flying machines-第21章
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18。03 squared X 0。00327 = 1。063 pounds per square foot。
If we apply Lilienthal's co…efficients for an angle of
6 degrees 26'； we have for the force in action：
Normal： 4。57 X 1。063 X 0。912 = 4。42 pounds。
Tangential： 4。57 X 1。063 X 0。074 = … 0。359 pounds；
which latter； being negative； is a propelling force。
Results Astonish Scientists。
Thus we have a bird weighing 4。25 pounds not only
thoroughly supported； but impelled forward by a force
of 0。359 pounds； at seventeen miles per hour； while the
experiments of Professor A。 F。 Zahm showed that the
resistance at 15。52 miles per hour was only 0。27 pounds；
17 squared
or 0。27 X … = 0。324 pounds； at seventeen miles an
15。52 squared
hour。
These are astonishing results from the data obtained；
and they lead to the inquiry whether the energy of the
rising air is sufficient to make up the losses which occur
by reason of the resistance and friction of the bird's body
and wings； which； being rounded； do not encounter air
pressures in proportion to their maximum cross…section。
We have no accurate data upon the co…efficients to apply
and estimates made by myself proved to be much
smaller than the 0。27 pounds resistance measured by
Professor Zahm； so that we will figure with the latter
as modified。 As the speed is seventeen miles per hour； or
24。93 feet per second； we have for the work：
Work done； 0。324 X 24。93 = 8。07 foot pounds per second。
Endorsed by Prof。 Marvin。
Corresponding energy of rising air is not sufficient at
four miles per hour。 This amounts to but 2。10 foot pounds
per second； but if we assume that the air was rising at
the rate of seven miles per hour （10。26 feet per second）；
at which the pressure with the Langley coefficient would
be 0。16 pounds per square foot； we have on 4。57 square
feet for energy of rising air： 4。57 X 0。16 X 10。26 = 7。50
foot pounds per second； which is seen to be still a little
too small； but well within the limits of error； in view of
the hollow shape of the bird's wings； which receive
greater pressure than the flat planes experimented upon
by Langley。
These computations were chiefly made in January；
1899； and were communicated to a few friends； who found
no fallacy in them； but thought that few aviators would
understand them if published。 They were then submitted
to Professor C。 F。 Marvin of the Weather Bureau； who
is well known as a skillful physicist and mathematician。
He wrote that they were； theoretically； entirely sound
and quantitatively； probably； as accurate as the present
state of the measurements of wind pressures permitted。
The writer determined； however； to withhold publication
until the feat of soaring flight had been performed by
man； partly because he believed that； to ensure safety； it
would be necessary that the machine should be equipped
with a motor in order to supplement any deficiency in
wind force。
Conditions Unfavorable for Wrights。
The feat would have been attempted in 1902 by Wright
brothers if the local circumstances had been more favorable。
They were experimenting on 〃Kill Devil Hill；〃
near Kitty Hawk； N。 C。 This sand hill； about 100 feet
high； is bordered by a smooth beach on the side whence
come the sea breezes； but has marshy ground at the back。
Wright brothers were apprehensive that if they rose on
the ascending current of air at the front and began to
circle like the birds； they might be carried by the
descending current past the back of the hill and land in
the marsh。 Their gliding machine offered no greater
head resistance in proportion than the buzzard； and their gliding
angles of descent are practically as favorable； but
the birds performed higher up in the air than they。
Langley's Idea of Aviation。
Professor Langley said in concluding his paper upon
〃The Internal Work of the Wind〃：
〃The final application of these principles to the art of
aerodromics seems； then； to be； that while it is not likely
that the perfected aerodrome will ever be able to dispense
altogether with the ability to rely at intervals on
some internal source of power； it will not be indispensable
that this aerodrome of the future shall； in order to
go any distanceeven to circumnavigate the globe without
alightingneed to carry a weight of fuel which
would enable it to perform this journey under conditions
analogous to those of a steamship； but that the fuel and
weight need only be such as to enable it to take care of
itself in exceptional moments of calm。〃
Now that dynamic flying machines have been evolved
and are being brought under control； it seems to be
worth while to make these computations and the succeeding
explanations known； so that some bold man will
attempt the feat of soaring like a bird。 The theory
underlying the performance in a rising wind is not new；
it has been suggested by Penaud and others； but it has
attracted little attention because the exact data and the
maneuvers required were not known and the feat had
not yet been performed by a man。 The puzzle has always
been to account for the observed act in very light
winds； and it is hoped that by the present selection of
the most difficult case to explaini。 e。； the soaring in a
dead horizontal calmsomebody will attempt the exploit。
Requisites for Soaring Flights。
The following are deemed to be the requisites and
maneuvers to master the secrets of soaring flight：
1stDevelop a dynamic flying machine weighing
about one pound per square foot of area； with stable
equilibrium and under perfect control； capable of gliding
by gravity at angles of one in ten （5 3/4 degrees） in still air。
2nd。Select locations where soaring birds abound and
occasions where rising trends of gentle winds are frequent
and to be relied on。
3rd。Obtain an initial velocity of at least 25 feet per
second before attempting to soar。
4th。So locate the center of gravity that the apparatus
shall assume a negative angle； fore and aft； of about 3 degrees。
Calculations show； however； that sufficient propelling
force may still exist at 0 degrees； but disappears entirely at
＋4 degrees。
5th。Circle like the bird。 Simultaneously with the
steering； incline the apparatus to the side toward which
it is desired to turn； so that the centrifugal force shall
be balanced by the centripetal force。 The amount of the
required inclination depends upon the speed and on the
radius of the circle swept over。
6th。Rise spirally like the bird。 Steer with the
horizontal rudder； so as to descend slightly when going
with the wind and to ascend when going against the
wind。 The bird circles over one spot because the rising
trends of wind are generally confined to small areas or
local chimneys； as pointed out by Sir H。 Maxim and
others。
7th。Once altitude is gained； progress may be made
in any direction by gliding downward by gravity。
The bird's flying apparatus and skill are as yet infinitely
superior to those of man； but there are indications that
within a few years the latter may evolve more accurately
proportioned apparatus and obtain absolute control over
it。
It is hoped； therefore； that if there be found no radical
error in the above computations； they will carry the conviction
that soaring flight is not inaccessible to man； as
it promises great economies of motive power in favorable
localities of rising winds。
The writer will be grateful to experts who may point
out any mistake committed in data or calculations； and
will furnish additional information to any aviator who
may wish to attempt the feat of soaring。
CHAPTER XXI。
FLYING MACHINES VS。 BALLOONS。
While wonderful success has attended the development
of the dirigible （steerable） balloon the most ardent
advocates of this form of aerial navigation admit that it
has serious drawbacks。 Some of these may be described
as follows：
Expense and Other Items。
Great Initial Expense。The modern dirigible balloon
costs a fortune。 The Zeppelin； for instance； costs more
than 100；000 （these are official figures）。
Expense of Inflation。Gas evaporates rapidly； and a
balloon must be re…inflated； or partially re…inflated； every
time it is used。 The Zeppelin holds 460；000 cubic feet
of gas which； even at 1 per thousand； would cost 460。
Difficulty of Obtaining Gas。If a balloon suddenly
becomes deflated； by accident or atmospheric conditions；
far from a source of gas supply； it is practically worthless。
Gas must be piped to it； or the balloon carted to
the gas housean expensive proceeding in either event。
Lack of Speed and Control。
Lack of Speed。Under the most favorable conditions
the maximum speed of a balloon is 30 miles an hour。
Its great bulk makes the high speed attained by flying
machines impossible。
Difficulty of Control。While the modern dirigible balloon is
readily handled in calm or light winds； its bulk
makes it difficult to control in heavy winds。
The Element of Danger。Numerous balloons have
been destroyed by lightning and similar causes。 One of
the largest of the Zeppelins was thus lost at Stuttgart
in 1908。
Some Balloon Performances。
It is only a matter of fairness to state that； under
favorable conditions； some very creditable records have
been made with modern balloons； viz：
November 23d； 1907； the French dirigible Patrie； travelled
187 miles in 6 hours and 45 minutes against a
light wind。 This was a little over 28 miles an hour。
The Clement…Bayard； another French machine； sold
to the Russian government； made a trip of 125 miles at
a rate of 27 miles an hour。
Zeppelin No。 3； carrying eight passengers； and having
a total lifting capacity of 5；500 pounds of ballast in
addition to passengers； weight of equipment； etc。； was
tested in October； 1906； and made 67 miles in 2 hours
and 17 minutes； about 30 miles an hour。
These are the best balloon trips on record； and show
forcefully the limitations of speed； the greatest being not
over 30 miles an hour。
Speed of Flying Machines。
Opposed to the balloon performances we have flying
machine trips （of authentic records） as follows：
Bleriotmonoplanein 190852 miles an hour。
DelagrangeJune 22； 190810 1/2 miles in 16 minutes；
approximately 42 miles an hour。
WrightsOctober； 1905the machine was then in its
infancy24 miles in 38 minutes； approximately 44 miles
an hour。 On December 31； 1908； the Wrights made 77
miles in 2 hours and 20 minutes。
Lambert； a pupil of the Wrights； and using a Wright
biplane； on October 18； 1909； covered 29。82 miles in 49
minutes and 39 seconds； being at the rate of 36 miles
an hour。 This flight was made at a height of 1；312 feet。
LathamOctober 21； 1909made a short flight； about
11 minutes； in the teeth
