FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1957
1957 - 1729.PDF
22 November 1957 819 Reduction takes place in two stages; the first in the epicyclic gearbox and the second through the spur gears of the transfer train. Input from the power sections is via a compressor extensionshaft splined into the rotor and carrying a double-helical sunwheel at its forward end. Meshing with the sunwheel are three double-helical satellite gears which carry on a common shaft smaller dia- meter straight-cut spur gears running in an internally-toothedring restrained against rotation by the torquemeter mechanism. Essentially, this consists of arms on the ring gear which areattached to hydraulic pistons. As torque increases, a correspond- ing increase in hydraulic oil pressure at the pistons is transmittedto the tqrquemeter pressure indicator, where it is read-off as s.h.p. Rotation of the spur gears around the toothed rack rotates thesplit satellite carrier. This is a large steel forging carrying the roller bearings of the three satellite/spur gear combinations. Theinside faces of the two sections are pocketed to accommodate the spur and satellite gears and a Hirth coupling is formed on the twoabutting faces. The two halves are rigidly bolted togedier after the spur and satellite gears are inserted. The forward section of thecarrier is extended to form a splined shaft which carries a large spur gear forming the pinion of the transfer gear train and aninterposed idler transmits the drive into a further spur gear splined to the inner propeller shaft. The drive from the port power sectionis similar except that gear sizes in the transfer train have been chosen so that counter-rotation can be obtained by omitting theidler. The accessory drive is taken through spur gears of reduced width meshing with the propeller shaft gearing of the main drive.Output is via a Hardy Spicer joint and a suitable extension shaft. An internal drilling in the accessory drive gearbox castingcarries a supply of pressure oil to each of the bearings in the accessory drive gear train and a "one-shot" lubricator maintains oillevel in the housing by an injection at each engine start. Further drillings carry oil to each of the bearings in the reduction gearbox.Oil collects at the lowest point of the casing and is directed through a passage to the scavenge filter, scavenge pump, and via the Sin-diameter, 21-h.p. oil cooler. Each power section has its own annular air intake casing boltedto the rear face of the air duct unit gearbox casing. Aerofoil section webs carry the internal wall and a large boss supporting a frontmain bearing. Into a machined register in the rear face of this casing are fitted the carrier rings to which the inlet guide veins areslotted, and grub screws pressing axially into the stator casing prevent rotation. Through one of the hollow spokes in each airintake casting is taken a radial shaft driven by bevel gears from the compressor rotor extension shaft. A bevel drive on the ends ofthese shafts drives the oil and fuel pumps and life recorders. The parallel-sided stator casing, devoid of stiffening ribs, is amagnesium zirconium alloy casting. Flanges formed on each end allow the casing to be carried from the intake casting at itsfront end, and it is bolted to the centre section diffuser casing at the rear. Light alloy and stainless steel blades are dove-tailed tocarrier rings slotted circumferentially into machined grooves in the stator case. The compressor rotor, carrying ten rotor discs, consistsDf a parallel-sided M.A.T.101 drum bolted at either end to steel extension shafts. The first compressor stage disc is carried on theforward extension shaft where it is tightened against its register by a ring nut. This first compressor disc of reduced bore and thenext three discs mounted on the rotor drum are all of solid con- struction. The remaining discs are built up from two opposed:onical halves. Apart from the tenth and eleventh stages thin wall fees are used, and these built-up discs are riveted on their cir-:umference to the tangs of the rotor blades. Machined into the hub )f each disc are locating dogs and axial fit is machined-in. The first four stages of compressor blading were changed fromJght alloy to steel at an early stage in Mamba development. Stages 5ve to nine are aluminium and the remaining blade stages are ofitainless steel. The four rows of steel blades are tanged into he solid discs with longitudinal fir-tree attachments and areocked with pins. The remaining blades are integral, with the angs riveted between the compressor discs. Between the platformsormed on the base of each blade rotating shrouds are fitted. Carried by the rear stub of the compressor drum is the innernember of a labyrinth seal. The mating static member fits into 1 register on the centre casing in line with the straightener blades. The entire end-thrust of the rotative assembly is carried by theront main bearing. This is a heavy-duty ball bearing with the sntre race split into two halves to permit the use of the largest»ssible number and diameter of balls. The centre main bearing, arried by the light alloy centre section, is a single-row parallel-oiler bearing supporting journal loads only. Cast within the entre section are the diffuser passages, and tb<* rear face of theasting carries a semi-cantilevered forged tubular centre-section xtension. This casting terminates in a flange to which is bolted' cylindrical iron casting carrying the rear main bearing. Lubrication is by flood feed from a gear-type pressure pump,'assed through filters to a distribution chamber, and from there >y drillings or piping to the bearings, throttle delay servo box,nticipator unit and propeller controller. *"e shafting connecting the turbine and compressor assemblies The ASMD.8 head-on; frontal area is modest for a 3,600 s.h.p. twin. Blanking plates are fitted over the intakes. is in five sections: the compressor rear extension shaft, the turbinemainshaft, a tapered turbine front extension shaft and the turbine stub shaft. The latter, which is carried in the rear main bearing,is splined to the turbine extension shaft and locked with a ringnut. The turbine extension shaft is bolted in turn to the mainshaft tubewhich drives the compressor extension shaft through a gear-type coupling and spherical self-aligning bush. The annular vaporizing combustion chamber follows usualArmstrong Siddeley practice; it comprises an inner and outer gas-tight annular casing, inner and outer annular flame tubes anda flat circular support plate bearing the vaporizers. Provision for lighting-up is made by conventional high-energy igniters and Ki-gass primers pressurized by an electric fuel pump. The turbine outer casing is a parallel-sided thin-wall tubewelded to flanges at eidier end and bolted at the rear to the com- bustion chamber outer casing and at the rear to the exhaust cone.The first-stage nozzle blades are bolted directly to carrier rings cantilevered from the combustion chamber flange, and the twostages of stators are carried between channel section rings, the rearmost of which is dogged to the casing flange to prevent rotationand to allow for differential expansion. Nozzle and stator blades have integral shrouds formed at their tips, and on to an internalflange on the stator shrouds is riveted a diaphragm plate which forms the static part of the inter-stage labyrinth seal.The three discs of the turbine rotative assembly are located by Hirth couplings between the front disc and the flange of theturbine stub shaft, the shaft and the second disc, and between die second and third discs. The first stage rotor blades (Nimonic100) are plain, but the blades on the second (Nimonic 100) and third (Nimonic 80A) stages have integral shrouds; all are securedto the discs with helical fir-tree serrations, and are locked by longitudinal strips. The discs are cooled by air tapped from thefinal compressor stage which, being at high pressure, can flow up the faces of the discs to join the main stream. Eleventh stage airis used also as a thrust equaliser to relieve bearing thrust loads. The exhaust cones are conventional, but the inner cone is sup-ported by stay bolts shrouded by aerofoil section struts and precision-cast collars and sleeves are welded to these bars and tothe skin. Aerofoils are cambered to bring them into line with the jet efflux swirl—which allows an increase of pressure ratio.The Double Mamba ASMD.8 is rated in an unusual way. Instead of ratings for take-off, intermediate and maximum con-tinuous cruising power, only one rating is employed. Hence, the take-off power available is not twice the 1,950 s.h.p. of the Mamba 8but 2 x 1,800 s.h.p. This is a nominal power that represents a higher continuous cruising power than would have been grantedif 1,950 s.h.p. per side had been quoted as maximum. The Double Mamba 8 went into production early this monthand will soon be officially type tested. The engine in this form probably represents die ultimate in a long line of Mambaengine development since, with the turbine already making use of advanced materials, a considerable mechanical re-design wouldbe required to extend the stretch process any further. A double engine based on the power available from the AS M.I would havegiven 1.960 s.h.p., whereas die present engine has the brochure power of 3,600 s.h.p.—a figure which has been more dian equalledin development. This engine is now being flight-tested from Bit- terswell in a standard Gannet 1, a rather odd-looking aeroplane,since the exhaust pipes of the raised eneine are brought out below and in front of die leading edges. The Double Mamba could pos-sibly make an attractive power unit for installation widiin the wing of a civil aircraft. But this is largely a pipe dream; the most pro-fitable fruit of eleven years of Mamba and Double Mamba experi- ence, Armstrong Siddeley say, will be in die P.182 engine, thedesign of which in its final form, is now well advanced.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
