SOME RECENT MACHINES.

Fig. 58.—In a recently published mathematical treatise on Aerodynamics, an illustration is shown, representing the path that the air takes on encountering a rapidly moving curved aeroplane. It will be observed that the air appears to be attracted upwards before the aeroplane reaches it, exactly as iron filings would be attracted by a magnet, and that the air over the top of the aeroplane is thrown off at a tangent, producing a strong eddying effect at the top and rear. Just why the air rises up before the aeroplane reaches it is not plain, and as nothing could be further from the facts, mathematical formulas founded on such a mistaken hypothesis can be of but little value to the serious experimenter on flying machines.

Fig. 59.—An illustration from another scientific publication also on the Dynamics of Flight. It will be observed that the air in striking the underneath side of the aeroplane is divided into two streams, a portion of it flowing backwards and over the top of the edge of the aeroplane where it becomes compressed. An eddy is formed on the back and top of the aeroplane, and the air immediately aft the aeroplane is neither rising nor falling. Just how these mathematicians reason out that the air in striking the front of the aeroplane would jump backwards and climb up over the top and leading edge against the wind pressure is not clear.

Fig. 60.—This shows another illustration from the same mathematical work, and represents the direction which the air is supposed to take on striking a flat aeroplane. With this, the air is also divided, a portion moving forward and over the top of the aeroplane where it is compressed, leaving a large eddy in the rear, and, as the dotted lines at the back of the aeroplane are horizontal, it appears that the air is not forced downwards by its passage. Here, again, formula founded on such hypothesis is misleading in the extreme.

Fig. 61.—This shows the shape and the practical angle of an aeroplane. This angle is 1 in 10, and it will be observed that the air follows both the upper and the lower surface, and that it leaves the plane in a direction which is the resultant of the top and bottom angle.

Fig. 62.—This shows an aeroplane of great thickness, placed at the highest angle that will ever be used—1 in 4—and even with this the air follows the upper and lower surfaces. No eddies are formed, and the direction that the air takes after leaving the aeroplane is the resultant of the top and bottom angles.

Fig. 63.—Section of a screw blade having a rib on the back. The resistance caused by this rib is erroneously supposed to be skin friction.

Fig. 64.—Shows a flat aeroplane placed at an angle of 45°, an angle which will never be used in practical flight, but at this angle the momentum of the approaching air and the energy necessary to give it an acceleration sufficiently great to make it follow the back of the aeroplane are equal, and at this point, the wind may either follow the surface or not. Sometimes it does and sometimes it does not. Seeexperiments with screws.

Fig. 65.—The aeroplane here shown is a mathematical paradox. This aeroplane lifts, no matter in which direction it is driven. It encounters air which is stationary and leaves it with a downward trend; therefore it must lift. However, if we remove the sectionb, and only subjectato the blast, as shown atFig. 66, no lifting effect is produced. On the contrary, the air has a tendency to pressa, downwards. The path which the air takes is clearly shown; this is most important, as it shows that the shape of the top side is a factor which has to be considered. All the lifting effect in this case is produced by the top side.

Fig. 66.

Fig. 67.—In this drawingarepresents an aeroplane, or a bird’s wing. Suppose that the wind is blowing in the direction of the arrows; the real path of the bird as relates to the air is fromitoj,—that is, the bird is falling as relates to the air although moving on the linec,d, against the wind. In some cases, a bird is able to travel along the lineg,h, instead of in a horizontal direction, thus rising and apparently flying into the teeth of the wind at the same time.

Professor S. P. Langley, of the Smithsonian Institute, Washington, D.C., made a small flying model in 1896. This, however, only weighed a few pounds; but as it did actually fly and balance itself in the air, the experiment was of great importance, as it demonstrated that it was possible to make a machine with aeroplanes so adjusted as to steer itself automatically in a horizontal direction. In order to arrive at this result, an innumerable number of trials were made, and it was only after months of careful and patient work that the Professor and his assistants succeeded in making the model fly in a horizontal direction without rearing up in front, and then pitching backwards, or plunging while moving forward.

The Wright Brothers of Dayton, Ohio, U.S.A., often referred to as “the mysterious Wrights,” commenced experimental work many years ago. The first few years were devoted to making gliding machines, and it appears that they attained about the same degree of success as many others who were experimenting on the same lines at the same time; but they were not satisfied with mere gliding machines, and so turned their attention in the direction of motors. After some years of experimental work, they applied their motor to one of their large gliding machines, and it is said that with this first machine they actually succeeded in flying short distances. Later on, however, with a more perfect machine, they claim to have made many flights, amongst which I will mention three: 12 miles in 20 minutes, on September 29th, 1905; 20·75 miles in 33 minutes, on October 4th; and 24·2 miles in 38 minutes, on October 5th of the same year. As there seems to be much doubt regarding these alleged flights, we cannot refer to them as facts until the Wright Brothers condescend to show their machine and make a flight in the presence of others; nevertheless, I think we are justified in assuming that they have met with a certain degree of success which may or may not be equal to the achievements of Messrs Farman and De la Grange. It is interesting to note in this connection that all flying machines that have met with any success have been made on the same lines; all have superposed aeroplanes, all have fore and aft horizontal rudders, and all are propelled with screws; and in this respect they do notdiffer from the large machine that I made at Baldwyn’s Park many years ago. I have seen both the Farman and the De la Grange machines; they seem to be about the same in size and design, and what is true of one is equally true of the other; I will, therefore, only describe the one that seems to have done the best—the De la Grange. The general design of this machine is clearly shown in the illustrations (Figs. 68and69). The dimensions are as follows: The two main aeroplanes are 32·8 feet long and 4·9 feet wide; the tail or after rudder is made in the form of a Hargrave’s box kite, the top and bottom sides of the box being curved and covered with balloon fabric, thus forming aeroplanes. This box is 9·84 feet long from port to starboard, and 6·56 feet wide in a fore and aft direction. The diameter of the screw is 7·2 feet and it has a mean pitch of 5·7 feet. The screw blades are two in number and are extremely small, being only 6·3 inches wide at the outer end and 3·15 inches at the inner end, their length being 2·1 feet. The space between the fore and aft aeroplanes is 4·9 feet. The total weight is about 1,000 lbs. with one man on board. The speed of this machine through the air is not known with any degree of certainty; it is, however, estimated to be 32 to 40 miles per hour. When the screw is making 1,100 revolutions per minute, the motor is said to develop 50 H.P.

Fig. 68.—The De la Grange machine on the ground and about to make a flight.

Fig. 69.—The De la Grange machine in full flight and very near the ground.

In the following calculations, I have assumed that the machine has the higher speed—40 miles per hour. I have been quite unable to obtain any reliable data regarding the angle at which the aeroplanes are set, but it would appear that the angle is about 1 in 10. The total area of the two main aeroplanes is 321·4 square feet. A certain portion of the lower main aeroplane is cut away, but this is compensated for by the forward horizontal rudder placed in the gap thus formed. The two rear aeroplanes forming the tail of the machine have an area of 128·57 square feet. The area of all the aeroplanes is, therefore, 450 square feet. As the weight of the machine is 1,000 lbs., the lift per square foot is 2·2 lbs. Assuming that the angle of the aeroplanes is 1 in 10, the screw thrust would be 100 lbs., providing, however, that the aeroplanes were perfect and no friction of any kind was encountered. Forty miles per hour is at the rate of 3,520 feet in a minute of time, therefore,3,520 × 10033,000= 10·66 H.P. If we allow another 10 H.P. foratmospheric resistance due to the motor, the man, and the framework of the machine, it would require 20·66 H.P. to propel the machine through the air at the rate of 40 miles per hour. If the motor actually develops 50 H.P., 29 H.P. will be consumed in screw slip and overcoming the resistancedue to the imperfect shape of the screw. The blades of the De la Grange screw propeller are extremely small, and the waste of energy is, therefore, correspondingly great—their projected area being only 1·6 square feet for both blades. Allowing 200 lbs. for screw thrust, we have the following:2001·60= 125 lbs. pressure per square foot on the blades. If we multiply the pitch of the screw in feet by the number of revolutions per minute, we find that if it were travelling in a solid nut it would advance over 70 miles an hour. By the Eiffel tower formula P = 0·003 V², a wind blowing at a velocity of 70 miles per hour produces a pressure of 14·7 lbs. per square foot on a normal plane; therefore, assuming that the projected area of the screw blades is 1·6, we have 1·6 × 14·7 = 23·52 lbs., which is only one-fifth part of what the pressure really is when the screws are making 1,100 turns a minute. It is interesting to note that the ends of the screw blades travel at a velocity of 414 feet per second, which is about one-half the velocity of a cannon ball fired from an old-fashioned smooth bore.

Fig. 70.—Farman’s machine in flight.

A flying machine has, of course, to be steered in two directions at the same time—the vertical and the horizontal. In the Farman and De la Grange machines, the horizontal steering is effected by a small windlass provided with a hand wheel, the same as on a steam launch, and the vertical steering is effected by a longitudinal motion of the shaft of the same windlass. As the length of the machine is not very great, it requires very close attention on the part of the man at the helm to keep it on an even keel; if one isnot able to think and act quickly, disaster is certain. On one occasion, the man at the wheel pushed the shaft of the windlass forward when he should have pulled it back, and the result was a plunge and serious damage to the machine;happily no one was injured, though some of the bystanders were said to have had very narrow escapes. The remedy for this is to make all hand-steered machines of great length, which gives more time to think and act; or, still better, to make them automatic by the use of a gyroscope.

Fig. 71.—Bleriot’s machine. This machine raised itself from the ground, but as the centre of gravity was very little, if any, above the centre of lifting effect, it turned completely over in the air.

Fig. 72.—Santos Dumont’s flying machine.

Velocity and Pressure of the Wind.

The pressure varies as the square of the velocity or P ∝ V². The old formula for wind blowing against a normal plane was P = 0·005 × V². The latest or Eiffel Tower formula gives a much smaller value, being P = 0·003 × V², where V represents the velocity in miles per hour, and P the pressure in pounds per square foot.

[2]With apologies to Mark Twain.

Fig. 72a.—Angles and degrees compared. It will be observed that an angle of 1 in 4 is practically 14°.

Table of Equivalent Inclinations.

Table of Equivalent Velocities.

To convert feet per minute intometres per second, multiply by ·00508.

Table Showing Velocity and Thrust Corresponding with Various Horse-Powers.

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