898,

——.

vithin ys at ir in

SON,

1 to nda

cle ble

THE AERONAUTICAL JOURNAL.

APRIL,

1898.

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NOTICES

Che Aeronautical Sotiety.

; Of soaring and non-soaring bird’s

The Possibility of Soaring in Horizontal Wind.

(Paper read before the Royal Society of New South Wales by L. HARGRAVE, )

There is a publication called the Aeronauti- cal Annual,” edited by®James Means, Boston, Mass. In No. Z and 3 of that work, Mr. Octave Chanute goes exhaustively intu the question of sailing flight, and specifies every letter and article that bears on the subject. This paper may be said to take up the running where Mr. Chanute leaves off. My reasons for not writing

| to that periodical straight, are that publication

would be delayed for many months; and the state of the art is such that at any moment some one of the many who are investigating this subject may drop on the facts stated in this paper, take out a master patent which would rule the construction of all future flying machines, and tax us all round for our good, as the protectionists say, thus throwing our work back for years. I therefore, with your permission, read this paper, and show the models that work as I describe, and thereby destroy the novelty of the invention for all time.

The point of doubt has been, how to account for the phenomenon of soaring in a horizontal wind. There is no difficulty in soaring if we assume an upward trend in the wind such as a cliff, building, or sloping hill will produce. But when we see birds soaring in light wind and storm, something beyond our knowledge is recognised as being at work.

Mr. Chanute shows the profile of a number wings, and

| points out the downward projecting lobe at the

| |

A Meeting of the Council was held on

Feb. 24th, when the following gentlemen were elected Members of the Society :— Mr. W. F. Rew, C.E. Mr. B. F. Brooke Sewetu. Capt. L. S. Buackpen, West India Regt.

B. BADEN-POWELL, Carr., Hon. Sec.

front edge of the former, and also that there

| isa sharp curve just abaft the lobe on the under side.

(Figure 1.)

akariag Wing

ies 2

A few experiments have been made at Stan- well Park to show how this affects the effective direction of the wind when soaring, with the

30 ; i s

result, as I previously surmised, that it was found to create a vortex, and that the direction of the air current beneath the wing was that indicated by the arrows in Figure 1.

The apparatus used was a small bellows, a bent piece of sheet aluminium and a candle.

THE AERONAUTICAL JOURNAL.

The centre of the vortex was found to be ap- | | strongly in the direction of the arrow (Fig. 6).

proximately at the centre of the curve of the fore part of the aluminium sheet. (Figure2).

The candle, you obserye, is not masked by the |

leading edge.

3, and the candle was blown in a

manner showing that in this case the vortex was elliptic. The pressure at A must be greater than at C or the candle flame would blow parallel to the blast. As a first attempt to show that the pressure at A was greater than at B, I cut a small hole at B and gummed a tissue paper valve opening towards B. I could not be certain that air was passing through it.

A portable forge was now arranged to deliver air through a two-inch horizontal tin tube, and various devices were used for hanging things in front of the blast. Among others an old and rough gull’s wing showed the loose feathers blowing towards the front edge. (Figure 4.)

Culls wir

cise sr i aaa fe Te Bie: cial

When a piece of the wing was cut off and hung at eleven inches from the blast with a negative angle of about 28 degs., it at once began to revolve in an elliptic orbit, the feathers on iue under side of the wing being

rufied back at positions A and B (Figure 5). When attempting to repeat this ex-

periment the wing could only be made to re- volve in a contrary orbit to that shown in the

{April 898.

——»

figure. A piece of aluminium without a bulb would only swing very slightly in the line of blast.

A piece of tin folded with a bulb at the forward edge and some pieces of down gummed on the concave side, was set at a positive angle of about 6 degs., the down at the bulb blew

Fig 6

Thirty-two three-quarter inch square holes

| were cut in a curved piece of aluminium

|

The quasi-wing was then bent like Figure | flame

(Figure 7), and each hole was fitted with a

yr 2 eT

4

Aluminium acth » waders

/ i Fiq 7

| tissue paper valve lifting on the curved side.

| it towards the blast.

When the chord of the curve was at about zero, A and B sets of valves lifted tangential to the leading edge, and C and D sets of valves were fluttering with the blast.

A level sheet of glass with a little water on it was placed in the line of blast, and the curved tin (Figure 6) standing in the water with a sprinkling of red ochre, shows the vortex ata negative angle of about 30 degs. The tin was set at zero, but the after edge was slued round to 30 degs. by the rotation of the vortex.

This is all very well as far as it goes, but something .is wanted that would eliminate errors of direction of the wind, and some of the uncertainty as to the angles, and also to compare the curve with the plane surface. So I fixed a horizontal wire on a stand and pointed A sleeve was on the wire revolving freely. On opposite sides of the sleeve I attached a bulb ended curved piece of aluminium and a piece approximately flat, with set screws to fix them at any angle with the direction of blast. There was a lead weight for balancing in the plane of rotation. There was nothing to stop the sleeve from slipping along the wire, which it did not do.

You will observe that with this apparatus if my personal equation gave any advantage to the curve it would be eliminated when the sleeve revolved 180 degs., and that both sur- faces received a blast of equal intensity, and that placing the two surfaces on opposite sides of one axis is equivalent to weighing their re- spective lifting powers in a pair of scales.

The plane and chord of the curve were first set at a slight positive angle (Figure 8). In this case the curve easily rotated the sleeve against the lift of the plane. There might possibly be no vortex under the curve,

bulb > of

the ned igle lew

les

r0, he Te

on ed th

as

id

April, 1898.|

THE AERONAUTICAL ¥OURNAL. 31

and the stronger rotating force might be due to the greater angle of slope of the after part of the curve.

The plane and the chord of the curve were next set parallel to the line of blast (Figure 9). In this case the lifting force opposed

by the plane to the curve was nothing, although its resistance was that due to its area and the velocity of the blast, and the lift of the vortex under the curve easily overcame this.

In Figure 10 the plane was left parallel

Zs.2

to the blast, and the curve sloped at | a negative angle; this angle was increased to | at least 10 degs., and the lift of the curve still |

rotated the sleeve against the resistance of | the plane. In Figure

put at

11 the plane was

a positive angle of 6 degs., that is, 16 degs. between the plane and the curve. The plane was now able to rotate the curve against the vortex. Figs. 12, 13, 14, 15, show the stream lines of the air when it meets a curve set at various angles.

To recapitulate, the experiments show—

1. That the profile of a soaring bird’s wing and pieces of metal of a somewhat similar curve generate vortices on the concave sur- faces when the chord of the curves makes a negative angle with the direction of the wind.

2. All the concave surfaces are in contact with air moving towards the mean direction of the wind.

3. That the mean pressure on the concave surface is higher than on the convex side.

4. That the chord of the curved metal may make a negative angle of 10 deg. with the direction of the wind, and still have a higher pressure on the concave side than on the con- vex.

And the direct inference is that gravity can be entirely counteracted by a volume of dis- turbed air moving in a horizontal direction ; and that flying machines of great weight can be held suspended in a horizontal wind, and rise vertically without the expenditure of any contained motor force.

Having put matters so that anyone can easily repeat my experiments and elaborate them to the last degree of precision, we now see why the pest soaring is done in steady winds. The answer is, the bird is less liable to lose its vortices by a sudden gust and have to take a flap or two to balance itself on a fresh pair. The difference between flying and soaring is that the air in contact with we underside of the wing is moving towards the bird’s head when soaring and towards the tail when flying. A soaring bird’s wing is a shield dividing two currents of air moving in contrary directions. The vortex draws towards the shield and pushes it into the low pressure above the wing.

There is a very similar experiment described at pages 79, 80, of this Society’s (R.S. of N.S.W.) Journal for 1893, but I then failed to see the true cause of the phenomenon, and thought the ar currents were those shown in the flying wing (Figure 1), whereas the currents were those of the soaring wing.

Mr. Chanute says that Dr. Thomas Young, the great physicist, showed in 1800 that a curve S-like surface suspended horizontally by a thread advanced against an air jet imping- ing upon its upper surface.” If this S-like surface proves to be like Figure 16, and he explains the cause to be the vortex shown

32

THE AERONAUTICAL $OURNAL.

[April 1898.

therein, it is only another proof that there is nothing new under the sun. The turn-up tail is now being experimented with, as I think

pe 5 Fig 6

it provides automatic stability in a fore and aft direction.

Having experienced much of the mono- tonous process of repairing broken models, I have now devised and am using a method of experimenting that practically enables me to

avoid all breakages. The apparatus used is well shown in the illustration which I think will advance the art of aerial navigation more than any amount of laboratory experiments. The two poles are twenty-four feet high and forty-eight feet apart. There is a cord between the tops of the poles, and the string of the soaring kite is tied to the middle of the cord at a sufficient height to prevent it striking the ground. I stand to leeward of the poles and

start the soaring kite at a positive angle; it then flies as an ordinary kite to near the zenith. The vortex then forms under the curved aluminium surfaces and draws the apparatus at the full stretch of the string and cord, through the 180 degs, of arc to windward of the poles. The flag shows the wind to be hori- zontal, and the string that is plainly visible in the photograph shows the soaring kite pull- ing about 20 degs. to windward of the zenith. The wind was blowing at twelve or fourteen miles per hour, which was inadequate to effect the best pull the affair is capable of.

The projected area of the two curved sur- faces is one hundred and eighty-nine square

inches, and the weight is one pound four and a half ounces. The cylindrical aluminium tail is a serviceable construction. As yet I have been unable to make the kite stop when at or beyond the zenith, but the wind has been re- markably light for many weeks and few trials have taken place.

A very few trials will convince the most sceptical that if we are not soaring in moder- ate breezes before the end of the century it

th. us

he ri- ble ill-

April, 1898.1]

will not be from ignorance of the way to do it. It is obvious that soaring sails for marine propulsion have a vast future before them: and it is probable that craft so rigged will make better weather with a gale in their teeth than our best screw steamers.

Kites: Their Theory and Practice.’

(By Captain B. F. 8. BApEn-PoweLt, Scots Guards. )

The Kite, one of the oldest of inventions, familiar to everyone and to every nation under the sun, is nevertheless but little understood. It has always been the custom to look upon this contrivance as a toy and nothing else. Very seldom indeed, until the last few years, has it been put to any practical use. Yet it is full of promise, and those few who have made regular and careful experiments in this line have all been impressed with the satis- factory results obtained. A kite sailing in a wind gives a very considerable pull on its line, which pull can be converted into lifting power or tractive power. This appliance may then be used for lifting great weights, such as that of a man, tugh into the air, or it may be used for towing carts or boats. Kites can be made to ascend to very great heights, carrying up automatically registering meteorological instru- ments, or may carry a string to communicate with places a long distance off. Why then, it may be asked, are they not more often made use of? I believe the sole reason is that so few men have devoted any time to studying the theory of their actions, and that when the well-known rule-of-thumb patterns are de- parted from, innumerable difficulties crop up, and the apparatus, for some inexplicable reason, becomes frequently unsatisfactory, so that a cursory investigation of the subject only opens up a vista of obstacles apparently almost impossible to surmount.

But with a little practice and study the way becomes somewhat clearer, and, as we grope along, fresh discoveries are made which raise our hopes and show what great results we may possibly attain.

* A paper read at the Sosiety of} Arts on March 2nd, 898, Prof, W. Grylls Adams, F.R.S., in the chair.

THE AERONAUTICAL $¥OURNAL. 33

I.—PRACTICAL EXPERIENCES. Having devoted a considerable time to re- searches in this line, and with a view of throw-

| ing some light on the intricacies and difficulties

to be met with in kite-flying, I will briefly re- late my own personal experiences in this sub- ject. To begin with, I had one definite object in view. For some time I had been interested in and had practically worked with captive balloons for military purposes, and finding the behaviour of them so erratic in strong winds,

, to say nothing of the difficulties of construction | and inflation with gas, and of the cumbrous- | ness of the necessary apparatus, I was looking

about for some other means by which a man might be lifted to a height above the ground. Kites naturally soon suggested themselves, and on investigation I found that trials had actually been made on several occasions to lift a man by this means, but that these had invari- ably proved failures.

In 1887, I made several trials with small cam- bric kites. The largest of them was 10 ft. high, and had two cross-pieces about 4 ft. wide. This only lifted a weight of 2 lbs., which was attached to the tail. Many varieties of kites were tried. Some were of the ordinary diamond pattern, some had a bowed top; one was circular. I even got a kite to fly which was absolutely frameless. However, I came to no very definite conclusions, my experiments were knocked off, and I had no opportunity of continuing them for five years.

In 1892, I made trials with a 20 sq. ft. kite, from which I obtained two most important re- sults. The first was that I found it possible to do away with that appendage known as a “tail,” which I had hitherto presumed to be in- dispensable, and the second result was that by attaching a bag to the string some distance from the kite, I found I could put weights into it until the kite was able to lift a weight of 6 lbs. or more in a fairly strong, though not exceptional, breeze. This result, the lifting of ‘3 Ibs. per square foot of kite surface, was most encouraging, and convinced me that, under such circumstances, I should be able to lift a man with a kite of 500 square feet. I, there- fore, determined to go to a suitable place and carry out a regular series of experiments for a week or two. I thus learnt many lessons, one of the principal being to appreciate the fickle- ness and variability of the wind. A kite which flew perfectly one day would scarcely rise on another. It would be impossible to give any- thing like a detailed account of my numerous experiments. I tried a great variety in forms of kites and attachments of string. I have records of twenty-seven different days’ experi-

34 THE AERONAUTICAL $OURNAL.

[April, 1898

ments in that year, and many of them were devoted to very small details of construction. These experiments were continued the next year, but it really seems extraordinary how little actual progress resulted, so often did one particular idea have to be tried again and again under all conditions, before any decided con- clusion could be arrived at; and as often as not did I finally conclude that that whole series of experiments was absolutely negative. Yet, again and again I had such successful

days of work that I was encouraged to con- | Here are some of the designs with |

tinue.

) > N\

I soon found that the wind force is always so variable from one moment to another that to record its velocity during experiments was hopeless, even though that may seem a neces- sity in careful scientific experimenting. 1 proved :

1. That a tail is an unnecessary appendage to a properly constructed kite.

2. That by means of two strings suitably attached a kite can be guided so as to fly well some 45 degs. to each side of the wind course, and under favourable circumstances more.

3. That a kite which is perfectly flat, in very

EE ies

1 \

/ 2

Fic. 1.—SHAPES oF EXPERIMENTAL KITES.

which, together with many others, I experi- mented (see Fig. 1). advantageous qualities, but each required end- less alterations before really satisfactory results were obtained.

These experiments have continued off and on up to the present, but, as I have said, it would be impossible for me to detail them all, though carefully recorded, I having up to date records of close upon 200 different days’ experi- ments. I will therefore endeavour to sum- marise the results which I obtained.

They all have certain |

light weather will fly well, but that in strong winds it will be very unsteady.

4, That if it be given much of a diedral” angle, that is, if the sides of the kite are thrown back like a butterfly’s wings, or if it presents a convex surface to the wind it will not rise to so great an elevation as if flat, but will be steadier in strong winds.

5. That a large kite flies more steadily than a small one.

6. That if the vertical section of a kite presents a concave curve from top to bottom

April, 1898.)

THE AERONAUTICAL $Y¥OURNAL.

35

(thus >) the kite will ascend to a certain height and then “top,” that is, dive over for- wards till it lies horizontally on the air, and will then sink to the ground. But that if the form of the kite is such that its section pre- sents two or more curves (thus ~~) this tendency is prevented.

7. That the angle which the string takes with the horizon is variable, depending on the form of the kite and on the strengtn and direc- tion of the wind (which sometimes has an up- ward trend). The most usual forms vary from 30 degs. to 50 degs.

8. That the weight which a kite can lift wil) of course depend very greatly on the wind force, but a concave form of kite is more powerful than a convex one. In a light wind about -1 lb. per sq. ft. of kite may be counted on, in medium winds °8 ]b., in strong °5 lb.

9. That if the weight to be lifted be affixed to the kite, or very close to it, it is very liable to upset the equilibrium of the kite and render it unsteady.

10. That “duplex” lines, that is two retain- ing lines fixed apart on the ground, and attached to two points, one on each side of the central axis of the kite, enable it to fly with great steadiness in all winds.

11. That in light winds the line may be attached higher up on the kite than in strong winds, and that this raising of the point of attachment causes the kite to rise easier, but to be more unsteady.

12. That a “regulator,” or line attached to the lower part of a kite, the pulling of which alters the angle it presents to the wind, causes it to rise or fall as desired.

13. That the pull of the string of a kite may be taken roughly as—in light winds +1 lb per sq. ft., in moderate °7 lb., in strong up to 2 lb. per sq. ft. of kite surface.

As for shapes, there are many kinds which fly well if properly adjusted. The following points have to be considered :—

1. Lightness, so as to ascend easily in light winds. For some purposes it may be desirable to construct special kites, but these very light ones should never be used in strong winds, else they might become strained or damaged. 2. Stability in strong winds, which quality may also necessitate heavy construction, rendering the kite useless in light airs, 3. Portability. —For most purposes, especially when large kites are desirable, it is necessary that they should be easily folded up. 4. Simplicity.— The more complicated forms of kites are very liable to damage, and one little detail going wrong may upset the balance and the whole efficiency of the kite, 5. Power to lift or

draw. Some forms of kite possessing these qualities may not have so much power as others. Thus a baggy concave kite is power- ful, though perhaps unsteady. 6. Good Pise, that is to say power of attaining a steep angle with its string. 7. Strength, both to with- stand the pressure of wind and to stand knock- ing about while on the ground.

Though not absolutely necessary, a vertical

| backbone down the centre of the kite seems

desirable. The crosspieces to hold out tne material transversely may be in front or behind the cover, but what is better still is to have them enclosed in seams in the material,

A difficult question to decide is that of flexi- bility or rigidity. If the framework of a kite be very flexible, it may in strong winds so bend when struck by a strong squall that it lessens ‘the effective area, and thus automati- cally regulates the pull on the line. ‘Lnis characteristic would appear to be most de- sirable. I have arranged kites with springs, so as to fold back diedrally when struck by un- duly strong puffs; but practically I must own that so far I have not succeeded in devising any very satisfactory arrangement. The same may be said as regards springs applied to the bridle so as to allow the kite to ‘automaticauy present a different angle to the wind, accord- ing as it is strong or light. In practice a stiff, rigid kite is generally the most satisfactory, even though the pull on the line may in conse- quence be as variable as the changes of wind force.

What I have hitherto found to be the best form all round, is one nearly hexagonal in out- line, stretched on a framework consisting of three poles of equal length, one forming an up- right backbone,” the other two placed across it at right angles to form “crosspieces.” This form of kite is very simple and portable, as, when the backbone is unshipped, the kite (with its bridle) can be rolled up on the crosspieces. When flying, all the central square forms a powerful concavity, or rather two concavities divided diedrally by the backbone to give steadiness, while the top triangle prevents all tendency to “top.” This pattern, for dis- tinction, I have designated “levitor.” As re- gards size, I find the most convenient to be 12 feet high and 12 feet wide. This is about the largest size that can be handled easily. The poles are as long as can be conveniently trans- ported in one piece. Such kites weigh com- plete from 5 Ibs. to 7 lbs. according as they are intended for light winds or strong, and have an area of about 110 square feet. I have about fourteen such kites. My largest kite

36

was 36 feet high, containing 500 square feet, but this, though I flew it on some twenty different occasions, I found to be rather un- wieldy. I have one 24 feet high which is more convenient. whether it is practically best to use one or two large kites, or a number of small ones, for

I am still not quite decided ,

lifting weights such as a man. Small kites |

are handier—they are lighter for a given area (since very large kites necessitate very large poles), and if one becomes damaged it is more easily replaced, and if an accident occurs to one kite while flying in mid-air, there is not necessarily a sudden collapse of the whole apparatus. On the other hand, big kites are simpler to make, and require but one adjust- ment. They seem to float more steadily in gusty winds (since they are acted on by a number of variable currents), there is less complication of strings, and tuey are probably

more efficient. I have frequently tried an | appendage like the rudder of a ship, which |

has a decidedly steadying effect. There is one form of kite which calls for Xpecial comment.

It is known as the “Har- |

THE AERONAUTICAL JOURNAL.

grave” or “box” kite, having been invented |

by Mr. Hargrave in Australia. specimen which will more readily convey an idea of its peculiar construction than a long description. their lids and bottoms knocked out and connected a short distance apart. This kind of kite has found great favour in America, where it has been used for many purposes, including the high ascents for meteorological purposes at the Blue Hill Observatory.

My own experience with such kites is rather limited, but in practice I have found them

You see it is like two boxes with |

I have here a |

(April, 1898.

As regards retaining lines, I have generally used one of three systems: (1) the usual single line; (2) the “duplex,” with the two lines fixed apart so that they join the kite at an angle of about 60 degs. ; and (3) the “rein” or steering lines (for small kites), in which tue duplex lines are held together in the hand, and used like reins for steering the kite.

The first system is employed if it is desirable to get out a great length of line, or for towing, and when steadiness is not a matter of import- ance; the second, when great steadiness is desired; and the third for steering kites.

In using several kites together, there are several different methods of attaching them, best explained by diagrams.

a. The “duplex” applied to several kites (difficult to apply more than two or three kite

b. “Parallel” system, each kite presenting the same angle as the one below it, and thus the whole system is under control.

c. Single line passing through the kites.

d. Single lines, each lower kite having a “back bridle.”

e. Independent kites buoying” the line.

flach of these systems is applicable under vertain circumstances, and a combination of

| one or more is often used.

possess very little advantage over other good | | in many different varieties, some not so suitable

forms, and I am unable to comprehend any very special theoretical advantage in them. Such a form of kite is bound to be heavy, and I will endeavour to show later on the theo- retical objections to a heavy kite. The average weight of those used at the Blue Hill Observa- tory is about -1 lb, per sq. ft. of sustaining surface. My “levitor” kites (which are of much larger size, and should therefore be heavier in proportion) averaging ‘05 lb. per sq. ft. That is just half the weight for a given area. It is almost bound to be more compli-

cated and difficult to fold up. Being heavier, |

I have always found a Hargrave more difficult to get up in light winds. In very strong winds, though the Hargrave may perhaps be steadier than any other single line kite, there is no comparing it for steadiness with one on a sys- tem of duplex lines. Still, for certain purposes, such as attaining great elevations in strong winds, it may be useful.

| as others.

I have here a specimen of a kite fully fitted. By this system of running thimbles it can be used so as to fly independently on a single line, or duplex on two lines.

I also have a model to show what I believe is the best method of suspending the car to lift the man. In this he is perfectly steady. It cannot swing or rotate.

As regards materials, I have found that for the framework of all kites there is nothing like bamboo, though this material may be obtained

I have tried various sorts iof wood, but have always been dissatisfied with it, It is generally either too heavy or too brittle. Male bamboo, though very strong, is too heavy or too flexible. The same in an increased de- gree may be said of steel tubing. The thin- nest steel I could obtain is very much heavier than bamboo of somewhat the same diameter, even though it may be stronger. If of muca less diameter it does not possess the requisite rigidity. It is of course also much more ex- pensive.

The cover I have usually made of light cam- bric, which is very satisfactory, seldom tearing unless through catching in some tree, etc. For very light kites I have tried silk, and also gold- beaters’ skin. Paper is a wretched material, even for the roughest models. It is so liable to get torn even betore an experiment can be

completed with it.

Ap

al, bie be

April, 1898.] THE AERONAUTICAL FOURNAL. 37 ——< a b | °c. J

Fic. 2.—Merruops or CoNNECTING SEVERAL KITEs.

for cordage 1 have generally used Italian or Russian hemp. Steel wire ought to possess great advantages; but in practice—at all events for experimental work—its liability to kink, to get rusty, to attract lightning, and its awkwardness to handle, render hemp prefer- able.

Let me add a word against all metal clip- hooks, spring swivels, etc., which I at first used much, but soon found to be unreliable, heavy, and generally unsatisfactory. Wooden toggles and eye-splices are much to be pre- ferred.

I might emphasize the fact that these re- marks on the materials used in kite construc- tion are derived from my own experience. Careful experimenters in America have come to other conclusions. (Vide Marvin, Millet, Lamson, etc.)

I will now say a few words as regards the practical working of kites.

In very light winds there may be a difficulty in getting a kite up. Then it is best to lay out a long single line along the ground, say 200 or 300 yards ‘long, let one end be attached to the kite, and a man hold the other end and run with it. The kite will thus rise up jinto the air some 300 or 400 feet, even though it be a dead calm. But often there is a light breeze above which is imperceptible below, and if the kite floats of ‘itself its string may be affixed to a second kite, which it will gradually draw up, and thus a whole series carried up to the upper current.

Even very large kites may be got up in this way. kites with about a dozen men running, or by attaching the kite line to a waggon drawn by horses. By both these methods a man has been lifted up.

The subject of the upper currents of the air has been discussed by Mr. Douglas Archibald, who conducted a series of kite experiments

I have several times tried towing such:

38 THE AERONAUTICAL ¥FOURNAL.

which tend to prove that the velocity always |

increases with altitude, and in the proportion of | cup eae Pa _ teresting work, Progress in Flying Machines,

v + g-- or >

when V and v represent the velocities, and |

H h the corresponding heights.

(April, 1898.

balloon, which may be very useful in military operations as well as for all purposes Where a lofty look-out may be desirable. 1 have actually been lifted up on about eighteen different occasions, sometimes going as high as 100 feet (the limit of the perpendicular rope). I jhave also let up weights, equal to that of a man, 300 feet high; ‘and I believe that the height attainable is chiefly dependent on the length of rope available. The kite area has varied from 300 .o 800 square feet. In most cases I have used from three to eight kites, but have also made ascents with one kite of 500 square feet.

2. To lift a torpedo or large charge of ex- plosive to be wafted over a fortification, etc., I have tet up some hundreds of pounds weight and sent it off over a place half-a-mile off.

3. To take up a photographic camera so arranged as to obtain a photograph of the country beneath. I have here some specimens taken.

4. To sail boats, for which purpose kites seem most suitable as the boat can sail very close to the wind, and with no fear of cap- sizing.

5. To draw a cart, ‘which may be very useful in open country. It is surprising the amount of power the kites possess even in a light wind.

6. Communication between ships at sea, by which letters and parcels can be conveyed without the necessity of lowering a boat.

Also for signalling, getting ropes to other- wise inacessible places, and many other pur- poses.

II.—THEORETICAL PRINCIPLES.

The theoretical principles of kite flying seems to have received but little attention from scientists. Professor C. F. Marvin, of Washington, has recently published two mono- graphs, “Kite Experiments at the Weather Bureau,” and “The Mechanics and Equilibrium of Kites,” which practicaliy constitute the en- tire literature (in English) on the subject, ex- cept for a few remarks in Mr. Chanute’s in-

| and in the Aeronautical Annual, 1896,” while

In strong winds it is usually best to use | duplex lines, the ground end fixed to pegs or | to trees, etc., so that the wind blows up be- |

tween them. line or lines should always be securely fixed before the kites are let up, else it may be im possible to hold them.

In strong winds the retaining |

As far as practical utility goes, I have used |

kites for the following purposes : 1. To lift a man similarly to a

ae captive

the scientific researches of Professor S. P. liangley (“Aerodynamics”) also throw great light on the subject.

In order to jinvestigate the results of the forces acting on a kite we will assume that it is a flat plane, and that ‘the wind blows in a steady, horizontal course. These conditions are practically but seldom met with, the kite surface usually forming a variety of curves and planes at various angles, while the wind is always variable both in force and direction.

There are two forces acting on the kite in opposition to the retaining line—viz., the wind,

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April, 1898.]

THE AERONAUTICAL JOURNAL. 39

and the weight of the kite. The wind acts in | several ways; it presses on the whole under- | smaller, while, on the other hand, the force

| of gravity or weight remains the same in in-

surface normally to the