CHAPTER XII LESSONS OF THE MAN-CARRYING AEROPLANES
THE builder of model aeroplanes will do well to keep in touch with the development of the passenger-carrying air craft. The development of both types of machines will always be more or less parallel. It is especially important that you watch the design and position of wings, and the modeling of propellers, since here the problem confronting both classes of builders is practically the same. The use of ailerons and vertical surfaces and all improvement in steering the large machines again may have a direct application on model aeroplane buildings.
The photographs of the new models of the large machines published in the newspapers will often give valuable hints, while the technical aeronautical papers will, of course, give more detailed information. In a few years, at the present rate of model aeroplane development, the designers and pilots of large machines may be looking to the new designs of model aeroplanes with much the same interest.
There is at present but one passenger-carrying monoplane, the Valkyrie, flown "tail first." It is built in two sizes, the smaller, fitted with high-powered engines, being intended for racing. The general lines of the Valkyrie resemble those of many of the model aeroplanes, but there are some features which deserve careful study. The main plane of the Valkyrie is set at a pronounced elevation, and has a high aspect ratio.
The front and rear planes are separated by a distance equal to about five times their width. Both planes have a slight camber. One of the most novel features of this model is that the forward plane is tilted upward at a positive angle, while the rear plane is elevated considerably less, thus giving the machine a longitudinal dihedral angle. This arrangement makes for fore and aft stability much the same as the dihedral angle of the wings makes for lateral stability, and suggests an interesting field of experiment.
The new type of Bleriot XI follows the general lines of the famous machine which first crossed the Channel. The fuselage of the new machine, however, is completely covered, tapering to a broad flat surface at the rear. This plan of gaining more surface by covering the frame is becoming general. In model building, it is unsafe to follow this plan, unless the motor base be comparatively small. The new Bleriot carries a larger horizontal rudder than formerly, placed aft, while the vertical rudder above it has been increased in size. The general design of the main plane, which is placed forward, remains unchanged. A single tractor screw is carried in front as usual.
In the new Blackburn aeroplane, the fuselage is covered with wood as far back as the pilot's seat, and with cloth to its extreme end. The use of thin board for this purpose suggests interesting possibilities. One of the most novel features of this model is the light skid attached to the outer ends of the main plane. The skid is very light, adding little to the weight or head resistance, and prevents the end of the plane from digging into the ground on landing. Such an attachment may readily be added to model aeroplanes when they will save many a broken wing.
A novelty in plane-designing is shown in the Handley Page monoplane. The main plane, carried forward, as in the Bleriot, is cambered just back of the entering edge, flows back to a flat surface at the middle and then tilts upward toward the rear edge. The two sides, in turn, are set at a slight dihedral angle to the horizontal. This modeling is believed to secure automatic stability in two dimensions, both longitudinal and transverse. The planes are unusually broad in their fore and aft dimension, extending back nearly one-half the length of the motor base. The horizontal and vertical rudders are very small. The design should work well in models.
Builders of biplane models will find some interesting suggestions in the new Bristol biplane. The forward planes are of the biplane form, the lower surface being much narrower than the superimposed plane, the comparative width being one-third wider. Another original feature of this machine is that the planes are connected by only four struts instead of by rows of struts along both the front and rear edges. The planes are held rigid by a series of braces. It is believed that this arrangement decreases the head resistance, at the same time insuring considerable lateral automatic stability. The rear plane is of the monoplane type.
The friends of the Dunn monoplane believe that the question of automatic stability has been practically solved in this ingenious machine. The Dunn machine has flown on an even keel for five miles without the pilot once touching the controlling levers. The trick is in the design of the main wings.
The greater part of the wing, extending out from the central stick, has a slight camber and is slightly elevated, besides being set at a dihedral angle. Near the outer edge the wings are bent sharply down, much as the wings of a swallow are bent, and are given a considerable negative angle both forward and outward. The tips, therefore, form pockets at either end under the arched tips.
Wings modeled in this way are remarkably stable even when traveling across the wind. When a gust of wind strikes the outer edge of the plane, it tends to thrust it down rather than up, as is the case when a gust gets under a wing of the ordinary design. The wing quickly rights itself, however, since the angle of the plane tends to lift it. The pockets in turn by compressing the air tend to counteract this tipping tendency. These pockets are besides closed to an extent by ailerons or flaps, which may be pulled down, thus confining the air still further.
An effective device for securing lateral control appears in the new Grahame-White machine. Narrow ailerons are placed on the forward edge of the front plane near the outer tips. The tips at the opposite ends are hinged and so connected that as one is raised the corresponding tip is lowered, or the other way about. Now as one of these tips is lowered, tending to lift the machine, the opposite aileron working in the other direction tends to depress it.
The increased resistance offered by the lowered flap again tends to keep the machine from swinging around in the direction of the side on which the other aileron is lowered. The lateral control is thus much more quickly applied than in the case of the rear ailerons. In applying this principle to model construction, it must be borne in mind that the resistance of these forward tips is tending to retard the machine and must be used with care when the motive power is limited.
As far as general appearance is concerned, the Piggot monoplane is probably the greatest novelty of the year. It is the first aeroplane to carry a cabin, as it were, in which the pilot sits completely enclosed. In general appearance it suggests a great whale with exaggerated fins. The pilot looks out through elliptical windows at the sides and bottom, covered with mica, to protect him from the wind.
The wings of the Piggot aeroplane resemble the Bleriot machine, the propeller, or rather tractor, being carried forward. It is extremely interesting, however, since it suggests for the first time what the appearance of a cabined, passenger-carrying aeroplane of the future may be.
On the Farman aeroplane, the arrangement for providing stability is very interesting. The ailerons in this case are attached to the rear of one of the main planes, the lower one, by hinges. This general plan will be followed in the case of the model aeroplanes. In a number of successful model aeroplanes, the Farman ailerons have been closely imitated. The Curtiss biplane depends for its stability upon ailerons mounted midway between the two main planes and partly within them. This plan is scarcely practicable in the case of model aeroplanes, since they increase air resistance and are difficult to control.
The Baldwin biplane has introduced a new feature for obtaining stability which may be closely imitated. A large plane is set vertically, directly above the upper main plane which may be swung from side to side by the pilot. The theory of this stabilizing surface is that it will restore equilibrium from side to side, since it works in undisturbed air while meeting with very little head resistance.
Many builders of model aeroplanes have introduced a similar vertical plane directly above the main plane, or have placed it well forward at the extreme front of the motor base. By removing this rudder as far as possible from the main supporting surface, it exerts a greater leverage, and a very small plane carried well forward will be more effective than a larger plane directly above the main supporting surface. It has the disadvantage of catching any chance side current and thereby knocking the aeroplane off its course.
Percy Pierce, winner of the distance record
A well-proportioned model, capable of long flights
A well designed aeroplane built by James MacPherson
The same principle has been carried somewhat further in the case of the new Herring biplane, which carries six triangular stabilizing fins set vertically above the upper plane. It is believed that these fins offer considerable resistance to any tipping motion of the planes, and if the machine slants to one side or the other, for any cause, there is a tendency, of course, to dart downward at an abrupt angle. The fins retard this motion as far as the upper plane is concerned, and the lower plane without such an equipment tends to swing back like a pendulum, thus bringing the aeroplane to an even keel.
In the case of the Antoinette aeroplane, of a monoplane type, a somewhat different device is depended upon for stability. The ailerons in this case are attached to the outer edges of the rear wing and are hinged so that they may be raised or lowered at will. One of these may be turned up while the other is turned down. Although these resemble the Farman ailerons, they are believed to be twice as effective since they may work in opposite directions, while those of the Farman aeroplane may only be inclined downward.
It will be noticed in the photographs of many successful model aeroplanes that the tips of the wings are flexed upward at an angle often as much as 45 degrees. These planes, it is believed, tend to lower the center of gravity, and in the case of a turn tend to bring the aeroplane to an even keel. Their head resistance in a straight flight is, of course, rather great. It is claimed that the Antoinette aeroplane is the easiest of all aeroplanes for a beginner, largely because of this adjustment of ailerons.
One of the most novel devices for gaining stability which has appeared during the year, is that of the Pfitzner monoplane, which gains lateral stability by means of an ingenious sliding wing tip which may be pushed out or drawn back at will. When the aeroplane begins to fall from its level, one of these wing tips is shot out, while the other is pulled in. This increased surface tends to throw one plane upward while the shorter plane, which for the time exerts less lifting power, falls correspondingly. The Pfitzner monoplane makes many sharp turns with very little tipping.
A New York aviator has succeeded, it is reported, in building a practicable aeroplane, which combines the best features of both the lighter and heavier than air machines. In the earlier stages of the development of aeronautics many believed that the solution of the problem was to be found in some such combination. The attempts usually consisted in adding large planes to dirigible balloons. Gradually, however, the combination was given up as impossible. The great dirigibles of to-day carry considerable plane surface, but this is intended to lend stability for guiding and not support.
The New York aviator, however, reverses matters and retaining the aeroplane form attempts to gain additional support from gas pockets. He does this by building his plane after the general Bleriot model but with a considerable space between the upper and lower surfaces, which he fills with gas. The machine has not yet been exhibited, but it is understood that this space is upwards of one foot in thickness and as wide and long as the planes. The front entering edge is kept sharp so that the wings, for all their size, meet as little resistance as possible. Whether the support gained from so small a body of gas is worth while, and counteracts the increased resistance of the enlarged wing, is of course an open question. The dirigible aeroplane has been flown successfully several times, however, with a passenger and is reported to have behaved well.
The new Paulhan biplane introduces an entirely new form of plane which is being watched with great interest. The wings have the appearance of being fluted or corrugated. The frames of the planes consist of a great number of ribs, running from front to rear, placed but a few inches apart. These ribs are made very flexible. The canvass covering of the planes is sewn with a series of pockets, exactly corresponding to the ribs. The wings are covered by merely pulling the canvass on the ribs and fastening it rigidly in place. This gives the canvass a tendency to arch between the ribs so that the planes consist of a series of corrugations. It is believed by some aviators that the supporting power of the aeroplane is increased in this way. It has the advantage at least of being very easy to adjust. A model aeroplane built on these lines should fly well and have a distinctive appearance.
Another feature of the new Paulhan which should appeal to the builder of model aeroplanes is its ingenious trussed girder. It is known as the Fabre girder. It is interesting to note here that the built-up girder was used in the model aeroplanes even before it was adopted in the man-carrying machines. The Fabre girder consists of two long strips of light wood connected by crosspieces of steel running diagonally. This form of construction gives unusual strength and is very light. It has its parallel in the beautifully built-up trusses to be found for instance in the models built by Mr. Mungokee. In this case the girders are made entirely of wood.
The question is often asked whether the rear edge of the front plane should be straight or brought back and tipped at either end. A study of the various models of the standard manufacturers shows that there is considerable difference of opinion among the experts. The builders of model aeroplanes in America still retain the straight line, while in England the tips are brought well back in a great many of the designs. The theory of this form is, obviously, that this tip tends to damp out any lateral motion, and makes for stability. In the most successful American models the rear line of the plane is kept straight without apparent loss of stability.
Turning now to the large machines, we find a similar contrast. In none of the Bleriot models is the rear line broken. The Wright, Curtis and Antoinette machines, even in their latest form, still retain the straight line. The Etrich monoplane has had good results with rear wing tips. The model has been accepted by the Austrian Minister of War who has ordered a fleet of twenty of these craft for the army.
The rear tip was first suggested by Lilienthal. The friends of this form claim that it more nearly approaches the form of a bird's wing than any of the other planes now in use. The depth of the main plane is nine and three-quarter feet and at the tips twelve feet. The entire tip is so adjusted that it may be flexed at will from the pilot's seat. It will be seen that this arrangement makes it possible to imitate the flight of a bird very closely. In adopting this idea in model aeroplanes it will be well to attach the extension by a hinge so that it may be turned up or down at will. Since it is placed well out from the main axis of the machine its leverage is naturally great.
In the large machines as well as in the models there seems to be a general tendency to increase the aspect ratio of the main planes. The Bleriot XI still retains its broad deep plane, but in several of the models the depth of the model has been greatly reduced. In the new Voisin monoplane the main wing has a width of thirty-seven feet and a depth of but five feet, thus giving it an aspect ratio of nearly one to eight. The machine flies with great ease, its resistance is very low and it answers well to its stabilizing devices. The Cody biplane again has supporting planes measuring fifty-two feet by only seven feet six inches.
The same tendency to reduce the size of the planes is noticeable in the recent Wright models. The Wright machines (model R), are the smallest yet used on an aeroplane. They have a spread of but twenty-six feet six inches and a chord of only three feet seven inches, giving them an exceedingly high aspect ratio. In the racing machines the spread has been cut down to twenty-one feet six inches. Attention has been called in an earlier chapter to this same tendency to reduce the wing area in model aeroplanes. It is interesting to find our amateur aviators increasing the aspect ratio of their planes although working independently.
In many of the large machines the front and rear planes are brought much closer together in the more recent models. It would seem that as the front and rear planes are brought closer together there would be a loss in fore and aft stability, but on the other hand the reduction in weight made possible by shortening the frame is very important.
A careful report has been prepared in France recently of all the serious accidents to aeroplanes with the idea of classifying them. The record of fatal accidents shows a total of thirty-one up to the beginning of the present year, resulting in thirty-four deaths. Although these figures taken alone are appalling, they are found on analysis to indicate that aviation is nevertheless growing safer and not more dangerous. In 1910 there were twice as many fatal accidents as in the previous year, but on the other hand there were more than five times as many flights made, so that the percentage of accidents, as a matter of fact, was but forty per cent. as great as for the preceding year.
The commonest cause of accidents according to these tables has been faulty construction. Next in turn came the accidents due to the errors of the pilots. Atmospheric conditions rank third in the list and fourth the carelessness of the spectators. There were in all some forty-seven accidents in 1909, and 101 in 1910. An increase is to be noticed last year in the accidents due to atmospheric conditions. This was caused in most cases by the unusual daring, even foolhardiness of the pilots. In their attempts to amaze their audience by performing hazardous dives and volplanes from great heights many machines were wrecked and several aviators met their death.
Since the main cause of fatal accidents has not been structural weakness or the carelessness of the pilots, it is clear that the science of aviation itself cannot be blamed. It is of course a comparatively easy matter to build machines sufficiently strong to fly without breaking down. The number of accidents, especially fatal accidents, due to the inherent danger of flying, to dangers which cannot be overcome, has been very trifling, and is steadily diminishing.