In a study covering a certain period of time, it is normal to choose the flight state immediately

prior to this period as a reference.
3.1.7
control input
action on aircraft intended to alter or to maintain the flight state (3.1.2)
3.1.8
disturbance
involuntary action which results in a modification in the flight state (3.1.2)
Note 1 to entry: The nature of this action can be, for example:
— human;
— atmospheric;
— mechanical.
3.1.9
input variable

element of the set of quantities characterizing the control input (3.1.7) or disturbance (3.1.8)

3.1.10
output variable

element of the set of flight variables (3.1.1), the developments of which over time characterize the

response of aircraft to the control input (3.1.7) or disturbance (3.1.8) considered

3.2 Types of aircraft motion
3.2.1
flight-path
trajectory

three-dimensional locus of origin of the flight-path axis system, usually the centre of mass, relative to

the Earth
3.2.2
aircraft plane motion

motion of aircraft characterized by a flight-path (3.2.1) contained within a plane

3.2.3
straight flight
aircraft plane motion (3.2.2) characterized by a straight flight-path (3.2.1)
3.2.4
horizontal flight

aircraft plane motion (3.2.2) characterized by a flight-path (3.2.1) contained within a horizontal plane

3.2.5
symmetrical flight
flight state (3.1.2) of aircraft with zero angle of sideslip
Note 1 to entry: The angle of sideslip is defined in ISO 1151-1:1988, 1.2.1.1.

Note 2 to entry: The geometry of aircraft and the flow are not necessarily symmetrical.

© ISO 2022 – All rights reserved
---------------------- Page: 6 ----------------------
ISO 1151-8:2022(E)
3.2.6
turn
motion of aircraft resulting in a change of flight-path (3.2.1) azimuth angle

Note 1 to entry: The flight-path azimuth angle is defined in ISO 1151-2:1985, 2.3.1.

3.2.7
horizontal turn
turn (3.2.6) in horizontal flight (3.2.4)
3.2.8
steady turn

horizontal turn (3.2.7) for which the airspeed and the load factor are held constant

Note 1 to entry: If the wind speed, V (ISO 1151-2:1985, 2.2.3), is zero, the flight-path (3.2.1) is circular.

3.2.9
longitudinal motion
isolated longitudinal motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom in

the aircraft plane of symmetry

Note 1 to entry: Longitudinal motion is characterized by variations in relation to a reference flight state (3.1.6) of

— angle of attack, α (ISO 1151-1:1988, 1.2.1.2),
— inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2),
— airspeed, V (ISO 1151-1:1988, 1.3.1),
— flight-path (3.2.1) inclination angle, γ (ISO 1151-2:1985, 2.3.2), and
— rate of pitch, q (ISO 1151-1:1988, 1.3.6),
while the variations of
— angle of sideslip, β (ISO 1151-1:1988, 1.2.1.1),
— rate of roll, p (ISO 1151-1:1988, 1.3.6), and
— rate of yaw, r (ISO 1151-1:1988, 1.3.6)
are zero or negligible.
3.2.10
lateral motion
isolated lateral motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom

outside of the aircraft plane of symmetry

Note 1 to entry: Lateral motion is characterized by variations in relation to a reference flight state (3.1.6) of

— angle of sideslip, β (ISO 1151-1:1988, 1.2.1.1),
— bank angle, Φ (ISO 1151-1:1988, 1.2.2.3),
— azimuth angle, Ψ (ISO 1151-1:1988, 1.2.2.1),
— rate of roll, p (ISO 1151-1:1988, 1.3.6), and
— rate of yaw, r (ISO 1151-1:1988, 1.3.6),
while the variations of
— angle of attack, α (ISO 1151-1:1988, 1.2.1.2),
© ISO 2022 – All rights reserved
---------------------- Page: 7 ----------------------
ISO 1151-8:2022(E)
— airspeed, V (ISO 1151-1:1988, 1.3.1),
— flight-path (3.2.1) inclination angle, γ (ISO 1151-2:1985, 2.3.2), and
— rate of pitch, q (ISO 1151-1:1988, 1.3.6)
are zero or negligible.
3.2.11
aerodynamic stall

aerodynamic loss of lift caused by the angle of attack, α, exceeding its critical value

Note 1 to entry: The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2.
3.2.12
aeroplane upset

flight state (3.1.2) characterized by aircraft flight variables (3.1.1) unintentionally exceeding their limits

normally experienced in line operations or training

Note 1 to entry: Aeroplane upset is normally defined by the existence of at least one of the following parameters:

a) inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2) (pitch attitude), greater than 25°, nose up;

b) inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2) (pitch attitude), less than −10°, nose down;

c) absolute value of bank angle, Φ (ISO 1151-1:1988, 1.2.2.3), greater than 45°;

d) within the above parameters, but flying at airspeed, V (ISO 1151-1:1988, 1.3.1), inappropriate for the

conditions.
3.3 Types of aircraft motion and natural modes of aircraft motion
3.3.1
short period oscillation

oscillatory longitudinal motion characterized by variations in the angle of attack, α, and the rate of

pitch, q, at a nearly constant airspeed, V, with a frequency, f, higher than that of the phugoid (3.3.2) mode

Note 1 to entry: The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2. The rate of pitch, q, is defined in

ISO 1151-1:1988, 1.3.6. The airspeed, V, is defined in ISO 1151-1:1988, 1.3.1.

Note 2 to entry: The damping coefficient, δ (3.4.2), of short period oscillation is generally large.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft following a control input or disturbance.

3.3.2
phugoid
phugoid oscillation

oscillatory longitudinal motion (3.2.9) characterized by variations in the horizontal and vertical

components of the aircraft velocity, V , and the inclination angle, Θ, of the aircraft, at a nearly constant

angle of attack, α

Note 1 to entry: The aircraft velocity, V , is defined in ISO 1151-1:1988, 1.3.1. The inclination angle, Θ, is defined

in ISO 1151-1:1988, 1.2.2.2. The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2.

Note 2 to entry: The frequency, f, and the damping coefficient, δ (3.4.2), are generally low.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft
...

© ISO/DIS 1151-8 – All rights reserved
ISO/DIS 1151-8:20212022(E)
ISO TC 20/SC 20/WG 2
Secretariat: GOST R
Date: 2022-09-19
Flight dynamics — Concepts, quantities and symbols —
Vocabulary — Part 8: Concepts and quantities used in the study of the
dynamicDynamic behaviour of aircraft
WD/CD/DIS/FDIS stage
Warning for WDs and CDs

This document is not an ISO International Standard. It is distributed for review and comment. It is subject to

change without notice and may not be referred to as an International Standard.

Recipients of this draft are invited to submit, with their comments, notification of any relevant patent rights of

which they are aware and to provide supporting documentation.
---------------------- Page: 1 ----------------------
© ISO 2021
---------------------- Page: 2 ----------------------
ISO/DIS 1151-8:20212022(E)
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation,

no part of this publication may be reproduced or utilized otherwise in any form or by any means,

electronic or mechanical, including photocopying, or posting on the internet or an intranet,

without prior written permission. Permission can be requested from either ISO at the address

below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
© ISO/DIS 1151-8 – All rights reserved
ii © ISO 2022 – All rights reserved
---------------------- Page: 3 ----------------------
ISO/DIS 1151-8:2021 2022(E)
Contents

Foreword ......................................................................................................................................................................... iv

1 Scope .................................................................................................................................................................... 1

2 Normative references .................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................... 1

3.1 General ................................................................................................................................................................ 1

3.2 Types of aircraft motion ................................................................................................................................ 3

3.3 Types of aircraft motion and natural modes of aircraft motion ..................................................... 5

3.4 Characteristic parameters of individual modes of motion ............................................................... 7

3.5 Standard input signals ................................................................................................................................... 9

3.6 Response of aircraft to a step ................................................................................................................... 18

Bibliography ................................................................................................................................................................. 23

© ISO/DIS 1151-8 – All rights reserved © ISO 2022 – All iii
rights reserved
---------------------- Page: 4 ----------------------
ISO/DIS 1151-8:20212022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national

standards bodies (ISO member bodies). The work of preparing International Standards is normally

carried out through ISO technical committees. Each member body interested in a subject for which a

technical committee has been established has the right to be represented on that committee.

International organizations, governmental and non-governmental, in liaison with ISO, also take part in

the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all

matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to the

World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 08, Concepts, quantities and symbols for flight dynamics8, Aerospace terminology.

This second edition cancels and replaces the first edition (ISO 1151-8:1992-06-15), which has been

technically revised.
The main changes compared to the previous edition are as follows:

— new terms for subclause “Typesrelated to types of aircraft motion” have been supplementedadded.

A list of all parts in the ISO 1151 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
© ISO/DIS 1151-8 – All rights reserved
iv © ISO 2022 – All rights reserved
---------------------- Page: 5 ----------------------
ISO/DIS 1151-8:2021 2022(E)
Introduction

The International Organization for Standardization (ISO) draw attention to the fact that it is claimed

that compliance with this document may involve the use of a patent.

ISO take no position concerning the evidence, validity and scope of this patent right.

The holder of this patent right has assured ISO that he/she is willing to negotiate licences under

reasonable and non-discriminatory terms and conditions with applicants throughout the world. In this

respect, the statement of the holder of this patent right is registered with ISO. Information may be

obtained from the patent database available at .

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights other than those in the patent database. ISO shall not be held responsible for identifying

any or all such patent rights.
© ISO/DIS 1151-8 – All rights reserved © ISO 2022 – All v
rights reserved
---------------------- Page: 6 ----------------------
INTERNATIONAL STANDARD ISO 1151-8:2022(E)
Flight dynamics — Concepts, quantities and symbols —
Vocabulary — Part 8: Concepts and quantities used in the study of
the dynamicDynamic behaviour of aircraft
1 Scope

This documentsdocument defines terms relatingrelated to the concepts and quantities characterizing

some classes of aircraft motion and their fundamental dynamic characteristics.

The aircraft is assumed to be rigid, of constant mass and of constant inertia. It is not equipped with

systems modifying its natural dynamic behaviour. However, most of the definitions can be applied to

the case of a flexible aircraft, of variable mass and of variable inertia.

The general concepts defined in this part of the ISO 1151document are applicable to the atmospheric

flight phase.
2 Normative references
There are no normative references in this document.
3 Terms and definitions

For the purposes of this document,ISO and IEC maintain terminology databases for use in

standardization at the following terms and definitions apply.addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
3.1 — IEC Electropedia: available at https://www.electropedia.org/ Terms
related to general concepts
3.1 General
3.1.1
flight variable

physical quantity, the value of which as a function of time characterizes aircraft motion

3.1.2
flight state
set of values of the flight variables (3.1.1)

Note 1 to entry: This concept should not be confused with that of flight point [(ISO 1151, Part -7:1985, 7.5.5]

[4].).
3.1.3
© ISO 2022 – All rights reserved 1
---------------------- Page: 7 ----------------------
ISO 1151-8:2022(E)
steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered remain constant with time

3.1.4
quasi-steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered vary so slowly with time that their

variations can be disregarded in the study
3.1.5
unsteady flight state

flight state (3.1.2) in which at least one of the flight variables (3.1.1) considered varies so rapidly with

time that its variations cannot be disregarded in the study
3.1.6
reference flight state
flight state (3.1.2) chosen as reference in a given study

Note 1 to entry: In most cases, a steady flight state (3.1.3) or a quasi-steady flight state (3.1.4) is chosen as

reference.

Note 2 to entry: In a study covering a certain period of time, it is normal to choose the flight state (3.1.2)

immediately prior to this period as a reference.
3.1.7
control input
action on aircraft intended to alter or to maintain the flight state (3.1.2)
3.1.8
disturbance
involuntary action which results in a modification in the flight state (3.1.2)
Note 1 to entry: The nature of this action can be, for example:
- — human;
- — atmospheric;
- — mechanical;.
- etc.
3.1
3.1.9
input variable

element of the set of quantities characterizing the control input (3.1.7) or disturbance (3.1.8)

3.1.10
output variable

element of the set of flight variables (3.1.1), the developments of which over time characterize the

response of aircraft to the control input (3.1.7) or disturbance (3.1.8) considered

© ISO/DIS 1151-8 – All rights reserved
2 © ISO 2022 – All rights reserved
---------------------- Page: 8 ----------------------
ISO 1151-8:2022(E)
3.2 Terms related to typesTypes of aircraft motion
3.2.1
flight-path
trajectory

three-dimensional locus of origin of the flight-path axis system, usually the centre of mass, relative to

the Earth
3.2.2
aircraft plane motion

motion of aircraft characterized by a flight-path (3.2.1) contained within a plane

3.2.3
straight flight
aircraft plane motion (3.2.2) characterized by a straight flight-path (3.2.1)
3.2.4
horizontal flight

aircraft plane motion (3.2.2) characterized by a flight-path (3.2.1) contained within a horizontal plane

3.2.5
symmetrical flight

flight state (3.1.2) of aircraft with zero angle of sideslip (ISO 1151, Part 1, 1.2.1.1) [1]

Note 1 to entry: The angle of sideslip is defined in ISO 1151-1:1988, 1.2.1.1.

Note 2 to entry: The geometry of aircraft and the flow are not necessarily symmetrical.

3.2.6
turn
motion of aircraft resulting in a change of flight-path (3.2.1) azimuth angle (

Note 1 to entry: The flight-path azimuth angle is defined in ISO 1151, Part -2:1985, 2.3.1) [2].

3.2.7
horizontal turn
turn (3.2.6) in horizontal flight (3.2.4)
3.2.8
steady turn

horizontal turn (3.2.7) for which the airspeed and the load factor are held constant

Note 1 to entry: If the wind speed, V , (ISO 1151, Part -2:1985, 2.2.3) [2]), is zero, the flight-path (3.2.1) is circular.

3.2.9
longitudinal motion
(isolated) longitudinal motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom in

the aircraft plane of symmetry

Note 1 to entry: longitudinalLongitudinal motion (3.2.9) is characterized by variations in relation to a reference

flight state (3.1.56) of
© ISO/DIS 1151-8 – All rights reserved © ISO 2022 – All 3
rights reserved
---------------------- Page: 9 ----------------------
ISO 1151-8:2022(E)
— angle of attack, α,α (ISO 1151, Part -1:1988, 1.2.1.2) [1];),
— inclination angle, Θ,Θ (ISO 1151, Part-1:1988, 1, 1.2.2.2.2) [1];),
— airspeed, V, (ISO 1151, Part -1:1988, 1.3.1) [1];),

— flight-path (3.2.1) inclination angle, γ,γ (ISO 1151, Part -2:1985, 2.3.2) [2];), and

— rate of pitch, q, (ISO 1151, Part -1:1988, 1.3.6) [1],),
while the variations of
— angle of sideslip, β,β (ISO 1151, Part -1:1988, 1.2.1.1) [1];),
— rate of roll, p, (ISO 1151, Part -1:1988, 1.3.6) [1];), and
— rate of yaw, r, (ISO 1151, Part -1:1988, 1.3.6) [1]
are zero or negligible.
3.2.10
lateral motion
(isolated) lateral motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom

outside of the aircraft plane of symmetry

Note 1 to entry: lateralLateral motion (3.2.9) is characterized by variations in relation to a reference flight state

(3.1.56) of
— angle of sideslip, β,β (ISO 1151, Part -1:1988, 1.2.1.1) [1];),
— bank angle, Φ,Φ (ISO 1151, Part -1:1988, 1.2.2.2.3) [1];),
— azimuth angle, Ψ,Ψ (ISO 1151, Part -1:1988, 1.2.2.2.1) [1];),
— rate of roll, p, (ISO 1151, Part -1:1988, 1.3.6) [1];), and
— rate of yaw, r, (ISO 1151, Part -1:1988, 1.3.6) [1]),
while the variations of
— angle of attack, α,α (ISO 1151, Part -1:1988, 1.2.1.2) [1];),
— airspeed, V, (ISO 1151, Part -1:1988, 1.3.1) [1];),

— flight-path (3.2.1) inclination angle, γ,γ (ISO 1151, Part 2, -2:1985, 2.3.2) [2];), and

— rate of pitch, q, (ISO 1151, Part -1:1988, 1.3.6) [1]
are zero or negligible.
3.2.11
aerodynamic stall
© ISO/DIS 1151-8 – All rights reserved
4 © ISO 2022 – All rights reserved
---------------------- Page: 10 ----------------------
ISO 1151-8:2022(E)

aerodynamic loss of lift caused by the angle of attack, α, (ISO 1151, Part 1, 1.2.1.2) [1],α, exceeding the its

critical value of

Note 1 to entry: The angle of attack, α, (α, is defined in ISO 1151, Part -1:1988, 1.2.1.2.

3.2.1.2) [1]12
aeroplane upset

flight state (3.1.2) characterized by aircraft flight variables (3.1.1) unintentionally exceeding the their

limits normally experienced in line operations or training.

Note 1 to entry: aeroplaneAeroplane upset (3.2.12) is normally defined by the existence of at least one of the

following parameters:

a) inclination angle, Θ,Θ (ISO 1151, Part -1:1988, 1.2.2.2) [1] (pitch attitude)), greater than 25 degrees,°, nose

up; or

b) inclination angle, Θ,Θ (ISO 1151, Part-1:1988, 1, 1.2.2.2.2) [1]) (pitch attitude)), less than -−10 degrees,°, nose

down; or

c) absolute value of bank angle, Φ,Φ (ISO 1151, Part -1:1988, 1.2.2.2.3) [1],), greater than 45 degrees; or °;

d) within the above parameters, but flying at airspeed, V, (ISO 1151, Part -1:1988, 1.3.1) [1],), inappropriate for

the conditions.

3.3 Terms related to typesTypes of aircraft motion and natural modes of aircraft motion

In the following term entries, the modes considered correspond to small motions superimposed on a steady or

quasi-steady reference flight state. These are motions of aircraft following a control input or disturbance.

3.3.1
short period oscillation

oscillatory longitudinal motion characterized by variations in the angle of attack,α, (ISO 1151, Part 1,

1.2.1.2) [1], α, and the rate of pitch, q, (ISO 1151, Part 1, 1.3.6) [1] at a nearly constant airspeed, V, (ISO

1151, Part 1, 1.3.1) [1], with a frequency, f, higher than that of the phugoid (3.3.2) mode

Note 1 to entry: The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2. The rate of pitch, q, is defined in ISO

1151-1:1988, 1.3.6. The airspeed, V, is defined in ISO 1151-1:1988, 1.3.1.

Note 2 to entry: The damping coefficient δ, δ (3.4.2), of short period oscillation (3.3.1) is generally large.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft following a control input or disturbance.

3.3.2
phugoid (
phugoid oscillation)

oscillatory longitudinal motion (3.2.9) characterized by variations in the horizontal and vertical

��⃗

components of the aircraft velocity, V V, (ISO 1151, Part 1, 1.3.1) [1], and the inclination angle, Θ, (ISO

1151, Part 1, 1.2.2.2) [1] ofΘ, of the aircraft, at a nearly constant angle of attack, α, (ISO 1151, Part 1,

1.2.1.2) [1]α
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rights reserved
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ISO 1151-8:2022(E)

Note 1 to entry: The aircraft velocity, V , is defined in ISO 1151-1:1988, 1.3.1. The inclination angle, Θ, is defined in

ISO 1151-1:1988, 1.2.2.2. The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2.

Note 2 to entry: The frequency, f, and the damping coefficient, δδ (3.4.2), are generally low.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft following a control input or disturbance.

3.3.3
aperiodic longitudinal mode

longitudinal motion (3.2.9) characterized by variations in the vertical component of the aircraft velocity,

��⃗
V V, (ISO 1151, Part 1, 1.3.1) [1]

Note 1 to entry: The aircraft velocity, V , is defined in ISO 1151-1:1988, 1.3.1.

Note 2 to entry: The damping coefficient, δ,δ (3.4.2), is generally large.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraf
...

INTERNATIONAL ISO
STANDARD 1151-8
Second edition
Flight dynamics — Vocabulary —
Part 8:
Dynamic behaviour of aircraft
PROOF/ÉPREUVE
Reference number
ISO 1151-8:2022(E)
© ISO 2022
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ISO 1151-8:2022(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2022

All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may

be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on

the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below

or ISO’s member body in the country of the requester.
ISO copyright office
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Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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ISO 1151-8:2022(E)
Contents Page

Foreword ........................................................................................................................................................................................................................................iv

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ..................................................................................................................................................................................... 1

3 Terms and definitions .................................................................................................................................................................................... 1

3.1 General ........................................................................................................................................................................................................... 1

3.2 Types of aircraft motion ................................................................................................................................................................. 2

3.3 Types of aircraft motion and natural modes of aircraft motion ................................................................ 4

3.4 Characteristic parameters of individual modes of motion ............................................................................. 5

3.5 Standard input signals ..................................................................................................................................................................... 7

3.6 Response of aircraft to a step ................................................................................................................................................. 11

Bibliography .............................................................................................................................................................................................................................15

Index .................................................................................................................................................................................................................................................16

iii
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ISO 1151-8:2022(E)
Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards

bodies (ISO member bodies). The work of preparing International Standards is normally carried out

through ISO technical committees. Each member body interested in a subject for which a technical

committee has been established has the right to be represented on that committee. International

organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.

ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of

electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are

described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the

different types of ISO documents should be noted. This document was drafted in accordance with the

editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

Attention is drawn to the possibility that some of the elements of this document may be the subject of

patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of

any patent rights identified during the development of the document will be in the Introduction and/or

on the ISO list of patent declarations received (see www.iso.org/patents).

Any trade name used in this document is information given for the convenience of users and does not

constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and

expressions related to conformity assessment, as well as information about ISO's adherence to

the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see

www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 20, Aircraft and space vehicles,

Subcommittee SC 8, Aerospace terminology.

This second edition cancels and replaces the first edition (ISO 1151-8:1992), which has been technically

revised.
The main changes are as follows:
— new terms related to types of aircraft motion have been added.
A list of all parts in the ISO 1151 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A

complete listing of these bodies can be found at www.iso.org/members.html.
PROOF/ÉPREUVE © ISO 2022 – All rights reserved
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INTERNATIONAL STANDARD ISO 1151-8:2022(E)
Flight dynamics — Vocabulary —
Part 8:
Dynamic behaviour of aircraft
1 Scope

This document defines terms related to the concepts and quantities characterizing some classes of

aircraft motion and their fundamental dynamic characteristics.

The aircraft is assumed to be rigid, of constant mass and of constant inertia. It is not equipped with

systems modifying its natural dynamic behaviour. However, most of the definitions can be applied to

the case of a flexible aircraft, of variable mass and of variable inertia.

The general concepts defined in this document are applicable to the atmospheric flight phase.

2 Normative references
There are no normative references in this document.
3 Terms and definitions

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1 General
3.1.1
flight variable

physical quantity, the value of which as a function of time characterizes aircraft motion

3.1.2
flight state
set of values of the flight variables (3.1.1)

Note 1 to entry: This concept should not be confused with that of flight point (ISO 1151-7:1985, 7.5.5).

3.1.3
steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered remain constant with time

3.1.4
quasi-steady flight state

flight state (3.1.2) in which the flight variables (3.1.1) considered vary so slowly with time that their

variations can be disregarded in the study
3.1.5
unsteady flight state

flight state (3.1.2) in which at least one of the flight variables (3.1.1) considered varies so rapidly with

time that its variations cannot be disregarded in the study
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ISO 1151-8:2022(E)
3.1.6
reference flight state
flight state (3.1.2) chosen as reference in a given study

Note 1 to entry: In most cases, a steady flight state (3.1.3) or a quasi-steady flight state (3.1.4) is chosen as

reference.

Note 2 to entry: In a study covering a certain period of time, it is normal to choose the flight state immediately

prior to this period as a reference.
3.1.7
control input
action on aircraft intended to alter or to maintain the flight state (3.1.2)
3.1.8
disturbance
involuntary action which results in a modification in the flight state (3.1.2)
Note 1 to entry: The nature of this action can be, for example:
— human;
— atmospheric;
— mechanical.
3.1.9
input variable

element of the set of quantities characterizing the control input (3.1.7) or disturbance (3.1.8)

3.1.10
output variable

element of the set of flight variables (3.1.1), the developments of which over time characterize the

response of aircraft to the control input (3.1.7) or disturbance (3.1.8) considered

3.2 Types of aircraft motion
3.2.1
flight-path
trajectory

three-dimensional locus of origin of the flight-path axis system, usually the centre of mass, relative to

the Earth
3.2.2
aircraft plane motion

motion of aircraft characterized by a flight-path (3.2.1) contained within a plane

3.2.3
straight flight
aircraft plane motion (3.2.2) characterized by a straight flight-path (3.2.1)
3.2.4
horizontal flight

aircraft plane motion (3.2.2) characterized by a flight-path (3.2.1) contained within a horizontal plane

3.2.5
symmetrical flight
flight state (3.1.2) of aircraft with zero angle of sideslip
Note 1 to entry: The angle of sideslip is defined in ISO 1151-1:1988, 1.2.1.1.

Note 2 to entry: The geometry of aircraft and the flow are not necessarily symmetrical.

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ISO 1151-8:2022(E)
3.2.6
turn
motion of aircraft resulting in a change of flight-path (3.2.1) azimuth angle

Note 1 to entry: The flight-path azimuth angle is defined in ISO 1151-2:1985, 2.3.1.

3.2.7
horizontal turn
turn (3.2.6) in horizontal flight (3.2.4)
3.2.8
steady turn

horizontal turn (3.2.7) for which the airspeed and the load factor are held constant

Note 1 to entry: If the wind speed, V (ISO 1151-2:1985, 2.2.3), is zero, the flight-path (3.2.1) is circular.

3.2.9
longitudinal motion
isolated longitudinal motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom in

the aircraft plane of symmetry

Note 1 to entry: Longitudinal motion is characterized by variations in relation to a reference flight state (3.1.6) of

— angle of attack, α (ISO 1151-1:1988, 1.2.1.2),
— inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2),
— airspeed, V (ISO 1151-1:1988, 1.3.1),
— flight-path (3.2.1) inclination angle, γ (ISO 1151-2:1985, 2.3.2), and
— rate of pitch, q (ISO 1151-1:1988, 1.3.6),
while the variations of
— angle of sideslip, β (ISO 1151-1:1988, 1.2.1.1),
— rate of roll, p (ISO 1151-1:1988, 1.3.6), and
— rate of yaw, r (ISO 1151-1:1988, 1.3.6)
are zero or negligible.
3.2.10
lateral motion
isolated lateral motion

motion characterized by variations of flight variables (3.1.1), related to the three degrees of freedom

outside of the aircraft plane of symmetry

Note 1 to entry: Lateral motion is characterized by variations in relation to a reference flight state (3.1.6) of

— angle of sideslip, β (ISO 1151-1:1988, 1.2.1.1),
— bank angle, Φ (ISO 1151-1:1988, 1.2.2.3),
— azimuth angle, Ψ (ISO 1151-1:1988, 1.2.2.1),
— rate of roll, p (ISO 1151-1:1988, 1.3.6), and
— rate of yaw, r (ISO 1151-1:1988, 1.3.6),
while the variations of
— angle of attack, α (ISO 1151-1:1988, 1.2.1.2),
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ISO 1151-8:2022(E)
— airspeed, V (ISO 1151-1:1988, 1.3.1),
— flight-path (3.2.1) inclination angle, γ (ISO 1151-2:1985, 2.3.2), and
— rate of pitch, q (ISO 1151-1:1988, 1.3.6)
are zero or negligible.
3.2.11
aerodynamic stall

aerodynamic loss of lift caused by the angle of attack, α, exceeding its critical value

Note 1 to entry: The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2.
3.2.12
aeroplane upset

flight state (3.1.2) characterized by aircraft flight variables (3.1.1) unintentionally exceeding their limits

normally experienced in line operations or training

Note 1 to entry: Aeroplane upset is normally defined by the existence of at least one of the following parameters:

a) inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2) (pitch attitude), greater than 25°, nose up;

b) inclination angle, Θ (ISO 1151-1:1988, 1.2.2.2) (pitch attitude), less than −10°, nose down;

c) absolute value of bank angle, Φ (ISO 1151-1:1988, 1.2.2.3), greater than 45°;

d) within the above parameters, but flying at airspeed, V (ISO 1151-1:1988, 1.3.1), inappropriate for the

conditions.
3.3 Types of aircraft motion and natural modes of aircraft motion
3.3.1
short period oscillation

oscillatory longitudinal motion characterized by variations in the angle of attack, α, and the rate of

pitch, q, at a nearly constant airspeed, V, with a frequency, f, higher than that of the phugoid (3.3.2) mode

Note 1 to entry: The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2. The rate of pitch, q, is defined in

ISO 1151-1:1988, 1.3.6. The airspeed, V, is defined in ISO 1151-1:1988, 1.3.1.

Note 2 to entry: The damping coefficient, δ (3.4.2), of short period oscillation is generally large.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft following a control input or disturbance.

3.3.2
phugoid
phugoid oscillation

oscillatory longitudinal motion (3.2.9) characterized by variations in the horizontal and vertical

components of the aircraft velocity, V , and the inclination angle, Θ, of the aircraft, at a nearly constant

angle of attack, α

Note 1 to entry: The aircraft velocity, V , is defined in ISO 1151-1:1988, 1.3.1. The inclination angle, Θ, is defined

in ISO 1151-1:1988, 1.2.2.2. The angle of attack, α, is defined in ISO 1151-1:1988, 1.2.1.2.

Note 2 to entry: The frequency, f, and the damping coefficient, δ (3.4.2), are generally low.

Note 3 to entry: The modes considered correspond to small motions superimposed on a steady or quasi-steady

reference flight state. These are motions of aircraft following a control input or disturbance.

PROO
...

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