New-York tribune. [volume] (New York [N.Y.]) 1866-1924, 1906-02-05
THE THEORY OF FLIGHT.
Conditions Under Which Alone 1t
Would BE of Service to Mankind.
To the Editor OF The Tribune.

Would BE of Service to Mankind.
To the Editor OF The Tribune
Sir: Being Ike The Tribune interested n ths
attempts Of inventors 10 navigate the air 7 am
prompted by your editorial OF the 18th instant to
offer brief discussion OF the subject In the first
place. flight 20 be OF value man must be dirfgi-
bic. controIabe. and reasonably safe and speedy
The flyer must be able 70 start and alight al will
that is bird fight Is the only true. practicable OF
useful flight II Is easily seen that projectory Is
not true flight in any sense neither is kitinz or
any device by which surface plane Is held
against air current In such way that IL will
be caused 10 rise It derives its power rise from
the cord or equivalent arrangement by which il Is
held. and will Immediately fan helpless II II Is sep
arated from H. 1t is equally true that useful flight
cannot be secured by charging the flying machine
so that its specific gravity will be the same al
that OF the atmosphere for this renders its size
great that any reasonable speed would be tmpossi-
ble and. furthermore. it would be entirely helpless
In adverse air currents. Air navigation by such
means Is more nearly analogous 10 the swimming
OF the fish than true aerial flight. Nature FUR
nishes no swimmers for the atmosphere. and "
man ever flies he will make OF the same me-
chanical principles that the bird does sustain
and propel himself The crucial query IN this whole
study is. then. How does the bird Ay7
We observe. first. that the bird is heavier IN bulk
weight than the element in which he moves. u
takes power to keep him up. His wings him
for this purpose. We observe that he has no d.
rect means for propulsion He cannot use his TAIL
as the fish can, TO move himself either forward or
backward Whence, then does he get his speed
In flight? First. notice that his wings
attached 70 his body above its Of gravity
and to the OF It. Now. If the wing power were
exerted directly over the centre Of the weight Of
the body and were sufficient to overcome gravita-
tton the bird could raise himself vertically with
no forward movement, but with the centre OF
gravity forward Of the line Of the wing lift some
thing else happens. The wings instead OF lifting
,ne bird in vertical direction opposing gravity.
nit to pitch q the ne boy Of me q b Eafy 20
me me wings lift him 50 that between The tive
as Wing ft preventing the Srd from falling ne
this theory OF flight is c0rrect that the furtha-
forward the centre of weight is from the wing nft
Observe the hawk When slowly crciinE over
forward. nearly balancing his weight but when he
darts with great speed toward his prey his wings
The Same thing can be noticed in the fight OF the
fSMSTd baa SoW sT gat hi bis wings are held vel
he holds his wings.
Birds which are most skilfuI and artistic flyers
are those which have the ability hold their wings
forward or backward, thus shifting the relative
OF the body It viii be seen that IL is impossiofs
Wtbog 9 OFa 70 ny 6aSswsTd or IN fact 70 ny at an
that to sustain flight the bird must have a bulk
wise gravity would supply the necessary pulling
SowI stra!n upon which his forward movement
sneed In the water. and can remain stationary,
ward or in any direction The bird opposes gravity
with his wings only The downward stroke OF tbs
wing llfts the bird. After the stroke the wing
must be raised to position for another stroke. az
some loss OF power The bird has to depend for
support upon the excess IN effectiveness Of tbs
downward over the upward stroke OF its wings. II
would seem that art could improve upon nature bv
the use OF wings OF rotary motion, whereby they
would exert constant instead OF intermittent lift
ing power, practically The same il has improved
upon nature in the matter OF terrestrial locomoton
by the substitution of wheels for legs and feet
New-MlfOrd Ohio. Jan. 81. 1905. H NJ d
lin the main this correspondent Is correct. but
he is hardly justified IN saying that bird flight
Is "the only true. practicable and useful flight"
In the first place by whatever name II be called.
progress through the air is effected by machines
of the Santos-DumOnt model which do not resem-
bic birds at all That method OF aerial navigation.
too. promises great usefulness as any other
Finally. H. NJ D. comedies that IL IL desirable
he might have said necessary-to improve on
nature in respect. The use OF wings for
propulsion has not been proved practicable in
aeronautics, and probably never viii be- A DIFF
ferent sort OF mechanism is required for human
service Rotary motion. instead Of reciprocating
motion. has already been employed with sue
cess. that the advice on that score has been
anticipated. Whether anything better than the
screw propeller can be devised for the purpose
is doubtful Devotees OF both the gas bag and
aeroplane depend on that device its superiority
over the paddle wheel being more obvious in
aerial navigation than the water. Finally IL
is due 10 Professor Bell and other men who are
experimenting with kites to remember that
towing with cord is only temporary expedi-
ent adopted while testing some other feature
Of their inventions. Eventually Professor Bell
means to add light engine and propelIers TO his
design