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1 80 Engine Yearbook 2007 ENGINE YEARBOOK 2007CF6-80C2 engine historyand evolution Paolo Lironi,senior technicalmanager at InternationalAviation Services GroupEngine Services analyses theCF6-80C2 range of engines,one of the most successfulengine families ever built. Helooks at the family spedigree, technicalcharacteristics, in-servicedifficulties, maintenancecosts, values and CF6 engines have a classictwo-shaft design. Theconfiguration mounts the low-pressure compressor (LPC) and lowpressure turbine (LPT) on the sameshaft as the intake fan. To betterunderstand the great success of theCF6-80 model, it is necessary toreview its predecessors in the CF6range. The CF6 has its origins in theTF39 military engine, the power plantfor the Galaxy C-5 military transportaircraft. Experience gained by GE onthe TF39 was invaluable to the CF6programme since it allowed the engineto be exposed to many of its initialteething problems, through a largenumber of flight hours under rigorousoperating conditions.

2 These problemswere subsequently overcome. The first of the CF6 engines wasthe CF6-6D which had sole supplierstatus on the DC-10-10 and was ratedat 39,300 lb thrust. The CF6-6 serieshas four LPC stages, 16 HPC stages,two HPT stages and five LPT a fan diameter of inchesthe -6D achieves a bypass ratio GE designed the CF6 to havereserve capability for growth withoutmaking major changes to the coreengine and thanks to its higherbypass ratio, its fuel economy wasbetter than many of its later version, the CF6-6D1 wasoffered with thrust increased to40,300 lb. Subsequently, the CF6-50C serieswas designed and produced for theDC-10-30 and the first variants of theAirbus A300B, the -B2 and -B4versions. However, few parts werecommon with the CF6-6 since majorchanges had been made to coreengine design and to the improvedaerodynamics, the HPC was shortenedfrom 16 to 14 stages and the LPCstages were reduced to three. The LPCwas also reduced by one stage andturbine cooling was also size was not changed from theoriginal CF6-6 series but the primaryflow had to be increasedconsiderably, thus decreasing thebypass ratio to The -50C wasrated at 50,400 lb.

3 Since the CF6 was the only engineavailable to power the DC-10-10, mostDC-10 operators later selected the CF6to power their 747, 767, A300, A310and MD-11 fleets. This allowedGeneral Electric to increase its marketshare and take number one positionfrom Pratt & Whitney in thewidebody market. The -50E is the same basic engineas the -50C, but it has variable statorvanes in the HPC. The -50E is ratedat 51,800lbs, has a bypass ratio , powers the DC-10-30 and wasthe first CF6 variant to power the747. The -50C2B is the highest thrustvariant of the -50 series and is ratedat 53,200lbs. This version powers thehighest gross weight variant of theDC-10-30 and higher gross weightmodels of the next engine variant to comeout of the CF6 stable was the CF6-80A. The CF6-80A series did notfeature any major changes to coreengine configuration fan diameterfrom the CF6-50 However, earliermodels received criticism for beinglong, giving the engine a tendencyfor the shafts to bend in use. Theconsequence of this excessivebending was significant rubbing ofblade tips resulting in a high rate ofEYB2007_3B:EYb2007_3B 8/9/06 4:26 pm Page 8082 Engine Yearbook 2007 ENGINE YEARBOOK 2007engine stall margin, the engine isprovided with a variable stator vane(VSV) system .

4 The first five HPCstages can change stator vanes angledepending on the engine operatingregime. The system is controlled bytwo fuel controlled actuators,moving the VSV levers. The engine is also equipped with avariable bleed valve (VBV) in thebooster. Through this system ,booster air is vented into thesecondary flow when the engine is inthe start phase. In order to optimise engine fuelconsumption and minimisedeterioration, the HPT and the LPTare cooled externally with air bledfrom the HPC. Through controlvalves managed by the main enginecontrol (MEC) or full authoritydigital electronic control (FADEC),HPT and LPT tip clearances areoptimised for each engine regime. The first versions of the engine weremechanically controlled with theMEC and the power managementengine performance deterioration andhigher removal and overhaul rates. The new -80A series had a shortenedcore making the engine stiffer and lessprone to bending. The engine also had are-matched turbine and improved CF6-80A series was rated at lowerthrusts than the CF6-50 series andpowered the A310-200/-300 and early 767-200 and 767-300 models.

5 The CF6-80A1 israted at 46,900 lb takeoff thrust, while theCF6-80A2/A3 is rated at 48,800 lbs. Development and technicalcharacteristicsIn IASG s view, GE really broke into themarket with the CF6-80C2 series and thisengine was the defining point in creatingthe leadership position which it has sinceattained. The CF6-80C2 series featured thefirst major changes to engineconfiguration since the development ofthe CF6-50 series. The CF6-80C2 has alarger fan and one additional LPC andLPT stage. Primary engine characteristicsare listed in the table within this technical characteristics: In order to minimise fuelconsumption, and to control thecontrol (PMC) jointly acting as theengine controlling controlled engines canhave their thrust ratings changed byreplacing the MEC and the , the CF6-80C2B1F version(powering the B747-400) introduced thefirst FADEC system on the CF6 electronically controlled engineshave additional sensors on the engine,allowing a more precise control ofsystems, thereby decreasing specificfuel consumption (SFC).

6 On suchengines the MEC and PMC aresubstituted by the electronic enginecontrol (EEC). FADEC family modelsrange from the CF6-80C2B1F to the CF6-80C2B8F. One of the CF6-80C2 s notable featureswas the new commonality variant is interchangeable betweenall the aircraft types it powers andhigher thrust ratings can be achievedby turning the engine at a faster rate toincrease air flow. This can be easilydone by changing the rating plug in theEEC. PMC-controlled engines cannot bemodified to FADEC issuesIt is common knowledge that themajority of the technical issues on theengine are within the HPC. Over thepast years, several airworthinessdirectives (ADs) have been issued tomanage problems with HPC spools: HPC 3-9 spoolinspections/installation:Cracks havebeen found on the 3-9 spool at shopvisits since 1997. Improved spools havebeen proposed to operators and basedon IASG experience, only a few engineswith old spools remain in operation. HPC 10-14 spool inspection of thestage 14 web:This spool has evidencedcracking in the stage 14 web wheninspected at piece part level leading tothe scrapping of such parts.

7 Theproblem has been known to GE since2003 and inspections are in place at theshop visit level to detect these cracks. Anew spool design is not yet available. VSV stage 5 lever arms and HPCVSV new bushing and washer:This isa primary cause of aborted take offs andin-flight shut-downs. There have beenseveral instances of lever arm fractureLPC 1 fan 3 primary stagesHPC 14 primary stages 5 stages with variable stator vanesHPT 2 primary stagesLPT 5 primary stagesMax diameter (inches) 106 Length (inches) 168 Dry weight (lb) - 9,860 Overall pressure ratio - maximum powerBypass ratio 5 - characteristics and componentsEYB2007_3B:EYb2007_3B 8/9/06 4:26 pm Page 8283 Engine Yearbook 2007 ENGINE YEARBOOK 2007and bushing wear.

8 In both instances,the vane is free to move in the flowpath, either generating an engine stallor physically breaking-up andliberating debris into the gas pathwhich leads to engine damage. Since2002, GE has provided newly designedVSV lever arms and bushings. IASG experience shows that around 30 percent of the engine population still havethe old configuration. For pre-modification engines, a repetitive on-wing inspection has to be carried to the new design can beinstalled only in some locations withthe engine on-wing although IASG believes that this practice only providesminor benefit. HPC stage 3 to 5 blades:A newdesign of blades was introduced intoservice by GE and experience hasshown that these are susceptible toimpact damage and when FOD isexperienced they can fracture and causefurther internal engine damage. Since2001, GE has required a regular on-wing inspection to be carried andreplacement of the complete set ofblades at first shop visit. The latestblades have improved geometry andmaterials to reduce stress and crackingand IASG believes that half of theengine population has been modified tothe new recent issues include: Stage 11 HPC rear case wear:Wearhas been found on the HPC case at thestage 11 vane rail track.

9 This problemcan lead to vane separation and internalengine damage. An on-wing inspectionis required and an inspection has to becarried out when the engine is removedfor a shop visit. The fix for thisproblem is the introduction ofdifferently coated stage 11 vanes. Inlet gearbox (IGB) Teflon seal:Asimilar problem of IDG Teflon sealleakage and failure has beenexperienced by CF6-50 operators. SomeThe Engine Yearbook is the only publication dedicated tothe commercial aero-engine professional. Now entering its13th successful year it covers all aspects of the commercialjet propulsion business, including: Design Manufacturing Testing Market Analysis MRO Leasing Trading Spare Parts Software If you want to advertise in The Engine Yearbook 2008please contact Simon Barker on Tel: +44 (0) 207 932 5583 or E-mail: Ad Space Booking Deadline: July 30th 2007Ad Materials Copy Deadline: August 15th 2007 The next edition will be published in September 2007and will be relevant for all of 2008. It will benefit frombonus distribution at the Aero-Engine Expo 2007 plusall AIC engine-related conferences in the potential lessor anddebt provider, the CF6-80C2appears to be a robust assetwith a strong market basewhich has a very good creditrating.

10 Since the FADEC familyis more recent and flexible, itsvalue is proportionally :EYb2007_3B 19/9/06 9:20 am Page 8384 Engine Yearbook 2007 ENGINE YEARBOOK 2007 IGB horizontal gear shafts have beenfound to be dis-bonding resulting inthe loosening and separation of piecesof the Teflon seal. Ultimately, thescavenge screen becomes clogged or theIGB fills up with oil, leading to oil inthe HPC and in the cabin. GE hasindicated thresholds for IGB Teflon sealreplacement at shop visit, depending onthe hour-to-cycles ratio operated by theengine. Stage 1 HPT disk inspection:Thisproblem appeared in 2000 with somecracks being found on disks withparticular part numbers during shoplevel inspections. Investors need to beaware that some part numbers are morelikely to be scrapped because of thisadditional inspection being carried outduring a shop visit. HP Stage 2 nozzle:Old HPT nozzleswere cracking in the outer platformproducing rearward movement of theairfoil and inner platform causingcontact with the leading edges of theHPT stage 2 blades, resulting in bladefracture.