aeroplanes-第15章
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overturning of the machine。 Many have had accidents
where the machine landed right side up； even
where the fall was from a great height； and the
only damage to the aviator was bruises。 Few； if
any； pilots have escaped where the machine has
overturned。
It is far better； in case the tank is light； to have
it detached from its position； when the ship strikes
the earth； because in doing so； it will not be so
likely to burn the imprisoned aviator。
In all cases the tank should be kept as far away
from the engine as possible。 There is no reason
why it cannot be placed toward the tail end of
the machine； a place of safety for two reasons：
First； it is out of the reach of any possible
danger from fire； and； second； the accidents in the
past show that the tail frame is the least likely to
be injured。
In looking over the illustrations taken from the
accidents； notice how few of the tails are even
disarranged； and in many of them； while the entire
fore body and planes were crushed to atoms；
the tail still remained as a relic； to show its
comparative freedom from the accident。
In all monoplanes the tail really forms part of
the supporting surface of the machine； and the
adding of the weight of the gasoline would be
placing but little additional duty on the tail； and
it could be readily provided for by a larger tail
surface； if required。
THE CLOSED…IN BODY。The closed…in body is a
vast improvement； which has had the effect of
giving greater security to the pilot； but even this
is useless in case of overturning。
STARTING THE MACHINE。The direction in which
improvements have been slow is in the starting
of the machine。 The power is usually so mounted
that the pilot has no control over the starting；
as he is not in a position to crank it。
The propeller being mounted directly on the
shaft； without the intervention of a clutch； makes
it necessary； while on the ground； for the propeller
to be started by some one outside； while
others hold the machine until it attains the proper
speed。
This could be readily remedied by using a
clutch； but in the past this has been regarded as
one of the weight luxuries that all have been trying
to avoid。 Self starters are readily provided；
and this with the provision that the propeller can
be thrown in or out at will； would be a vast improvement
in all machines。
PROPELLERS WITH VARYING PITCH。It is growing
more apparent each day； that a new type of
propeller must be devised which will enable the
pilot to change the pitch； as the speed increases；
and to give a greater pitch； when alighting； so
as to make the power output conform to the conditions。
Such propellers； while they may be dangerous；
and much heavier than the rigid type； will； no
doubt； appear in time； and the real improvement
would be in the direction of having the blades
capable of automatic adjustment； dependent on
the wind pressure； or the turning speed； and thus
not impose this additional duty on the pilot。
CHAPTER XI
FLYING MACHINE ACCESSORIES
THE ANEMOMETER。It requires an expert to
judge the force or the speed of a wind； and even
they will go astray in their calculations。 It is
an easy matter to make a little apparatus which
will accurately indicate the speed。 A device of
this kind is called an Anemometer。
Two other instruments have grown out of this；
one to indicate the pressure； and the other the
direction of the moving air current。
THE ANEMOGRAPH。While these instruments indicate；
they are also made so they will record the
speed； the pressure and the direction； and the device
for recording the speed and pressure is called
a Anemograph。
All these instruments may be attached to the
same case； and thus make a handy little device；
which will give all the information at a glance。
THE ANEMOMETROGRAPH。This device for recording；
as well as indicating the speed； pressure
and direction； is called an Anemometrograph；
The two important parts of the combined
apparatus； for the speed and pressure； are illustrated；
to show the principle involved。 While the speed
will give the pressure； it is necessary to make a
calculation to get the result while the machine does
this for you。
_Fig。 61。 Speed Indicator。_
THE SPEED INDICATOR。Four hemispherical
cups A are mounted on four radiating arms B；
which are secured to a vertical stem C； and
adapted to rotate in suitable bearings in a
case； which； for convenience in explaining； is not
shown。
On the lower end of the stem C； is a small bevel
pinion； which meshes with a smaller bevel pinion
within the base。 This latter is on a shaft which
carries a small gear on its other end； to mesh
with a larger gear on a shaft which carries a
pointer D that thus turns at a greatly reduced
speed； so that it can be easily timed。
_Fig。 62。 Air Pressure Indicator。_
AIR PRESSURE INDICATOR。This little apparatus
is readily made of a base A which is provided
with two uprights B； C； through the upper ends of
which are holes to receive a horizontally…disposed
bar D。 One end of the bar is a flat plane
surface E； which is disposed at right angles to the
bar； and firmly fixed thereto。
The other end of the bar has a lateral pin to
serve as a pivot for the end of a link F； its other
end being hinged to the upper end of a lever G；
which is pivoted to the post C； a short distance
below the hinged attachment of the link F； so
that the long end of the pointer which is constituted
by the lever G is below its pivot； and has；
therefore； a long range of movement。
A spring I between the upper end of the pointer
G and the other post B； serves to hold the pointer
at a zero position。 A graduated scale plate J；
within range of the pointer will show at a glance
the pressure in pounds of the moving wind； and
for this purpose it would be convenient to make
the plane E exactly one foot square。
DETERMINING THE PRESSURE FROM THE SPEED。
These two instruments can be made to check each
other and thus pretty accurately enable you to
determine the proper places to mark the pressure
indicator； as well as to make the wheels in the
anemometer the proper size to turn the pointer
in seconds when the wind is blowing at a certain
speed； say ten miles per hour。
Suppose the air pressure indicator has the scale
divided into quarter pound marks。 This will
make it accurate enough for all purposes。
CALCULATING PRESSURES FROM SPEED。The following
table will give the pressures from 5 to 100
miles per hour：
Velocity of wind in Pressure Velocity of wind in Pressure
miles per hour per sq。 ft。 miles per hour per sq ft
5 。112 55 15。125
10 。500 60 18。000
15 1。125 65 21。125
20 2。000 70 22。500
25 3。125 75 28。125
30 4。600 80 32。000
35 6。126 86 36。126
40 8。000 90 40。500
45 10。125 95 45。125
50 12。5 100 50。000
HOW THE FIGURES ARE DETERMINED。The foregoing
figures are determined in the following manner：
As an example let us assume that the velocity
of the wind is forty…five miles per hour。 If
this is squared； or 45 multiplied by 45； the product
is 2025。 In many calculations the mathematician
employs what is called a constant； a figure that
never varies； and which is used to multiply or
divide certain factors。
In this case the constant is 5/1000； or； as usually
written； 。005。 This is the same as one two hundredths
of the squared figure。 That would make
the problem as follows：
45 X 45 = 2025 / 200 = 10。125； or；
45 X 45 … 2025 X 。005 = 10。125。
Again； twenty…five miles per hour would be
25 X 25 = 625； and this multiplied by 。005 equals
2 pounds pressure。
CONVERTING HOURS INTO MINUTES。It is sometimes
confusing to think of miles per hour； when
you wish to express it in minutes or seconds。 A
simple rule； which is not absolutely accurate； but
is correct within a few feet； in order to express
the speed in feet per minute； is to multiply the
figure indicating the miles per hour； by 8 3/4。
To illustrate： If the wind is moving at the
rate of twenty miles an hour； it will travel in that
time 105；600 feet （5280 X 20）。 As there are sixty
minutes in an hour； 105；600 divided by 60； equals
1760 feet per minute。 Instead of going through
all this process of calculating the speed per minute；
remember to multiply the speed in miles per
hour by 90； which will give 1800 feet。
This is a little more then two per cent。 above
the correct figure。 Again； 40 X 90 equals 3600。
As the correct figure is 3520； a little mental calculation
will enable you to correct the figures so
as to get it within a few feet。
CHANGING SPEED HOURS TO SECONDS。As one…
sixtieth of the speed per minute will represent the
rate of movement per second； it is a comparatively
easy matter to convert the time from speed in
miles per hour to fraction of a mile traveled in
a second； by merely taking one…half of the speed
in miles； and adding it； which will very nearly express
the true number of feet。
As examples； take the following： If the wind
is traveling 20 miles an hour； it is easy to take
one…half of 20； which is 10； and add it to 20； making
30； as the number of feet per second。 If the
wind travels 50 miles per hour； add 25； making
75； as the speed per second。
The correct speed per second of a wind traveling
20 miles an hour is a little over 29 feet。 At
50 miles per hour； the correct figure is 73 1/3 feet；
which show that the figures under this rule are
within about one per cent。 of being correct。
With the table before you it will be an easy
matter； by observing the air pressure indicator；
to determine the proper speed for the anemometer。
Suppose it shows a pressure of two pounds；
which will indicate a speed of twenty miles an
hour。 You have thus a fixed point to start from。
PRESSURE AS THE SQUARE OF THE SPEED。Now
it must not be assumed that if the pressure at
twenty miles an hour is two pounds； that forty
miles an hour it is four pounds。 The pressure
is as the square of the speed。 This may be explained
as follows： As the speed of the wind
increases； it has a more effective push against an
object than its rate of speed indicates； and this
is most simply expressed by saying that each time
the speed is doubled the pressure is four times
greater。
As an example of this； let us take a speed of ten
miles an hour； wh
