Chapter 22 — Aeronautical Decision Making — Gyroplane — Part 1

As with any aircraft, the ability to pilot a gyroplane

safely is largely dependent on the capacity of the pilot

to make sound and informed decisions. To this end,

techniques have been developed to ensure that a pilot

uses a systematic approach to making decisions, and

that the course of action selected is the most appropri-

ate for the situation. In addition, it is essential that you

learn to evaluate your own fitness, just as you evaluate

the airworthiness of your aircraft, to ensure that your

physical and mental condition is compatible with a safe

flight. The techniques for acquiring these essential

skills are explained in depth in Chapter 14—

Aeronautical Decision Making (Helicopter).

As explained in Chapter 14, one of the best methods to

develop your aeronautical decision making is learning

to recognize the five hazardous attitudes, and how to

counteract these attitudes. [Figure 22-1] This chapter

focuses on some examples of how these hazardous atti-

tudes can apply to gyroplane operations.

IMPULSIVITY

Gyroplanes are a class of aircraft which can be acquired,

constructed, and operated in ways unlike most other air-

craft. This inspires some of the most exciting and

rewarding aspects of flying, but it also creates a unique

set of dangers to which a gyroplane pilot must be alert.

For example, a wide variety of amateur-built gyroplanes

are available, which can be purchased in kit form and

assembled at home. This makes the airworthiness of

these gyroplanes ultimately dependent on the vigilance

of the one assembling and maintaining the aircraft.

Consider the following scenario.

Jerry recently attended an airshow that had a gyro-

plane flight demonstration and a number of gyroplanes

on display. Being somewhat mechanically inclined and

retired with available spare time, Jerry decided that

building a gyroplane would be an excellent project for

him and ordered a kit that day. When the kit arrived,

Jerry unpacked it in his garage and immediately began

the assembly. As the gyroplane neared completion,

Jerry grew more excited at the prospect of flying an air-

craft that he had built with his own hands. When the

gyroplane was nearly complete, Jerry noticed that a

rudder cable was missing from the kit, or perhaps lost

during the assembly. Rather than contacting the manu-

facturer and ordering a replacement, which Jerry

thought would be a hassle and too time consuming, he

went to his local hardware store and purchased some

cable he thought would work. Upon returning home, he

was able to fashion a rudder cable that seemed func-

tional and continued with the assembly.

Jerry is exhibiting “impulsivity.” Rather than taking the

time to properly build his gyroplane to the specifica-

tions set forth by the manufacturer, Jerry let his

excitement allow him to cut corners by acting on

impulse, rather than taking the time to think the matter

through. Although some enthusiasm is normal during

assembly, it should not be permitted to compromise the

airworthiness of the aircraft. Manufacturers often use

high quality components, which are constructed and

tested to standards much higher than those found in

hardware stores. This is particularly true in the area of

cables, bolts, nuts, and other types of fasteners where

strength is essential. The proper course of action Jerry

should have taken would be to stop, think, and consider

the possible consequences of making an impulsive

decision. Had he realized that a broken

rudder cable in flight could cause a loss of control of

the gyroplane, he likely would have taken the time to

contact the manufacturer and order a cable that met the

design specifications.

INVULNERABILITY

Another area that can often lead to trouble for a gyro-

plane pilots is the failure to obtain adequate flight

HAZARDOUS ATTITUDE ANTIDOTE

Anti-authority:□

"Don't tell me!"

"Follow the rules. They are□

usually right."

Impulsivity:□

"Do something—quickly!" "Not so fast. Think first."

Invulnerability:□

"It won't happen to me!" "It could happen to me."

Macho:□

"I can do it." "Taking chances is foolish."

Resignation:□

"What's the use?"

"I'm not helpless. I can make the□

difference."

Figure 22-1. To overcome hazardous attitudes, you must

memorize the antidotes for each of them. You should know

them so well that they will automatically come to mind when

you need them.

instruction to operate their gyroplane safely. This can

be the result of people thinking that because they can

build the machine themselves, it must be simple

enough to learn how to fly by themselves. Other

reasons that can lead to this problem can be simply

monetary, in not wanting to pay the money for adequate

instruction, or feeling that because they are qualified in

another type of aircraft, flight instruction is not neces-

sary. In reality, gyroplane operations are quite unique,

and there is no substitute for adequate training by a

competent and authorized instructor. Consider the

following scenario.

Jim recently met a coworker who is a certified pilot and

owner of a two-seat gyroplane. In discussing the gyro-

plane with his coworker, Jim was fascinated and

reminded of his days in the military as a helicopter

pilot many years earlier. When offered a ride, Jim read-

ily accepted. He met his coworker at the airport the

following weekend for a short flight and was immedi-

ately hooked. After spending several weeks researching

available designs, Jim decided on a particular

gyroplane and purchased a kit. He had it assembled in

a few months, with the help and advice of his new friend

and fellow gyroplane enthusiast. When the gyroplane

was finally finished, Jim asked his friend to take him

for a ride in his two-seater to teach him the basics of

flying. The rest, he said, he would figure out while

flying his own machine from a landing strip that he had

fashioned in a field behind his house.

Jim is unknowingly inviting disaster by allowing him-

self to be influenced by the hazardous attitude of

“invulnerability.” Jim does not feel that it is possible to

have an accident, probably because of his past experi-

ence in helicopters and from witnessing the ease with

which his coworker controlled the gyroplane on their

flight together. What Jim is failing to consider, how-

ever, is the amount of time that has passed since he was

proficient in helicopters, and the significant differences

between helicopter and gyroplane operations. He is

also overlooking the fact that his friend is a certificated

pilot, who has taken a considerable amount of instruc-

tion to reach his level of competence. Without adequate

instruction and experience, Jim could, for example,

find himself in a pilot-induced oscillation without

knowing the proper technique for recovery, which

could ultimately be disastrous. The antidote for an

attitude of invulnerability is to realize that accidents

can happen to anyone.

MACHO

Due to their unique design, gyroplanes are quite

responsive and have distinct capabilities. Although

gyroplanes are capable of incredible maneuvers, they

do have limitations. As gyroplane pilots grow more

comfortable with their machines, they might be

tempted to operate progressively closer to the edge of

the safe operating envelope. Consider the following

scenario.

Pat has been flying gyroplanes for years and has an

excellent reputation as a skilled pilot. He has recently

built a high performance gyroplane with an advanced

rotor system. Pat was excited to move into a more

advanced aircraft because he had seen the same design

performing aerobatics in an airshow earlier that year.

He was amazed by the capability of the machine. He

had always felt that his ability surpassed the capability

of the aircraft he was flying. He had invested a large

amount of time and resources into the construction of

the aircraft, and, as he neared completion of the assem-

bly, he was excited about the opportunity of showing

his friends and family his capabilities.

During the first few flights, Pat was not completely

comfortable in the new aircraft, but he felt that he was

progressing through the transition at a much faster

pace than the average pilot. One morning, when he was

with some of his fellow gyroplane enthusiasts, Pat

began to brag about the superior handling qualities of

the machine he had built. His friends were very excited,

and Pat realized that they would be expecting quite a

show on his next flight. Not wanting to disappoint them,

he decided that although it might be early, he would

give the spectators on the ground a real show. On his

first pass he came down fairly steep and fast and recov-

ered from the dive with ease. Pat then decided to make

another pass only this time he would come in much

steeper. As he began to recover, the aircraft did not

climb as he expected and almost settled to the ground.

Pat narrowly escaped hitting the spectators as he was

trying to recover from the dive.

Pat had let the “macho” hazardous attitude influence

his decision making. He could have avoided the conse-

quences of this attitude if he had stopped to think that

taking chances is foolish.

RESIGNATION

Some of the elements pilots face cannot be controlled.

Although we cannot control the weather, we do have

some very good tools to help predict what it will do,

and how it can affect our ability to fly safely. Good

pilots always make decisions that will keep their

options open if an unexpected event occurs while

flying. One of the greatest resources we have in the

cockpit is the ability to improvise and improve the

overall situation even when a risk element jeopardizes

the probability of a successful flight. Consider the fol-

lowing scenario.

Judi flies her gyroplane out of a small grass strip on

her family’ s ranch. Although the rugged landscape of

the ranch lends itself to the remarkable scenery, it

leaves few places to safely land in the event of an emer-

gency. The only suitable place to land other than the

grass strip is to the west on a smooth section of the road

leading to the house. During Judi’ s training, her traffic

patterns were always made with left turns. Figuring

this was how she was to make all traffic patterns, she

applied this to the grass strip at the ranch. In addition,

she was uncomfortable with making turns to the right.

Since, the wind at the ranch was predominately from

the south, this meant that the traffic pattern was to the

east of the strip.

Judi’s hazardous attitude is “resignation.” She has

accepted the fact that her only course of action is to fly

east of the strip, and if an emergency happens, there is

not much she can do about it. The antidote to this

hazardous attitude is “I’m not helpless, I can make a dif-

ference.” Judi could easily modify her traffic pattern so

that she is always within gliding distance of a

suitable landing area. In addition, if she was uncomfort-

able with a maneuver, she could get additional training.

ANTI-AUTHORITY

Regulations are implemented to protect aviation

personnel as well as the people who are not involved in

aviation. Pilots who choose to operate outside of the

regulations, or on the ragged edge, eventually get

caught, or even worse, they end up having an accident.

Consider the following scenario.

Dick is planning to fly the following morning and real-

izes that his medical certificate has expired. He knows

that he will not have time to take a flight physical

before his morning flight. Dick thinks to himself “The

rules are too restrictive. Why should I spend the time

and money on a physical when I will be the only one at

risk if I fly tomorrow?”

Dick decides to fly the next morning thinking that no

harm will come as long as no one finds out that he is

flying illegally. He pulls his gyroplane out from the

hangar, does the preflight inspection, and is getting

ready to start the engine when an F AA inspector walks

up and greets him. The F AA inspector is conducting a

random inspection and asks to see Dick’ s pilot and

medical certificates.

Dick subjected himself to the hazardous attitude of “anti-

authority.” Now, he will be unable to fly, and has invited

an exhaustive review of his operation by the FAA. Dick

could have prevented this event if had taken the time to

think, “Follow the rules. They are usually right.”

ABSOLUTE ALTITUDE—The act-

ual distance an object is above the

ground.

ADV ANCING BLADE—The blade

moving in the same direction as the

helicopter or gyroplane. In rotorcraft

that have counterclockwise main rotor

blade rotation as viewed from above,

the advancing blade is in the right half

of the rotor disc area during forward

movement.

AIRFOIL—Any surface designed to

obtain a useful reaction of lift, or neg-

ative lift, as it moves through the air.

AGONIC LINE—A line along which

there is no magnetic variation.

AIR DENSITY—The density of the

air in terms of mass per unit volume.

Dense air has more molecules per unit

volume than less dense air. The densi-

ty of air decreases with altitude above

the surface of the earth and with

increasing temperature.

AIRCRAFT PITCH —When refer-

enced to an aircraft, it is the move-

ment about its lateral, or pitch axis.

Movement of the cyclic forward or aft

causes the nose of the helicopter or

gyroplane to pitch up or down.

AIRCRAFT ROLL —Is the move-

ment of the aircraft about its

longitudinal axis. Movement of the

cyclic right or left causes the helicop-

ter or gyroplane to tilt in that direction.

AIRWORTHINESS DIRECTIVE

—When an unsafe condition exists

with an aircraft, the FAA issues an air-

worthiness directive to notify con-

cerned parties of the condition and to

describe the appropriate corrective

action.

ALTIMETER—An instrument that

indicates flight altitude by sensing

pressure changes and displaying alti-

tude in feet or meters.

ANGLE OF ATTACK —The angle

between the airfoil’s chord line and

the relative wind.

ANTITORQUE PEDAL—The pedal

used to control the pitch of the tail

rotor or air diffuser in a NOTAR ®

system.

ANTITORQUE ROTOR —See tail

rotor.

ARTICULATED ROTOR—A rotor

system in which each of the blades is

connected to the rotor hub in such a

way that it is free to change its pitch

angle, and move up and down and

fore and aft in its plane of rotation.

AUTOPILOT —Those units and

components that furnish a means of

automatically controlling the aircraft.

AUTOROTATION—The condition

of flight during which the main rotor

is driven only by aerodynamic forces

with no power from the engine.

AXIS-OF-ROTATION—The imagi-

nary line about which the rotor

rotates. It is represented by a line

drawn through the center of, and per-

pendicular to, the tip-path plane.

BASIC EMPTY WEIGHT —The

weight of the standard rotorcraft,

operational equipment, unusable fuel,

and full operating fluids, including

full engine oil.

BLADE CONING —An upward

sweep of rotor blades as a result of lift

and centrifugal force.

BLADE DAMPER —A device

attached to the drag hinge to restrain

the fore and aft movement of the rotor

blade.

BLADE FEATHER OR FEATH-

ERING—The rotation of the blade

around the spanwise (pitch change)

axis.

BLADE FLAP —The ability of the

rotor blade to move in a vertical direc-

tion. Blades may flap independently

or in unison.

BLADE GRIP—The part of the hub

assembly to which the rotor blades are

attached, sometimes referred to as

blade forks.

BLADE LEAD OR LAG—The fore

and aft movement of the blade in the

plane of rotation. It is sometimes

called hunting or dragging.

BLADE LOADING —The load

imposed on rotor blades, determined

by dividing the total weight of the hel-

icopter by the combined area of all the

rotor blades.

BLADE ROOT —The part of the

blade that attaches to the blade grip.

BLADE SPAN —The length of a

blade from its tip to its root.

BLADE STALL—The condition of

the rotor blade when it is operating at

an angle of attack greater than the

maximum angle of lift.

BLADE TIP—The further most part

of the blade from the hub of the rotor.

BLADE TRACK —The relationship

of the blade tips in the plane of rota-

tion. Blades that are in track will move

through the same plane of rotation.

BLADE TRACKING—The mechan-

ical procedure used to bring the blades

of the rotor into a satisfactory relation-

ship with each other under dynamic

conditions so that all blades rotate on a

common plane.

BLADE TWIST —The variation in

the angle of incidence of a blade

between the root and the tip.

BLOWBACK—The tendency of the

rotor disc to tilt aft in forward flight as

a result of flapping.

GLOSSARY

BUNTOVER—The tendency of a

gyroplane to pitch forward when rotor

force is removed.

CALIBRATED AIRSPEED (CAS)

—Indicated airspeed of an aircraft,

corrected for installation and instru-

mentation errors.

CENTER OF GRA VITY—The the-

oretical point where the entire weight

of the helicopter is considered to be

concentrated.

CENTER OF PRESSURE —The

point where the resultant of all the

aerodynamic forces acting on an air-

foil intersects the chord.

CENTRIFUGAL FORCE —The

apparent force that an object moving

along a circular path exerts on the

body constraining the object and that

acts outwardly away from the center

of rotation.

CENTRIPETAL FORCE —The

force that attracts a body toward its

axis of rotation. It is opposite centrifu-

gal force.

CHIP DETECTOR —A warning

device that alerts you to any abnormal

wear in a transmission or engine. It

consists of a magnetic plug located

within the transmission. The magnet

attracts any metal particles that have

come loose from the bearings or other

transmission parts. Most chip detec-

tors have warning lights located on the

instrument panel that illuminate when

metal particles are picked up.

CHORD—An imaginary straight line

between the leading and trailing edges

of an airfoil section.

CHORDWISE AXIS—A term used

in reference to semirigid rotors

describing the flapping or teetering

axis of the rotor.

COAXIL ROTOR—A rotor system

utilizing two rotors turning in opposite

directions on the same centerline. This

system is used to eliminated the need

for a tail rotor.

COLLECTIVE PITCH CON-

TROL—The control for changing the

pitch of all the rotor blades in the main

rotor system equally and simultane-

ously and, consequently, the amount

of lift or thrust being generated.

CONING—See blade coning.

CORIOLIS EFFECT—The tenden-

cy of a rotor blade to increase or

decrease its velocity in its plane of

rotation when the center of mass

moves closer or further from the axis

of rotation.

CYCLIC FEATHERING —The

mechanical change of the angle of

incidence, or pitch, of individual rotor

blades independently of other blades

in the system.

CYCLIC PITCH CONTROL—The

control for changing the pitch of each

rotor blade individually as it rotates

through one cycle to govern the tilt of

the rotor disc and, consequently, the

direction and velocity of horizontal

movement.

DELTA HINGE—A flapping hinge

with a skewed axis so that the flapping

motion introduces a component of

feathering that would result in a restor-

ing force in the flap-wise direction.

DENSITY ALTITUDE —Pressure

altitude corrected for nonstandard

temperature variations.

DEVIATION—A compass error

caused by magnetic disturbances from

the electrical and metal components in

the aircraft. The correction for this

error is displayed on a compass cor-

rection card place near the magnetic

compass of the aircraft.

DIRECT CONTROL —The ability

to maneuver a rotorcraft by tilting the

rotor disc and changing the pitch of

the rotor blades.

DIRECT SHAFT TURBINE —A

shaft turbine engine in which the com-

pressor and power section are mount-

ed on a common driveshaft.

DISC AREA—The area swept by the

blades of the rotor. It is a circle with

its center at the hub and has a radius of

one blade length.

DISC LOADING —The total heli-

copter weight divided by the rotor disc

area.

DISSYMMETRY OF LIFT —The

unequal lift across the rotor disc

resulting from the difference in the

velocity of air over the advancing

blade half and retreating blade half of

the rotor disc area.

DRAG—An aerodynamic force on a

body acting parallel and opposite to

relative wind.

DUAL ROTOR—A rotor system uti-

lizing two main rotors.

DYNAMIC ROLLOVER—The ten-

dency of a helicopter to continue

rolling when the critical angle is

exceeded, if one gear is on the ground,

and the helicopter is pivoting around

that point.

FEATHERING—The action that

changes the pitch angle of the rotor

blades by rotating them around their

feathering (spanwise) axis.

FEATHERING AXIS —The axis

about which the pitch angle of a rotor

blade is varied. Sometimes referred to

as the spanwise axis.

FEEDBACK —The transmittal of

forces, which are initiated by aerody-

namic action on rotor blades, to the

cockpit controls.

FLAPPING HINGE —The hinge

that permits the rotor blade to flap and

thus balance the lift generated by the

advancing and retreating blades.

FLAPPING —The vertical move-

ment of a blade about a flapping

hinge.

FLARE—A maneuver accomplished

prior to landing to slow down a rotor-

craft.

FREE TURBINE —A turboshaft

engine with no physical connection

between the compressor and power

output shaft.

FREEWHEELING UNIT—A com-

ponent of the transmission or power

train that automatically disconnects

the main rotor from the engine when

the engine stops or slows below the

equivalent rotor r.p.m.

FULLY ARTICULATED ROTOR

SYSTEM—See articulated rotor sys-

tem.

GRA VITY—See weight.

GROSS WEIGHT—The sum of the

basic empty weight and useful load.

GROUND EFFECT —A usually

beneficial influence on rotorcraft per-

formance that occurs while flying

close to the ground. It results from a

reduction in upwash, downwash, and

bladetip vortices, which provide a cor-

responding decrease in induced drag.

GROUND RESONANCE —Self-

excited vibration occurring whenever

the frequency of oscillation of the

blades about the lead-lag axis of an

articulated rotor becomes the same as

the natural frequency of the fuselage.

GYROCOPTER —Trademark

applied to gyroplanes designed and

produced by the Bensen Aircraft

Company.

GYROSCOPIC PRECESSION —

An inherent quality of rotating bodies,

which causes an applied force to be

manifested 90° in the direction of

rotation from the point where the

force is applied.

HUMAN FACTORS—The study of

how people interact with their

environment. In the case of general

aviation, it is the study of how pilot

performance is influenced by such

issues as the design of cockpits, the

function of the organs of the body, the

effects of emotions, and the interac-

tion and communication with other

participants in the aviation communi-

ty, such as other crew members and air

traffic control personnel.

HUNTING—Movement of a blade

with respect to the other blades in the

plane of rotation, sometimes called

leading or lagging.

INERTIA—The property of matter

by which it will remain at rest or in a

state of uniform motion in the same

direction unless acted upon by some

external force.

IN GROUND EFFECT (IGE)

HOVER—Hovering close to the sur-

face (usually less than one rotor diam-

eter distance above the surface) under

the influence of ground effect.

INDUCED DRAG—That part of the

total drag that is created by the pro-

duction of lift.

INDUCED FLOW—The component

of air flowing vertically through the

rotor system resulting from the pro-

duction of lift.

ISOGONIC LINES —Lines on

charts that connect points of equal

magnetic variation.

KNOT—A unit of speed equal to one

nautical mile per hour.

L/DMAX—The maximum ratio

between total lift (L) and total drag

(D). This point provides the best glide

speed. Any deviation from the best

glide speed increases drag and reduces

the distance you can glide.

LATERIAL VIBRATION—A vibra-

tion in which the movement is in a lat-

eral direction, such as imbalance of the

main rotor.

LEAD AND LAG —The fore (lead)

and aft (lag) movement of the rotor

blade in the plane of rotation.

LICENSED EMPTY WEIGHT —

Basic empty weight not including full

engine oil, just undrainable oil.

LIFT—One of the four main forces

acting on a rotorcraft. It acts perpendi-

cular to the relative wind.

LOAD FACTOR —The ratio of a

specified load to the total weight of

the aircraft.

MARRIED NEEDLES —A term

used when two hands of an instrument

are superimposed over each other, as

on the engine/rotor tachometer.

MAST—The component that sup-

ports the main rotor.

MAST BUMPING —Action of the

rotor head striking the mast, occurring

on underslung rotors only.

MINIMUM LEVEL FLIGHT

SPEED—The speed below which a

gyroplane, the propeller of which is

producing maximum thrust, loses alti-

tude.

NA VIGATIONAL AID (NA V AID)

—Any visual or electronic device, air-

borne or on the surface, that provides

point-to-point guidance information,

or position data, to aircraft in flight.

NIGHT—The time between the end

of evening civil twilight and the

beginning of morning civil twilight, as

published in the American Air

Almanac.

NORMALLY ASPIRATED ENGINE

—An engine that does not compen-

sate for decreases in atmospheric pres-

sure through turbocharging or other

means.

ONE-TO-ONE VIBRATION —A

low frequency vibration having one

beat per revolution of the rotor. This

vibration can be either lateral, vertical,

or horizontal.

OUT OF GROUND EFFECT

(OGE) HOVER —Hovering greater

than one diameter distance above the

surface. Because induced drag is

greater while hovering out of ground

effect, it takes more power to achieve

a hover out of ground effect.

PARASITE DRAG —The part of

total drag created by the form or shape

of helicopter parts.

PAYLOAD—The term used for pas-

sengers, baggage, and cargo.

PENDULAR ACTION—The lateral

or longitudinal oscillation of the fuse-

lage due to it being suspended from

the rotor system.

PITCH ANGLE—The angle between

the chord line of the rotor blade and

the reference plane of the main rotor

hub or the rotor plane of rotation.

PREROTATION—In a gyroplane, it

is the spinning of the rotor to a suffi-

cient r.p.m. prior to flight.

PRESSURE ALTITUDE—The height

above the standard pressure level of

29.92 in. Hg. It is obtained by setting

29.92 in the barometric pressure win-

dow and reading the altimeter.

PROFILE DRAG —Drag incurred

from frictional or parasitic resistance

of the blades passing through the air. It

does not change significantly with the

angle of attack of the airfoil section,

but it increases moderately as airspeed

increases.

RESULTANT RELATIVE WIND—

Airflow from rotation that is modified

by induced flow.

RETREATING BLADE—Any blade,

located in a semicircular part of the rotor

disc, where the blade direction is oppo-

site to the direction of flight.

RETREATING BLADE STALL —

A stall that begins at or near the tip of

a blade in a helicopter because of the

high angles of attack required to com-

pensate for dissymmetry of lift. In a

gyroplane the stall occurs at 20 to 40

percent outboard from the hub.

RIGID ROTOR —A rotor system

permitting blades to feather but not

flap or hunt.

ROTATIONAL VELOCITY —The

component of relative wind produced

by the rotation of the rotor blades.

ROTOR—A complete system of

rotating airfoils creating lift for a heli-

copter or gyroplane.

ROTOR DISC AREA —See disk

area.

ROTOR BRAKE—A device used to

stop the rotor blades during shutdown.

ROTOR FORCE —The force pro-

duced by the rotor in a gyroplane. It is

comprised of rotor lift and rotor drag.

SEMIRIGID ROTOR—A rotor sys-

tem in which the blades are fixed to the

hub but are free to flap and feather.

SETTLING WITH POWER —See

vortex ring state.

SHAFT TURBINE —A turbine

engine used to drive an output shaft

commonly used in helicopters.

SKID—A flight condition in which

the rate of turn is too great for the

angle of bank.

SKID SHOES —Plates attached to

the bottom of skid landing gear pro-

tecting the skid.

SLIP—A flight condition in which

the rate of turn is too slow for the

angle of bank.

SOLIDITY RATIO —The ratio of

the total rotor blade area to total rotor

disc area.

SPAN—The dimension of a rotor

blade or airfoil from root to tip.

SPLIT NEEDLES—A term used to

describe the position of the two nee-

dles on the engine/rotor tachometer

when the two needles are not superim-

posed.

STANDARD ATMOSPHERE —A

hypothetical atmosphere based on

averages in which the surface temper-

ature is 59°F (15°C), the surface pres-

sure is 29.92 in. Hg (1013.2 Mb) at

sea level, and the temperature lapse

rate is approximately 3.5°F (2°C) per

1,000 feet.

STATIC STOP—A device used to

limit the blade flap, or rotor flap, at

low r.p.m. or when the rotor is

stopped.

STEADY-STATE FLIGHT—A con-

dition when a rotorcraft is in straight-

and-level, unaccelerated flight, and all

forces are in balance.

SYMMETRICAL AIRFOIL —An

airfoil having the same shape on the

top and bottom.

TAIL ROTOR—A rotor turning in a

plane perpendicular to that of the main

rotor and parallel to the longitudinal

axis of the fuselage. It is used to con-

trol the torque of the main rotor and to

provide movement about the yaw axis

of the helicopter.

TEETERING HINGE —A hinge

that permits the rotor blades of a semi-

rigid rotor system to flap as a unit.

THRUST—The force developed by

the rotor blades acting parallel to the

relative wind and opposing the forces

of drag and weight.

TIP-PATH PLANE—The imaginary

circular plane outlined by the rotor

blade tips as they make a cycle of

rotation.

TORQUE—In helicopters with a sin-

gle, main rotor system, the tendency of

the helicopter to turn in the opposite

direction of the main rotor rotation.

TRAILING EDGE —The rearmost

edge of an airfoil.

TRANSLATING TENDENCY —

The tendency of the single-rotor heli-

copter to move laterally during hover-

ing flight. Also called tail rotor drift.