This republication has been made possible thanks to the assistance of
The Society of Automotive Engineers and Dr. James C. Floyd. This is quite a lengthy lecture and was presented in January 1950. We hope you enjoy this piece of aviation history.
Scott McArthur. Webmaster, Arrow Recovery Canada
DIRECT OPERATING COSTS
While it is not the purpose of this paper to join in the merry-go-round of comparisons of the conventional and jet-powered transports on a ton-mile per lb. of fuel basis, nevertheless, the operating costs had to be considered very carefully, and their consideration played an important part in the final design confimration of the aircraft.
The two important efficiency factors in the cost analysis are the cost per mile and the payload for a given range.
The cost per mile is obviously governed by speed, as manv of the direct costs such as, crew salaries, depreciation, insurance, etc. are fixed hourly costs. Neglecting fuel consumption, if the blockspeed is increased from say 250 mph to 350 mph, the cost per mille would be decreased by approximately 30%. It can and has been shown elsewhere, that this decrease in cost due to speed more than compensates for the increase due to higher fuel consumption.
The effect of blockspeed can possibly be seen more clearly by considering the number of aircraft required for a given scheduling. The equation in its simple form is shown below.
For a given yearly utilization, traffic density and passenger capacity, it can be seen that if the blockspeed is doubled, the number of aircraft required is halved, and consequently, the earning power of each aircraft is considerably increased.
To take advantage of the higher blockspeeds, however, maintenance and turn-around time at the airport has to be cut down to a minimum, and the optimum climb and descent procedure from operating altitude taken into account.
The high degree of pressurization and the incorporation of dive flaps to allow a rapid descent; the use of special accessories and radio compartments where practically all items that required frequent servicing are housed; and the employment of underwing pressure refueling are only a few of the items, which have been incorporated to increase the economic efficiency of the aircraft.
So far as the payload portion of the cost per ton mile efficiency datum goes, the fuselage was laid out to give the best compromise between a full passenger version and combined passengers and cargo. Two typical lavouts are the 40 passenger version with an additional 4,100 lb. of freight making a total pay-load of 12,500 lb., and the 50 passenger version with a payload of 10,500 lb. Payload Vs. range with all ,allowances is shown on figure 6.
While the final analysis of economy must be left to the individual airline, the results of a detailed analysis show that the direct operating costs compare very favourably with those of present transports, despite the relatively high fuel consumption of present jet engines, and the fact that the present allowances for stooge and flight to an alternative airport are severe on the jet transport.
It is obvious that as the specific fuel consumption for the jet engine improves, with the use of ceramic blade materials, and higher compression ratios, and the flight procedures are modified to cut down the stooge time, the picture will be even brighter.
Although, the final seating arrangement and cabin layout will depend on the customer's choice, it appears to be fairly definite that the high density passenger version will be the one of greatest interest,.
Two typical layouts are shown in figure 7. Accommodation for 40 or 50 passengers is shown with provision for their baggage on the left hand side of the cabin, adjacent to the front entrance door. The washroom is situated opposite this baggage compartment, and a small commissary and hostess station is situated at the rear of the passenger cabin.
The ten ft. diameter fuselage allows for wide seats, and a generous aisle with a head room of 82 inches. Seat pitching is at 38 inches.
Emergency exits are situated in the centre section and rear section above the wing, and a crew emergency exit is fitted in the ceiling of the crew compartment.
A permissible C. G. travel of approximately 23%.of the mean chord or approximately 35 inches provides for flexibility of loading with the least number of restrictions.
Noise Level and Vibration
Noise level in the cabin is considerably reduced by the use of turbojets, and this, coupled by a complete lack of vibration, will add enormously to passenger comfort.
The four Derwent 5 engines are mounted in pairs in two under-slung nacelles, each nacelle being made up as a single integrated structure. The engines are toed-in toward the centre line by 5 deg, and set at approximately 11 1/2 deg to the horizontal in order to take the jet pipes under the main spars without cutting away any of the spar structure.
Tubular engine mounts are used, and these can be removed or replaced separately. The nacelle geometry is shown in figure 8. All nacelle air loads are taken back into the two engine mounts, which are attachedto the centre section front spar.
Engine servicing and maintenance is made particularly easy by the low position of the nacelles. All engine adjustments can be made without the necessity of using service ramps or ladders, see figure 9.
Engine removal is carried out by detaching the services and gear drive at the break points, swinging the trunnion locating caps down, and dropping the engine on to the special trolley. The engine is then wheeled away sideways to make way for the replacement engine. With this unique arrangement, a complete engine change can be made in a very short time.
The jet pipes are parallel in plan and are supported on trunnions and links. Two spherical joints are incorporated to give flexibility to the pipes on expansion, and also for the withdrawal of the jet pipe for engine removal. Although, a relatively long jet pipe is used, it Is estimated that less than 1% of thrust is sacrificed from the combined effects of length and shape of the pipe.
A sixteen inch nozzle is fitted and the jet emerges at 7 deg. to the datum line of the aircraft, to bring the line of action of thrust as close to the C. G. as possible.
The jet pipe runs through a tunnel of stainless steel formed by firewalls attached to the adjacent structure. The jet pipe itself is insulated, and is cooled by a flow of air passing through the firewall tunnell and induced by the extractor nozzle. The vena-contractor at the nozzle sucks the cooling air through the nacelle, after it enters through louvres at the forward end of the cowling.
The main accessories driven by the engines are mounted on an accessory gearbox located between the engines in each nacelle,and attached to the wing front spar. The gearbox contains two completely independent gearing systems, each driven by one engine, and each having independent lubrication.
Each inboard engine drives a cabin blower, a vacuum pump, and a Tachometer generator, and each outboard engine drives a 50 KW alternator, a 9 KW generator, an hydraulic pump, and a Tachometer generator.
The gearbox drives are connected with the engines by a system of drive shafts linked by means of flexible couplings, as shown in figure 10.
Derwant 5 Modified Engines
The C-102 engines are standard Rolls-Royee Derwent 5 engines but with a completely redesigned oil tank. The cast oil tank is sited at the front of the engine, underneath the forward gear drive. The engines are handed only by the oil tank filler and the gear take-off, see figure 11.
The change from starboard to port engines is made simply by interchanging the filler neck and blanking plate on the oil tank and swinging the gear take-off around in the opposite direction. The oil tank and system are integral parts of the engine.
The engine is supported by mounting trunnions at approximately the center of gravity of the engine, and is steadied at the rear and by a shackle plate bolted to the top of the nozzle box.
The upper part of the cowling is developed as a permanent structure provided with small access doors for engine slinging, and a larger door to permit access to the upper part of the accessory gearbox.
The lower half of the cowling consists of two large access doors hinged at the sides and a smaller door beneath the accessory gearbox swinging aft. All access doors are locked by means of flush-type quick release fasteners, and the two main curved doors can be quickly detached by swinging them out and unhooking the special hinge locators.
"Copyright 1951 Society of Automotive Engineers, Inc. This paper is published on this web-site with permission from the Society of Automotive Engineers, Inc. As a user of this web-site, you are permitted to view this paper on-line, download the pdf file and to print a copy at no cost for your use only. Downloaded pdf files and printouts of the SAE paper contained on this web-site may not be copied or distributed to others or for the use of others."
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