“ Making haste with a model aeroplane is poor policy. It never pays to use slipshod methods. Take the time to make sure every part is the best that you can make it. Care with the little details will insure success.
Model aeroplanes are exasperating to the extreme. A new model will swerve to the right and left or dive with unerring precision to the ground or nearest object. They seem to defy all attempts to make them behave and in the first few flights usually perform a "new one" every time. This is the point where success comes to the model aeroplanist who possesses patience and perseverance. ”

“ The hard knocks and battering which a model usually receives at the hands of a novice will soon wreck any flimsy construction.
To design model aeroplanes will at first seem like "robbing Peter to pay Paul," that is, no one part can be developed to an extreme without seriously affecting the efficiency of the other parts. The successful machine is a sort of "happy medium" arrived at solely through experiment. A thorough understanding, however, of the part played by each individual member of a model and its characteristics will make it possible to avoid much unnecessary work in that connection. ”

“ As the elastic unwinds, the tension, and with it also, the friction becomes less so that the propeller revolves more rapidly and maintains a somewhat even speed. The importance of preserving as far as possible an even propeller speed can hardly be overestimated and that is why such emphasis has been laid in several places upon the desirability of a model whose propeller is driven by a long skein of rubber composed of the fewest possible number of strands. ”

“ A theoretical aeroplane consists of a flat surface or plane. When the propeller is set into motion the plane is driven through the air in an oblique manner and compels the gaseous molecules to glide under its surface. Since the plane is at an angle, the front edge being higher than the back, the air must necessarily leave at the rear in a downward direction. The air molecules in traveling under the surface exercise a resistance upon it which is really a pressure against the plane. ”

“ If the screw penetrates wood or metal nut it will advance a certain distance known as the pitch which is always the same, namely, the distance separating two consecutive turns of the threads. The revolving blades of the propeller cut their way through the air in identically the same manner. But since air is a very thin medium as compared to wood or iron the propeller slips a little just like a screw going into an unsteady nut and does not advance the distance it theoretically should considering the angle of the blades. The distance lost in each revolution is called the slip. ”

“ If the planes are given too great an angle, the drift becomes so great that the propeller thrust is severely taxed. The smaller the angle, the less will be the drift and consequently the greater the speed. However, if the surface is curved the angle must not be made too small or not much lift will result.
FIG. 19. The various ways two planes may be combined to secure stability or form a biplane. The angle of the tail planes should be adjustable. If too great, the machine will slow down and the tail will drop, destroying the equilibrium of the machine and consequently the flight. ”

“ When the machine flies with the wind the effect is largely reduced. If the wind is of just the right strength and comes from the rear, the machine will fly quite steadily. If too strong, however, the model will dive to the ground. A tail somewhat dampens the swing while an elevator will slightly increase it.
The only other methods of partially mitigating the evils of a single screw are to ballast the machine, that is, place a weight on one side or to give one plane an increased sustaining surface. ”

“ 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. ”

“ The propeller should be placed as nearly as possible on a level with the planes. The centre of pressure on the planes and the centre of gravity should coincide if true stability is desired. The centre of pressure on a machine having the planes set at a dihedral angle is halfway between the lowest point and the highest providing the planes are the same width all the way along. If they taper towards the ends it is slightly lower while if they are wider at the extremities it is higher. The rubber skein and the propeller are usually placed on top of the fusellage of a dihedral winged machine. ”

“ The next indispensable feature might be called lightness, but at the same time it must be borne in mind that strength is also "second to none" and it would be fatal to sacrifice the one for the other. ”

“ The centres of gravity, of pressure and of head resistance should be at the same point. The centre of thrust of the propeller should also pass through this point. In this will be found the secret of the successful model aeroplane. It is only arrived at by careful experiment and calculation.
Head resistance increases stability while weight and speed lessen it. When an aeroplane is gliding (traveling downwards) its stability is greater than when it is rising or flying horizontally. It is the least stable when rising. ”

“ Skids of course weigh something and offer a certain amount of resistance, but the advantages more than outweigh those drawbacks.
Skids are usually made of piano wire, split bamboo or rattan. The skids should not be made any larger than is necessary to protect the machine. They do not usually take any special shape but are formed to fit each individual case.
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. ”

“ From these statements it must not be inferred that the successful model aeroplane builder is necessarily an individual possessed of consummate skill in the handling of tools or a person of unusual judgment. A few simple tools and trifling mechanical ability will enable any one to build the simple little machines herein described. The greatest asset required in the work is patience, patience spelled with a capital "P." Not only patience in building the machines, but patience in adjusting them and patience in flying them. ”

“ The power absorbed varies directly with the volume of air acted upon and the square of the speed with which it moves away. If the pitch of the propeller or its rate of revolution were doubled, four times the power previously required would be necessary. Vice versa, decreasing the rate of revolution or the pitch by one-half will make only one-fourth the power previously required necessary.
Doubling the speed and doubling the diameter requires eight times more power. Doubling the diameter, halving the pitch and halving the speed will give twice the thrust for the same power as in the first case. ”

“ There could be no direct benefit derived, however, from an aeroplane which must remain attached to a machine running over the earth and travel in its wake. Some other means of producing the required relative motion is necessary so that the aeroplane may be free to fly in any direction and either with or against the wind. This is accomplished by a propeller driven by a motor revolving at high speed in the aeroplane itself. ”

“ It is only by the constant use of a pair of scales and an accurate knowledge of materials with the ability to combine them in the most efficient manner that the weight and strength may be kept in harmony. Such knowledge and experience come only with practice. They may, however, be acquired by any one. In this regard, a notebook forms an almost indispensable aid to the experimenter. ”

“ 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 Strands increases the power of the motor but cuts down the number of turns which it is possible to give the propeller. ”

“ Piano wire is excellent for small machines since it is springy and light and able to withstand shocks. It is easily bent to any shape and offers considerably less head resistance than rattan because of its small diameter. Rattan can be bent into almost any shape by wetting.
Nothing is better for the cross pieces, ribs, etc., of the planes or framework than split bamboo. Bulk for bulk it is heavier but infinitely stronger than other woods. It is easily worked and can be bent into all kinds of shapes. Bamboo must always be bent while hot. ”

“ It requires only very little experience with model aeroplanes to prove the need of efficient skids on the machine. After the rubber band motor has run down, the propeller offers considerable resistance to the forward travel of the machine so that it does not glide properly and causes it to land on its "nose," often damaging the propeller or front planes. At the least, the framework of the machine is strained by such a shock. ”

“ Sandpapering to secure a smooth surface. Calculation in fitting a model with a propeller is almost useless. The experimental error is so large that the empirical or "cut and try" method is the only reliable one. It is best to make a number of propellers of varying pitch and diameter and give to each a thorough tryout on the machine before making a decision.
The Single Screw Machine. A propeller placed in the rear of a machine is usually more efficient than a "tractor" screw placed in front. A machine drags along considerable air with it (due to skin friction of the planes, etc.) ”

“ A small pitched propeller is less wasteful of power than one having a high pitch and so it is of no advantage to make a small screw do the work of a larger one. It is not only wasteful of energy but also permits the rubber skein to untwist too rapidly. ”

“ In order for a model to fly really well the propeller must usually be out of all proportion to the rest of the machine. In fact its size will make the machine appear very awkward and unsightly.
FIG. 38. Quasi-helical propeller. The enormous slip of small screw propellers when turning rapidly makes them very inefficient. The thrust of the propeller is dependent upon the volume of air sent backwards. A large propeller naturally deflects more air than a small one and so in order for the latter to equal the work of a large propeller it must either have an increased pitch or revolve more rapidly. ”

“ When planing down the wood do not butt one end against a bench stop, because as the wood becomes thin, the pressure exerted by the plane against the wood will cause it to rise in the middle and thereby become thinner at that part. Instead, use a clamp to fasten the wood at one end to the bench and plane away from the clamp—Plane down to a smooth surface and avoid the use of sand-paper. ”

“ If a propeller blade had a uniform angle throughout its entire length the portions of the blade near the centre would not have as great a pitch as the extreme tips because the diameter of the circle they travel in one revolution is not as great as that at the tips. For this reason it is usual to give the blades an increasing angle as they approach the centre. ”

“ Aeroplanes are usually of two general types, monoplanes and biplanes. A monoplane, as its name implies, is a machine having a single pair of wings or supporting surfaces. The Bleriot, Antoinette and Santos Dumont machines are the most prominent representatives of this type of aeroplane.
The "elevator" on a monoplane is usually in the rear of the main supporting surfaces. When in this position it also acts as a tail to furnish longitudinal stability to the machine in the same way that a feather on an arrow steadies its flight.
FIG 3. Diagram showing the makeup of a biplane (Wright) . ”