FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1913
1913 - 0063.PDF
While the presence of a fin can lie shown to confer the power of automatic recovery of balance in still air, it is apparent that the tin itself is a target for a gust of real wind. If, therefore, while flying the relative wind veers or backs there will be a greater force causing the machine to cant. Again, bearing in mind the significance of compass directional stability on the power of recovery of balance, it is apparent that on a machine with a tendency to weathercock directional stability, the pilot may have to rudder outwards in order to avoid a spin that otherwise might culminate in a nose dive. Ruddering inwards when overbanked, appears to me to be in any circumstances, a serious error in control. Ruddering out wards and increasing the angle of the lower wing by the warp appears to me to be the proper combination for enhancing the quickness of recovery on modern machines. Other considerations in practical flight that I have not taken into account, may, perhaps, vitiate this argument, which is, of course, presented with all deference to the judgment of pilots. Thus, the argument proceeds in a circle around the fundamental instability of the positive wing tips. Wings with positive tips are laterally stable if spin is prevented. Fore and aft fins will prevent the system spinning in a calm, but they will neither prevent nor neutralise the relative spin of a veering wind. Wings with positive tips are thus necessarily liable to be canted, but they may equally have the power of recovering their balance. Even this, however, still leaves them with the funda mental objection of being unsuited for steering purposes. In the apparent fact that a gust is a phenomenon of very brief duration in itself, lies, I think, the essence of the quick recovery of a well-designed modern machine, which is another reason why the problem seems to me to be wrapped up in the steering control. The characteristics of different positive wing tip systems might, owing to the variety of fin combinations tint is possible, be expected to show marked differences of behaviour in the air. There is, for example, the relative steadiness and the damping effect of the wings to be considered : the more lightly loaded and faster machines being potentially the steadier in their flight. Again, those in which compass directional stability has been made a predominant feature of design by the use of up-turned wing tips to project a forward tin, would be likely to slide bodily side ways at slow speeds in windy weither, and to roll with a slow period as compared with machines that have a higher fin not so far forward of the e.g. as with dihedral wings. Vet another important factor is the influence of automatic warping, some wings being so constructed that thty tend to warp auto matically in very windy weather and thus conceivably may " spill" the gust. This may be provided for with wings that have in them selves a rigid construction ; there are, however, also examples of machines having flexible wings that would presumably act in a similar manner. According to individual tastes so I imagine could a machine be designed with characieristics to suit. But, so far as I can see, it is impossible for it to possess absolute lateral stability under the practical conditions of flight unless it has negative wing lips. (To be continued.) ® ® ® ® THE COLLAPSE By L, IN his article in last week's FLIGHT, Mr. Griffith Brewer draws attention to conditions lhat he believes may be a source of danger to monoplanes, and asks that his remarks should be discussed. As I differ from his conclusion?, I will, therefore, set out the contrary argument. In the first place, as Mr. Griffith Brewer referred to Bleriot wings in his article, I will refer to Eiffel's aile No. 13 bis:— " Without changing the path of flight of the machine the speed of tiavel may increase, and this causes the centre of pressure to travel backwards, thus tending to turn the wings over forwards, &c. &c." Firstly, without changing the attitude of the machine to its flight path, it is impossible to increase the speed. A pilot on a machine properly equipped with instruments, can see on his instruments both the air speed of his machine and its attitude to the horizon. He can cause the machine to fly within the limits considered safe by the designer. In Eiffel, the exact position of the c.p. of the plane for all angles is clearly set out, hence by simple arithmetic it is possible to discover the correct position and strength of the rear spar and main spar. Hence, why should there be any tendency to twist the plane ? It is customary to brace the rear spar as well as the main spar, and to allow for all movements of the c.p. In fact, it is not clear what is meant by this " twisting." If self warping is meant, it is as well to remember, when considering self warping, that as one plane decreases in angle the other plane increases in angle, and it is in no way caused by effective position of the c.p. of the machine as a whole. The angle of no lift ("critical angle" [sit]) for 13 bis is about — 3°, as the angle of the plane is altered either positive or negative from this angle there is no sadden increase of lift (or depression) as the increase of lift curve in this region is approximately a straight line. Hence there can be no " flip over " at this point. Further, it is possible and usual to brace an aeroplane with suitable materials and in such a manner that there is no slack in the bracing at any time. In his article Mr. Brewer says, " a quick downward angular movement of the ends of the wings takes place, the upper stays then receive the strain of the slack being taken up," &c. I ask, however, why have any slack in the upper bracing wires? It is surely a s:gn of careless fining. Again, if Mr. Griffith Brewer will take the trouble accurately to follow the flight path of a mono- OF MONOPLANE HOWARD-FLANDERS. WINGS. Aviation at Birmingham. OWING to the snowstorm which prevailed all day last Saturday, the proposed flight by Mr. Hamel on the Birmingham Aero Club's aerodrome had to be abandoned. The club, however, is by no means disheartened by this set back, but will erdeavour plane while performing this evolution and make a few accurate- calculations he will be unable to prove this mysterious top pressure. I do not attempt to disprove the possibility of top pressure, but it is obvious that top pressure cannot be produced by the cause men tioned. If Mr. Griffith Brewer wishes to make a practical experiment on the question of top pressure, let him try this simple experiment : Place a stone in the passenger's seat (or other spot on the aeroplane at or near the c.p.), then if the machine is flown in such a manner that top pressure occurs, the pilot will see the stone leaves the seat. Relative to the aeroplane, it will appear to be thrown upwards into the air, as when top pressure occurs the aeroplane will be falling faster than the stone. On the same argument, the pilot should wear a safety belt. Furthermore, a simple air-speed indicator may be fitted to the aeroplane showing the relative air velocity of the planes, this will soon give figures from which the position of the c.p. may be discovered. It will be found that the movement shown on the air speed indicator is not great even in considerable winds. I will now quote Mr. Griffith Brewer in respect to biplanes v. monoplanes: "The truss systems of the biplane structures make the wings equally strong in both directions, so that this collapse danger is entirely absent." If Mr. Griffith Brewer will inspect the wings of several famous makes of biplanes in which the wings are warped, he will find that the angle of the bracing to the rear spar is worse than in many monoplanes. Further, it is usual when designing monoplanes to calculate the stres-es for all po.-itions of the c.p., taking the maximum possible lift at the various angles, also to make due provision for top pressure. Further, considering the much-vaunted superiority of the biplane as regards stresses. If steps be taken to design a monoplane and a biplane of equal weight, speed, gliding angle, and efficiency, it will be found in fast, efficient machines having a fine gliding angle, that the sum of the stresses in top and bottom spars of the biplane are at least as high as \ of the stress in the spar of the monoplane. It is preferable when using timber for construction to employ one large piece of wood instead of two smaller pieces. This is due to drying out and becoming short. Moreover, two spars do not increase the saiety, as the failure of either one of them is as bad as the failure of the single monoplane spar. Furthermote the low loading usually employed on a biplane allows of much greater overloads, and hence necessitates a considerably higher factor of safety. ® ® ® ® 63 in the near future to arrange for a series of exhibitions by Mr. Hamel extended over three or more weeks. In the meantime there will be plenty of interest on the aerodrome at Billesley with the experiments of the full-sized glider and the construction of a full-sized aeroplane which will shortly be started.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
