He Wharekura-tini Kaihautu 0 Aotearoa
THE OPE N P0|.YTE(HN|( OF NEW ZEALAND
K
B3810 He//capters 555-3-1_
CONTENTS
“knew - tau
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 be reproduced without the written authority of the Principal, TOPNZ.
55573/1
AIRCRAFT ENGINEERING" AIRFRAMES 111
ASSIGNMENT 1 BASIC HELICOPTERS
This assignment is intended to serve as an introduction to the rest of the assignments in the 5S5~3 series. The complete series consists of Assignment
1
Basic Helicopters
Assignment
2
Basic Flying Controls
Assignment
3
Basic Rotors
Assignment Assignment
Q S
Piston Engine Installations Rotating Flying Controls
Assignment
6
Main and Tail Rotor Heads and Blades
Assignment Assignment Assignment
7 8 9
Transmission Systems Helicopter Vibrations Turbine Engine Installations
Assignment 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 when people of many nationalities began making models of helicopters of all shapes and sizes, powered in a variety of ways, such as gunpowder, steam, and electricity. However, vertical flight was known much earlier.
It was first described by the Chinese
alchemist Ko—Hung, who wrote in 320 AD about a toy now known as the "Chinese flying top". In 1907, Paul Carnu, a Frenchman, made the world's first free helicopter flight. His machine reached a height of about 1.7 metres
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.w
_ 2 _ and was airborne for but a'few seconds. In the years that followe d many helicopters were made and flown. In 1936, the successful Focke-Wulf Fw 61 flew for the first time. In 1939, Igor Sikorsky flew his VS 300, which became the RH production model and is the forerunner of the present—day Sikorsky helicopter models. Many of the advances made in the design of the helicopter rotor are due to the work of Juan de La Cierva who, during the development of his "autogyro" re~invented the flapping hinge, invented the drag hinge and its damper, and developed cyclic pitch control of the rotor. So far, several terms associated with helicopters have been used. Before going any further, and to avoid confusion, a list of words and terms as they are used on helicopters and on fixed-wing aircraft is given in the Appendix at the end of this assignment. As part of your work on this assignment you should now read the Appendix and than dg Practice Exercise A that follows here. PRACTICE EXERCISE A
State whether each of the following statements is True or False. 1.
Disc area is the sum of the area of all the blades of a rotor.
2.
The angle between the chord line of a rotor blade and its plane of rotation is called the angle of incidence.
3.
The control that changes the main rotor blade pitch angles 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 or less 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 pitch angles differently to each other is the collective pitch lever.
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_ 3 _ 9.
10.
The angle between the chord line of an airfoil and the direction of the airflow (relative airflow) is called the angle of attack. An aircraft rolls about its
lateral axis-
(Answers on page
27)
BASIC OPERATING PRINCIPLES
If two or more airfoils (see Fig. 1) are fioined together, pivoted at the centre, held
horizontal, and then spun around quickly, they will rise straight upwards because of the lift developed by the airfoils as they move through the air. This device FIG. l
is the Chinese flying top mentioned earlier. Should a gust
of wind tilt it to one side while it is flying, then it will move in the direction of the tilt. All the time that the lift generated exceeds its weight, the top climbs, and when the lift is
equal to the weight the top hovers, and when it becomes less, the top descends. The helicopter main rotor operates in a similar way to the flying top, except that it is power driven and its tilt is controlled by the pilot.
Because the main rotor is power driven, a torque reaction equal and opposite to the torque turning the rotor is developed. (Newton's third law of motion.) If this torque reaction were allowed to act unhindered, then the fuselage of the helicopter would turn in the opposite direction to the main rotor. The c component that controls the effect of the torque reaction is usually 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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_ u _ to a negative pitch to vary the side thrust produced.
/'
Besides
controlling the effect of the torque reaction, the tail rotor is also used to control the helicopter
I \°’ I
about its vertical (yaw) axis when
Dimzciion of rototbn
it is hovering.
The pilot
controls the pitch angle of the tail rotor blades through the tail rotor pedals.
The lift developed by the “h-III T‘o*'cLuQ.'-
Hmochorz
FIG. 2
1
main rotor is altered not by
'Tbfl
_ ‘ - flfotor
pbvoz
Main rotor torque and tail rotor force
speeding up or slowing down the rotor but by increasing/decreasing the pitch angle of all the blades together by the same amount, in
the same direction, and at the same time. This is known as collective pitch. Lifting up the collective pitch lever increases the pitch angles and causes the helicopter to climb. down causes the helicopter to descend.
Pushing it
The reason for changing the pitch angles and not the rev/min is that the inertia of the main rotor would cause a time delay between the opening or closing of the engine throttle and the rev/min of the main rotor increasing or decreasing. By, say, increasing the pitch of the main rotor blades and increasing the engine power output at the same time, the main rotor rev/min stays constant and the power delivered to the main rotor is increased without the time delay due to inertia. The main rotor is tilted through the cyclic pitch control column by progressively increasing and then decreasing the angles of the blades in their orbit. Thus, to move into forward flight, the pitch angle of a rearwardgmoving blade is increased, which causes the blade to develop more lift while a forward—moving blade has its pitch angle decreased to develop less lift. The result is to tilt the total reaction into a forward—leaning position ~— see Fig. H. The main rotor can be tilted in any direction by moving
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_ 5 _ the cyclic pitch control column in the direction desired for the tilt, the helicopter then flies in the direction of the tilt. The actual tilting may be done by 1.
Using a gimbal-mounted main rotor. is called a semi—rigid rotor.
This assembly
See Fig.
3(a).
2.
Aerodynamic forces moving the blades, each pivoted on a horizontal hinge pin, up and down in relation to the centre of the fixed main rotor hub. This assembly is called an articulated rotor. See Pig. 3(b).
3.
Using aerodynamic forces to bend relatively flexible blades and their mount elements up and down in relation 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 FIG. 3
(c)
Rigid rotor
Types of main rotor
The main rotor gives energy to a large mass airflow, and because the airflow is accelerated to a low speed only, this offers a most efficient method of hovering.
As a theoretical example, a
helicopter that hovers by passing 500 kg of air each second at a velocity 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 .;“\
k
= -2-gin-(N) In both equations the answer is in newtons (N). 555/3/i
it
- 5 _ ;.
F
=
500 (kg) X 20 (m)
1 (s)
=
1 (S)
10 000 (kg m) l (s7) 8
= 10 000 kg m/52 0
= 10 000 N The energy needed to generate this force of 10 000 N is found from Ke
=
i mV
2
=
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 needed is 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. r-
Momentum
=
mass X velocity
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- 7 _ _
10 O00 (momentum)
=
40 m/s
New “e1°°i’°Y " “E§6
The energy needed has become
K8
=
5 X 250 X 402
=
200 O00 J
Because this amount of energy is used each second Power needed
=
200 O00
(J)
1
(s)
= 200 000 w = £92=§E This is a twofold increase in power just to do the same job as before.
The comparison becomes even more marked if we take a theoretical VTOL jet aircraft of the same weight but with a jet velocity of Q00 m/s. As the momentum of the air lS the same, its mass is now as follows: Mass
=
momentum velocity 10 O00 400
New mass
=
2.§1.=1<.e
The energy needed is now K
e
= § X 25 X 4002
= 2 000 000 J
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_ 3 _ Power'needed
=
2 000 O00 W
=
2000 kW
You can thus see that the helicopter is quite efficient compared with the VTOL jet aircraft when both are hovering.
High-
speed flight is another story, and here the helicopter becomes severely handicapped partly because of its large-diameter main
rotor.
This is discussed in a later assignment.
The force generated by the turning main rotor acts at right
angles to the plane of rotation of the rotor blades.
Figure H shows
a helicopter in steady level forward flight with the total reaction acting in a forward direction. _Té+ca| reacifion
so’
Forwarcl
Total reaction
The name total reaction is used because this force is resolved into
1.
A horizontal force (thrust) to propel the helicopter, and
2.
A vertical force (lift) to sustain the weight of the helicopter.
As with a fixed-wing aircraft in steady level flight Thrust
=
drag, and
Lift
=
weight.
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_ 9 i' *
@ .
reaction resolved into thrust and lift, together with the opposing forces of drag and weight for steady, level forward flight. In this respect, the helicopter is
‘ 1 ?L§%
| 75*? rzochon I I
E‘..-’*“
no different from a fixed~wing aircraft where forces act through
‘
' cg?‘ Di. Q-I Fwd‘
FIG. 5
Figure 5 shows the total
moment arms about the centre of gravity (c.g.) and the centre of
1I
‘ llft
1“@Bb+
In practice, the c.g. position in a helicopter lies on
Total reaction resolved
(CL).
or very close to the centre of lift (CL) so that the lift and
weight forces will give an effect ranging from slight nose down to slight nose up. But, unlike the usual fixed-wing aircraft, the thrust and drag forces act to give a nose—down attitude. To correct this nose~down tendency, many helicopters have a horizontal stabiliser similar to that on a fixed-wing aircraft. controllable.
This stabiliser may be either fixed or
To gain altitude, the total reaction is increased, which, if nothing else is changed, also results in an increase in forward speed.
This acceleration up and forward will continue until the
total reaction is again equalled by the new, greater weight—drag resultant. To provide greater forward speed while flying straight and level, a forward movement of the cyclic control is made.
This
gives an increase in the pitch angle of the rear—going blades to cause them to develop more lift and a decrease in pitch angle of the forward—going blades to cause them to develop less lift.
The
difference in lift between the rear—going and forward—going blades tilts the rotor disc forward, perhaps causing a slight loss of altitude, but giving the desired acceleration. At the same time, the line of total reaction moves slightly to the rear of the rotor
555/3/1
_ 19 _ disc.
See Fig. 6.
The small couple that this produces is enough
to tilt the helicopter in the direction that the cyclic stick was moved. 'TE>+oJ r':za<;-1-ic;r~, -H-1 +
Téioi reaction of’ o‘F r +01»-I
hM'§°§§\Q+;§-fiige
-,,,--if
I
I
_
hub ==~=-c-3'1-1~Y\<= '
Reta" ‘file pa+H hfih
V
_.-=-"
‘ lZc+c-P -Hp Pa‘H"1 low
(ca)
T12LJ+YQl
5'h'¢\<
FIG. 6
‘Pqrwqrd a
Result of cyclic movement
Figure 7 shows the action of the forces in a vertical climb and in level, accelerating flight.
upe Z'_\\_
ct
,Q§§h
-'
7
\
;:-
\
I
1
X \
f"' IF!‘
K
, 51>
Lift exceeds weight for vertical climb. Thrust === Qgg =-= Zero
Weight (a)
Vertical climb flight
555/3/1
——/
l
_
————
‘======—a
_ 11 _ R,
'
R:
Lm~
///’ ,.
'
§\\\\s,\\\
CL
-4?
F,;@s; ’ H
,
‘wt
\
I
91
\
fil
”,//’ ;?5l5“q_“\’////,»///
/
Z
,»-/'
‘ A\ I
R1, T1, D; show slraigl-nt and level flight ai‘ conslanl Spfled
I I
Moving R1 Forward to R1 will Increase
T; to T; , causing nose—down athtude
l;%%¢¢ (b)
we cadences-
Level and accelerating flight
FIG. 7
Forces on a helicopter
SUMMARY All aircraft, including helicopters, are subject to the same 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 and vertical components. Provided rotor rev/min are maintained, an increase in pitch of a rotating airfoil will increase its lifting force. A tail rotor may be used to provide a force to balance the main rotor torque reaction and to give directional control when the helicopter is hovering. A difference in lift between one part of the rotor disc and another will cause it to tilt.
555/3/1
....j_2_
PRACTICE EXERCISE B
'
State whether each of the following statements is True or False. l.
Due to torque reaction, the fuselage of a powerdriven single—main helicopter will try to turn in the same direction as the main rotor.
2.
The lift of a main rotor is varied by altering the pitch angles of its blades while keeping its rev/min constant.
3.
The total reaction from a main rotor is resolved into lift and drag forces.
4.
When a helicopter is hovering in still air, it has no thrust and drag, and its lift just exceeds its weight.
5.
When the cyclic control is moved forward, the line of total reaction moves to a position slightly aft of the rotor hub centre line.
(Answers on page 27)
CONTROLS
From the Table of Definition in the Appendix and the Basic Operating Principles on page 29, you will know that 1.
Yaw and main rotor torque reaction is controlled by the tail rotor through the movement of the tail rotor (rudder) pedals.
2.
The in-flight directions of forwards, sideways, and backwards are controlled through the cyclic pitch control column, sometimes called the Azimuth control or cyclic stick.
3.
Climb and descent are controlled by the collective pitch control lever, or collective.
By co-ordinating the use of these three controls, the pilot can make the helicopter bank, dive, and climb like a fixed-wing aircraft, as well as fly it sideways and backwards and make it climb and descend vertically.
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_ 13 _ Earlier in this assignment, we said that the power deiivered to the main rotor was increased by increasing its blade angles collectively and by increasing the engine power at the same time. To achieve this, a throttle twist grip is mounted on the end of the collective pitch lever. This twist grip, very much like a motorcycle throttle grip, is mechanically connected to the engine carburettor or fuel control unit, and interconnected with the collective pitch control. The engine power will be automatically increased when the collective is raised, and if too little or too much power is then delivered, delivery can be corrected by use of the throttle grip. Thus raising/lowering the collective will increase/decrease the 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 its operational rev/min without raising the collective. In gas turbine-powered helicopters, fine adjustments to the throttle setting can be made using a "beep" switch on the collective control hand grip. Figure 8 shows the flying controls and the throttle twist grip in an S55 helicopter. All modern helicopters have a similar layout.
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‘_
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. . . . .
RUDDER PEDAL LEG REACH CONTROL RUDDER PEDALS CYCLIC-PITCH CONTROL COLUMN FORE-AND-AFT FRICTION CONTROL LATERAL FRICTION CONTROL
. ~IOU\-Lil )!-I .
\\\\|—
O<>§> Q
THROTTLE TWIST GRIP FRICTION CONTROL RING,
@.
'r1-mo'r'ru=: -rwxsr am? FRICTION CONTROL, COLLECTIVE-PITCH usvsn conuzcnvs-vrrcn uzvxa
8. 9.
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y 3
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8 FIG. 8
7
6
4
Flying controls in the cockpit
STRUCTURES
The two most common construction methods used at present for helicopters are 1.
Semi-monocoque, and
2.
Girder.
Each method has its advantages, the former leaving a large open box for crew, baggage and payload, but requiring a complex structure and reinforcing for strength.
555/3/1
The materials used in this
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QW,\ # L \ _ ’
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Ip ih£3 .5
4g ‘L
M, _;‘/ ‘X ’/I1i
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\
J/
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.0-
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Fuselage structure assembly
A third form of construction now coming into use is the composite structure, which uses carbon fibre reinforced stiffeners, frames, and bulkheads, plus impact»resistant fibre reinforced skinning (Kevlar) in the primary structure and high—quality glass fibre in the secondary structure. The use of these materials gives a great saving of weight.
THE POWERTRAIN
The components that transmit the engine power to the main and tail rotors are collectively called the powertrain or the transmission.
The essential components of a powertrain are 1.
An engine-driven clutch (on piston-engined helicopters);
2.
A freewheel unit, which may be called a sprag clutch OP a one—way clutch;
555/3/1
_ 17 _
3.
A main—rotor gearbox;
M
H.
A tail-rotor gearbox;
5.
Driveshafts from the engine to the main-
and
rotor gearbox and from the main—rotor
gearbox 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 than the engine. This could occur when the engine is throttled back to idle rev/min. The mainmrotorggearbgi changes the direction of the engine drive and reduces the engine rev/min to the much lower rev/min needed by the main rotor. ancillary equipment.
It also provides drive pads for
rhe tail~rotq;mgea;box changes the direction of the drive to suit the need of the tail rotor. Depending on the helicopter type, this gearbox may increase, decrease, or make no change in the rev/min of the output shaft relative to the input shaft. This gearbox may house the blade pitch—changing mechanism of the tail rotor.
The driveshafts transmit the power from the engine to the gearboxes. These shafts may also drive ancillary components, such as cooler fan units. In all powertrains, the main rotor is always mechanically connected to the tail rotor so that at no time can one rotor turn without the other. This fact, coupled with the function of the freewheel unit means that, should the engine fail, both rotors will keep turning and the pilot can make a safe and controlled landing. This flying condition, known as autorotation, is the equivalent of a fixed-wing aircraft gliding.
Figure 11 shows three different
powertrains in schematic form.
555/3/i
-13-
Rofor brake
Main-roinr gur-bur-|"','
F
. .. .
Q
I
___
I ‘Y -' '" - "i1 “,,‘f§,’ -=II C‘
Engine -cnolfng fa H
,
”\ Drive-shzfi
——
, u..a.....1¢~»-V.
Tail rotor gearbox
R
(a)
Vertical piston engine
,.'.......
Min rotor
__ ,
_
Fru--whul unit ' — .
/—
Drive.-Sheff
.___W _ 0
"'
Tail-shaft 5881‘-ha:
Clunch
“ii Engin:-cooling Flfl
(b)
Horizontal piston engine
‘
Free-wi\c¢|uni1'
Milin nior
gearbox
(c)
'
Um‘ shin I _ OH coohng uni?
\__ _
’'
Gas turbine engine
FIG. ll
Powertrains
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 throttle control are interconnected.
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\
Tail 1-afar gar-ma
_ 19 _
l
The movements of the-flying controls are natural ones for the response desired. That is Cyclic forward
+
fly forward
Collective down
+
descent
Right tail rotor pedal forward
+
yaw right
All helicopters have a freewheel unit between the engine and the rest of the powertrain. The main and tail rotors are mechanically connected so that one cannot turn without the other.
.
y T I
PRACTICE EXERCISE C Match each of the items in the left—hand column with its correct item in the rightwhand column and write the numbers of the items in the box below. Each item is to be used only once. A.
Tail rotor
1.
Azimuth control
B.
Cyclic pitch
2.
Interconnected with the collective
C.
Collective pitch
3.
Lateral control
D.
Engine throttle
4.
Directional control
5.
Control of climb—descent
6.
Yaw and torque control
IA I
B
I
C
I
D
(Answers on page 33)
I
.
SAFETY IN AND AROUND HELICOPTERS Because of the ability of a helicopter to hover, the loading crew may come into its close proximity while it is flying. They could thus also find themselves in positions where they cannot be seen by the pilot. For this and other situations, a series of 555/3/1
_ 23 _ hand signals has been devised which, if used sensibly, can make a useful contribution to both the safety and the economics of helicopter operation. For the signalS to be of real use, both the helicopter marshaller 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 helicopter using a lot of effort amidst the confusion of noise and a buffeting ground cushion of air. The hand signals are shown in Fig. 12.
STAHT ENGINE
ENGAGE ROTOR
O‘?<9
STOP ROTOR
1% F‘ fiog
nova BACK
O "mm: OFF
O
5
O
movs FORWARD
MOVE mo:-n~
O
11°11
non
co UP
co DOWN
2‘
LANDING nzazonon O<)==:|
MOVE LEFT
c==(>Q
SWING TAIL TD RIGHT
FIG. 12
STOP
SWING TAIL TO LEFT
Helicopter hand signals
For safety in and around helicopters the FAA Advisory Circular 91-32A of that name is important reading. We reproduce it here in full. 555/3/1
_ 21 _
AC 91-32A DATE 6/21/79
ADVISORY CIRCULAR a
ex-‘O FT I4“-no
'4
DEPARTMENT OF TRANSPORTATION Federal Aviation Administration
Diguqr n
en“ 6,)-
.'¢44-MO“ ‘*5
Washington, D.C.
"4715 04 '
Subject:
SAFETY IN AND AROUND HELICOPTERS
1} PURPOSE. This advisory circular provides suggestions to improve helicopter safety by means of acquainting flight and non~flight crew personnel and passengers with the precautions and procedures necessary to avoid undue hazards. 2. CANCELLATION. is canceled.
AC 91-32, Safety In and Around Helicopters, dated 5/7/71
3. GENERAL. People have been injured, some fatally, in helicopter acci— dents which would not have occurred had they been informed of the proper method of boarding or deplaning. A properly briefed passenger should never be endangered by a spinning tail rotor. The simplest method of avoiding accidents of this sort is to have the rotors stopped before passengers are boarded or allowed to depart. Because this action is not always practicable, and to realize the vast and unique capabilities of the helicopter, it is often necessary to take on passengers or to deplane them while the engine and rotors are turning. Therefore, if accidents are to be avoided, it is essential that all persons associated with helicopter operations, including passengers, be made aware of all possible hazards, and instructed as to how they can be avoided. 4. FLIGHI AND NON—FLIQHT CREW PERSQEQEL. Persons directly involved with boarding or deplaning passengers, aircraft servicing, rigging or hooking up of external loads, etc., should be instructed as to their duties. It would be difficult, if not impossible, to cover each and every type of operation or non~flight crew training matter related to helicopters. A few of the more obvious and common ones are covered below: a. Ramp attendants and aircraft servicing personnel. These personnel should be instructed as to their specific duties, and the proper method of fulfilling them. In addition, the ramp attendant should be taught to:
Iniuated by: 555/8/1
AF5-gg0
_ 22 _ AC 91-31A
5/21/79
(1) Keep passengers and unauthorized persons out of the helicopter landing and takeoff area. (2) Brief passengers on the best way to approach and board a helicopter with its rotors turning (see paragraph 4a). b.
Aircraft servicing.
(1) The helicopter rotor blades aircraft and the refueling unit properly operation. The pilot should ensure that required, the proper additives are being
should be stopped and both the grounded prior to any refueling the proper grade of fuel and, when dispensed.
(2) Refueling the aircraft, while the blades are turning ("hot refueling"), may be practical for certain types of operation. However, this can be hazardous if not properly conducted. Pilots should remain at the flight controls and refueling personnel should be knowledgeable with respect to proper refueling procedures and properly briefed for specific makes and models. ‘ (3) Refueling units should be positioned to ensure adequate rotor blade clearance and persons not involved with the refueling operation should be kept clear of the area. (4) Smoking must be prohibited in and around the aircraft during all refueling operations. c. External~load”riggers. Rigger training is possibly one of the most difficult and continually changing problems of the helicopter external—load operator. A poorly rigged cargo net, light standard, or load pallet could result in a serious and costly accident. It is imperative that all riggers be thoroughly trained to meet the needs of each individual external—load operation. Since rigging requirements may vary several times in a single day, 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 "quick turnaround" ground operation to avoid delays at airport terminals and to minimize stop/start cycles of the engine. As part of this quick turnaround, the pilot will leave the cockpit with the engine and rotors turning. Such an operation can be extremely hazardous if a gust of wind disturbs the rotor disc or the collective flight control moves causing lift to be generated by the rotor system. Either occurrence may cause the helicopter to roll or pitch resulting in a rotor blade striking the tailboom or the ground. (2) Good operating procedures dictate that pilots remain at the flight controls whenever the engine is running and rotors are turning. On occasion, however, the pilot may find it necessary to leave the controls of a "running machine." On these occasions the pilot should:
2
Par 4
555/3/1
-28..
6/21/79
"
AC 91-32A
(i) Ensure that all controls are secured in accordance with the aircraft flight manual. (ii) Reduce rotor and/or engine RPM to ground idle or minimum recommended settings. (iii)
e.
Turn off hydraulic boost when appropriate.
External"load hookup personnel.
(1) Know the lifting capability of the helicopters inyolved. Since some operators have models of helicopters that have almost identical physical characteristics but with different lifting capabilities, this knowledge is essential.
For example, a hookup person may be working with a
supercharged helicopter on a high altitude project and without any warning a non—supercharged helicopter, which looks exactly the same to the ground crew, 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 too heavy for the non~supercharged helicopter to lift. (2) Know the pilots. The safest plan would be to standardize all pilots insofar as the manner in which sling loads are picked up and released. Without pilot standardization, the hookup person should learn the technique used by each pilot. Does the pilot come in fast or slow, high or low? Does the pilot try to lift the load off with a combination of collective and cyclic? The hookup person should specifically demand standardization on the pilot technique for any sort of emergency occurring while 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 hazardous article is involved, and the nature of the hazard; such as explosives, radioactive materials, and toxic chemicals. In addition to knowing this, they should be familiar with the types of protective gear or clothing or 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 meaning of hand signals should be coordinated prior to operations. ' (5) Know emergency procedures. Ground and flight personnel should fully agree to and understand actions to be taken by all participants in the event of emergencies. This prior planning is essential to avoid injuries to all concerned. .
Par 4
3
555/3/1
_ gu _ AC 91-32A
6/21/79
5. PASSENGERS. The term "passenger" used throughout this advisory circular refers to all non-flight crew personnel that ride in helicopters, and is not limited to the fare-paying customer. All persons that board a helicopter while its rotors are turning should be instructed as to the safest means of doing so. Naturally, if the pilot is at the controls, he/she may not be able to conduct a boarding briefing. Therefore, the individual who arranged for the passenger flight or assigned as the ramp attendant should accomplish this task. The exact procedures may vary slightly from one helicopter model to another, but in general the following should 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's line of vision. (4)
Hold firmly to hats and loose articles.
(5) Never reach up or dart after a hat or other object that might be 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 — crouch lower — or better yet — sit down — and await help. (8) helicopter.
Never grope or feel your way toward or away from the
b. Pre—takeoff briefing. Since few helicopters carry cabin attendants, this briefing must be made by the pilot. The type of operation will dictate what sort of briefing is necessary. Passengers should always be briefed on: (1) Seatbelts. en route and landing.
The use and operation of seatbelts for takeoff,
(2) Overwater flights. The location and use of flotation gear and other survival equipment that might be on board. How and when to abandon ship should a ditching be necessary. (3) Flights over rough or isolated terrain. be told where maps and survival gear are located.
All occupants should
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Par 5 555/3/1
_25...
.-
AC 91-32A
(4) Emergency instructions. In the event of an emergency, each passenger should be instructed as to what actions and precautions to take; such as the body position for best spinal protection against a high vertical impact landing (erect with back firmly against the seat back); and when and how to exit after landing. Ensure that passengers are aware of fire extinguisher and survival equipment locations. (5) Smoking. Smoking within 50 feet of an aircraft on the ground should be prohibited. Smoking could be permitted, at the discretion of the pilot, except under the following conditions: (i)
During all ground operations;
(ii)
Immediately before, during, or after takeoff or landing;
(iii)
when carrying flammable or hazardous materials.
or
c. Rreelanding briefing. The nature of the landing will determine what the passengers need to be told. A few items to consider are: (1) If on a hill, depart downhill. If this involves walking around the helicopter to avoid the area of lowest rotor clearance, always go around the front, never the rear. (2)
Repetition of the basic instructions shown in paragraph 4a.
6. SAFETX AROUND HELICOPTERS. The material appearing in Appendix 1 was taken from the June 1970 issue of ROTORNEWS, a publication of the Helicopter Association of America.
[Z4 L§~’l~-E '
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AMES M. VINES
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Acting Director Flight Standards Service
Par 5
5
555/3/1
-25..
6/21/79
AC 91- 32A
Appendix 1 SAFETY AROUND HELICOPTERS $ hi
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min.
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1. Approach or leeve machine ln e crouchlng manner
(for extra clururwo twm main wlorl _ '___ .1 * ""'""' "
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9. Keep hellspot cleer cl loose erllcles - ureter begs. groundaheets. empty cane. etc.
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2. Approach or leeve on the down slope slde (to avoid
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10. Keep cooking lites well clear of hellspol.
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3. Approach or leeve In pilot’: tleld ol vision (to avoid tell rotor).
11. Loading assistants should always be supplied with plastic eye shields. —
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12. Alter hooking up cargo sling, move lorwerd and to
4. Carry tools horizontally, below weiet level (MW!
aide to signal pilot (lo avoid entanglement and
upright or over shoulder). f
nevi. '*
getting struck, with loaded sling). ""1le| '*
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when directing machine tor Iendlng. stand with beck l 3. to vvlnd wllh errna outstretched toward lending ped.
5. Hm‘:cm:':'°um:;‘ In t h d net cm“ when ‘mmapproaching m um, or leevlng
t4. when dlrectlng pilot by mole. give no lending In6. 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. '
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('1 5"‘! 3'1"“ °“ “my ” “°"'°(bl Keep them together end well beck It side cl
lendrng zone_(lhis gives the pilot e chance In the
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event he hes to land suddenly either during
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lending or take-otl).
(cl Have them face away from machine during lend-
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lng and lake-ell.
(cl) Have each men look elter hie own personal geer. (Q
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GOVERNMENT
l Hive mlnpaired off and reudyto get aboard. es tl
8. Do not touch bubble or eny.ol the moving pens (tell rotor linkage. etc.).
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15. when moving terger crews:
7 ll leaving machine at the hover. get out and oil in ' i _ am Smooth‘ unhurmd mm on
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1979-28l“S6B/159
— 27 PRACTICE EXERCISE D
"
Which suggestion in AC 91-32A, if followed, will make it impossible for a passenger to be struck by the rotating tail 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
3.
False:
See page 30
4.
False: axis.
5.
False:
30
An aircraft pitches about its lateral See page 29
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 longitudinal axis. See page 29
EXERCISE B Items 2 and 5 are True. 1.
False: Due to torque reaction, the fuselage will try to turn in the opposite direction to the main rotor. See Fig. 2.
3.
False: The total reaction from a main rotor is resolved 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 its weight. If the lift just exceeds the weight, there would be a nett upward force and so the helicopter would climb.
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_ 23 _ EXERCISE C
A
B
C
D
6
l
5
2
EXERCISE D
The suggestion in paragraph 5.a.(3) that says "Approach from the side or front, but never out of the pilot's line of vision" will, if followed, ensure that a passenger will not be struck by the tail
I‘O'tOI"
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_ 29 _
..
APPENDIX
Table 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 chiefly from reaction to the air through which it passes §5;rni1= A body shaped to produce an aerodynamic reaction when moved through the air Angle of attack: The angle between the chord line of an airfoil and the direction of the airflow approaching it Angle of incidence: The angle between the chord line of a rotor blade (or an airfoil) and its plane of rotation (or the longitudinal axis of the aircraft) Articulated rotor: A rotor whose blades are joined to the rotor hub through one or more hinges (pivots) 2 Aspect ratio: The ratio spanz : area, éfiggry of an airfoil,
sometimes written as 5§EEL chord 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 parallel to a line from wingtip to wingtip. An aircraft pitches nose up and nose down about the lateral axis
2.
Longitudinal: A straight line through the c.g. running fore and aft along the centre line of the aircraft. The aircraft rolls about the longitudinal axis
3.
Normal: A straight line passing vertically through the c.g. at right angles to the other two axes. The aircraft yaws about the normal axis
Bank: To cause the lateral axis to assume an angle to the Earth's horizon Boundary lager: The "sheath" of air directly in contact with the airfoil and moving with it, out to (at a progressively increasing 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 which the total weight can be said to act
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-39.. Centre of lift (CL): on a wing or a rotor
The resultant of all centres of pressure
Centre of pressure (CP): The point on the chord of an airfoil through which the lift and drag appear to act Chord: The straight line joining the leading and trailing edges of an airfoil Collective pitch lever: A control by which all a helicopter's main rotor blades’ pitch angles are changed together by equal amounts Cyclic pitch control: A column, similar to an aeroplane control column, that changes the main rotor blade pitch angles cyclically, that is, in a recurring sequence Disc area: The area of the circle described by the tips of the blades of a rotor Dragging: The lagging of a rotor blade behind where it would be if 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 rotor blade) about a horizontal hinge or by bending. The see—sawing of 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 horizontal thrust system (propeller) and supported by a rotor free to turn under action of air flowing upwards through the disc, that is, by autorotating Helicopter: A rotorcraft deriving lift, thrust, and control from power-driven rotors causing air to flow downwards through the disc Induced drag: Drag caused by an airfoil deriving lift from passing air by changing the direction of the air Laminar flow: Flow of air past a surface whose boundary layer remains flowing smoothly without turbulence Lift: The component of the total aerodynamic force that acts vertically upwards (opposite to weight) Main rotor: The rotor that provides the major aerodynamic forces of a rotorcraft Pitch angle:
Angle of incidence
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_ 31 _
Rigid rotor: A rotor whose blades cannot pivot with respect to the hub except to change their pitch angle and whose hub is attached rigidly to the drive shaft Rotorcraft: rotors
An aerodyne that derives lift from a rotor or
Rotor head: blades
The entire rotor assembly, except for the rotor
Rotor hub: The central rotating member of the rotor head that carries the blade arms and hinge assemblies Rudder ——-tail_rot9r pedals: tail rotor for yaw control
Pedals that operate the rudder or
Semi~rigid rotor: A two-bladed rotor system freely pivoted to see—saw as one unit about a central axis
Separation point:
Point of detachment of the airflow from the
solid surface on which it formed a boundary layer STOL:
Short take off and landing
Stability:
The quality of resisting disturbance from an existing
condition and a tendency to return to that condition once the disturbance is removed Stall: Complete separation of the boundary layer from the upper surface of the airfoil and with a large reduction in lift Tail boom: A projection rearwards from the fuselage designed to carry the tail unit or tail rotor Tail rotor: An anti—torque and yaw control rotor rotating, at the tail, in a more or less vertical plane Teetering rotor:
Semi—rigid rotor
Tracking: The procedure of ensuring that each rotor blade follows 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 a wing or rotor blade Wash—out: Decrease in angle of incidence towards the tip of a wing or rotor blade
555/3/1
_ 32 i
.TEST PAPER l
'
State whether each of the following statements is true false, and give a correction for each false statement 2 . s an Aspect ratio = :§;;;y or span X chord. An articulated rotor has one or more hinges that join each blade to the rotor hub. The resultant of all centres of gravity on a wing or rotor is called the centre of lift (CL). A gyroplane is a rotorcraft that is propelled by a horizontal thrust system and supported by a rotor free to turn under action of air flowing downward through the disc, that is, by autorotation. The rudder pedals operate the rudder or tail rotor to give yaw control about the lateral axisInduced drag is caused by an airfoil deriving lift from the passing air by changing its direction.
The straight line from the leading edge of an airfoil running parallel to the relative airflow is called the
chord. A helicopter is defined as a rotorcraft deriving lift,
thrust, and control from power—driven rotors causing air to flow upwards through the rotor disc. The point on the chord of an airfoil through which the total lift appears to act is called the centre of pressure (CP). The up and down bending movements of a main rotor blade on a rotor head are called flapping.
Draw a freehand sketch of a helicopter viewed from above showing a
The main rotor turning counter-clockwise, The direction of the main rotor torque reaction and
c
The direction of the_tail rotor force in hovering flight.
555/3/1
_33._.
Explain, with the aid'of a sketch, how a movement of the cyclic control to the left will produce a small couple to tilt the fuselage to the left. Draw a helicopter powertrain and identify the components shown. In tabulated form, give a reason for each of the instructions in Para 5.5 (1) to (8) of AC 93-82A (page 2% of the assignment). would these rules be good for people leaving as well as boarding the helicopter?
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