CHAPTER VIII DIRECTIONAL CONTROLThe unerring flight of birds is, of course, the model for the builders of heavier-than-air machines. Much of the birds' skill in directing their motive power remains a mystery to us, but we are learning to analyze and, in a measure, imitate them. The builder of model aeroplanes again must not alone imitate the methods of the birds; he must make their system of maintaining stability automatic. A study of a variety of successful models shows that there is great difference of opinion as to the best plan for stabilizing the aeroplane.Directional stability is gained by the use of horizontal elevators or tails for controlling vertical movement, by vertical rudders or fins for steering to right or left, and by flexible wing tips to guard against tipping.In designing any system of rudders, or ailerons, for gaining stability, one should always have in mind the general principles upon which such surfaces act. The movement of the horizontal planes or ailerons has an important effect upon the direction of the flight, because they change the angle of incidence.In other words, they alter the angle of the plane with the line along which the aeroplane is flying. If you bend the rear edge of the plane, or aileron, downward, the angle of incidence is increased. What happens is this. As the plane is lowered, the air is compressed beneath it, which tends to lift the plane, throwing up the front edge and changing the course of the flight.This method of securing stability, which was invented and patented by the Wright Brothers, has been widely imitated. In their later machines, the Wrights have even abandoned the front elevating surfaces and depend upon the movement of the main plane and a small elevating plane placed just back of the rear rudder for their directional control.They have thus done away with the friction encountered by the front planes, which has resulted in giving the machine greatly increased speed. Now in the model aeroplane, it is, of course, impossible to flex the planes up or down during flight. Some adjustment must be hit upon which will give the machine automatic stability. The principle of the action of the stabilizer remains, of course, exactly the same.In designing rudders for controlling horizontal flight, it should be borne in mind that their stabilizing power varies largely in proportion to their distance from the center of gravity. In most models the further they are removed, either front or back, the greater is their leverage, and the smaller need be their surface. By placing the rudder on an outrigger carried far out, a very small plane will suffice.Illustrating the proper position of right and left propellersA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliThe vertical rudders or fins, as they are sometimes called, are, of course, intended to control the movement to right or left and keep the model from sliding sideways. They have no counterpart in the wings of birds, and are believed by some aviators to have little effect. At any rate, they can do little harm since their head resistance is practically nothing. Unlike the horizontal forward planes, these fins should not be carried too far forward.In practice it is found that they often get in the way, and a slight side gust of wind striking them, with their great leverage, will knock the aeroplane completely off its course, perhaps upset it. The best position for such rudders is either above or below the main plane, or behind it, where they are out of the way of cross currents. In last year's models, these vertical surfaces were often very large, presenting as much surface as the planes themselves. It has been found that they may be cut down in size, thus saving weight without losing their efficiency.A long vertical fin, or keel, has the disadvantage of presenting a dangerously broad surface to any cross current of wind. The question of the position of the rudder was taken up in a previous volume. A glance at the successful model aeroplanes of the year shows that the vertical rudders have been adopted very generally. Considerable ingenuity is displayed in adjusting them.The use of wing tips of any form is intended to control both the horizontal and vertical movement. The general theory or equilibrium, of course, applies in both cases. The most perfectly adjusted model is subject to many forces which tend to tip it to one side or the other. A gust of wind,—and the air is never perfectly quiet,—will tip one end of the plane up or down.Various Steering DevicesVarious Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.In the early models, this tendency was met by fixing the plane at a dihedral angle. An examination of last year's models will show how common was this design. The dihedral angle lowers the center of gravity. Now, after one side of the model is raised and the plane rights itself, the center of gravity swings through a considerable arc, like a pendulum, before it can come to rest, so that the center must swing back and forth several times.This tendency to tipping is fatal to a steady flight. It was first observed by the Wright Brothers while studying the early Langeley type of machine. The Wrights abandoned the dihedral angle entirely, as all the world knows, and replaced it by the horizontal plane with a straight entering edge. The keel will in a measure overcome this side motion.Much of the advantage of the dihedral angle may be borrowed, however, by turning up the extreme ends of the plane, without materially lowering the center of gravity. In several of the successful models of the year, these tips have been made equal to about one-fifth the width of the plane, and are raised as high as forty-five degrees.The theory is that, when the oscillation commences, these surfaces damp out the swinging tendency, and bring the model to an even keel. Sometimes the tips are rounded off, although in some cases they are made triangular and brought to a point. As a rule, they are added to the rear plane, although one notable exception is the case of the Lester Robinson model, which carries these tips on both planes.The tips, or ailerons, at the ends of the planes maybe made of the same material as the planes themselves. In case you are using wire frames, it is, of course, a very simple matter to bend up the tips to any desired angle. When the frames of the planes are made of reed, as is generally the case, the tips should be made separately. Bend your reeds to the desired shape and cover them with the same material used for the planes.It is quite as important that they be covered smoothly as in the case of the planes. They may then be attached to the ends of the planes by wiring rigidly in position. It will be found convenient to adjust them so that they may be bent up or down to suit conditions. The same plan should be followed in building and attaching the ailerons to the rear of the main stability planes.Some interesting experiments have been made by placing several vertical surfaces above the main stability plane. A series of four or six vertical rudders are sometimes spaced apart at equal distances, extending from the front to the rear edge, with a height of about half their length. In some cases the corners are rounded off, while others prefer to cut away the front edge sharply.In the Vinet monoplane, the vertical fin appears in an entirely new form. The fin is attached near the outer edge of the main plane and the upper edges curled inward, forming an arc of a circle. The theory of the curve is that it tends to keep the air from slipping off the ends, after the manner of the curtains of the Vaison biplane.As a rule, these curled fins are about three-fourths the depth of the plane and are attached with the front ends on a line with the entering edge of the plane. These curled planes may be stretched on frames of light wire or thin reed. As the model tilts to one side, the air striking the curved surface of the outer side of the fin meets with little resistance, while the fin at the opposite side, acting with its concave surface against the wind, offers considerably more resistance, thus tending to check the side motion and bring the aeroplane to an even keel.An effective form of aileron consists of an "L" shaped plane set closely against the rear corner of the main wing. These ailerons are made in pairs and hinged to a rear edge. The side should extend about half the width of the plane. The action of the hinged plane at the rear is, of course, familiar.The extension at the side, which should be kept rather narrow, not more than one-fourth the depth of the main plane, is likely to prove very efficient. If the aileron be turned too far either up or down it will offer considerable resistance. In one of the new English models, these ailerons are so connected that as one rises the opposite aileron is lowered. Here is a fascinating field for experiment in automatic control.The vertical rudder used on the new Bleriot, the result of an immense amount of experiment, suggests interesting possibilities for the model builder. The rudder is built in the form of a long triangle and is mounted by hinging one of its shorter sides to the upper surface of the rear plane, so that its corner will extend upward and outward. In this position it suggests a fish's fin. The receding angle of the front edge offers very trifling resistance.The new Baby Wright racer depends for its lateral control largely upon a novel form of rudders known as "blinkers." These rudders are triangular in shape and extend out in front of and below the forward planes with their longer edges forward. They act much the same as the jib of a sailing vessel, and, because of their position well in front of the center of gravity, act with considerable leverage.The design appeals especially to the builder of model aeroplanes, since they can be added with very trifling weight by curving the front skids forward and stretching the cloth across their forward corners. The Valkyrie monoplane is equipped with similar rudders, in the form of half circles carried in the same position.In addition to the vertical and horizontal stability planes, many aeroplanes are now equipped with stability planes extending diagonally from the vertical axis. These are placed below the main planes, extending outward not unlike the runners of a sleigh. This box-like form tends to confine the air and affords increased support.There is even an upward tendency from this pressure of air. These planes are usually rectangular in shape, the forward or entering edge being cut away sharply. By mounting these planes on the skids, their additional weight is practically nothing. Several interesting applications of this principle are shown in the accompanying illustrations of models.
CHAPTER VIII DIRECTIONAL CONTROLThe unerring flight of birds is, of course, the model for the builders of heavier-than-air machines. Much of the birds' skill in directing their motive power remains a mystery to us, but we are learning to analyze and, in a measure, imitate them. The builder of model aeroplanes again must not alone imitate the methods of the birds; he must make their system of maintaining stability automatic. A study of a variety of successful models shows that there is great difference of opinion as to the best plan for stabilizing the aeroplane.Directional stability is gained by the use of horizontal elevators or tails for controlling vertical movement, by vertical rudders or fins for steering to right or left, and by flexible wing tips to guard against tipping.In designing any system of rudders, or ailerons, for gaining stability, one should always have in mind the general principles upon which such surfaces act. The movement of the horizontal planes or ailerons has an important effect upon the direction of the flight, because they change the angle of incidence.In other words, they alter the angle of the plane with the line along which the aeroplane is flying. If you bend the rear edge of the plane, or aileron, downward, the angle of incidence is increased. What happens is this. As the plane is lowered, the air is compressed beneath it, which tends to lift the plane, throwing up the front edge and changing the course of the flight.This method of securing stability, which was invented and patented by the Wright Brothers, has been widely imitated. In their later machines, the Wrights have even abandoned the front elevating surfaces and depend upon the movement of the main plane and a small elevating plane placed just back of the rear rudder for their directional control.They have thus done away with the friction encountered by the front planes, which has resulted in giving the machine greatly increased speed. Now in the model aeroplane, it is, of course, impossible to flex the planes up or down during flight. Some adjustment must be hit upon which will give the machine automatic stability. The principle of the action of the stabilizer remains, of course, exactly the same.In designing rudders for controlling horizontal flight, it should be borne in mind that their stabilizing power varies largely in proportion to their distance from the center of gravity. In most models the further they are removed, either front or back, the greater is their leverage, and the smaller need be their surface. By placing the rudder on an outrigger carried far out, a very small plane will suffice.Illustrating the proper position of right and left propellersA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliThe vertical rudders or fins, as they are sometimes called, are, of course, intended to control the movement to right or left and keep the model from sliding sideways. They have no counterpart in the wings of birds, and are believed by some aviators to have little effect. At any rate, they can do little harm since their head resistance is practically nothing. Unlike the horizontal forward planes, these fins should not be carried too far forward.In practice it is found that they often get in the way, and a slight side gust of wind striking them, with their great leverage, will knock the aeroplane completely off its course, perhaps upset it. The best position for such rudders is either above or below the main plane, or behind it, where they are out of the way of cross currents. In last year's models, these vertical surfaces were often very large, presenting as much surface as the planes themselves. It has been found that they may be cut down in size, thus saving weight without losing their efficiency.A long vertical fin, or keel, has the disadvantage of presenting a dangerously broad surface to any cross current of wind. The question of the position of the rudder was taken up in a previous volume. A glance at the successful model aeroplanes of the year shows that the vertical rudders have been adopted very generally. Considerable ingenuity is displayed in adjusting them.The use of wing tips of any form is intended to control both the horizontal and vertical movement. The general theory or equilibrium, of course, applies in both cases. The most perfectly adjusted model is subject to many forces which tend to tip it to one side or the other. A gust of wind,—and the air is never perfectly quiet,—will tip one end of the plane up or down.Various Steering DevicesVarious Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.In the early models, this tendency was met by fixing the plane at a dihedral angle. An examination of last year's models will show how common was this design. The dihedral angle lowers the center of gravity. Now, after one side of the model is raised and the plane rights itself, the center of gravity swings through a considerable arc, like a pendulum, before it can come to rest, so that the center must swing back and forth several times.This tendency to tipping is fatal to a steady flight. It was first observed by the Wright Brothers while studying the early Langeley type of machine. The Wrights abandoned the dihedral angle entirely, as all the world knows, and replaced it by the horizontal plane with a straight entering edge. The keel will in a measure overcome this side motion.Much of the advantage of the dihedral angle may be borrowed, however, by turning up the extreme ends of the plane, without materially lowering the center of gravity. In several of the successful models of the year, these tips have been made equal to about one-fifth the width of the plane, and are raised as high as forty-five degrees.The theory is that, when the oscillation commences, these surfaces damp out the swinging tendency, and bring the model to an even keel. Sometimes the tips are rounded off, although in some cases they are made triangular and brought to a point. As a rule, they are added to the rear plane, although one notable exception is the case of the Lester Robinson model, which carries these tips on both planes.The tips, or ailerons, at the ends of the planes maybe made of the same material as the planes themselves. In case you are using wire frames, it is, of course, a very simple matter to bend up the tips to any desired angle. When the frames of the planes are made of reed, as is generally the case, the tips should be made separately. Bend your reeds to the desired shape and cover them with the same material used for the planes.It is quite as important that they be covered smoothly as in the case of the planes. They may then be attached to the ends of the planes by wiring rigidly in position. It will be found convenient to adjust them so that they may be bent up or down to suit conditions. The same plan should be followed in building and attaching the ailerons to the rear of the main stability planes.Some interesting experiments have been made by placing several vertical surfaces above the main stability plane. A series of four or six vertical rudders are sometimes spaced apart at equal distances, extending from the front to the rear edge, with a height of about half their length. In some cases the corners are rounded off, while others prefer to cut away the front edge sharply.In the Vinet monoplane, the vertical fin appears in an entirely new form. The fin is attached near the outer edge of the main plane and the upper edges curled inward, forming an arc of a circle. The theory of the curve is that it tends to keep the air from slipping off the ends, after the manner of the curtains of the Vaison biplane.As a rule, these curled fins are about three-fourths the depth of the plane and are attached with the front ends on a line with the entering edge of the plane. These curled planes may be stretched on frames of light wire or thin reed. As the model tilts to one side, the air striking the curved surface of the outer side of the fin meets with little resistance, while the fin at the opposite side, acting with its concave surface against the wind, offers considerably more resistance, thus tending to check the side motion and bring the aeroplane to an even keel.An effective form of aileron consists of an "L" shaped plane set closely against the rear corner of the main wing. These ailerons are made in pairs and hinged to a rear edge. The side should extend about half the width of the plane. The action of the hinged plane at the rear is, of course, familiar.The extension at the side, which should be kept rather narrow, not more than one-fourth the depth of the main plane, is likely to prove very efficient. If the aileron be turned too far either up or down it will offer considerable resistance. In one of the new English models, these ailerons are so connected that as one rises the opposite aileron is lowered. Here is a fascinating field for experiment in automatic control.The vertical rudder used on the new Bleriot, the result of an immense amount of experiment, suggests interesting possibilities for the model builder. The rudder is built in the form of a long triangle and is mounted by hinging one of its shorter sides to the upper surface of the rear plane, so that its corner will extend upward and outward. In this position it suggests a fish's fin. The receding angle of the front edge offers very trifling resistance.The new Baby Wright racer depends for its lateral control largely upon a novel form of rudders known as "blinkers." These rudders are triangular in shape and extend out in front of and below the forward planes with their longer edges forward. They act much the same as the jib of a sailing vessel, and, because of their position well in front of the center of gravity, act with considerable leverage.The design appeals especially to the builder of model aeroplanes, since they can be added with very trifling weight by curving the front skids forward and stretching the cloth across their forward corners. The Valkyrie monoplane is equipped with similar rudders, in the form of half circles carried in the same position.In addition to the vertical and horizontal stability planes, many aeroplanes are now equipped with stability planes extending diagonally from the vertical axis. These are placed below the main planes, extending outward not unlike the runners of a sleigh. This box-like form tends to confine the air and affords increased support.There is even an upward tendency from this pressure of air. These planes are usually rectangular in shape, the forward or entering edge being cut away sharply. By mounting these planes on the skids, their additional weight is practically nothing. Several interesting applications of this principle are shown in the accompanying illustrations of models.
CHAPTER VIII DIRECTIONAL CONTROLThe unerring flight of birds is, of course, the model for the builders of heavier-than-air machines. Much of the birds' skill in directing their motive power remains a mystery to us, but we are learning to analyze and, in a measure, imitate them. The builder of model aeroplanes again must not alone imitate the methods of the birds; he must make their system of maintaining stability automatic. A study of a variety of successful models shows that there is great difference of opinion as to the best plan for stabilizing the aeroplane.Directional stability is gained by the use of horizontal elevators or tails for controlling vertical movement, by vertical rudders or fins for steering to right or left, and by flexible wing tips to guard against tipping.In designing any system of rudders, or ailerons, for gaining stability, one should always have in mind the general principles upon which such surfaces act. The movement of the horizontal planes or ailerons has an important effect upon the direction of the flight, because they change the angle of incidence.In other words, they alter the angle of the plane with the line along which the aeroplane is flying. If you bend the rear edge of the plane, or aileron, downward, the angle of incidence is increased. What happens is this. As the plane is lowered, the air is compressed beneath it, which tends to lift the plane, throwing up the front edge and changing the course of the flight.This method of securing stability, which was invented and patented by the Wright Brothers, has been widely imitated. In their later machines, the Wrights have even abandoned the front elevating surfaces and depend upon the movement of the main plane and a small elevating plane placed just back of the rear rudder for their directional control.They have thus done away with the friction encountered by the front planes, which has resulted in giving the machine greatly increased speed. Now in the model aeroplane, it is, of course, impossible to flex the planes up or down during flight. Some adjustment must be hit upon which will give the machine automatic stability. The principle of the action of the stabilizer remains, of course, exactly the same.In designing rudders for controlling horizontal flight, it should be borne in mind that their stabilizing power varies largely in proportion to their distance from the center of gravity. In most models the further they are removed, either front or back, the greater is their leverage, and the smaller need be their surface. By placing the rudder on an outrigger carried far out, a very small plane will suffice.Illustrating the proper position of right and left propellersA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil PeoliThe vertical rudders or fins, as they are sometimes called, are, of course, intended to control the movement to right or left and keep the model from sliding sideways. They have no counterpart in the wings of birds, and are believed by some aviators to have little effect. At any rate, they can do little harm since their head resistance is practically nothing. Unlike the horizontal forward planes, these fins should not be carried too far forward.In practice it is found that they often get in the way, and a slight side gust of wind striking them, with their great leverage, will knock the aeroplane completely off its course, perhaps upset it. The best position for such rudders is either above or below the main plane, or behind it, where they are out of the way of cross currents. In last year's models, these vertical surfaces were often very large, presenting as much surface as the planes themselves. It has been found that they may be cut down in size, thus saving weight without losing their efficiency.A long vertical fin, or keel, has the disadvantage of presenting a dangerously broad surface to any cross current of wind. The question of the position of the rudder was taken up in a previous volume. A glance at the successful model aeroplanes of the year shows that the vertical rudders have been adopted very generally. Considerable ingenuity is displayed in adjusting them.The use of wing tips of any form is intended to control both the horizontal and vertical movement. The general theory or equilibrium, of course, applies in both cases. The most perfectly adjusted model is subject to many forces which tend to tip it to one side or the other. A gust of wind,—and the air is never perfectly quiet,—will tip one end of the plane up or down.Various Steering DevicesVarious Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.In the early models, this tendency was met by fixing the plane at a dihedral angle. An examination of last year's models will show how common was this design. The dihedral angle lowers the center of gravity. Now, after one side of the model is raised and the plane rights itself, the center of gravity swings through a considerable arc, like a pendulum, before it can come to rest, so that the center must swing back and forth several times.This tendency to tipping is fatal to a steady flight. It was first observed by the Wright Brothers while studying the early Langeley type of machine. The Wrights abandoned the dihedral angle entirely, as all the world knows, and replaced it by the horizontal plane with a straight entering edge. The keel will in a measure overcome this side motion.Much of the advantage of the dihedral angle may be borrowed, however, by turning up the extreme ends of the plane, without materially lowering the center of gravity. In several of the successful models of the year, these tips have been made equal to about one-fifth the width of the plane, and are raised as high as forty-five degrees.The theory is that, when the oscillation commences, these surfaces damp out the swinging tendency, and bring the model to an even keel. Sometimes the tips are rounded off, although in some cases they are made triangular and brought to a point. As a rule, they are added to the rear plane, although one notable exception is the case of the Lester Robinson model, which carries these tips on both planes.The tips, or ailerons, at the ends of the planes maybe made of the same material as the planes themselves. In case you are using wire frames, it is, of course, a very simple matter to bend up the tips to any desired angle. When the frames of the planes are made of reed, as is generally the case, the tips should be made separately. Bend your reeds to the desired shape and cover them with the same material used for the planes.It is quite as important that they be covered smoothly as in the case of the planes. They may then be attached to the ends of the planes by wiring rigidly in position. It will be found convenient to adjust them so that they may be bent up or down to suit conditions. The same plan should be followed in building and attaching the ailerons to the rear of the main stability planes.Some interesting experiments have been made by placing several vertical surfaces above the main stability plane. A series of four or six vertical rudders are sometimes spaced apart at equal distances, extending from the front to the rear edge, with a height of about half their length. In some cases the corners are rounded off, while others prefer to cut away the front edge sharply.In the Vinet monoplane, the vertical fin appears in an entirely new form. The fin is attached near the outer edge of the main plane and the upper edges curled inward, forming an arc of a circle. The theory of the curve is that it tends to keep the air from slipping off the ends, after the manner of the curtains of the Vaison biplane.As a rule, these curled fins are about three-fourths the depth of the plane and are attached with the front ends on a line with the entering edge of the plane. These curled planes may be stretched on frames of light wire or thin reed. As the model tilts to one side, the air striking the curved surface of the outer side of the fin meets with little resistance, while the fin at the opposite side, acting with its concave surface against the wind, offers considerably more resistance, thus tending to check the side motion and bring the aeroplane to an even keel.An effective form of aileron consists of an "L" shaped plane set closely against the rear corner of the main wing. These ailerons are made in pairs and hinged to a rear edge. The side should extend about half the width of the plane. The action of the hinged plane at the rear is, of course, familiar.The extension at the side, which should be kept rather narrow, not more than one-fourth the depth of the main plane, is likely to prove very efficient. If the aileron be turned too far either up or down it will offer considerable resistance. In one of the new English models, these ailerons are so connected that as one rises the opposite aileron is lowered. Here is a fascinating field for experiment in automatic control.The vertical rudder used on the new Bleriot, the result of an immense amount of experiment, suggests interesting possibilities for the model builder. The rudder is built in the form of a long triangle and is mounted by hinging one of its shorter sides to the upper surface of the rear plane, so that its corner will extend upward and outward. In this position it suggests a fish's fin. The receding angle of the front edge offers very trifling resistance.The new Baby Wright racer depends for its lateral control largely upon a novel form of rudders known as "blinkers." These rudders are triangular in shape and extend out in front of and below the forward planes with their longer edges forward. They act much the same as the jib of a sailing vessel, and, because of their position well in front of the center of gravity, act with considerable leverage.The design appeals especially to the builder of model aeroplanes, since they can be added with very trifling weight by curving the front skids forward and stretching the cloth across their forward corners. The Valkyrie monoplane is equipped with similar rudders, in the form of half circles carried in the same position.In addition to the vertical and horizontal stability planes, many aeroplanes are now equipped with stability planes extending diagonally from the vertical axis. These are placed below the main planes, extending outward not unlike the runners of a sleigh. This box-like form tends to confine the air and affords increased support.There is even an upward tendency from this pressure of air. These planes are usually rectangular in shape, the forward or entering edge being cut away sharply. By mounting these planes on the skids, their additional weight is practically nothing. Several interesting applications of this principle are shown in the accompanying illustrations of models.
The unerring flight of birds is, of course, the model for the builders of heavier-than-air machines. Much of the birds' skill in directing their motive power remains a mystery to us, but we are learning to analyze and, in a measure, imitate them. The builder of model aeroplanes again must not alone imitate the methods of the birds; he must make their system of maintaining stability automatic. A study of a variety of successful models shows that there is great difference of opinion as to the best plan for stabilizing the aeroplane.
Directional stability is gained by the use of horizontal elevators or tails for controlling vertical movement, by vertical rudders or fins for steering to right or left, and by flexible wing tips to guard against tipping.
In designing any system of rudders, or ailerons, for gaining stability, one should always have in mind the general principles upon which such surfaces act. The movement of the horizontal planes or ailerons has an important effect upon the direction of the flight, because they change the angle of incidence.
In other words, they alter the angle of the plane with the line along which the aeroplane is flying. If you bend the rear edge of the plane, or aileron, downward, the angle of incidence is increased. What happens is this. As the plane is lowered, the air is compressed beneath it, which tends to lift the plane, throwing up the front edge and changing the course of the flight.
This method of securing stability, which was invented and patented by the Wright Brothers, has been widely imitated. In their later machines, the Wrights have even abandoned the front elevating surfaces and depend upon the movement of the main plane and a small elevating plane placed just back of the rear rudder for their directional control.
They have thus done away with the friction encountered by the front planes, which has resulted in giving the machine greatly increased speed. Now in the model aeroplane, it is, of course, impossible to flex the planes up or down during flight. Some adjustment must be hit upon which will give the machine automatic stability. The principle of the action of the stabilizer remains, of course, exactly the same.
In designing rudders for controlling horizontal flight, it should be borne in mind that their stabilizing power varies largely in proportion to their distance from the center of gravity. In most models the further they are removed, either front or back, the greater is their leverage, and the smaller need be their surface. By placing the rudder on an outrigger carried far out, a very small plane will suffice.
Illustrating the proper position of right and left propellersA serviceable model showing excellent workmanship built by Cecil Peoli
A serviceable model showing excellent workmanship built by Cecil Peoli
A serviceable model showing excellent workmanship built by Cecil PeoliA serviceable model showing excellent workmanship built by Cecil Peoli
A serviceable model showing excellent workmanship built by Cecil Peoli
The vertical rudders or fins, as they are sometimes called, are, of course, intended to control the movement to right or left and keep the model from sliding sideways. They have no counterpart in the wings of birds, and are believed by some aviators to have little effect. At any rate, they can do little harm since their head resistance is practically nothing. Unlike the horizontal forward planes, these fins should not be carried too far forward.
In practice it is found that they often get in the way, and a slight side gust of wind striking them, with their great leverage, will knock the aeroplane completely off its course, perhaps upset it. The best position for such rudders is either above or below the main plane, or behind it, where they are out of the way of cross currents. In last year's models, these vertical surfaces were often very large, presenting as much surface as the planes themselves. It has been found that they may be cut down in size, thus saving weight without losing their efficiency.
A long vertical fin, or keel, has the disadvantage of presenting a dangerously broad surface to any cross current of wind. The question of the position of the rudder was taken up in a previous volume. A glance at the successful model aeroplanes of the year shows that the vertical rudders have been adopted very generally. Considerable ingenuity is displayed in adjusting them.
The use of wing tips of any form is intended to control both the horizontal and vertical movement. The general theory or equilibrium, of course, applies in both cases. The most perfectly adjusted model is subject to many forces which tend to tip it to one side or the other. A gust of wind,—and the air is never perfectly quiet,—will tip one end of the plane up or down.
Various Steering DevicesVarious Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.
Various Steering Devices. "a" and "b," simple aileron forms. "A" novel fin on Vinet plane. "B" L-shaped aileron. "C" vertical rudder (Bleriot type). "D" "Blinkers," an effective rudder. "E" stability planes not unlike the runners of a sleigh.
In the early models, this tendency was met by fixing the plane at a dihedral angle. An examination of last year's models will show how common was this design. The dihedral angle lowers the center of gravity. Now, after one side of the model is raised and the plane rights itself, the center of gravity swings through a considerable arc, like a pendulum, before it can come to rest, so that the center must swing back and forth several times.
This tendency to tipping is fatal to a steady flight. It was first observed by the Wright Brothers while studying the early Langeley type of machine. The Wrights abandoned the dihedral angle entirely, as all the world knows, and replaced it by the horizontal plane with a straight entering edge. The keel will in a measure overcome this side motion.
Much of the advantage of the dihedral angle may be borrowed, however, by turning up the extreme ends of the plane, without materially lowering the center of gravity. In several of the successful models of the year, these tips have been made equal to about one-fifth the width of the plane, and are raised as high as forty-five degrees.
The theory is that, when the oscillation commences, these surfaces damp out the swinging tendency, and bring the model to an even keel. Sometimes the tips are rounded off, although in some cases they are made triangular and brought to a point. As a rule, they are added to the rear plane, although one notable exception is the case of the Lester Robinson model, which carries these tips on both planes.
The tips, or ailerons, at the ends of the planes maybe made of the same material as the planes themselves. In case you are using wire frames, it is, of course, a very simple matter to bend up the tips to any desired angle. When the frames of the planes are made of reed, as is generally the case, the tips should be made separately. Bend your reeds to the desired shape and cover them with the same material used for the planes.
It is quite as important that they be covered smoothly as in the case of the planes. They may then be attached to the ends of the planes by wiring rigidly in position. It will be found convenient to adjust them so that they may be bent up or down to suit conditions. The same plan should be followed in building and attaching the ailerons to the rear of the main stability planes.
Some interesting experiments have been made by placing several vertical surfaces above the main stability plane. A series of four or six vertical rudders are sometimes spaced apart at equal distances, extending from the front to the rear edge, with a height of about half their length. In some cases the corners are rounded off, while others prefer to cut away the front edge sharply.
In the Vinet monoplane, the vertical fin appears in an entirely new form. The fin is attached near the outer edge of the main plane and the upper edges curled inward, forming an arc of a circle. The theory of the curve is that it tends to keep the air from slipping off the ends, after the manner of the curtains of the Vaison biplane.
As a rule, these curled fins are about three-fourths the depth of the plane and are attached with the front ends on a line with the entering edge of the plane. These curled planes may be stretched on frames of light wire or thin reed. As the model tilts to one side, the air striking the curved surface of the outer side of the fin meets with little resistance, while the fin at the opposite side, acting with its concave surface against the wind, offers considerably more resistance, thus tending to check the side motion and bring the aeroplane to an even keel.
An effective form of aileron consists of an "L" shaped plane set closely against the rear corner of the main wing. These ailerons are made in pairs and hinged to a rear edge. The side should extend about half the width of the plane. The action of the hinged plane at the rear is, of course, familiar.
The extension at the side, which should be kept rather narrow, not more than one-fourth the depth of the main plane, is likely to prove very efficient. If the aileron be turned too far either up or down it will offer considerable resistance. In one of the new English models, these ailerons are so connected that as one rises the opposite aileron is lowered. Here is a fascinating field for experiment in automatic control.
The vertical rudder used on the new Bleriot, the result of an immense amount of experiment, suggests interesting possibilities for the model builder. The rudder is built in the form of a long triangle and is mounted by hinging one of its shorter sides to the upper surface of the rear plane, so that its corner will extend upward and outward. In this position it suggests a fish's fin. The receding angle of the front edge offers very trifling resistance.
The new Baby Wright racer depends for its lateral control largely upon a novel form of rudders known as "blinkers." These rudders are triangular in shape and extend out in front of and below the forward planes with their longer edges forward. They act much the same as the jib of a sailing vessel, and, because of their position well in front of the center of gravity, act with considerable leverage.
The design appeals especially to the builder of model aeroplanes, since they can be added with very trifling weight by curving the front skids forward and stretching the cloth across their forward corners. The Valkyrie monoplane is equipped with similar rudders, in the form of half circles carried in the same position.
In addition to the vertical and horizontal stability planes, many aeroplanes are now equipped with stability planes extending diagonally from the vertical axis. These are placed below the main planes, extending outward not unlike the runners of a sleigh. This box-like form tends to confine the air and affords increased support.
There is even an upward tendency from this pressure of air. These planes are usually rectangular in shape, the forward or entering edge being cut away sharply. By mounting these planes on the skids, their additional weight is practically nothing. Several interesting applications of this principle are shown in the accompanying illustrations of models.