按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！
the plane pushes up from below； and is arrested by the top of the arch； but
the downward dip of the rear portion of the plane is of service in actually
DRAWING THE AIR FROM ABOVE。 The rapid air stream which has
been cut by the entering edge passes above the top of the curve； and
〃sucks up〃； as it were； so that the whole wing is pulled upwards。 Thus
there are two lifting impulses： one pushing up from below； the other
sucking up from above。
It naturally follows that when the camber is very pronounced the
machine will fly much slower； but will bear a greater weight than a
machine equipped with planes having little or no camber。 On high…speed
machines； which are used chiefly for racing purposes； the planes have very
little camber。 This was particularly noticeable in the monoplane piloted by
Mr。 Hamel in the Aerial Derby of 1913： the wings of this machine seemed
to be quite flat； and it was chiefly because of this that the pilot was able to
maintain such marvellous speed。
The scientific study of the wing lift of planes has proceeded so far that
the actual 〃lift〃 can now be measured； providing the speed of the machine
is known； together with the superficial area of the planes。 The designer can
calculate what weight each square foot of the planes will support in the air。
Thus some machines have a 〃lift〃 of 9 or 10 pounds to each square foot of
wing surface； while others are reduced to 3 or 4 pounds per square foot。
76
… Page 77…
THE MASTERY OF THE AIR
CHAPTER XXV The Wright Biplane （Cont。）
The under part of the frame of the Wright biplane； technically known
as the CHASSIS； resembled a pair of long 〃runner〃 skates； similar to those
used in the Fens for skating races。 Upon those runners the machine moved
along the ground when starting to fly。 In more modern machines the
chassis is equipped with two or more small rubber…tyred wheels on which
the machine runs along the ground before rising into the air； and on which
it alights when a descent is made。
You will notice that the pilot's seat is fixed on the lower plane； and
almost in the centre of it； while close by the engine is mounted。 Alongside
the engine is a radiator which cools the water that has passed round the
cylinder of the engine in order to prevent them from becoming overheated。
Above the lower plane is a similar plane arranged parallel to it； and the
two are connected by light upright posts of hickory wood known as
STRUTS。 Such an aeroplane as this； which is equipped with two main
planes； known as a BIPLANE。 Other types of air…craft are the
MONOPLANE； possessing one main plane； and the TRIPLANE；
consisting of three planes。 No practical machine has been built with more
than three main planes； indeed； the triplane is now almost obsolete。
The Wrights fitted their machine with two long…bladed wooden screws；
or propellers； which by means of chains and sprocket…wheels； very like
those of a bicycle； were driven by the engine； whose speed was about
1200 revolutions a minute。 The first motor engine used by these clever
pioneers had four cylinders； and developed about 20 horsepower。
Nowadays engines are produced which develop more than five times that
power。
In later machines one propeller is generally thought to be sufficient； in
fact many constructors believe that there is danger in a two…propeller
machine； for if one propeller got broken； the other propeller； working at
full speed； would probably overturn the machine before the pilot could cut
off his engine。
Beyond the propellers there are two little vertical planes which can be
moved to one side or the other by a control lever in front of the pilot's seat。
77
… Page 78…
THE MASTERY OF THE AIR
These planes or rudders steer the machine from side to side； answering the
same purpose as the rudder of a boat。
In front of the supporting planes there are two other horizontal planes；
arranged one above the other； these are much smaller than the main planes；
and are known as the ELEVATORS。 Their function is to raise or lower the
machine by catching the air at different angles。
Comparison with a modern biplane； such as may be seen at an
aerodrome on any 〃exhibition〃 day； will disclose several marked
differences in construction between the modern type and the earlier Wright
machine； though the central idea is the same。
78
… Page 79…
THE MASTERY OF THE AIR
CHAPTER XXVI How the Wrights launched their
Biplane
Those of us who have seen an aeroplane rise from the ground know
that it runs quickly along for 50 or 60 yards； until sufficient momentum
has been gained for the craft to lift itself into the air。 The Wrights； as stated；
fitted their machine with a pair of launching runners which projected from
the under side of the lower plane like two very long skates； and the
method of launching their craft was quite different from that followed
nowadays。
The launching apparatus consisted of a wooden tower at the starting
end of the launching waysa wooden rail about 60 or 70 feet in length。 To
the top of the tower a weight of about 1/2 ton was suspended。 The
suspension rope was led downwards over pulleys； thence horizontally to
the front end and back to the inner end of the railway； where it was
attached to the aeroplane。 A small trolley was fitted to the chassis of the
machine and this ran along the railway。
To launch the machine； which； of course； stood on the rail； the
propellers were set in motion； and the 1/2…ton weight at the top of the
tower was released。 The falling weight towed the aeroplane rapidly
forward along the rail； with a velocity sufficient to cause it to glide
smoothly into the air at the other end of the launching ways。 By an
ingenious arrangement the trolley was left behind on the railway。
It will at once occur to you that there were disadvantages in this
system of comm