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Aviation History
1955
1955 - 0140.PDF
140 FLIGHT, 4 February 1955 TRADEWIND TURBOPROPS... shown to be necessary by XP5Y testing. These included single-levercontrol, mechanical coupling between engine and airscrew control, improved over-temperature amplifier system, and improved engine/airscrew decoupler. (2) Extension shafting would not be considered, since no positivesolution had been found. Design studies were conducted on an in- stallation with power sections submerged between the spars in orderto retain the low-drag nacelle. These studies indicated that such an installation would reduce both the wing fuel capacity and engineaccessibility. (3) The results of test experience with the P5Y indicated that con-siderable thought had to be applied to intake icing and water ingestion problems. Tests were conducted on plenum-chamber inlets and it wasfound possible to maintain substantially the same efficiency with intakes of this type as with the best ram-duct design feasible—while at the same time reducing the icing problem and eliminating the water ingestion problem. As a result of these studies, the R3Y Tradewind has an AllisonT40-A-10 turboprop mounted above the wing and driving an Aeroproducts six-bladed contraprop through a short shaft. Air is taken in immediately beneath the spinner and rammedinto a plenum chamber, from which it is then extracted by bell- mouths fixed to the main compressor inlets. All the engine-drivenaccessories are mounted on the back of the reduction gearbox, which lies in the upper forward part of the plenum chamber. Theoil-coolers are thin, flat, plate-type units by the Harrison company, the cooling airflow being controlled by a dual exhaust flap whichis opened and shut thermostatically. These oil coolers have been found to be much lighter, either dry or wet, than the previouslyused tubular type. The power unit is separated from the wing by a vertical firewallimmediately ahead of the main spar, which joins a horizontal firewall extending back to the trailing edge between the engineand the wing. This provides a fire barrier between the engine and the wing, the latter being an integral fuel tank. The vertical The final R3Y Tradewind installation is shown here with the top (left) and bottom hatches opened. The underneath view is looking forward, and shows the oil-cooler installation and associated ducting. firewall of the inboard nacelles separatesthe engine compartment from the plumbing and wiring mounted on thefront spar and leading to the outboard engines. A continuous-resetting fire-detection system is installed, in con- junction with methyl-bromide extin-guishers. The engine compartment ahead ofthe vertical firewall is divided approxi- mately in the 'plane of the compressorbell-mouths by an insulated lateral baffle, which serves to separate theplenum chamber from the engine power-section accessories compartment.This nacelle compartment houses all the engine controls and accessories, to-gether with the oil tank and essential instrumentation. The oil tank is mounted low on the right-hand side, and has to be pres-surized to ensure satisfactory supply to the engine pumps at altitude. This pressure is supplied by the pneumatic startingsystem during the starting cycle, and by compressor-bleed air during flight operation; the pressure is controlled by a regulatingvent valve, and the tank itself is a sheet metal shell with a readily removable synthetic rubber bladder. The engine controls are mounted above the power section andare fully accessible when the forward upper nacelle doors are open. Access to the oil tank and underside of the power sectionsis given through a door in the left-hand side of the nacelle, which can be opened from above the wing to permit inspection andrepair of equipment installed in the plenum chamber and engine accessory compartment without removing the engine. The hot part of the engine behind the firewall is contained ina compartment lined with 0.008in stainless steel. The exhaust tailpipes incorporate two flexible bellows sections which providea form of universal jointing, and the final outlets are nozzled to 80 per cent of the engine-connection area; each discharges intothree bell-mouths in series, the ejector effect from which drives cool air through the turbine companment in order to maintainthe surrounding structure within temperature limits during flight or prolonged on-the-water operation. This arrangement reducesthe shaft-power available at sea level, but the engine/airframe characteristics are such that there is an increase in jet thrust inthe high-altitude cruising condition. Air for the tailpipe compartment is introduced through a high-aspect-ratio scoop in the top of the door immediately above the combustion chamber. Cool air is also introduced from the leadingedge into the region between the floor of the hot compartment and the wing upper surface, and is discharged overboard underthe wing flaps. The cooling air which flows through the tailpipe compartment, as well as the exhaust gas discharged from the tail-pipe nozzles, finally flows overboard through long troughs above the trailing edge of the wing. These troughs are of stainless This diagram outlines the main portions of the Tradewind engine installation and nacelle arrangement. It shows the manner in which very low drag has been sacrificed to gain accessibility, safety, light weight and more reliable performance. 5 'I "•• :"r. •• ' •'• •""••• ' •--•' -"-•-•• ••'.-••••' ••;-••• -. to \A (3 12 I, gear-case access doors; 2, com- pressor access doors; 3, turbine access door; 4, tailpipe access door; 5, tail- pipe support bulkhead at station 281; 6, ejector troughs; 7, horizontal fire- wall; 8, afterbody compartment; 9, fuel tank bay; 10, fire seal diaphragm; II, vertical firewall at stn. 165.15; 12, turbine fire-seal access door; 13, fire-wall tunnel access door; 14, accessory compartment; IS, side access door; 16, plenum chamber bulkhead; 17, plenum chamber access door; 18, plenum chamber; 19, air-intake diffuser flap. White arrows, intake air; black arrows, accessory-cooling air; black/white dotted arrows, afterbody cooling, cross-shaded arrows, horizontal firewall air.
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