FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1915
1915 - 0363.PDF
MAY 21, 1915- QfOsS weights and powers. In order to simplify the equations and minimise the possibility of error, it is necessary to make simple assumptions and work up to the more complex relations. Despite the fact that the assumptions made by Bryan reduce the problem to as simple a form as is compatible with usefulness, it may at once be seen, by a study of the mathematical work, that it is beyond the scope of the laymen and, indeed, of many engineers. Not only this, but the experimental work required to make practical use of the equations has entailed very heavy work and involved the expenditure of thousands of pounds at the National Physical Laboratory and elsewhere. Nevertheless, the importance of the results obtained, when realised, makes us wonder, not that so much time and money should be used up on filling paper with symbols, but that much more time and much more money has not hitherto been available for work which has, it is to be hoped, been brought home to all, by the aerial happenings in the present war, as of national importance. It can be safely said that the future of England depends very largely on the efficiency of her aerial fleet. One of the main objects of the paper now being considered is to ascertain the conditions which render it easiest to steer an aeroplane in a horizontal circle of any radius that is not too small, and Pro fessor Bryan has introduced the idea of "inherent controllability" to denote the property which an aeroplane may possess of freely describing a circular path without any pressure on the controlling rudders, i.e., an aeroplane in which, when turning on a chosen path, the rudders are not in action except as guides to prevent the machine from leaving that path. He finds that aeroplanes approach ing this ideal can be obtained by several designs, but he makes quite clear that he has not investigated the question as to how far it is desirable on other grounds to follow these designs in actual prac tice. These investigations he must, owing to lack of time, at which restraint he rightly girds, perforce leave to others. He appeals for mathematicians to sharpen their wits on aeroplane problems in preference to the more esoteric exercises in which they so often delight. He says :—" I cannot help thinking that a study of the present work, followed by a few experiments, will either lead to improve ments in the steering of aeroplanes, or if the present arrangements are the best, it will now be easier to understand the reason why." For the benefit of the uninitiated, it may be said at once that the National Aeronautical Services are fully aware of the value of Bryan's methods and are making use of them. At the same time private enterprise could find a rich field for accomplishment in study and experiment on the lines advocated by Bryan. The detailed summary of conclusions are given below, but it is of very great interest to note that one form of " inherently con trollable " aeroplane would have wings shaped somewhat like a gull's when circling, i.e., bent down at the tips, which are pointed. Another form would have bent-up wings that were wider at the tips than at the base. This latter form is of much interest owing to the fact that a bird which performs the most alarming twists and turns with the utmost nonchalance is the peewit, which has wings which are distinctly " spatulate " in plan form. This aerial gymnast may be watched at his feats at the present time in our fields. An interesting point to note is that the Germans have not failed to recognise the importance of studying aeroplane stability on the lines that Bryan has envolved, and this fact has in reality acted to their disadvantage in the present war. Owing to their national characteristics of methodical thoroughness they have given most of their aeroplanes great stability at a sacrifice of speed, while ours have been, generally speaking, less stable but more speedy. Now, in the evolution of the perfect aeroplane for which we are all striving, it has been found that too great stability is undesirable, not only because it slows the machine, but because it opposes " control lability "—the ideal dealt with in the present lecture. The perfect aeroplane will contain the best compromise between absolute stability and controllability, and we may hope that our national characteristic of common sense will lead us nearest to that goal. In the quest, work such as that of Bryan in the Wilbur Wright Lecture, IO^S, is of the highest importance. Summary and Conclusions. 1. In steady motion in a horizontal circle, both the longitudinal and the lateral equations of equilibrium are affected. 2. The turning point may be in front of or behind the centre of gravity, its distance when in front being denoted here by b. ® ® Gramophones Wanted for the R.F.C. . IN connection with the excellent work which is being done toy the Royal Flying Corps Aid Committee, Lady Henderson, the president of the Fund, would be very grateful for «°5 °r two gramo- —-£-. ~~~, -pyfes'sor Bryan 'and the late Mr. E. T. Busk, Phones and some records for the -enofjtheuRoyamy.ngf Corpsjt ^^^^J^^.G^JK. M. Ruck, C.B, (Chairman of The axis o, the aeroplane then envelopes a circle of a certain radius a, the real radius of the circle described lieing y'ia1 + P). The system usually cants over sideways through a certain angle «». 3. Given the velocity and radius of the circle it is not usually possible to satisfy the three equations of lateral equilibrium by assigning suitable values to b and <p, but when this is possible the system is said to be inherently controllable. In an inherently controllable system the rudder planes merely act as guides, and it is necessary that they should be so placed as to render the motion laterally stable. In other cases steady motion can only be maintained by pressure exerted by the rudders or a couple applied by means of ailerons or some such action representing the third unknown variable required for the solution of the three simultaneous equations of lateral equilibrium. 4. In a system of straight planes sin <p is proportional to the radius a of the envelope, but it also appears that the other conditions of lateral equilibrium are only possible when pressure is applied by means of a rudder and when a and $ have certain definite values. The only way of varying the radius of the circle actually described is by varying the position of the turning point which may be in front of or behind the centre of gravity. The addition of txixed in ends or vertical partitions improves the steering, but it still leaves sin <f> proportional to a. The inference one would naturally derive from the formula- is that all such systems, would be liable to sway from side to side of the straight path in curved arcs of finite radius. In no case can the radius of the circular envelope exceed the limit corresponding to <p — 90". 5. With bent up wings, as in the " Antoinette type," it is possible to satisfy the conditions of equilibrium so that a is no longer limited and <p no longer large. Such a system can lie steered in a circle of large radius without being inclined at a large angle. In general circular motion can only be maintained when pressure is applied by means of a rudder or a couple applied by means of ailerons, but if the two principal moments of inertia about axes perpendicular to the line of flight are equal, the rudder exerts no pressure and the system is inherently controllable, the inclination satisfying the relation IP = xa tan <p. 6. Another kind of " inherent controllability " in which the system always remains level, the inclination q> being ttto, is possible in certain systems. A necessary condition is that the wings should be bent downwards and not upwards at the tips, and it will be usually advantageous that they should be most bent down at their extremities. The condition representing this fact is that the space between the wings and a chord joining their tips should be as large as possible. This arrangement of the wings somewhat reproduces the action of gulls' wings in circling flight, and it will be found that differences in the form and curvature of the wings may have a considerable influence in the problems of this class. 7. A third kind of "inherent controllability" is only possible when portions of the wing surface are in front of or behind the rest; and a possible solution exists in the form of a system suggested by me in the Aeronautical Journal with front and rear planes, one set being turned upwards and the other downwards. It appears, however, from the analysis that the necessary condi tions cannot be satisfied in the case of surfaces of uniform breadth bent up into a plane dihedral angle at the centre or bent into a trihedral angle at some points intermediate between the centre and tips. They can, however, be readily satisfied by suitably curving the wings or by varying their shape so as to make them as a rule broader towards the tips than near the base. The present arrange ment has the further advantage that the system would not tend to turn round sideways if struck by a side gust of wind, and I should consider it worth trying experimentally. 8. Although no attempt has been made to discuss the analytical conditions of inherent stability further than has been done in " Stability in Aviation," it appears from general considerations that the rudder plane at least in an inherently controllable system should be placed on the opposite side of the centre of gravity to the turning point, and that difficulties, probably instability, must necessarily occur if the rudder is between the centre of gravity and the turning point. It seems almost certain that the best position for the rudder is when it and the turning point are in the relative positions of the centres of suspension and oscillations of the system when treated as a compound pendulum. ® ® Presentation of Aeronautical Society's Medals. PREVIOUS to the reading of the third Wilbur Wright Memorial Lecture by Professor G. H. Bryan at the meeting of the Aero nautical Society yesterday (Thursday), the Gold Medals of the the Front. They should be sent to Lady Henderson at the Head quarters of the Fund, Surrey House, Marble Arch, W. Council), to Prof. Bryan and to Mrs. Busk (on behalf of her son). 363
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
