FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1956
1956 - 0527.PDF
FLIGHT, 4 May 1956 527 IMPACT OF THE HEAVY JETS . . . it may not be severe enough. (This is where temperature"accountability" in the calculation of turbine aircraft perform- ance is brought in to settle all arguments.) Obviously, at someplaces in the hottest months it will be possible to schedule departures for the cooler hours of the night.Example: Runway paved length, 8,000ft. Elevation, 1,000ft: correc- tion factor = 1.07. Temperature, 25 deg C (i.e., 12 deg C above 13 deg Cstandard at 1,000ft): correction factor= 1.12. Combined correction fac- tor= 1.07 x 1.12 = 1.20. Assuming DC-8 or 707 gross-weight take-offfield length at sea level and 15 deg C to be 9,000ft (see below), total approximate field length required is 9,000ft x 1.20= 10,800ft. Thusadditional length needed is 10,800- 8,000ft = 2,800ft. Clearly this method of determining a runway correction isonly an approximation, and special studies have to be made for individual aircraft and airports if accuracy of the first order isrequired. Where the method produces a correction greater than about 35 per cent (e.g., Entebbe, Johannesburg, Mexico City,Nairobi, Sao Paulo) it becomes less accurate (i.e., too harsh); but for the purpose of this analysis, which seeks to provide a general ORDER BOOKS ' (Correct to April 30th, 1956) BOEING 707 Customer PanAm American Braniff ContinentalAir France ... Sabena T.W.A. Lufthansa No. 23 30 S 4 10 48 + 22 opt. 4 Model (6) 120 (17) 320120 120 120 320 320 120 320 Delivery date Dec, 1958, to Nov., 1959From March, 1959 From Oct., 1959 1959Nov., 1959, to Nov., 1960 From Dec, 1959 From April, 1959 Spring, 1960 Price $140m app. $135m $30m $21.3m$71 m $20m app. Total: 88 — 22 options. DOUGLAS DC-8 Customer PanAm United Notion QI K.L.M Eastern J.A.L S.A.SPanagra Swissair Delta No. 25 30 68+ 4 opt.18+ 8 opt. 4 7 4 2 6 Model J57 and J75 (15)J57 (IS) J/S J57J75 (6)J57 (12)J75 J75 J75 J75 J75 J57 Delivery date From Dec, 1959 From May, 1959 Midsummer, 1959 From March, 1960 May, 1959 March, 1960 1960 1960 Early 1960 Spring, 1960 June, 1959 Price $160m $175m $37m$50m Incl. opt. $165 $27m plus App. $50m$25m $16.4m App. $36m Total: 110 + 12 options. picture, the method has been regarded as appropriate for everyairport. It should be borne in mind that the lengthening figures calculated for some runways may be purely hypothetical,because of permanent local obstructions such as buildings or railways. Few runways are of less than 150ft width, which is assumedto be adequate for both aircraft, since they are not likely to be more critical than current aircraft in regard to ground-manoeuvr-ing, crosswind landings, or instrument approaches. The most up-to-date figures for the J75 -powered DC-8 and 707(intercontinental versions) gross weight and take-off are as fol- lows: DC-8, 287,500 lb and 8,760ft C.A.A. balanced fieldlength*; Boeing 707, 290,000 1b and 9,000ft B.F.L. There has been talk of diese weights being increased over the 300,000 lbmark, and it is possible that this might happen: certainly there are few if any aircraft whose design gross weight has not goneup in the course of development, either to improve payload- range, or just through the growth of structure weight. However,this possibility has been ignored in the present study, and a round figure of 9,000ft for the take-off field length of both air-craft in International Standard Atmosphere conditions, i.e., sea level and 15 deg C, has been assumed for full-weight operationfrom the main airports. The assumptions made in gauging the suitability of alternatesfrom the performance aspect are different, being based on the ability of these airports to take the two aircraft at their landingweights. The latter are taken to be 180,000 lb for each machine, giving a landing distance of the order of 6,000ft with reversethrust. A landing weight of 180,000 1b has been chosen because it is less than the maximum permissible landing weight (about200,000 lb for each aircraft) and more than the zero fuel weight (about 170,000 for each). The alternate's subsequent abilityto enable the aircraft to get out again is assumed not to be critical. *Accelerate-stop distance assuming engine-cut at critical point. The importance of suitable alternates cannot be overrated:without them safe and regular world-wide operations are doomed. Those chosen in this study are the best from the point of viewof length and strength. There is no hard-and-fast rule about the choice of an alternate diversion-airport: different airlines oftenprefer different alternates for the same main terminal, particularly in Europe and the U.S.A. where airports lie thick on the ground.In other parts of the world, of course—e.g., Hong Kong, Fiji— alternates are more critical, and some main airports have fewfrom which to choose. But the majority have what might be termed their "official alternates"—usually airports two or threehundred miles away, out of the same weather area. In picking the best likely diversibn airports for the DC-8 and 707 in thisstudy, many of these official alternates have been discarded on the score of length or strength in favour of others that are betterin these respects. Some of those rejected were considerably below requirements. Many of those substituted (where possible twofor each main airport) shape up poorly, but they are believed to be the best available. Some may be unfamiliar, others may notbe usable by operators for economic or other reasons; but when taken altogether they provide the general picture which is the aimof the present analysis. Distances from the respective main airports are given in each case. Their lengths have not beencorrected for elevation and temperature, since landing distance is rarely sensitive enough to engine reverse thrust to be takeninto account, but elevation and temperature data have been included for good measure. Some of the alternates picked are,of course, main airports in their own right. Runway length, however, is but half the problem. Ask mostairport authorities how their runways will measure up to the DC-8's and 707's runway requirements, and they will perhapsshrug and say that extension plans will be put in hand. Ask them how they will stand up to 290,000 lb gross weights, and they willprobably laugh. For very few airports were designed to with- stand such mighty loads, and beefing up to the requisite strengthwill in many instances involve pretty well the complete reinforcing of all runways, taxi-tracks and aprons.The full-page tables include the bearing strength of each air- port. The different forms in which this is presented is a measureof the vagueness that exists about pavement strengths. Most authorities supply a figure for "isolated single-wheel load," avalue which is relatively easily established by mechanical test; others quote the maximum gross weight acceptable; some justsay "DC-4" and leave it at that (where this is the case the appro- priate gross weight has been inserted). The more sophisticatedairports give a Load Classification Number, which is the most realistic index of all, since it is the basic design parameter, takinginto account weight, tyre pressure and undercarriage geometry, and incorporating single-wheel load. The L.C.N. system sets astandard to which both the runway engineer and the aircraft designer can work: without the system it is well-nigh impossiblefor either to take all the variables into account. The L.C.N. to which the Douglas and Boeing designers are working has notyet been published, but the geometry of each main undercarriage appears to be a conventional bogie (Douglas started off with aco-axial quad, later changing to tandem pairs) and an approxima- tion for equivalent isolated single-wheel load can be calculated.This impressive-sounding quantity is that which, at a given tyre pressure, produces the same effect on a pavement as the multiple-wheel load. Some measure of a four-wheel bogie's load-spreading ability Load spreader: One of the main bogies of the Boeing 707 prototype.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
