CLEANLINESS.--The fabric must be kept clean and free from oil, as that
will rot it. To take out dirt or oily patches, try acetone. If that will
not remedy matters, then try petrol, but use it sparingly, as otherwise
it will take off an unnecessary amount of dope. If that will not remove
the dirt, then hot water and soap will do so, but, in that case, be
sure to use soap having no alkali in it, as otherwise it may injure the
fabric. Use the water sparingly, or it may get inside the planes and
rust the internal bracing wires, or cause some of the wooden framework
to swell.
The wheels of the undercarriage have a way of throwing up mud on to
the lower surface. This should, if possible, be taken off while wet. It
should never be scraped off when dry, as that may injure the fabric. If
dry, then it should be moistened before being removed.
Measures should be taken to prevent dirt from collecting upon any
part of the aeroplane, as, otherwise, excessive skin-friction will be
produced with resultant loss of flight speed. The wires, being greasy,
collect dirt very easily.
CONTROL CABLES.--After every flight the rigger should pass his hand over
the control cables and carefully examine them near pulleys. Removal of
grease may be necessary to make a close inspection possible. If only one
strand is broken the wire should be replaced. Do not forget the aileron
balance wire on the top surface.
Once a day try the tension of the control cables by smartly moving the
control levers about as explained elsewhere.
WIRES.--All the wires should be kept well greased or oiled, and in the
correct tension. When examining the wires, it is necessary to place the
aeroplane on level ground, as otherwise it may be twisted, thus throwing
some wires into undue tension and slackening others. The best way, if
there is time, is to pack the machine up into its “flying position.”
If you see a slack wire, do not jump to the conclusion that it must
be tensioned. Perhaps its opposition wire is too tight, in which case
slacken it, and possibly you will find that will tighten the slack wire.
Carefully examine all wires and their connections near the propeller,
and be sure that they are snaked round with safety wire, so that the
latter may keep them out of the way of the propeller if they come
adrift.
The wires inside the fuselage should be cleaned and regreased about once
a fortnight.
STRUTS AND SOCKETS.--These should be carefully examined to see if any
splitting has occurred.
DISTORTION.--Carefully examine all surfaces, including the controlling
surfaces, to see whether any distortion has occurred. If distortion can
be corrected by the adjustment of wires, well and good; but if not, then
some of the internal framework probably requires replacement.
ADJUSTMENTS.--Verify the angles of incidence; dihedral, and stagger, and
the rigging position of the controlling-surfaces, as often as possible.
UNDERCARRIAGE.--Constantly examine the alignment and fittings of the
undercarriage, and the condition of tyres and shock absorbers. The
latter, when made of rubber, wear quickest underneath. Inspect axles and
skids to see if there are any signs of them becoming bent. The wheels
should be taken off occasionally and greased.
LOCKING ARRANGEMENTS.--Constantly inspect the locking arrangements of
turnbuckles, bolts, etc. Pay particular attention to the control cable
connections, and to all moving parts in respect of the controls.
LUBRICATION.--Keep all moving parts, such as pulleys, control levers,
and hinges of controlling surfaces, well greased.
SPECIAL INSPECTION.--Apart from constantly examining the aeroplane with
reference to the above points I have made, I think that, in the case of
an aeroplane in constant use it is an excellent thing to make a special
inspection of every part, say once a week. This will take from two to
three hours, according to the type of aeroplane. In order to carry it
out methodically, the rigger should have a list of every part down to
the smallest split-pin. He can then check the parts as he examines them,
and nothing will be passed over. This, I know from experience, greatly
increases the confidence of the pilot, and tends to produce good work in
the air.
WINDY WEATHER.--The aeroplane, when on the ground, should face the
wind; and it is advisable to lash the control lever fast, so that the
controlling surfaces may not be blown about and possibly damaged.
“VETTING” BY EYE.--This should be practiced at every opportunity, and,
if persevered in, it is possible to become quite expert in diagnosing by
eye faults in flight efficiency, stability and control.
The aeroplane should be standing upon level ground, or, better than
that, packed up into its “flying position.”
Now stand in front of it and line up the leading edge with the main
spar, rear spar, and trailing edge. Their shadows can usually be seen
through the fabric. Allowance must, of course, be made for wash-in and
wash-out; otherwise, the parts I have specified should be parallel with
each other.
Now line up the centre part of the main-plane with the tail-plane. The
latter should be horizontal.
Next, sight each interplane front strut with its rear strut. They should
be parallel.
Then, standing on one side of the aeroplane, sight all the front struts.
The one nearest to you should cover all the others. This applies to the
rear struts also.
Look for distortion of leading edges, main and rear spars, trailing
edges, tail-plane and controlling surfaces.
This sort of thing, if practiced constantly, will not only develop an
expert eye for diagnosis of faults, but will also greatly assist in
impressing upon the memory the characteristics and possible troubles of
the various types of aeroplanes.
MISHANDLING OF THE GROUND.--This is the cause of a lot of unnecessary
damage. The golden rule to observe is: PRODUCE NO BENDING STRESSES.
Nearly all the wood in an aeroplane is designed to take merely the
stress of direct compression, and it cannot be bent safely. Therefore,
in packing an aeroplane up from the ground, or in pulling or pushing it
about, be careful to stress it in such a way as to produce, as far
as possible, only direct compression stresses. For instance, if it is
necessary to support the lifting surface, then the packing should be
arranged to come directly under the struts so that they may take the
stress in the form of compression for which they are designed. Such
supports should be covered with soft packing in order to prevent the
fabric from becoming damaged.
When pulling an aeroplane along, if possible, pull from the top of the
undercarriage struts. If necessary to pull from elsewhere, then do so by
grasping the interplane struts as low down as possible.
Never lay fabric-covered parts upon a concrete floor. Any slight
movement will cause the fabric to scrape over the floor with resultant
damage.
Struts, spars, etc., should never be left about the floor, as in such
position they are likely to become scored. I have already explained the
importance of protecting the outside fibres of the wood. Remember
also that wood becomes distorted easily. This particularly applies to
interplane struts. If there are no proper racks to stand them in, then
the best plan is to lean them up against the wall in as near a vertical
position as possible.
TIME.--Learn to know the time necessary to complete any of the various
rigging jobs. This is really important. Ignorance of this will lead
to bitter disappointments in civil life; and, where Service flying
is concerned, it will, to say the least of it, earn unpopularity with
senior officers, and fail to develop respect and good work where men are
concerned.
THE AEROPLANE SHED.--This should be kept as clean and orderly as
possible. A clean, smart shed produces briskness, energy, and pride of
work. A dirty, disorderly shed nearly always produces slackness and poor
quality of work, lost tools and mislaid material.
GLOSSARY
Aeronautics--The science of aerial navigation.
Aerofoil--A rigid structure, of large superficial area relative to its
thickness, designed to obtain, when driven through the air at an
angle inclined to the direction of motion, a reaction from the air
approximately at right angles to its surface. Always cambered when
intended to secure a reaction in one direction only. As the term
“aerofoil” is hardly ever used in practical aeronautics, I have,
throughout this book, used the term SURFACE, which, while academically
incorrect, since it does not indicate thickness, is a term usually
used to describe the cambered lifting surfaces, i.e., the “planes” or
“wings,” and the stabilizers and the controlling aerofoils.
Aerodrome--The name usually applied to a ground used for the practice
of aviation. It really means “flying machine,” but is never used in that
sense nowadays.
Aeroplane--A power-driven aerofoil with stabilizing and controlling
surfaces.
Acceleration--The rate of change of velocity.
Angle of Incidence--The angle at which the “neutral lift line” of a
surface attacks the air.
Angle of Incidence, Rigger's--The angle the chord of a surface makes
with a line parallel to the axis of the propeller.
Angle of Incidence, Maximum--The greatest angle of incidence at which,
for a given power, surface (including detrimental surface), and weight,
horizontal flight can be maintained.
Angle of Incidence, Minimum--The smallest angle of incidence at which,
for a given power, surface (including detrimental surface), and weight,
horizontal flight can be maintained.
Angle of Incidence, Best Climbing--That angle of incidence at which an
aeroplane ascends quickest. An angle approximately halfway between the
maximum and optimum angles.
Angle of Incidence, Optimum--The angle of incidence at which the
lift-drift ratio is the highest.
Angle, Gliding--The angle between the horizontal and the path along
which an aeroplane at normal flying speed, but not under engine power,
descends in still air.
Angle, Dihedral--The angle between two planes.
Angle, Lateral Dihedral--The lifting surface of an aeroplane is said to
be at a lateral dihedral angle when it is inclined upward towards its
wing-tips.
Angle, Longitudinal Dihedral--The main surface and tail surface are said
to be at a longitudinal dihedral angle when the projections of their
neutral lift lines meet and produce an angle above them.
Angle, Rigger's Longitudinal Dihedral--Ditto, but substituting “chords”
for “neutral life lines.”
Angle, Pitch--The angle at any given point of a propeller, at which
the blade is inclined to the direction of motion when the propeller is
revolving but the aeroplane stationary.
Altimeter--An instrument used for measuring height.
Air-Speed Indicator--An instrument used for measuring air pressures or
velocities. It consequently indicates whether the surface is securing
the requisite reaction for flight. Usually calibrated in miles per hour,
in which case it indicates the correct number of miles per hour at only
one altitude. This is owing to the density of the air decreasing with
increase of altitude and necessitating a greater speed through space
to secure the same air pressure as would be secured by less speed at a
lower altitude. It would be more correct to calibrate it in units of air
pressure.
Air Pocket--A local movement or condition of the air causing an
aeroplane to drop or lose its correct attitude.
Aspect-Ratio--The proportion of span to chord of a surface.
Air-Screw (Propeller)--A surface so shaped that its rotation about an
axis produces a force (thrust) in the direction of its axis.
Aileron--A controlling surface, usually situated at the wing-tip, the
operation of which turns an aeroplane about its longitudinal axis;
causes an aeroplane to tilt sideways.
Aviation--The art of driving an aeroplane.
Aviator--The driver of an aeroplane.
Barograph--A recording barometer, the charts of which can be calibrated
for showing air density or height.
Barometer--An instrument used for indicating the density of air.
Bank, to--To turn an aeroplane about its longitudinal axis (to tilt
sideways) when turning to left or right.
Biplane--An aeroplane of which the main lifting surface consists of a
surface or pair of wings mounted above another surface or pair of wings.
Bay--The space enclosed by two struts and whatever they are fixed to.
Boom--A term usually applied to the long spars joining the tail of a
“pusher” aeroplane to its main lifting surface.
Bracing--A system of struts and tie wires to transfer a force from one
point to another.
Canard--Literally “duck.” The name which was given to a type of
aeroplane of which the longitudinal stabilizing surface (empennage)
was mounted in front of the main lifting surface. Sometimes termed
“tail-first” aeroplanes, but such term is erroneous, as in such a design
the main lifting surface acts as, and is, the empennage.
Cabre--To fly or glide at an excessive angle of incidence; tail down.
Camber--Curvature.
Chord--Usually taken to be a straight line between the trailing and
leading edges of a surface.
Cell--The whole of the lower surface, that part of the upper surface
directly over it, together with the struts and wires holding them
together.
Centre (Line) of Pressure--A line running from wing-tip to wing-tip, and
through which all the air forces acting upon the surface may be said to
act, or about which they may be said to balance.
Centre (Line) of Pressure, Resultant--A line transverse to the
longitudinal axis, and the position of which is the resultant of the
centres of pressure of two or more surfaces.
Centre of Gravity--The centre of weight.
Cabane--A combination of two pylons, situated over the fuselage, and
from which anti-lift wires are suspended.
Cloche--Literally “bell.” Is applied to the bell-shaped construction
which forms the lower part of the pilot's control lever in a Bleriot
monoplane, and to which the control cables are attached.
Centrifugal Force--Every body which moves in a curved path is urged
outwards from the centre of the curve by a force termed “centrifugal.”
Control Lever--A lever by means of which the controlling surfaces
are operated. It usually operates the ailerons and elevator. The
“joy-stick”.
Cavitation, Propeller--The tendency to produce a cavity in the air.
Distance Piece--A long, thin piece of wood (sometimes tape) passing
through and attached to all the ribs in order to prevent them from
rolling over sideways.
Displacement--Change of position.
Drift (of an aeroplane as distinct from the propeller)--The horizontal
component of the reaction produced by the action of driving through the
air a surface inclined upwards and towards its direction of motion PLUS
the horizontal component of the reaction produced by the “detrimental”
surface PLUS resistance due to “skin-friction.” Sometimes termed
“head-resistance.”
Drift, Active--Drift produced by the lifting surface.
Drift, Passive--Drift produced by the detrimental surface.
Drift (of a propeller)--Analogous to the drift of an aeroplane. It is
convenient to include “cavitation” within this term.
Drift, to--To be carried by a current of air; to make leeway.
Dive, to--To descend so steeply as to produce a speed greater than the
normal flying speed.
Dope, to--To paint a fabric with a special fluid for the purpose of
tightening and protecting it.
Density--Mass of unit volume, for instance, pounds per cubic foot.
Efficiency--Output Input
Efficiency (of an aeroplane as distinct from engine and propeller)--
Lift and Velocity
Thrust (= aeroplane drift)
Efficiency, Engine--Brake horse-power
Indicated horse-power
Efficiency, Propeller--
Thrust horse-power
Horse-power received from engine
(= propeller drift)
NOTE.--The above terms can, of course, be expressed in foot-pounds. It
is then only necessary to divide the upper term by the lower one to find
the measure of efficiency.
Elevator--A controlling surface, usually hinged to the rear of the
tail-plane, the operation of which turns an aeroplane about an axis
which is transverse to the direction of normal horizontal flight.
Empennage--See “Tail-plane.”
Energy--Stored work. For instance, a given weight of coal or petroleum
stores a given quantity of energy which may be expressed in foot-pounds.
Extension--That part of the upper surface extending beyond the span of
the lower surface.
Edge, Leading--The front edge of a surface relative to its normal
direction of motion.
Edge, Trailing--The rear edge of a surface relative to its normal
direction of motion.
Factor of Safety--Usually taken to mean the result found by dividing the
stress at which a body will collapse by the maximum stress it will be
called upon to bear.
Fineness (of stream-line)--The proportion of length to maximum width.
Flying Position--A special position in which an aeroplane must be placed
when rigging it or making adjustments. It varies with different types of
aeroplanes. Would be more correctly described as “rigging position.”
Fuselage--That part of an aeroplane containing the pilot, and to which
is fixed the tail-plane.
Fin--Additional keel-surface, usually mounted at the rear of an
aeroplane.
Flange (of a rib)--That horizontal part of a rib which prevents it from
bending sideways.
Flight--The sustenance of a body heavier than air by means of its action
upon the air.
Foot-pound--A measure of work representing the weight of 1 lb. raised 1
foot.
Fairing--Usually made of thin sheet aluminum, wood, or a light
construction of wood and fabric; and bent round detrimental surface in
order to give it a “fair” or “stream-like” shape.
Gravity--Is the force of the Earth's attraction upon a body. It
decreases with increase of distance from the Earth. See “Weight.”
Gravity, Specific--Density of substance Density of water.
Thus, if the density of water is 10 lb. per unit volume, the same unit
volume of petrol, if weighing 7 lb., would be said to have a specific
gravity of 7/10, i.e., 0.7.
Gap (of an aeroplane)--The distance between the upper and lower surfaces
of a biplane. In a triplane or multiplane, the distance between a
surface and the one first above it.
Gap, Propeller--The distance, measured in the direction of the thrust,
between the spiral courses of the blades.
Girder--A structure designed to resist bending, and to combine lightness
and strength.
Gyroscope--A heavy circular wheel revolving at high speed, the effect of
which is a tendency to maintain its plane of rotation against disturbing
forces.
Hangar--An aeroplane shed.
Head-Resistance--Drift. The resistance of the air to the passage of a
body.
Helicopter--An air-screw revolving about a vertical axis, the direction
of its thrust being opposed to gravity.
Horizontal Equivalent--The plan view of a body whatever its attitude may
be.
Impulse--A force causing a body to gain or lose momentum.
Inclinometer--A curved form of spirit-level used for indicating the
attitude of a body relative to the horizontal.
Instability--An inherent tendency of a body, which, if the body is
disturbed, causes it to move into a position as far as possible away
from its first position.
Instability, Neutral--An inherent tendency of a body to remain in the
position given it by the force of a disturbance, with no tendency to
move farther or to return to its first position.
Inertia--The inherent resistance to displacement of a body as distinct
from resistance the result of an external force.
Joy-Stick--See “Control Lever.”
Keel-Surface--Everything to be seen when viewing an aeroplane from the
side of it.
King-Post--A bracing strut; in an aeroplane, usually passing through a
surface and attached to the main spar, and from the end or ends of which
wires are taken to spar, surface, or other part of the construction in
order to prevent distortion. When used in connection with a controlling
surface, it usually performs the additional function of a lever, control
cables connecting its ends with the pilot's control lever.
Lift--The vertical component of the reaction produced by the action
of driving through the air a surface inclined upwards and towards its
direction of motion.
Lift, Margin of--The height an aeroplane can gain in a given time and
starting from a given altitude.
Lift-Drift Ratio--The proportion of lift to drift.
Loading--The weight carried by an aerofoil. Usually expressed in pounds
per square foot of superficial area.
Longeron--The term usually applied to any long spar running length-ways
of a fuselage.
Mass--The mass of a body is a measure of the quantity of material in it.
Momentum--The product of the mass and velocity of a body is known as
“momentum.”
Monoplane--An aeroplane of which the main lifting surface consists of
one surface or one pair of wings.
Multiplane--An aeroplane of which the main lifting surface consists of
numerous surfaces or pairs of wings mounted one above the other.
Montant--Fuselage strut.
Nacelle--That part of an aeroplane containing the engine and pilot and
passenger, and to which the tail plane is not fixed.
Neutral Lift Line--A line taken through a surface in a forward direction
relative to its direction of motion, and starting from its trailing
edge. If the attitude of the surface is such as to make the said line
coincident with the direction of motion, it results in no lift, the
reaction then consisting solely of drift. The position of the neutral
lift line, i.e., the angle it makes with the chord, varies with
differences of camber, and it is found by means of wind-tunnel research.
Newton's Laws of Motion--1. If a body be at rest, it will remain at
rest; or, if in motion, it will move uniformly in a straight line until
acted upon by some force.
2. The rate of change of the quantity of motion (momentum) is
proportional to the force which causes it, and takes place in the
direction of the straight line in which the force acts. If a body be
acted upon by several forces, it will obey each as though the others did
not exist, and this whether the body be at rest or in motion.
3. To every action there is opposed an equal and opposite reaction.
Ornithopter (or Orthopter)--A flapping wing design of aircraft intended
to imitate the flight of a bird.
Outrigger--This term is usually applied to the framework connecting the
main surface with an elevator placed in advance of it. Sometimes applied
to the “tail-boom” framework connecting the tail-plane with the main
lifting surface.
Pancake, to--To “stall ”
Plane--This term is often applied to a lifting surface. Such application
is not quite correct, since “plane” indicates a flat surface, and the
lifting surfaces are always cambered.
Propeller--See “Air-Screw.”
Propeller, Tractor--An air-screw mounted in front of the main lifting
surface.
Propeller, Pusher--An air-screw mounted behind the main lifting surface.
Pusher--An aeroplane of which the propeller is mounted behind the main
lifting surface.
Pylon--Any V-shaped construction from the point of which wires are
taken.
Power--Rate of working.
Power, Horse--One horse-power represents a force sufficient to raise
33,000 lbs. 1 foot in a minute.
Power, Indicated Horse--The I.H.P. of an engine is a measure of the rate
at which work is done by the pressure upon the piston or pistons, as
distinct from the rate at which the engine does work. The latter is
usually termed “brake horse-power,” since it may be measured by an
absorption brake.
Power, Margin of--The available quantity of power above that necessary
to maintain horizontal flight at the optimum angle.
Pitot Tube--A form of air-speed indicator consisting of a tube with open
end facing the wind, which, combined with a static pressure or suction
tube, is used in conjunction with a gauge for measuring air pressures or
velocities. (No. 1 in diagram.)
Pitch, Propeller--The distance a propeller advances during one
revolution supposing the air to be solid.
Pitch, to--To plunge nose-down.
Reaction--A force, equal and opposite to the force of the action
producing it.
Rudder--A controlling surface, usually hinged to the tail, the operation
of which turns an aeroplane about an axis which is vertical in normal
horizontal flight; causes an aeroplane to turn to left or right of the
pilot.
Roll, to--To turn about the longitudinal axis.
Rib, Ordinary--A light curved wooden part mounted in a fore and aft
direction within a surface. The ordinary ribs give the surface its
camber, carry the fabric, and transfer the lift from the fabric to the
spars.
Rib, Compression--Acts as an ordinary rib, besides bearing the stress of
compression produced by the tension of the internal bracing wires.
Rib, False--A subsidiary rib, usually used to improve the camber of the
front part of the surface.
Right and Left Hand--Always used relative to the position of the pilot.
When observing an aeroplane from the front of it, the right hand side of
it is then on the left hand of the observer.
Remou--A local movement or condition of the air which may cause
displacement of an aeroplane.
Rudder-Bar--A control lever moved by the pilot's feet, and operating the
rudder.
Surface--See “Aerofoil.”
Surface, Detrimental--All exterior parts of an aeroplane including
the propeller, but excluding the (aeroplane) lifting and (propeller)
thrusting surfaces.
Surface, Controlling--A surface the operation of which turns an
aeroplane about one of its axes.
Skin-Friction--The friction of the air with roughness of surface. A form
of drift.
Span---The distance from wing-tip to wing-tip.
Stagger--The distance the upper surface is forward of the lower surface
when the axis of the propeller is horizontal.
Stability--The inherent tendency of a body, when disturbed, to return to
its normal position.
Stability, Directional--The stability about an axis which is vertical
during normal horizontal flight, and without which an aeroplane has no
natural tendency to remain upon its course.
Stability, Longitudinal--The stability of an aeroplane about an axis
transverse to the direction of normal horizontal flight, and without
which it has no tendency to oppose pitching and tossing.
Stability, Lateral--The stability of an aeroplane about its longitudinal
axis, and without which it has no tendency to oppose sideways rolling.
Stabilizer--A surface, such as fin or tail-plane, designed to give an
aeroplane inherent stability.
Stall, to--To give or allow an aeroplane an angle of incidence greater
than the “maximum” angle, the result being a fall in the lift-drift
ratio, the lift consequently becoming less than the weight of the
aeroplane, which must then fall, i.e., “stall” or “pancake.”
Stress--Burden or load.
Strain--Deformation produced by stress.
Side-Slip, to--To fall as a result of an excessive “bank” or “roll.”
Skid, to--To be carried sideways by centrifugal force when turning to
left or right.
Skid, Undercarriage--A spar, mounted in a fore and aft direction, and to
which the wheels of the undercarriage are sometimes attached. Should
a wheel give way the skid is then supposed to act like the runner of a
sleigh and to support the aeroplane.
Skid, Tail--A piece of wood or other material, orientable, and fitted
with shock absorbers, situated under the tail of an aeroplane in order
to support it upon the ground and to absorb the shock of alighting.
Section--Any separate part of the top surface, that part of the bottom
surface immediately underneath it, with their struts and wires.
Spar--Any long piece of wood or other material.
Spar, Main--A spar within a surface and to which all the ribs are
attached, such spar being the one situated nearest to the centre of
pressure. It transfers more than half the lift from the ribs to the
bracing.
Spar, Rear--A spar within a surface, and to which all the ribs are
attached, such spar being situated at the rear of the centre of pressure
and at a greater distance from it than is the main spar. It transfers
less than half of the lift from the ribs to the bracing.
Strut--Any wooden member intended to take merely the stress of direct
compression.
Strut, Interplane--A strut holding the top and bottom surfaces apart.
Strut, Fuselage--A strut holding the fuselage longerons apart. It should
be stated whether top, bottom, or side. If side, then it should be
stated whether right or left hand. Montant.
Strut, Extension--A strut supporting an “extension” when not in flight.
It may also prevent the extension from collapsing upwards during flight.
Strut, Undercarriage--
Strut, Dope--A strut within a surface, so placed as to prevent the
tension of the doped fabric from distorting the framework.
Serving--To bind round with wire, cord, or similar material. Usually
used in connection with wood joints and wire cable splices.
Slip, Propeller--The pitch less the distance the propeller advances
during one revolution.
Stream-Line--A form or shape of detrimental surface designed to produce
minimum drift.
Toss, to--To plunge tail-down.
Torque, Propeller--The tendency of a propeller to turn an aeroplane
about its longitudinal axis in a direction opposite to that in which the
propeller revolves.
Tail-Slide--A fall whereby the tail of an aeroplane leads.
Tractor--An aeroplane of which the propeller is mounted in front of the
main lifting surface.
Triplane--An aeroplane of which the main lifting surface consists of
three surfaces or pairs of wings mounted one above the other.
Tail-Plane--A horizontal stabilizing surface mounted at some distance
behind the main lifting surface. Empennage.
Turnbuckle--A form of wire-tightener, consisting of a barrel into each
end of which is screwed an eyebolt. Wires are attached to the eyebolts
and the required degree of tension is secured by means of rotating the
barrel.
Thrust, Propeller--See “Air-Screw.”
Undercarriage--That part of an aeroplane beneath the fuselage or
nacelle, and intended to support the aeroplane when at rest, and to
absorb the shock of alighting.
Velocity--Rate of displacement; speed.
Volplane--A gliding descent.
Weight--Is a measure of the force of the Earth's attraction (gravity)
upon a body. The standard unit of weight in this country is 1 lb., and
is the force of the Earth's attraction on a piece of platinum called
the standard pound, deposited with the Board of Trade in London. At the
centre of the Earth a body will be attracted with equal force in
every direction. It will therefore have no weight, though its mass
is unchanged. Gravity, of which weight is a measure, decreases with
increase of altitude.
Web (of a rib)--That vertical part of a rib which prevents it from
bending upwards.
Warp, to--To distort a surface in order to vary its angle of incidence.
To vary the angle of incidence of a controlling surface.
Wash--The disturbance of air produced by the flight of an aeroplane.
Wash-in--An increasing angle of incidence of a surface towards its
wing-tip.
Wash-out--A decreasing angle of incidence of a surface towards its
wing-tip.
Wing-tip--The right- or left-hand extremity of a surface.
Wire--A wire is, in Aeronautics, always known by the name of its
function.
Wire, Lift or Flying--A wire opposed to the direction of lift, and used
to prevent a surface from collapsing upward during flight.
Wire, Anti-lift or Landing--A wire opposed to the direction of gravity,
and used to sustain a surface when it is at rest.
Wire, Drift--A wire opposed to the direction of drift, and used to
prevent a surface from collapsing backwards during flight.
Wire, Anti-drift--A wire opposed to the tension of a drift wire, and
used to prevent such tension from distorting the framework.
Wire, Incidence--A wire running from the top of an interplane strut
to the bottom of the interplane strut in front of or behind it.
It maintains the “stagger” and assists in maintaining the angle of
incidence. Sometimes termed “stagger wire.”
Wire, Bracing--Any wire holding together the framework of any part of
an aeroplane. It is not, however, usually applied to the wires described
above unless the function performed includes a function additional to
those described above. Thus, a lift wire, while strictly speaking a
bracing wire, is not usually described as one unless it performs the
additional function of bracing some well-defined part such as the
undercarriage. It will then be said to be an “undercarriage bracing lift
wire.” It might, perhaps, be acting as a drift wire also, in which
case it will then be de-scribed as an “undercarriage bracing lift-drift
wire.” It should always be stated whether a bracing wire is (1) top, (2)
bottom, (3) cross, or (4) side. If a “side bracing wire,” then it should
be stated whether right- or left-hand.
Wire, Internal Bracing--A bracing wire (usually drift or anti-drift)
within a surface.
Wire, Top Bracing--A bracing wire, approximately horizontal and situated
between the top longerons of fuselate, between top tail booms, or at the
top of similar construction.
Wire, Bottom Bracing--Ditto, substituting “bottom” for “top.”
Wire, Side Bracing--A bracing wire crossing diagonally a side bay of
fuselage, tail boom bay, undercarriage side bay or centre-section side
bay. This term is not usually used with reference to incidence wires,
although they cross diagonally the side bays of the cell. It should be
stated whether right- or left-hand.
Wire, Cross Bracing--A bracing wire, the position of which is diagonal
from right to left when viewing it from the front of an aeroplane.
Wire, Control Bracing--A wire preventing distortion of a controlling
surface.
Wire, Control--A wire connecting a controlling surface with the pilot's
control lever, wheel, or rudder-bar.
Wire, Aileron Gap--A wire connecting top and bottom ailerons.
Wire, Aileron Balance--A wire connecting the right- and left-hand top
ailerons. Sometimes termed the “aileron compensating wire.”
Wire, Snaking--A wire, usually of soft metal, wound spirally or tied
round another wire, and attached at each end to the framework. Used to
prevent the wire round which it is “snaked” from becoming, in the event
of its displacement, entangled with the propeller.
Wire, Locking--A wire used to prevent a turnbuckle barrel or other
fitting from losing its adjustment.
Wing--Strictly speaking, a wing is one of the surfaces of an
ornithopter. The term is, however, often applied to the lifting surface
of an aeroplane when such surface is divided into two parts, one being
the left-hand “wing,” and the other the right-hand “wing.”
Wind-Tunnel--A large tube used for experimenting with surfaces and
models, and through which a current of air is made to flow by artificial
means.
Work--Force X displacement.
Wind-Screen--A small transparent screen mounted in front of the pilot to
protect his face from the air pressure.
FOOTNOTES:
[1] Propeller Slip: As the propeller screws through the air, the
latter to a certain extent gives back to the thrust of the propellor
blades, just as the shingle on the beach slips back as you ascend it.
Such “give-back” is known as “slip,” and anyone behind the propellor
will feel the slip as a strong draught of air.
[2] Helicopter. An air-screw revolving upon a vertical axis. If driven
with sufficient power, it will lift vertically, but having regard to the
mechanical difficulties of such construction, it is a most inefficient
way of securing lift compared with the arrangement of an inclined
surface driven by a propeller revolving about a horizontal axis.
[3] Pancakes: Pilot's slang for stalling an aeroplane and dropping
like a pancake.
[4] Morane parasol: A type of Morane monoplane in which the lifting
surfaces are raised above the pilot in order to afford him a good view
of the earth.
[5] Skin friction is that part of the drift due to the friction of the
air with roughnesses upon the surface of the aeroplane.
[6] Banking: When an aeroplane is turned to the left or the right
the centrifugal force of its momentum causes it to skid sideways and
outwards away from the centre of the turn. To minimize such action the
pilot banks, i.e., tilts, the aeroplane sideways in order to oppose the
underside of the planes to the air. The aeroplane will not then skid
outwards beyond the slight skid necessary to secure a sufficient
pressure of air to balance the centrifugal force.
[7] An explanation of the way in which the wash-out is combined with a
wash-in to offset propellor torque will be found on p. 82.
[8] A.M.'s: Air Mechanics.
[9] Butt means to thicken at the end. Screw means to machine a
thread on the butt-end of the wire, and in this way the wire can make
connection with the desired place by being screwed into a metal fitting,
thus eliminating the disadvantage of the unsatisfactory loop.
[10] Deviation curve: A curved line indicating any errors in the
compass.
[11] A propeller screws through the air, and the distance it advances
during one revolution, supposing the air to be solid, is known as the
pitch. The pitch, which depends upon the angle of the propeller blades,
must be equal to the speed of the aeroplane, plus the slip, and if, on
account of the rarity of the air the speed of the aeroplane increases,
then the angle and pitch should be correspondingly increased. Propellers
with a pitch capable of being varied by the pilot are the dream of
propeller designers. For explanation of “slip” see Chapter IV. on
propellers.
[12] Getting out of my depth? Invading the realms of fancy? Well,
perhaps so, but at any rate it is possible that extraordinary speed
through space may be secured if means are found to maintain the impulse
of the engine and the thrust-drift efficiency of the propeller at great
altitude.
[13] Box-kite. The first crude form of biplane.
[14] See Newton's laws in the Glossary at the end of the book.
[15] See “Aerofoil” in the Glossary.
[16] “In effect” because, although there may be actually the greatest
proportion of keel-surface In front of the vertical axis, such surface
may be much nearer to the axis than is the keel-surface towards the
tail. The latter may then be actually less than the surface in front,
but, being farther from the axis, it has a greater leverage, and
consequently is greater in effect than the surface in front.