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Background for Designers

Background for Designers Aircraft Engineering THE MONTHLY SCIENTIFIC AND TECHNICAL ORGAN OF THE AERONAUTICAL ENGINEERING PROFESSION MARCH 1952 VOL XXIV No 277 shortly a report dealing with this matter in more detail in relation to what are known as 'aero-isoclinic' wings. HE pioneer work of WILBUR and ORVILLE WRIGHT in produc­ ing the first aeroplane to fly nearly fifty years ago has been A Well-Tried Method Tsplendidly perpetuated in the wonderful series of WILBUR It must not be taken that this experimenting with models in any WRIGHT MEMORIAL LECTURES (of which the fortieth will be read this way takes the place of full-scale structural tests, of the value and year) in England, and, in America, WRIGHT BROTHERS LECTURES. importance of which DR WALKER gives convincing statistical For the benefit, particularly, of our home readers we have long made evidence. A point of outstanding importance here, which he brings a practice of publishing the latter series in full, with the kind per­ out, is the support an analysis of the results gives to a widely followed mission and co-operation of the INSTITUTE OF THE AERONAUTICAL but hitherto perhaps unproved philosophy of design. This is that the SCIENCES, when they have been, as happens in alternate years, lightest structure for a given strength is likely to be produced when written by a British author, and consequently the fifteenth lecture— the designer deliberately takes chances at the calculation stage and by DR P. B. WALKER of Farnborough—appears in this issue. relies on full-scale structural strength tests to detect weaknesses. A New Technique The Philosophical Approach He starts with an account of the method of experimentally study­ Once the principle is accepted it becomes, in fact, fairly obvious that ing structural phenomena by resort to small-scale models con­ a lighter structure must inevitably result by adding a limited amount structed in xylonite. In the latest development of this work exact of extra weight only where failures under test have shown it to be replicas of the original structures to be tested are no longer made, necessary as compared with making the whole structure stronger owing to the well-known difficulty of reproducing to scale all the and therefore heavier to meet estimated load conditions. As the details, the lack of which may lead to an untrue 'picture'. Instead, author mentions, this philosophy of design is not new and has been therefore, a simplified version only of the original is produced in intuitively followed, but it lacked the support which he is able to which attention can be concentrated on a specific phenomenon give it in a striking and, so far as our knowledge goes, hitherto which it is desired to study. This has the advantage that deflexions unattempted manner. can be comparatively large and therefore not only measurable but In referring to the section of the lecture dealing with the large capable of visual observation. Furthermore, the method makes 'universal test frame' evolved at the R.A.E. we may perhaps be per­ it possible to explore trends in design as an early part of a general mitted to recall an article by M R A. W. HOTSON entitled 'Methods structural research. The author gives interesting examples of the of Strength-Testing Aeroplane Wings' which we published in April two types of investigation. 1946. The basic principles underlying the system were then consid­ ered and the development and detailed design of the well-known 'Temple' and 'Cathedral' test rigs described. A scale model is illus­ A Case in Point trated of what might be called a 'bigger and better' Cathedral which In the first, a xylonite model showed the reason for the puzzling it is now contemplated to instal at Farnborough. failure of a wing in the neighbourhood of the attachments of an engine. This was found to be due to flexibility in certain ribs, Total Immersion assumed for design purposes to be infinitely stiff, with the result that Coming to deal with the testing of pressure cabins the author it was found quite easy, to cure the trouble by local strengthening. dramatically demonstrates the terrifying possibilities of air-pressure In connexion with the longer-term investigation of general trends testing of a fuselage, which make it hardly surprising that it was three examples are given, all relating to swept back or delta wings. decided to use water instead. Owing to the light weight of the struc­ The first interestingly showed the fallacy of treating, for structural ture, and thin gauge of the material of which it is made, the static purposes, a swept back wing as merely a straight wing inclined back­ head is by no means to be ignored—as compared, for instance, with wards, by revealing the 'short cut' taken by the loads to the fuselage, its trifling incidence in the testing of pressure vessels—and the tech­ and proved that it is possible to estimate with reasonable accuracy nique has therefore been developed of immersing the whole structure the consequent increased load in the rear spar at the root. The second in a tank of water. example relates to the relative structural merits of aligning the main We have only room to comment on one more of the matters dealt ribs in the direction of the line of flight or perpendicular to the spars. with in the lecture. In connexion with fatigue the positive tightening of bolts is referred to as an important antidote to fatigue failures in Delta Ribs joints. Here again we hope to help those interested by publishing A third example of the type of investigation that can be made shortly a report on work carried out on this subject. Meanwhile, it cheaply and rapidly by the method shows that there is a slight advan­ may be remarked that it is one more example of those self-evident truths which only awaited discovery to be instantly accepted; in tage to be gained from supporting the trailing portion of a delta this case that two parts which are made in effect into a homogene­ wing by a fan-shaped arrangement of ribs taken from the root of the rear spar. We may perhaps mention that we are hoping to publish ous whole will not be subject to inter-vibration. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Aircraft Engineering and Aerospace Technology Emerald Publishing

Background for Designers

Aircraft Engineering and Aerospace Technology , Volume 24 (3): 1 – Mar 1, 1952

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Publisher
Emerald Publishing
Copyright
Copyright © Emerald Group Publishing Limited
ISSN
0002-2667
DOI
10.1108/eb032137
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Abstract

Aircraft Engineering THE MONTHLY SCIENTIFIC AND TECHNICAL ORGAN OF THE AERONAUTICAL ENGINEERING PROFESSION MARCH 1952 VOL XXIV No 277 shortly a report dealing with this matter in more detail in relation to what are known as 'aero-isoclinic' wings. HE pioneer work of WILBUR and ORVILLE WRIGHT in produc­ ing the first aeroplane to fly nearly fifty years ago has been A Well-Tried Method Tsplendidly perpetuated in the wonderful series of WILBUR It must not be taken that this experimenting with models in any WRIGHT MEMORIAL LECTURES (of which the fortieth will be read this way takes the place of full-scale structural tests, of the value and year) in England, and, in America, WRIGHT BROTHERS LECTURES. importance of which DR WALKER gives convincing statistical For the benefit, particularly, of our home readers we have long made evidence. A point of outstanding importance here, which he brings a practice of publishing the latter series in full, with the kind per­ out, is the support an analysis of the results gives to a widely followed mission and co-operation of the INSTITUTE OF THE AERONAUTICAL but hitherto perhaps unproved philosophy of design. This is that the SCIENCES, when they have been, as happens in alternate years, lightest structure for a given strength is likely to be produced when written by a British author, and consequently the fifteenth lecture— the designer deliberately takes chances at the calculation stage and by DR P. B. WALKER of Farnborough—appears in this issue. relies on full-scale structural strength tests to detect weaknesses. A New Technique The Philosophical Approach He starts with an account of the method of experimentally study­ Once the principle is accepted it becomes, in fact, fairly obvious that ing structural phenomena by resort to small-scale models con­ a lighter structure must inevitably result by adding a limited amount structed in xylonite. In the latest development of this work exact of extra weight only where failures under test have shown it to be replicas of the original structures to be tested are no longer made, necessary as compared with making the whole structure stronger owing to the well-known difficulty of reproducing to scale all the and therefore heavier to meet estimated load conditions. As the details, the lack of which may lead to an untrue 'picture'. Instead, author mentions, this philosophy of design is not new and has been therefore, a simplified version only of the original is produced in intuitively followed, but it lacked the support which he is able to which attention can be concentrated on a specific phenomenon give it in a striking and, so far as our knowledge goes, hitherto which it is desired to study. This has the advantage that deflexions unattempted manner. can be comparatively large and therefore not only measurable but In referring to the section of the lecture dealing with the large capable of visual observation. Furthermore, the method makes 'universal test frame' evolved at the R.A.E. we may perhaps be per­ it possible to explore trends in design as an early part of a general mitted to recall an article by M R A. W. HOTSON entitled 'Methods structural research. The author gives interesting examples of the of Strength-Testing Aeroplane Wings' which we published in April two types of investigation. 1946. The basic principles underlying the system were then consid­ ered and the development and detailed design of the well-known 'Temple' and 'Cathedral' test rigs described. A scale model is illus­ A Case in Point trated of what might be called a 'bigger and better' Cathedral which In the first, a xylonite model showed the reason for the puzzling it is now contemplated to instal at Farnborough. failure of a wing in the neighbourhood of the attachments of an engine. This was found to be due to flexibility in certain ribs, Total Immersion assumed for design purposes to be infinitely stiff, with the result that Coming to deal with the testing of pressure cabins the author it was found quite easy, to cure the trouble by local strengthening. dramatically demonstrates the terrifying possibilities of air-pressure In connexion with the longer-term investigation of general trends testing of a fuselage, which make it hardly surprising that it was three examples are given, all relating to swept back or delta wings. decided to use water instead. Owing to the light weight of the struc­ The first interestingly showed the fallacy of treating, for structural ture, and thin gauge of the material of which it is made, the static purposes, a swept back wing as merely a straight wing inclined back­ head is by no means to be ignored—as compared, for instance, with wards, by revealing the 'short cut' taken by the loads to the fuselage, its trifling incidence in the testing of pressure vessels—and the tech­ and proved that it is possible to estimate with reasonable accuracy nique has therefore been developed of immersing the whole structure the consequent increased load in the rear spar at the root. The second in a tank of water. example relates to the relative structural merits of aligning the main We have only room to comment on one more of the matters dealt ribs in the direction of the line of flight or perpendicular to the spars. with in the lecture. In connexion with fatigue the positive tightening of bolts is referred to as an important antidote to fatigue failures in Delta Ribs joints. Here again we hope to help those interested by publishing A third example of the type of investigation that can be made shortly a report on work carried out on this subject. Meanwhile, it cheaply and rapidly by the method shows that there is a slight advan­ may be remarked that it is one more example of those self-evident truths which only awaited discovery to be instantly accepted; in tage to be gained from supporting the trailing portion of a delta this case that two parts which are made in effect into a homogene­ wing by a fan-shaped arrangement of ribs taken from the root of the rear spar. We may perhaps mention that we are hoping to publish ous whole will not be subject to inter-vibration.

Journal

Aircraft Engineering and Aerospace TechnologyEmerald Publishing

Published: Mar 1, 1952

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