CHAPTER V. MOTIVE POWER.By far the simplest and most efficient form of power which could be installed in a model aeroplane to drive the propeller is a twisted skein of rubber. Nothing is lighter, or more easily handled and repaired.The wordelastic, in physics, is the name given to the tendency which a body exerts, when distorted, to return to its original shape. Rubber possesses more elasticity than any other material known, it being possible to stretch a piece of rubber cord to eight or nine times its original length without fracture. Rubber also possesses the added requisite of lightness and will store up more energy than any form of steel spring.The Simplest Form of Motoris a single skein of elastic stretched between two hooks, one fixed and the other to which the propeller is attached, free to rotate. In some cases it is a decided advantage to divide the motor into one or more parts. One phase of this question has already been considered. The others will be discussed in the following chapter.The type of Elasticwhich gives at once the longest life and the greatest power is thesquarerubber, preferably about 3/32 x 3/32 inches, and not the flat strip. When examined under the microscope the edges of the square rubber show to be cleaner and sharper and not so ragged as those of the flat strips. To be of any value for use in a model aeroplane, the rubber should be absolutely pure and fresh.There are certain precautions which if observed will add greatly to the power and efficiency of a rubber band motor.Always remove the elastic from the machine when the flights are over for the time being. Rubber spoils very quickly when kept under tension. It also deteriorates if warm, so keep in a cool place. Strong sunlight causes rubber to harden and lose its elasticity, due to the presence of the sulphur used in vulcanizing. If talcum powder or finely powdered soapstone is rubbed on the bands from time to time it will prevent them from sticking together. The strands will then run and slip more easily upon each other, making it possible to store up a greater number of propeller revolutions.In spite of the use of talcum powder, however, when a skein of rubber is twisted very tightly, the strands stick together, causing it to soon break up.This nuisance may be somewhat alleviated if the strands are lubricated withpure redistilledglycerine free from grease, etc. Such a precaution will not always greatly lengthen the life of the rubber, but will increase the number of turns which it is possible to give the skein (and this is a very important advantage in model contests). Due to its sticky nature, however, the glycerine will cause the rubber to gather dust and particles of dirt which, if allowed to grind into the rubber, would soon weaken it. The skein should therefore be washed from time to time in warm soda and water and fresh glycerine applied. By all means, avoid all oils or substances of a greasy nature, such as lubricants. They quickly soften and rot the rubber.The Amount of Elasticrequired for a model will vary considerably for propellers of the same pitch and diameter. There is always a tendency to use too much rather than too little and this fault should be carefully guarded against. In nine cases out of ten it is the cause of the unsatisfactory behavior of a model.The motor should always be "stranded," that is, made up of a skein of bands. It is then possible to secure a larger number of turns than if a single strip were used.Always start a new machine with a small number of strands and gradually add to the number until the proper amount of power is obtained. The distance between the propeller and the fixed hook should always be as great as possible so as to secure the maximum number of turns.Doubling the Number of Elastic Strandsincreases the power of the motor but cuts down the number of turns which it is possible to give the propeller. That is to say, a certain skein composed of six strands of rubber will take perhaps two hundred and twenty-five turns while a twelve strand skein of he same sized rubber strands strands is only capable of less than half or about one hundred turns before it is wound tight.Doubling the number of strands and at the same time keeping them the same length increases the torque more than three times but diminishes the number of turns from one-half to one-third.Doubling the lengthof the strands does not materially reduce the torque for the first hundred turns. After two hundred turns have been reached, the torque is only about one-half as great as it would be in case the length were not doubled.Doubling the length of the strands doubles the number of turns it is possible to give the skein. It is easy to see from this why it is always advisable to make themotor as long as possibleand to compose it of the fewest number of strands if long flights are desirable.By using several separate skeins geared together so as to apply their energy to one screw, it is possible to obtain a greatly increased number of turns. The weight of the gearing is very small and hardly a factor, considering the advantages derived therefrom. Since the skeins revolve in opposite directions the frame of the machine is relieved of the harmful twisting effect so often present in a single skein.The gears should be of steel accurately cut and of no larger diameter than is necessary to separate the rubber skeins the requisite distances so that they will not rub.Holes may be bored in the gears to lighten them. The gears are easily and conveniently cut out of steel pinion wire.
CHAPTER V. MOTIVE POWER.By far the simplest and most efficient form of power which could be installed in a model aeroplane to drive the propeller is a twisted skein of rubber. Nothing is lighter, or more easily handled and repaired.The wordelastic, in physics, is the name given to the tendency which a body exerts, when distorted, to return to its original shape. Rubber possesses more elasticity than any other material known, it being possible to stretch a piece of rubber cord to eight or nine times its original length without fracture. Rubber also possesses the added requisite of lightness and will store up more energy than any form of steel spring.The Simplest Form of Motoris a single skein of elastic stretched between two hooks, one fixed and the other to which the propeller is attached, free to rotate. In some cases it is a decided advantage to divide the motor into one or more parts. One phase of this question has already been considered. The others will be discussed in the following chapter.The type of Elasticwhich gives at once the longest life and the greatest power is thesquarerubber, preferably about 3/32 x 3/32 inches, and not the flat strip. When examined under the microscope the edges of the square rubber show to be cleaner and sharper and not so ragged as those of the flat strips. To be of any value for use in a model aeroplane, the rubber should be absolutely pure and fresh.There are certain precautions which if observed will add greatly to the power and efficiency of a rubber band motor.Always remove the elastic from the machine when the flights are over for the time being. Rubber spoils very quickly when kept under tension. It also deteriorates if warm, so keep in a cool place. Strong sunlight causes rubber to harden and lose its elasticity, due to the presence of the sulphur used in vulcanizing. If talcum powder or finely powdered soapstone is rubbed on the bands from time to time it will prevent them from sticking together. The strands will then run and slip more easily upon each other, making it possible to store up a greater number of propeller revolutions.In spite of the use of talcum powder, however, when a skein of rubber is twisted very tightly, the strands stick together, causing it to soon break up.This nuisance may be somewhat alleviated if the strands are lubricated withpure redistilledglycerine free from grease, etc. Such a precaution will not always greatly lengthen the life of the rubber, but will increase the number of turns which it is possible to give the skein (and this is a very important advantage in model contests). Due to its sticky nature, however, the glycerine will cause the rubber to gather dust and particles of dirt which, if allowed to grind into the rubber, would soon weaken it. The skein should therefore be washed from time to time in warm soda and water and fresh glycerine applied. By all means, avoid all oils or substances of a greasy nature, such as lubricants. They quickly soften and rot the rubber.The Amount of Elasticrequired for a model will vary considerably for propellers of the same pitch and diameter. There is always a tendency to use too much rather than too little and this fault should be carefully guarded against. In nine cases out of ten it is the cause of the unsatisfactory behavior of a model.The motor should always be "stranded," that is, made up of a skein of bands. It is then possible to secure a larger number of turns than if a single strip were used.Always start a new machine with a small number of strands and gradually add to the number until the proper amount of power is obtained. The distance between the propeller and the fixed hook should always be as great as possible so as to secure the maximum number of turns.Doubling the Number of Elastic Strandsincreases the power of the motor but cuts down the number of turns which it is possible to give the propeller. That is to say, a certain skein composed of six strands of rubber will take perhaps two hundred and twenty-five turns while a twelve strand skein of he same sized rubber strands strands is only capable of less than half or about one hundred turns before it is wound tight.Doubling the number of strands and at the same time keeping them the same length increases the torque more than three times but diminishes the number of turns from one-half to one-third.Doubling the lengthof the strands does not materially reduce the torque for the first hundred turns. After two hundred turns have been reached, the torque is only about one-half as great as it would be in case the length were not doubled.Doubling the length of the strands doubles the number of turns it is possible to give the skein. It is easy to see from this why it is always advisable to make themotor as long as possibleand to compose it of the fewest number of strands if long flights are desirable.By using several separate skeins geared together so as to apply their energy to one screw, it is possible to obtain a greatly increased number of turns. The weight of the gearing is very small and hardly a factor, considering the advantages derived therefrom. Since the skeins revolve in opposite directions the frame of the machine is relieved of the harmful twisting effect so often present in a single skein.The gears should be of steel accurately cut and of no larger diameter than is necessary to separate the rubber skeins the requisite distances so that they will not rub.Holes may be bored in the gears to lighten them. The gears are easily and conveniently cut out of steel pinion wire.
By far the simplest and most efficient form of power which could be installed in a model aeroplane to drive the propeller is a twisted skein of rubber. Nothing is lighter, or more easily handled and repaired.
The wordelastic, in physics, is the name given to the tendency which a body exerts, when distorted, to return to its original shape. Rubber possesses more elasticity than any other material known, it being possible to stretch a piece of rubber cord to eight or nine times its original length without fracture. Rubber also possesses the added requisite of lightness and will store up more energy than any form of steel spring.
The Simplest Form of Motoris a single skein of elastic stretched between two hooks, one fixed and the other to which the propeller is attached, free to rotate. In some cases it is a decided advantage to divide the motor into one or more parts. One phase of this question has already been considered. The others will be discussed in the following chapter.
The type of Elasticwhich gives at once the longest life and the greatest power is thesquarerubber, preferably about 3/32 x 3/32 inches, and not the flat strip. When examined under the microscope the edges of the square rubber show to be cleaner and sharper and not so ragged as those of the flat strips. To be of any value for use in a model aeroplane, the rubber should be absolutely pure and fresh.
There are certain precautions which if observed will add greatly to the power and efficiency of a rubber band motor.
Always remove the elastic from the machine when the flights are over for the time being. Rubber spoils very quickly when kept under tension. It also deteriorates if warm, so keep in a cool place. Strong sunlight causes rubber to harden and lose its elasticity, due to the presence of the sulphur used in vulcanizing. If talcum powder or finely powdered soapstone is rubbed on the bands from time to time it will prevent them from sticking together. The strands will then run and slip more easily upon each other, making it possible to store up a greater number of propeller revolutions.
In spite of the use of talcum powder, however, when a skein of rubber is twisted very tightly, the strands stick together, causing it to soon break up.
This nuisance may be somewhat alleviated if the strands are lubricated withpure redistilledglycerine free from grease, etc. Such a precaution will not always greatly lengthen the life of the rubber, but will increase the number of turns which it is possible to give the skein (and this is a very important advantage in model contests). Due to its sticky nature, however, the glycerine will cause the rubber to gather dust and particles of dirt which, if allowed to grind into the rubber, would soon weaken it. The skein should therefore be washed from time to time in warm soda and water and fresh glycerine applied. By all means, avoid all oils or substances of a greasy nature, such as lubricants. They quickly soften and rot the rubber.
The Amount of Elasticrequired for a model will vary considerably for propellers of the same pitch and diameter. There is always a tendency to use too much rather than too little and this fault should be carefully guarded against. In nine cases out of ten it is the cause of the unsatisfactory behavior of a model.
The motor should always be "stranded," that is, made up of a skein of bands. It is then possible to secure a larger number of turns than if a single strip were used.
Always start a new machine with a small number of strands and gradually add to the number until the proper amount of power is obtained. The distance between the propeller and the fixed hook should always be as great as possible so as to secure the maximum number of turns.
Doubling the Number of Elastic Strandsincreases the power of the motor but cuts down the number of turns which it is possible to give the propeller. That is to say, a certain skein composed of six strands of rubber will take perhaps two hundred and twenty-five turns while a twelve strand skein of he same sized rubber strands strands is only capable of less than half or about one hundred turns before it is wound tight.
Doubling the number of strands and at the same time keeping them the same length increases the torque more than three times but diminishes the number of turns from one-half to one-third.
Doubling the lengthof the strands does not materially reduce the torque for the first hundred turns. After two hundred turns have been reached, the torque is only about one-half as great as it would be in case the length were not doubled.
Doubling the length of the strands doubles the number of turns it is possible to give the skein. It is easy to see from this why it is always advisable to make themotor as long as possibleand to compose it of the fewest number of strands if long flights are desirable.
By using several separate skeins geared together so as to apply their energy to one screw, it is possible to obtain a greatly increased number of turns. The weight of the gearing is very small and hardly a factor, considering the advantages derived therefrom. Since the skeins revolve in opposite directions the frame of the machine is relieved of the harmful twisting effect so often present in a single skein.
The gears should be of steel accurately cut and of no larger diameter than is necessary to separate the rubber skeins the requisite distances so that they will not rub.
Holes may be bored in the gears to lighten them. The gears are easily and conveniently cut out of steel pinion wire.