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Aviation History
1950
1950 - 1983.PDF
458 FLIGHT, 23 November^ 1950 \ V t Helicopter Reliability Maintenance at \ Man-hour per Flying Hour Claimed for Hiller 360 The 1950 Hiller helicopter for agricultural duties, showing the new cylindrical tanks capable of holding over 80 gallons of fluid. AREPORT recently issued on the maintenancerequirements of the Hiller 360 light helicopter con-tains some interesting figures based on the accumu- lation of facts from a wide variety of Hiller operators. It is pointed out that, in the compilation of the report, there was a wide variation in the man-hours required for mainten- ance operations, this being a function of the varying experi- ence of mechanics, auxiliary maintenance equipment avail- able, and " progressive " maintenance undertaken. In deriving operating costs, an average of 0.66 man-hours per flying hour was used, but subsequent improvements to the serviceability of the Hiller 360 tend to indicate that this figure is high, and that the average will be closer to 0.5 man-hour maintenance per flying hour. On this basis, the operation of a single helicopter in most circumstances will not warrant the employment of a full-time mechanic and, in fact, one would be needed only for relatively high utilization figures involving two or three Type 360 helicopters. The present standard of manpower requirements is as follows: — Man-hours Type of check Aircraft Engine Total 25-hour 2 3 S 100-hour 16 12 28 00-hour 6 »24 40 SOO-hour 4 f32 56 * Includes top overhaul of engine. t Includes engine exchange for major overhaul and transmission inspection. Most of the operations undertaken at the 25-hour checks need not be handled at one time, and it has been found practicable to operate the helicopter normally and under- take the operation of such a check during non-flying time on two or three consecutive days. Further analysis of the various checks required for different annual utilizations indicate that the maintenance day requirements can be tabulated as follows: — Days required for : •25-hour |AII other Max days Hours flown per year checks checks required 400 hours 6 4± 104 500 hours 7£ 5± 13 600 hours 9 j\ I6j 700 hours ... IOi 8$ 19 800 hours 12 9J 211 900 hours I3£ II 24^ 1,000 hours 5 12 27 * Only required if Hiller 360 operation is such that no time is available during day for checks ; this occurs rarely. t Minimum " out-of-service " time for 100, 300- and 600-hour checks. It is significant that for 1,000 hours'operation per year, the aircraft would be unavailable for service on an average of only one day per month, provided that the 25-hour checks could be handled in the manner suggested. In actual practice, it is claimed, there have been numerous occasions when these helicopters have operated for months on end without undergoing any maintenance other than occasional checks by the pilot. At the end of these 100- and 200-hour operational periods, the most careful inspection has indicated that no significant problems are likely to be encountered. The study of maintenance materials was handled in a somewhat different manner from that outlined for mainten- ance man-hours, and lists were compiled covering every item which could possibly have to be replaced at the end of certain operating periods. The figures are thus conserva- tive in that they embrace the maximum possible replace- ments rather than those indicated by experience. All estimates on the engine include the assumption that an engine exchange will be effected at the end of 600 hours' operation. For such cases, where the engine overhaul is handled by the operator's personnel, it has been found that the material costs average $250 (£89), and that the labour requirement is 120 man-hours. This figure has to be com- pared with the allowance of $1.25 (9s) per flying hour, or the $750 (£268) for engine exchange at the end of 600 hours. The costs of engine parts for other operations are respec- tively $12.16 (£4 7s) at 100 hours and $54.32 (£14 10s) at 300 hours. In addition to the above amounts, an allowance of $0.20 (Is 6d) per hour is made to cover those small items which have to be replaced occasionally in between major overhaul periods. Averaging out the above figures, it would appear that an allowance of 3s per operating hour is ample to pro- vide a reserve to purchase all engine parts and supplies which could be required, with the exception of those in- volved in major overhauls. The helicopter itself has the following parts costs: — 100-hour check J3.I8 (£1 2s. 9d.). 300-hour check $70.17 (£25 Is. 3d.). 1865.37 (£309 2s. 2d.).600-hour check 1,200-hour check $1,165.77 (£416 7s. 2d.). Again averaging these figures for the annual operation of the Hiller 360, and adding $0.20 (Is 6d) per hour to cover such items as grease, safety wire and so forth, it would appear that a figure of $1.68 (12s) per operating hour should amply cover every possible maintenance-part requirement. In this country Pest Control, Ltd., who are very interested in the Hiller, now own three examples. Two were shipped from America, and as soon as they had been inspected at Hum were despatched to the Sudan (by Hunting Air Travel). The third is being assembled at Cambridge under A.R.B. observation. The two despatched to the Sudan had sprayed their first 6,000 acres within a week of arrival and, their work completed, they are expected home next month. The United Kingdom agent for the Hiller Heli- copters Inc. of America is C. Colin Cooper, c/o The Heli- copter Association, Londonderry House, 19, Park Lane, London, W.I.
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