Rotorcrafts – Flight dynamics – Vocabulary

This document defines terms used in the field of rotorcrafts flight dynamics and aerodynamics, for example, rotorcraft design documents, with regard to rotorcrafts geometry and dynamic characteristics.

Giravions – Dynamique de vol – Vocabulaire

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Publication Date
18-Nov-2021
Current Stage
5060 - Close of voting Proof returned by Secretariat
Start Date
14-Oct-2021
Completion Date
14-Oct-2021
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INTERNATIONAL ISO
STANDARD 5224
First edition
2021-11
Rotorcrafts – Flight dynamics –
Vocabulary
Giravions – Dynamique de vol – Vocabulaire
Reference number
ISO 5224:2021(E)
© ISO 2021
---------------------- Page: 1 ----------------------
ISO 5224:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021

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

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Phone: +41 22 749 01 11
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Published in Switzerland
© ISO 2021 – All rights reserved
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ISO 5224:2021(E)
Contents Page

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

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

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

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

3.1 Basic definitions and classification ...................................................................................................................................... 1

3.2 Basic elements ......................................................................................................................................................................................... 3

3.3 Coordinate axis and planes ......................................................................................................................................................... 6

3.4 Angles ............................................................................................................................................................................................................. 8

3.5 Geometry .................................................................................................................................................................................................. 10

3.6 Dynamic characteristic ................................................................................................................................................................12

3.7 Forces and moments ....................................................................................................................................................................... 14

3.8 Performance ..........................................................................................................................................................................................15

3.9 Flight quality (according to ADS–33-PRF).................................................................................................................. 17

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

iii
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ISO 5224:2021(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

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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.

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 2021 – All rights reserved
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INTERNATIONAL STANDARD ISO 5224:2021(E)
Rotorcrafts – Flight dynamics – Vocabulary
1 Scope

This document defines terms used in the field of rotorcrafts flight dynamics and aerodynamics,

for example, rotorcraft design documents, with regard to rotorcrafts geometry and dynamic

characteristics.
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 Basic definitions and classification
3.1.1
rotorcraft
rotary wing aircraft

heavier-than-air aircraft that depends principally for its support in flight on the aerodynamical

generated by one or more rotors
3.1.2
helicopter

rotorcraft (3.1.1) that primarily depends on engine driven rotors for motion at all stage of flight

3.1.3
gyroplane
autogyro
gyrocopter
rotaplane

rotorcraft (3.1.1) whose rotors are not engine-driven, except for initial starting, but are made to rotate

by action of the air when the rotorcraft is moving; and whose means of propulsion, consisting usually of

conventional propellers, is independent of the rotor system
3.1.4
gyrodyne
compound helicopter
compound gyroplane

rotorcraft (3.1.1) with a rotor system that is normally driven by its engine for takeoff, hovering and

landing like a helicopter (3.1.2), and has an additional propulsion system that is independent of the

rotor system
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ISO 5224:2021(E)
3.1.5
convertiplane

aircraft which uses rotor power for vertical takeoff and landing (vtol) and converts to fixed-wing lift in

normal flight

Note 1 to entry: Convertiplanes may be divided into two broad classes, based on whether the rotor is fixed as in

a helicopter (3.1.2) or tilts to provide thrust in forward flight, as a proprotor. a proprotor may be in a tilt rotor or

tilt wing configuration.
3.1.6
tiltrotor aircraft

rotorcraft (3.1.1) which generates lift and propulsion by way of one or more tiltable (rotating) powered

propellers, or proprotors, mounted on rotating engine pods or nacelles usually at the ends of a fixed

wing

Note 1 to entry: Orientation of wings is fixed. For vertical flight, the rotors are angled so the plane of rotation is

horizontal.
3.1.7
tiltwing aircraft

aircraft with a wing that is horizontal for conventional forward flight and rotates up for vertical takeoff

and landing
3.1.8
helicopter configuration

combination of features, defining main rotor (3.2.1) system, anti-torque system (for single rotor

helicopter (3.1.9)), flight control system
3.1.9
single rotor helicopter
helicopter (3.1.2) with one (main) rotor that provides lift and propulsive force

Note 1 to entry: Single rotor helicopters may be divides into four or more types depending of anti-torque system:

— with tail rotor (3.2.2) (classic configuration);
— with fenestrone (3.2.25);
— with notar (3.2.26) (no tail rotor) system;
— tip jets (3.2.24) (no anti-torque system required).
3.1.10
dual rotor helicopter
twin-rotor helicopter
helicopter (3.1.2) with two counter-rotating main rotors (3.2.1) rotors
3.1.11
tandem rotors helicopter

dual rotor helicopter (3.1.10) with two horizontal main rotors (3.2.1) assemblies mounted one behind

the other
3.1.12
side-by-side rotors
transverse rotors helicopter

dual rotor helicopter (3.1.10) with a set of counter-rotating main rotors (3.2.1) assemblies which are

located in the same plane side-by-side on the helicopter (3.1.2) and where the stagger (3.5.15) is greater

than the diameter of the disk
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ISO 5224:2021(E)
3.1.13
coaxial rotors helicopter

dual rotor helicopter (3.1.10) with a pair of counter-rotating main rotors (3.2.1) mounted one above the

other on the same shaft and turning in opposite directions
3.1.14
intermeshing rotors helicopter
synchropter

dual rotor helicopter (3.1.10) with a set of two counter-rotating main rotors (3.2.1) with each rotor mast

mounted on the helicopter (3.1.2) with a slight angle to the other so that the blades (3.2.5) intermesh

without colliding
3.1.15
multicopter
multirotor
rotorcraft (3.1.1) with more than two rotors that provide lift
3.1.16
quadcopter
quadrocopter
quadrotor
multicopter (3.1.15) that is lifted and propelled by four rotors
3.1.17
hexacopter
multicopter (3.1.15) that is lifted and propelled by six rotors
3.1.18
octocopter
multicopter (3.1.15) that is lifted and propelled by eight rotors
3.2 Basic elements
3.2.1
main rotor

combination of a rotary wing and a control system that generates the aerodynamic lift force that

supports the weight of the helicopter (3.1.2), and the thrust that counteracts aerodynamic drag in

forward flight
3.2.2
tail rotor

smaller rotor mounted so that it rotates vertically or near-vertically at the end of the tail of a traditional

single rotor helicopter (3.1.9) to compensate main rotor (3.2.1) torque moment
3.2.3
main rotor hub
toe unit for the rotor blades (3.2.5) attachment to rotor shaft
Note 1 to entry: The hub is located at the top of the mast.
3.2.4
hinge

mechanism that holds the blades (3.2.5) proper to the hub and allows free angular motion with zero

moment transfer
3.2.5
blade

main working unit of rotor working as rotating wing which provides lift due to rotation about rotor

shaft axis
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ISO 5224:2021(E)
3.2.6
horizontal hinge
flapping hinge

hinge (3.2.4) which allows the blade (3.2.5) to move up and down with respect to the plane of rotor

rotation
Note 1 to entry: This movement is called flapping.
3.2.7
vertical hinge
lead-lag hinge
drag hinge

hinge (3.2.4) which allows the blade (3.2.5) to move back and forth in the plane of rotor rotation

Note 1 to entry: This movement is called lead-lag, dragging, or hunting.
3.2.8
axial hinge
feathering hinge

hinge (3.2.4) along the feathering (3.2.32) axis of blade (3.2.5) that allows to change the pitch of rotor

blades due to pilot input to the collective or cyclic control
3.2.9
articulated rotor

rotor system with each blade (3.2.5) attached to the rotor hub through a series of hinges (3.2.4)

(horizontal and (or) vertical) that let the blade move independently of the others

3.2.10
fully articulated rotor

rotor system with each blade (3.2.5) attached to the rotor hub through a series of hinges (3.2.4)

(horizontal and vertical) that let the blade move independently of the others

Note 1 to entry: The blades in this case are allowed to flap, and lead or lag independently of each other.

3.2.11
hingeless rotor

rotor with no actual mechanical hinges (3.2.4) that achieves flapping and lead-lag motion by elastically

flexing
3.2.12
rotor with separated hinges

rotor system for which the distances of horizontal hinge (3.2.6) from the rotor hub isn’t equal to zero

3.2.13
rotor with joined hinges

fully articulated rotor (3.2.10) system for which the horizontal hinge (3.2.6) and vertical hinge (3.2.7) are

located at the same distances from the rotor hub
3.2.14
rigid rotor

rotor system in which the blades (3.2.5) accommodate flapping and lead-lag motions by bending the

elastic elements at the corner part of blade without horizontal hinge (3.2.6) and vertical hinge (3.2.7)

3.2.15
semirigid rotor
teetering
seesaw

rotor system normally composed of two blades (3.2.5) that meet just under a common flapping or

teetering hinge (3.2.4) perpendicular to rotor shaft axis and mounted at the top of rotor shaft

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ISO 5224:2021(E)
3.2.16
semi-articulated rotor

rotor in which the blade (3.2.5) is attached to hub by two hinges (3.2.4) instead of three (without

horizontal hinge (3.2.6) or vertical hinge (3.2.7))
3.2.17
rotor head with universal joint

gimballed rotor hub tilts with respect to the rotor shaft to accommodate blade (3.2.5) flapping or which

tilts the blades (rotor disk) creating a force that pulls the autogiro in the direction of the tilt

3.2.18
swashplate

device that translates input via the helicopter (3.1.2) flight controls into motion of the main rotor (3.2.1)

blades (3.2.5)

Note 1 to entry: A swashplate is used to transmit three of the pilot's commands from the non-rotating fuselage to

the rotating rotor hub and main rotor blades.
3.2.19
blade element
spanwise piece of the blade (3.2.5)

Note 1 to entry: A blade element has a spanwise dimension of any length (usually an elementary spanwise length).

3.2.20
blade tip
part of rotor blade (3.2.5) which is the most distant from rotor axis
3.2.21
blade root
part of the blade (3.2.5) that attaches to the blade grip (3.2.22)
3.2.22
blade grip
blade fork
part of the hub assembly to which the rotor blades (3.2.5) are attached
3.2.23
external point of rotor blade

crossing point of rotor blade axis (3.3.9) with the plane tangential to surface of blade tip (3.2.20) and

perpendicular to blade (3.2.5) axis
3.2.24
tip jets

rotor system which is driven by jet nozzles at the tip of rotor blades (3.2.5) powered by ram-jets, pulse-

jets, or rockets or by high pressure air provided by a compressor
3.2.25
fenestrone
fan-in-tail
ducted fan

protected tail rotor (3.2.2) of a helicopter (3.1.2) operating like a rotor mounted within a cylindrical

shroud or duct
3.2.26
notar
air-blowing system to compensate main rotor (3.2.1) torque moment
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ISO 5224:2021(E)
3.2.27
interleaving rotors

two rotor disks which are located in the same horizontal plane and where the stagger (3.5.15) is greater

than the radius of the disk, but less the diameter of the disk
3.2.28
intermeshing rotors

two rotor disks which are located in different planes and where the stagger (3.5.15) is less than the

radius of the disk
3.2.29
bearringless rotor

hingeless rotor (3.2.11) wherein the feathering (3.2.32) bearing is replaced by a torsionally soft elastic

element
3.2.30
advancing blade
blade (3.2.5) moving in the same direction as the helicopter (3.1.2)
3.2.31
retreating blade

blade (3.2.5), located in a semicircular part of the rotor disk, in which the blade direction is opposite to

the direction of flight
3.2.32
blade feather
feathering
rotation of the blade (3.2.5) around the spanwise (pitch change) axis
3.3 Coordinate axis and planes
3.3.1
helicopter body axis coordinate system

right rectangular system of the coordinates which has been rigidly connected with a fuselage. the

origin o is the centre of mass of a fuselage

Note 1 to entry: The longitudinal axis (O X ) is directed to a helicopter (3.1.2) nose perpendicular to a shaft of the

1 1
main rotor (3.2.1).

Note 2 to entry: The normal axis (Z Y ) is directed parallel to a shaft of the main rotor and points downwards.

1 1
Note 3 to entry: The transverse axis (O Z ) is completing system.
1 1
3.3.2
longitudinal axis of helicopter body axis

axis (O X ) which is directed to a helicopter (3.1.2) nose perpendicular to a shaft of the main rotor (3.2.1)

1 1
3.3.3
normal axis of helicopter body axis

axis (O Y ) which is directed parallel to a shaft of the main rotor (3.2.1) and points downwards

1 1
3.3.4
transverse axis of helicopter body axis
axis (O Z ) which completes the system
1 1
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ISO 5224:2021(E)
3.3.5
stability axis coordinate system
hub-wind axis

rectangular coordinate system, with origin in a point of intersection of an axis of rotor rotation with

the plane of main rotor (3.2.1), having the normal axis (O Y ) parallel to axis of the main rotor rotation,

h h

directions of longitudinal axis (O X ) and transverse axis (O Z ) are defined by the direction of the air

h h h h
speed vector projection to the plane of rotation of a main rotor
3.3.6
longitudinal axis of stability coordinate system

longitudinal axis (O X ) which is perpendicular to rotor rotation axis (3.3.10) and having the same

h h

direction as the rotor air speed vector projection to the plane of rotation of a main rotor (3.2.1)

3.3.7
normal axis of stability coordinate system

normal axis (O Y ) coinciding with the axis of rotor rotation and having opposite direction as direction

h h
of lift
3.3.8
transverse axis of stability coordinate system

transverse axis (O Z ) which is perpendicular to the plane formed by (O X ) and (O Y ) axis and

h h h h h h
directed to forward moving blade (3.2.5)
3.3.9
rotor blade axis

straight line around which the angular orientation of blade (3.2.5) cross-section is changed due to

influence of actuator of rotor control system
3.3.10
rotor rotation axis

geometric axis of main rotor (3.2.1) shaft or bearing, rotor being rotating around this axis

3.3.11
rotor rotation plane

plane perpendicular to rotor rotation axis (3.3.10), forming by rotated blade (3.2.5) axis with zero

flapping angle
3.3.12
blade rotation plane
plane parallel to the tip path plane through the hub centre
3.3.13
hub plane
plane perpendicular to the shaft axis through the centre of the hub
3.3.14
tip pass plane
TPP
no-flapping plane

plane containing flight path of blade tips (3.2.20) at their rotation around shaft axis

3.3.15
tip path axis
disc axis

axis perpendicular to the plane through the blade tips (3.2.20) and, for zero offset horizontal hinges

(3.2.6), which is therefore the axis of no flapping
3.3.16
no-feathering axis

axis relative to which the cyclic feathering (3.2.32) vanishes the axis through the centre of the hub and

perpendicular to the swash plates
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ISO 5224:2021(E)
3.3.17
control axis plane

plane of the rotor wherein there is no cyclic feathering (3.2.32) (i.e. the plane of the swash plate)

3.3.18
hub axis coordinate system

coordinate system O X Y Z used to determine the rotor aerodynamic loads and rotor blades (3.2.5)

s s s s
flapping due to controls and body angular rates

Note 1 to entry: The origin O of axes is at centre of rotor hub. The normal axis (O Y ) points downwards and aligns

s s s

with the rotor shaft. The longitudinal axis (O X ) points toward the nose of helicopter (3.1.2) and is perpendicular

s s
to axis O Y . The transverse axis (O Z ) points to the right side.
s s s s
3.3.19
blade section common plane axis system

right rectangular coordinate system, with origin O in a point of intersection of blade (3.2.5) pitch axis

and in-plane blade section

Note 1 to entry: The longitudinal axis (O X ), which is in the in-plane blade section, parallel to the formed

BS BS

rotation plane, points to leading edge of blade section airfoil (3.5.11). The transverse axis (O Z ), which is

BS BS

coincident with blade pitch axis, points to blade tip (3.2.20). The normal axis (O Y ), which is in the in-plane

BS BS
blade section, points upwards.
3.4 Angles
3.4.1
blade azimuth angle

angle of blade (3.2.5) axis rotation measured in a plane normal to the shaft of the main rotor (3.2.1)

Note 1 to entry: Blade azimuth angle is zero when the blade is over the tail.
Note 2 to entry: Blade azimuth angle is positive in the direction of rotation.
Note 3 to entry: ψ is the azimuth (angle) of the i-th blade.
3.4.2
blade flapping angle
blade flap angle

angle between a line drawn along the span of the blade (3.2.5) and a plane normal to the shaft axis

Note 1 to entry: Blade flapping angle is positive when the blade tip (3.2.20) is higher than the blade cuff.

Note 2 to entry: β is the flapping angle of the i-th blade.
3.4.3
blade coning
upward sweep of rotor blades (3.2.5) as a result of lift and centrifugal force
3.4.4
blade lag-lead angle

angle of rotation of an axis of the blade (3.2.5) around axis of the vertical hinge (3.2.7) (or the line

equivalent to this axis in case of the blade mounting the elastic unit), measured from the plane passing

through the axis of main rotor (3.2.1) rotation and an axis of the blade at β = 0

Note 1 to entry: Blade lag-lead angle is positive in case of the blade axis deviation in the direction opposite to

main rotor rotation.
Note 2 to entry: ξ is the lead-lag angle of the i-th blade.
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ISO 5224:2021(E)
3.4.5
blade pitch angle

angle between the chord line of the rotor blade (3.2.5) and the reference plane of the main rotor (3.2.1)

hub or the rotor plane of rotation
Note 1 to entry: θ is the lead-lag angle of the i-th blade.
Note 2 to entry: Blade pitch is positive when the leading edge is up.
3.4.6
rotor angle of attack

angle between a vector of main rotor (3.2.1) air speed and the rotor plane

of rotation

Note 1 to entry: Rotor angle of attack is positive if the projection of air speed to a normal axis is negative.

3.4.7
collective pitch angle
longitudinal cyclic pitch angle
lateral cyclic pitch angle

average value and the first harmonic cosine and sine components of blade pitch angles (3.4.5) as function

of blade azimuth angle (3.4.1)
3.4.8
mast angle
tilt angle calculated with respect to the vertical axis on the ground
3.4.9
angle between rotors axis

inclination of one main rotor (3.2.1) shaft with respect to another main rotor shaft for intermeshing and

transverse dual rotor helicopter (3.1.10)
3.4.10
pitch of the blade element
blade element pitch angle
angle between blade chord (3.5.9) and rotor plane of rotation (at the radius r)
3.4.11
pitch of the main rotor
blade incidence angle
0,7
pitch of the blade element (3.4.10) at a relative radius (3.5.7) of ,r = 07
3.4.12
geometric twist of the blade

difference of the pitch of the blade elements (3.4.10) of the main rotor (3.2.1) with respect to the pitch of

the blade element at a relative radius (3.5.7) of r = 07,
3.4.13
collective pitch

part of a helicopter’s (3.1.2) control system wherein all blades (3.2.5) change pitch simultaneously by

the same amount
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ISO 5224:2021(E)
3.4.14
cyclic pitch

part of a helicopter’s (3.1.2) control system wherein the blades (3.2.5) change pitch in a sinusoidal

fashion as they traverse around the rotor azimuth, each blade having the same amount of such pitch

change when it reaches any given rotor azimuth
3.5 Geometry
3.5.1
radius of the main rotor
radius of the circle swept out by the blade tips (3.2.20)
3.5.2
diameter of the main rotor
diameter of the circle swept out by the blade tips (3.2.20)
Note 1 to entry: D = 2 * R.
3.5.3
radius of the tail rotor
radius of the circle swept out by the tail rotor (3.2.2) blade tips (3.2.20)
3.5.4
diameter of the tail rotor
diameter of the circle swept out by the tail rotor (3.2.2) blade tips (3.2.20)
Note 1 to entry: D = 2 * R .
TR TR
3.5.5
rotor disk area
area covered by rotor blades (3.2.5) at its rotation at β = ξ = 0
3.5.6
radius of rotor blade section

distance from rotor axis to blade (3.2.5) cross-section by plane perpendicular to blade axis at β = ξ = 0

Note 1 to entry: r is the radial location, measured from the centre of rotation (r = 0) to the blade tip (3.2.20)

(r = R).
3.5.7
relative radius
ratio of the radius of a blade element (3.2.19) to the radius of the rotor (r =)
3.5.8
blade cross-section chord

straight line joining the leading edge of blade (3.2.5) cross-section with its trailing edge

Note 1 to entry: Blade cross-section at fixed radius is designated by a subscript, for example, b is the blade

0,7
cross-section at relative radius (3.5.7) r = 0,7 .
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ISO 5224:2021(E)
3.5.9
blade chord
blade (3.2.5) width, that is, local dimension perpendicular to blade radius
3.5.10
blade span
length of a blade (3.2.5) from its tip to its root
3.5.11
airfoil
shape of a cross-section of a rotor blade (3.2.5)
3.5.12
rotor solidity ratio
zb⋅
b0,7

ratio of the lifting area of the blades (3.2.5) to the area of the rotor(s), σ = , where z is the

π⋅R
number of blades of the rotor
3.5.13
rotor blade horizontal hinge offset
distance between horizontal blade (3.2.5) hinge (3.2.4) axis and rotor axis
3.5.14
rotor blade vertical hinge offset
distance between vertical blade (3.2.5) hinge (3.2.4) axis and rotor axis
3.5.15
stagger
stagger distance
horizontal centre-to-centre distance between two rotor disks

Note 1 to entry: It is applicable to intermeshing, interleaving, side-by-side, tandem and quad helicopters (3.1.2).

3.5.16
overlap ratio

percentage of the overlapped area to that of the total area of the two rotor disks (for dual rotor

interference)
3.5.17
pitch-flap coupling

automatic kinematic pitch change caused by flapping motion, as results from the delta-three hinge

(3.2.4)
3.5.18
aspect ratio
ratio of the blade (3.2.5) radius to the average blade chord (3.5.9) length
3.5.19
thickness ratio
ratio of maximum thickness to airfoil (3.5.11) chord
3.5.20
taper ratio

ratio of the chord length at the tip of blade (3.2.5) to the chord length at the root of blade

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ISO 5224:2021(E)
3.6 Dynamic characteristic
3.6.1
disc loading
ratio of weight of helicopter (3.1.2) to the total main rotor (3.2.1) disc area
3.6.2
blade flap and pitch static moments of inertia

static moment of inertia of main rotor (3.2.1) blade (3.2.5) and other assembled units, flapping with

blade:
— around horizontal hinge (3.2.6);
— around vertical hinge (3.2.7)
3.6.3
blade flap and pitch moments of inertia

moment of inertia of main rotor (3.2.1) blade (3.2.5) and other assembled units, flapping with blade:

— around horizontal hinge (3.2.6);
— around vertical hinge (3.2.7)
3.6.4
main rotor moment of inertia

total inertia moment of all blades (3.2.5) and other rotating units, connected with blades, referred to

main rotor (3.2.1) axis of rotation
3.6.5
lock’s inertia number

ratio of the aerodynamic and inertial forces on the aerodynamic and inertial forces acting on an

articulated rotor (3.2.9) blade (3.2.5)
ρ⋅⋅ca ⋅R
γ =
where

a is the derivative of aerodynamics load factor of blade with respect to blade angle of attack;

c is the rotor blade chord (3.5.9);
ρ is the air density
3.6.6
main rotor airspeed
speed of centre O of stability system with reference to free air
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ISO 5224:2021(E)
3.6.7
main rotor speed
rotor RPM

angular speed of main rotor (3.2.1) rotation around rotor axis with respect to helicopter (3.1.2) fuselage

Note 1 to entry: RPM stands for revolution per minute.
3.6.8
blade tip speed
tip speed
average speed of blade tip (3.2.20) motion due to rotor rotation at β = ξ = 0
3.6.9
inflow
downward component of air velocity through and perpendicular to the rotor disk
3.6.10
rotor induced velocity

increment of the air velocity component along the rotor axis at the rotor disc induced by the lift of the

blades (3.2.5)
3.6.11
total inflow velocity

sum of the component of helicopter (3.1.2) velocity normal to the plane of the rotor disk and induced

velocity
Vv⋅+sinα
HH i
3.6.12
advance ratio
tip speed ratio

non-dimensional forward speed, which is the ratio of component of helicopter (3.1.2) vel

...

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