JT8D engine performance retention

JTSDENGINE PERFORMANCE RETENTION

Albert D. James and David R. Weisel

Pratt & Whitney Aircraft Group

SUMMARY

The attractive performance retention characteristics of the JTSD engine

are described. Because of its moderate bypass ratio and turbine temperature,

and stiff structural design, the performance retention versus flight cycles of

the JTSDengine sets a standard that is difficult for other engines to equal.

In addition 9 the significant benefits of refurbishment of the JT8D engine

are presented. Cold section refurbishment offers thrust specific fuel consump-

tion improvements of up to 2 percent and payback in less than a year_ making a

very attractive investment option for the airlines.

INTRODUCTION

The ability of an aircraft powerplant to retain its marketed performance

is one of the primary considerations in its development or selection. Escalat-

ing price of fuel during the last decade has placed greater emphasis on defin-

ing the performance retention characteristics of current, as well as new

powerplants. Any performance loss can be directly related to increased operat-

ing costs, and fuel is an ever increasing portion of those operating costs.

The Pratt & Whitney Aircraft JT8D engine is a first generation turbofan

engine_ i.e., a low bypass ratio_ dual spool_ axial flow turbofan that enjoys the distinction of being the most widely used engine in commercial service. To date_ over I0,000 units have been delivered and power more than 3,000 aircraft for 175 airline operators worldwide. To assist these operators in minimizing fuel costs and maximizing time on-wing 9 Pratt & Whitney Aircraft has conducted an extensive analysis of the JT8D engine in order to define the industry po- tential for performance recovery 9 the modes of performance loss within the component modules and cost effective means of recovering that lost performance.

PERFORMANCE CHARACTERISTICS Quantifying performance losses as a function of engine service time has been an industry problem since the initiation of commercial service. Manufac- turer development processes include many tests with cyclic power adjustments that provide advanced notice of problems arising from thermal distress and fatigue. They do not have the means of accelerating the normal erosion process that the gas path hardware is subjected to daily in commercial service.

However_ operators have all these conditions occurring continuously_ but usually do not have the facilities_ manpower_ financial commitment or time to do the extra testing that would provide this basic knowledge.

Reams of inflight cruise monitoring data could be reviewed. Almost all airlines require the flight crew to record one data point during cruise on each engine during each flight leg. Five performance parameters are recorded: engine pressure ratio, high and low spool rotor speeds, fuel flow and exhaust gas temperature. The data quality suffers due to the use of aircraft instru- mentation. The principal use of the data is to monitor the engine parameters for abrupt changes that would signal a potential incidence of part failure.

Data scatter is significant. Considerable massaging is required to smooth out the data enough to generate trending information that will identify a severe deviation thereby making the identification of small performance losses very difficult. It was, therefore, decided to base the on-wing (pre-repair) deteri- oration characteristic on ground engine cell data acquired from engines run prior to repair.

Figure 1 provides the average performance retention characteristics of the JT8D engine and the individual sea level static data points used as the basis for this curve. The average curve is described by a second order curve fit through all the data, and is considered representative for all JTSD-I through JT8D-17 models.

Figure 2 shows this characteristic in relation to the industry average post repair performance levels. Three levels of performance are shown that exist in commercial service today. The uppermost curve represents the average on-wing (pre-repair) deterioration. Individual operators may experience dete- rioration rates significantly different from this curve, either better or worse, since there are a multitude of factors that can influence the deterior- ation rate. These factors will be discussed in the later paragraphs.

Average industry performance levels after repair are represented by the middle curve. Industry repair practices have reflected the philosophy of on- condition maintenance, which were directed at minimizing engine maintenance cost. Cheap fuel prices and known operating limits have allowed operation un- der this maintenance philosophy. Engines are operating today that have accumu- lated operating times in the 30_000 hour or cycle region with periodic hot section repair and only occasional minor cold section work to repair airfoil damage from Bill of Material or foreign objects. Refurbishment of the compres- sors to recover performance loss (particularly specific fuel consumption) was dismissed by operators as not being cost effective. These components were generally refurbished only when incidences of compressor surge were en- countered.

This curve then reflects the results of on-condition maintenance philoso- phy with an implied penalty because of limited cold section repair. The curve flattens to a relatively constant loss resulting from the imposition of the operating temperature limit. Gas path deterioration and increasing exhaust gas temperature coexist. Generally, the JT8D engine has not had a problem with the exhaust gas temperature measuring system indicating temperatures that are falsely high or low. Therefore, as the gas path deteriorates, the exhaust gas temperature limit restricts takeoff power setting, forcing the engine back to the repair shop. The practice of minimum repair then manifests itself in ever shorter periods of operation between repair cycles and exhaust gas temperature limiting operation.

Fuel shortages and the continuing escalation of fuel prices have refocused the industry emphasis on fuel economy, both in operation and maintenance.

Practices that were not cost effective a few years ago, now have reasonable payback periods.

In the interest of identifying effective refurbishment, Pratt & Whitney Aircraft funded a JT8D Engine Maintenance Technology study to define the pri- mary modes of deterioration in the engine, identify the modules where maximum performance restoration could be attained and develop cost effective methods of recovering that lost performance. Cooperation of four major airlines (three domestic and one foreign), two years of studying hardware, scrap records and available data, and an in-house testing program using a loaned high time ser- vice engine, have identified and demonstrated that significant performance could be recovered through fan and high pressure compressor refurbishment.

The lower curve (Figure 2) represents the average level of performance attainable through a revised maintenance philosophy that recognizes periodic cold section refurbishment as a major part of performance recovery.

It would appear that a significant improvement is still available, since the average remains approximately 2.0 percent above the new engine baseline.

The curve should not be interpreted to conclude that refurbishment to the "as new" performance level cannot be achieved. A few of the engines came within 0.5 percent of their production acceptance levels. Current production perform- ance levels were used as a consistent base for all the post repair tests and the average engine performance has improved over the years. This would tend to make the difference appear larger than it actually was. Realistically_ achievement of "as new" performance can be accomplished through refurbishment.

Although material lost to erosion cannot be restored_ airfoil shape and sur- face finish, which are the prime performance factors, can be restored with only a residual reduction in performance life.

FACTORS INFLUENCING PERFORMANCE RETENTION Assuming large amounts of usable data were available to define the per- formance retention characteristics for each operator, a wide variation in operator average retention and engine to engine variations about each average could be expected. Engine deterioration rates are dependent on many factors other than engine to engine differences of gas path geometry and cycle match- ing. Of major influence are operational environment, operational philosophy and maintenance philosophy, which are particular to each individual airline.

Gaspath Geometry The JT8D engine is a first generation turbofan engine 9 i. e. , a dual spool, axial flow, low bypass turbofan. It is constructed with a full length annular fan duct that directs fan air rearward to mix with primary air in a common convergent exhaust nozzle. This results in rigid case construction so the installed engine is not adversely affected by the axial bending forces exerted by inlet air loads during aircraft rotation and maneuvering.

In comparison to more current state of the art engines, the gas path is

built with relatively loose clearances between rotating and stationary parts,

therefore_ compressor and turbine airfoil tip rub is not a factor. The primary

forms of performance loss are hot section thermal distress, compressor airfoil

roughness and compressor airfoil erosion.

Airfoil roughness is the result of environmental contamination and gener-

ally occurs in the first 1,000 hours of operation after installation or clean-

ing. Contamination is the minor mode of compressor performance loss that ap-

pears to reach its maximumand then remains relatively constant throughout the

operational phase.

High gas velocities and thinner airfoils in the high pressure compressor

account for a large measure of the performance impact. In addition to the

leading edge erosion exhibited in the fan and low pressure compressor_ blade

pressure side erosion also occurs. Both leading edge and pressure side erosion

occur concurrently until approximately 4.0 percent chord is lost near the

blade tip. At this point, the blade trailing edge has becomeexcessively thin

and begins to tear away. Figure 3 graphically shows the relative performance

loss of each deterioration mode and the accelerated rate for performance loss

that takes places when the trailing edge shreds.

Operational Environment

Operational route structure and geographical area have a definite impact

on the deterioration rate. The JT8D engine is used in the short to medium

range segment of the industry. Aircraft cyclic times, the time between takeoff

and landing_ vary between 20 minutes to two hours per cycle. The industry

average is about one hour per cycle, which is considerably shorter than the

typical long range aircraft which run four to seven hours per cycle.

Hot section distress, the primary mode of engine performance loss in all

engines, is cyclic dependent. Time at high temperature is the key parameter in

determining turbine hardware lives. Since maximumtemperature is achieved dur-

ing takeoff_ deterioration as a function of engine cycles becomesmost signi-

ficant. On this basis, the JT8D engine performance retention characteristic is

very attractive.

Cold section airfoil erosion, the principal mode of performance loss in

the compressor, is cyclic dependent, and also dependent on geographical area.

A Middle East operator typically exhibits more airfoil erosion due to sand

ingestion_ in 2,000 cycles than a large domestic operator may see in 30,000

cycles. Figure 4 illustrates the variation in erosion rates by assuming that

the rates are linear.

Other geographical areas have their own particular problems, although not

as severe as the desert operations. Operators in Alaska also have an erosion

problem with volcanic ash and operators near salt water or highly industrial-

ized areas have problems with corrosion and sulphidation.

Operational Philosophy

Power setting procedures that reduce the impact of hot section thermal

shock during takeoff have been defined by engine and airframe manufacturers

and are available to the operators. The procedures simply require the flight

crew to compute the required power necessary to get airborne based on the am-

bient temperature, aircraft gross weight and runway length. Dependent on these

variables_ reduced power may be used instead of the full rating. This results

in the engine operating at a lower turbine inlet temperature. A significant

reduction in turbine distress and_ consequentlyp a reduced deterioration rate

can be realized if reduced power takeoffs are used whenever possible.

Figure 5 shows an analytical assessment of maintenance material cost re-

suiting from reduced power takeoffs. The relative cost is shown as a function of engine time per cycle with lines of constant percentage of power reduction.

Maintenance material savings are directly related to a reduction in turbine distress. Similar savings can be realized by using reduced climb power when- ever aircraft loading and routing permit.

Maintenance Philosophy Maintenance policy has been an evolving process as illustrated in Figure 6. During the early years of operation_ maintenance was on a hard time basis.

Engines were removed_ inspected and repaired at specific intervals. As confi- dence in the hardware integrity became proven, the time intervals were extend- ed based on operator experience.

Logical progression led to on-condition maintenance. This was considered at one time to be the ultimate policy. Engines stay on-wing until removal is forced by a fault or the inability to set power because of reaching an oper- ational limit. Some parts still retain hard time limits based on maximum cycles for useful life 9 but generally these are long term limits. All interim maintenance is based on a problem developing or the engine reaching the ex- haust gas temperature limit prior to meeting the power setting requirement.

This was an acceptable maintenance policy during an era where fuel cost was a small portion of total airline operating cost.

Minimal maintenance results in increased fuel consumption and turbine tem- perature levels. Turbine distress occurs with increasing regularity and is readily evident during disassembly. Compressor deterioration is not as ap- parent, therefore, the extent of cold section maintenance was to blend repair obvious Bill of Material and foreign object damage.

The tightened world supply of fuels and strategic materials highlighted the need to change philosophies. Fuel became a major part of the airline oper- ating cost and the maintenance emphasis was redirected toward reducing fleet fuel consumption. The impact of the cold section_ fan and high pressure com- pressor particularly, became more obvious_ forcing maintenance philosophy to swing back towards scheduled cold section refurbishment.

PERFORMANCE OPTIMIZATION

With the maintenance philosophy shift towards scheduled compressor refur-

bishment, the next logical progression is towards complete engine maintenance

management.The deterioration rates of each module, and the potential to re-

cover lost performance are recognized in this concept. This utilizes a cost

effective mix of repair techniques and new parts to attain a service goal.

This also must address on-wing maintenance to retain the performance re-

covered through refurbishment for as long as possible. Periodic engine water

wash and fuel nozzle cleaning should be included in any engine management pro-

gram.

Compressor airfoil roughness has been found to occur in the first 1,000

hours of operation. Experience has shown that long term water washing is not

very effective in removing compressor contamination. However, short term per-

iodic washing (250 hour intervals) has demonstrated that performance loss due

to contamination can be held off for 4,000 to 5,000 cycles. Intervals recom-

mendedfor compressor water wash have been in 1,000 hour increments or less,

but as more data is accumulated, the most significant results are associated

with the shorter time interval wash procedures.

Considerable data from hot section inspections have correlated burned tur-

bine nozzle vanes and streaked combustion chambers with coked fuel nozzles.

Non-uniform fuel flow from plugged nozzles results in excessive temperature

and burned vanes. On-wing fuel nozzle cleaning procedures have been proven ef-

fective in eliminating moderate coke deposits. Therefore, periodic cleaning in

the recommended 19000 hour intervals will maintain coke free operation and op-

timize turbine hardware performance.

PERFORMANCE RETENTION MODELING

In order to determine more cost and fuel efficient maintenance practices,

an accurate model of engine performance loss must be constructed. This model

can be used to quantify performance loss for a particular engine model as a

function of usage. Additionally, a complete model will identify losses both by

module and cause, such as erosion of airfoils, thermal distortion of hot sec-

tion parts, and clearance increases between rotating and stationary parts due

to erosion or rubs.

To begin the process of model construction, appropriate data sources must

be selected. Inflight monitoring data is available, but its usefulness as a

primary source is limited. The quality limitations of flight data have been

discussed previously; large amounts of data must be trended in order to be

meaningful. In addition, flight data furnishes far fewer parameters than the

number of module losses to be defined. In particular, the lack of thrust mea-

surement makes determination of low spool losses very difficult. Finally,

flight data is affected by aircraft systems, particularly the pneumatic

system, which makes analysis of the data even more difficult.

Two data sources were used to construct the JTBDengine performance reten-

tion model. The first of these was pre-repair data obtained from airline test

cell runs. Because of the nature of airline operations, particularly with a

well-proven engine like the JTSDand prevailing on-condition maintenance prac-

tices, pre-repair data is not normally obtained. However, there is a limited

amount of first run data available. This data is relatively accurate and

furnishes pressure ratios and thrust, in addition to more accurate definition

of those parameters measured inflight. By comparing the pre-repair data for a

particular engine to its production run data_ it is possible to use a computer

simulation of the engine to calculate efficiency and flow capacity change for

every module. This analysis depends on use of known relationships between cold

sections efficiency and flow capacity changes, referred to as "coupling" rela-

tionships.

The other data source used for the model was teardown inspection data.

Used parts with known service times were collected and analyzed to determine

performance changes from the new part configuration. Such data furnishes know-

ledge of the causes, as well as the magnitude of module performance loss. From

the estimates of individual module performance changes from new, total engine

performance change from new can be synthesized with the engine computer simul-

ation. The results of this analysis can then be compared to the pre-repair

analysis and then both analyses can be iterated until reasonable closure is

obtained_ as shown in Figure 7. Since each analytical approach has its limita-

tions, such iteration enhances the validity of the solution.

This process was performed for the JTSD-9 engine. Figure 8 shows a compar-

ison of increase in sea level takeoff exhaust gas temperature from production

as predicted by the modelt compared to the pre-repair data. Figure 9 shows the

same comparison for thrust specific fuel consumption. Reasonably good correla-

tion between the average of the data and the model is shown. The used part

analysis showed that the component deterioration for a typical operator was

most strongly related to flight cycles for reasons previously discussed. How-

ever, there can be considerable operator-to-operator variation associated with

operating environment differences.

Modules losses at 49000 and 81000 cycles that result from the analysis are

shown in Figure i0. Cold section losses are dominated by erosion and roughness

damage, while hot section losses occur primarily in the high pressure turbine

and are largely the result of thermal distortion (vane bow). There are no

module losses due to clearance increases. The low bypass ratio of the JTBDen-

gine minimizes thrust bending loads, and the long, stiff one piece fan duct

effectively isolates the internal engine cases from nacelle aerodynamic loads.

These features, plus the moderate hot section temperatures, result in a stand-

ard of performance retention that is difficult for other engines to equal.

Figures ii and 12 show the overall impact of cold section versus hot sec-

tion losses on exhaust gas temperature and thrust specific fuel consumption_ measured at sea level takeoff conditions. The hot section dominates exhaust gas temperature increase D while cold section losses have greater thrust speci- fic fuel consumption impact. Historically_ engine overhaul has been directed primarily toward restoring exhaust gas temperature margin, and airline efforts were accordingly concentrated on hot-section repair. However_ in the current era of constantly escalating fuel prices, Figure 12 shows the importance of periodic cold section refurbishment to minimize fuel burned.

In order to analyze the potential benefits of performance restoration on

fuel burned, fuel consumption at altitude conditions must be evaluated. This

can be done with the engine computer simulation. Analysis shows that there is

an effect of both flight condition and power setting on thrust specific fuel

consumption change due to component performance changes. A weighted thrust

specific fuel consumption change has been defined which combines both climb

and cruise thrust specific fuel consumption at typical altitude conditions, in

proportion to the fuel consumedduring a typical mission. For the JT8D engine

in a typical 727 application, the weighted thrust specific fuel consumption

change is approximately the average of climb and cruise changes.

Takeoff exhaust gas temperature and weighted thrust specific fuel consump-

tion increases are shownby module and cause in Figures 13 and 14. Exhaust gas

temperature increase is primarily controlled by the high pressure turbine;

however, high pressure compressor losses also contribute significantly. Thrust

specific fuel consumption increases are dominated by the fan and high pressure

turbine; the high pressure compressor again contributing significantly.

The performance retention model can also be used to predict the impact of

hot section repair, and project performance losses for multiple run engines.

Figures 15 and 16 show the impact of hot section repair only. Typical first

removal is shown at about 6,000 cycles, which would probably be for foreign

object damageor hot section inspection. At this point, a change in high pres-

sure turbine outer airseal from bill-of-material knife edge to honeycomb

(typical airline practice) is shown. Erosion of the replacement outer airseal

plus worse bow for repaired vanes results in more rapid exhaust gas tempera-

ture and thrust specific fuel consumption increase with flight cycles, so that

an exhaust gas temperature-limited condition may be encountered at about

i0,000 cycles. The effect of hot section only repair is that the interval

between the exhaust gas temperature-limited shop visits decreases with succes-

sive shop visits. This is because of the underlying cold section damagewhich

has not been corrected.

IMPACT OF COLD SECTION REFURBISHMENT

The assumedworkscope for cold section restoration is shown in Figure 17.

If cold section refurbishment is accomplished at "soft" time intervals of

12,000 to 17,000 cycles (nearest convenient time when the engine is in the

shop), the model predicts the results of Figure 18. Fan and low pressure com-

pressor restoration are accomplished at 13,500 cycles, along with high pres-

sure turbine repair. At 17,000 cycles, the high pressure compressor and tur-

bine are repaired. The benefits in improved thrust specific fuel consumption

are readily apparent.

A number of studies have illustrated the cost-effectiveness of cold sec-

tion refurbishment for the JTSDengine. Figure 19 illustrates summaryresults

from one study. The study showed fan and low pressure compressor refurbishment

to be most cost effective (earliest payback). Refurbishment of fan, low pres-

sure compressor and high pressure compressor combined, resulted in 1.6 percent

weighted thrust specific fuel consumption recovery at refurbishment, 21°F

exhaust gas temperature recovery and payback in less than a year for a typical

operator, based on 50 cents per gallon of fuel. Current fuel costs would

further enhance cost effectiveness of cold section refurbishment, notwith-

standing increased labor and parts costs since this study was conducted.

REFERENCES

IQ Sallee, G. P., JTSD Maintenance Technology Study, United Technologies Cor- poration, Pratt & Whitney Aircraft Group, Commercial Products Division, June 1980.

o 1980 JT9D Engine Regional Engineering and Maintenance Conference, Pratt & Whitney Aircraft Group_ Commercial Products Division.

October 1980, Zurich_ Switzerland and Washington, D.C.

November 1980, San Diego, California and Singapore Prerepair/Takeoff thrust I +7 1 (_ • +6 +5-

Percent

change in

thrust

+4- /% /% _.

specific

/% / 0 JTSD-9 + 3 a _ m _, JT_-_5

fuel

_ C_ 0 JT8D-17

consumption

+ 2 _ D _ '_ Open symbols - _st run ,Z_ . (noprevloos repairs) + 1 O/_/% O Closed _mbots- "mulbpie run t (havehadat leastone O:J previous repair) 0 J _ I L l l l l 1 I 0 2 4 6 8 10 12 14 16 18 20

Flightcycles, 1000

Figure 1 Sea Level Static Test Cell Data JTSD Engine Performance Retention +6- Applicable to all JT8Dmodels

Percent

+4

change in

k

thrust

specific

fuel

+2

consumption

Demonstrated post refurbishment I I ! I 4 8 12 16

Flight cycles,1000

Figure 2 Industry Average Post Repair Level Shows Significant Potential for Performance Recovery I / = / Tipsection Rap_chord k_s / / / / / ._z, / / ?=

Change in

_- / / /

TSFCand

i /

EGT; / / /

lossof

stall

/ / Trailr_edge i /

margin

/ damaee), / Leading edge an_e /// / Tipclear_ance 0 1 2 3 6 8 10

Averagechordloss(percentat 0.100 inchesfrom tip)

Figure 3 High Pressure Compressor Performance Retention Directly Related to Chord Loss Middle Eastdesert operator jf Loss of trailing edge

Chord

loss

0 2 4 6 8 10 12 14 16

Flightcycles,1000

Figure 4 High Pressure Compressor Blade Chord Loss Rate Varies Greatly Between Operators 1.5 Fullyrated _/Avera,,,/10% id_:_rY ratings(4% derated)

Relative

maintenance

material

1.0

cost

1 I I 2.0 1.0 1.5

Hours/flight cycle

Reduced takeoff thrust canreduce maintenance material costsubstantially Mostcosteffective benefit realized w_ 10% derate Figure 5 Maintenance Cost Reduced by Thrust Derate Procedures 100% \ x, Percent of airline maintenance programs 1963 1969 1980 JT8D Widebody introduction introduction Figure 6 Engine Maintenance Concepts are Changing Iterate to analyze module losses Iterate to _ synthesize engine performance Figure 7 JTSD Engine Performance Retention Model-Approach First run JT8D-9engine Sea level statJclStdday/Takeoff thrust

,° I

6O

Changein

• O

exhaust gas

temperature, 4o

f_ • /'\ •

OF

Model J I I i I I 0 o 10 12 2 4 6 8

Flight cycles, 1000

Model Agrees with Test Data Figure 8

FirstrunJT8D-9 engine

Sea level staticlStd day/Takeoff thrust

+6-

Percent

change

+ 4 - • .7Model P

in thrust

specific

fuel

+2-

consumption

i OK I l _ L I 0 2 4 6 8 10 12

Flightcycles, 1000

Figure 9 Model Agrees with Test Data First runJT8D-9engine Oamalle m 8,000 cy_s 4,000 cyms -2 E_] _ Fall [] Airfoilr_ Change _:_ Vzee bow Fan in -I • Vane leak_e efficiency, Clearance

points

HPT LPT +6 HPT _\\\, Percent + 4 HPT chanse ifl +2 flow Fan LPC HPCL_ LPT capacity LPT Fan LPC HPC Model Losses Derived from Teardown Data io F i gure First run JT8D-9 enginemodel Sea level statJclStdday/Takeoff thrust 60-

Change in 4o

exhaust gas

temperature,

OF 20

_" I 1 I I 2 4 6 8

Flight cycles,1000

Figure Exhaust Gas Temperature Increase Dominated by Hot Section First run JT8D-9enginemodel Sea level staticlStd day/Takeoff thrust B

Percent 4

change in

Hot section

specific

fuel

B

consumption 2

Coldsection 0_ 1 I I I 0 2 4 6 8

Flight cycles,1000

Figure 12 Thrust Specific Fuel Consumption Increase Controlled by Cold Section First run JT8D-9enginemodel Sea level staSclStd day/Takeoffthrust Damage mechanism 40_ [7 Erosion 8,000 cycles _J Airfoilroughness HPT 30_ [_ Vanebow BB Vaneleakage

Change in

[] Clearance

exhaust gas 2o_

temperature, 4,000 cycles

o F

HPT 10_ HPC LPC I Fan v;_7;_7/z4 LPT LPT O,

Total = + 22°F Total = +48°F

Figure 13 High Pressure Turbine Losses Major Cause of Exhaust Gas Tempera- ture Increase First run JT8D-9e_ne model 30,000 ft air/0.8 MnlStd day/Constant thrust Damagemechanism D Erosion r_ Airfoilroughness +1.5 [] Vanebow 8,000 cycles • Vaneleakage

Percent

[] Clearance HPT

change in

weighted+ 1.o 4,000 cycles

thrust

Fan

specific

Fan HPT fuel +o.,, I HPC

consumption

I i LPT LPT

Total = + 1.2% Total- + 2.35%

Figure 14 Cold Section Erosion and High Pressure Turbine Vane Bow Major Causes of Thrust Specific Fuel Consumption Loss

Hotsection repaironly

+70 AverageEGTmargin installedin aircraft +60 --

Change ÷ 50

in

exhaust +4o

gas

temperature, +3o

OF

+20 +10 | [ [ I _ I I I I I 2 4 6 8 10 12 14 16 18

Flightcycles,1000

Gas Figure 15 JT8D-9 Engine Multi-Run Model Projects Realistic Exhaust Temperature-Limited Removals

Hotsection repaironly

30,000 ft/O,80 Mn/Std.day/Constant _rust

Percent

change + 3

in

weighted + 2

thrust

specific + 1

fuel o

2 4 6 8 10 12 14 16 18

consumption o

Flight cycles,1000

Figure 16 JT8D-9 Engine Multi-Run Model Shows Importance of Cold Section Losses

Module Workscope

- All blades- SWECO clean,chamfercut Fan - All blades- SWECO clean,chordcheck, leadingedgeradius Low restoration,replaceas necessary pressure compressor - All stators - vaporclean,checkvane angle, re-angle as necessary - All blades- SWECO clean,chordcheck, leading edge radius High pressure restoration,replaceas necessary compressor - All stators - vaporclean,checkvane angle,re-angleas necessary Assumed Workscope for Compressor Restoration Figure 17 30,000 ftlO.8OMn/Std, day/Constant thrust Hot sectionrepair and fan/LPCrefurbishment Withoutcompressor _ refurb_hme_

Percent

change + 3

in

weighted ÷2

thrust

specific + 1

fuel

HPCrefurbishment I I I I J I I I I

consumption o

2 4 6 8 10 12 14 16 18

Flightcycles, 1000

Multi-Run Model Shows Benefits of Cold Section F i gure 18 JTSD-9 Engine Refurbishment 8O

• Weighted TSFCrecovery at refurbishment = 1.6%

Fan,LPC,HPConly

• EGT recovery at refurbishment = 21OF

• Payback period lessthanoneyear (typicaloperator)

Figure 19 Cold Section Refurbishment Cost Benefit Analysis