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In such a case it would now be over 5500 miles
from the center of the earth； and the centrifugal
pull would be decreased to such an extent that the
ball would go on and on until it came within the
sphere of influence from some other celestial
body。
EQUALIZING THE TWO MOTIONS。But now let us
assume that the line of flight is like that shown
at E； in Fig。 2； where it travels along parallel
with the surface of the earth。 In this case the
force of the ball equals the centripetal pull；or；
to put it differently； the centrifugal equals the
gravitational pull。
The constant tendency of the ball to fly off at
a tangent； and the equally powerful pull of
gravity acting against each other； produce a
motion which is like that of the earth； revolving
around the sun once every three hundred and
sixty…five days。
It is a curious thing that neither Langley； nor
any of the scientists； in treating of the matter of
flight； have taken into consideration this quality
of momentum； in their calculations of the elements
of flight。
_Fig。 2 Horizontal Flight_
All have treated the subject as though the
whole problem rested on the angle at which the
planes were placed。 At 45 degrees the lift and
drift are assumed to be equal。
LIFT AND DRIFT。The terms should be explained；
in view of the frequent allusion which
will be made to the terms hereinafter。 Lift
is the word employed to indicate the amount
which a plane surface will support while in flight。
Drift is the term used to indicate the resistance
which is offered to a plane moving forwardly
against the atmosphere。
_Fig。 3。 Lift and Drift_
In Fig。 3 the plane A is assumed to be moving
forwardly in the direction of the arrow B。 This
indicates the resistance。 The vertical arrow C
shows the direction of lift； which is the weight
held up by the plane。
NORMAL PRESSURE。Now there is another term
much used which needs explanation； and that is
normal pressure。 A pressure of this kind
against a plane is where the wind strikes it at
right angles。 This is illustrated in Fig。 4； in
which the plane is shown with the wind striking
it squarely。
It is obvious that the wind will exert a greater
force against a plane when at its normal。 On the
other hand； the least pressure against a plane is
when it is in a horizontal position； because then
the wind has no force against the surfaces； and
the only effect on the drift is that which takes
place when the wind strikes its forward edge。
_Fig。 4。 Normal Air Pressure_
_Fig。 5。 Edge Resistance_
HEAD RESISTANCE。Fig。 5 shows such a plane；
the only resistance being the thickness of the
plane as at A。 This is called head resistance；
and on this subject there has been much controversy；
and many theories； which will be considered
under the proper headings。
If a plane is placed at an angle of 45 degrees
the lift and the drift are the same； assumedly； because；
if we were to measure the power required
to drive it forwardly； it would be found to equal
the weight necessary to lift it。 That is； suppose
we should hold a plane at that angle with a heavy
wind blowing against it； and attach two pairs of
scales to the plane； both would show the same
pull。
_Fig。 6。 Measuring Lift and Drift_
MEASURING LIFT AND DRIFT。In Fig。 6； A is the
plane； B the horizontal line which attaches the
plane to a scale C； and D the line attaching it to
the scale E。 When the wind is of sufficient force
to hold up the plane； the scales will show the same
pull； neglecting； of course； the weight of the
plane itself。
PRESSURE AT DIFFERENT ANGLES。What every
one wants to know； and a subject on which a
great deal of experiment and time have been expended；
is to determine what the pressures are at
the different angles between the horizontal； and
laws have been formulated which enable the pressures
to be calculated。
DIFFERENCE BETWEEN LIFT AND DRIFT IN MOTION。The
first observation is directed to the differences
that exist between the lift and drift；
when the plane is placed at an angle of less than
45 degrees。 A machine weighing 1000 pounds
has always the same lift。 Its mass does not
change。 Remember； now； we allude to its mass；
or density。
We are not now referring to weight； because
that must be taken into consideration； in the
problem。 As heretofore stated； when an object
moves horizontally； it has less weight than when
at rest。 If it had the same weight it would not
move forwardly； but come to rest。
When in motion； therefore； while the lift； so
far as its mass is concerned； does not change； the
drift does decrease； or the forward pull is less
than when at 45 degrees； and the decrease is less
and less until the plane assumes a horizontal position；
where it is absolutely nil； if we do not consider
head resistance。
TABLES OF LIFT AND DRIFT。All tables of Lift
and Drift consider only the air pressures。 They
do not take into account the fact that momentum
takes an important part in the translation of an
object； like a flying machine。
A mass of material； weighing 1000 pounds while
at rest； sets up an enormous energy when moving
through the air at fifty； seventy…five； or one hundred
miles an hour。 At the latter speed the movement
is about 160 feet per second； a motion which
is nearly sufficient to maintain it in horizontal
flight； independently of any plane surface。
Such being the case； why take into account only
the angle of the plane？ It is no wonder that
aviators have not been able to make the theoretical
considerations and the practical demonstrations
agree。
WHY TABLES OF LIFT AND DRIFT ARE WRONG。
A little reflection will show why such tables are
wrong。 They were prepared by using a plane
surface at rest； and forcing a blast of air against
the plane placed at different angles； and for determining
air pressures； this is； no doubt； correct。
But it does not represent actual flying conditions。
It does not show the conditions existing
in an aeroplane while in flight。
To determine this； short of actual experiments
with a machine in horizontal translation； is impossible；
unless it is done by taking into account
the factor due to momentum and the element
attributable to the lift of the plane itself due to its
impact against the atmosphere。
LANGLEY'S LAW。The law enunciated by
Langley is； that the greater the speed the less the
power required to propel it。 Water as a propelling
medium has over seven hundred times
more force than air。 A vessel having； for instance；
twenty horse power； and a speed of ten
miles per hour； would require four times that
power to drive it through the water at double the
speed。 The power is as the square of the speed。
With air the conditions are entirely different。
The boat submergence in the water is practically
the same； whether going ten or twenty miles a