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The experimenter learns； after many attempts；
that gliding is a matter of a few feet only； and he
anticipates landing too soon； and the moment he
leaps from the ground the legs are swung forwardly
ready to alight。
This is done unconsciously； just as a jumper
swings his legs forwardly in the act of alighting。
Such a motion naturally disturbs the fore and aft
stability of the gliding machine； by tilting up the
forward margin； and it banks against the air；
instead of gliding。
The constant fear of all gliders is； that the
machine will point downwardly； and his motion；
as well as the position of the body； tend to shoot
it upwardly； instead。
CHAPTER IX
AEROPLANE CONSTRUCTION
As may be inferred from the foregoing statements；
there are no definite rules for the construction
of either type of flying machine； as the
flying models vary to such an extent that it is
difficult to take either of them as a model to represent
the preferred type of construction。
LATERAL； AND FORE AND AFT。The term lateral
should be understood； as applied to aeroplanes。
It is always used to designate the direction at
right angles to the movement of the machine。
Fore and aft is a marine term meaning lengthwise；
or from front to rear； hence is always at right
angles to the lateral direction。
The term transverse is equivalent to lateral；
in flying machine parlance； but there is this
distinction： Transverse has reference to a machine
or object which； like the main planes of an aeroplane；
are broader； （that is；from end to end）
than their length； （from front to rear）。
On the other hand； lateral has reference to side
branches； as； for instance； the monoplane wings；
which branch out from the sides of the fore and
aft body。
STABILITY AND STABILIZATION。These terms constantly
appear in describing machines and their
operations。 If the flying structure； whatever it
may be； has means whereby it is kept from rocking
from side to side； it has stability； which is usually
designated as lateral stability。 The mechanism
for doing this is called a stabilizer。
THE WRIGHT SYSTEM。The Wright machine has
reference solely to the matter of laterally controlling
the flying structure； and does not pertain
to the form or shape of the planes。
In Fig。 49 A designates the upper and lower
planes of a Wright machine； with the peculiar
rounded ends。 The ends of the planes are so
arranged that the rear margins may be raised or
lowered； independently of the other portions of
the planes； which are rigid。 This movement is
indicated in sketch 1； where the movable part B
is； as we might say； hinged along the line C。
The dotted line D on the right hand end； shows
how the section is depressed； while the dotted
lines E at the left hand end shows the section
raised。 It is obvious that the downturned ends；
as at D； will give a positive angle at one end of the
planes； and the upturned wings E at the other end
will give a negative angle； and thus cause the right
hand end to raise； and the other end to move
downwardly； as the machine moves forwardly
through the air。
CONTROLLING THE WARPING ENDS。Originally
the Wrights controlled these warping sections by
means of a cradle occupied by the aviator； so that
the cradle would move or rock； dependent on the
tilt of the machine。 This was what was termed
automatic control。 This was found to be unsatisfactory；
and the control has now been placed so
that it connects with a lever and is operated by
the aviator； and is called Manually…operated control。
In all forms of control the wings on one side are
depressed on one side and correspondingly elevated
on the other。
THE CURTIS WINGS。Curtis has small wings；
or ailerons； intermediate the supporting surfaces；
and at their extremities； as shown in sketch 2。
These are controlled by a shoulder rack or swinging
frame operated by the driver； so that the body
in swinging laterally will change the two wings
at the same time； but with angles in different
directions。
THE FARMAN AILERONS。Farman's disposition
is somewhat different； as shown in sketch 3。 The
wings are hinged to the upper planes at their rear
edges； and near the extremities of the planes。
Operating wires lead to a lever within reach of the
aviator； and； by this means； the wings are held at
any desired angle； or changed at will。
The difficulty of using any particular model； is
true； also； of the arrangement of the fore and aft
control； as well as the means for laterally stabilizing
it。 In view of this we shall submit a general
form； which may be departed from at will。
FEATURES WELL DEVELOPED。Certain features
are fairly well developed； however。 One is the
angle of the supporting plane； with reference to
the frame itself； and the other is the height at
which the tail and rudder should be placed above
the surface of the ground when the machine is at
rest。
DEPRESSING THE REAR END。This latter is a
matter which must be taken into consideration；
because in initiating flight the rear end of the
frame is depressed in order to give a sufficient
angle to the supporting planes so as to be able to
inaugurate flight。
In order to commence building we should have
some definite idea with respect to the power； as
this will； in a measure； determine the area of the
supporting surfaces； as a whole； and from this
the sizes of the different planes may be determined。
DETERMINING THE SIZE。Suppose we decide on
300 square feet of sustaining surface。 This may
require a 30； a 40 or a 50 horse power motor；
dependent on the speed required； and much higher
power has been used on that area。
However； let us assume that a forty horse power
motor is available； our 300 square feet of surface
may be put into two planes； each having 150 square
feet of surface； which would make each 5' by 30'
in size； or； it may be decided to make the planes
narrower； and proportionally longer。 This is immaterial。
The shorter the planes transversely；
the greater will be the stability； and the wider the
planes the less will be the lift； comparatively。
RULE FOR PLACING THE PLANES。The rule for
placing the planes is to place them apart a distance
equal to the width of the planes themselves；
so that if we decide on making them five feet wide；
they should be placed at least five feet apart。
This rule； while it is an admirable one for slow
movements or when starting flight； is not of any
advantage while in rapid flight。
If the machine is made with front and rear
horizontally…disposed rudders； or elevators； they
also serve as sustaining surfaces； which； for the
present will be disregarded。
Lay off a square A； Fig。 49a； in which the vertical
lines B； B； and the horizontal lines C； C； are
5' long； and draw a cross D within this； the lines
running diagonally from the corners。
Now step off from t