THE combination of reciprocating engines with a Parsons low-pressure turbine, which has been adopted for the propelling machinery of the Olympic and Titanic, is one of the latest examples of progress in marine engineering. The superior economy of the system is due to the fact that increased power is obtained with the same steam consumption by expanding the steam in the low-pressure turbine beyond the limits possible with the reciprocating engine. Messrs. Harland & Wolff were among the first to see the advantages of the combination arrangement and to put the system to the test of actual experience. This was done in the case of the Laurentic, already referred to, and the successful results obtained with this vessel led to the introduction of engines of the combination type in the new White Star liners and other vessels built and building at Belfast.
Arrangement of Machinery.
As will be seen from the general arrangement plans of the ships (Plates III. and V.) and the elevations and plans of the boiler and engine rooms (Plates VI., VII., and VIII.), in the Olympic and Titanic nearly the whole of the space beneath the upper deck E is occupied by the steam-generating plant, coal bunkers, and propelling machinery. The boiler installation and bunkers occupy six watertight compartments, having a total length of 320 feet. The engine rooms take up a further length of 123 feet, and the electric engine room and shaft tunnels occupy the remaining portion of the ship below the orlop deck. Of the four funnels provided, the foremost three are required for the boiler rooms, while the fourth is used for ventilating purposes and has also built into it the chimney from the extensive galleys.
As is well known, the Olympic and Titanic are triple-screw steamers, each wing propeller being driven by one set of reciprocating engines, and the central propeller by the low-pressure turbine. Owing to the great size of the units, it was found necessary to place the latter in a separate compartment abaft the reciprocating engine room and divided from it by a watertight bulkhead. The reciprocating engine room is placed immediately abaft the aftermost boiler room, and contains, in addition to the main engines, a large amount of auxiliary machinery. In the wings are placed the main feed and botwell, bilge, sanitary, ballast, and fresh water pumps, the auxiliary condenser, the surface heater, and the contact heater, which latter is placed high up in the casing at the centre line ; while on the port side space has been found for the extensive refrigerating plant, and on the starboard side for a large engineers’ workshop, situated on a flat some distance above the floor level and well equipped with machine tools.
The after engine room contains, in addition to the low-pressure turbine, the main condensers with their circulating pumps, twin air pumps, etc., the evaporators and distilling plant, the forced lubrication pumps with two oil coolers, and a pump for circulating water through them, besides several pumps for bilge and other purposes.
Boilers.
Altogether there are twenty-four double-ended and five single-ended boilers in each vessel, designed for a working pressure of 215 lb., which it is anticipated will be maintained under natural draught conditions. The aftermost, or No. 1 boiler room contains the five single-ended boilers, boiler rooms 2, 3, 4 and 5 contain five double-ended, and the foremost, or No. 6 boiler room contains four double-ended boilers. Owing to the great width of the ships, it was found possible to arrange five boilers abreast, as shown in Fig. 44, except in No. 6 boiler room, where, owing to increased fineness, only four abreast could be fitted.
Each of the double-ended boilers is 15ft. 9in. diameter and 20ft. long, and contains six furnaces ; while the single-ended boilers, which are of the same diameter as the double-ended but are 11ft. 9in. long, contain three furnaces, so that the total number of furnaces is 159. The latter are all of the Morison type, 3ft. 9in. inside diameter, and are provided with fronts of the Downie “ boltless ” pattern. The firebars are of the Campbell type, supplied by Messrs. Bailton, Campbell & Crawford, of Liverpool. The shells of the single-ended boilers are formed in one strake, the double-ended boilers having, as usual, three strakes. All the shell plates are of mild steel 111⁄16in. thick. A view of the boilers arranged in Messrs. Harland & Wolff’s works is given in Fig. 45.The arrangement of uptakes, by which the smoke and waste gases are conveyed to the funnels, is necessarily of a very elaborate nature, no less than twenty branches being required to one funnel in the case of boiler rooms 3 and 4. The branches from adjoining boiler rooms are united immediately above the watertight bulkhead separating the rooms, the bulkhead thus forming a valuable support to the uptakes and funnel above. One set of uptakes is shown in Fig. 46 and well illustrates their numerous ramifications. The four funnels have an elliptical cross section and measure 24ft. 6in. by 19ft. Oin. Their average height above the level of the furnace bars is 150ft. A striking photograph of the last funnel of the Olympic leaving the shops is reproduced in Fig. 47.
Bunker Arrangements
The arrangements in the Olympic and Titanic for loading and storing coal and feeding the coal to the stokeholds are the result of great experience. The bunkers consist of a ’tween deck space, on each side of the ship between the lower and middle decks, into which the coal is first shipped and from thence distributed into the cross bunkers extending the full width of the vessel in each boiler room. The stokers obtain the coal from doors in the cross bunker end bulkheads at the stokehold level immediately opposite the furnaces (see Plate VI.), an arrangement which reduces the amount of handling of the fuel for each boiler to a minimum. A further advantage of the bunker arrangement is that no watertight doors are required in the bunker ends, as each set of boilers has the necessary coal supply provided in the same watertight compartment, the watertight bulkheads dividing the boiler rooms being placed at the centre of the cross bunkers.
Ash Hoists and Ejectors.
The arrangements for discharging ashes on each of the two new White Star liners consists of ten See’s ash ejectors, of which there are two in each large boiler room, placed as shown on Plate VI. The ash ejectors are worked by the large duplex feed pumps, placed in a separate room adjoining each boiler room. One of the See’s ash ejectors is shown on the right-hand section of Fig. 44. The ashes are discharged by shovelling them into the hopper placed on the stokehold floor, whence they are drawn down by the rush of air to a water jet which is being discharged through the long inclined pipe shown, at a pressure of about 150 lb., the jet being maintained by. the pump already referred to. The water jet carries the ashes up the inclined pipe till, at the upper bend, they are deflected and discharged well clear of the ship’s side.
In addition, there are four ash hoists supplied by Messrs. Railton, Campbell and Crawford, for use when the vessel is in port. Ash hoists of this type have proved remarkably free from wear and tear and require a very small supply of steam, a ¼-in. pipe only being used for the steam inlet. Fig. 48 shows clearly their arrangement and method of working.
Induced Draught and Fans.
No forced draught is provided, it being the practice of the White Star Line to have forced ventilation only to the boiler rooms of their ships. For the latter purpose twelve Sirocco fans, two for each boiler room, have been supplied by Messrs. Davidson & Co., of Belfast, fitted with Allen motors. The fans are placed at the middle deck level and draw in air through ventilating shafts from the boat deck, supplying the same through trunks led down the bulkheads to the level of the furnaces. Eight of them are 55in. diameter, two 50in., and two 40in., a pair being illustrated by Fig. 49. One of the stokehold fan controllers with the cover removed is shown in Fig. 50. It will be seen that the cables are fitted permanently into screw plugs, the holes for which are bored and tapped in the joint of the cover, so that they can be placed in position and the cover screwed down, making a simple and yet watertight joint. The controllers can also be worked from the stokeholds by rods supported on ball thrusts. The ball thrusts so greatly eliminate friction that the different positions on the controller can be easily felt below.
Steam and Exhaust Pipes and Valves.
The steam supply is carried from the boilers to the engines by two maln steam pipes made of welded steel, with a butt strap riveted over the weld, from which branches are carried to the various boilers, and which gradually increase in diameter as they approach the engine room forward bulkhead. On the forward side of this bulkhead, on each pipe line, is placed a balanced emergency stop valve (see Plate VI.), which can be closed in a few seconds in case of need. On the after side of the same bulkhead are the main stop valves, 21½in. diameter (see Plates VII. and VIII.), each provided with a large separator and a cross connection, which allow either range of piping to be used for either or both engines. The main stop valves are of the equilibrium double-beat type, and are operated by hand wheels and screws from the starting platform, which is situated in the centre of the reciprocating engine room.
From the stop valves the steam passes to the reciprocating engines, and after expanding through the various stages is led from the low- pressure cylinders of each set by a 61-in. pipe to a huge change-over valve, 64in. diameter, situated on each side just abaft the forward bulkhead of the turbine room. By means of these change valves the exhaust steam is deflected downwards through large strainers to the turbine, or directly across to the condenser. The arrangement will be better understood by reference to Plates VII. and VIII. and the section through the turbine room given in Fig. 51, from which it will be seen that all these parts are in duplicate, there being an exhaust pipe, change-over valve, and steam admission to the turbine, and a main condenser on each side of the centre-line of the ship. The exhaust pipes, which have been supplied by Thos. Piggott & Co., Ltd., of Birmingham, are of steel, lapwelded, with a strap riveted over the weld, and are provided with concertina or bellows joints between each rigid connection, to allow for expansion without endangering the airtightness of the pipes leading to the condensers. These joints consist of two thin steel discs riveted together at their periphery through a steel ring, and are about 2ft. 6in. larger in diameter than the pipes to which they are connected by flanges. The slightly conical form of the disc plates enables any difference in length due to contraction or expansion to be taken up.
The change-over valves are of the piston type with a ring of special form. Fig. 52 illustrates the casing of one of these valves and clearly shows the ports. Steam is admitted to the strainer and thence to the turbine when the piston of the change-over valve is at its highest position, and to the condenser when the piston is lowered. The pistons of both change-over valves are connected to levers, the other ends of which (see Fig. 51) are controlled by a Brown’s hydraulic reversing engine of the type adopted in reciprocating engine practice, which is in turn controlled by a lever on the starting platform close to the main reversing lever. When the order to reverse is given, the engineer at once pulls over the change-over valve reversing lever, the steam passes direct from the low-pressure cylinder to the condensers, and the machinery is handled as an ordinary reciprocating installation until the manoeuvring is finished and steam is again admitted to the turbine by restoring the change valves to their original position. From the turbine the steam exhausts to each condenser through large welded steel eduction pipes of rectangular section. Each pipe is provided with an immense sluice valve, 8ft. 6in. by 10ft. 6in., to shut off the turbine entirely from the condensers in case of accident to the former. These sluice valves are electrically operated, the closing slides, which are in two pieces, being worked together by worm and rack gear. To control the steam supply in case of the propellers racing or in the event of a break-down, each reciprocating engine is provided with an Aspinall governor which works in conjunction with a Brown’s engine connected to the throttle valve, while in the case of the turbine a ball governor is provided, which controls the Brown’s engine operating the change-over valves.
In regard to the auxiliary steam pipe system, it may briefly be said that the five single-ended boilers in No. 1 boiler room are arranged for running the auxiliary machinery when in port, while two boilers in each of the other compartments have separate steam leads to the auxiliary machinery, which includes the very large dynamo engines. The only auxiliaries exhausting into the main condensers are the steering engines. The electric engines exhaust through an independent pipe to the surface heater, and all other auxiliaries exhaust into the contact-heater. For port use a large auxiliary condenser is fitted.
The Reciprocating Engines
The two sets of reciprocating engines are of the four-cylinder triple-expansion direct-acting inverted type, balanced on the Yarrow, Schlick and Tweedy system, and are arranged to take steam at 2151b. per sq. in. and exhaust at a pressure of about 91b. per sq. in. absolute. The cylinders are 54in., 84in., 97in., and 97in. diameter, with a stroke of 75in. in all cases, and each set of engines is expected to indicate about 15,000 H.P. at 75 revolutions per minute. In general design the engines follow the long-tried practice of Messrs. Harland & Wolff.A section through the reciprocating engine room is given in Fig. 53, a view of the starboard engines erected in the shops in Fig. 54, and of the port intermediate cylinder in Fig. 55. From the elevation, Plate VII., it will be seen that the columns are of the “ split ” type, each column near its centre being divided into two sections which are well spread out to form a strong base. The engine bedplate weighs 195 tons, the columns 21 tons each, and the heaviest cylinder with liner 50 qtons. The two low-pressure cylinders are placed one at each end of each set of engines, as is usual with the balancing system adopted, the order of the cylinders, beginning forward, being low-pressure, high-pressure, intermediate-pressure, and low-pressure; see Plates VII. and VIII. Each^L.P. cylinder is provided with two slide valves, worked from the same crosshead by a single set of double bar links and eccentrics. The H.P. cylinder is provided with a single piston valve and the I.P. cylinder with two piston valves similarly operated to the twin slide valves on the L.P. cylinders. The valves are operated by Stephenson link motion. The reversing gear for each set is operated by a Brown engine of the usual type, and, in order that the latter may always be at full stroke whatever the cut-off required in the various cylinders, each set of links has its own separate adjustment. Elaborate electrically-operated lifting gear for the cylinder covers, etc., has been necessitated owing to the great weights to be handled, while in addition several electric winches have been provided to> deal with the smaller weights. The turning engines are steam-driven.
Fig. 53.—Section through Reciprocating Engine Room.
Fig. 54.—One Set of Reciprocating Engines in the Erecting Shop.
Fig. 55.—Port Intermediate Cylinder.
Low-Pressure Turbines.
The low-pressure turbine, which is of the usual Parsons. type, will take steam from the reciprocating engines at about 9 lb. absolute pressure and exhaust at 1 lb. absolute. It is intended to develop about 16,000 shaft horse-power when running at 165 revs, per minute. No astern turbine has been fitted, as the centre shaft is put out of action when the ship is being manoeuvred. The turbine, as will be seen from the illustrations, is of immense size, its weight complete being no less than 420 tons. The rotor is 12ft. diameter and 13ft. 8in. long between the extreme edges of the first and last ring of blades. It consists of steel forgings built up in the usual way, as illustrated in the photograph of the rotor in the lathe reproduced in Fig. 56. The rotor in process of blading is shown in Fig. 57. The blading is of the Parsons laced type, with distance pieces at the roots and binding soldered on the edge. The blades range in length from 18in. to 25Jin. The complete rotor has a weight of about 130 tons. A view of the massive turbine casing, which is of cast iron, is shown in Fig. 58. Both hand and motor gear is provided for turning the turbine when under repair. The lifting gear for removing the upper half of the turbine casing is also electrically driven.
Fig. 56.—Turbine Rotor in the Lathe.
Shafting and Propellers.
The crank and thrust shafts for the reciprocating engines are 27in. diameter with a 9-in. hole through the centre. The line shafting is 26¼in. and tail-end shaft 28½in. diameter with a 12-in. hole through the centre. The crank shaft for each engine weighs 118 tons, its massive proportions being shown by Fig. 59, which illustrates part of a crank shaft in the lathe. One of the thrust shafts is shown in Fig. 60, from which it will be seen that there are fourteen collars provided, arranged seven at each end, with space for an intermediate bearing at the middle. Each tail shaft has a loose coupling to facilitate withdrawal outboard for examination. The turbine shaft is 20Jin. diameter, increased at the tail-end to 22Jin., with a 10-in. hole through the centre throughout.The plummer blocks for the turbine shaft, of which there are eleven, are provided with forced lubrication at a pressure of about 201b. per sq. in. The oil gravitates to the bearings from a tank placed high up on the casing, and of sufficient capacity to hold a ten minutes’ supply. The oil escaping from the bearings is collected in two drain tanks placed beneath the engine room floor, from whence it is pumped back through filters and coolers to the supply tank. All the -plummer blocks are also provided with a watercooling service.
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Fig. 57.—Turbine Rotor in Process of Blading.
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Fig. 58.—Turbine Casing.
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Fig. 59.—Crank Shaft in the Lathe.
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Fig. 60.—One of the Thrust Shafts.
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The wing propellers of the Olympic are three-bladed and have a diameter of 23ft. 6in. The bosses are of cast steel and the blades of bronze. The centre or turbine propeller, which is illustrated by Fig. 61, has four blades and is built solid of manganeze bronze.The diameter in this case is 16ft. 6in.
Fig. 61.—The Centre Propeller.
Condensers.
The condensing plant has been designed to allow a vacuum of 28½in. with the barometer at 30in. and a temperature of circulating water of from 55 to 60° Fahrenheit. As already stated, there are two main condensers placed in the turbine engine room. They follow in design Messrs. Harland & Wolff’s standard practice, and are pear-shaped in outline, as will be seen from Fig. 51 and the view of one of the condensers with the casing removed reproduced in Fig. 62, the object of the pear shape being to concentrate the tube surface where the largest volume of steam is admitted. The inlet extends the full length of the condenser, as is usual in turbine installations, and is well stayed vertically with division plates, which are in line with corresponding division plates in the condenser body, so that an equal distribution of steam over the whole of the tube area may be secured.
Fig. 62.—One of the Main Condensers with Casing partly removed.`
The auxiliary condenser, which is placed on the starboard side of the reciprocating engine room, is of similar design to the main condensers, and has a cooling surface of 3,600 sq. ft.
Circulating Pumps.
The circulating pumps have been constructed by Messrs. Harland & Wolff themselves. The main installation consists of four gunmetal pumps, two being placed on each side of the ship in the turbine room, for each main condenser, as shown on Plate VIII. The pumps have 29-in. inlet pipes and 5ft. 3in. impellers. Each is driven by a compound engine having cylinders 13in. and 22Jin. diameter with a stroke of 15in. and working at 1201b. pressure. A plan of one complete pump and engine is given in Fig. 63. The auxiliary circulating pump, which is placed near the auxiliary condenser (see Plate VIII.), is of similar type. The inlet pipe in this case is 12-in. bore, and the engine has cylinders 8in. diameter with a stroke of 9in.
Fig. 63.—One of the Main Circulating Pumps and Engines
Air Pumps.
The main air pumps are placed in the turbine room adjoining the condensers, and have been supplied by Messrs. G. & J. Weir, Ltd. Altogether there are four pumps of the “ Dual ” type, illustrated in Fig. 64, each suitable for about 11,000 I.H.P., and having both air and water barrels 36in. diameter by 21 in. stroke. The pump barrels are of gunmetal, with cast iron bases and tops, and are fitted with gunmetal buckets, manganeze bronze pump rods, steel piston rods, and Kinghorn valves in gunmetal seats. The pumps are capable of performing their duty with a steam pressure of 1201b. per sq. in., but the steam cylinders can withstand the full boiler pressure of 2151b.An independent twin air pump 17in. dia. by 15in. stroke, worked by a single steam cylinder 10in. dia. by 15in. stroke, is provided in conjunction with the auxiliary condenser.
The Return Feed System.
From each condenser the water passes into a feed tank placed on each side of the ship just abaft the bulkhead dividing the engine rooms. From thence the water drains into a control tank on each side adjacent to the hotwell pumps in the reciprocating engine room. Prom the control tanks the water is drawn by four Weir single-cylinder direct-acting hotwell pumps (two on each side of the ship) 14in. diameter by 24in. stroke, the diameter of the steam cylinder being 14in., and is discharged through the main feed filters to the Weir surface feed-heater. The main feed filters are placed against the forward engine room bulkhead (see Plate VIII.) and are four in number, two on each side of the ship. They have been supplied by Messrs. Railton, Campbell and Crawford, and the Titanic set is illustrated in Fig. 65. The total filtering area is 1,008 square feet.
Fig. 64.—One Set of “Dual” Twin Air Pumps.
The surface feed-heater is capable of dealing with 700,0001b. of water per hour when supplied with 50,0001b. of exhaust steam per hour from the dynamo engines at a pressure of about 51b. per sq. in., the temperature of the water being raised from 70° to 140°. The surface heater shell is of mild steel, the doors of cast iron, the tube plates of rolled brass, and the tubes .of solid drawn brass. From the surface feed-heater the water passes to the direct-contact heater, placed high on the engine room forward bulkhead; see Plate VII. The direct-contact heater is suitable for dealing with 700,0001b. of feed water per hour, and when using exhaust steam from the auxiliaries is capable of raising the temperature of the feed water from 140° F. to 212 or 230° F. An illustration of this heater is given in Fig. 66. The shell is of mild steel. The direct-contact heater is so arranged that it will automatically regulate the feed pumps and hotwell pumps, and thus ensure these auxiliaries working in unison. From the contact heater* the water gravitates to the main feed pumps, which are of Weir’s vertical direct-acting type having a diameter of 14in. by 28in. stroke and steam cylinders of 19in. Four pairs of pumps are provided, but two pairs alone are capable of dealing with all feed water for 44,000 I.H.P. An illustration of one pair of the feed pumps is given in Fig. 67. In the case of both the main feed and the -hotwell pumps, the water ends are of cast iron and are fitted with gunmetal liners, gunmetal buckets, ma'n- ganeze bronze pump rods, and bronze valves in gunmetal seats. The water valve chests for the feed pumps are of cast iron, bolted to the pump chambers.
All the feed pumps are interchangeable so far as feeding the boilers is concerned. In addition to the main feed pumps, a large duplex pump of Messrs, Harland & Wolff’s own make—intended for auxiliary feed purposes, working the ash ejectors, boiler circulation, and other duties— is placed adjacent to> each boiler room (see Plate VI.) in a separate dust-tight compartment, so that the working parts may not be injuriously affected by coal dust.
Evaporating Plant.
The evaporators, three in number, are placed on the starboard side at the after end of the turbine room ; see Plate VIII. They are of the latest Quiggin’s type, and have been supplied by the Liverpool Engineering and Condenser Co. Two of them are shown in Fig. 68. Each evaporator has capacity for the production of 60 tons of distilled water per 24 hours, which can be maintained even after being in use for several days. The heating surface in each case is of the flat grid type, made from solid drawn copper tubes, and the shell is of cast iron. Each heating surface unit is interchangeable and can be separately withdrawn from the evaporator. The joints are of the grooved type. Being metal to metal, they do not require any jointing material, and are perfectly tight under any pressure and variation of temperature. The shells are lagged with double-ply hair felt and sheathed with galvanized sheet iron. An independent duplex steam feed pump supplies the evaporators with feed water, the supply being automatically controlled by the automatic regulator fitted for this purpose on each evaporator.
Sundry Pumps.
Space does not permit a detailed reference to the very numerous pumps provided and their duties. Many of these pumps have been made by Messrs. Harland and Wolff, Ltd., while others have been supplied by Messrs, Gr. & J. Weir, Ltd. Notable among the latter are three direct-acting fresh-water pumps, each capable of dealing with 5,100 gallons of water per hour when running at 30 double strokes per minute, and one fresh-water pump capable of dealing with 2,800 gallons per hour when running at the same speed. Messrs. Weir have also supplied the three single-cylinder oil pumps used in connection with the forced lubrication system, and which are capable of discharging oil through a cooler to a head of about 90 feet.
Telegraphs.
The engine telegraphs for transmitting orders from the captain's bridge to the starting platform are of the usual type fitted in large vessels and call for no special comment.
A system of illuminated telegraphs has been provided between the starting platform and the various boiler rooms to enable the engineer on watch to communicate his orders to each stokehold. With eleven stokeholds to control, the foremost of which is 320ft. from the engine room, the necessity for such an arrangement is evident. Fig. 69 shows the transmitter and one of the receivers belonging to the installation, which has been supplied by Messrs. Evershed & Vignoles, Ltd., of London. The same firm have also supplied a set of Kilroy's stoking indicators for each stokehold, of which a regulator and one of the indicators are illustrated in Fig. 70. The regulator is set to the rate of firing desired by the engineer, and the indicators, which are electrically operated by current switched on from the ship's circuit, give visible and audible intimation to the fireman at the exact moment when each furnace is to- be fired. Five indicators are provided in each stokehold, one for each boiler, and are regulated so that the minimum number of furnace doors will be open at the same time, and no' opposite doors in a double-ended boiler open together.
Fig 65.—Main Feed Filters of the “Titanic.”
Whistles.
The whistles are the largest ever made. Each set consists of three bell domes grouped together with a suitable branch plate, as shown in Fig. 71. The three domes are 9in., 15in., and 12in. diameter. The total height from the base of the branch piece to the top of the centre dome is 4ft. 2½in., and the extreme width over the outer dome is 3ft. 6in. The total weight of the three domes and branch pieces is about 6¾cwt.
One set has been fitted on each of the two foremost funnels. The whistles are electrically operated, the officer on the bridge having merely to' close a switch to give the blast, and there is also an electric time-control arrangement, fitted on the Willett-Bruce system, whereby the whistles are automatically blown for 8 to 10 seconds every minute during thick weather.
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Fig. 66.—Direct-Contact Heater.
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Fig. 67.—One Pair of Vertical Direct-Acting Feed Pumps.
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Fig. 68.—Two of the Evaporators.
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Fig. 69.—Boiler Room Telegraph.
Fig. 70.—Kilroy’s Stoking Indicator.
Ventilation of the Engine Rooms.
Over the reciprocating engine room is situated the usual light and air shaft, which extends above the boat deck and is surmounted by a large skylight. The similar shaft from, the turbine room is surmounted by the fourth funnel, which is a most valuable adjunct for ventilating purposes.
The ventilation of the engine rooms is further assisted by four electrically-driven Sirocco fans, of which three are placed in the reciprocating engine room and one in the turbine room. All are 30in. diameter and of the discharge type. Of the three fans in the reciprocating engine room, one is placed in the skylight and supplies air in the vicinity of the starting platform through a series of trunks, while the other two are situated on the port and starboard sides respectively and ventilate the wings. The single fan in the turbine room is used for ventilating the wings of that compartment.
Comment and discuss