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possibility of flutter, whereas previously calcula tions with any combination of the binary systems had given stable results. Several remarkable Mosquito accidents during the last year of the war might be attributed to high-speed stalling of An Important Monograph Issued by The Aeronautical the wing resulting in violent pitching manoeuvres due to a sudden change of the downwash, which Research Council on How to Obtain the Maximum of induced loads far in excess of the design values. A number of other typical accidents to Stirlings, Information from the Examination of Wreckage Lancasters and Wellingtons are also discussed in the report. The Investigation of Aircraft Accidents Involving aircraft starts. Fractures caused by the final im The last chapters of the report give a review of Airframe Failure. Aeronautical Research Council pact have to be distinguished from those having accidents and the lessons and conclusions to be R. & M. No. 2300. By J. B. B. Owen and F. occurred in the air. Careful examination of the drawn. Poor detail design has already been Grinsted. (H.M. Stationery Office. 15s.) latter can indicate the direction of the forces mentioned as one of the principal categories of which have caused the failure, as in most tensile, Abstracts of the Reports and Memoranda of causes of accidents. Ranging from an oiling compressive, bending, transverse or torsional the Aeronautical Research Council are usually nipple which allows water to get in and freeze in loadings produce differently shaped fractures. A published on the pages specially reserved for the bearing to be lubricated to insufficient local number of photographs illustrate how these stability in structural components these causes 'Research Reports and Memoranda'. The Editor different fractures can be recognized in the prin emphasize the need for close attention to be paid feels that an exception should be made for this cipal structural materials. In many cases, however, to every detail of the aircraft design. Quite often report because of its importance not only to those additional laboratory tests will be necessary to a good aircraft has been spoilt by bad detail de directly associated with accident investigation, but clearly establish which kind of loading has caused sign and the reviewer wishes to impress on all to all concerned with aeronautical research and the failure. detail designers and draughtsmen the fact that the development. The results of the examination may indicate one quality of their work is vital to the success of the The very well written and amply illustrated or more primary failures to satisfy the evidence. aircraft and the safety of its occupants. report gives a survey of how wreckage may be re Consideration of the loads which might occur in constructed to indicate in which order the Flying qualities are listed second in the review a variety of flight conditions and consideration of different components have failed and where the of accident causes. Longitudinal stability has often the strength of the aircraft structure may be primary failure occurred. It describes a number been insufficient to prevent the aircraft from helpful in deciding which failure has in fact been of typical cases from the large number of war attaining dangerous speeds or attitudes once con the primary one. At this juncture one is im time accidents, studied at the Royal Aircraft trol has been lost in clouds, through lack of oxy pressed by the versatility required of the accident Establishment, indicating the defects of several gen or through other causes. In this connexion investigator. Although he can call upon the types of aircraft, how the causes of these defects one might ask whether the recent trend to accept a services of specialists for any specific questions have been established from accident investiga slight static instability if the manoeuvring margin that may arise he himself should have ample tions and which remedies have successfully been is positive, is acceptable from a safety point of knowledge of aerodynamics, flying qualities, aero- applied. view. Balancing of one aileron against its partner elasticity and aircraft structures in order to be able Upon reading this absorbing report one is im may in some instances give rise to trouble if the to put the different clues together and draw the pressed by the thoroughness with which the ailerons are not properly matched in production right conclusions. Also it becomes clear that he difficult task of investigating the large number flight tests. should not be of the type that jumps to a con of accidents has been performed and by the clusion; he has to have the patience to work out Flutter is still one of the main causes of struc lessons t o be learned from its results. The diversity tural failure in the air and although the introduc all possible solutions before deciding upon a of the causes indicates that in all different branches tion of stiffness criteria in recent airworthiness particular one. of the aeronautical sciences our knowledge is still requirements has contributed much towards the The large number of accidents which occurred far from complete and it emphasizes the need for elimination of flutter, much work remains to be during the war when thousands of aircraft were further research. Especially the subject of how to done on the prediction of flutter characteristics in service have provided valuable data for re predict the air loads resulting from various of more complicated systems. search. In peacetime the number of aircraft of a manoeuvres deserves further attention, as in many Accidents due to dynamic loadings indicate the single type is relatively small and happily only cases forces must have been generated which fall need for recording such loadings in flight in order seldom does a series of accidents occur pointing far beyond the limits of the design envelope. The to amplify the data upon which to base require to a defect particular to the aircraft type con relatively large number of accidents resulting ments in much the same way as has been done cerned. In wartime, however, this has been the from poor detail design makes one hope that by collecting v-g records as a basis for the flight case for nearly all successful types of aircraft used every designer and draughtsman in the aircraft envelope. in large numbers. Some typical cases have been industry reads this report and takes its lessons to described in the report. heart. In a paragraph dealing with the development of Perhaps the most intriguing of these is that of the accident investigation technique some sug After introducing the subject by describing a the Typhoon. Some twenty accidents occurred in gestions are made concerning possible ways in particular accident investigation and the reason which the rear end of the fuselage failed in the which to supplement the existing methods. The ing by which the cause has been established, the air. The absence of any satisfactory explanation of collecting of more data on the drag of pieces of method of investigation is treated in more detail. the early accidents initiated an extensive pro wreckage, for instance from dropping tests, can The field work consists of locating the wreckage, gramme of structural tests, wind tunnel tests, put the calculations of trajectories of parts de which sometimes is spread over many miles, and flight tests and flutter calculations. Several modi tached in the air on a more accurate basis. The collecting it after all details of the position, fications failed to remove the cause of these suggestion to collect data by telemetering from attitude and general condition of the wreckage accidents, which has not yet been precisely estab pilotless aircraft which are broken on purpose is parts have been recorded. lished, although the available evidence points an interesting one, particularly as it can eliminate The wreckage trail can give valuable informa towards either flutter or buffeting loads on the the greatest uncertainty in static tests, namely the tion on the order of disintegration. From the tail plane being responsible for the failures. estimation of the air loads on the distorted air different points along the trail where various parts Much valuable information of a more general frame. More information on how to detect have been located approximate trajectories can character has been collected during the above- whether fractures have been caused by loads be drawn, estimated from measurements of their mentioned tests, among other things on the be arising from flutter is another problem still to be weights and sizes. The intersections of these haviour of structures under repeated loads and solved. trajectories can indicate the height at which the on fuselage-tail plane flutter. aircraft broke and possibly help in establishing the The reference list contains a large number of order of failure. Mosquito accidents have been caused by unpublished reports on various accidents and Throughout the investigation painstaking atten elevator failures due to low torsional stiffness of related subjects. Although one regrets that some tion to details is essential but especially in this of these are not available—mentioning parti the fabric-covered elevators, undercarriage doors first phase of collecting the data care should be cularly the report on the calculation of trajectories becoming detached if not properly closed, and taken that even the tiniest bit of wreckage be of wreckage pieces—it is felt that the publishing wing failures. The latter have been caused by collected and examined. It is essential for the of such a large number of reports, dealing with high positive accelerations in flight manoeuvres, success of the investigation that the wreckage is particular accidents, would be too much of a mostly during recovery from dives entered through left undisturbed until the party of investigators good thing. It is the more appreciated, however, loss of control in clouds. A form of g-restrictor has examined it. How often a smear of paint or a tab was developed, but during flight trials the that in such a comprehensive and yet condensed small piece of fabric, which often constitutes the aircraft to which it was fitted broke up and dis report the principal features of this subject have keystone of an investigation, has been removed integrated extensively. Elevator flutter was estab been discussed to make us remember that—to by helpful but untrained fingers. quote from the concluding sentence of the report lished as the cause of this particular accident. —'a wise man learns from the folly of others, a Once the wreckage has been removed to a Special flutter calculations with three degrees of fool seldom by his own.' hangar or workshop the tedious work of putting freedom—tail plane vertical translation, elevator all pieces together and trying to 'reconstruct' the rotation and tab rotation—have confirmed the L. H. Aircraft Engineering
Aircraft Engineering and Aerospace Technology – Emerald Publishing
Published: May 1, 1950
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