From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Report from Joseph Lucas Ltd. on the examination and failure analysis of a returned pair of defective WT13 horns.
| Identifier | ExFiles\Box 166\9\ img195 | |
| Date | 10th March 1939 | |
| C O P Y. JOSEPH LUCAS, LTD. ENGINEERING & DESIGNS DEPARTMENT. Date. 10th.March,1939. Ref. O/7/12. Note No. 8239. DEFECTIVE SERVICE APPARATUS. 1 - Pair of WT13 Horns returned from Messrs.Rolls Royce, Ref: Their letters 9th. & 13th.February, Note No: N.97. These horns, which are some of the original WT13 'Engineering Samples', were supplied either in August or November,1937. Messrs.Rolls Royce's letter of 9th.February states that they were removed from experimental Bentley No.7.B.V. on account of the occasional failure to blow of the low note horn. This was particularly noticeable in cold weather. The horns were examined carefully in the condition in which they were received. The low note horn functioned reasonably well under all conditions, although it was obvious that it had had good use and would be improved somewhat by contact adjustment, but the high note horn was intermittent and required only a very little change of conditions to cease working altogether. It was found that the contacts on this horn were just on the point of open circuit. The contacts were very badly and abnormally burnt and this led to the early failure. The cause for the rapid burning was as follows:- The contact resistance was burned out due to the resistance card having been pushed down so that the resistance wire touched the base. This would cause a temporary short circuit or heavy discharge until the resistance wire burned out. An accident like this, might have happened in replacing the cover at some time. With the contact resistance open circuited, the contact arcing was very severe and caused the rapid wear. It was possible, however to get good note from the horn temporarily simply by contact adjustment. | ||