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Aviation History
1953
1953 - 0233.PDF
FLIGHT, 20 February 1953 231 Discussing Helicopter Maintenance Further Opinions at the Helicopter Association Meeting THREE of the main papers given before the Helicopter Association on Saturday, February 7th, at the Royal Aero nautical Society were summarized in last week's issue of Flight. Mr. A. McClements, A.R.T.C, M.I.Mech.E., of the Ministry of Supply, spoke on the general background of main tenance; Mr. J. H. Spaull, of the Air Registration Board, described the licensing procedure for helicopter maintenance engineers; and Mr. H. E. le Sueur, A.F.R.Ae.S., also of the A.R.B., con sidered helicopter airworthiness requirements. The practical aspects of the maintenance of helicopters was the subject of a paper by Mr. W. L. Shippey, a maintenance engineer of the B.E.A. Helicopter Unit, and a summarized account of this contribution, and of the remaining discussion, follows. The lecturer opened his remarks by pointing out that a helicopter engineer must obtain both his A and C licences from one examination. It was known that every helicopter power plant, although of a standard basic design, was specially modified for its job; and this point, together with the fact that the helicopter's transmission system was so akin to engine practice, made it most desirable, even essential, that the engineer signing his Certificate of Safety for Flight certified the engine as well. After commenting on specific points from the licensing syllabus, Mr. Shippey suggested that lubrication—a vitally important part of helicopter maintenance—should perhaps be included. The maintenance system as practised by the B.E.A. Helicopter Unit did not differ basically from those in use by the two Corporations and the charter companies. A progressive system of checks was carried out in the cycles of flying time laid down in a master schedule and approved by the A.R.B. During the Liverpool-Cardiff operations with S-51 heli copters operating on the 5-25-100 hr cycles, the following schedule was adopted: Check 1, at 5 hr (daily); check 2, at 25 hr; check 3, at 100 hr; check 4, at 200 hr; and check 5, at 400 hr. Checks 1, 2 and 3 were purely maintenance inspections of the complete airframe, engine and ancillaries, whereas checks 4 and 5 were component- changes. There were further checks at multiples of 400 hr for such items as fuel tanks and undercarriages; also, the engine had an overhaul-life of 700 hr. Broadly speaking, every component was changed once or more times during each 1,200-hr period. Reverting to the progressive portion of the maintenance schedule, i.e. checks 1, 2 and 3, it would be remembered that at each check 1 there was carried out part of check 2 and part of check 3, so that at the end of every 25 hr of flying, the check 2 cycle had been completed, and like wise at the end of every 100 hr, the check 3 cycle. Whilst this method had the disadvantage of using up more man-hours on actual maintenance, it had been found possible to utili2e the aircraft continuously, thus obviat ing the need to withdraw it from service for periods of from one to three days to carry out the 25- and 100-hr inspections. For future operations, however, especially where an operator was employing much larger fleets of aircraft on high-intensity services, it was doubtful if there would be any advantage at all in the progressive system. The maintenance system in the B.E.A. Helicopter Unit had been slightly modified some six months ago, continued the speaker. Pre viously, all maintenance work had been inspected by full-time licensed inspectors, although this was not strictly necessary under the terms of the Corporation's inspection approval. Now, however, licensed engineers were employed to carry out the actual operations, to supervise unlicensed personnel, and to sign for their own work—a much more efficient method. Oveihaul work contained anomalies, however. Although this work required an equal or a higher degree of skill, it could be certified by a virtually unqualified inspector (there being no helicopter "B" or "D" licence), while the licensed engineer could not certify anything that was not strictly included in the terms of his "A" and "C" licence. Something like a Board of Trade certificate, to replace the "B" licence and to serve as an inspector's qualification, was the speaker's suggestion. Speaking of defect diagnosis, or "trouble-shooting," Mr. Shippey said that his material for this part of the lecture had been accumulated over a period of seven years of operation and maintenance of five types cf helLopter, i.e. R.4, R.6, Bell 47-B3 and Bristol 171 on experimental flying, and that old faithful the S-51. The helicopter as such had proved amazingly reliable; the majority of faults had occurred in ancillary equipment, such as electrics, instruments, radio, etc., and could occur in any aeroplane. Vibration had proved one of the chief sources of worry to helicopter engineers and operators. The main concern of the maintenance engineer was to be able to form a rapid and accurate opinion as to the seriousness of the trouble. It was here that the pilot, in making his report, could provide valuable help by giving a concise and accurate description of the symptoms. There was no hard-and-fast set of rules, however, which could be applied in all cases, and past experience had shown that it was only by a sometimes tedious process of trial and elimination that the faulty part could be brought to account. Even then there had been cases where a perfectly serviceable rotor head or set of blades had given continual trouble on one aircraft and had been quite acceptable on another. Other causes of roughness on the S-51 had been faulty tracking, backlash in controls, or brinnelled bearings. These invariably showed up as "stick- stirring" and were more or less obvious. They could usually be detected by test flying or close visual inspection. The Bell 47-B3 had been, in general, less problematical than the S-51. There had been only one instance of roughness in the Bristol 171, and Maintenance on a B.E.A. Sikorsky S-51 at Gatwick. Mr. Shippey, of the Corporation's Helicopter Unit, spoke on such work from the ground engineer's viewpoint at the recent Helicopter Association meeting. that had been cured by tracking the blades. Indeed, one of the most out standing qualities of this aircraft was its remarkable smoothness—piob- ably due to the greater flexibility of the rotors and its higher rotor r.p.m. The number of snags encountered in gearboxes, clutches, fans, drive- shafts and couplings had been conspicuous by their absence. This applied to all the Corporation's helicopters. It had been necessary to contend with no moie, and no less, than the normal number of engine snags. Most of the other troubles encountered had recurred in spells, and in some cases had been obviated by modification action. Many man-hours had been used up in the rectification of cabin heaters and rotor brakes, both weak points on the S-51. These faults would not ground a machine or cancel a service, however, and engineers were entitled to use their own discretion in the event of a last-minute failure of this nature. There was sometimes a tendency, in the interests of speed, for main tenance engineers to remove complete components for replacement in the event of trouble. Closer investigation could in many cases reveal that the fault lay in some very small part of the component or perhaps in the need for slight adjustment. It was stressed, therefore, that to avoid cases of engineers having cured the trouble without knowing the cause, all information from investigations should be made available to maintenance personnel. It was conclusive that the overhaul-life of some of the less important components could be extended and in some cases doubled with beneficial results. The lecturer concluded by quoting a recent case of an aircraft being grounded for a fortnight because two replacement auxiliary fuel- pumps both leaked, whereas the one that had been removed, time- expired, was functioning perfecdy. The Open Discussion "FOLLOWING the reading of the four main papers, and a break -T for*tea in Londonderry House, the chairman, Mr. J. Shapiro, Dipl.Ing., A.F.R.Ae.S., invited general discussion on what had been said. The first speaker was MR. B. S. SHENSTONE, M.A.SC, F.R.Ae.S., A.F.I.Ae.S., chief engineer, British European Airways, who questioned the wisdom of the main speakers' modesty in strenuously denying that their views were those of the bodies they represented. The engineers could reduce unnecessary aircraft time on the ground, he continued, by making the machines available at the right time of day—or by making the tiaffic staff use them whatever the time of day. While the worth of the unlicensed expert in particular cases should not be underestimated, it was a fact that many of B.E.A.'s helicopter inspectors did possess licences. MR. W. TYE, O.B.E., B.Sc, F.R.Ae.S., of the A.R.B. expressed the (personal) view that, in helicopters, there were "just too many things that whizz round and waggle," and that this resulted in their being more prone to failure than things which stayed relatively still. The degree of reli ability must be improved, he continued, for even with well-tried aircraft engines, catastrophic failures still occurred. Admittedly, these remarks applied mainly to the design staffs, but licensed engineers, nevertheless, had an important responsibility to eliminate serious defects. The importance of the Navy as a source of potential civil maintenance engineers was stressed by CDR. R. H. WEBBER, R.N., of R.N. Air Station
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