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K B3810 He//capters He Wharekura-tini Kaihautu 0 Aotearoa THE OPE N P0|.YTE(HN|( OF NEW ZEALAND 555-3-1_

01 - Basic Helicopters

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Basic Helicopters

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K

B3810 He//capters

He Wharekura-tiniKaihautu 0 Aotearoa

THE OPE NP0|.YTE(HN|(OF NEW ZEALAND

555-3-1_

CONTENTS

Basic Operating Principles

Controls

Structures

The Powertrain

Safety In and Around Helicopters

Appendix: Table of Definitions

Copyright

{his material is for the sole use of enrolled students and may not bereproduced without the written authority of the Principal, TOPNZ.

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“knew--tau

AIRCRAFT ENGINEERING"

AIRFRAMES 111 ASSIGNMENT 1

BASIC HELICOPTERS

This assignment is intended to serve as an introduction to therest of the assignments in the 5S5~3 series. The complete seriesconsists of

Assignment 1 Basic HelicoptersAssignment 2 Basic Flying ControlsAssignment 3 Basic RotorsAssignment Q Piston Engine InstallationsAssignment S Rotating Flying ControlsAssignment 6 Main and Tail Rotor Heads and BladesAssignment 7 Transmission SystemsAssignment 8 Helicopter VibrationsAssignment 9 Turbine Engine InstallationsAssignment 10 Basic Helicopter Flight Aerodynamics

The word Helicopter is derived from the two Greek words:

Helicon = helix

Pteron = wing

and so literally the word helicopter means spiral wing.

The history of helicopter flight starts in the mid 1700s whenpeople of many nationalities began making models of helicoptersof all shapes and sizes, powered in a variety of ways, such asgunpowder, steam, and electricity. However, vertical flight wasknown much earlier. It was first described by the Chinesealchemist Ko—Hung, who wrote in 320 AD about a toy now known asthe "Chinese flying top".

In 1907, Paul Carnu, a Frenchman, made the world's first freehelicopter flight. His machine reached a height of about 1.7 metres

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and was airborne for but a'few seconds. In the years that followemany helicopters were made and flown. In 1936, the successfulFocke-Wulf Fw 61 flew for the first time. In 1939, Igor Sikorskyflew his VS 300, which became the RH production model and is theforerunner of the present—day Sikorsky helicopter models.

Many of the advances made in the design of the helicopterrotor are due to the work of Juan de La Cierva who, during thedevelopment of his "autogyro" re~invented the flapping hinge,invented the drag hinge and its damper, and developed cyclic pitchcontrol of the rotor.

So far, several terms associated with helicopters have beenused. Before going any further, and to avoid confusion, a list ofwords and terms as they are used on helicopters and on fixed-wingaircraft is given in the Appendix at the end of this assignment.As part of your work on this assignment you should now read theAppendix and than dg Practice Exercise A that follows here.

PRACTICE EXERCISE A

State whether each of the following statements is Trueor False.

1. Disc area is the sum of the area of all the bladesof a rotor.

2. The angle between the chord line of a rotor bladeand its plane of rotation is called the angle ofincidence.

3. The control that changes the main rotor blade pitchangles all together is the cyclic pitch control

4. An aircraft pitches about its longitudinal axis.

S. The propulsion rotor sited at the tail in a more orless vertical plane is the tail rotor-

6. An aircraft yaws about its normal axis.

7. The study of the motion of air is called dynamics.

8. The control that changes the main rotor blade pitchangles differently to each other is the collectivepitch lever.

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9. The angle between the chord line of an airfoil andthe direction of the airflow (relative airflow) iscalled the angle of attack.

10. An aircraft rolls about its lateral axis-

(Answers on page 27)

BASIC OPERATING PRINCIPLES

If two or more airfoils (seeFig. 1) are fioined together,pivoted at the centre, heldhorizontal, and then spun aroundquickly, they will rise straightupwards because of the liftdeveloped by the airfoils as theymove through the air. This device

FIG. lmentioned earlier. Should a gust

of wind tilt it to one side while it is flying, then it will movein the direction of the tilt. All the time that the liftgenerated exceeds its weight, the top climbs, and when the lift isequal to the weight the top hovers, and when it becomes less, thetop descends. The helicopter main rotor operates in a similar wayto the flying top, except that it is power driven and its tilt iscontrolled by the pilot.

Because the main rotor is power driven, a torque reactionequal and opposite to the torque turning the rotor is developed.(Newton's third law of motion.) If this torque reaction wereallowed to act unhindered, then the fuselage of the helicopterwould turn in the opposite direction to the main rotor. The ccomponent that controls the effect of the torque reaction isusually a tail rotor, which is a vertical, side-mounted propeller 'WhOS@ blade angles can be moved from a positive pitch through 0°

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is the Chinese flying top -

/'

I \°’ I Dimzciionof

rototbn

“h-III 1 'TbflT‘o*'cLuQ.'- _ ‘ - flfotorHmochorz pbvoz

FIG. 2 Main rotor torque andtail rotor force

the same direction, and at the

_ u _

to a negative pitch to vary theside thrust produced. Besidescontrolling the effect of thetorque reaction, the tail rotor isalso used to control the helicopterabout its vertical (yaw) axis whenit is hovering. The pilotcontrols the pitch angle of thetail rotor blades through thetail rotor pedals.

The lift developed by themain rotor is altered not by

speeding up or slowing down therotor but by increasing/decreasingthe pitch angle of all the bladestogether by the same amount, in

same time. This is known ascollective pitch. Lifting up the collective pitch lever increasesthe pitch angles and causes the helicopter to climb. Pushing itdown causes the helicopter to descend.

The reason foris that the inertiabetween the opening or closingrev/min of the main

changing the pitch angles and not the rev/minof the main rotor would cause a time delay

of the engine throttle and therotor increasing or decreasing. By, say,

increasing the pitch of the main rotor blades and increasing theengine power output at the same time, the main rotor rev/min staysconstant and the power delivered to the main rotor is increasedwithout the time delay due to inertia.

The main rotor is tilted through the cyclic pitch controlcolumn by progressively increasing and then decreasing the anglesof the blades in their orbit. Thus, to move into forward flight,the pitch angle of a rearwardgmoving blade is increased, whichcauses the blade to develop more lift while a forward—moving bladehas its pitch angle decreased to develop less lift. The result isto tilt the total reaction into a forward—leaning position ~— seeFig. H. The main rotor can be tilted in any direction by moving

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the cyclic pitch control column in the direction desired for thetilt, the helicopter then flies in the direction of the tilt.

The actual tilting may be done by

1. Using a gimbal-mounted main rotor. This assemblyis called a semi—rigid rotor. See Fig. 3(a).

2. Aerodynamic forces moving the blades, each pivotedon a horizontal hinge pin, up and down in relationto the centre of the fixed main rotor hub. Thisassembly is called an articulated rotor. See Pig.3(b).

3. Using aerodynamic forces to bend relatively flexibleblades and their mount elements up and down inrelation to the centre of the fixed main rotor hub.This assembly is called a rigid rotor. See Fig. 3(0)

(a) Semi—rigid rotor (b) Articulated rotor (c) Rigid rotor

FIG. 3 Types of main rotor

The main rotor gives energy to a large mass airflow, andbecause the airflow is accelerated to a low speed only, this offersa most efficient method of hovering. As a theoretical example, ahelicopter that hovers by passing 500 kg of air each second at avelocity of 20 m/s downwards through its main rotor generates a"lifting force where

Force = mass per second (%§) X velocity (%>/

= §§Ll§ (N)*B

* This is a variation of the familiar

Force = mass (kg) X acceleration.;“\S it

k= -2-gin-(N)In both equations the answer is in newtons (N).

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;. F = 500 (kg) X 20 (m)1 (s) 1 (S)

= 10 000 (kg m)l (s7)

= 10 000 kg m/52

= 10 000 N

The energy needed to generate this force of 10 000 N is foundfrom

= 2Ke i mV

= i X 500 X 202

= 100 000 J

where Ke is kinetic energy,

m is mass, and

V is velocity.

This amount of energy is used each second, so the-power neededis

100 O00 (J)1 (S) = 100 O00 W

= 100 kW

If, by some means a smaller mass of air is moved, say, 250 kg,then, to keep momentum the same, the velocity must be increased.

Momentum = mass X velocity

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8

0

r-

New “e1°°i’°Y " “E§6

- 7 _

_ 10 O00 (momentum)

= 40 m/s

The energy needed has become

K8 = 5 X 250 X 402

Because this amount of energy is used each second

Power needed =

This is a twofold increase in power just to do the same jobas before.

The comparison becomes even more marked if we take atheoretical VTOL jet aircraftvelocity of Q00 m/s. As the momentum of the air lS the same, itsmass is now as follows:

Mass =

New mass =

The energy needed is now

Ke

= 200 O00 J

200 O00 (J)1 (s)

= 200 000 w

= £92=§E

of the same weight but with a jet

momentumvelocity

10 O00400

2.§1.=1<.e

= § X 25 X 4002

= 2 000 000 J

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Power'needed = 2 000 O00 W

= 2000 kW

You can thus see that the helicopter is quite efficientcompared with the VTOL jet aircraft when both are hovering. High-

speed flight is another story, and here the helicopter becomesseverely handicapped partly because of its large-diameter mainrotor. This is discussed in a later assignment.

angles to the plane of rotation of the rotor blades. Figure H showsa helicopter in steady level forward flight with the total reaction

The force generated by the turning main rotor acts at right

acting in a forward direction.

_Té+ca| reacifion

so’

Forwarcl

<i

into

FIG. 4 Total reaction

The name total reaction is used because this force is resolved

1. A horizontal force (thrust) to propel thehelicopter, and

2. A vertical force (lift) to sustain the weightof the helicopter.

As with a fixed-wing aircraft in steady level flight

Thrust = drag, and

Lift = weight.

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* Figure 5 shows the totalreaction resolved into thrust and

‘ lift, together with the opposing@ | 1 forces of drag and weight for

75*? ?L§% steady, level forward flight. Inrzochon

. I this respect, the helicopter isI

no different from a fixed~wingE‘..-’*“ ‘ aircraft where forces act through

' moment arms about the centre ofcg?‘ Di. gravity (c.g.) and the centre of

Q-I 1 ‘Fwd‘ I llft (CL).

In practice, the c.g.1“@Bb+ position in a helicopter lies on

or very close to the centre oflift (CL) so that the lift andweight forces will give an effect

FIG. 5 Total reaction resolved

ranging from slight nose down to slight nose up. But, unlike theusual fixed-wing aircraft, the thrust and drag forces act to givea nose—down attitude. To correct this nose~down tendency, manyhelicopters have a horizontal stabiliser similar to that on afixed-wing aircraft. This stabiliser may be either fixed orcontrollable.

To gain altitude, the total reaction is increased, which, ifnothing else is changed, also results in an increase in forwardspeed. This acceleration up and forward will continue until thetotal reaction is again equalled by the new, greater weight—dragresultant.

To provide greater forward speed while flying straight andlevel, a forward movement of the cyclic control is made. Thisgives an increase in the pitch angle of the rear—going blades tocause them to develop more lift and a decrease in pitch angle ofthe forward—going blades to cause them to develop less lift. Thedifference in lift between the rear—going and forward—going bladestilts the rotor disc forward, perhaps causing a slight loss ofaltitude, but giving the desired acceleration. At the same time,the line of total reaction moves slightly to the rear of the rotor

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disc. See Fig. 6. The small couple that this produces is enough

_ 19 _

to tilt the helicopter in the direction that the cyclic stick wasmoved.

'TE>+oJ r':za<;-1-ic;r~, Téioi reaction-H-1 + of’ o‘F r +01»-I _hM'§°§§\Q+;§-fiige hub ==~=-c-3'1-1~Y\<= ' Reta" ‘filepa+H hfih

-,,,--if V _.-=-"

‘ lZc+c-P -HpPa‘H"1 low

(ca) T12LJ+YQl 5'h'¢\< ‘Pqrwqrd

FIG. 6 Result of cyclic movement a

Figure 7 shows the action of the forces in a vertical climband in level, accelerating flight.

upe

Z'_\\_

f"'IF!‘

KWeight

ct ,Q§§h \-' 7 ;:- \

I 1X\

, ——/

51> ————

Lift exceeds weightfor vertical climb.

Thrust === Qgg =-= Zero

(a) Vertical climb flight

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I I

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_ 11 _

R, '

, I /\ Z

”,//’ -;?5l5“q_“\’////,»///fil

‘ R1, T1, D; show slraigl-nt andA\ I I level flight ai‘ conslanl Spfled

I

Moving R1 Forward to R1 will IncreaseT; to T; , causing nose—down athtude

l;%%¢¢ we cadences-

(b) Level and accelerating flight

FIG. 7 Forces on a helicopter

R: Lm~ ///’ \

,. §\\\\s,\\\

' CL -4?

F,;@s; ’H ‘wt 91

SUMMARY

All aircraft, including helicopters, are subject to thesame aerodynamic forces.

For equilibrium in flight

Thrust = drag

Lift = weight

The thrust—drag couple equals the lift~weight couple.Angled vectors can be resolved into horizontal andvertical components.

Provided rotor rev/min are maintained, an increase inpitch of a rotating airfoil will increase its liftingforce.

A tail rotor may be used to provide a force to balancethe main rotor torque reaction and to give directionalcontrol when the helicopter is hovering.

A difference in lift between one part of the rotor discand another will cause it to tilt.

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....j_2_

PRACTICE EXERCISE B '

State whether each of the following statements is Trueor False.

l. Due to torque reaction, the fuselage of a power-driven single—main helicopter will try to turn inthe same direction as the main rotor.

2. The lift of a main rotor is varied by altering thepitch angles of its blades while keeping itsrev/min constant.

3. The total reaction from a main rotor is resolvedinto lift and drag forces.

4. When a helicopter is hovering in still air, ithas no thrust and drag, and its lift just exceedsits weight.

5. When the cyclic control is moved forward, the lineof total reaction moves to a position slightlyaft of the rotor hub centre line.

(Answers on page 27)

CONTROLS

From the Table of Definition in the Appendix and the BasicOperating Principles on page 29, you will know that

1. Yaw and main rotor torque reaction is controlledby the tail rotor through the movement of thetail rotor (rudder) pedals.

2. The in-flight directions of forwards, sideways,and backwards are controlled through the cyclicpitch control column, sometimes called theAzimuth control or cyclic stick.

3. Climb and descent are controlled by the collectivepitch control lever, or collective.

By co-ordinating the use of these three controls, the pilotcan make the helicopter bank, dive, and climb like a fixed-wingaircraft, as well as fly it sideways and backwards and make itclimb and descend vertically.

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Earlier in this assignment, we said that the power deiiveredto the main rotor was increased by increasing its blade anglescollectively and by increasing the engine power at the same time.To achieve this, a throttle twist grip is mounted on the end ofthe collective pitch lever. This twist grip, very much like amotorcycle throttle grip, is mechanically connected to the enginecarburettor or fuel control unit, and interconnected with thecollective pitch control.

The engine power will be automatically increased when thecollective is raised, and if too little or too much power is thendelivered, delivery can be corrected by use of the throttle grip.

Thus raising/lowering the collective will increase/decreasethe power, as will twisting the throttle grip.

The throttle grip also makes it possible to "throttle back"in flight and to start up the engine and bring it up to itsoperational rev/min without raising the collective.

In gas turbine-powered helicopters, fine adjustments to thethrottle setting can be made using a "beep" switch on the collectivecontrol hand grip.

Figure 8 shows the flying controls and the throttle twistgrip in an S55 helicopter. All modern helicopters have a similar ‘_layout.

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~IOU\-Lilli)!-I

. RUDDER PEDAL LEG REACH CONTROL

. RUDDER PEDALS

. CYCLIC-PITCH CONTROL COLUMN

. FORE-AND-AFT FRICTION CONTROL

. LATERAL FRICTION CONTROL

. THROTTLE TWIST GRIP. FRICTION CONTROL RING,

8.

9.

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9 8 7 6 4

FIG. 8 Flying controls in the cockpit

STRUCTURES

The two most common construction methods used at present forhelicopters are

1. Semi-monocoque, and

2. Girder.

Each method has its advantages, the former leaving a largeopen box for crew, baggage and payload, but requiring a complexstructure and reinforcing for strength. The materials used in this

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@ \ (‘ \'r1-mo'r'ru=: -rwxsr am? . ,1 ,_ . » .,FRICTION CONTROL, qR " - _

COLLECTIVE-PITCH usvsn -"’ Q \j_. \§_/ K =\ W,conuzcnvs-vrrcn uzvxa 1; " \\'~ N) ._ .‘ ._v -=»» \ 1

cs. J I/R

/ //I §§;. _ Q-.._ 5 , .1 . » \K s \\

‘ff/fix” '::{“~ Q , I --GEX ‘__.-‘ A _ \.......................3!§;! I44’! f /

i X :,/

O §‘- y3

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E“‘gmi5$$h‘fi%\fiii“HJ‘4b¢ _~A3‘J‘I/aw“gWHy4 g‘LQ\W,

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.._/FIG. 10 Fuselage structure assembly

A third form of construction now coming into use is thecomposite structure, which uses carbon fibre reinforced stiffeners,frames, and bulkheads, plus impact»resistant fibre reinforcedskinning (Kevlar) in the primary structure and high—quality glassfibre in the secondary structure. The use of these materials givesa great saving of weight.

THE POWERTRAIN

The components that transmit the engine power to the mainand tail rotors are collectively called the powertrain or thetransmission.

The essential components of a powertrain are

1. An engine-driven clutch (on piston-enginedhelicopters);

2. A freewheel unit, which may be called asprag clutch OP a one—way clutch;

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3. A main—rotor gearbox; M

H. A tail-rotor gearbox; and

5. Driveshafts from the engine to the main-rotor gearbox and from the main—rotorgearbox to the tail—rotor gearbox.

The functions of these components are as follows.

The engine~driven clutch is fitted to allow the engine to be

started without turning the rest of the powertrain.

Ehewfreewheel unit permits the two rotors to turn faster thanthe engine. This could occur when the engine is throttled backto idle rev/min.

The mainmrotorggearbgi changes the direction of the enginedrive and reduces the engine rev/min to the much lower rev/minneeded by the main rotor. It also provides drive pads forancillary equipment.

rhe tail~rotq;mgea;box changes the direction of the drive tosuit the need of the tail rotor. Depending on the helicopter type,this gearbox may increase, decrease, or make no change in therev/min of the output shaft relative to the input shaft. Thisgearbox may house the blade pitch—changing mechanism of the tailrotor.

The driveshafts transmit the power from the engine to thegearboxes. These shafts may also drive ancillary components, suchas cooler fan units.

In all powertrains, the main rotor is always mechanicallyconnected to the tail rotor so that at no time can one rotor turnwithout the other. This fact, coupled with the function of thefreewheel unit means that, should the engine fail, both rotors willkeep turning and the pilot can make a safe and controlled landing.This flying condition, known as autorotation, is the equivalentof a fixed-wing aircraft gliding. Figure 11 shows three differentpowertrains in schematic form.

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-13-

Main-roinr gur-bur-|"',' . .. . I ___ , ——F - i1 I ‘Y -' ”\ ,'" " “,,‘f§,’ -=II Drive-shzfi u..a.....1¢~»-V.

Rofor brake Q

C‘ Tail rotor

Engine -cnolfng -Hfa

R

(a) Vertical piston engine

Fru--whul unitMin rotor __ , _ ' — . — "' .___W _,.'....... /

Drive.-Sheff Tail-shaft 5881‘-ha:

Clunch

“iiEngin:-cooling Flfl

(b) Horizontal piston engine

‘ Free-wi\c¢|uni1' Um‘ shinMilin nior \__ _gearbox ' I _ ’ ' \

OH coohng uni?Tail 1-afargar-ma

(c) Gas turbine engine

FIG. ll Powertrains

gearbox

0

SUMMARY

The pilot flies a helicopter by using

1. The cyclic pitch control column,

2. The collective pitch control lever, and

3. The tail rotor pedals.

The collective pitch control and the engine throttlecontrol are interconnected.

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The movements of the-flying controls are natural ones forthe response desired. That isl .

Cyclic forward + fly forward

Collective down + descent

Right tail rotorpedal forward + yaw right

All helicopters have a freewheel unit between the engineand the rest of the powertrain. y

TThe main and tail rotors are mechanically connected so Ithat one cannot turn without the other.

PRACTICE EXERCISE C

Match each of the items in the left—hand column with itscorrect item in the rightwhand column and write thenumbers of the items in the box below. Each item is tobe used only once.

A. Tail rotor 1. Azimuth control

B. Cyclic pitch 2. Interconnected with the collectiveC. Collective pitch 3. Lateral controlD. Engine throttle 4. Directional control

5. Control of climb—descent

6. Yaw and torque control

IA I B I C I D I

(Answers on page 33) .

SAFETY IN AND AROUND HELICOPTERS

Because of the ability of a helicopter to hover, the loadingcrew may come into its close proximity while it is flying. Theycould thus also find themselves in positions where they cannot beseen by the pilot. For this and other situations, a series of

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hand signals has been devised which, if used sensibly, can make auseful contribution to both the safety and the economics ofhelicopter operation.

For the signalS to be of real use, both the helicoptermarshaller and the pilot must know exactly what the signals mean,and the pilot must be aware that, when a sling load is being"hooked on", there can be a third man underneath the helicopterusing a lot of effort amidst the confusion of noise and abuffeting ground cushion of air. The hand signals are shown inFig. 12.

STAHT ENGINE ENGAGE ROTOR STOP ROTOR STOP

1% F‘fiog O 5 O

nova BACK movs FORWARD MOVE mo:-n~ MOVE LEFT

O‘?<9

O O 11°11 non2‘

"mm: OFF LANDING co UP co DOWNnzazonon

O<)==:| c==(>Q

SWING TAIL SWING TAILTD RIGHT TO LEFT

FIG. 12 Helicopter hand signals

For safety in and around helicopters the FAA AdvisoryCircular 91-32A of that name is important reading. We reproduceit here in full.

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_ 21 _

AC 91-32ADATE 6/21/79

ADVISORY CIRCULARFTa ex-‘O I4“-no

nDiguqr

'4 DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

Washington, D.C.en“6,)-

.'¢44-MO“‘*5

"4715 04 '

Subject: SAFETY IN AND AROUND HELICOPTERS

1} PURPOSE. This advisory circular provides suggestions to improvehelicopter safety by means of acquainting flight and non~flight crewpersonnel and passengers with the precautions and procedures necessary toavoid undue hazards.

2. CANCELLATION. AC 91-32, Safety In and Around Helicopters, dated 5/7/71is canceled.

3. GENERAL. People have been injured, some fatally, in helicopter acci—dents which would not have occurred had they been informed of the propermethod of boarding or deplaning. A properly briefed passenger should neverbe endangered by a spinning tail rotor. The simplest method of avoidingaccidents of this sort is to have the rotors stopped before passengers areboarded or allowed to depart. Because this action is not always practicable,and to realize the vast and unique capabilities of the helicopter, it isoften necessary to take on passengers or to deplane them while the engineand rotors are turning. Therefore, if accidents are to be avoided, it isessential that all persons associated with helicopter operations, includingpassengers, be made aware of all possible hazards, and instructed as to howthey can be avoided.

4. FLIGHI AND NON—FLIQHT CREW PERSQEQEL. Persons directly involved withboarding or deplaning passengers, aircraft servicing, rigging or hooking upof external loads, etc., should be instructed as to their duties. It wouldbe difficult, if not impossible, to cover each and every type of operationor non~flight crew training matter related to helicopters. A few of themore obvious and common ones are covered below:

a. Ramp attendants and aircraft servicing personnel. These personnelshould be instructed as to their specific duties, and the proper method offulfilling them. In addition, the ramp attendant should be taught to:

Iniuated by: AF5-gg0

555/8/1

_ 22 _

AC 91-31A 5/21/79

(1) Keep passengers and unauthorized persons out of the helicopterlanding and takeoff area.

(2) Brief passengers on the best way to approach and board ahelicopter with its rotors turning (see paragraph 4a).

b. Aircraft servicing.

(1) The helicopter rotor blades should be stopped and both theaircraft and the refueling unit properly grounded prior to any refuelingoperation. The pilot should ensure that the proper grade of fuel and, whenrequired, the proper additives are being dispensed.

(2) Refueling the aircraft, while the blades are turning ("hotrefueling"), may be practical for certain types of operation. However, thiscan be hazardous if not properly conducted. Pilots should remain at theflight controls and refueling personnel should be knowledgeable with respectto proper refueling procedures and properly briefed for specific makes andmodels. ‘

(3) Refueling units should be positioned to ensure adequate rotorblade clearance and persons not involved with the refueling operation shouldbe kept clear of the area.

(4) Smoking must be prohibited in and around the aircraft duringall refueling operations.

c. External~load”riggers. Rigger training is possibly one of the mostdifficult and continually changing problems of the helicopter external—loadoperator. A poorly rigged cargo net, light standard, or load pallet couldresult in a serious and costly accident. It is imperative that all riggersbe thoroughly trained to meet the needs of each individual external—loadoperation. Since rigging requirements may vary several times in a singleday, proper training is of the utmost importance to safe operations.

d. Pilot at the flight controls.

. (1) Many helicopter operators have been lured into a "quickturnaround" ground operation to avoid delays at airport terminals and tominimize stop/start cycles of the engine. As part of this quick turnaround,the pilot will leave the cockpit with the engine and rotors turning. Suchan operation can be extremely hazardous if a gust of wind disturbs the rotordisc or the collective flight control moves causing lift to be generated bythe rotor system. Either occurrence may cause the helicopter to roll orpitch resulting in a rotor blade striking the tailboom or the ground.

(2) Good operating procedures dictate that pilots remain at theflight controls whenever the engine is running and rotors are turning. Onoccasion, however, the pilot may find it necessary to leave the controls ofa "running machine." On these occasions the pilot should:

2 Par 4

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-28..

6/21/79 " AC 91-32A

(i) Ensure that all controls are secured in accordance withthe aircraft flight manual.

(ii) Reduce rotor and/or engine RPM to ground idle or minimumrecommended settings.

(iii) Turn off hydraulic boost when appropriate.

e. External"load hookup personnel.

(1) Know the lifting capability of the helicopters inyolved. Sincesome operators have models of helicopters that have almost identicalphysical characteristics but with different lifting capabilities, thisknowledge is essential. For example, a hookup person may be working with asupercharged helicopter on a high altitude project and without any warning anon—supercharged helicopter, which looks exactly the same to the groundcrew, comes to a hover to pick up a load. It does not take a vivid imagina~tion to see what could happen if the hookup person connects a load far tooheavy for the non~supercharged helicopter to lift.

(2) Know the pilots. The safest plan would be to standardize allpilots insofar as the manner in which sling loads are picked up andreleased. Without pilot standardization, the hookup person should learn thetechnique used by each pilot. Does the pilot come in fast or slow, high orlow? Does the pilot try to lift the load off with a combination ofcollective and cyclic? The hookup person should specifically demandstandardization on the pilot technique for any sort of emergency occurringwhile personnel are beneath the helicopter.

(3) Know the cargo. Many items carried via sling are very fragile,others can take a beating. The hookup person should always know when a haz-ardous article is involved, and the nature of the hazard; such as explo-sives, radioactive materials, and toxic chemicals. In addition to knowingthis, they should be familiar with the types of protective gear or clothingor actions that are necessary for their and the operations safety.

(4) Know appropriate hand signals. When direct radio communica—tions between ground and flight personnel are not used, the specific meaningof hand signals should be coordinated prior to operations. '

(5) Know emergency procedures. Ground and flight personnel shouldfully agree to and understand actions to be taken by all participants in theevent of emergencies. This prior planning is essential to avoid injuries toall concerned. .

Par 4 3

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AC 91-32A 6/21/79

5. PASSENGERS. The term "passenger" used throughout this advisorycircular refers to all non-flight crew personnel that ride in helicopters,and is not limited to the fare-paying customer. All persons that board ahelicopter while its rotors are turning should be instructed as to thesafest means of doing so. Naturally, if the pilot is at the controls,he/she may not be able to conduct a boarding briefing. Therefore, theindividual who arranged for the passenger flight or assigned as the rampattendant should accomplish this task. The exact procedures may varyslightly from one helicopter model to another, but in general the followingshould suffice:

a. Boarding.

(1) Stay away from the rear of the helicopter.

(2) Crouch low before getting under the main rotor.

(3) Approach from the side or front, but never out of the pilot'sline of vision.

(4) Hold firmly to hats and loose articles.

(5) Never reach up or dart after a hat or other object that mightbe blown off or away.

(6) Protect eyes by shielding with a hand or by squinting.

(7) If suddenly blinded by dust or a blowing object,stop — crouchlower — or better yet — sit down — and await help.

(8) Never grope or feel your way toward or away from thehelicopter.

b. Pre—takeoff briefing. Since few helicopters carry cabin attendants,this briefing must be made by the pilot. The type of operation will dictatewhat sort of briefing is necessary. Passengers should always be briefed on:

(1) Seatbelts. The use and operation of seatbelts for takeoff,en route and landing.

(2) Overwater flights. The location and use of flotation gear andother survival equipment that might be on board. How and when to abandonship should a ditching be necessary.

(3) Flights over rough or isolated terrain. All occupants shouldbe told where maps and survival gear are located.

A Par 5

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.- AC 91-32A

(4) Emergency instructions. In the event of an emergency, eachpassenger should be instructed as to what actions and precautions to take;such as the body position for best spinal protection against a highvertical impact landing (erect with back firmly against the seat back); andwhen and how to exit after landing. Ensure that passengers are aware offire extinguisher and survival equipment locations.

(5) Smoking. Smoking within 50 feet of an aircraft on the groundshould be prohibited. Smoking could be permitted, at the discretion of thepilot, except under the following conditions:

(i) During all ground operations;

(ii) Immediately before, during, or after takeoff or landing;or

(iii) when carrying flammable or hazardous materials.

c. Rreelanding briefing. The nature of the landing will determine whatthe passengers need to be told. A few items to consider are:

(1) If on a hill, depart downhill. If this involves walking aroundthe helicopter to avoid the area of lowest rotor clearance, always go aroundthe front, never the rear.

(2) Repetition of the basic instructions shown in paragraph 4a.

6. SAFETX AROUND HELICOPTERS. The material appearing in Appendix 1 wastaken from the June 1970 issue of ROTORNEWS, a publication of the HelicopterAssociation of America.

[Z4 L§~’l~-E ' .-if’! ' "'1_“ v\\.\..§\AMES M. VINES

‘ Acting DirectorFlight Standards Service

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6/21/79 AC 91- 32AAppendix 1

SAFETY AROUND HELICOPTERS

$ ~ min. _-is a W’hi T A

1. Approach or leeve machine ln e crouchlng manner(for extra clururwo twm main wlorl 9. Keep hellspot cleer cl loose erllcles - ureter begs.

groundaheets. empty cane. etc.

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J2. Approach or leeve on the down slope slde (to avoid H

'°‘°"' i. 10. Keep cooking lites well clear of hellspol.

' .... "3. Approach or leeve In pilot’: tleld ol vision (to avoid

tell rotor). 11. Loading assistants should always be supplied withplastic eye shields. —

i ’ i 12. Alter hooking up cargo sling, move lorwerd and to4. Carry tools horizontally, below weiet level (MW! aide to signal pilot (lo avoid entanglement and

upright or over shoulder). getting struck, with loaded sling).

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3. when directing machine tor Iendlng. stand with beck5. H In t h d net when approaching or leevlng lm‘:cm:':'°um:;‘ cm“ ‘mm m um, to vvlnd wllh errna outstretched toward lending ped.

t4. when dlrectlng pilot by mole. give no lending In-6. Feeten seat belt on entering helicopter and leave it $"'\l¢!l°l'l$ "131 Ffiqlllffi fl¢=k"°\"16¢l§9mll"l I! P"°|

buckled untll pilot signals you to get out. "Vi" "I" b°"l "BM! b"!Y- .

' - ' 0'eee eeeeeeeeeeeee

W _____ 15. when moving terger crews:

7 ll leaving machine at the hover. get out and oil in ('1 5"‘! 3'1"“ °“ “my ” “°"'°-' - i _ (bl Keep them together end well beck It side clam Smooth‘ unhurmd mm on lendrng zone_(lhis gives the pilot e chance In the

_____ event he hes to land suddenly either duringc"1*""""fi-- J lending or take-otl).(cl Have them face away from machine during lend-% lng and lake-ell.

l t (Q(cl) Have each men look elter hie own personal geer.

" all T A W * * l Hive mlnpaired off and reudyto get aboard. esOtl t ' h ‘ _8. Do not touch bubble or eny.ol the moving pens “an i pk gw” ‘ Q men“

(tell rotor linkage. etc.). 1

QU.5. GOVERNMENT PRINTING OFFICES 1979-28l“S6B/159

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PRACTICE EXERCISE D "

Which suggestion in AC 91-32A, if followed, will make itimpossible for a passenger to be struck by the rotatingtail rotor of the helicopter?

(Answer on page 28)

ANSWERS TO PRACTICE EXERCISES

EXERCISE A

Items 2, 6, and 9 are True.

1. False: See page 30

3. False: See page 30

4. False: An aircraft pitches about its lateralaxis. See page 29

5. False: The tail rotor is not a propulsion rotor.See page 31

7. Egigg: See page 29

8. fglse: See page 80

10. False: An aircraft rolls about its longitudinalaxis. See page 29

EXERCISE B

Items 2 and 5 are True.

1. False: Due to torque reaction, the fuselage willtry to turn in the opposite direction to the mainrotor. See Fig. 2.

3. False: The total reaction from a main rotor isresolved into lift and thrust forces.

H. False: when a helicopter is hovering in still air,there is no thrust and drag and its lift equals itsweight. If the lift just exceeds the weight, therewould be a nett upward force and so the helicopterwould climb.

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EXERCISE C

EXERCISE

Thethe sidewill, if

the tail

D

suggestion in paragraph 5.a.(3) that says "Approach fromor front, but never out of the pilot's line of vision"followed, ensure that a passenger will not be struck byI‘O'tOI"

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A B C D

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.. APPENDIXTable of Definitions

Aerodynamics: The study of motion of air (and other gases),particularly its reaction to moving bodies therein

Aerodgne: An aircraft that derives its lift in flight chieflyfrom reaction to the air through which it passes

§5;rni1= A body shaped to produce an aerodynamic reactionwhen moved through the air

Angle of attack: The angle between the chord line of an airfoiland the direction of the airflow approaching it

Angle of incidence: The angle between the chord line of arotor blade (or an airfoil) and its plane of rotation (or thelongitudinal axis of the aircraft)

Articulated rotor: A rotor whose blades are joined to therotor hub through one or more hinges (pivots)

2Aspect ratio: The ratio spanz : area, éfiggry of an airfoil,

sometimes written as 5§EELchord

Autorotation: The continuous rotation about an axis of a body(usually an airfoil) due to aerodynamic forces on that body

Axes:

l. Lateral: A straight line through the c.g. running parallelto a line from wingtip to wingtip. An aircraft pitchesnose up and nose down about the lateral axis

2. Longitudinal: A straight line through the c.g. runningfore and aft along the centre line of the aircraft. Theaircraft rolls about the longitudinal axis

3. Normal: A straight line passing vertically through thec.g. at right angles to the other two axes. The aircraftyaws about the normal axis

Bank: To cause the lateral axis to assume an angle to theEarth's horizon

Boundary lager: The "sheath" of air directly in contact withthe airfoil and moving with it, out to (at a progressivelyincreasing speed) the layer of air flowing at normal speed.(It is often only a few molecules thick.)

Camber: The curved upper and/or lower surfaces of an airfoil

¢entre_q§Wgravity (c.g.): The point in a body through whichthe total weight can be said to act

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Centre of lift (CL): The resultant of all centres of pressureon a wing or a rotor

Centre of pressure (CP): The point on the chord of an airfoilthrough which the lift and drag appear to act

Chord: The straight line joining the leading and trailing edgesof an airfoil

Collective pitch lever: A control by which all a helicopter'smain rotor blades’ pitch angles are changed together byequal amounts

Cyclic pitch control: A column, similar to an aeroplane controlcolumn, that changes the main rotor blade pitch anglescyclically, that is, in a recurring sequence

Disc area: The area of the circle described by the tips of theblades of a rotor

Dragging: The lagging of a rotor blade behind where it would beif it was fixed, and not hinged, to a hub rotating about an axis

Eeathering: Variation of the pitch angle of an airfoil

Flapping: Movement of a rotor blade (up and down for a main rotorblade) about a horizontal hinge or by bending. The see—sawingof a semi-rigid rotor about its central pivot is also called"flapping"

Frame: A transverse structural member of a fuselage

Ggroplane_(autogyro): A rotorcraft propelled by a horizontalthrust system (propeller) and supported by a rotor free to turnunder action of air flowing upwards through the disc, that is,by autorotating

Helicopter: A rotorcraft deriving lift, thrust, and control frompower-driven rotors causing air to flow downwards through thedisc

Induced drag: Drag caused by an airfoil deriving lift frompassing air by changing the direction of the air

Laminar flow: Flow of air past a surface whose boundary layerremains flowing smoothly without turbulence

Lift: The component of the total aerodynamic force that actsvertically upwards (opposite to weight)

Main rotor: The rotor that provides the major aerodynamic forcesof a rotorcraft

Pitch angle: Angle of incidence

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Rigid rotor: A rotor whose blades cannot pivot with respectto the hub except to change their pitch angle and whose hub isattached rigidly to the drive shaft

Rotorcraft: An aerodyne that derives lift from a rotor orrotors

Rotor head: The entire rotor assembly, except for the rotorblades

Rotor hub: The central rotating member of the rotor head thatcarries the blade arms and hinge assemblies

Rudder ——-tail_rot9r pedals: Pedals that operate the rudder ortail rotor for yaw control

Semi~rigid rotor: A two-bladed rotor system freely pivoted tosee—saw as one unit about a central axis

Separation point: Point of detachment of the airflow from thesolid surface on which it formed a boundary layer

STOL: Short take off and landing

Stability: The quality of resisting disturbance from an existingcondition and a tendency to return to that condition once thedisturbance is removed

Stall: Complete separation of the boundary layer from the uppersurface of the airfoil and with a large reduction in lift

Tail boom: A projection rearwards from the fuselage designed tocarry the tail unit or tail rotor

Tail rotor: An anti—torque and yaw control rotor rotating, atthe tail, in a more or less vertical plane

Teetering rotor: Semi—rigid rotor

Tracking: The procedure of ensuring that each rotor bladefollows in precisely the path of the one ahead of it

VTOL: Vertical take off and landing

Wash—in: Increase in angle of incidence towards the tip of awing or rotor blade

Wash—out: Decrease in angle of incidence towards the tip of awing or rotor blade

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.TEST PAPER l '

State whether each of the following statements is truefalse, and give a correction for each false statement

2. s anAspect ratio = :§;;;y or span X chord.

An articulated rotor has one or more hinges that joineach blade to the rotor hub.

The resultant of all centres of gravity on a wing orrotor is called the centre of lift (CL).

A gyroplane is a rotorcraft that is propelled by ahorizontal thrust system and supported by a rotor freeto turn under action of air flowing downward throughthe disc, that is, by autorotation.

The rudder pedals operate the rudder or tail rotor togive yaw control about the lateral axis-

Induced drag is caused by an airfoil deriving lift fromthe passing air by changing its direction.

The straight line from the leading edge of an airfoilrunning parallel to the relative airflow is called thechord.

A helicopter is defined as a rotorcraft deriving lift,thrust, and control from power—driven rotors causingair to flow upwards through the rotor disc.

The point on the chord of an airfoil through which thetotal lift appears to act is called the centre ofpressure (CP).

The up and down bending movements of a main rotor bladeon a rotor head are called flapping.

Draw a freehand sketch of a helicopter viewed from aboveshowing

a The main rotor turning counter-clockwise,

The direction of the main rotor torque reactionand

c The direction of the_tail rotor force in hoveringflight.

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Explain, with the aid'of a sketch, how a movement of thecyclic control to the left will produce a small coupleto tilt the fuselage to the left.

Draw a helicopter powertrain and identify the componentsshown.

In tabulated form, give a reason for each of theinstructions in Para 5.5 (1) to (8) of AC 93-82A(page 2% of the assignment). would these rules be goodfor people leaving as well as boarding the helicopter?

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