EMPLOYING the broadest possible classification, the science of aviation may be divided into two epochs— before man flew and afterward. The former might be called the Experimental Period and the latter the Practical Period. To be sure, at present there seems to be considerable discussion as to the exact line of demarkation separating these periods, tout this resolves itself largely into a definition of the word “ fly,” as applied to the particular subject in hand. Lilienthal and other early experimenters with gliding machines undoubtedly imitated nature more closely than many later workers who used power-driven aeroplanes; but, remarkable as were many of these early experiments, they did but pave the way for real man-flight, which may be considered to have been accomplished only when man left the ground with a power-driven sustaining surface, under more or less stable conditions. The object of the discussion which is raging so fiercely throughout the world of aviation at the present time is to ascertain who was the first to fly in a power-driven aeroplane, with the machine under the control of the operator, particularly as applied to lateral stability. Any one who has given the subject even casual examination cannot but be impressed by the remarkable similarity of some of the more advanced machines of the Experimental Period as compared with many of the successful fliers of the Practical Period. Indeed, this similarity is so marked that the enthusiast seeks further for the cause, and has not gone far before he realizes that the development of the light and efficient internal combustion motor has done more than anything else to lift, aviation from mental stage to that of practical man-flight. In the automobile field we find a parallel state of affairs. Clumsy self-propelled steam vehicles existed years before the brilliant inventions of De Dion and Daimler gave to the world the wonderfully light and comparatively simple prime mover which has made the automobile the universally successful vehicle it is to-day. It is the same with the aeroplane. Examine Langley"s man-carrying machine. which unfortunately was never properly tested, and the large, ingeniously constructed aeroplane of Sir Hiram Maxim, not to mention other models of early experimenters, and one is impressed by the enormous handicap they labored under in not having a simple, light motor. In the early development of the aviation motor, extreme lightness was the object sought for, and was at first obtained only at an entirely dispropor-tiona te sacrifice of efficiency and reliability. Fortunately for aviation, however, the development of a suitable motor did not have to start from the heavy, stationary gas engines, for at the dawn of the Practical Period in avi- the experi- Recent Developments in France By Earle L. Ovington, Licensed Aviator ation the automobile engine had already reached a comparatively high state of perfection. Designers of aviation motors at first simply took the more advanced types of automobile motors, and, adhering to their general design, eliminated weight by reducing the Fig. 1. — The new 70-horse-power Gnome motor. factor of safety of each member to the lowest practical point, and by employing the very highest grade of material and workmanship. The Antoinette motor, which proved so successful in racing motor boats and the early aeroplanes, is a sample' of this type. And it speaks well for Monsieur Levavasseur, the designer and constructor of this motor, that even to-day, in spite of the fact that the latest type of motor differs little from the earlier models, the Antoinette engine is considered in the foremost class among aviation motors. At the present time, extreme lightness for a given output is as much sought for in aviation motors as it was in the first stages of development of the practical aeroplane. But this is due largely to the fact that an artificial state of affairs exists in the development of the aeroplane by the world' s greatest designers and builders. During the Experimental Period of aviation, man was satisfied to progress slowly and along rational lines. Theory was far in advance of practice. During this period L.angley, Lanchester and Maxim gave to the science of aviation their unparalleled researches, not to mention the works of less known writers. But from the moment man really flew, Practice vanquished Theory, and designers proceeded along almost entirely empirical lines to develop a flying machine for exhibition and racing purposes. From the opening of the Practical Period to the present time, designers have been too busy actually building machines to meet the comparatively enormous demand, to worry very much about the theoretical side of the subject. Very great progress has been made, to be sure, but it has been largely confined to making the machines stronger and faster, and in standardizing, to a certain extent, the several types. The demand for a light aeroplane for exhibition purposes, and a fast one for racing, has forced the designers of aviation motors ,to tax their inventive capacities to the utmost in an effort to produce a motor of the greatest possible power for a given weight. And when it is considered that there now exists a motor which weighs only about three pounds per horse-power, which has run continuously over eight hours in actual flight, we can get an idea of the wonderful strides made in the development of the aviation engine. Although to-day lightness and speed seem to be the greatest aims of the designer, the time is not far distant when extreme reliability and high efficiency will be the objects sought for. By its very nature an aeroplane remains in the air only so long as it is moving rapidly forward, and a properly working motor is necessary for this condition; hence reliability, without any question whatever, is the first essential in an aviation engine, assuming, of course, that the motor is light enough for the purpose. Duplicate power plants, or possibly a smaller power plant for emergency use, will do much to add to the security of aerial .travel; but even under such circumstances the motive power should be as reliable as it is possible to make it. And as we understand more fully the design of the supporting surfaces in an aeroplane, and the engineers more fully appreciate the desirability of reducing head resistance to a minimum, great power in a light weight will become of less and less importance. The designer of the little Nieuport monoplane made giant strides in this direction when he produced a machine carefully' calculated to reduce head resistance. This machine, although fitted with only a 30-horse-power motor, almost equaled the speed record made by Leblanc at Belmont Park with his fourteen-cylinder, 100-horse-power, Gnome-driven Bleriot. Birds soar for hours under propitious circumstances with practically no expenditure of energy, and even under very adverse conditions fly with an efficiency which should make the intelligent aeroplane designer drop from his self-erected pinnacle as “ conqueror of the air,” and realize how poor indeed, from the standpoint of the natural fliers, is his flying machine. Aviation motors may be broadly divided into two general classes— reciprocating and rotary motors. In the former the cylinders and crank case remain stationary while the crank shaft rotates, and in the latter type the crank shaft is stationary while the crank case and cylinders revolve around it. All automobile engines, and most aero motors, are in the recipro-eating class, while the Gnome is by far the most prominent engine in the rotary class. It is interesting to note the various and often ingenious expedients adopted by the leading manufacturers to attain the same end, i. e., the production of a light motor. The designer of the Anzani reciprocating engine, who was one of the very first to devote his time to the production of a practical aviation motor, developed his product from the power plants he used on his motorcycle pacing machines. His first engine was a three-cylinder one, having the cylinders all in one plane and arranged radially around the crank case. By this arrangement he was able to use a crank case for three cylinders which was only slightly larger than that for one. With this motor, rated at 25 horse-power, Bleriot first crossed the English Channel, and in spite of the remarkable strides which have been made in more powerful aero motors, this original type of Anzani, almost; im-changed, is to-day one of the most reliable engines made, and is the one used by Bleriot and other leading manufacturers in their aeroplanes made for sch° ° i purposes. The writer, who obtained his Freiich brevet de piZote-aviateMr at Bleriot' s school at pau, France, was surprised at the enormous amenmt; of abuse these little motors stood without materially losing their power. Anzani' s latest product is a six-cylinder, star-shaped motor of the same tyi)^ which s0mewhat resembles in appearance, when stationary, the r0tating motor so much used in French aer° planes. The R. E. P. reciprocating engine, the product of Robert Esnault-Pelterie, is another motor- of this class where the cylinders are arranged radially around a common crank case. The designer- has carried this principle very much farther however, than any one else, for- Uie writer saw last February, at the factor near Paris, a new R. E. P. engine having no less than ten cylinders. In the Antoinette engine the factor of safety has been reduced to a minimum. and made as uniform as possible for the component parts, by the use of the very highest class of material and workmanship. Every little detail has received the attention of its experienced designer, Monsieur Levavasseur, and most ingenious are some of the structural details. The flywheel, for m-stance, which ordinarily is by far the heaviest member of an engine, in the Antoinette is simply a steel rim connected to a central hub by a flange of very thin and flexible steel. When the motor is building up its speed, this flange is so flexible the whole flywheel seems “ out of true,” but at normal engine speeds centrifugal force is sufficiently strong to make the flywheel as rigid as if it were the usual heavy cast affair. In the Antoinette flywheel almost every ounce of weight is where its effect is greatest— in the periphery. Other equally novel artifices are employed in order to reduce weight. Among American engines of the reciprocating class the Curtiss is probably the best known and most widely used. Curtiss, like the designer of the Antoinette, has carefully studied every part of his design and produced a motor remarkably light and efficient. It was with this motor, in his own aeroplane, that. Curtiss won the first Gordon Bennett race at Rheims, France, in 1909, triumphing over the best European productions. The question has yet to be definitely settled among designers of reciprocating engines as to whether cooling by air or water is the most desirable for aero engines. Of the engines mentioned, the Antoinette and Curtiss use water cooling, while the Anzani and The writer spent a most interesting afternoon going R. E. P. depend upon air. It is perhaps significant over the Gnome factory, which is just outside of to note, in this connection, that the Renault motor Paris, with Monsieur Seguin, the chief engineer This is air cooled, while the famous automobile engine, factory is literally engaged in turning out steel shav- made by the same concern, is cooled by water circu- ings, for every part of the entire motor is turned lation. Simplicity being such a desirable point where from the solid metal. In the rough the cylinders are reliability is sought for, and reliability being such drop-forged nickel-steel bars; but when the lathes and an essential in the aviation motor, the writer strongly boring tools have completed their work they are favors the air-cooled motor, even for engines of the engine cylinders with radiating fins as thin as paper reciprocating class. We now come to the consideration of what is undoubtedly the most interesting and promising type of internal combustion motor to-day— the rotary engine. The designers of this comparative newcomer made a giant stride into the unknown when they entirely Fig. 6.— The lOO-horse-power fourteen-cylinder Gnome, as used by Leblanc and Hamel in the recent International Cup race. A 7-cylinder, 70-H. P. engine on a Nieuport monoplane won the race. reversed the operation of the component parts of the gasoline engine. Incidentally, in doing so, they banished forever certain inherent difficulties found with motors of the reciprocating class. In the ordinary reciprocating motor, the cylinders, whether air or water cooled, are stationary, as is the crank case, while the crank shaft revolves. In the rotary motor, the crank shaft is the stationary member, while the cylinders, arranged radially and air cooled, rotate with the crank case around it. As there is to-day only one representative of the rotary class, which has universally proved its right to be classed as unquestionably reliable, we will confine our remarks to that particular make— the wonderful Gnome rotary motor. Fig. 1 is the very latest product of the Gnome factory— the new 70 horse-power. Fig. 2 shows the writer' s 1911 model Bleriot, fitted with this motor, it being the first machine sent out from the Bleriot factory employing the motor of 70 horse-power, and the first Bleriot with the new “ inverse curve” tail brought to America. Comparing the 50-horse-power and the 70-horse-power engines, the method of attaching the cylinders to the crank case has been greatly improved. In the case of the 50 horse-power it requires a mechanic of the highest order, who knows the Gnome motor thoroughly, to dismount and assemble it, but with the new 70 horse-power it is necessary only to unscrew a few nuts when the front half of the crank case may be removed, leaving the cylinders readily detachable. The method of clamping the cylinders, too, is far more secure than in the older model. and walls not much heavier. It is interesting to note, in speaking of the Gnome cylinder construction, that the receptacles into which the spark plugs screw are internally threaded steel tubes welded into the sid” of the cylinder head by a secret welding process, the arrangement being shown in Fig. 3. The crank shaft is hollow, and through it pass the gasoline vapor and oil for lubrication. The construction is indicated in Fig. 3, the carbureter being plainly visible at the end of the shaft, while the oil pJpes enter the shaft from above as shown. Just to the left and below the oil pipes may be seen the pumps which force the fuel and oil under pressure to perform their duties. The vapor from the carbureter, after passing into the crank case through the hollow crank shaft, is admitted to the combustion space in the head of the cylinders through automatic inlet valves which are balanced by counter weights to eliminate the action of centrifugal force. The wonderful ingenuity of construction of these valves, making them easily removable through the cylinder head without the necessity of taking down the engine, must be remarked upon. The exhaust valves are of course mechanically operated, the construction being clearly evident by an examination of the illustration. The magneto is behind the mounting framework in Fig. 3, while the segment bearing part of the distributer rotates, and from the segments wires lead to the spark plugs, as clearly indicated. Fig. 4 shows one of the testing “ gun carriages” in use at the Gnome works, with a motor in place. Fig. 5 gives an idea of the appearance of this wonderful motor in action, while Fig. 6 is a view of the 100-horse-power engine with fourteen cylinders. This is the motor used by Leblanc and Grahame-White when the latter won the Gordon Bennett race at Belmont Park last fall. The writer has made a deep study of internal combustion motor design, and is firmly of the opinion that the rotary engine is the aviation motor of the future, not to say the present. The Gnome motor to-day holds practically all the world' s speed records, which is remarkable when the handicap in favor of the reciprocating engine from the standpoint of time taken in development is considered. In the case of the rotary motor, the cylinders and crank case serve as an efficient flywheel, thereby eliminating dead weight which is of no other use on the reciprocating engine. Vibration, due in the reciprocating engine to the unbalanced moving parts, is practically done away with in the rotary motor. With the rotary cylinders, water cooling, with its additional weight and complication, is not even thought of, for the rapid movement of the cylinders themselves through the cooling medium is all that can be desired. A closer examination of the two types emphasizes many other advantages of the rotary motor, such as a reduction in size and weight for a given power, reduction of the number of bearing surfaces, etc. The principal disadvantage of the rotary motor at present is the fact that castor oil is the only lubricant which has been found so far to be satisfactory, and on account of the nature of the oil used, comparatively large quantities must be employed. Critics have even called it “ the oil-cooled motor.” Furthermore, the use of this oil in such large quantities (varying from one part of oil to three or four of gasoline) makes frequent cleaning necessary. In spite of this, however, the Gnome engine has forced its way to the front rank, against the adverse criticism and even abuse which has always stood in the path of true progress, until to-day it is the engine above all others where the greatest power and reliability are derived for the least weight. The idea of the writer in speaking so forcibly of the superiority of the Gnome motor is to awaken engine designers in America to the evident superiority of the rotating type over the reciprocating, with the hope that American manufacturers will attack the problem of rotary motor design, and, with their characteristic ingenuity and enterprise, produce an American aviation engine which will stand second to none. The rotary motor of the Gnome type is the nearest approach yet made to the ideal internal combustion engine— the gas turbine— and as such demands recognition by every American manufacturer. Incidentally, the writer has heard on good authority that the Gnome company are experimenting with a two-cycle engine of the rotary type. Since the proper cooling and scavenging of the cylinder of this class of motor are the two hitherto almost insurmountable obstacles, it would seem the rotary principle is particularly adapted to the development of this class of engine. The Tallest of Tall Buildings WORK is now in progress at Broadway and Barclay Street on the foundations of one of those huge steel-and-concrete office buildings, which are such a characteristic feature of the modern architecture of New York city. The Woolworth building, as it will be called, will have a. frontage of about 155 feet on Broadway, between Barclay Street and Park Place, and it will extend into the Mock for a depth of about 200 feet. Its most distinguishing characteristic, at least to the popular eye, will be its great height, for its crowning element, ball or lantern, or finial, or whatever it may be called, will stand exactly 775 feet above street level. At the site there is the characteristic deep bed of quicksand, and through this the foundations are now being carried down everywhere to solid rock, which is about 110 feet below the sidewalk. Hence the structure, from lowest foundation to its topmost point, will have a total height of 885 feet. The main building, which will cover the whole area except for a 35 by 96 foot interior rear court, will contain 31 stories, and above this there will rise from the center of the Broadway facade a great tower, 84 by 86 feet square, which will extend, with vertical walls, to the 50th floor, with an offset at the 42nd floor, where the dimensions are reduced to 69 by 71 feet, and at the 47th floor, where there is a further reduction to 59 by 61 feet. The .height from the sidewalk to the 31st floor, which marks the top of the main roof, will be 400 feet. The tower extends another 270 feet, from the 31st to the 50th floor, making the height above sidewalk to this point 670 feet. Here it is surmounted by a pyramid which is 54 feet square at the base, in which are five additional floors and an observation gallery, the last-named being at an elevation of 730 feet above the sidewalk. There are two floors below street level, and the general height of each story throughout is 12% feet. The WoolworthBuilding is designed in accordance with the Building Code of this city, which allows 150 pounds per square food load on the first and basement floors and 75 pounds per square foot on each of the other floors. When we remember that a uniform wind pressure of 30 pounds per square foot over the whole surface of (the building has been provided for, it can be understood that the stresses from wind alone reach enormous figures. The maximum direct compression from wind pressure on one single column of the building reaches 2,500,000 pounds, to which must be added 200,000 pounds delivered from the portal bracing. The steel framework alone will contain 20,000 tons of steel. Its various columns will be supported on 69 piers of partly reinforced concrete, which are now being sunk to solid rock at an average depth of 110 feet below street lever. Except where conditions call for rectangular shapes, the caissons are cylindrical, and they vary from 8 feet 3 inches to 18 feet 9 inches in diameter. They are loaded to a maximum of 18 tons per square foot. Generally speaking, the axes of the columns stand in line with the axes of the caissons; but ' in some cases they are placed eccentrically, and their load is transferred to the center of the caisson by means of heavy steel girders acting as cantilevers. These girders are very massive and stiff, being as much as 2 inches in thickness in the web, and having an average depth of 8 feet, with a maximum weight of 60 tons. From the 55ith to the 50th floor, the inclined members of the pyramid take oare of the wind stresses. From the 50th to the 47th floor, deep floor girders ' with solid gusset plates serve the same purpose. From the 42nd to- the 28th floor, the exterior wail columns are braced against the wind by extra deep wall girders, and by knee braces, reaching well in to the center of each story. From the 28th floor to the street, every panel between the outside columns facing Broadway and the opposite face of the building is stiffened by a full-depth web portal with heavy flanges. Transversely to Broadway, the bracing is by means of single portals, reaching across the full width of the tower. There are in the building 60 main columns of closed box section. The maximum load on a single column reaches the enormous figure of 4,750 tons, and this column measures at the base, 2 feet 6 inches by 3 feet 8 inches, the total cross section of metal being 650 square inches. The architect of the building, Mr. Cass Gilbert, and his consulting and designing engineer, Mr. Gunvald Aus, are to be congratulated on the design. The Scientific American has frequently suggested that for good architectural effect it would be advisable, in these tall buildings, to accentuate the vertical lines at the expense of the horizontal. Mr. Gilbert has done this to a marked degree, and in. his treatment of .the tower he has introduced those open-work pinnacles or “ towerettes,” if we may coin a word, whioh the medieval builders used to such happy effect in the towers of their Gothic cathedrals. The exterior walls are to be built of granite up to the fifth floor, and above that of terra cotta. The building will be served by 26 elevators, all of which will be thoroughly fireproofed; also there will bs four commodious fire-escape stairways, widely separated from one another, and each built in a fireproof shaft. The structural steel will have a coating of one inch of cement mortar; their interior spaces wiU be filled in solid with concrete or mortar, and the whole will be inclosed in a shell of terra cotta 3 inches thick. There will be no wood whatever nor any inflammable substance in the building. Doors, windows and trim will be of pressed steel, floors of mosaic, and exposed exterior windows will be glazed with wire clamps.