FM 1-506 Fundamentals of Aircraft Power Plants ... - Survival Books

WWW.SURVIVALEBOOKS.COMFM 1-506exiting both by trailing edge holes and by inner bandholes. There, it cools the interstage seal. The turbineblades are convection-cooled through radial holes in thedovetail. Air exits through tip holes. The stage 1 bladesalso employ trailing edge holes for cooling.EXTERNAL COOLINGCooling air inlets are frequently provided around theexterior of the engine to permit entrance of air to cool theturbine case, the bearings, and the turbine nozzle (Figure7-4). In some instances internal air is bled from the enginecompressor section and is vented to the bearings andother parts of the engine. Air vented into or from theengine is ejected into the exhaust stream. When anaccessory case is mounted at the front of the engine, it iscooled by inlet air. When located on the side of theengine, the case is cooled by outside air flowing around it.The engine exterior and the engine nacelle arecooled by passing air between the case and the shell ofthe nacelle. The engine compartment frequently isdivided into two sections. The forward section is builtaround the engine air inlet duct; the aft section is builtaround the engine. A fume-proof seal is providedbetween the two sections. The advantage of such anarrangement is that fumes from possible leaks in the fueland oil lines contained in the forward section cannotbecome ignited by contact with the hot sections of theengine. In flight ram air provides ample cooling of thetwo compartments. On the ground air circulation isprovided by the effect of reduced pressure at the rear ofthe engine compartment produced by gases flowing fromthe exhaust nozzle.7-3