Many aviators are flying without the use of speed indicators, or any other efficient scientific instruments, to warn them when they are in danger and it is probable that many skillful airmen who now depend entirely upon the senses of hearing and touch to warn them of danger, would be able to fly in safety during weather that they are now too prudent to fly in, if it were common practice to use practical and dependable navigating instruments to guide them.
I can readily understand the prejudice that exists among experienced airmen to the use of automatic stabilizers, especially if such devices require adding a considerable weight to the machine. They realize that mechanism is apt to get out of order or to fail at a critical moment and that, at such times, the real bird instinct is necessary to secure safety.
It is apparent from French efforts that their leaders in aviation are seeking to improve safety in flight by an extensive use of scientific instruments to guide or to assist them, and I quote freely some French articles for the purpose of disseminating a more extensive knowledge in this country of two notable French efforts in the direction of safety and of presenting the question of good airmanship in a clear and profitable manner.
To my mind these articles serve to show that the use of such instruments makes for precision in aerial navigation, avoids the folly of haphazard flight and tends to educate the airman in the instincts of the bird.
Bearing in mind the desire to obtain illumination for night use and to embody adjustable electric terminals, for automatic stabilizing, I have in mind a compact design to embody all of these advantages. This design is not complete but, as I have hastily prepared it, will soon be published for comment and criticism. I hope it will stimulate others in this important field to experiment with such a device at the earliest opportunity.
There are two important limits to the speed of an aeroplane, (1) a high speed which it is not prudent to exceed for fear of rupturing the planes, and (2) a low speed, below which the control system will not work to restore equilibrium.
A prudent pilot will always aim to maintain the speed between these two critical limits and will keep away from each extreme sufficiently to avoid being thrown beyond either in times of unexpected danger. When the air is disturbed and wind variable, the aerial billows alternately oppose or follow the machine or strike it at varying angles, under which circumstances the limits of critical speed approach each other. In other words, the range through which the speed may safely vary diminishes as the waves increase either in violence or eccentricity.
During a flight, with the motor running in a normal way, to each increment of speed there corresponds a certain angle of inclination which is the most efficient for that speed, but it is certain that no danger is risked when the speed oscillates in a sector of which the extreme sides correspond to the critical speeds. The angle or gap of this sector is usually ample and when the air is calm it is easy to keep the speed of the aeroplane within the sector of safety. But when the air is disturbed, the flight becomes more difficult as the amplitude of the sector diminishes.
Also, when the motor power suddenly varies, the angle of the sector diminishes proportionately. The pilot must then execute a quick maneuver to bring the speed within the more restricted sector of safety; he must be quick to act in case of weakness of the motor and incline the aeroplane to the angle which appears best to maintain equilibrium. Experienced aviators readily feel the position of the machine's equilibrium, but inexperienced aviators are apt to risk their lives in forcing an ascent at starting, or even during a flight, with a motor which works badly. Also, in checking the descent, during a vol plane, they sometimes lose their speed and capsize or drop.
The speed indicator was designed to afford a clear ocular view of the variations in speed and to enable the pilot, in a systematic manner, to maintain the speed always within the sector of safety and under the best control to suit the various conditions that are met in flight.
A Speed Indicator and Flexible Automatic Controller.—The instrument is designed for mounting to the right of the pilot. Fig. 1 is a view of the left side. Fig. 1a is a view of the rear end. Fig. 2 is a vertical longitudinal section through the rod G. Fig. 2a is a vertical dross-section through the rod G and shows the box to be divided into two compartments, A containing the pressure regulators and B containing the control regulators. Fig. 3 shows the left side open (the left covering plate being removed) exposing the control regulators, or critical limit arms, sl and fl. Fig. 4 is a view of the top.
The rod G, carrying the adjustable pressure sphere S, penetrates compartment A to the axis 0, to which it is rigidly attached. The left end of O carries the pointer H, the right end of which is shown in Figs, 1 and 1a just above the reference mark R.
The pressure regulators (Figs. 2 and 2a) comprise the spring M, the tension of which is adjusted by the nut N, and the balancing weights K. These weights are connected with the rod G, above the axis O, by the flat springs s, at the crosshead a-, which is adjustable on the rod G. The springs s are also adjustable on the arm a and the weights K are adjustable on their stems. The variety of adjustments, (1) the sphere S, (2) the spring M, (3) the arm a, (4) the springs s, and (5) the weight K, provides ample flexibility for the power and the sensitiveness of the pressure sphere and for the power and sensitiveness of the accelerating action of K, which operates above the axis O and in accord with the principles of the Doutre Stabilizer.
The right side of the instrument carries a covering plate r which may be removed to make the adjustments, the brace u providing a support for the right end of the axle 0 and also providing direct electric connection between the pointer H and the binding post e.
An electric light is introduced into the sub-compartment L and a rotatable cylinder p occupies the adjoining sub-compartment P, the bulkhead between them being provided with a slot for the escape of light; p is also provided with two slots and the admission of light to the dial sector C may be made as bright or as dim as desired by rotating p.
In Figures 1 and 3 the critical limit arms sl and fl are seen, at different angles of separation, extending across the face of the transparent windows of the dial sector C. These arms are made of non-conducting material, such as ebonite, and the rear portion of compartment B (that containing the dial sector C, see Fig. 3) is also of the same material. The critical limit arms rotate on a sleeve (Fig. 20) which is part of the bulkhead separating compartments A and B, and the axle O rotates, independently, inside of this sleeve.
The rear ends of the arms sl and fl are provided with metal tips which are grooved and brushed to fit over the metal guide rods tt which form separate electric conductors to the binding posts ut and lt. These metal tips are also provided with spring buffers b either one of which, by contact with the metal pointer H, as it moves up and down, energizes one or the other of two oppositely rotating magnets (as in the Ellsworth stabilizer), thus rotating the armature and the drum, upon which is wound the elevator wires, and thus moving the elevator either up or down. Contact of H with the upper buffer b moves the elevator for descent and in the same manner contact with the lower buffer causes ascent. That portion of H which passes beyond the point of contact and around the rear windows of C is also made of non-conducting material.
If the arms sl and fl are widely separated, as in Fig. 3, the mechanism provides a wide range for semi-automatic control, the drum upon which the elevator wires are wound may be freely worked by the control lever when the electro-magnets are not energized by the contact at b. If sl and fl be brought near to the reference mark R, full automatic control is provided and it is a simple matter to arrange a separate switch, near the pilot, by which the magnets may be rendered inoperative, if desired.
The pilot may quickly adjust the critical limit arms, to suit any conditions, while in flight. By moving a small lever on a dumb sector, such as shown in miniature, Fig. 5, by means of which the drum d (Figs. 3 and fl) is revolved, and by suitable belts in operating corresponding drums attached to the arms sl and fl, these arms may be moved as desired.
A mounting board D (Figs. 4 and 10), adaptable for shaping to any specific location of the instrument, is attached to the right side of compartment A.
A 2-inch barometer (or a larger one if desired) with a conspicuous pointer may be neatly mounted above compartment A, as indicated by dotted lines at J, Fig. 2, receiving its light through a slit, as at v, the light being reflected to the barometer dial from a small semicircular reflector, above its face, secured to the housing box.
Thus we combine a flexible automatic stabilizing device, of light weight and sound principles, with an effective speed indicator which is always adjustable to suit the conditions of flight and is always available for use in event of motor derangement. Reserve tanks and batteries to work the stabilizer in case of motor derangement are, therefore, superfluous with this device.
The variable speed friction control would work well with this device and the generating power for operating the wireless is sufficient to work the stabilizer as well as the self-starter, the speed indicator always remaining as the main reliance when the automatic power is cut out.
Now that the French have secured an enormous sum for additions to their aerial army, some anxiety is being manifested in the public press as to the fitness of their machines, notably in L'Eclair, L'Aurore and Le Figaro, and attention is being focused upon means for securing safety in flight.
To my mind there is no need for apprehension, although I have long felt that in matters of such importance false moves should be avoided, as far as possible. I am convinced that reasonable safety in flight can be assured in the best American machines, by the general use of certain mechanical agencies which are already on the market, and that the inherent stability of aeroplane as well as the reliability of motors will steadily improve.
Nevertheless, it is evident that apprehension is felt in France, in quarters where least expected, and, although it is also evident that those who are directing affairs and who are best informed are doing the correct thing, there is danger that a panicky feeling may result in a serious blow to the art of aviation during its most critical phase.
As an example of the sentiment in some quarters the following quotations are extracted from a contribution by "X" to La Technique Aeronautique, April 15, 1912:
Lately the public demand, as voiced by debates in Parliament, was for an annual sum of not less than 75 millions (francs) or enough to acquire a fleet of 1000 aeroplanes.
Inspired by the efforts of Germany, is was said, France cannot go slow without danger of losing a supremacy dearly acquired. We believe that there is in this manifestation many illusions which are dangerous to manufacturers as well as to aviation.
We have seen that Germany is conservative in devoting a more modest, but still a considerable sum to the creation of an aerial fleet. They surely understand the military value of aeroplanes as engines of reconnaissance, but they also recognize that to pilot 1000 aeroplanes 1000 aviators are necessary. We now possess no more than a hundred, civil and military, capable of rendering the practical services demanded of them in time of war. As for the Germans they regard aviation with a cold and positive enthusiasm and they know very well the hour has arrived to show their confidence in those who are qualified to make the conquest of the air a reality.
Now, in France, we are beginning to show that we no longer believe that the conquest of the air is an accomplished fact, because each week increases the number of mourners over the martyrs to aviation. If we are not careful it will be aviation itself for which we will be in mourning.
Civil opinion is indicated by the fact that the number of aeroplanes purchased for public use is gradually decreasing. If the public becomes blasé in the matter, as it is very near to being now, public sentiment will close the purse and condemn aviation en bloc. It is ominous that manufacturers no longer wish to race, notwithstanding the large prizes offered. For the want of something convincing, all that concerns aviation is under suspicion.
The reflections of the public run something like this:
What change has come over the machines since Bleriot crossed the channel?
The effective performances are due to the pilots not to the machines. They are obtained at the cost of a veritable squandering of motive power, of money and of human life.
The exhibitions (salons) follow one another, but they are all alike.
When a pilot has made a fortune he gives up his place to others. What a singular symptom! Certain constructors who were revealed as marvelous pilots and who had their triumphal march in the debut of aviation, no longer pilot their machines in the great trials.
One hesitates long before writing about things of fear and of injury tothe grand cause of aviation, but it should do no harm to discuss these matters, for everyone knows the blue side of the facts and it will not do to ignore what has already gained public notoriety.
It was announced in advance that great revelations would be made at the last military competitions. Everyone knows that the great revelations did not materialize. Why was no greater improvement shown? Is the industry dead or is it true that further progress is impossible? Public opinion hesitates between these two questions.
The great improvement that is demanded is safety.
To affirm that accidents are due to the blunders of pilots, to wind eddies, to "holes" in the air, is no solution. That is only shirking responsibility and there is attached to it a serious Bareback.
To put it mildly we cannot take liberties with the good sense of the public. The public does not wish to become an acrobat to avoid being killed in an aeroplane and it is now time to design the machines to "master wind eddies and 'holes' in the air."
All of this seems hysterical, but it is valuable as a sign-post showing1 which road to take and which to avoid. The same journal states editorially:
Current opinion, very characteristic and very emphatic, pronounces more and more in favor of researches having for their object the safety of aviators.
The Union for Safety comprises representatives of all the societies, happily very numerous, which are interested in the future of aerial navigation, such as the Aero Club of France, the General Aeronautical Association, the Syndicated Chamber of Aeronautical Industries, the Automobile Club of France, the National Aerial League, the French Society of Aerial Navigation, the Touring Club of France, etc.
The delegation of this Union, having at its head M. de la Vaulx, was lately received by the Minister of Marine, who assured its members of his co-operation and who promised to take up without delay, with the Ministers of War and Public Works, the consideration of the best measures for the expenditure of a sum of 500,000 francs donated to reward inventors and constructors who could assure the safety of flying machines in an efficacious manner.
This is an eminently useful work and of the greatest urgency. We should not, however, count on the immediate production of perfect machines.
As soon as a means for diminishing the chances of accidents has been found it should be immediately applied to our avions. Public interest is excited in favor of all aviators but those for whom aviation has become a military duty are entitled to special consideration.
The Presidents of the syndicates for War material and Naval Construction, and the Committee of Iron Industries and Railroad Material have placed at the disposal of the Ministers of War and Marine the sum of 150,000 francs, subscribed by their patrons, to be applied to naval and military aviation. In response to the intentions of the subscribers this sum isdonated to the Government with full discretion for employing it in solving the problem of safety in aerial navigation.
To my mind the sums above mentioned should be credited to M. Eiffel, M. Doutre and Captain Eteve.
The following comments on the fact that Prince Henry of Prussia had opened up an aviation subscription list similar to that lately completed in France appear in the same journal:
The German tendencies are very instructive and we should watch them very closely…The most important things recognized are, above all, the quality and the safety of the machines much more than the number and quantity.
In the same number of this publication appears an article by one of the pioneers of aeronautics, Commandant Paul Renard. I hope that this article will do something towards hastening the more general use, in this country, of mechanical aids for safety in flight.
The safety of aviators rightly concerns all who are interested in aerial navigation. The frequency and the gravity of accidents, independently of humanitarian considerations, is deplorable from the point of view of aeronautical progress and requires us to seek the means, wherever to be found, for avoiding or for limiting the consequences.
One of the most troublesome causes of catastrophe is that of instability of aeroplanes. An aviator takes flight, he rises without difficulty, travels over the atmosphere at great speed; all seems going well when, suddenly, the machine rears, or plunges by the head, or it tips over on one side, then quickly falls to earth crushed with its human freight.
What are the causes of these mysterious accidents? They are wind gusts, "holes in the air," it is said. Almost always the caprices of the atmosphere are accused, sometimes it is the strength of the apparatus and sometimes false maneuvers are blamed.
How can we discover the cause? Those who investigate find on the earth only a mass of wood, cloth and steel wires mixed up with fragments of motor and propeller. In the midst of this chaos is the victim. All the explanations given are extremely inaccurate, but that which is certain is that it happened, in the midst of most satisfactory flights, from unforeseen circumstances which compromised the stability of the apparatus either in a longitudinal or in a transverse direction.
All technicians agree in saying that an ideal aeroplane should, when its equilibrium is disturbed, in one direction or the other, re-establish its balance automatically. Most of the existing aeroplanes possess this property to a certain degree, but the re-establishment of equilibrium requires a certain time during which the aeroplane almost always approaches the earth. If it is not sufficiently high up, it strikes before being able to recover the normal position. This is already one cause of frequent accidents, but there are others.
The stability of existing aeroplanes is generally limited, i. e., they recover their normal positions only on condition that they do not pass a certain inclination. Furthermore, they are "compromised," that is to say, they have passed their zone of stability and instead of returning to their normal positions they incline more and more. The chute and the unexplained death follows.
A skillful pilot can immediately combat ruptures of equilibrium by convenient maneuvers. If they are always made in time, he is certain not to pass the limits of stability and will avoid the compromising position.
Unfortunately, it requires great skill always to maneuver opportunely and with the necessary rapidity, even the best of pilots may tire and grow careless. At other times the disturbing causes may be unexpected and manifested in a manner or at a time when the pilot is already too late to combat them.
Several persons have endeavored to ameliorate this situation by providing the pilot with mechanical agencies for his guidance. Some, like Captain Eteve, recommend the use of indicators which inform the pilot of the modifications in the behavior of the apparatus which he could not otherwise pereceive soon enough and notably as to changes in speed with respect to the surrounding air. Thus warned, the pilot can execute, in proper time, the maneuvers that without the instrument he would have performed, perhaps, too tardily.
M. Doutre goes further, his apparatus does not indicate the maneuvers which must be done, it executes them. His apparatus is a real automatic stabilizer.
The inventor has concerned himself, so far, with longitudinal stability only, but it is understood that he expects ultimately to master the problem of lateral stability.
His apparatus moves the elevator and modifies the longitudinal inclination of the aeroplane automatically. These movements are controlled by two distinct and separate organs, an accelerator and anemometer.
The accelerator acts in obedience to the absolute variations in the speed of the machine. When, from whatever cause, the forces which drive the machine forward are augmented, the speed tends to increase, but, by virtue of its inertia, the center of gravity of the machine does not obey, instantly, the increase in force and there results, according to the conditions of the increase, inclinations either up or down which may become dangerous.
M. Doutre combats them in a convenient way by maneuvering the elevator, which maneuver is controlled by the displacement of the accelerator, the position of which, with respect to the aeroplane, is influenced by the accelerations, positive or negative, and which move the elevator through the medium of the valve on a servo-motor operated by compressed air.
In the other case it is not the absolute speed which changes, but the apparent speed or the relative speed with respect to the surrounding air. If this speed increases no great inconvenience is caused. The trajectory rises more or less by reason of the increase in the sustaining force and, at the end of a certain time, conditions are established which do not give serious concern.
It is not the same, however, if the apparent speed diminishes. Then the sustaining power becomes insufficient and the machine seeks the earth, but at the same time its longitudinal equilibrium is compromised. It is necessary, at all hazard, to render the relative or apparent speed normal, and, to this end, to have recourse to an auxiliary motor which is always ready to speed up and which is no other than the weight of the machine. In other words, it is necessary to incline the machine in such a manner that it will follow a descending trajectory at such a slope that the action of the weight combined with that of the motor, which alone would be insufficient, restores the normal speed.
For this purpose the Doutre stabilizer carries a plate of palette perpendicular to the axis of the aeroplane which constitutes an anemometer measuring the relative speed. When that speed exceeds the normal the palatte is immobilized, but in the contrary case it is displaced under the combined action of the springs and the air resistance and, by its displacement, moves the elevator so as to cause a descent and thus increases the speed.
If the accelerator and the anemometer work in consonance their combined effect in moving the elevator, is to increase the movement. If, on the contrary, their respective impulses are contrary their combined effect is to decrease the movement.
The conception of such an apparatus is eminently rational, but it is important to remember that M. Doutre has no thought of presenting his stabilizer as a universal panacea for assuring the longitudinal stability of a machine that is deficient in stability. No, the inventor expects the aeroplane to be as stable as possible, but as the ordinary stabilizing influences act slowly, if they are always relied on occasions will occur when the equilibrium will be re-established too late. It is necessary to anticipate the perturbations and to execute quickly the maneuver required to return to the normal position.
All the slow perturbations will be corrected by the disposition of the aeroplane surfaces themselves. The role of the stabilizer is essentially that of intervening in case of rapid perturbations.
In regard to the mathematical theories of M. Doutre which have been developed in an interesting manner, one can raise several objections in detail. I am assured that most of the expressions in respect to aeronautical terminology are not sufficiently fixed and that M. Doutre employs some which depart a little from general usage. But these are criticisms of form and not of foundation.
The best argument in support of M. Doutre's conception is the prolonged experience, and to my mind it is conclusive as to the value of his stabilizer. For several months it has been used on machines of which the stability is not ideal and under atmospheric conditions often troublesome. The results have always been excellent, and I can only wish the greatest success to the Doutre stabilizer and base upon its employment the greatest hopes for the safety of aviators.
In an address delivered at the inauguration of the Aerodynamic Laboratory of Auteuil, March 19, 1912, M. Eiffel, after describing how he overcame some of the difficulties connected with the very successful work in his laboratory at the Eiffel Tower, on the Champ dc Mars, made the following- significant remarks:
I intend to follow up my researches on stability, already commenced. This is a subject of primary interest in aeronautics at present. It is an obstacle which must be overcome, for the good of aviation, and I am confident of our success.
I am confirmed in my belief, among other reasons, by the results actually obtained by M. Drzewiecki, who, guided solely by our experiments at the Champ dc Mars, has arranged a disposition which realizes automatic longitudinal stability. This was tried out the other day with a model carefully made to the 1/10th scale and freely suspended in horizontal equilibrium at its center of gravity around which it could oscillate in the air blast of the laboratory. Under these conditions the equilibrium was disturbed in various ways and the model returned instantly and very positively to the normal position. The experiment was very encouraging.
One of Mr. Eiffel's recent interesting discoveries is a confirmation of the results obtained by Professor Langley with respect to the inherent stability of his successful motor-driven model with tandem planes. M. Eiffel has found that when the planes are properly located and proportioned and the rear plane set at an angle of 2 ½ degrees with the front plane, the longitudinal stability is improved and the sustentation is even greater, at certain angles of inclination, than that of a monoplane of the same area.
In view of all the facts and accomplishments up to date it seems to me that the outlook for safety in flight and the sane progress of aviation is very bright and that the spirit of unrest in France on the subject of safety is more of a healthy indication than otherwise.
An address delivered on Langley Day, May 6, 1912, at Chevy Chase Club, under auspices of Aero Club of Washington.
In reviewing the subject of aviation on Langley Day from a naval viewpoint, it is appropriate to quote the trite words of a recent writer, as follows:
Warfare to-day is a question of science against science, of education and training against education and training. It is largely an engineering proposition and is altogether an economic and a business proposition.
This quotation would be equally true if the word aviation were substituted for warfare.
In view of the valuable pioneer work of Langley, under the auspices of the government, for the scientific development of aviation, why is it that the name of Langley and the value of his work is so little appreciated among his countrymen generally? The reason is this: He was so absorbed and zealous in his work that he had little time or inclination for providing representatives of the press with the usual pabulum that would enable these agents of popular demand to furnish the necessary thrills of sensation demanded by the average reader. The result was that, in spite of his success, the few hitches that occurred were placed before the people in a disadvantageous light and even held up to ridicule.
Nevertheless, his work and his fame and, incidentally, the credit that belongs to the country through his efforts are honored abroad, if not at home.
Now what caused the revival of aviation in this country? It was public interest in the achievements of the Wright brothers, not so much through what they accomplished here as what they and Glenn H. Curtiss demonstrated abroad. The American public was awakened then by the pride of American success in competition abroad, and the press has ever since endeavored to supply the demand for startling feats of American prowess to such an extent that the scientific aspect has been overshadowed by the spectacular. The result is that without the same encouragement in development for military purposes that has been given abroad, through natural causes, this noble art, which is so pregnant with engineering possibilities is regarded largely, in this country, as finding its most useful application here among the acrobats and hippodrome performers.
This, to my mind, has diverted attention from the most useful sphere of aviation and in some respects has done more harm than good.
What is the naval viewpoint of aviation and what has been accomplished?
Before making use of this new art it was clearly desirable to demonstrate whether or not aeroplanes could be used successfully in scouting, in communicating between a fleet commander afloat and a commanding general on shore, and whether or not they could discover an enemy's submerged mines and torpedo craft.
That all this will be possible is now practically assured. The eyes of the fleet may thus be extended far beyond the old limitsat a comparatively small outlay. But the machine must be such as may abide with the ships for the sake of the constant instruction, training, tests and demonstration that are necessary in order to make efficient use of them in the maneuvers. The first thing to accomplish then was to obtain vehicles with which constant training could proceed from the ships themselves, surrounded as they usually are, by ideal aerodromes, the water.
This could be done satisfactorily by the hydro-aeroplane or "airboat" only, and it is gratifying to note that in this respect we have led the world. I may say, in fact, that little interest was manifested in naval aviation abroad until the success of our small beginning was known there. Very recently, it has been taken up seriously and actively in France, England, Germany, Russia, Italy and Japan.
Some good scientific work has been done in the investigation of hydroplane models at the Naval Model Basin here in Washington, and this basin has demonstrated that it is a fine asset to the development of aviation in this country.
These models are being tested on the three machines that have been purchased from our small appropriation, and tests of wireless or radio apparatus are proceeding in conjunction with other experiments and the little instruction we can give with a small outfit, before such machines are issued to the ships for service use.
In the second place, it was natural that a mariner should regard with skepticism any effort at aerial navigation while yet there existed any doubt as to the possibility of directing a flight accurately from one point to another, over sea or at night, or in a fog.
Little attention has been paid by believers in aviation generally to the fact that an aviator was unable to navigate, under such circumstances (except in a calm) by the ordinary mariner's compass, notwithstanding the lamentable example of Cecil Grace, an American, who was lost about a year ago, while endeavoring to fly across the English Channel in a fog. There are officers in the navy to-day who look upon naval aviation as farcical because they do not yet know that an instrument can be provided by which an aeroplane may be navigated out of sight from a ship at sea with a reasonable surety of her being able to go where sent and to return to the ship that sent her.
But this important instrument, the airship compass, is now practically assured through the efforts of the American Navy in the development of naval aviation.
The next point to be sure of was that of reliability in long flights, which has chiefly to do with the improvement of motors, and, although it is now only a very close approach to an accomplished fact, it is a purely scientific problem and one which, through my knowledge of what is being done in the United States today, leaves no room for me to doubt that a fully satisfactory development may be looked for in the near future.
The last point is the question of safety in flight. The advent of the airship compass will practically settle the navigational aspect of this question, but from the maneuvering standpoint that of semi-automatic control, combined with good airmanship, something remains to be done. The solution is clearly evident to my mind and rests with a more general use of scientific instruments in the control of equilibrium. The machines are sure to be improved in stability but are safe enough at present if the instruments, already available for the safe control of equilibrium are used by those aviators whose ambitions lead to greater fields of usefulness than those of acrobatic stunts. In long flights, flying will be safe when the aviator is able temporarily to be relieved from much of the physical tension and strain of uncertainty by the use of scientific mechanical agencies. In my opinion, aviation will soon be as safe as automobiling, and its sphere of usefulness will be extended far beyond the limits of good roads.
Now, aviation in this country and naval aviation in particular has had a fair beginning only, and no further substantial progress can be made, in competition with other countries, until we continue the work inaugurated by Professor Langley on scientific lines.
It is pertinent to note that some of the results obtained by M. Eiffel very recently, at his aerodynamic laboratory in Paris, confirm the discoveries of Langley in a remarkable degree. I refer particularly to the tandem arrangement of planes which, in Langley's motor-driven model, showed great longitudinal stability. This arrangement has appealed to me for some time as possessing features sufficiently advantageous for airboats to be worth investigation, but I have been met by clouds of mathematical demonstrations, by both English and French investigators, tending to prove a theoretical inefficiency of this arrangement. Now comes M. Eiffel, with the facilities of his laboratory, to make it clear that when such surfaces are properly proportioned and set at a proper distance apart, if the following surface is set with its chord at anegative angle of 2 ½ degrees with the leading surface, the longitudinal stability is improved and the sustentation is not only equal to that of a monoplane of the same area, but for certain inclinations is greater, and Langley's work is vindicated beyond expectation.
In an address to the 5th International Aeronautic Congress, at Turin, August n, Commandant Renard, President of the International Aeronautic Commission, stated that aerodynamic laboratories have existed for several years in different countries, and he noted that they exist in the United States, having in mind, of course, the world renowned work of Professor Langley and believing that it still continued at the Smithsonian Institution.
To revive and continue this work in accordance with the spirit of foreign progress, the establishment of a modern national aerodynamic laboratory is necessary. The facilities here in Washington exceed those of any other country in the world. It is possible to establish here, at a comparatively small cost, an ideal institution which will co-ordinate the work, not only for the best interests of commerce and business, but for the best interests of both the army and the navy.
This, in my opinion, is one of the most important steps yet to be taken and, when inaugurated, the laboratory should be dedicated to the memory of Langley.
The Latest Discoveries of M. Eiffel
Notwithstanding the importance of the results obtained last year by M. Eiffel, in his aerodynamic laboratory at Paris, his recent discoveries, at the same place, promise more for the progress of aviation than any other information obtained throughout the year.
Aspect-Ratio and Center Pressure
The results of his latest experiments show the relation between the efficiency of an aeroplane wing and its aspect-ratio. The efficiency of a wing of given curvature increases with the aspect-ratio of the wing until the aspect-ratio of 6 is reached. The results are nearly the same for the aspect-ratios of 6 and 9, and it does not seem that there is any advantage, therefore, in designing a wing with a span greater than 6 times its chord or depth.
In last year's disclosures he showed that the position of the center of pressure of a curved surface gradually moves forward towards the leading edge, as the angle of incidence diminishes, until a certain inclination is reached, when it travels backward towards the following edge as the angle of incidence is further diminished. The angle at which this change in the travel of the center of pressure takes place has been designated “the angle of retrogression” and, for a curved surface, has now been found to vary with the aspect-ratio. Thus, for a particular surface it is found that with an aspect-ratio of 6 the angle of retrogression is 15 degrees, that it is 30 degrees when the aspect-ratio is 1 and 60 degrees when the aspect-ratio is 1/6.
The general conclusion is that for inclinations of the chords of the surfaces beyond 15 degrees—such as are met in the practice of aviation—the center of pressure travels towards the following edge as the angle of incidence diminishes.
The lack of longitudinal stability in many existing aeroplanes has been ascribed to this cause, and it was in search of a remedy that a wing curvature has been sought whereby the center of pressure would not travel backwards in this manner. M. Eiffel’s discoveries now confirm the claims of the Italians in respect to the flexible rear edge of the Antoni machine and of others. He finds that, in the case of wings having a double curvature, the back portion of which is turned upward, the center of pressure for small angles travels in a direction the reverse of that of ordinary surfaces with single curvature, i.e., for small angles of inclination the center of pressure travels forward as the angle diminishes and backwards as the angle increases. This is important, as it increases the natural stability of the machine. If for some reason during a flight an aeroplane with a double curvature wing suddenly dips forward, the angle being diminished, the center of pressure travels forward and tends to restore the machine to its original inclination. If, however, the inclination is suddenly increased, as by an upward puff of wind, the center of pressure moves to the rear to restore equilibrium.
But these surfaces of double curvature have a relatively small “lift co-efficient,” and he shows that this is also true for surfaces which embody varying angles of chord inclination.
Experiments with a single curvature wing, having chords varying regularly and continuously from the center line towards the lateral edges, show that, for all practical purposes, the position of center of pressure is constant within the limits of inclination which interest practical aviation. This is due to the fact that the center of pressure of the whole wing is the resultant of the combined centers of pressure of the different parts making up the whole wing. But, as before stated, the experiments show that wings with varying angles of inclination, although more stable, are not very efficient. This result is what one would naturally expect because the different portions of such wings do not work together simultaneously for efficiency at the best inclination.
One of the most interesting discoveries is this late vindication of Professor Langley’s work, notwithstanding the volumes of mathematical fog that have been evolved to show that tandem planes are unstable and inefficient.
Some of M. Eiffel’s interesting experiments prove that when curved wings are made to move in tandem it is possible to obtain a displacement of the resultant center of pressure in a direction contrary to that of the single wing and that it is possible thus to obtain the efficient lift co-efficient of “unvarying” surfaces and at the same time to increase their longitudinal stability.
Three different arrangements are referred to, but in all cases the wings were of a circular curvature with a maximum camber of 1/13.5 of the chord, and they had a span of 90 cm. (35.4”) with a depth of 15 cm. (5.9”). In the first arrangement the two wings were parallel to each other and the chords were in the same plane. In the second the chord of the following surface made a negative angle of 2 ½ degrees with the chord of the leading surface. In the third arrangement the chord of the following surface made a negative angle of 5 degrees with the chord of the leading one. In all three cases the distance between the following edge of the leading surface and the leading edge of the following surface was twice the depth of either surface.
In the first arrangement the displacement of the resultant center of pressure is found to be similar to that of a single curved surface, i.e., for small angles of incidence it moves backwards as the inclination diminishes. The second and third arrangements, however, show that the center of the pressure, instead of retrograding as in the preceding arrangement, travels forward, a result which is advantageous for longitudinal stability. The second arrangement (2 ½ degrees negative for the rear surface) is the better, its sustentation being equal to that of a monoplane of the same area, and for certain inclinations it is even greater.
Two series of experiments were made with regard to staggered planes, with the following results:
- It does not seem advantageous to stagger biplanes for the purpose of improving sustentation.
- A great gap, or distance between superposed surfaces, is advantageous so far as lift is concerned.
Thickness of Wings
To determine the influence of wing thickness on the lift and drift, comparative experiments were made with three wings, the curves of which were arcs of circles and the greatest mean heights of camber were 1/13.5 of the chord.
The models of these wings were 10 mm. (.39”), 14 mm. (.55”) and 18 mm (.6”) thick respectively at their central section and the thickness of corresponding full-sized wings ten times the model scale would be 10 cm. (3.9”), 14 cm. (5.5”), and 18 cm. (6.0”) respectively. Examination of the results relating to the three wings shows that for all inclinations the thinnest wing has the smallest drift for a given lift and that it also has the greatest lift. However, the advantages of the thin wing are not so great as to prevent increasing the strength of the wing by slightly increasing its thickness.
The distribution of pressure on the under as well as on the upper surface is practically the same in all three cases, and this is also true with respect to the variation in the position of the center of pressure.