FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1946
1946 - 0624.PDF
7,20 FLIGHT MARCH 28TH, 1946 KEEPING THEM RUNNING A normal daily inspection on a jet turbine may be sum- marised to consist of an external examination for oil and fuel leaks, checking the correct level of the lubricating oil in the oil reservoir, viewing up the jet pipe (by torch or mirror reflection) for any signs of turbine blade damage or heat effect, and a "motoring" check for freeness of rotation (by operating the engine through the normal method of starting with the H.P. cock "off"). It is not normal to remove the main engine nacelle cowlings for D.I.s, and in certain instances ground mn checks are not considered essential. Inspected in Airframe Minor inspections are so arranged as to synchronise withthe airframe inspection periods. This arrangement has a direct reflection on the operating costs and flight planningof the aircraft. The average time taken to carry out a minor inspection on a centrifugal installation representsapproximately 10-12 man-hours per power plant and does not necessitate removing the engine from the airframe.Such work occupies but a fraction of the time taken to complete the airframe inspection. Again by comparison,it shows a marked contrast to the reciprocating engine, which may take up to 60 man-hours. MOUNTING FOR CABiN SUPERCHARGER FUEL VALVE CONTROLS FUEL PUMP STARTINGVALVE 13 Front end of the de Havilland Goblin showing the single-sidedmpcllor, accessories and drives. The items most likely to require attention are mentioned in the text. 10 Barometric Pressure Control Unit. 1, Capsule chamber ; 2, VaJve chamber ; 3, Pivot plate; 4, Rocker ; 5, Half. ball ; 6, Orifice ; 7, Filter ; 8, Diaphragm ; 9, Piston ; 10, Operating rod ; ii, Eccentric adjusting sleeve ; 12, Barometric capsule ; 13, Vent to atmosphere. A typical minor inspection for the centrifugal compressor gas turbine will include: — (a) Impellor-blade inspection for signs of cracks, etc. (visual).(b) Removal and partial inspection of the combustion assembly for distortion or flame tube buckling, also for any signs of carbonformation, due to fuel spray impingement or flame chilling. (c) Air casing inspection (for distortion and fracture) (visual).(d) Turbine nozzle guide vane inspection (visual). Jet pipe removed for the examination of cracks, blade distortion or localoverheating. (e) Turbine blade inspection (with jet pipe removed) for signs offatigue cracks, buckling or loose blades. (f) Turbine blade tip clearance check. It is normal to check thetip clearances at 45 deg intervals around the periphery of the shroud ring to determine the minimum blade clearance. This action givesa mechanical check on the growth of the turbine disc and blades or distortion of the shroud ring. (Turbine blades usually carry asafety lip at the tip which is designed to give way in the event of a turbine " rub." Such troubles, however, are now very rare.)Conversely, excessive tip clearances are detrimental to the turbine efficiency since the gas leak rate is increased. (g) Exhaust cone inspection for buckling and cracks,(h) Oil scavenge filter inspection. (i) L.P. and H.P. fuel filter inspection, (j) General visual inspection of the engine. Major overhauls necessitate the removal of the enginefrom the airframe and the carrying out of a complete strip for both visual and dimensional checking. In the past ithas sometimes been found necessary to renew the flame tubes and refit new burners Little deterioration is ex-perienced with the main rotor assembly. Ground Handling Practically all ground equipment required for the normalservicing and maintenance of jet aircraft is standard. Typical items peculiar to jet engines (apart from the rele-vant tool kits and engine slings) may be considered to consist of high-capacity, close-mesh fuel filters from thebowser supply to the aircraft fuel tanks, air intake and propelling nozzle covers to protect the compressor ana'turbine when not operating, and portable pyrometry test gear for thermo-couple testing. Certain essential precautions are enforced in theinterests of safety during all ground running of jet engines installed in aircraft, particularly during proof runs whenthe nacelle cowlings are not fitted. Apart from the dis- comfort of noise, it is unwise to approach the vicinity ofthe compressor intake when the turbine is operating under power, due to the high suction effect in the proximity ofthe air intake. Possible consequences may be serious to the individual and disastrous to the engine. In this respect, loose items of clothing or articles are agreat source of potential trouble. One-piece boiler suits are considered the ideal clothing for ground personnelengaged on this work. It is also highly recommended that all ground personnel associated with continual ground
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
