TL 353 ,5 T7 RPLdNt-S ri SAFETY GIFT OF COPYRIGHT BY WILL H. LOW. ICARUS From a mural painting by Will H. Low, in the New York State Education Building, Albany, New York. Airplanes and Safety "Soon shall thy arm^ un conquered Steam, afar Draw the slow barge, or drive the rapid car; Or, on wide waving wings expanded,, bear The flying chariot through the field of air" Erasmus Darwin. [1781] THE TRAVELERS HARTFORD, CONNECTICUT 22031 4-13-21 Copyright, 1921, by THE TRAVELERS INSURANCE COMPANY, Hartford, Connecticut GIFT PREFACE T^EFORE aircraft can be extensively utilized for J~J -private and commercial purposes^ and before aerial navigation can be developed to a point where it will afford an attractive field to insurance companies^ it will be necessary to effect a substantial readjustment of present- day conditions. The public^ for example^ will have to acquire a considerable amount -of aeronautical knowledge before it will be prepared to admit the practicability of aerial navigation. There is also a crying need for a vastly greater number of official landing fields > laid out and managed in accordance with approved safety principles. It is likewise necessary to establish standard airways^ duly provided with aerial lighthouses and wireless signal stations; and to pass uniform and stringent laws govern- ing the licensing of pilots^ the construction and use of air- craft 3 and the conduct of air-navigation generally. In the present stage of development it is impossible to discuss the subject of "AIRPLANES AND SAFETY" exhaustively and fully ^ and the present book does not attempt to do so. We are putting it forth , however , in the ' 7 456657 VI AIRPLANES AND SAFETY belief that it will assist in promoting aerial navigation by presenting an elementary account of the construction and operation of airplanes, and by discussing some of the means by which flying may be made a safer mode of travel and transportation. Rapid changes of many kinds are inevitable in connection with so new a subject, changes relating not only to apparatus, but also to the training and licensing of pilots, to the insurance coverage, to the legal aspect, and to many other phases. With increasing study and ex- perience the subject is sure to develop quickly, and it is quite within the range of possibility that fundamental modifications along any of these lines may be forthcoming within a year or two. If we had the gift of prophecy we should include all these future advances and improvements in the present book. Not having any such gift, however, we have merely endeavored to represent the subject as it stands to-day. The text is based primarily upon our own experience and observation, though we have naturally consulted numerous books, pamphlets, reports, and technical jour- nals. Furthermore, we have had friendly personal coun- sel from many eminent and qualified sources, and notably from Colonel E. A. Deeds ' of the Equipment Division, Air Service, U. S. Army; from Lieut. -Colonel H. M. Hickam, Major E. L. Jones, and L. D. Seymour, M. E., of the Information Group, Office of the Director of Air Service; from Lieut. -Commander Eyrd and Mr. Lane Lucy, of the Navy Department; from Second Assistant Postmaster General Otto Prager; and from Nelson S. Hopkins, President of the Phenix Aircraft Products Company. But although we desire to express our fullest appreciation of the generous assistance we have received PREFACE Vll from these gentlemen, it must be clearly understood that they have acted only in an advisory capacity ', and that they are not in any way responsible for the statements that are made. The responsibility is wholly our own, and we accept it in full. THE TRAVELERS INSURANCE COMPANY THE TRAVELERS INDEMNITY COMPANY HARTFORD, CONNECTICUT CONTENTS Introduction: The Legend of Icarus I Early Balloons . 3 The Beginnings of the Airplane 6 Influence of the World War 9 The Future of Aerial Navigation 1 1 Commercial Uses of Aircraft 1 1 I. Airplane Construction: Types of Machines 13 Aeronautical Engines 18 The Structural Parts of Airplanes 18 The Body 19 The Wings 19 The Tail 23 The Landing Gear 24 Structural Materials Used 25 Control 29 Plan and Performance 31 II. The Operation of Airplanes: Introductory 36 Tuning-up 36 Standard Clothing and Equipment 41 III. Airplane Accidents: General Causes of Accidents ........ 43 Errors of the Pilot 45 Failure of the Machine 47 Fire 47 Superchargers and Variable-pitch Propellers ... 52 Instruments 52 Safety Straps 54 Emergency Stations 55 X AIRPLANES AND SAFETY IV. Pilots: The Importance of Legal Regulation 57 Physical and Mental Qualifications of Pilots ... 58 Training 61 Examination and Licensing 63 Care of the Pilot's Health 64 V. The Maintenance and Repair of Airplanes: The Repair Shop 67 Repair Shop Hazards 69 General Fire Prevention 70 Woodworking 71 Doping . 73 Machine Shop 76 Motor Testing 78 VI. Landing Fields, Airways, and Aerial Laws: Landing Fields in General 79 Airdromes 79 Emergency Fields 85 Airways and Air Routes 85 - Aerial Laws 86 VII. Meteorological Service 89 VIII. Aircraft Insurance: Limited Character of the Field 91 The Development of Transportation 92 Possibilities and Limitations of Aircraft 93 The Dangers of Aerial Transportation 95 Making Insurance Rates 96 Unreliability of the Airplane 97 The Cost of Airplanes 98 Why Should Aircraft be Insured? 99 Nature of the Insurance Contracts 101 The Future of Aerial Navigation 104 Glossary of Aviation Terms 107 ILLUSTRATIONS Icarus Frontispiece The Reconstructed Langley "Aerodrome" 8 A Non-rigid Dirigible or Blimp 14 An Airplane 16 A Hydroairplane 17 A Flying Boat 18 Diagram Showing the Parts of an Airplane ..... 22 An All-metal Monoplane 27 An All-metal Biplane 28 Sand-testing an Airplane Wing 33 Airplane after Turning Turtle 44 A Result of Deficient Vision 46 A Typical Airplane Fire 49 Testing a Candidate's Eyes 59 An Orientator in Action 62 The Crash in which Resnati met his Death at Mineola . . 65 Testing a Landing Gear 68 Sand-testing a Fuselage 69 A Well-regulated Workshop 71 Testing an Engine 77 Specifications for Landing Fields and Field Markers . . 80 An Airdrome, Showing Wind Indicators 82 The Type of Wind-cone used at Curtiss Field .... 83 A Well-arranged Airdrome ....'...... 84 An Aerial Lighthouse 87 A Seaplane Crash 100 After the Accident 100 An Airplane that Fell in a City Street 102 Airplanes and Safety INTRODUCTION THE LEGEND OF ICARUS: Men dreamed of navigating the air long before any means were devised for realizing such dreams. Legends, some of which run back into remote antiquity, tell of men who succeeded in rising into the air by one means or another, the best known story of this kind being the one in which Daedalus and Icarus figure. It may be remem- bered that Daedalus, who was a talented Greek inventor, fled for certain reasons to the Island of Crete, where he constructed a famous labyrinth for King Minos, pre- sumably about the year 2000 B. C. Subsequently, Daedalus was himself imprisoned in this labyrinth, together with his son Icarus; and we are told that they saved up the feathers that fell into their prison from birds passing overhead, and eventually fashioned these feathers into wings, by means of which they effected their escape. Daedalus told Icarus to keep up high enough to avoid the dampness from the sea, but warned him not to fly too near the sun lest the heat from it melt the wax by which the feathers in his wings were held together. The young man disregarded the latter 2 INTRODUCTION part of this counsel, however, and the accident that his father had foreseen came to pass. He flew too high, the wax softened, the wings became unmanage- able, and the youthful aviator fell into the sea and was drowned. Tradition even records the place of his fall, locating it near the island of Samos; and the part of the Aegean Sea in that vicinity is still called the Icarian Sea. According to this evidence, the young man must have flown something like 200 miles before he came to grief. The father escaped in safety, and eventually reached Sicily. Every legend probably has some measure of founda- tion in fact, but in the case of Icarus it would be hard to identify the elements of reality, and separate them from the frills and wrinkles that forty centuries have added. The labyrinth to which the story refers has recently been discovered and explored, and we also know that Crete, in the time of Minos arid Daedalus, was one of the world's most influential and important centers of progress and civilization. All this, however, proves nothing about the reality of the overseas flight of Icarus. The most realistic and probable element of the tale, from our point of view, is the disregard that Icarus showed for the safety advice that his father gave him. The older man was an experienced mechanic and in- ventor, who realized that accidents are likely to happen, and who was thoughtful enough to consider, in advance, how safety could best be assured. But the younger man, just like millions of others down to the present day, let the counsel pass in at one ear and out at the other; and when he was soaring up into the sky he "took a chance," and almost immediately thereafter he was killed. That doesn't sound the least bit like forty EARLY BALLOONS 3 centuries ago. It sounds more like last Wednesday afternoon, in the little shop across the street. Mr. Will H. Low has painted a beautiful panel in the New York State Education Building, depicting the fall of Icarus; and by special permission of the artist and the New York State Education Department we have used a photo-engraving of it as the frontispiece of this book. The modern airplane, high up in the sky of the painting, typifies the success that has finally followed in the wake of so many years of dream- ing and experimenting. The body of Icarus lies upon the rocky shore where it has been cast up by the sea, the nearness of which is suggested, or symbolized, by the water in the immediate foreground. EARLY BALLOONS: Passing, now, .from legend to history, we find that the first successful at- tempt to navigate the air was made in France, by two brothers, Stephen and Joseph Montgolfier. Toward the end of 1782 they had found that light bags would ascend if filled with heated air, and on June 5, 1783, they gave a public exhibition near Lyons, in the course of which a linen globe more than thirty feet in diameter was inflated with hot air and liberated. It rose to a great height, remained in the air about ten minutes, and came down again about a mile and a half from the starting point. This experiment naturally attracted a great deal of attention, and the French physicist J. A. C. Charles, realizing that a hot air balloon would be impracticable except for extremely short flights, suggested that the necessary levity be obtained by filling the bag with hydrogen gas (which was then called "inflammable air"). The money required for INTRODUCTION testing the practicability of the idea was raised by popular subscription; and on August 27, 1783, a gas-filled balloon, thirteen feet in diameter, constructed by the Robert brothers under the direction of Charles, ascended from the Champ-de-Mars, Paris. It rose to a height of 3000 feet and remained in the air for three quarters of an hour. On September 19, 1783, Joseph Montgolfier sent up another hot-air balloon at Versailles in the presence of the King and Queen and a vast assemblage of other spectators, and on this occasion a cage was taken up, containing a sheep, a rooster, and a duck. The rooster and the duck behaved themselves with due dignity, but the sheep, failing to understand that it was about to become famous as a member of the first party of living creatures to go up in a balloon, or not appreciat- ing the honor thus thrust upon it, kicked the rooster just before the start, and injured it somewhat. The ascent was made successfully, however, and without further harm to the creatures in the cage, although they ascended to a height of about 1500 feet and came down two miles from the starting point, after a trip lasting eight minutes. The practicability of making a balloon ascent being thus demonstrated, men were soon found who were willing to take the attendant risks. The first human being to ascend was Jean Francois Pilatre de Rozier, who went up in a captive balloon on October 15, 1783, with a lighted brazier suspended below the bag to keep the air heated. After a number of ex- periences of this kind he ventured to go up in a free fire balloon, on November 21, 1783, in company with the Marquis d'Arlandes, They remained in the air more EARLY BALLOONS 5 than twenty minutes, and came down safely after drifting more than five miles. Ten days later (namely, on December i) Charles, the physicist whom we have already mentioned, ascended from Paris, accompanied by one of the Robert brothers, in a balloon filled with hydrogen. The two men were in the air about two hours, and landed some twenty-seven miles from the starting point. Robert then left the car, and Charles made a second ascent alone, rising on this occasion to a height of about two miles. Honorable mention must be made, at this point, of Rittenhouse and Hopkinson, of Philadelphia, who were experimenting with balloons almost as early as the Montgolfiers, and who also constructed a successful gas-filled balloon of the composite type, in which James Wilcox made an ascent. Girond de la Villette, who had accompanied de Rozier in one of his early ascents, proposed to employ balloons in warfare; and in 1794 a French company of "aerostiers" was formed, an air-park was established, and balloon reconnaissances were actually made against the Austrians. Balloons were used extensively for observation work during the siege of Paris, in 1870-71. They were also used in considerable numbers in our own War between the States, and in the Spanish War of 1898, and the Russo-Japanese War. All these military balloons were of the spherical type, and were moored to the ground by means of cables. The modern stream-lined observation balloon was not developed until a few years prior to 1914, but before the close of the World War, it had practically displaced all other means of directing artillery fire. 6 INTRODUCTION THE BEGINNINGS of the Airplane: The first steps towards the development of the heavier-than- air flying machine that is, of the type of aircraft that has no supporting gas-bag may be assigned to various periods, according to the views that we may hold with regard to what constitutes a first step. If we chose to go back to the most elementary principles of mechanical flight, in which other elements than mere momentum are utilized for keeping the apparatus in the air, it would doubtless be necessary to credit the prehistoric aborigi- nes of Australia with the earliest invention, because the boomerang certainly involves some of the principles that underlie the operation of the modern airplane. If, on the other hand, we are to pass over the boomerang, as well as the kite (including the scientific species as well as the juvenile one), and the various small-sized "helicop- ters" and other toy-like devices that have appeared from time to time, and are' to begin our survey with the earl- iest form of apparatus that held out distinct promise of an actual, early solution of the problem of navigating the air with a heavier-than-air mechanism, we shall have come down to the latter part of the Nineteenth Century, when Lilienthal, Chanute, Pilcher, the Wright brothers, and many others, laid the foundation, by means of their gliding planes, for the rapid development of the art in a useful and practical direction. Dr. Samuel Pierpont Langley, Secretary of the Smithsonian Institution, will always be regarded as the first to establish the principles of mechanical flight upon a sound scientific basis. He began his serious work along this line about the year 1887, publishing his "Experiments in Aerodynamics" in 1891, and "The Internal Work of the Wind" in 1894. EARLY AIRPLANES 7 Sir Hiram Maxim constructed an enormous steam- driven airplane in 1894, for experimental purposes. It was supposed to be confined to a long track that was erected for the purpose, but it tore loose, left the track, wrecked itself, and was never rebuilt. Langley built a quarter-size steam-driven airplane which made a sustained flight over the Potomac river near Washington, D. C., on May 6, 1896. Encouraged by this result, he afterward constructed a full-sized machine, also driven by steam, and flights were at- tempted near Washington on October 7, 1903, and again on December 8. Owing to mishaps in launching, the machine fell into the Potomac on both occasions, and on the second trial it was wrecked by the poorly- directed efforts of a tug to rescue it. The failure of the experiment was witnessed by hundreds of news- paper correspondents, who published supposedly hu- morous accounts of the proceedings, and the ridicule caused Congress to refuse further contributions toward the work, and also had a profound effect upon Langley himself, so that many believe that it hastened his death. The machine was raised and placed on exhibi- tion in the Smithsonian Institution. In recent years it has been repaired, and after being provided with new wings and with a gasoline engine, it has been successfully flown, the soundness of Langley's general design being thereby proved. In 1903 Wilbur and Orville Wright built a self- propelled machine in which they used a twelve-horse- power gasoline engine and two propellers. Their first successful flight with this design was made on Decem- ber 17, 1903. In 1904 and 1905 they made many flights, some in public and some in private. They 8 INTRODUCTION Photo by Benner. THE RECONSTRUCTED LANGLEY "AERODROME." originally undertook their aerial experiments out of pure scientific interest, and with no thought of a possible commercial return. As their investigations proceeded, however, they became so absorbed in the subject that they gave up all other business and de- voted themselves solely to their aircraft researches. In the winter of 1907-8 the U. S. Signal Corps called for bids on an airplane and an airship, and the Wright brothers undertook to comply with the conditions and deliver a practical airplane. With this in view they did a great amount of experimental work during 1908, and in the fall of that year they began, at Washington, a series of demonstration flights which terminated in the unfortunate death of Lieut. Selfridge, who was a pas- senger with Orville Wright. Delivery of the machine to the United States Government was finally made in 1909. The pioneer flights made by the Wright brothers in 1904 and 1905 were followed in 1908 by the work of the Aerial Experiment Association, composed of Dr. INFLUENCE OF THE WORLD WAR 9 A. G. Bell, Glenn Curtiss, Lieut. Thomas E. Selfridge, F. W. Baldwin, and J. A. D. McCurdy, and by the flights of Curtiss in his own machine in 1909. The achievements of Langley, the Wright brothers, and Curtiss, gave to the United States the distinction of being unquestionably the first country in the world to build what were conceded to be successful airplanes. INFLUENCE of the World War: From the begin- nings here outlined, progress was slow. At the outset there was practically no demand for airplanes, and the few that were used for sport were of a prim- itive type. The United States Army did a little flying, but no serious attempt was made to develop this branch of the service until 1914. Five officers of the United States Army were then sent to the Massachu- setts Institute of Technology to study aeronautics, and in August, 1914, these five men constituted the entire technically-trained personnel of our Army air service, though there were, in all, twenty-four officers and one hundred and fifteen enlisted men on aeronautical duty on that date. The problem that confronted the United States in connection with aerial navigation at the time we entered the World War was a staggering one. With no stock of material, and with practically no personnel experienced in airplane designing, and with an utter lack of knowledge of the requirements of the most advanced aircraft for war purposes, or of the appliances essential to their operation, the government faced a serious situation. But the war brought forth marvelous unrealized resources, both of materials and of technical knowledge, and in spite of contradictory opinion, the IO INTRODUCTION development of our Air Service reflects the greatest credit upon the men who handled the situation; and if the war had continued six months longer, the United States would have supplied more airplanes than all of our Allies combined. At the time of the armistice, some of our heavy planes were already superior in de- sign to those of European make. By the co-operation of the manufacturers in this country, and with the assistance of our European Allies, flying fields and training schools were developed and engines and planes were perfected with great rapidity; and at the end of the World War our air forces numbered nearly 200,000, including 20,708 trained officers and 174,456 enlisted men and civilian employees. Twenty-seven flying fields were then in operation, and 9,503 training airplanes and 642 observa- tion balloons of various sorts had been built. In ad- dition to this, 17,673 aeronautical engines for training purposes had been completed, and the work was still in a state of rapid development when it was stopped by the ending of the war. Considerable money was doubtless spent without commensurate material re- turns, but this was unavoidable in view of the nature of the problems that had to be handled, and the pres- sure under which the work was done. The material output was immense, however, and highly creditable under the circumstances. In addition, our knowledge of aeronautics was vastly increased, aeronautical en- gineers were developed, new methods of doing work were evolved, and special materials were devised for fulfilling special needs. During this period the advance was so rapid, in fact, that airplanes sometimes became obsolete almost before they could be completed. THE FUTURE OF AERIAL NAVIGATION I I THE FUTURE of Aerial Navigation: With the close of the war, it became necessary to consider the future of aeronautics. Many persons believed that aircraft would be found to be useful in connection with the arts of peace, and the success of aerial navigators in crossing the Atlantic Ocean certainly took the question of the commercial possibilities of aircraft out of the pro- vince of the dreamer, and forced the practical business man to give serious consideration to the subject. Yet the difficulties to be overcome are undeniably great, and many of our best engineers have been profoundly skep- tical with regard to every suggestion involving the use of aircraft as a means of transportation in time of peace; and the general public, remembering the numerous acci- dents that have been recorded in our newspapers during the past few years, is strongly disposed to question the feasibility of this mode of travel. But it should not be forgotten that the experience during the war is not a fair index of what can be accomplished in the future, not only because the conditions existing at that time were far from normal, but also because the entire art was wholly new, and involved difficulties that are only now coming to be fully understood. /COMMERCIAL USES of Aircraft: European ^^ countries took to commercializing aircraft before the United States gave much thought to the subject, and several regular aerial lines of travel have already been established over there. In our own country, an aerial mail service has been in operation on certain routes since 1918. Experience shows this service to be prac- tical and worthy of further development in the future. New routes are being established, and the size of the 12 INTRODUCTION Division of Aerial Mail Service is rapidly increasing. Aircraft have also been employed, for a considerable time, by the Forest Service in fire-patrol duty. The forests of California from San Francisco to the Mexican border are regularly patrolled in this way, and the record established has been excellent. Observation balloons are used as stationary outlooks, and airplanes are employed to cover specified routes daily. The practicability of using aircraft for photo- graphic survey purposes, and to some extent for mer- cantile delivery and passenger service, has been demonstrated beyond a doubt; and if commercial avia- tion receives the necessary financial support, it will probably be only a short time before this means of rapid transportation will be established on a sound business basis; provided a sufficient number of suitable landing fields are established, and adequate flying laws and regulations are enacted and enforced. I. AIRPLANE CONSTRUCTION TYPES OF MACHINES: Self-propelled aircraft may be divided into two main classes, according as they are (i) lighter than air, or (2) heavier than air. Lighter-than-air machines (technically known as air- ships or dirigibles when they are provided with engines and propellers so that they are capable of independent locomotion) are of the balloon type, and owe their lifting power largely or wholly to bags filled with a gas that is lighter than air. Such machines may be divided into (i) rigid, (2) semi-rigid, and (3) non-rigid types. In rigid airships the gas envelopes are sup- ported by a rigid framework. The semi-rigid airships have a framework to support the cars, fins, rudders, and elevators, and non-rigid types owe their firmness entirely to the pressure in the gas envelope. The heavier-than-air machine is of totally different con- struction and owes its lifting power to the action of wings, or to the rotation of propellers analogous to the screw propellers that are used on steamships. If the machine were supported by wings that flapped like those of a bird, it would be called an "ornithopter;" AIRPLANE CONSTRUCTION s 2= O w =E O I Q O 5 O TYPES OF MACHINES 15 and if it were sustained in the air by the direct thrust of downwardly-directed propellers, it would be called a "helicopter/' Neither of these types has yet been de- veloped to a practical point in connection with gasless machines, although some authorities believe that the helicopter will become practicable in the near future. At the present time, all gasless machines of the "air- plane" type owe their lifting power to the action of wings or supporting surfaces which are fixed and prac- tically rigid, save for the fact that certain relatively small portions of them can be set or adjusted in varying positions. The fixed wings or "planes" are designed and located so that when the machine is in rapid forward motion, the air presses against their lower surfaces and also produces a vacuum over the top of the wing, behind the leading edge. It is usually considered that about 60 per cent, of the lift is due to the presence of this vacuum over the upper surfaces of the planes. The wings were originally made thin and nearly flat, and it was then appropriate to call them "planes." In recent machines the wings are often quite thick, and they invariably have a strongly-curved shape also. It is hardly appropriate, therefore, to call them "planes" at the present day, though the name still persists, and the machine itself will doubtless always be known as an "airplane." Airplanes (to which our attention will be almost wholly confined in the remaining part of this book) may be classified in various ways. First, they may be grouped in accordance with the number of main sup- porting surfaces employed, "monoplanes" using one pair of such surfaces, "biplanes" using two, and "multi- planes" using more than two. They are also classified i6 AIRPLANE CONSTRUCTION < J CL, & < < TYPES OF MACHINES Photo by Benner. A HYDROAIRPLANE. according to the nature of the service for which they are designed, being known simply as "airplanes" if they are to operate exclusively from the land, and as "seaplanes" if they are to be used for marine flying. Seaplanes are further divided into float seaplanes or "hydroair- planes," and boat seaplanes or "flying boats." Hydro- airplanes are similar to ordinary airplanes in construction, except that instead of having landing carriages and wheels, each machine is provided with a float or a set of floats, for landing purposes. A flying boat is a seaplane in which the body of the machine acts as the float. i8 AIRPLANE CONSTRUCTION Photo by Benner. A FLYING BOAT. Aeronautical Engines: Aeronautical engines are of the internal-combustion type, and use gasoline as fuel. They are all multicylinder in design, and may be either rotative or fixed. Fixed engines may be fur- ther subdivided, according to the arrangement of the cylinders, into radial, upright, and V-shaped types. The number of engines carried by an airplane varies, some planes employing but one each, while others have two, and some designs call for three or more. In the matter of locomotion, airplanes are usually either "tractors" (in which the propellers are located in front of the engines and* pull the machines through the. air) or "pushers" (in which the propellers are in the rear of the engines, and force the airplanes forward by a pushing action). In a pusher plane, the motor is usually mounted above the body; while in a tractor airplane it is commonly placed at the nose of the fuselage. Some multimotored types, however, com- bine the pusher and tractor principles in a single machine. The Structural Parts of Airplanes : Excluding the power plant, an airplane can be divided into four THE BODY 19 principal parts: (i) body; (2) wings; (3) tail; and (4) landing-gear. We proceed to describe these briefly, as they are constituted in airplanes of the usual types. In all-metal planes, which will be mentioned later, the construction of the various parts is quite different. The Body: The body of a tractor plane is termed the "fuselage," and in the pusher-type of machine it is shorter and is called the "nacelle." The fuselage or nacelle of the airplane usually carries the dead weight, consisting of the power plant, the fuel and oil tanks, and the pilot, passengers, and freight. It must be strongly built, and be constructed so that it will easily and safely transmit the forward pull or thrust from the propeller to the rest of the machine. This requires rigid attachment between the body and the wings. In flying boats the body construction is heavier than in other airplanes, because in this type the body serves also as a large landing pontoon, and keeps the plane afloat when it is resting on the surface of the water. The Wings: The main supporting surfaces of an airplane are made up of several parts, namely, wing spars, wing ribs, and the wing covering; and wires and cables are used for internal bracing. The wing spars run longitudinally along the wings, receiving the stress to which the wings are subjected, and trans- mitting it to the framework of the body. There are usually two of these spars in each wing, one being lo- cated near the leading edge, while the other is ordi- narily placed at about one-fourth of the length of the wing chord from the trailing edge. The wing spars are usually made of wood, and they may be either solid or built up of several pieces glued together. If solid, they 2O AIRPLANE CONSTRUCTION are ordinarily made of ash or silver spruce; and if built up, they are made in differing combinations, varying from plain strip plywood to "I", "U", and box-shaped sections. Wing ribs are employed to give the wing its shape and to complete the framework over which the wing covering is stretched. They are fitted transversely between the wing spars, and specially designed ones take the compression between these front and rear members. The ribs may be either solid or built-up; and in airplanes of some types special lightly-con- structed intermediate ribs are used for maintaining the shape of the wings, especially in the nose of the wings. The wing covering, and sometimes the covering for the body frame, consists of linen or cotton cloth drawn tightly over the framework and sewed in place. This fabric covering must be perfectly smooth and taut. When in position, it is coated with a special varnish-like preparation, technically called "dope," which shrinks the cloth and at the same time makes it waterproof. The warp and filling threads of the wing cloth should be of uniform thickness throughout their length, and they should be as long as possible, because knots are likely to cause weak, uneven spots in the cloth. Some kinds of wing cloth, however, have extra stout threads (known as guide threads) woven at intervals in both the warp and filling, for the purpose of preventing the extension of any split or flaw that may develop in the fabric. Linen is much stronger than cotton cloth of the same weight, and it also takes the dope better. It should be used when its cost, per yard, is not more than 50 per cent, greater than that of special airplane cotton. THE WINGS 21 In the assembled biplane or multiplane, wires, cables, and interplane struts are used to form a truss- work between the main supporting surfaces. The interplane struts of a biplane or multiplane machine are all in compression, and (like the wing spars) they may be either solid or built up. They serve to keep the wings at the proper distance apart, and in most planes they are placed vertically, or nearly so, between the wings. Struts are usually made of spruce or ash, but steel struts are now used to some extent, and are giv- ing excellent results. The struts are attached to the wing spars by a metal-socket arrangement, and it is best to fasten the socket to the spar by means of a U-shaped bolt which passes around the spar instead of piercing it. The wiring in the wings of an airplane is one of the most important factors in the construction of the machine. For practical purposes, the wires may be divided, according to their uses, into four classes, flying, landing, drag, and incidence wires. Flying wires are used to support the weight of the fuselage or body, when the machine is in the air. They extend from the bases of the struts on the lower wings, upward and outward to the tops of the struts on the upper wings. The landing wires pass from the base of each strut on the lower wings, upward and inward to the top of the next strut. They cross the flying wires nearly at right angles, and are under tension only while the airplane is on the ground. When a machine is flying, the resistance of the air has a tendency to push the wings backward. This drift-back is counteracted by the drag wires, which, in a tractor machine, are usually attached to the front of the fuselage and extend back to the lower ends of the 22 AIRPLANE CONSTRUCTION o a C/3 o THE WINGS 23 struts. In a pusher-type machine the wires are usually attached to the front of the outrigging, or to the nacelle, 'and extend to the outer struts. Incidence wires are used to adjust and maintain the angle of incidence. They take the form of cross- bracing between each front strut and the corresponding rear strut. Incidence wires are sometimes called "stag- ger-wires," because they are also used in regulating the stagger of the wings. As a rule, all wires are adjustable by means of turn- buckles. This arrangement makes it possible to slacken or tighten the wires when necessary. The threads on the turnbuckles should be strong enough to insure safety, and a locking device of some kind should be used on them, to avoid any possible chance of the ad- justment becoming changed accidentally, or in conse- quence of the vibration of the machine. Modern airplanes have "ailerons," or hinged flaps, attached to the rear edges of the wings, at or near their outer ends. These are used to stabilize the machine laterally. As long as the ailerons remain in a neutral position they do not disturb the equilibrium; but as soon as the ailerons on either side are raised or lowered, the machine tends to tilt sidewise; that is, to rotate one way or the other about its fore-and-aft axis. They permit the pilot to right his machine in case it should be tilted by a gust of wind, and to tilt or "bank" the machine when a turn is made. Ailerons that are long and narrow are said to be more effective and more easily operated than short ones having the same area. The aileron surface should be equal to about 10 per cent, of the wing area. The Tail: There are two distinct types of tails, 24 AIRPLANE CONSTRUCTION the lifting and non-lifting. The lifting tail may have a surface cambered similarly to the main support- ing surface, but in most cases the angle of incidence at which the^ tail planes are set causes a slight lift. A lifting itail supports only its own weight however, and contributes nothing to the support of other parts of the machine. The non-lifting tail has a surface either flat or possessing a slightly convex camber on both sides. It is designed to act as a horizontal fin or stabilizer, and is set so as not to have a lifting effect, but to give steadiness in a fore-and-aft direction, and prevent motions of the airplane analogous to the "pitching" of a ship. The trailing edge of the horizontal stabilizer is usually constructed of metal tubing to form the rear spar, and the elevator planes are hinged to this spar. The stabilizers and elevators should have a combined area equal to about 15 per cent, of the total wing sur- face. Elevators are said to be more effective if built long and narrow. A vertical stabilizer or fin is placed along the upper center-line of the tail, and extends back to the tail post of the body. The rudder is attached to the trailing edge of this fin, and to the tail-post, by hinges and pins, in a manner similar to that employed in attaching a rudder to a ship. The rudders and fins should have a combined area equal to about one-half that of the stabilizers, and should be located so that they will not be blanketed by the airplane body. The Landing Gear: The chassis of an air plane is usually a V-shaped structure, strongly cross- braced and fitted to the lower side of the fuselage. Similar cross-braced construction is employed on sea- MATERIALS USED 25 planes. The landing gear or undercarriage has two distinct forces to resist: (i) the vertical shock ex- perienced upon landing, and (2) the horizontal force that tends to sweep the landing gear backward when the airplane is running along the ground. The former of these forces is greatest when a machine is "pan- caked/' and the latter reaches its maximum when a fast landing is made on soft or rough ground. A large factor in the landing stress of an airplane is what is commonly known as "side-swipe". This is partially counteracted by means of cross bracing in the landing gear. The vertical shock is relieved to some extent by the use of rubber shock-absorbers, and the horizontal resistance is reduced, on airplanes, by means of wheels, and on seaplanes by the use of long, narrow pontoons. Structural Materials Used: The choosing of material for aircraft construction is a study in itself. It is necessary to insure great strength and absolute reliability, without sacrificing lightness. The problem has been solved sufficiently to permit successful flying, but further study and research will doubtless result in marked improvement in the selection of material. Wood is largely used in the construction of the framework. The chassis struts, skids, longerons, and engine-bearers are usually made of ash. This is a straight-grained, tough wood, but it is rather heavy. Spruce is extensively used for the main spars, wing spars, and struts. It is not so strong as ash, but it is considerably lighter and is quite dependable, and hence it is always used when it can be obtained in clear, sound, straight-grained lengths. Members are frequently built up of sections of ash and spruce, glued together. Ribs are usually made of white pine. Hick- 26 AIRPLANE CONSTRUCTION ory is used for landing-gear struts, especially in the construction of heavy machines. Canadian elm is very tough and is sometimes used instead of ash for engine bearers and longerons. It is easily twisted and warped, however, and for that reason it is not wholly ideal. Basswood is used in the webs of ribs; and wal- nut, mahogany, and ash are used in propeller con- struction. Aluminum is employed in constructing cowl sup- ports, wind-screen frames, and control wheels. It is not particularly desirable in connection with seaplanes or flying boats, because it corrodes easily in the presence of water, and when it is used it must be constantly watched and frequently cleaned. Manganese bronze is quite tough, and on account of its resistance to cor- rosion it is used largely in airplanes operating from the water. It is also employed in making wood screws, and for bearings for rotating parts. Phosphor-bronze has properties resembling those of manganese bronze, and it is used for similar purposes. Steel is used for sockets and control leads, and for wire and wire attachments; in fact, for all kinds of airplane fittings. Some builders have employed steel for the entire framework, but such construction is heavy and difficult to repair. Steel tubes may be used as struts, and in some cases a stream-line cross- section is given to these tubes by the application of sheet metal or balsa wood, externally. Duralumin a special alloy of aluminum, copper, and magnesium, has recently been used in aircraft construction for all the purposes for which wood has hitherto been employed, except for making propellers. This alloy is tough, strong, and light in weight, and is MATERIALS USED Courtesy JL Aircraft Corporation. AN ALL-METAL MONOPLANE. likely to play an important part in the aircraft of the future. An incidental but important advantage as- sociated with the use of duralumin in the construction of all-metal machines consists in the fact that when an accident occurs the metallic construction-members bend and crumple up, thereby absorbing part of the energy of motion of the machine and lessening the violence of the shock. Wood, under similar stress, splits and snaps, and the broken ends often cause serious injuries. To obtain the best results with duralumin, the alloy must be heat-treated before working, by subject- ing it to a temperature of from 350 to 380 C. and then quenching in oil or hot water. The metal is thereby rendered plastic, so that it can be easily forged, stamped, drawn, or rolled. After working, a final heat treatment is necessary in order to give the alloy its .28 AIRPLANE CONSTRUCTION maximum hardness and strength. For this purpose it is heated to 500 C. or 520 C., quenched in oil or hot water, and then allowed to stand for about a week, at the end of which time it will have become permanently hard and durable. The heating is a delicate operation and is usually performed by the aid of a salt bath composed of equal parts of nitrate of sodium and nitrate of potassium, the mixed nitrates melting at a tem- perature that is materially lower than the melting point of either one when used alone. Accurate ther- mometers or pyrometers must be used in this work, and the temperature of the bath must be closely watched and carefully regulated; because if the metal is heated above 550 C. it becomes permanently hard and brittle, and its strength is also materially reduced. If heated Courtesy Air Service, U. S. A. AN ALL-METAL BIPLANE. CONTROL 29 even a few degrees above 520 C. the alloy loses some of its desirable qualities. Equal care is required in the preliminary heat treatment used in preparing the metal for working, because if a temperature of 400 C. is reached during this annealing process, the metal becomes hard and difficult to work. Linen and Egyptian cotton cloth are the principal fabrics used for covering the framework of the wings, and the fuselage or nacelle. Recently, thin sheets of corrugated duralumin have been used experimentally in place of fabric for wing and body coverings, and it is said that the metal has served this purpose admirably. Control: There are three points of control in the standard type of airplane, namely, (i) the ailerons located along the trailing edges of the wings and near their outer ends, (2) the elevators at the rear of the fuselage, and (3) the rudder (or rudders, when there are more than one) located in the rear of the body. These parts are operated from the pilot's seat by means of levers and wire cables. The rudder is normally operated by means of a foot-bar, and is used for the same purpose as the rudder of a boat. A lever, called a control-stick or "joy-stick," is commonly used for controlling the ailerons and the elevators. In some cases, however, a wheel is employed instead of a control-stick. A fore-and-aft movement of the wheel or stick controls the elevators, and the ailerons are operated by rotating the wheel or by moving the stick sidewise. The elevators control the vertical movements of the airplane, while the ailerons, which control the movements that correspond to the "rolling" of a ship, are used principally in banking for turns. The ailerons are usually of the double-acting type, in which 30 AIRPLANE CONSTRUCTION compensating wires are used. When the aileron on one side is deflected upward by means of the control lever, the opposite aileron is simultaneously lowered by means of the compensating wires. In other words, the construc- tion is such that the elevation of one of the ailerons is nec- essarily attended by the depression of the opposite one. The method of running the control cables, as well as the construction of them, is extremely important. They should always run through well lubricated leads, and every precaution should be taken against clogging or jamming. Sharp angles in the cables should be avoided by the use of chains or bell-cranks or other similar arrangements. All control cables should be flexible, and it is advisable to have them in duplicate, wherever possible. The main point is to insure absolute freedom and certainty of movement, because the safety of the airplane depends at all times upon the positive operation of its controls. Certain special stabilizing devices, embodying the principle of the gyroscope, are used in some machines. To what extent they will be employed in commercial aviation (if at all) is thus far undetermined. Even the value of them is not yet universally conceded. Stabil- izers of some forms can be set or fixed in position so that the airplanes in which they are installed will run in a predetermined course, subject only to wind-drift- ing, as long as the motor operates. Aviators have been known to start their stabilizers and then sit in their seats writing letters, paying no attention to their controls. This is an exceedingly unwise practice, because it is always dangerous to place too implicit a dependence upon automatic devices of any kind, especially when failure would be followed by disas- PLAN AND PERFORMANCE 3! trous consequences. The aviator should give his personal and immediate attention to the control of his machine at all times, and should never rely upon automatic apparatus. Such apparatus is useful in so far as it assists the aviator, but he must be watchful of his machine at every moment that he is in the air. Plan and Performance: Airplanes of nu- merous makes and models are now produced com- mercially, and each of them has its own good points. As in selecting an automobile, the use to which the machine is to be put should be the chief factor in making a choice. There are certain points in airplane construction, however, that determine the usefulness of the craft for any purpose, and these should receive serious consideration. In the first place, the airplane should be of a clean- cut design, and stream-lined, and the gaps between the control surfaces and the main sections should be small. The stability required in a machine will depend largely upon the purpose for which the airplane is to be used. A certain amount of stability is essential to safety, but in low-powered aircraft excessive stability causes the machine to be subject to violent reactions in a gusty wind, and makes it hard to handle. When such planes have too much stability, they are extremely safe but very uncomfortable to ride in. Lateral stability is secured by a combination of rear fin area and wing dihedral; and longitudinal stability depends upon the location of the center of gravity relatively to the wings. The airplane will be unstable unless the horizontal tail surfaces are set at a negative angle with respect to the wings; that is, unless the entering edges of the horizon- tal stabilizers are slightly lower than the trailing edges. 32 AIRPLANE CONSTRUCTION The ease with which an airplane can get off the ground depends primarily upon the design of the wings. A low load per horse-power will enable a plane to lift quickly, and ability to do this is also obtained if the load per square foot of wing surface is low. A propeller of small diameter is desirable in obtaining the maximum number of revolutions per minute from the motor while the plane is still on the ground, but is not desirable when the plane is in the air. A large propeller is then pre- ferable, in order to obtain a maximum amount of power. Increased ease of "get-away" involves a corresponding sacrifice in lifting power or useful load. Speed in the air, and climbing ability, are not paramount considerations in commercial planes, yet these characteristics are sometimes highly desirable when it becomes necessary to avoid trees, houses, smokestacks, and other obstacles near a flying field. If an airplane travels at its maximum speed a consider- able part of the time, the engine is subjected to an enor- mous amount of wear and tear and it will not stand up long under the strain. A plane should have a flying speed compatible with the work it is engaged in, and still have some speed in reserve for use in an emergency. A high ceiling is desirable in a mountainous country, where flying at considerable altitudes is necessary in order to clear high peaks. An airplane having deeply cambered wings is likely to possess great lifting power. Commercial planes should have wings that are moderately cambered, a compromise between those of a speed plane and those of the extremely slow type. Low flying speed enables a plane to land with less shock, and also to come to rest soon after striking the ground. This is import- PLAN AND PERFORMANCE 33 ant in connection with planes that may have to land in restricted areas, but on the other hand too low a land- ing speed is undesirable on account of the reactions to which the plane is subjected in gusty winds. It is possible to reduce the landing speed by flattening out the dive, and landing with the speed slightly below the theoretical value. The head resistance of the airplane and the drag of the tail skid reduce the distance a machine must taxi after landing. A large angle of incidence in the wings creates a large amount of head resistance. With the tail skid on the ground, a sixteen-degree angle of inci- dence between the wing surfaces and the line of flight is considered to be about the minimum value for general work. The center of gravity of the machine should be at least twelve inches back of the wheel axis of the land- ing gear, to resist the tendency of the machine to Courtesy Curtiss Aeroplane and Motors Corporation. SAND-TESTING AN AIRPLANE WING. 34 AIRPLANE CONSTRUCTION "nose over." This position of the center of gravity also insures a reasonable amount of drag on the tail skid. The factor of safety should be at least six in the construction-members of large, stable planes, but in smaller types that are subject to manoeuvers it should be increased to at least twelve or fourteen. The materi- als used in all the members of an airplane should be thoroughly tested, to be sure they are sufficiently strong. In the power plant, high-compression engines are not considered as reliable as low-compression ones, especially when high compression is coupled with high piston speed. Most airplane engines are equipped with two sets of spark plugs, and it is still better to have two or more entirely separate ignition systems. Ignition trouble frequently causes engine failure, but if two or more separate ignition units are used, the failure of one of them will not force the pilot to stop flying. He can continue to operate on his duplicate or reserve unit until he can get to a suitable place to land and make repairs. Multiple engines are desirable for the same reason; for if one of them fails, the pilot can usually continue flying under partial power long enough to reach a suitable landing place. Multi-motored airplanes require extra large and extra strong rudders, to compensate for the one-sided pull that is exerted if some of the engines are not working properly. Without reliable rudder control, the machine is likely to side-slip under these conditions. It is important to have the gasoline feed-pipe arranged so that there will be no chance of accidental PLAN AND PERFORMANCE 35 ignition of the fuel supply. The feed-pipe is frequently installed in such a way that it passes close to the ignition apparatus, where a leak would surely produce a fire. This is a serious error in design. Gasoline feed-pipes should be kept well away from all sparking devices, fuse blocks, and switches, and from all the highly heated parts of the motors. They should also be made of soft copper or other satisfactorily flexible tubing, so that the chance of breakage will be reduced to the lowest practicable point. II. THE OPERATION OF AIRPLANES TNTRODUCTORY: The safe operation of an air- A plane depends largely upon two factors: (i) the efficiency and fitness of the pilot, and (2) the phys- ical condition of the machine he is operating. To make sure that the airplane is in proper condition for flying, it is necessary for the pilot to inspect his machine thoroughly before leaving the ground. This inspection should be carried out in accordance with a definite plan or system, in order to be sure that none of the vital parts of the machine are overlooked. Tuning-up: In making an inspection, it is good practice for the pilot to take a position on the right or left side of the fuselage, and then make a complete circuit of the machine, either to the right or to the left, carefully looking over and testing the various parts as he goes along. The fabric or wing coverings, cables, bracing wires, interplane struts, landing gear, tail skid, control surfaces, and control cables should receive special attention. The fabric should be tight and free from rips and tears, and all small holes should be patched and well TUNJNG-UP 37 protected by dope or varnish. Loose fabric increases what is known as "skin friction/' and retards speed in flying. Exposed fabric deteriorates with extreme rapidity, and airplanes should therefore be protected from the weather when not in use. Oil destroys the fabric varnish and for that reason any grease or oil that may be found upon the wings should be carefully and thoroughly removed. The cables and bracing wires should receive a light coating of grease or oil to protect them from rust. Cables that show frayed or broken strands should not be repaired, but should be immediately replaced by new cables. The flying and landing wires should be under sufficient tension to keep the framework rigid, but it should be remembered that too much tension subjects the parts of the framework to needless strain, and thereby lowers the factor of safety that has been provided for the purpose of taking care of the unforeseen stresses to which the machine may be subjected in its regular operation. Examine all turnbuckles for loose or missing safety or locking wires. If these locking wires are absent or loose, the barrels of the turnbuckles may turn and release the tension on the bracing wires. See if any of the cotter pins or nuts have been lost, and replace those that are missing. The interplane struts should be examined for splits, cracks, and warping. Warped struts are likely to break down under the pressure to which they are subject. The socket arrangements by which the struts are fastened are usually connected to the wing fixtures by pins or bolts, and these pins or bolts should be locked in position by means of split pins. Wing skids are not always provided, but their 38 OPERATION OF AIRPLANES use is highly recommended. They are not needed in a perfect landing, but on rough ground, or in landing with one wing low, they are of great advantage in avoiding the possibility of a serious crash. They are specially valuable if the airplane has ailerons attached to the lower wing. The landing gear struts should be well bedded in their sockets, because otherwise the shock of a rough landing will drive them in further, and in this way loosen the tension on the cross-bracing wires. This would throw the whole undercarriage out of alinement and might greatly weaken it. It would also prevent the machine from taxying straight. The shock-ab- sorbers should be examined closely, particularly if they are composed of rubber, because this material deteriorates even from mere exposure to sunlight, and is quickly destroyed by the action of lubricating oil or grease. Make sure, also, that the wheels are securely fastened to the chassis and that they are properly oiled. They should revolve freely, and the tires should be properly inflated. The tail skid and post are frequently overlooked during an inspection, but they are important parts of the airplane and should receive proper consideration. They are probably broken and repaired more frequently than any other airplane parts. If the shock-absorber portion should become loose or permanently stretched, the shock of landing (which is relieved by the tail skid) would be received by the fuselage, and the whole frame- work would be likely to be severely strained. The control surfaces should be examined to see that they operate easily and positively. The horns should be tight, and the hinges should be secure and in TUNING-UP 39 perfect condition, and the hinge-pins should be in place and properly locked. The cable attachments should also be carefully examined. The cables should be followed throughout their entire length, and any defec- tive places should be noted and remedied. Lubricating oil should be applied freely wherever a lead passes through a pulley or sheave, and special care should be taken to see that the cable is not frayed at such points. Unnecessary slack in the cable leads will cause the control surfaces to act sluggishly, and will make it difficult to handle the machine effectively in an emer- gency. The general examination of the airplane being com- pleted, attention is next directed to the engine, and to the fuel and water supplies, the instruments, and the person- al equipment. The supplies of fuel and water are nor- mally taken care of by an attendant assigned to that duty, but it is well to check up his work, especially if a cross-country flight is contemplated. Personal in- spection of the engine is not absolutely necessary, because defects in this part of the mechanism will probably betray themselves during the warming-up process. It is important, however, to look it over in a general way, and the aviator should at all events make sure that there are no leaks in the gasoline tank or the feed pipes, or see that any such leaks that exist are immediately repaired. On entering the airplane, the safety belt should be adjusted promptly. Examine the instruments and make sure that the altimeter is set at zero. If the fuel is supplied to the engine under pressure, pump up the necessary pressure by means of the hand pump provided. Test the controls to see that they operate freely and 4O OPERATION OF AIRPLANES effectively. The spark control, and the switches, gasoline shut-off, oil-pressure gage, air release, and other controls and appliances should be tried, and ad- justed so that they work properly. When ready to start the engine, see that the blocks are secure in front of the chassis wheels, and be spe- cially sure that the throttle is only partly open, be- cause many serious accidents have occurred in conse- quence of turning over the engine while the throttle was open too wide. Orders given to the attendant should be clear and distinct, and they should be repeat- ed by him before being carried out. It is advisable to pull the control stick well back, in order to prevent the tail from lifting and to avoid turning a somersault over the blocks. The use of mechanical starters cannot be too strongly recommended, because they largely elimi- nate the accidents associated with starting. Various kinds of starters are available, ranging from small compressed-air devices to large separate cranking machines mounted on light motor-trucks. On com- mercial routes it has been suggested that the planes be equipped with starting motors, and that the batteries needed to operate these motors be mounted on small trucks that can be wheeled around to the different planes on the field as needed. This plan would provide electric starting apparatus and yet it does not require each plane to carry a storage battery. Never run the speed of the motor up beyond 600 revolutions per minute, until the temperature of the engine is at least 60 Fahr. Undue speed when starting strains the motor and causes it to heat up too quickly, and quick heating is likely to warp the valves and CLOTHING AND EQUIPMENT 4! prevent them from seating properly. After the motor has attained a temperature of 60 Fahr. it may be run faster, and the throttle may be slowly opened to make a full-speed test for vibration, and to see that the engine works properly. The throttle should be opened up gradually until it is wide open, and full speed should not be maintained for more than a few seconds. Then slow the engine down to about three-quarters of its maximum rate, and run it at that speed until you are thoroughly satisfied that everything is working properly, and you are ready to take the air. If the engine misses fire while taxying to the "take-off" or if it does not work properly in any other respect, do not "take off\ but return to the starting point and test out the engine and make the necessary adjustments until it operates satisfactorily. An engine that does not work smoothly is likely to cause the machine to lose speed in taking off, and a sudden fall may result. Standard Clothing and Equipment: The selection of clothing and other personal equipment is largely a matter of taste and circumstances. Pro- vision should be made for cold weather, especially if an extended flight is contemplated. The regulation leather coat is desirable because it keeps out wind and moisture, and at the same time retains the heat of the body. The one-piece flying suit and sheep-lined fly- ing moccasins are recommended. Nearly all flyers wear goggles, because they afford comfort and protection for the eyes. If goggles are not worn, flying is likely to produce spasm in the eyes, and it sometimes brings on a special form of conjunc- tivitis. The lenses of the goggles should be constructed 42 OPERATION OF AIRPLANES so that the eyes will not be damaged by splinters of glass in case of an accident. One well-known method of achieving this end is to make each lens of two thin pieces of glass, with a film of transparent celluloid cemented between them. In case of fracture the broken pieces then adhere to the central layer of celluloid, and the danger to the eyes is thereby materially reduced. The nose-piece of the goggles should be made of some soft, non-metallic substance, that will not injure the nose. Safety helmets are valuable for protecting the head from injury in a crash. They should be light in weight and should fit properly, so they will not be dislodged easily. III. AIRPLANE ACCIDENTS /GENERAL CAUSES OF ACCIDENTS: An air- VJ plane accident is hardly ever due to a single cause. Usually several factors are involved, among which may be mentioned structural defects, engine trouble, error in judgment, physical illness, fatigue, and "loss of head." If only one of these factors influenced the situation, an airplane could usually be landed safely; but if (for example) the engine stops, the pilot is likely to "lose his head" and do something he should not do, or, if he is fatigued, his condition will probably affect the soundness of his judgment and the result may be quite serious. A survey of the accidents that occurred during a period of six months at one flying field, shows that in 9,000 flights there were fifty-eight crashes, in which six- teen men were seriously injured. Four of these accidents were considered unavoidable, and only one was caused by the failure of the airplane. The re- mainder were due to the ineptitude of the pilots, forty-two being caused by lack of judgment, seven by loss of head, and four by fatigue. 44 AIRPLANE ACCIDENTS I H I 2 ERRORS OF THE PILOT 45 In their relative proportions, these figures are fairly representative of the experience on most flying fields, both in Europe and in the United States. They serve admirably to show the importance of having the very best type of pilot obtainable; one who is physically, morally, and mentally fit, and competent in every way. Errors of the Pilot: An error in judgment is perhaps the most common cause of airplane accidents. A pilot frequently misjudges his distance from the ground when landing and flattens out too soon or too late, and an accident may easily occur before the mis- take is realized. In the air, he may bank too much or too little or he may climb on a turn. Accidents from attempting to make turns too near the ground, where a side slip means disaster, are notably frequent. A pilot often subconsciously senses a danger to which he is subjected, but under the sudden strain of the emergency he may be unable to think, decide, and act quickly. This momentary lapse of co-ordination between reason and action is called "loss of head/' In flying, a fraction of a second often counts greatly, and may be all that stands between safety and danger; and in an emergency there is seldom time to correct an error. Loss of head is closely associated with fatigue and with fear. When fatigued, a pilot is unable to think and act quickly, because his brain no longer responds, with its normal promptness, to the demands that are made upon it. The pilot works in a sort of stupor, and takes but little conscious part in controlling his plane. If a crash occurs from this cause, and the pilot escapes, he usually has no distinct recollection of what happened during the flight; his memory appears to have been temporarily stunned. AIRPLANE ACCIDENTS -is closely associated with fatigue and loss of head, but it does not appear to produce many acci- dents. There is little time to think of danger during flight, and consequently, even though there may be a sense of fear lurking somewhere in the back of a pilot's head, it rarely asserts itself in such a way as to affect his management of the machine. When it does, how- ever, the effects are similar to those produced by loss of head and fatigue. Courtesy Air Service, U. S. A. ? 17 A RESULT OF DEFICIENT VISION. FIRE 47 Failure of the Machine: In the early days of flying, accidents were frequently caused by the failure of some vital part of the plane, but this difficulty has now been largely overcome. There is, however, a great need of inspection before attempting to take a machine off the ground. During flight the plane is subjected to severe strain and vibration and its parts are likely to become worn or loosened. A pilot should always see that his airplane is mechanically safe before he attempts to use it, and the subject of inspection is discussed in some detail in another section of this book. (See page 36.) Fire: It is not uncommon for a plane to catch fire in the air, and investigations of several accidents of this nature show that defective gasoline feed systems have been the primary cause. It has developed in some cases that inadequate drainage of the fuselage has allowed an accumulation of gasoline immediately under the engine, and the fumes from this exposed fuel catch fire, either by a back-fire, or from an insufficiently protected exhaust manifold, or from a spark from one of the magnetos. There is always more or less free gasoline around an aeronautical engine, coming from a flooded carbure- tor, a leaking feed-pipe, or some other source. Ample drainage facilities, in the form of fair-sized drainage holes in the fuselage bottom, should be provided so as to allow the oil and gasoline to drain out freely when the machine is in any possible position. The entire gaso- line supply system should be inspected for leaks before every flight, and any leaks that may be found should be repaired before the flight is attempted. It has been demonstrated that there is less likelihood of leakage 48 AIRPLANE ACCIDENTS occurring in the gasoline feed system if the supply tanks are connected to the other parts of the system by means of flexible tubes of copper or other material that will withstand vibration. To remove the fumes of gasoline, the engine com- partment should be adequately ventilated. In spite of good ventilation, however, there is always a possibility of inflammable vapors remaining near the engine, and to prevent ignition of these fumes by back-fires it is necessary to carry the open end of the carburetor air-intake outside of the engine compartments. With this arrangement flames from a back-fire are blown out into the open air instead of into a space that may be filled with inflammable fumes. As a protection against the accidental ignition of inflammable fumes and vapors by sparks from the magnetos, it appears to be possible and practicable to inclose the magnetos on aeronautical engines by means of gauze covers similar to the kind used in safety lamps and on explosion-proof motors and dynamos. Pro- tection of this kind might not prevent fire in case the magneto became drenched with liquid gasoline, but it would almost certainly prevent the accidental igni- tion of inflammable vapors in the engine compartment, so long as the gauze remained whole and sound. To prevent a fire from attaining serious propor- tions, a pressure-actuated sprinkler system has been found efficient in many cases. Such systems operate on a principle similar to that used in connection with the sprinkler systems found in large buildings, except that the fire-extinguishing medium in the airplane is not water, but pyrene, fire-foam, or some other material effective in quenching oil-fires, and that the system is FIRE 49 w 5O AIRPLANE ACCIDENTS actuated by air pressure. A tank is installed in the airplane, and small pipes or tubes are run from it to various parts of the engine compartment. A valve, actuated by the release of a fuse of soft alloy, is pro- vided, and when a fire breaks out the fuse melts and instantly the entire engine compartment is flooded with an effective fire-extinguishing spray. The main ob- jection to the pressure fire-extinguishing system is that it makes considerable additional weight for the airplane to carry, but this objection is offset by the protection that the system affords. The danger from fire is not confined to the period of actual flight, for it must be remembered that when a "crash" occurs the aviator may be pinned down by the wreckage or rendered helpless in some other way, and he is then in great danger if the wrecked machine takes fire. Airplane fires that occur in consequence of crashes are caused largely by the bursting or puncturing of the gasoline tanks, or the rupture of the tubing, from the violence of the impact. In most airplanes it is neces- sary to carry the gasoline under pressure, in order that the fuel may reach the engine when the machine is "nosed up" at a considerable angle. When the gasoline tank is perforated at any point below the level of the liquid surface, the air pressure forces the fuel out in a fine spray, and the pilot, passengers, and machine are likely to become drenched with it. If, as frequently happens, this fuel becomes ignited by a spark from any source, the results are usually extremely serious. Experiments have been carried on with the intent of producing a tank that will not burst or puncture in a crash, or which will not distribute the gasoline over FIRE 51 the machine in case of an accident. These attempts have been fairly successful, and safety tanks of various kinds are now available. In the main, safety gasoline tanks consist in a metal shell of medium thickness, covered with fabric and vulcanized rubber of varying degrees of elasticity. The whole is further covered with galvanized wire netting. The idea is to provide a flexible form of construction that will withstand severe shock. The tubing used in connection with these safety tanks should be of soft copper or other flexible material. It is altogether probable that many of the fatal airplane accidents, in which the serious features have been due to the outbreak of fire after the crash, could have been prevented or rendered far less serious if safety tanks had been installed on the machines. To prevent the spreading of fire in an airplane, the dope used on the fabric should be as nearly fire- proof as possible, and to insure greater safety, the cloth also should be fireproofed before the dope is applied to it. Fire-resistive dopes have been produced in various ways, the most common method being by the addition of certain fire-retarding substances to the ordinary acetate dope. Many of the dopes prepared in this way are objectionable on account of the fact that they are much heavier than ordinary dope and consequently their use materially increases the weight of the doped surface. Recent developments in some of these fireproofing methods, however, have reduced the added weight to a negligible quantity. The use of oils and varnishes in finishing the woodwork in airplanes increases the fire hazard in these parts considerably, and the use of fire-resistive 52 AIRPLANE ACCIDENTS paint on all interior wooden parts, and especially in the engine compartment, is highly desirable. Fireproofing materials may be a little more expensive than the materials ordinarily used, but the added protection that they give appears to be well worth the difference in cost. Superchargers and Variable-pitch Propel- lers: For use in flying at high altitudes, where the air pressure is considerably below normal, superchargers and variable-pitch propellers have been developed. Superchargers compress the air that is used by the en- gine, and deliver it to the cylinders under a pressure that is approximately the same as that prevailing at sea level. Propellers with a variable pitch can be so chang- ed that their effect on the rarefied air at high altitudes will be practically the same as that of normal propellers on the air at sea level. Variable-pitch propellers might also be of considerable advantage in landing, because by reversing the pitch the head resistance of the airplane could be greatly increased, and the machine could be brought to a stop within a short distance after the wheels touch the ground. The practicability of the variable- pitch propeller is questioned by some authorities, how- ever, on the ground that any mechanism that would vary the pitch of a propeller would in all probability tend to reduce the solidity of the propeller as a whole. This is a matter worthy of serious consideration. Instruments: Although well trained and experi- enced pilots and mechanically perfect machines are the first requisites of safety in flying, various other factors are also of great importance in this connection. For example, dependable instruments are needed, to keep the pilot informed with respect to the speed, altitude, attitude, and direction of motion of the airplane. INSTRUMENTS 53 The speed of the airplane is read from an air-speed indicator. This instrument indicates the speed with which the craft is moving, relatively to the air through which it passes. In still air and in low altitudes the air-speed meter also indicates the ground speed of the craft with fair accuracy, but if the wind is blowing the ground speed must be calculated from the reading of the instrument and the velocity and direction of the wind. The direction in which the nose of an airplane is pointed is indicated by a compass. This instrument also enables a pilot or passenger to locate objects on the ground by bearings, when the position of the plane is known; and it is likewise employed, to some extent, for determining the position of the airplane itself, by taking cross-bearings upon known objects. The com- pass is one of the most essential of all airplane instru- ments, and one that is most likely to give false in- formation unless particular attention is given to its installation, and unless the readings are taken while the machine is flying level and on a straight course. The altimeter is used for determining the height of an aircraft above the surface of the earth. This instru- ment is usually of the aneroid barometer type, and may be either indicating or recording in its operation. A bubble statoscope is also desirable, to indicate short, rapid changes in altitude, too small to be shown clearly on the altimeter. Its use assists a pilot in holding his machine at a constant level. The purpose of the inclinometer is to show at what angle the airplane is flying, indicating the lateral as well as the longitudinal angle that the plane makes with the horizontal. In order to insure the effective opera- tion of an inclinometer, the instrument must be stabil- 54 AIRPLANE ACCIDENTS ized by a gyrostat or other equivalent means, and all readings must be made when flying in a straight line at a uniform speed. In planes equipped with radio apparatus, the radio directionfinder is rapidly coming into use. In operat- ing this device, closed-coil aerials, fastened in the wings of the machine, are used. A closed flat coil possesses strong directional characteristics, because when the edge of such a coil is pointed directly toward the incoming electrical waves, the signals received are of maximum strength; but as the coil is turned to one side or the other, the signals rapidly become weaker and less dis- tinct. With a radio direction finder it is possible to guide an airplane with considerable accuracy toward any selected radio transmitting station, even though the station is entirely invisible, on account of distance or bad atmospheric conditions. Safety Straps: It should hardly be necessary to emphasize the importance of using safety straps in the seats of airplanes, but experienced aviators not infrequently fly with their safety straps undone. Such practice is foolhardy, yet it would be easy to mention some distinguished aviators who have been killed by carelessness in this respect. It is ab- solutely essential that the pilot and passengers in air- planes be strapped to their seats, to prevent falls when the machine turns on its side or on its back. The straps that are used should be broad and exceedingly strong, and be securely fastened to the framework of the machine. The device employed for fastening the belt around the person using it should be constructed so that it can be released quickly and with one hand; and it is recommended that this release be effected by EMERGENCY STATIONS 55 means of a small hand lever, located where it will be easily accessible under all circumstances, but where it cannot be operated accidentally. Emergency Stations: Since only a small num- ber of airplane accidents occur outside of landing fields, the airdromes are the scenes of the greatest catastrophes. A_ surgeon should be employed at every permanent landing field, to furnish assistance in Case of accidents. Every airdrome should also maintain an emergency station and an ambulance, and a number of men trained in first-aid work should be available to assist in treating injured persons. The emergency station should be well supplied with materials necessary for treating injuries of all kinds. The ambulance should carry a supply of stretchers, bandages, splints, surgeons' plaster, field dressings, slings, morphine, hypodermic syringes, anesthetics, and anesthetic face-masks, as well as scissors, knives, and other instruments that may be needed by a surgeon in field work. Wirecutters (suit- able for cutting airplane wires), saws, hammers, crow- bars, and other tools that may be needed for clearing away wreckage should also be carried on the ambulance. Fire extinguishers are likewise essential. In the event of a crash or a bad accident of some other kind, the surgeon and a staff of first-aid men and mechanics should proceed with the ambulance to the scene of the accident, at the earliest possible moment. The persons involved in the crash should be removed from the wreckage at once, and placed on stretchers if they are injured. The surgeon should make a rapid examination of the injured persons and direct such first-aid treatment as he deems advisable. Only 56 AIRPLANE ACCIDENTS such treatment should be given on the field as is necessary to relieve pain and to make the removal of the patient safe. In releasing an injured person from the wreckage, cut away the debris that is holding him down, instead of trying to drag him out. Pulling persons from the wreckage may convert simple fractures into compound ones, and add materially to the seriousness of the injury. In case of fire, use the fire extinguishers on the parts near the injured or imprisoned persons, and be careful to direct the streams in such a way that the injured persons will not be suffocated by the vapors. After the injured and other persons have been removed from the wreck, a corps of men should be assigned to take the damaged plane from the field. This should be done as soon as possible, because any obstruction remaining on the field may seriously inter- fere with the safe operation of other airplanes using the airdrome. IV. PILOTS THE IMPORTANCE OF LEGAL REGULA- TION: In the earlier days of aeronautics, little consideration was given to the qualifications that a man should possess, to become a flyer. Anyone who was suf- ficiently daring and self-possessed was considered fit for the work, and no other special characteristics were thought to be necessary. The result was, that many accidents were unexplained and there was an enormous avoidable waste, both of men and of machines. Under present conditions, it is not a difficult matter to obtain an airplane-pilot's license from the Interna- tional Aeronautic Federation, an organization founded in 1905 for the purpose of regulating aeronautics, but confining its activities to the control of aeronautic sports. There is no other civilian body in the United States that issues or requires licenses at the present time, save in a few states and municipalities where laws or ordinances, suggestive of those established in connec- tion with automobile traffic, have been enacted for the local regulation of aeronautics. With these excep- tions, and with the important additional exception of 58 PILOTS X^ 1 the United States Air Service, the operation of aircraft and the licensing of pilots are nowhere officially con- trolled or provided for. Relief from this highly unsatisfactory condition of affairs is promised for the near future, however. The United States has declared its adherence to the International Convention Relative to Air Navigation, and as a sequence to this action Congress will doubtless take appropriate action for establishing an Air Naviga- tion Commission, and drafting rules and regulations affecting aerial navigation in general. When this has been accomplished, air pilots will probably be licensed by the Federal Government, in accordance with some definite plan yet to be determined. Pending the establishment of a national bureau for carrying on this work, we offer, below, some con- structive suggestions which may be useful to local authorities who are desirous of taking immediate action with regard to air navigation and the licensing of aerial pilots. Physical and Mental Qualifications of Pilots: Flying does not require a super-man, and in fact a super-man is undesirable. A flier must be normal in every way and any variation from this condition re- duces his ability to manage , a flying machine. Many authorities assert that if the machine is properly controlled, flying is .not much more hazardous than riding in an automobile; but even if this were true, we must surely admit that the act of providing this con- trol imposes unique demands upon the pilot. He is the heart and brain of the airplane and it has been said that no other occupation subjects a man to strains as varied and intense as those that he sustains QUALIFICATIONS 59 Courtesy Air Service, U. S. A. TESTING A CANDIDATE'S EYES. 60 PILOTS while operating a heavier-than-air flying machine. Moreover, he is working in an unnatural environment, and is almost wholly unaware of its effect upon his nervous system. The machine itself may fail in some part and still be brought to the earth without serious injury; but if the pilot relaxes even momentarily, the whole machine is without a director, and unless it possesses a degree of stability far in excess of that usually provided, it may easily crash to the ground. A pilot must be physically and mentally fit for his work before he is taught to fly, and he must keep in proper physical and mental condition all the time that he is engaged in aeronautical work. The importance of properly selecting the men who are to engage in such activities, and the desirability of keeping these men in perfect condition, have been fully demonstrated by the Medical Department of the United States Air Service. A pilot should be at least nineteen years of age, and he must be physically perfect in every way, showing no abnormality, congenital or otherwise, that might prevent him from effectively and safely opera- ting an aircraft. His heart, lungs, kidneys, and nervous system must be sound and healthy and capable of withstanding the effects of prolonged flight and of rapid changes of altitude. Moreover, his family history should show no inherent ailments or diseases of a nerv- ous type, which might develop quickly in his own case and cause a temporary or permanent mental collapse. His various special senses should be normal in every way. His eyes should show normal stereoscopic and color perception, and his general field of vision should be good. Persons whose eyes show more than two dioptrics of hypermetropia (far-sightedness) or TRAINING 6 1 myopia (near-sightedness) should be rejected. The middle ear should be healthy, and the vestibular apparatus should be intact and neither more nor less sensitive than the normal. The nose should show free, air passages on both sides, and there should be no evi- dence of any serious acute or chronic affection of the upper respiratory tract. Training: If the candidate is found, by ex- amination, to conform to these requirements, he is ready for his aeronautical training. This should begin with technical instruction, to teach him the principles involved in flying and to make him entirely familiar with the construction and operation of aeronautical engines and airplanes. This work should be thorough, and it should be done under the personal guidance and supervision of an experienced mechanician. When the technical training of the candidate is satisfactorily completed and he thoroughly under- stands the operation of airplanes and aeronautical engines, he may be taught how to fly. In connection with flying instruction, an ingenious special training apparatus known as an "orientator" has been found to be extremely useful. It consists in an airplane cockpit suspended within concentric rings or gimbals, in such a way that a person in the pilot's seat can exe- cute any manoeuver that can be accomplished with an airplane, except a motion of translation. He can spin around in any way whatsoever, but cannot move in a straight line either forward, backward, sidewise, or up or down. This machine can be used by the avia- tor, with entire safety, in acquiring a tolerance for vertigo, and in learning to adapt himself to the rapidly changing conditions that are experienced while flying. 62 PILOTS Courtesy Ruggles Orientator Corporation. AN ORIENTATOR IN ACTION. LICENSING 63 The use of the orientator in flying schools promises to materially shorten the time of flying instruction, and to save many lives and many machines. The actual flying instruction, in the free air, should be given in a dual-control machine, and under the direction of an expert flyer. At first the candidate should do but little of the actual operating, and he should never be allowed to manage the machine throughout the entire flight, until he has thoroughly proved his efficiency in controlling it. Before being allowed to ''solo" (that is, to fly alone), the student- pilot should make quite a number of flights in which he does all of the actual manipulating of the machine, including the preliminary inspection, the take-off, spirals, turns, spins, glides, dives, and landing, accom- panied by his instructor but receiving no assistance from him. When the novice has demonstrated in this way that he is competent to fly, he should be allowed to take a machine up alone; but his flying should be. con- fined to the vicinity of the airdrome until he has com- pleted at least eighty-five hours of solo work. Examination and Licensing: When the stu- dent-pilot has eighty-five hours of solo flying to his credit, and has made not less than eighty safe land- ings, he should be ready to qualify for a commercial pilot's license. He then presents himself to be re- examined physically by a competent medical board, and he should also undergo practical tests at the hands of an examining board composed of expert flyers. If these boards both find the candidate physically qualified, and competent to manage an airplane, a license, bearing the date of issue and valid for six months (except in case of sickness or accident), may be issued to him. 64 PILOTS He should be re-examined every six months thereafter, however, and if he is still found to be physically fitted to fly, the date of the re-examination should be recorded on his certificate. Re-examination should likewise be made after every illness or accident that the aviator may experience, and in all such cases he should be pronounced physically and mentally qualified to fly, before being allowed to resume his aerial duties. No pilot's license should be valid for more than six months from the date of the last physical examination. Care of the Pilot's Health: In the larger permanent airdromes, where a number of pilots are on duty or in training, a certified physician or flight- surgeon should be employed to supervise the recreation and physical training of the aviators. He should study the habits, temperament, and general fitness of each individual flyer, and act as a medical advisor to whom the men may turn for counsel in time of need. An aviator may be suffering from some tem- porary mental disturbance, for example, or he may be slightly out of condition physically, and to fly under such circumstances might spell disaster. In cases of this kind the counsel of the flight-surgeon should be sought and his advice followed. The aviator, if he is to maintain his highest efficiency, must be careful as to what he eats and when he eats it. It is advisable to provide a special eating place for pilots, and to have the food that is served to them prepared under the direction of some person who thoroughly understands dietetics and food values. College athletes have "training tables" provided for them, and an aviator surely has far greater reason than they, to keep himself in perfect condition. THE PILOT S HEALTH 1-1 <3 U w H 66 PILOTS Rational and well-considered exercise is essential to the maintenance of physical and mental alertness, and for this reason special flying calisthenics, particular- ly adapted to the needs of aviators, have been devised. These exercises should be executed at least once every day, by all pilots, and preferably under the direction of the flight-surgeon, not primarily for muscular de- velopment, but to promote rapid and accurate co- ordination in the pilots' mental and physical activities. V. THE MAINTENANCE AND REPAIR OF AIRPLANES THE REPAIR SHOP: Emergency repairs are us- ually made by the airplane pilot or his mechanic, but the constant strain and wear caused by continued operation also cause rapid general deterioration, and this makes it necessary to overhaul every airplane fre- quently and thoroughly. The engine should be fully inspected in all its parts after every 50 hours of oper- ation, and it should be completely overhauled after it has operated from 100 to 150 hours. For work of this kind the airplane is sent to the repair shop. Repair shops do not, in general, include facilities for making large castings or intricate parts, but small aluminum castings, and parts that are ordinarily made in a machine shop or blacksmith shop, can usually be turned out in the airplane repair shop. The parts kept in stock should include bolts, nuts, cylinder studs, piston rings, rocker arms, hinge pins, metal sockets, control-wire guides, longeron clips, shock-absorber guards, and in fact all of the small fittings used in airplane construction. The woodworking section of the repair shop should 68 MAINTENANCE AND REPAIR be equipped to make any of the wooden members found in a plane, including longerons, interplane struts, rudder posts, tail skids, wing skids, spars, compression and former ribs, and aileron beams. In repairing airplanes, a systematic course should be followed. When a plane comes into the shop for overhauling, the engine should be removed and sent to the machine shop. The rest of the airplane should be thoroughly inspected and tested, and parts that are found to be weak or otherwise defective should be removed and replaced by new material. Worn-out or deteriorated fabric should be torn off and replaced by new. The landing gear should be carefully examined and rebuilt if necessary. When finished, every part should be tested and inspected with extreme care. When the repairs are complete, the wings are Courtesy Col. T. H. Bane and "Mechanical Engineering." TESTING A LANDING GEAR. REPAIR SHOP HAZARDS 69 Courtesy Col. T. H . Bane and "Mechanical Engineering." SAND-TESTING A FUSELAGE. alined and the plane is assembled. The airplane is then given the correct stagger, incidence, and dihedral, and is thoroughly air-tested. In the machine shop, the engine is taken down and the various parts are thoroughly washed and cleaned. Every part is then inspected and repaired or replaced, as is necessary. When this has been done the engine is rebuilt and thoroughly tested on the testing block. Repair Shop Hazards: The making of ex- tensive repairs on airplanes involves practically the same hazards as those encountered in airplane manu- facturing; but owing to the fact that repair shops are usually smaller than the factories, the hazards of one department are likely to be associated more or less intimately with those of another, because the work- rooms are close together, and in some instances the various operations may be performed in the same room. The hazards that exist in shops under normal conditions 7O MAINTENANCE AND REPAIR were increased, during the war, by the necessity of realizing a high speed of production, by the unusual amount of night work that had to be done, and by the impossibility of exercising due discrimination in the employment of labor. In fact, the exigency of the times led manufacturers to close their eyes to many unsafe practices and conditions that would not be tolerated under normal or usual conditions. With the return of peace the continuance of hazards of this kind became unjustifiable, and there is no longer any good and sufficient reason why our workshops should not be made reasonably safe in all respects. General Fire Prevention : There is considerable danger from fire in an airplane repair shop, and the entire building should therefore be equipped with a powerful and efficient sprinkler system, and with ade- quate standpipes and hose. Hand extinguishers should also be provided at numerous points about the work- rooms, where they will be handy and available at all times. It is important to see that the water supply is ful- ly adequate to meet any emergency that may arise, and that a good water pressure will be constantly available. To prevent the spread of fire, it is advisable to subdivide each building into working areas as small as the nature of the work will allow. This may be accomplished by building fire-walls where space permits; and in other places, where the floor area cannot be subdivided, fire screens may be placed in the roof trusses, extending from the base of each truss to the roof planking. These screens tend to prevent the spread of flames along the roof, and they also reduce the horizontal drafts; and in both these ways they materially retard the progress of a fire. WOODWORKING 71 Woodworking: The framework of an airplane is usually constructed of small wooden parts, and the repairing of this skeleton involves the hazards usually associated with woodworking processes. The amount of waste is abnormally large, however, because only perfect material can be used, and considerable quantities of undesirable stock are therefore rejected. It is extremely important to remove all waste material from the workrooms as fast as it is produced, and before it can accumulate in any quantity. Blower systems and dust collectors should also be installed to remove the sawdust and fine shavings, and dust- Courtesy "U. S. Air Service," A WELL-REGULATED WORKSHOP. 72 MAINTENANCE AND REPAIR collecting hoods should be placed on all machines that produce dust. The wood-storage area should be well separated from the main buildings, and at a safe distance from railway tracks upon which steam locomotives operate. The storage areas should be provided with ample hydrant facilities, and equipped with suitable hose. The kilns that are used for drying the wood should be separate from the main building, and the practice of drying lumber in lofts over the boiler-rooms should be abolished. Kilns should preferably have brick walls and metal roofs, and they should be fitted with stout racks of steel or iron, for the wood to rest upon while drying. Caul boxes should be of metal, or of wood with a metal lining. The drying material should never be allowed to rest upon the steam-pipes; and the practice of using an extended smoke-pipe for heating the cauls is danger- ous and should not be allowed. In kilns and caul boxes the wood should always be kept at least twelve inches away from the surfaces from which the heat is obtained. The airplane framework is held together largely by gluing, and this frequently involves a fire hazard in the use of glue heaters. Flame heaters should be eliminated if possible, and steam or electric pots should be used for heating the glue. The use of glue heaters can be avoided by using casein glue, and casein glue is rapidly superseding fish glue in the better class of airplane work. In repairing the fabric covering of the wings and body of an airplane, a considerable amount of light, combustible material must be handled, in doing the DOPING 73 . necessary cutting, sewing, and fitting; and this means that there is a considerable fire hazard in this depart- ment. Work involving the use of fabric should there- fore be carried on in an isolated building, or at all events in rooms separated from the woodworking rooms by fire walls. Doping: For the purpose of making the fabric coverings taut and waterproof, they are covered with a special sort of varnish, after they have been fitted in place on the airplane framework. This varnish (or "dope" as it is called in the trade) varies in nature and may be divided into three kinds: (i) cellulose acetate dissolved in a solvent containing more or less tetrachlorethane; (2) cellulose acetate dissolved in a mixture containing no tetrachlorethane but consisting mainly of methyl acetate, methyl-ethyl ketone, acetone, diacetone, alcohol, and benzol; and (3) cellulose nitrate dissolved in a mixture of butyl acetate, ethyl acetate, alcohol, and benzol, or in other mixtures containing varying amounts of acetone, amyl acetate, alcohol, methanol, and benzol. Tetrachlorethane is not much used as a dope solvent at the present time. When dry, the nitrate dope has properties some- what similar to those of an ordinary moving-picture film. It burns with great rapidity, and if too highly nitrated it may also be explosive. The acetate dopes are far less inflammable when dry, but on account of the inflammable nature of most of the solvents that are used, they burn fiercely when in the dissolved state. The greatest danger from the use of dope lies, however, not in the fire hazard associated with it, but in the poisonous nature of certain of the solvents that 74 MAINTENANCE AND REPAIR are employed. Tetrachlorethane, for example, is extremely dangerous, and its fumes seriously affect the liver and kidneys and the muscles of the heart. In fact, tetrachlorethane is one of the most poisonous of the chlorine derivatives of the hydrocarbons, and permanent destructive changes in the liver, through fatty degeneration, are more marked in connection with tetrachlorethane inhalation than with any other substance except phosphorus. Benzol probably ranks next to tetrachlorethane in its harmfulness, severe chronic poisoning from this substance invariably producing extensive destruction of the white corpuscles of the blood, and not infre- quently giving rise to fatty degeneration of the liver, kidneys, and other internal organs. Benzol poisoning is characterized by a loss of weight and appetite, a quick, feeble pulse, a bluish appearance of the skin, digestive disorders, general weakness, and a tendency to fatigue after slight exertion. Methanol (wood alcohol) is poisonous, and it causes dilation of the pupils of the eyes, blurs the sight, and produces abdominal cramps, nausea, chills, and drowsiness. Instances of total blindness from methanol poisoning are numerous, and fatal cases due to its absorption are not uncommon. Chemically pure acetone fumes are said to be prac- tically harmless when inhaled in moderation; but the fumes arising from impure commercial acetone cause headache and a burning sensation in the eyes. Amyl acetate has a slight toxic effect, producing a smarting of the eyes, dry throat, sensations of tight- ness in the chest, and a tendency to cough. It also gives rise to serious nervous and circulatory symp- DOPING 75 toms including intense pain in the head. On account of the high cost of this substance it has been largely superseded by butyl acetate and ethyl acetate. Amy] alcohol is said to be four times as poisonous as methanol, and its toxic properties have been es- timated to be five times as great as those of ethyl alcohol (/.