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Aviation History
1959
1959 - 0855.PDF
420 FLIGHT POWER AND FREQUENCY Some Fresh Thoughts About the Comet 4 By J. M. RAMSDEN IN retrospect, 70-odd hours spent in a B.O.A.C. Comet 4 flying28,000 miles down B.O.A.C.'s eastern routes and back* leavetwo outstanding impressions. These can be summed up in the words power and frequency.Many other impressions crowd and jumble the memory. The passenger-address system was unintelligible to most passengers.The air conditioning was good, but temperature distribution was uneven: the floor grilles would be cool when the recirculationducts in the cabin ceiling were warm. The inboard engine blow-off valves, in use during the last half-hour or so of eachflight, were noisy. These relatively small matters of engineering, all of them to do with passenger well-being, need—and are in factgetting—attention, because the Comet 4 is an airliner whose passengers expect (and with these exceptions get) a superlativelyhigh standard of comfort. With power and frequency most passengers are less consciouslyconcerned. The power is certainly felt, and the take-off and climb-away are exhilaratingly unlike anything that new Comet 4travellers have experienced before. In what other airliner can you look down from 1,000ft on the terminal building you left a fewminutes ago—before you have passed the end of the runway? We did this at Rangoon and at Manila and at other places on dayswhen temperatures were up in the eighties. How does an airliner impress a passenger with its frequency?It does not, of course—except inasmuch as the passenger probably wouldn't be sitting in it if frequency had been lacking. He goesby the most comfortable service which leaves (and gets him where he wants to go) at the time which suits him best. Any airliner isable to offer frequency, provided it is the right size for the available traffic. This is a nice matter of economic judgment, and there isno doubt whatsoever that the Comet 4 is the right size for most of B.O.A.C.'s routes, with the exception of the North Atlantic, forwhich a bigger airliner is desirable. The relationship of the Comet's medium size (60-80 seats) to thetraffic on the eastern routes was discussed in a previous article. Here, more fully to illustrate the points then made, are theincreased number of services per week which B.O.A.C. are plan- ning to offer through typical points: — Point London Frankfurt . ZurichRome Beirut KarachiRangoon . Bangkok Hongkong . Tokyo Present number of services per week 7 2 1 2 S 4 2 2 5 3 Planned number of Comet 4 services per week 10 3 3 3 9 5 3 3 8 4 Thus is improved frequency of service being offered on routeswhich need it, virtually right from the start of B.O.A.C. Comet 4 operations on the eastern routes. Those points not listed retain,for the time being, existing frequencies. It is on this count—size—that the Comet 4 will undoubtedly *"Eastern Routes Jet," "Flight," February 6 and 13, 19S9. score over its biggest jet rivals, at least on routes other than theAtlantic. An aircraft of the same capacity as the type which it replaces can double frequency to handle double the traffic. Butan airliner which is double the capacity of existing types may actually have to reduce frequencies in order to achieve profitableloads. The day will come when the eastern routes, and others comparable, need airliners of 707 and DC-8 size. The day hasalready arrived when these routes need improved frequency of service, and the Comet 4 will be able to fulfil that need for sometime to come. It has been argued that the Comet 4, being roughly 50 m.p.h.slower in block speed than its larger American rivals, will put its operators at a disadvantage. The sanity of speed-competition forits own sake was well challenged by the remark of a young Indian B.O.A.C. traffic officer in Calcutta, who said: "No one ever rushesinto my office saying: 'I want to get to Tokyo as fast as possible.' He just wants a flight that gets there on a certain day at a certaintime . . ." In other words, the airliner that sells best to passengers is notonly the one with the power, but the one with the frequency- potential of medium size. Power is an asset which the Comet enjoys in a measure un-matched by any other airliner and, in particular, by any other jet airliner. Here are some typical thrust: weight ratios: — Aircraft Comet 4 Convair 880 Caravelle DC-8 Intercontinental 707-120 707-320 Engine RA.29/1 J79 RA.29/3 R.Co.12 J57(wet) J75 Max. thrust all engines (Ib) 42,000 44,800 23,400 72,000 52,000 62,000 Gross Weight (Ib) 158,000 184,500 99,000 310,000 247,000 295,000 Ratio 0.266 0.242 0.236 0.232 0.210 0.210 For cruising, the Comet 4 can use up to the Rolls-Royce"maximum recommended" figure of 7,350 r.p.m. In practice this figure is rarely used; even on the eastern routes 7,350 r.p.m. is notrequired except in the hottest conditions—i.e., I.S.A. +24 deg C and above. This means (1) that the Avon RA.29 spends a large proportionof its life running relatively relaxed, which probably helps to explain—as we have noted before—the long strides in RA.29overhaul life; and (2) that the Comet 4 is virtually insensitive to temperature so far as flight-plan cruising-height selection is con-cerned. The Comet 4's ability to cruise along an optimum "profile" tends to be taken for granted; it is made possible by theComet's plentiful power. This was emphasized by a recent report in Avianon Week, which said of PanAm's 707-120: "If thetemperature at 33,000ft is —40 deg C . . . the jet can get only to 27,000ft after a full gross take-off . . ." Only if temperatureswere down to —50 deg C, added the report, could the aircraft start to cruise-climb at 33,000ft. Our experience of Comet 4 flight-planning along the easternroutes—where take-off temperatures average 15-20 deg C higher than those over the North Atlantic—was that the aircraft can takeoff at its maximum weight of 158,000 Ib and can then select any initial cruising height up to about 35,OOOft irrespective of tempera-ture, climb-cruising or step-climb-cruising from that height as fuel is burnt off. The importance of freedom of height-selection toa jet airliner needs no emphasis. It will be extremely interesting to see, in a few months' time,how the B.O.A.C. Comet 4 and the Qantas 707-120 match up on the eastern routes between the U.K. and the Far East andAustralia. Qantas hope to inaugurate services on these routes in September. Will Qantas' choice of 707-120 (an order which wasa controversial Australian political issue when it was placed) prove justified when the aircraft is matched against a jet of the Comet's"fillable" size and excellent temperature performance? All that can be said now is that the B.O.A.C. Comets have notbeen limited as regards runway length or cruising-height-selection on the North Atlantic route; nor—and this is the significant point—will they be limited in these respects in the hot atmosphere of the temperate/tropical routes to the East. The 707-120 will seethe Comet 4 off handsomely so far as seating capacity is concerned on both the North Atlantic and the eastern routes: but whether (Concluded on page 422) "In what other airliner can you look down from 1,000ft on the terminal V building you left a few minutes ago—before you have passed the end : of the runway?" The Comet 4 taking off at full weight f
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