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Aviation History
1913
1913 - 0986.PDF
GYROSCOP WE continue to receive correspondence on the subject of the dangers of the gyroscopic couple in flight, and it may, perhaps, be interesting if we give our readers a specific numerical example on which they can base their criticisms and comment. We deprecate very strongly any attempt at spreading a general impression of danger without specific illustration of the cause, particularly since the report of the Monoplane Committee made a very definite statement to the effect that there is no reason for alarm. The case taken in the report is that of a 100-h.p. Gnome engine and propeller running at 1,200 revs, per min. on a machine that is supposed to describe a com plete circle in 20 seconds. The speed of rotation of the engine is a quantity that can be assumed with accuracy. The rate of turning on the part of the machine is possibly a factor of less certainty, and it is on this latter point that any material difference of opinion must be centred. It has been explained in the recent series of articles on stability and control that an aeroplane steers a circular course by virtue of the centripetal component of the wing pressure produced by canting the machine. Assuming the turn to be accomplished at the normal flying speed, the magnitude of the centripetal force is governed solely by the amount of banking. The greater the bank, the greater the centripetal force, the shorter the radius and the less the time required to make a complete circle. The bank is thus a factor in the problem that may to some extent serve as a guide for the limiting case. For example, let us take a flight-speed of 70 miles an hour, and assume that the circle is completed in 20 seconds. The relationship between radius, circumference, velocity and time shows that the radius of the circle that can be completed in 20 seconds at 70 miles an hour is 330 feet. Similarly, the relationship between force, mass, and acceleration, shows that the force required to pro duce the centripetal acceleration represented by motion in a circle of 330 feet radius at 70 miles an hour is approximately equal to the weight of the machine. The centripetal force is, therefore, equal to the vertical force supporting the weight, and it is hardly necessary to draw a diagram of forces in order to illustrate that this is produced by a bank of 450. A bank of 45° is a very fair amount for the average pilot, for it is not everyone who chooses to fly in the attitudes occasionally assumed by Hamel and Chevillard. Our main point, however, is that anyone who bases an argument on the dangers of gyroscopic force by supposing that the machine turns in much less time than this, must be careful to work out the corresponding bank required, and also be prepared to say that it is a feasible quantity. ® ® The Wight Seaplane Again In the Air. ON Monday afternoon Mr. Gordon England was again demon. gtratlng the flying qualities of the Wight seaplane in the Solent, remaining in the air for about half an hour, meantime gracefully flying over and about the yachts in the roadstead. On Tuesday, the Wight, fully loaded, was up nearly all day, and climbed 3,000 ft. to the low clouds. The behaviour of the floats both on leaving and alighting on the water appears to be good "Telller" Floats for the British Empire. From the Aircraft Co., of 47, Victoria Street, we learn that the sole rights of the above famous floats have been acquired by them for the whole of the British Empire. M. Tellier, who is probably one of the most renowned boat builders of the world, has for some time been constructing large quantities of these floats, most of which are employed on waterplanes in France. The new arrangement is actually between the Aircraft Co., Tellier, and Fabre C ACTION. The case for steering in a vertical plane is also subject to considerations of a limiting character. Thus, for example, it is not to be readily supposed that a pilot will voluntarily initiate a dive so suddenly as to throw himself out of his seat. The radius of the circle representing the machine's path must not, therefore, be such as to cause the centrifugal force to exceed the weight. Other wise, top pressure will be necessary on the wings, and the machine as a whole will tend to descend from beneath the pilot's body. We have seen in the preceding example that the centrifugal force is equal to the weight when the machine flies at 70 miles an hour about a radius of 330 ft. The conditions for turning in the horizontal and vertical planes are, therefore, more or less of the same numerical value, as is pointed out on page 10 of the Monoplane Committee's Report. Having established a plausible time factor for the turning circle, it is a simple matter to calculate the gyroscopic couple for a known engine and propeller, by the formula M = m A.2 <a Q, where m is the mass, A is the radius of its gyration, w is the angular velocity of its rotation, and Q is the precession or angular velocity of the displaced axis. In the absence of exact figures, we will suppose the engine to weigh 280 lbs., and to have a radius of gyration of 8^ ins. Corresponding figures for the pro peller we will suppose to be 32 lbs. and 2 ft. 6 ins. respectively. The couple in the case of the engine rotating at 1,200 r.p.m. works out at 170 pound-feet, while the propeller gives 240 pound-feet. The superiority of the propeller effect is most in teresting and important, because the propeller will be a factor to be considered on any machine, whether or not it has a rotating engine. The total couple is 410 pound- feet, and we will suppose that this has to be dealt with by some organ of control, such as the elevator or the rudder, situated at a radius of 20 feet from the point about which the machine pitches or slews. When a machine is steering to the right or left, the gyroscopic reaction makes itself felt as pitching ; con versely if a change of direction on the part of the machine takes place in a vertical plane, the reaction is in the nature of a swerve. If we assume that the rudder or the elevator has an area of only 10 sq. ft., the pressure required to counteract the gyroscopic couple is only 2 lbs. per sq. ft., which can hardly be called an alarming amount, particularly as it is a force against which the pilot is forewarned. ® ® who are working together in this respect, M. Fabre being one of the earliest pioneers in experiments with hydroaeroplanes. His knowledge of floats, combined with Tellier's experience in fast motor boat building, has brought about a very fine result. The two Maurice Farmans which shared the honours of the Deauville meeting, as also the Breguets, Deperdussin, &c, were equipped with these floats. We understand that the Aircraft Co. are prepared, not only to supply floats on the Tellier-Fabre principle to construc tors, but also to issue licence to constructors of waterplanes, to build themselves. It may be noticed that M. FabTe has an early patent in the position of floats, for the use of which nearly all French constructors pay a small fee. This patent has also been acquired by the Aircraft Co. As it is recognized that Tellier floats stand up well to their work, if the results of M. Fabre's experiments can be obtained from the Aircraft Co. in exchange for a small fee, there is little doubt but that much trouble and expense may be saved to waterplane builders.
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