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Aviation History
1950
1950 - 1132.PDF
712 FLIGHT JET-TRANSPORT CONFERENCE the aircraft out to where they can start up without throw-ing kerosene. Tow-trucks are best when designed for the individual aircraft. Designing one to be used by all typesis difficult. There are differences in starting methods, some startingon the aircraft battery, some using individual electric start- ing from outside points. An advantage of the tow-truckwas the fact that it had normally enough power for starting and for heat and other services on the ground. Trucksmight cost as much as $30,000, but they might eliminate much weight otherwise carried on board the aircraft. Start-ing noises might also make starting remote from apron desirable: fixed power lines at the parking apron to givestarting power have bten considered as an answer. BOEINGand U.S.A.F. agreed that noise was considerable—a scream in front and a roar behind. AVRO and others, however,disagreed. Turboprop manufacturers said their engines were quieter than pistons in starting and running-up. What flexibility is possible in flight planning and what is theeffect on range and payload of the following factors :— (a) Variation in cruising altitude to avoid storms and roughair? M.A.T.S. feels that aircraft cruising at 35,000-40,oooft are above most of the rough weather and can readily spot and avoid thunder-heads. Airborne radar is useful in this..;; respect, with an acceptable installation on board weighing about 60 to ioolb. (b) Variation in cruising altitude to seek optimum windconditions ? Turboprop and jet consume more fuel in descending, butit was felt that en route detours would not involve major problems and that jet aircraft would be more likely toclimb back to a higher cruising altitude than go to an alternate at low altitudes. On turboprops, however, it ispossible to go to the alternate at lower altitudes by shutting down two of the four engines. : (c) Catering for possibility of engine failure at any point ? The experience gained in full operations will probably make it possible to lower the high fuel reserves which must be allowed when an aircraft is first put into service. Also, -. it has been found that three-engine operation at altitude . . is practical. (d) Ascending or descending through rough air in such a wayas to avoid discomfort to passengers or the exceeding of struc- tural limits ? A high wind encountered at 30,000-ft levels frequentlyprevails at 20,000ft as well. The additional favourable wind necessary to make descent worth while is so great that theadvantage gained is negligible. For example, to descend 500ft, a 50-knot gain in favourable wind would be necessaryto justify the change. Losing altitude to avoid heavy head winds is not as likely as diverting or climbing. Loss of oneor two engines is not very important in jet airliners. What maximum rate of cabin ascent and descent should bedesigned for, and what is the maximum tolerable angle of the fuselage to the horizontal during climb and descent ? Jet aircraft do not have to descend at a faster rate thanpresent types. Also, the aerodynamic effect upon passengers • of turbulence in a jetliner is negligible. The most desirablerate of change in cabin altitude lies between 200 and 300ft (maximum) per minute for descent and ascent. Mentionedas examples of inside-outside ratios were 2,000ft cabin alti- tude at 30,000ft; 8,000ft cabin altitude at 40,000ft. Pressuxization failure and sudden depressurization werediscussed. It was estimated that a person has one minute of consciousness at 28,000ft, with a rapid decrease in con-scious time at higher altitudes, as for example, 28 sec at 35,000ft. U.S.A.F. requires its pilots to use oxygen masksand t<5 fasten seat-belts above certain altitude limits. A " With water methanol injection, runways can probably be kept to the present normal lengths. As a normal procedure the air- lines will not want to use Jato to get them past performance require- ments. Afterburning is not applicable to the turboprop and will probably not be used for civil jets."—D.H. Sprite rocket motor available to assist the take-off of the Comet in adverse conditions. balance between window size, weight and safety is neces-sary. Small, inward-opening doors are desirable. (See also under later heading "Passenger Comfort and Safety.") The maximum tolerable angle of fuselage to the horizontalin normal quick-descent operations should not exceed 8 deg and should preferably be less. In the COMET the angle variesfrom plus 6 to minus 4. Ground Operations What type of engine starting system is likely to be satisfac- tory ? If electrical, what voltage is required and what action is being taken, or should be taken, to standardize ground equipment? The type of starter is a matter of choice. Varying volt- ages are used with electric starters. Will it be possible to start engines if ground equipment is noi available ? Yes. The COMET can obtain two to three starts on its standard battery. Are special safety precautions necessary during starting ? There are no problems. Seven feet from the intake is considered a safe range. What special problems are likely to be caused by run-up, testand taxying of jet aircraft ? In particular:— (a) Will it be necessary to take special precautions to avoid the intake of foreign bodies by engines ? Guards are applied to prevent foreign articles being placed and left in intakes. (b) Will jet fuel and blast cause runway deterioration ?Concrete runways were considered almost essential be- cause of high blast temperatures, and because kerosene dis-solves asphalt. BOEING reported that at the runway level40ft from the jet pipe, the temperature is 200 deg Fahrenheit and the blast 250 ff7sec; 100ft behind, the temperature is100 deg and the blast 70 ft/sec. Kerosene spillage occurs during initial take-off blast, during deceleration for landingand at engine cut-off. Operational Allowances (Fuel) What reserves and allowances are realistic for both long andshort range, over land and over water, under present condi- tions, and what changes can be anticipated (with datesinvolved) due to forthcoming improvements in navigational aids ? Reserves and allowances in this case include fuel forevery stage of the operation, including possible fuel lost due to boiling, fuel required as a result of engine failure, fuelrequired to cover navigational and meteorological uncertain- ties, etc. Turbojets and turboprops will require the same compara-tive extra fuel reserves for thermal de-icing, etc. Rate of climb—greater in jet aircraft than in piston types—creates a heat and boiling problem. The amount of boiling-away might be as much as 10 per cent in a 1,500-mileleg, depending upon temperature, altitude, etc. For a considerable time to come, fuel reserves for turbineaircraft will remain proportionately higher than for con- ventional aircraft. Can anything be done to lessen the noise of turbine units during ground run-up and taxying ? Aircraft could be placed behind screens. There is some hope that impeller noise will be reduced. What special facilities should be developed for rapid servicing of turbine aircraft? Will fixed bays be essential ? What special equipment will be needed over and above those normally required for reciprocating engines ? Chief problem is refuelling, and under-wing fuelling will be essential. The hydrant system now being developed will be superior to servicing by truck. Manufacturers are work- ing on 200 gal/min procedure. Considerable thought is being given to in-flight refuelling, which can be done. Turbine units will require much less servicing than do piston engines. Passenger and cargo loading facilities must be improved to reduce ground time—especially by more and bigger doors and easy access to cargo holds. Discus- sion of inward- or outward-opening doors resulted in examination of advantages and disadvantages of each. Jet aircraft impose no particular problem in ramp handling. What length of time should be allowed between starting engines and taking-off ? And at what points will take-off clearances be obtained and cockpit checks made ? What fuel consumption will be involved in this phase by comparison with equivalent piston-engined aircraft ? At uncongested airports, it would be entirely practical to clear turbine aircraft right from the ramp. The high cost of ramp space, however, was cited as a factor in holding a*.
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