Flying Machines: Construction and OperationPart 2 out of 4
How to Distribute the Weight. Let us take 1,030 pounds as the net weight of the machine as against the same average in the Wright and Curtiss machines. Now comes the question of distributing this weight between the framework, motor, and other equipment. As a general proposition the framework should weigh about twice as much as the complete power plant (this is for amateur work). The word "framework" indicates not only the wooden frames of the main planes, auxiliary planes, rudders, etc., but the cloth coverings as well--everything in fact except the engine and propeller. On the basis named the framework would weigh 686 pounds, and the power plant 344. These figures are liberal, and the results desired may be obtained well within them as the novice will learn as he makes progress in the work. Figuring on Surface Area. It was Prof. Langley who first brought into prominence in connection with flying machine construction the mathematical principle that the larger the object the smaller may be the relative area of support. As explained in Chapter XIII, there are mechanical limits as to size which it is not practical to exceed, but the main principle remains in effect. Take two aeroplanes of marked difference in area of surface. The larger will, as a rule, sustain a greater weight in relative proportion to its area than the smaller one, and do the work with less relative horsepower. As a general thing well-constructed machines will average a supporting capacity of one pound for every one-half square foot of surface area. Accepting this as a working rule we find that to sustain a weight of 1,200 pounds --machine and two passengers--we should have 600 square feet of surface. Distributing the Surface Area. The largest surfaces now in use are those of the Wright, Voisin and Antoinette machines--538 square feet in each. The actual sustaining power of these machines, so far as known, has never been tested to the limit; it is probable that the maximum is considerably in excess of what they have been called upon to show. In actual practice the average is a little over one pound for each one-half square foot of surface area. Allowing that 600 square feet of surface will be used, the next question is how to distribute it to the best advantage. This is another important matter in which individual preference must rule. We have seen how the professionals disagree on this point, some using auxiliary planes of large size, and others depending upon smaller auxiliaries with an increase in number so as to secure on a different plan virtually the same amount of surface. In deciding upon this feature the best thing to do is to follow the plans of some successful aviator, increasing the area of the auxiliaries in proportion to the increase in the area of the main planes. Thus, if you use 600 square feet of surface where the man whose plans you are following uses 500, it is simply a matter of making your planes one-fifth larger all around. The Cost of Production. Cost of production will be of interest to the amateur who essays to construct a flying machine. Assuming that the size decided upon is double that of the glider the material for the framework, timber, cloth, wire, etc., will cost a little more than double. This is because it must be heavier in proportion to the increased size of the framework, and heavy material brings a larger price than the lighter goods. If we allow $20 as the cost of the glider material it will be safe to put down the cost of that required for a real flying machine framework at $60, provided the owner builds it himself. As regards the cost of motor and similar equipment it can only be said that this depends upon the selection made. There are some reliable aviation motors which may be had as low as $500, and there are others which cost as much as $2,000. Services of Expert Necessary. No matter what kind of a motor may be selected the services of an expert will be necessary in its proper installation unless the amateur has considerable genius in this line himself. As a general thing $25 should be a liberal allowance for this work. No matter how carefully the engine may be placed and connected it will be largely a matter of luck if it is installed in exactly the proper manner at the first attempt. The chances are that several alterations, prompted by the results of trials, will have to be made. If this is the case the expert's bill may readily run up to $50. If the amateur is competent to do this part of the work the entire item of $50 may, of course, be cut out. As a general proposition a fairly satisfactory flying machine, one that will actually fly and carry the operator with it, may be constructed for $750, but it will lack the better qualities which mark the higher priced machines. This computation is made on the basis of $60 for material, $50 for services of expert, $600 for motor, etc., and an allowance of $40 for extras. No man who has the flying machine germ in his system will be long satisfied with his first moderate price machine, no matter how well it may work. It's the old story of the automobile "bug" over again. The man who starts in with a modest $1,000 automobile invariably progresses by easy stages to the $4,000 or $5,000 class. The natural tendency is to want the biggest and best attainable within the financial reach of the owner. It's exactly the same way with the flying machine convert. The more proficient he becomes in the manipulation of his car, the stronger becomes the desire to fly further and stay in the air longer than the rest of his brethren. This necessitates larger, more powerful, and more expensive machines as the work of the germ progresses. Speed Affects Weight Capacity. Don't overlook the fact that the greater speed you can attain the smaller will be the surface area you can get along with. If a machine with 500 square feet of sustaining surface, traveling at a speed of 40 miles an hour, will carry a weight of 1,200 pounds, we can cut the sustaining surface in half and get along with 250 square feet, provided a speed of 60 miles an hour can be obtained. At 100 miles an hour only 80 square feet of surface area would be required. In both instances the weight sustaining capacity will remain the same as with the 500 square feet of surface area--1,200 pounds. One of these days some mathematical genius will figure out this problem with exactitude and we will have a dependable table giving the maximum carrying capacity of various surface areas at various stated speeds, based on the dimensions of the advancing edges. At present it is largely a matter of guesswork so far as making accurate computation goes. Much depends upon the shape of the machine, and the amount of surface offering resistance to the wind, etc. CHAPTER IX. SELECTION OF THE MOTOR. Motors for flying machines must be light in weight, of great strength, productive of extreme speed, and positively dependable in action. It matters little as to the particular form, or whether air or water cooled, so long as the four features named are secured. There are at least a dozen such motors or engines now in use. All are of the gasolene type, and all possess in greater or lesser degree the desired qualities. Some of these motors are: Renault--8-cylinder, air-cooled; 50 horse power; weight 374 pounds. Fiat--8-cylinder, air-cooled; 50 horse power; weight 150 pounds. Farcot--8-cylinder, air-cooled; from 30 to 100 horse power, according to bore of cylinders; weight of smallest, 84 pounds. R. E. P.--10-cylinder, air-cooled; 150 horse power; weight 215 pounds. Gnome--7 and 14 cylinders, revolving type, air-cooled; 50 and 100 horse power; weight 150 and 300 pounds. Darracq--2 to 14 cylinders, water cooled; 30 to 200 horse power; weight of smallest 100 pounds. Wright--4-cylinder, water-cooled; 25 horse power; weight 200 pounds. Antoinette--8 and 16-cylinder, water-cooled; 50 and 100 horse power; weight 250 and 500 pounds. E. N. V.--8-cylinder, water-cooled; from 30 to 80 horse power, according to bore of cylinder; weight 150 to 400 pounds. Curtiss--8-cylinder, water-cooled; 60 horse power; weight 300 pounds. Average Weight Per Horse Power. It will be noticed that the Gnome motor is unusually light, being about three pounds to the horse power produced, as opposed to an average of 4 1/2 pounds per horse power in other makes. This result is secured by the elimination of the fly-wheel, the engine itself revolving, thus obtaining the same effect that would be produced by a fly-wheel. The Farcot is even lighter, being considerably less than three pounds per horse power, which is the nearest approach to the long-sought engine equipment that will make possible a complete flying machine the total weight of which will not exceed one pound per square foot of area. How Lightness Is Secured. Thus far foreign manufacturers are ahead of Americans in the production of light-weight aerial motors, as is evidenced by the Gnome and Farcot engines, both of which are of French make. Extreme lightness is made possible by the use of fine, specially prepared steel for the cylinders, thus permitting them to be much thinner than if ordinary forms of steel were used. Another big saving in weight is made by substituting what are known as "auto lubricating" alloys for bearings. These alloys are made of a combination of aluminum and magnesium. Still further gains are made in the use of alloy steel tubing instead of solid rods, and also by the paring away of material wherever it can be done without sacrificing strength. This plan, with the exclusive use of the best grades of steel, regardless of cost, makes possible a marked reduction in weight. Multiplicity of Cylinders. Strange as it may seem, multiplicity of cylinders does not always add proportionate weight. Because a 4- cylinder motor weighs say 100 pounds, it does not necessarily follow that an 8-cylinder equipment will weigh 200 pounds. The reason of this will be plain when it is understood that many of the parts essential to a 4- cylinder motor will fill the requirements of an 8-cylinder motor without enlargement or addition. Neither does multiplying the cylinders always increase the horsepower proportionately. If a 4-cylinder motor is rated at 25 horsepower it is not safe to take it for granted that double the number of cylinders will give 50 horsepower. Generally speaking, eight cylinders, the bore, stroke and speed being the same, will give double the power that can be obtained from four, but this does not always hold good. Just why this exception should occur is not explainable by any accepted rule. Horse Power and Speed. Speed is an important requisite in a flying-machine motor, as the velocity of the aeroplane is a vital factor in flotation. At first thought, the propeller and similar adjuncts being equal, the inexperienced mind would naturally argue that a 50-horsepower engine should produce just double the speed of one of 25-horsepower. That this is a fallacy is shown by actual performances. The Wrights, using a 25-horsepower motor, have made 44 miles an hour, while Bleriot, with a 50-horsepower motor, has a record of a short-distance flight at the rate of 52 miles an hour. The fact is that, so far as speed is concerned, much depends upon the velocity of the wind, the size and shape of the aeroplane itself, and the size, shape and gearing of the propeller. The stronger the wind is blowing the easier it will be for the aeroplane to ascend, but at the same time the more difficult it will be to make headway against the wind in a horizontal direction. With a strong head wind, and proper engine force, your machine will progress to a certain extent, but it will be at an angle. If the aviator desired to keep on going upward this would be all right, but there is a limit to the altitude which it is desirable to reach--from 100 to 500 feet for experts--and after that it becomes a question of going straight ahead. Great Waste of Power. One thing is certain--even in the most efficient of modern aerial motors there is a great loss of power between the two points of production and effect. The Wright outfit, which is admittedly one of the most effective in use, takes one horsepower of force for the raising and propulsion of each 50 pounds of weight. This, for a 25-horsepower engine, would give a maximum lifting capacity of 1250 pounds. It is doubtful if any of the higher rated motors have greater efficiency. As an 8- cylinder motor requires more fuel to operate than a 4- cylinder, it naturally follows that it is more expensive to run than the smaller motor, and a normal increase in capacity, taking actual performances as a criterion, is lacking. In other words, what is the sense of using an 8-cylinder motor when one of 4 cylinders is sufficient? What the Propeller Does. Much of the efficiency of the motor is due to the form and gearing of the propeller. Here again, as in other vital parts of flying-machine mechanism, we have a wide divergence of opinion as to the best form. A fish makes progress through the water by using its fins and tail; a bird makes its way through the air in a similar manner by the use of its wings and tail. In both instances the motive power comes from the body of the fish or bird. In place of fins or wings the flying machine is equipped with a propeller, the action of which is furnished by the engine. Fins and wings have been tried, but they don't work. While operating on the same general principle, aerial propellers are much larger than those used on boats. This is because the boat propeller has a denser, more substantial medium to work in (water), and consequently can get a better "hold," and produce more propulsive force than one of the same size revolving in the air. This necessitates the aerial propellers being much larger than those employed for marine purposes. Up to this point all aviators agree, but as to the best form most of them differ. Kinds of Propellers Used. One of the most simple is that used by Curtiss. It consists of two pear-shaped blades of laminated wood, each blade being 5 inches wide at its extreme point, tapering slightly to the shaft connection. These blades are joined at the engine shaft, in a direct line. The propeller has a pitch of 5 feet, and weighs, complete, less than 10 pounds. The length from end to end of the two blades is 6 1/2 feet. Wright uses two wooden propellers, in the rear of his biplane, revolving in opposite directions. Each propeller is two-bladed. Bleriot also uses a two-blade wooden propeller, but it is placed in front of his machine. The blades are each about 3 1/2 feet long and have an acute "twist." Santos-Dumont uses a two-blade wooden propeller, strikingly similar to the Bleriot. On the Antoinette monoplane, with which good records have been made, the propeller consists of two spoon- shaped pieces of metal, joined at the engine shaft in front, and with the concave surfaces facing the machine. The propeller on the Voisin biplane is also of metal, consisting of two aluminum blades connected by a forged steel arm. Maximum thrust, or stress--exercise of the greatest air-displacing force--is the object sought. This, according to experts, is best obtained with a large propeller diameter and reasonably low speed. The diameter is the distance from end to end of the blades, which on the largest propellers ranges from 6 to 8 feet. The larger the blade surface the greater will be the volume of air displaced, and, following this, the greater will be the impulse which forces the aeroplane ahead. In all centrifugal motion there is more or less tendency to disintegration in the form of "flying off" from the center, and the larger the revolving object is the stronger is this tendency. This is illustrated in the many instances in which big grindstones and fly-wheels have burst from being revolved too fast. To have a propeller break apart in the air would jeopardize the life of the aviator, and to guard against this it has been found best to make its revolving action comparatively slow. Besides this the slow motion (it is only comparatively slow) gives the atmosphere a chance to refill the area disturbed by one propeller blade, and thus have a new surface for the next blade to act upon. Placing of the Motor. As on other points, aviators differ widely in their ideas as to the proper position for the motor. Wright locates his on the lower plane, midway between the front and rear edges, but considerably to one side of the exact center. He then counter-balances the engine weight by placing his seat far enough away in the opposite direction to preserve the center of gravity. This leaves a space in the center between the motor and the operator in which a passenger may be carried without disturbing the equilibrium. Bleriot, on the contrary, has his motor directly in front and preserves the center of gravity by taking his seat well back, this, with the weight of the aeroplane, acting as a counter-balance. On the Curtiss machine the motor is in the rear, the forward seat of the operator, and weight of the horizontal rudder and damping plane in front equalizing the engine weight. No Perfect Motor as Yet. Engine makers in the United States, England, France and Germany are all seeking to produce an ideal motor for aviation purposes. Many of the productions are highly creditable, but it may be truthfully said that none of them quite fill the bill as regards a combination of the minimum of weight with the maximum of reliable maintained power. They are all, in some respects, improvements upon those previously in use, but the great end sought for has not been fully attained. One of the motors thus produced was made by the French firm of Darracq at the suggestion of Santos Dumont, and on lines laid down by him. Santos Dumont wanted a 2-cylinder horizontal motor capable of developing 30 horsepower, and not exceeding 4 1/2 pounds per horsepower in weight. There can be no question as to the ability and skill of the Darracq people, or of their desire to produce a motor that would bring new credit and prominence to the firm. Neither could anything radically wrong be detected in the plans. But the motor, in at least one important requirement, fell short of expectations. It could not be depended upon to deliver an energy of 30 horsepower continuously for any length of time. Its maximum power could be secured only in "spurts." This tends to show how hard it is to produce an ideal motor for aviation purposes. Santos Dumont, of undoubted skill and experience as an aviator, outlined definitely what he wanted; one of the greatest designers in the business drew the plans, and the famous house of Darracq bent its best energies to the production. But the desired end was not fully attained. Features of Darracq Motor. Horizontal motors were practically abandoned some time ago in favor of the vertical type, but Santos Dumont had a logical reason for reverting to them. He wanted to secure a lower center of gravity than would be possible with a vertical engine. Theoretically his idea was correct as the horizontal motor lies flat, and therefore offers less resistance to the wind, but it did not work out as desired. At the same time it must be admitted that this Darracq motor is a marvel of ingenuity and exquisite workmanship. The two cylinders, having a bore of 5 1-10 inches and a stroke of 4 7-10 inches, are machined out of a solid bar of steel until their weight is only 8 4-5 pounds complete. The head is separate, carrying the seatings for the inlet and exhaust valves, is screwed onto the cylinder, and then welded in position. A copper water-jacket is fitted, and it is in this condition that the weight of 8 4-5 pounds is obtained. On long trips, especially in regions where gasolene is hard to get, the weight of the fuel supply is an important feature in aviation. As a natural consequence flying machine operators favor the motor of greatest economy in gasolene consumption, provided it gives the necessary power. An American inventor, Ramsey by name, is working on a motor which is said to possess great possibilities in this line. Its distinctive features include a connecting rod much shorter than usual, and a crank shaft located the length of the crank from the central axis of the cylinder. This has the effect of increasing the piston stroke, and also of increasing the proportion of the crank circle during which effective pressure is applied to the crank. Making the connecting rod shorter and leaving the crank mechanism the same would introduce excessive cylinder friction. This Ramsey overcomes by the location of his crank shaft. The effect of the long piston stroke thus secured, is to increase the expansion of the gases, which in turn increases the power of the engine without increasing the amount of fuel used. Propeller Thrust Important. There is one great principle in flying machine propulsion which must not be overlooked. No matter how powerful the engine may be unless the propeller thrust more than overcomes the wind pressure there can be no progress forward. Should the force of this propeller thrust and that of the wind pressure be equal the result is obvious. The machine is at a stand-still so far as forward progress is concerned and is deprived of the essential advancing movement. Speed not only furnishes sustentation for the airship, but adds to the stability of the machine. An aeroplane which may be jerky and uncertain in its movements, so far as equilibrium is concerned, when moving at a slow gait, will readily maintain an even keel when the speed is increased. Designs for Propeller Blades. It is the object of all men who design propellers to obtain the maximum of thrust with the minimum expenditure of engine energy. With this purpose in view many peculiar forms of propeller blades have been evolved. In theory it would seem that the best effects could be secured with blades so shaped as to present a thin (or cutting) edge when they come out of the wind, and then at the climax of displacement afford a maximum of surface so as to displace as much air as possible. While this is the form most generally favored there are others in successful operation. There is also wide difference in opinion as to the equipment of the propeller shaft with two or more blades. Some aviators use two and some four. All have more or less success. As a mathematical proposition it would seem that four blades should give more propulsive force than two, but here again comes in one of the puzzles of aviation, as this result is not always obtained. Difference in Propeller Efficiency. That there is a great difference in propeller efficiency is made readily apparent by the comparison of effects produced in two leading makes of machines--the Wright and the Voisin. In the former a weight of from 1,100 to 1,200 pounds is sustained and advance progress made at the rate of 40 miles an hour and more, with half the engine speed of a 25 horse-power motor. This would be a sustaining capacity of 48 pounds per horsepower. But the actual capacity of the Wright machine, as already stated, is 50 pounds per horsepower. The Voisin machine, with aviator, weighs about 1,370 pounds, and is operated with a so-horsepower motor. Allowing it the same speed as the Wright we find that, with double the engine energy, the lifting capacity is only 27 1/2 pounds per horsepower. To what shall we charge this remarkable difference? The surface of the planes is exactly the same in both machines so there is no advantage in the matter of supporting area. Comparison of Two Designs. On the Wright machine two wooden propellers of two blades each (each blade having a decided "twist") are used. As one 25 horsepower motor drives both propellers the engine energy amounts to just one-half of this for each, or 12 1/2 horsepower. And this energy is utilized at one-half the normal engine speed. On the Voisin a radically different system is employed. Here we have one metal two-bladed propeller with a very slight "twist" to the blade surfaces. The full energy of a 50-horsepower motor is utilized. Experts Fail to Agree. Why should there be such a marked difference in the results obtained? Who knows? Some experts maintain that it is because there are two propellers on the Wright machine and only one on the Voisin, and consequently double the propulsive power is exerted. But this is not a fair deduction, unless both propellers are of the same size. Propulsive power depends upon the amount of air displaced, and the energy put into the thrust which displaces the air. Other experts argue that the difference in results may be traced to the difference in blade design, especially in the matter of "twist." The fact is that propeller results depend largely upon the nature of the aeroplanes on which they are used. A propeller, for instance, which gives excellent results on one type of aeroplane, will not work satisfactorily on another. There are some features, however, which may be safely adopted in propeller selection. These are: As extensive a diameter as possible; blade area 10 to 15 per cent of the area swept; pitch four-fifths of the diameter; rotation slow. The maximum of thrust effort will be thus obtained. CHAPTER X. PROPER DIMENSIONS OF MACHINES. In laying out plans for a flying machine the first thing to decide upon is the size of the plane surfaces. The proportions of these must be based upon the load to be carried. This includes the total weight of the machine and equipment, and also the operator. This will be a rather difficult problem to figure out exactly, but practical approximate figures may be reached. It is easy to get at the weight of the operator, motor and propeller, but the matter of determining, before they are constructed, what the planes, rudders, auxiliaries, etc., will weigh when completed is an intricate proposition. The best way is to take the dimensions of some successful machine and use them, making such alterations in a minor way as you may desire. Dimensions of Leading Machines. In the following tables will be found the details as to surface area, weight, power, etc., of the nine principal types of flying machines which are now prominently before the public: MONOPLANES. Surface area Spread in Depth in Make Passengers sq. feet linear feet linear feet Santos-Dumont . . 1 110 16.0 26.0 Bleriot . . . . . 1 150.6 24.6 22.0 R. E. P . . . . . 1 215 34.1 28.9 Bleriot . . . . . 2 236 32.9 23.0 Antoinette. . . . 2 538 41.2 37.9 No. of Weight Without Propeller Make Cylinders Horse Power Operator Diameter Santos-Dumont. . 2 30 250 5.0 Bleriot. . . . . 3 25 680 6.9 R. E. P. . . . . 7 35 900 6.6 Bleriot. . . . . 7 50 1,240 8.1 Antoinette . . . 8 50 1,040 7.2 BIPLANES. Surface Area Spread in Depth in Make Passengers sq. feet linear feet linear feet Curtiss . . . 2 258 29.0 28.7 Wright. . . . 2 538 41.0 30.7 Farman. . . . 2 430 32.9 39.6 Voisin. . . . 2 538 37.9 39.6 No. of Weight Without Propeller Make Cylinders Horse Power Operator Diameter Curtiss . . . 8 50 600 6.0 Wright. . . . 4 25 1,100 8.1 Farman. . . . 7 50 1,200 8.9 Voisin. . . . 8 50 1,200 6.6 In giving the depth dimensions the length over all-- from the extreme edge of the front auxiliary plane to the extreme tip of the rear is stated. Thus while the dimensions of the main planes of the Wright machine are 41 feet spread by 6 1/2 feet in depth, the depth over all is 30.7. Figuring Out the Details. With this data as a guide it should be comparatively easy to decide upon the dimensions of the machine required. In arriving at the maximum lifting capacity the weight of the operator must be added. Assuming this to average 170 pounds the method of procedure would be as follows: Add the weight of the operator to the weight of the complete machine. The new Wright machine complete weighs 900 pounds. This, plus 170, the weight of the operator, gives a total of 1,070 pounds. There are 538 square feet of supporting surface, or practically one square foot of surface area to each two pounds of load. There are some machines, notably the Bleriot, in which the supporting power is much greater. In this latter instance we find a surface area of 150 1/2 square feet carrying a load of 680 plus 170, or an aggregate of 850 pounds. This is the equivalent of five pounds to the square foot. This ratio is phenomenally large, and should not be taken as a guide by amateurs. The Matter of Passengers. These deductions are based on each machine carrying one passenger, which is admittedly the limit at present of the monoplanes like those operated for record-making purposes by Santos-Dumont and Bleriot. The biplanes, however, have a two-passenger capacity, and this adds materially to the proportion of their weight-sustaining power as compared with the surface area. In the following statement all the machines are figured on the one-passenger basis. Curtiss and Wright have carried two passengers on numerous occasions, and an extra 170 pounds should therefore be added to the total weight carried, which would materially increase the capacity. Even with the two-passenger load the limit is by no means reached, but as experiments have gone no further it is impossible to make more accurate figures. Average Proportions of Load. It will be interesting, before proceeding to lay out the dimension details, to make a comparison of the proportion of load effect with the supporting surfaces of various well-known machines. Here are the figures: Santos-Dumont--A trifle under four pounds per square foot. Bleriot--Five pounds. R. E. P.--Five pounds. Antoinette--About two and one-quarter pounds. Curtiss--About two and one-half pounds. Wright--Two and one-quarter pounds. Farman--A trifle over three pounds. Voisin--A little under two and one-half pounds. Importance of Engine Power. While these figures are authentic, they are in a way misleading, as the important factor of engine power is not taken into consideration. Let us recall the fact that it is the engine power which keeps the machine in motion, and that it is only while in motion that the machine will remain suspended in the air. Hence, to attribute the support solely to the surface area is erroneous. True, that once under headway the planes contribute largely to the sustaining effect, and are absolutely essential in aerial navigation--the motor could not rise without them--still, when it comes to a question of weight- sustaining power, we must also figure on the engine capacity. In the Wright machine, in which there is a lifting capacity of approximately 2 1/4 pounds to the square foot of surface area, an engine of only 25 horsepower is used. In the Curtiss, which has a lifting capacity of 2 1/2 pounds per square foot, the engine is of 50 horsepower. This is another of the peculiarities of aerial construction and navigation. Here we have a gain of 1/4 pound in weight-lifting capacity with an expenditure of double the horsepower. It is this feature which enables Curtiss to get along with a smaller surface area of supporting planes at the expense of a big increase in engine power. Proper Weight of Machine. As a general proposition the most satisfactory machine for amateur purposes will be found to be one with a total weight-sustaining power of about 1,200 pounds. Deducting 170 pounds as the weight of the operator, this will leave 1,030 pounds for the complete motor- equipped machine, and it should be easy to construct one within this limit. This implies, of course, that due care will be taken to eliminate all superfluous weight by using the lightest material compatible with strength and safety. This plan will admit of 686 pounds weight in the frame work, coverings, etc., and 344 for the motor, propeller, etc., which will be ample. Just how to distribute the weight of the planes is a matter which must be left to the ingenuity of the builder. Comparison of Bird Power. There is an interesting study in the accompanying illustration. Note that the surface area of the albatross is much smaller than that of the vulture, although the wing spread is about the same. Despite this the albatross accomplishes fully as much in the way of flight and soaring as the vulture. Why? Because the albaboss is quicker and more powerful in action. It is the application of this same principle in flying machines which enables those of great speed and power to get along with less supporting surface than those of slower movement. Measurements of Curtiss Machine. Some idea of framework proportion may be had from the following description of the Curtiss machine. The main planes have a spread (width) of 29 feet, and are 4 1/2 feet deep. The front double surface horizontal rudder is 6x2 feet, with an area of 24 square feet. To the rear of the main planes is a single surface horizontal plane 6x2 feet, with an area of 12 square feet. In connection with this is a vertical rudder 2 1/2 feet square. Two movable ailerons, or balancing planes, are placed at the extreme ends of the upper planes. These are 6x2 feet, and have a combined area of 24 square feet. There is also a triangular shaped vertical steadying surface in connection with the front rudder. Thus we have a total of 195 square feet, but as the official figures are 258, and the size of the triangular- shaped steadying surface is unknown, we must take it for granted that this makes up the difference. In the matter of proportion the horizontal double-plane rudder is about one-tenth the size of the main plane, counting the surface area of only one plane, the vertical rudder one-fortieth, and the ailerons one-twentieth. CHAPTER XI. PLANE AND RUDDER CONTROL. Having constructed and equipped your machine, the next thing is to decide upon the method of controlling the various rudders and auxiliary planes by which the direction and equilibrium and ascending and descending of the machine are governed. The operator must be in position to shift instantaneously the position of rudders and planes, and also to control the action of the motor. This latter is supposed to work automatically and as a general thing does so with entire satisfaction, but there are times when the supply of gasolene must be regulated, and similar things done. Airship navigation calls for quick action, and for this reason the matter of control is an important one--it is more than important; it is vital. Several Methods of Control. Some aviators use a steering wheel somewhat after the style of that used in automobiles, and by this not only manipulate the rudder planes, but also the flow of gasolene. Others employ foot levers, and still others, like the Wrights, depend upon hand levers. Curtiss steers his aeroplane by means of a wheel, but secures the desired stabilizing effect with an ingenious jointed chair-back. This is so arranged that by leaning toward the high point of his wing planes the aeroplane is restored to an even keel. The steering post of the wheel is movable backward and forward, and by this motion elevation is obtained. The Wrights for some time used two hand levers, one to steer by and warp the flexible tips of the planes, the other to secure elevation. They have now consolidated all the functions in one lever. Bleriot also uses the single lever control. Farman employs a lever to actuate the rudders, but manipulates the balancing planes by foot levers. Santos-Dumont uses two hand levers with which to steer and elevate, but manipulates the planes by means of an attachment to the back of his outer coat. Connection With the Levers. No matter which particular method is employed, the connection between the levers and the object to be manipulated is almost invariably by wire. For instance, from the steering levers (or lever) two wires connect with opposite sides of the rudder. As a lever is moved so as to draw in the right-hand wire the rudder is drawn to the right and vice versa. The operation is exactly the same as in steering a boat. It is the same way in changing the position of the balancing planes. A movement of the hands or feet and the machine has changed its course, or, if the equilibrium is threatened, is back on an even keel. Simple as this seems it calls for a cool head, quick eye, and steady hand. The least hesitation or a false movement, and both aviator and craft are in danger. Which Method is Best? It would be a bold man who would attempt to pick out any one of these methods of control and say it was better than the others. As in other sections of aeroplane mechanism each method has its advocates who dwell learnedly upon its advantages, but the fact remains that all the various plans work well and give satisfaction. What the novice is interested in knowing is how the control is effected, and whether he has become proficient enough in his manipulation of it to be absolutely dependable in time of emergency. No amateur should attempt a flight alone, until he has thoroughly mastered the steering and plane control. If the services and advice of an experienced aviator are not to be had the novice should mount his machine on some suitable supports so it will be well clear of the ground, and, getting into the operator's seat, proceed to make himself well acquainted with the operation of the steering wheel and levers. Some Things to Be Learned. He will soon learn that certain movements of the steering gear produce certain effects on the rudders. If, for instance, his machine is equipped with a steering wheel, he will find that turning the wheel to the right turns the aeroplane in the same direction, because the tiller is brought around to the left. In the same way he will learn that a given movement of the lever throws the forward edge of the main plane upward, and that the machine, getting the impetus of the wind under the concave surfaces of the planes, will ascend. In the same way it will quickly become apparent to him that an opposite movement of the lever will produce an opposite effect--the forward edges of the planes will be lowered, the air will be "spilled" out to the rear, and the machine will descend. The time expended in these preliminary lessons will be well spent. It would be an act of folly to attempt to actually sail the craft without them. CHAPTER XII. HOW TO USE THE MACHINE. It is a mistaken idea that flying machines must be operated at extreme altitudes. True, under the impetus of handsome prizes, and the incentive to advance scientific knowledge, professional aviators have ascended to considerable heights, flights at from 500 to 1,500 feet being now common with such experts as Farman, Bleriot, Latham, Paulhan, Wright and Curtiss. The altitude record at this time is about 4,165 feet, held by Paulhan. One of the instructions given by experienced aviators to pupils, and for which they insist upon implicit obeyance, is: "If your machine gets more than 30 feet high, or comes closer to the ground than 6 feet, descend at once." Such men as Wright and Curtiss will not tolerate a violation of this rule. If their instructions are not strictly complied with they decline to give the offender further lessons. Why This Rule Prevails. There is good reason for this precaution. The higher the altitude the more rarefied (thinner) becomes the air, and the less sustaining power it has. Consequently the more difficult it becomes to keep in suspension a given weight. When sailing within 30 feet of the ground sustentation is comparatively easy and, should a fall occur, the results are not likely to be serious. On the other hand, sailing too near the ground is almost as objectionable in many ways as getting up too high. If the craft is navigated too close to the ground trees, shrubs, fences and other obstructions are liable to be encountered. There is also the handicap of contrary air currents diverted by the obstructions referred to, and which will be explained more fully further on. How to Make a Start. Taking it for granted that the beginner has familiarized himself with the manipulation of the machine, and especially the control mechanism, the next thing in order is an actual flight. It is probable that his machine will be equipped with a wheeled alighting gear, as the skids used by the Wrights necessitate the use of a special starting track. In this respect the wheeled machine is much easier to handle so far as novices are concerned as it may be easily rolled to the trial grounds. This, as in the case of the initial experiments, should be a clear, reasonably level place, free from trees, fences, rocks and similar obstructions with which there may be danger of colliding. The beginner will need the assistance of three men. One of these should take his position in the rear of the machine, and one at each end. On reaching the trial ground the aviator takes his seat in the machine and, while the men at the ends hold it steady the one in the rear assists in retaining it until the operator is ready. In the meantime the aviator has started his motor. Like the glider the flying machine, in order to accomplish the desired results, should be headed into the wind. When the Machine Rises. Under the impulse of the pushing movement, and assisted by the motor action, the machine will gradually rise from the ground--provided it has been properly proportioned and put together, and everything is in working order. This is the time when the aviator requires a cool head, At a modest distance from the ground use the control lever to bring the machine on a horizontal level and overcome the tendency to rise. The exact manipulation of this lever depends upon the method of control adopted, and with this the aviator is supposed to have thoroughly familiarized himself as previously advised in Chapter XI. It is at this juncture that the operator must act promptly, but with the perfect composure begotten of confidence. One of the great drawbacks in aviation by novices is the tendency to become rattled, and this is much more prevalent than one might suppose, even among men who, under other conditions, are cool and confident in their actions. There is something in the sensation of being suddenly lifted from the ground, and suspended in the air that is disconcerting at the start, but this will soon wear off if the experimenter will keep cool. A few successful flights no matter how short they may be, will put a lot of confidence into him. Make Your Flights Short. Be modest in your initial flights. Don't attempt to match the records of experienced men who have devoted years to mastering the details of aviation. Paulhan, Farman, Bleriot, Wright, Curtiss, and all the rest of them began, and practiced for years, in the manner here described, being content to make just a little advancement at each attempt. A flight of 150 feet, cleanly and safely made, is better as a beginning than one of 400 yards full of bungling mishaps. And yet these latter have their uses, provided the operator is of a discerning mind and can take advantage of them as object lessons. But, it is not well to invite them. They will occur frequently enough under the most favorable conditions, and it is best to have them come later when the feeling of trepidation and uncertainty as to what to do has worn off. Above all, don't attempt to fly too high. Keep within a reasonable distance from the ground--about 25 or 30 feet. This advice is not given solely to lessen the risk of serious accident in case of collapse, but mainly because it will assist to instill confidence in the operator. It is comparatively easy to learn to swim in shallow water, but the knowledge that one is tempting death in deep water begets timidity. Preserving the Equilibrium. After learning how to start and stop, to ascend and descend, the next thing to master is the art of preserving equilibrium, the knack of keeping the machine perfectly level in the air--on an "even keel," as a sailor would say. This simile is particularly appropriate as all aviators are in reality sailors, and much more daring ones than those who course the seas. The latter are in craft which are kept afloat by the buoyancy of the water, whether in motion or otherwise and, so long as normal conditions prevail, will not sink. Aviators sail the air in craft in which constant motion must be maintained in order to ensure flotation. The man who has ridden a bicycle or motorcycle around curves at anything like high speed, will have a very good idea as to the principle of maintaining equilibrium in an airship. He knows that in rounding curves rapidly there is a marked tendency to change the direction of the motion which will result in an upset unless he overcomes it by an inclination of his body in an opposite direction. This is why we see racers lean well over when taking the curves. It simply must be done to preserve the equilibrium and avoid a spill. How It Works In the Air. If the equilibrium of an airship is disturbed to an extent which completely overcomes the center of gravity it falls according to the location of the displacement. If this displacement, for instance, is at either end the apparatus falls endways; if it is to the front or rear, the fall is in the corresponding direction. Owing to uncertain air currents--the air is continually shifting and eddying, especially within a hundred feet or so of the earth--the equilibrium of an airship is almost constantly being disturbed to some extent. Even if this disturbance is not serious enough to bring on a fall it interferes with the progress of the machine, and should be overcome at once. This is one of the things connected with aerial navigation which calls for prompt, intelligent action. Frequently, when the displacement is very slight, it may be overcome, and the craft immediately righted by a mere shifting of the operator's body. Take, for illustration, a case in which the extreme right end of the machine becomes lowered a trifle from the normal level. It is possible to bring it back into proper position by leaning over to the left far enough to shift the weight to the counter-balancing point. The same holds good as to minor front or rear displacements. When Planes Must Be Used. There are other displacements, however, and these are the most frequent, which can be only overcome by manipulation of the stabilizing planes. The method of procedure depends upon the form of machine in use. The Wright machine, as previously explained, is equipped with plane ends which are so contrived as to admit of their being warped (position changed) by means of the lever control. These flexible tip planes move simultaneously, but in opposite directions. As those on one end rise, those on the other end fall below the level of the main plane. By this means air is displaced at one point, and an increased amount secured in another. This may seem like a complicated system, but its workings are simple when once understood. It is by the manipulation or warping of these flexible tips that transverse stability is maintained, and any tendency to displacement endways is overcome. Longitudinal stability is governed by means of the front rudder. Stabilizing planes of some form are a feature, and a necessary feature, on all flying machines, but the methods of application and manipulation vary according to the individual ideas of the inventors. They all tend, however, toward the same end--the keeping of the machine perfectly level when being navigated in the air. When to Make a Flight. A beginner should never attempt to make a flight when a strong wind is blowing. The fiercer the wind, the more likely it is to be gusty and uncertain, and the more difficult it will be to control the machine. Even the most experienced and daring of aviators find there is a limit to wind speed against which they dare not compete. This is not because they lack courage, but have the sense to realize that it would be silly and useless. The novice will find a comparatively still day, or one when the wind is blowing at not to exceed 15 miles an hour, the best for his experiments. The machine will be more easily controlled, the trip will be safer, and also cheaper as the consumption of fuel increases with the speed of the wind against which the aeroplane is forced. CHAPTER XIII. PECULIARITIES OF AIRSHIP POWER. As a general proposition it takes much more power to propel an airship a given number of miles in a certain time than it does an automobile carrying a far heavier load. Automobiles with a gross load of 4,000 pounds, and equipped with engines of 30 horsepower, have travelled considerable distances at the rate of 50 miles an hour. This is an equivalent of about 134 pounds per horsepower. For an average modern flying machine, with a total load, machine and passengers, of 1,200 pounds, and equipped with a 50-horsepower engine, 50 miles an hour is the maximum. Here we have the equivalent of exactly 24 pounds per horsepower. Why this great difference? No less an authority than Mr. Octave Chanute answers the question in a plain, easily understood manner. He says: "In the case of an automobile the ground furnishes a stable support; in the case of a flying machine the engine must furnish the support and also velocity by which the apparatus is sustained in the air." Pressure of the Wind. Air pressure is a big factor in the matter of aeroplane horsepower. Allowing that a dead calm exists, a body moving in the atmosphere creates more or less resistance. The faster it moves, the greater is this resistance. Moving at the rate of 60 miles an hour the resistance, or wind pressure, is approximately 50 pounds to the square foot of surface presented. If the moving object is advancing at a right angle to the wind the following table will give the horsepower effect of the resistance per square foot of surface at various speeds. Horse Power Miles per Hour per sq. foot 10 0.013 15 0 044 20 0.105 25 0.205 30 0.354 40 0.84 50 1.64 60 2.83 80 6.72 100 13.12 While the pressure per square foot at 60 miles an hour, is only 1.64 horsepower, at 100 miles, less than double the speed, it has increased to 13.12 horsepower, or exactly eight times as much. In other words the pressure of the wind increases with the square of the velocity. Wind at 10 miles an hour has four times more pressure than wind at 5 miles an hour. How to Determine Upon Power. This element of air resistance must be taken into consideration in determining the engine horsepower required. When the machine is under headway sufficient to raise it from the ground (about 20 miles an hour), each square foot of surface resistance, will require nearly nine-tenths of a horsepower to overcome the wind pressure, and propel the machine through the air. As shown in the table the ratio of power required increases rapidly as the speed increases until at 60 miles an hour approximately 3 horsepower is needed. In a machine like the Curtiss the area of wind-exposed surface is about 15 square feet. On the basis of this resistance moving the machine at 40 miles an hour would require 12 horsepower. This computation covers only the machine's power to overcome resistance. It does not cover the power exerted in propelling the machine forward after the air pressure is overcome. To meet this important requirement Mr. Curtiss finds it necessary to use a 50-horsepower engine. Of this power, as has been already stated, 12 horsepower is consumed in meeting the wind pressure, leaving 38 horsepower for the purpose of making progress. The flying machine must move faster than the air to which it is opposed. Unless it does this there can be no direct progress. If the two forces are equal there is no straight-ahead advancement. Take, for sake of illustration, a case in which an aeroplane, which has developed a speed of 30 miles an hour, meets a wind velocity of equal force moving in an opposite direction. What is the result? There can be no advance because it is a contest between two evenly matched forces. The aeroplane stands still. The only way to get out of the difficulty is for the operator to wait for more favorable conditions, or bring his machine to the ground in the usual manner by manipulation of the control system. Take another case. An aeroplane, capable of making 50 miles an hour in a calm, is met by a head wind of 25 miles an hour. How much progress does the aeroplane make? Obviously it is 25 miles an hour over the ground. Put the proposition in still another way. If the wind is blowing harder than it is possible for the engine power to overcome, the machine will be forced backward. Wind Pressure a Necessity. While all this is true, the fact remains that wind pressure, up to a certain stage, is an absolute necessity in aerial navigation. The atmosphere itself has very little real supporting power, especially if inactive. If a body heavier than air is to remain afloat it must move rapidly while in suspension. One of the best illustrations of this is to be found in skating over thin ice. Every school boy knows that if he moves with speed he may skate or glide in safety across a thin sheet of ice that would not begin to bear his weight if he were standing still. Exactly the same proposition obtains in the case of the flying machine. The non-technical reason why the support of the machine becomes easier as the speed increases is that the sustaining power of the atmosphere increases with the resistance, and the speed with which the object is moving increases this resistance. With a velocity of 12 miles an hour the weight of the machine is practically reduced by 230 pounds. Thus, if under a condition of absolute calm it were possible to sustain a weight of 770 pounds, the same atmosphere would sustain a weight of 1,000 pounds moving at a speed of 12 miles an hour. This sustaining power increases rapidly as the speed increases. While at 12 miles the sustaining power is figured at 230 pounds, at 24 miles it is four times as great, or 920 pounds. Supporting Area of Birds. One of the things which all producing aviators seek to copy is the motive power of birds, particularly in their relation to the area of support. Close investigation has established the fact that the larger the bird the less is the relative area of support required to secure a given result. This is shown in the following table: Supporting Weight Surface Horse area Bird in lbs. in sq. feet power per lb. Pigeon 1.00 0.7 0.012 0.7 Wild Goose 9.00 2.65 0.026 0.2833 Buzzard 5.00 5.03 0.015 1.06 Condor 17.00 9.85 0.043 0.57 So far as known the condor is the largest of modern birds. It has a wing stretch of 10 feet from tip to tip, a supporting area of about 10 square feet, and weighs 17 pounds. It. is capable of exerting perhaps 1-30 horsepower. (These figures are, of course, approximate.) Comparing the condor with the buzzard with a wing stretch of 6 feet, supporting area of 5 square feet, and a little over 1-100 horsepower, it may be seen that, broadly speaking, the larger the bird the less surface area (relatively) is needed for its support in the air. Comparison With Aeroplanes. If we compare the bird figures with those made possible by the development of the aeroplane it will be readily seen that man has made a wonderful advance in imitating the results produced by nature. Here are the figures: Supporting Weight Surface Horse area Machine in lbs. in sq. feet power per lb. Santos-Dumont . . 350 110.00 30 0.314 Bleriot . . . . . 700 150.00 25 0.214 Antoinette. . . . 1,200 538.00 50 0.448 Curtiss . . . . . 700 258.00 60 0.368 Wright. . . . .[4]1,100 538.00 25 0.489 Farman. . . . . . 1,200 430.00 50 0.358 Voisin. . . . . . 1,200 538.00 50 0.448 [4] The Wrights' new machine weighs only 900 pounds. While the average supporting surface is in favor of the aeroplane, this is more than overbalanced by the greater amount of horsepower required for the weight lifted. The average supporting surface in birds is about three-quarters of a square foot per pound. In the average aeroplane it is about one-half square foot per pound. On the other hand the average aeroplane has a lifting capacity of 24 pounds per horsepower, while the buzzard, for instance, lifts 5 pounds with 15-100 of a horsepower. If the Wright machine--which has a lifting power of 50 pounds per horsepower--should be alone considered the showing would be much more favorable to the aeroplane, but it would not be a fair comparison. More Surface, Less Power. Broadly speaking, the larger the supporting area the less will be the power required. Wright, by the use of 538 square feet of supporting surface, gets along with an engine of 25 horsepower. Curtiss, who uses only 258 square feet of surface, finds an engine of 50 horsepower is needed. Other things, such as frame, etc., being equal, it stands to reason that a reduction in the area of supporting surface will correspondingly reduce the weight of the machine. Thus we have the Curtiss machine with its 258 square feet of surface, weighing only 600 pounds (without operator), but requiring double the horsepower of the Wright machine with 538 square feet of surface and weighing 1,100 pounds. This demonstrates in a forceful way the proposition that the larger the surface the less power will be needed. But there is a limit, on account of its bulk and awkwardness in handling, beyond which the surface area cannot be enlarged. Otherwise it might be possible to equip and operate aeroplanes satisfactorily with engines of 15 horsepower, or even less. The Fuel Consumption Problem. Fuel consumption is a prime factor in the production of engine power. The veriest mechanical tyro knows in a general way that the more power is secured the more fuel must be consumed, allowing that there is no difference in the power-producing qualities of the material used. But few of us understand just what the ratio of increase is, or how it is caused. This proposition is one of keen interest in connection with aviation. Let us cite a problem which will illustrate the point quoted: Allowing that it takes a given amount of gasolene to propel a flying machine a given distance, half the way with the wind, and half against it, the wind blowing at one-half the speed of the machine, what will be the increase in fuel consumption? Increase of Thirty Per Cent. On the face of it there would seem to be no call for an increase as the resistance met when going against the wind is apparently offset by the propulsive force of the wind when the machine is travelling with it. This, however, is called faulty reasoning. The increase in fuel consumption, as figured by Mr. F. W. Lanchester, of the Royal Society of Arts, will be fully 30 per cent over the amount required for a similar operation of the machine in still air. If the journey should be made at right angles to the wind under the same conditions the increase would be 15 per cent. In other words Mr. Lanchester maintains that the work done by the motor in making headway against the wind for a certain distance calls for more engine energy, and consequently more fuel by 30 per cent, than is saved by the helping force of the wind on the return journey. CHAPTER XIV. ABOUT WIND CURRENTS, ETC. One of the first difficulties which the novice will encounter is the uncertainty of the wind currents. With a low velocity the wind, some distance away from the ground, is ordinarily steady. As the velocity increases, however, the wind generally becomes gusty and fitful in its action. This, it should be remembered, does not refer to the velocity of the machine, but to that of the air itself. In this connection Mr. Arthur T. Atherholt, president of the Aero Club of Pennsylvania, in addressing the Boston Society of Scientific Research, said: "Probably the whirlpools of Niagara contain no more erratic currents than the strata of air which is now immediately above us, a fact hard to realize on account of its invisibility." Changes In Wind Currents. While Mr. Atherholt's experience has been mainly with balloons it is all the more valuable on this account, as the balloons were at the mercy of the wind and their varying directions afforded an indisputable guide as to the changing course of the air currents. In speaking of this he said: "In the many trips taken, varying in distance traversed from twenty-five to 900 miles, it was never possible except in one instance to maintain a straight course. These uncertain currents were most noticeable in the Gordon-Bennett race from St. Louis in 1907. Of the nine aerostats competing in that event, eight covered a more or less direct course due east and southeast, whereas the writer, with Major Henry B. Hersey, first started northwest, then north, northeast, east, east by south, and when over the center of Lake Erie were again blown northwest notwithstanding that more favorable winds were sought for at altitudes varying from 100 to 3,000 meters, necessitating a finish in Canada nearly northeast of the starting point. "These nine balloons, making landings extending from Lake Ontario, Canada, to Virginia, all started from one point within the same hour. "The single exception to these roving currents occurred on October 21st, of last year (1909) when, starting from Philadelphia, the wind shifted more than eight degrees, the greatest variation being at the lowest altitudes, yet at no time was a height of over a mile reached. "Throughout the entire day the sky was overcast, with a thermometer varying from fifty-seven degrees at 300 feet to forty-four degrees, Fahrenheit at 5,000 feet, at which altitude the wind had a velocity of 43 miles an hour, in clouds of a cirro-cumulus nature, a landing finally being made near Tannersville, New York, in the Catskill mountains, after a voyage of five and one-half hours. "I have no knowledge of a recorded trip of this distance and duration, maintained in practically a straight line from start to finish." This wind disturbance is more noticeable and more difficult to contend with in a balloon than in a flying machine, owing to the bulk and unwieldy character of the former. At the same time it is not conducive to pleasant, safe or satisfactory sky-sailing in an aeroplane. This is not stated with the purpose of discouraging aviation, but merely that the operator may know what to expect and be prepared to meet it. Not only does the wind change its horizontal course abruptly and without notice, but it also shifts in a vertical direction, one second blowing up, and another down. No man has as yet fathomed the why and wherefore of this erratic action; it is only known that it exists. The most stable currents will be found from 50 to 100 feet from the earth, provided the wind is not diverted by such objects as trees, rocks, etc. That there are equally stable currents higher up is true, but they are generally to be found at excessive altitudes. How a Bird Meets Currents. Observe a bird in action on a windy day and you will find it continually changing the position of its wings. This is done to meet the varying gusts and eddies of the air so that sustentation may be maintained and headway made. One second the bird is bending its wings, altering the angle of incidence; the next it is lifting or depressing one wing at a time. Still again it will extend one wing tip in advance of the other, or be spreading or folding, lowering or raising its tail. All these motions have a meaning, a purpose. They assist the bird in preserving its equilibrium. Without them the bird would be just as helpless in the air as a human being and could not remain afloat. When the wind is still, or comparatively so, a bird, having secured the desired altitude by flight at an angle, may sail or soar with no wing action beyond an occasional stroke when it desires to advance. But, in a gusty, uncertain wind it must use its wings or alight somewhere. Trying to Imitate the Bird. Writing in _Fly_, Mr. William E. White says: "The bird's flight suggests a number of ways in which the equilibrium of a mechanical bird may be controlled. Each of these methods of control may be effected by several different forms of mechanism. "Placing the two wings of an aeroplane at an angle of three to five degrees to each other is perhaps the oldest way of securing lateral balance. This way readily occurs to anyone who watches a sea gull soaring. The theory of the dihedral angle is that when one wing is lifted by a gust of wind, the air is spilled from under it; while the other wing, being correspondingly depressed, presents a greater resistance to the gust and is lifted restoring the balance. A fixed angle of three to five degrees, however, will only be sufficient for very light puffs of wind and to mount the wings so that the whole wing may be moved to change the dihedral angle presents mechanical difficulties which would be better avoided. "The objection of mechanical impracticability applies to any plan to preserve the balance by shifting weight or ballast. The center of gravity should be lower than the center of the supporting surfaces, but cannot be made much lower. It is a common mistake to assume that complete stability will be secured by hanging the center of gravity very low on the principle of the parachute. An aeroplane depends upon rapid horizontal motion for its support, and if the center of gravity be far below the center of support, every change of speed or wind pressure will cause the machine to turn about its center of gravity, pitching forward and backward dangerously. Preserving Longitudinal Balance. "The birds maintain longitudinal, or fore and aft balance, by elevating or depressing their tails. Whether this action is secured in an aeroplane by means of a horizontal rudder placed in the rear, or by deflecting planes placed in front of the main planes, the principle is evidently the same. A horizontal rudder placed well to the rear as in the Antoinette, Bleriot or Santos-Dumont monoplanes, will be very much safer and steadier than the deflecting planes in front, as in the Wright or Curtiss biplanes, but not so sensitive or prompt in action. "The natural fore and aft stability is very much strengthened by placing the load well forward. The center of gravity near the front and a tail or rudder streaming to the rear secures stability as an arrow is balanced by the head and feathering. The adoption of this principle makes it almost impossible for the aeroplane to turn over. The Matter of Lateral Balance. "All successful aeroplanes thus far have maintained lateral balance by the principle of changing the angle of incidence of the wings. "Other ways of maintaining the lateral balance, suggested by observation of the flight of birds are--extending the wing tips and spilling the air through the pinions; or, what is the same thing, varying the area of the wings at their extremities. "Extending the wing tips seems to be a simple and effective solution of the problem. The tips may be made to swing outward upon a vertical axis placed at the front edge of the main planes; or they may be hinged to the ends of the main plane so as to be elevated or depressed through suitable connections by the aviator; or they may be supported from a horizontal axis parallel with the ends of the main planes so that they may swing outward, the aviator controlling both tips through one lever so that as one tip is extended the other is retracted. "The elastic wing pinions of a bird bend easily before the wind, permitting the gusts to glance off, but presenting always an even and efficient curvature to the steady currents of the air." High Winds Threaten Stability. To ensure perfect stability, without control, either human or automatic, it is asserted that the aeroplane must move faster than the wind is blowing. So long as the wind is blowing at the rate of 30 miles an hour, and the machine is traveling 40 or more, there will be little trouble as regards equilibrium so far as wind disturbance goes, provided the wind blows evenly and does not come in gusts or eddying currents. But when conditions are reversed--when the machine travels only 30 miles an hour and the wind blows at the rate of 50, look out for loss of equilibrium. One of the main reasons for this is that high winds are rarely steady; they seldom blow for any length of time at the same speed. They are usually "gusty," the gusts being a momentary movement at a higher speed. Tornadic gusts are also formed by the meeting of two opposing currents, causing a whirling motion, which makes stability uncertain. Besides, it is not unusual for wind of high speed to suddenly change its direction without warning. Trouble With Vertical Columns. Vertical currents--columns of ascending air--are frequently encountered in unexpected places and have more or less tendency, according to their strength, to make it difficult to keep the machine within a reasonable distance from the ground. These vertical currents are most generally noticeable in the vicinity of steep cliffs, or deep ravines. In such instances they are usually of considerable strength, being caused by the deflection of strong winds blowing against the face of the cliffs. This deflection exerts a back pressure which is felt quite a distance away from the point of origin, so that the vertical current exerts an influence in forcing the machine upward long before the cliff is reached. CHAPTER XV. THE ELEMENT OF DANGER. That there is an element of danger in aviation is undeniable, but it is nowhere so great as the public imagines. Men are killed and injured in the operation of flying machines just as they are killed and injured in the operation of railways. Considering the character of aviation the percentage of casualties is surprisingly small. This is because the results following a collapse in the air are very much different from what might be imagined. Instead of dropping to the ground like a bullet an aeroplane, under ordinary conditions will, when anything goes wrong, sail gently downward like a parachute, particularly if the operator is cool-headed and nervy enough to so manipulate the apparatus as to preserve its equilibrium and keep the machine on an even keel. Two Fields of Safety. At least one prominent aviator has declared that there are two fields of safety--one close to the ground, and the other well up in the air. In the first-named the fall will be a slight one with little chance of the operator being seriously hurt. From the field of high altitude the the descent will be gradual, as a rule, the planes of the machine serving to break the force of the fall. With a cool-headed operator in control the aeroplane may be even guided at an angle (about 1 to 8) in its descent so as to touch the ground with a gliding motion and with a minimum of impact. Such an experience, of course, is far from pleasant, but it is by no means so dangerous as might appear. There is more real danger in falling from an elevation of 75 or 100 feet than there is from 1,000 feet, as in the former case there is no chance for the machine to serve as a parachute--its contact with the ground comes too quickly. Lesson in Recent Accidents. Among the more recent fatalities in aviation are the deaths of Antonio Fernandez and Leon Delagrange. The former was thrown to the ground by a sudden stoppage of his motor, the entire machine seeming to collapse. It is evident there were radical defects, not only in the motor, but in the aeroplane framework as well. At the time of the stoppage it is estimated that Fernandez was up about 1,500 feet, but the machine got no opportunity to exert a parachute effect, as it broke up immediately. This would indicate a fatal weakness in the structure which, under proper testing, could probably have been detected before it was used in flight. It is hard to say it, but Delagrange appears to have been culpable to great degree in overloading his machine with a motor equipment much heavier than it was designed to sustain. He was 65 feet up in the air when the collapse occurred, resulting in his death. As in the case of Fernandez common-sense precaution would doubtless have prevented the fatality. Aviation Not Extra Hazardous. All told there have been, up to the time of this writing (April, 1910), just five fatalities in the history of power- driven aviation. This is surprisingly low when the nature of the experiments, and the fact that most of the operators were far from having extended experience, is taken into consideration. Men like the Wrights, Curtiss, Bleriot, Farman, Paulhan and others, are now experts, but there was a time, and it was not long ago, when they were unskilled. That they, with numerous others less widely known, should have come safely through their many experiments would seem to disprove the prevailing idea that aviation is an extra hazardous pursuit. In the hands of careful, quick-witted, nervy men the sailing of an airship should be no more hazardous than the sailing of a yacht. A vessel captain with common sense will not go to sea in a storm, or navigate a weak, unseaworthy craft. Neither should an aviator attempt to sail when the wind is high and gusty, nor with a machine which has not been thoroughly tested and found to be strong and safe. Safer Than Railroading. Statistics show that some 12,000 people are killed and 72,000 injured every year on the railroads of the United States. Come to think it over it is small wonder that the list of fatalities is so large. Trains are run at high speeds, dashing over crossings at which collisions are liable to occur, and over bridges which often collapse or are swept away by floods. Still, while the number of casualties is large, the actual percentage is small considering the immense number of people involved. It is so in aviation. The number of casualties is remarkably small in comparison with the number of flights made. In the hands of competent men the sailing of an airship should be, and is, freer from risk of accident than the running of a railway train. There are no rails to spread or break, no bridges to collapse, no crossings at which collisions may occur, no chance for some sleepy or overworked employee to misunderstand the dispatcher's orders and cause a wreck. Two Main Causes of Trouble. The two main causes of trouble in an airship leading to disaster may be attributed to the stoppage of the motor, and the aviator becoming rattled so that he loses control of his machine. Modern ingenuity is fast developing motors that almost daily become more and more reliable, and experience is making aviators more and more self-confident in their ability to act wisely and promptly in cases of emergency. Besides this a satisfactory system of automatic control is in a fair way of being perfected. Occasionally even the most experienced and competent of men in all callings become careless and by foolish action invite disaster. This is true of aviators the same as it is of railroaders, men who work in dynamite mills, etc. But in nearly every instance the responsibility rests with the individual; not with the system. There are some men unfitted by nature for aviation, just as there are others unfitted to be railway engineers. CHAPTER XVI. RADICAL CHANGES BEING MADE. Changes, many of them extremely radical in their nature, are continually being made by prominent aviators, and particularly those who have won the greatest amount of success. Wonderful as the results have been few of the aviators are really satisfied. Their successes have merely spurred them on to new endeavors, the ultimate end being the development of an absolutely perfect aircraft. Among the men who have been thus experimenting are the Wright Brothers, who last year (1909) brought out a craft totally different as regards proportions and weight from the one used the preceding year. One marked result was a gain of about 3 1/2 miles an hour in speed. Dimensions of 1908 Machine. The 1908 model aeroplane was 40 by 29 feet over all. The carrying surfaces, that is, the two aerocurves, were 40 by 6 feet, having a parabolical curve of one in twelve. With about 70 square feet of surface in the rudders, the total surface given was about 550 square feet. The engine, which is the invention of the Wright brothers, weighed, approximately, 200 pounds, and gave about 25 horsepower at 1,400 revolutions per minute. The total weight of the aeroplane, exclusive of passenger, but inclusive of engine, was about 1,150 pounds. This result showed a lift of a fraction over 2 1/4 pounds to the square foot of carrying surface. The speed desired was 40 miles an hour, but the machine was found to make only a scant 39 miles an hour. The upright struts were about 7/8-inch thick, the skids, 2 1/2 by 1 1/4 inches thick. Dimensions of 1909 Machine. The 1909 aeroplane was built primarily for greater speed, and relatively heavier; to be less at the mercy of the wind. This result was obtained as follows: The aerocurves, or carrying surfaces, were reduced in dimensions from 40 by 6 feet to 36 by 5 1/2 feet, the curve remaining the same, one in twelve. The upright struts were cut from seven-eighths inch to five-eighths inch, and the skids from two and one-half by one and one-quarter to two and one-quarter by one and three-eighths inches. This result shows that there were some 81 square feet of carrying surface missing over that of last year's model. and some 25 pounds loss of weight. Relatively, though, the 1909 model aeroplane, while actually 25 pounds lighter, is really some 150 pounds heavier in the air than the 1908 model, owing to the lesser square feet of carrying surface. Some of the Results Obtained. Reducing the carrying surfaces from 6 to 5 1/2 feet gave two results--first, less carrying capacity; and, second, less head-on resistance, owing to the fact that the extent of the parabolic curve in the carrying surfaces was shortened. The "head-on" resistance is the retardance the aeroplane meets in passing through the air, and is counted in square feet. In the 1908 model the curve being one in twelve and 6 feet deep, gave 6 inches of head-on resistance. The plane being 40 feet spread, gave 6 inches by 40 feet, or 20 square feet of head-on resistance. Increasing this figure by a like amount for each plane, and adding approximately 10 square feet for struts, skids and wiring, we have a total of approximately, 50 square feet of surface for "head-on" resistance. In the 1909 aeroplane, shortening the curve 6 inches at the parabolic end of the curve took off 1 inch of head-on resistance. Shortening the spread of the planes took off between 3 and 4 square feet of head-on resistance. Add to this the total of 7 square feet, less curve surface and about 1 square foot, less wire and woodwork resistance, and we have a grand total of, approximately, 12 square feet of less "head-on" resistance over the 1908 model. Changes in Engine Action. The engine used in 1909 was the same one used in 1908, though some minor changes were made as improvements; for instance, a make and break spark was used, and a nine-tooth, instead of a ten-tooth magneto gear-wheel was used. This increased the engine revolutions per minute from 1,200 to 1,400, and the propeller revolutions per minute from 350 to 371, giving a propeller thrust of, approximately, 170 foot pounds instead of 153, as was had last year. More Speed and Same Capacity. One unsatisfactory feature of the 1909 model over that of 1908, apparently, was the lack of inherent lateral stability. This was caused by the lesser surface and lesser extent of curvatures at the portions of the aeroplane which were warped. This defect did not show so plainly after Mr. Orville Wright had become fully proficient in the handling of the new machine, and with skillful management, the 1909 model aeroplane will be just as safe and secure as the other though it will take a little more practice to get that same degree of skill. To sum up: The aeroplane used in 1909 was 25 pounds lighter, but really about 150 pounds heavier in the air, had less head-on resistance, and greater propeller thrust. The speed was increased from about 39 miles per hour to 42 1/2 miles per hour. The lifting capacity remained about the same, about 450 pounds capacity passenger-weight, with the 1908 machine. In this respect, the loss of carrying surface was compensated for by the increased speed. During the first few flights it was plainly demonstrated that it would need the highest skill to properly handle the aeroplane, as first one end and then the other would dip and strike the ground, and either tear the canvas or slew the aeroplane around and break a skid. Wrights Adopt Wheeled Gears. In still another important respect the Wrights, so far as the output of one of their companies goes, have made a radical change. All the aeroplanes turned out by the Deutsch Wright Gesellschaft, according to the German publication, _Automobil-Welt_, will hereafter be equipped with wheeled running gears and tails. The plan of this new machine is shown in the illustration on page 145. The wheels are three in number, and are attached one to each of the two skids, just under the front edge of the planes, and one forward of these, attached to a cross- member. It is asserted that with these wheels the teaching of purchasers to operate the machines is much simplified, as the beginners can make short flights on their own account without using the starting derrick. This is a big concession for the Wrights to make, as they have hitherto adhered stoutly to the skid gear. While it is true they do not control the German company producing their aeroplanes, yet the nature of their connection with the enterprise is such that it may be taken for granted no radical changes in construction would be made without their approval and consent. Only Three Dangerous Rivals. Official trials with the 1909 model smashed many records and leave the Wright brothers with only three dangerous rivals in the field, and with basic patents which cover the curve, warp and wing-tip devices found on all the other makes of aeroplanes. These three rivals are the Curtiss and Voisin biplane type and the Bleriot monoplane pattern. The Bleriot monoplane is probably the most dangerous rival, as this make of machine has a record of 54 miles per hour, has crossed the English channel, and has lifted two passengers besides the operator. The latest type of this machine only weighs 771.61 pounds complete, without passengers, and will lift a total passenger weight of 462.97 pounds, which is a lift of 5.21 pounds to the square foot. This is a better result than those published by the Wright brothers, the best noted being 4.25 pounds per square foot. Other Aviators at Work. The Wrights, however, are not alone in their efforts to promote the efficiency of the flying machine. Other competent inventive aviators, notably Curtiss, Voisin, Bleriot and Farman, are close after them. The Wrights, as stated, have a marked advantage in the possession of patents covering surface plane devices which have thus far been found indispensable in flying machine construction. Numerous law suits growing out of alleged infringements
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