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Aviation History
1947
1947 - 0202.PDF
FLIGHT THE de HAVILLAND GHOST (DC/50) the turbine wheel which exerts a thrust to the rear. It follows that the main shaft connecting the two components is stressed in tension and only a small residual thrust remains to be taken by the locating bearing. Air Compressor The impeller is formed from a single forging in a special, low-silicon, high duty alloy. Characteristically, the nine- teen vanes are truly radial throughout their length, and the curved entry vanes, which are integral with the main vanes, are not bent to shape but machined from the solid. To the rear lace of the hub is bolted the tubular main shaft and to the front iace the stub shaft carrying the ball-type front main bearing. The Goblin had its air intake and upper and lower wheelcases integral with the front casing of the com- pressor, but on the Ghost all these components are separate castings. This promotes installation adapt- ability and allows the compressor casing to be truly symmetrical and thus less susceptible to thermal distortion, which might affect clear- ances. Three interchangeable in- takes, one axial and two bifurcated, are at present available. Integral with the compressor front casing is the diffuser, which has twenty vanes defining tangen- tial divergent ducts. Air delivered from the periphery of the impeller, and flowing through these ducts, undergoes a reduction in velocity and, in accordance with the Bern- oulli theorem, a corresponding increase in pressure. After passing through the diffuser it has a pres- sure of 481b/sq in gauge—equiva- lent to a compression ratio of 4.26:1. The air leaves the diffuser tangentially and is turned to a rear- ward direction by four cascade vanes in each duct outlet. Cascade vanes are cut from an extruded section bar, and four are mounted in a sheet metal shroud and inserted and secured as a unit from the front of the diffuser casing. The casting which forms the rear wall of the diffuser is channelled at its inner diameter and sealed by a pressed- in ring to furnish an annular manifold. By way of a series of tappings from the diffuser chamber a supply of cooling air is fed under pressure to the manifold. During compres- sion the temperature of the air is raised nearly 200 deg. C and, of course, must be lowered to render the air effective as* a coolant. External pipes conduct air from the manifold 0 TWO FUEL PUMPS The axial intakecan be interchanged with a bifurcatedintake for fuselage installation. TEN COMBUSTION CHAMBERS to a pair of segmental channels, formed in the front flange of the compressor and closed by the intake casting, where it is cooled by reason of its proximity to the incoming air stream. From each of the channels a pipe delivers air to a filter mounted on the support cone and thence by an internal pipe to the rear bearing. From here it passes between the insulating plate and the front face of the turbine disc and discharges at the blades. Four external pipes from the manifold carry air to the supports of the bullet in the exhaust cone and thence to the rear face of the disc. The compressor is completed by a backplate registered with and bolted to the rear half of the diffuser. Complementary labyrinth grooves are provided in the rear wall of the impeller and in the backplate to avoid air loss, and their diametral position is so chosen that the forward thrust of the impeller substantially balances the rearward thrust of the turbine. In the backplate three inspection plugs interrupting the labyrinth grooves can be withdrawn for checking the clearance. On the front wall twelve lead rubbing plugs, pitched at 90 deg., on three diameters, serve to check the clearance at idling and maximum speeds. Component items of the fuel and combustion system were developed in collaboration with the research team of Joseph Lucas, Ltd.* Each * Fuel burning and control equipment and tbe combustion researchfacilities of Joseph Lucas were described in detail in Flight srd and 10th January, 1946.
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