A feasibility analysis screening method for predicting the airline acceptance of a proposed engine performance improvement modification was developed. Technical information derived from available test data and analytical models is used along with conceptual/preliminary designs to establish the predicted performance improvement, weight and installation characteristics, the cost for new production and retrofit, maintenance cost and qualitative characteristics of the performance improvement concepts being evaluated. These results are used to arrive at the payback period, which is the time required for an airline to recover the investment cost of concept implementation, and to predict the amount of fuel saved by a performance improvement concept. The assumptions used to calculate the payback period and fuel saved are discussed. A summary of the results when the screening method is applied is presented for several representative JT8D and JT9D performance improvement concepts. An example of the input information used to develop the summary results is shown

Gaffin, W. O.

English

NASA Technical Reports Server

ENGINE COMPONENT IMPROVEMENT - 
JT8D AND JT9D 
PERFORMANCE IMPROVEMENTS 
W. 0. Gaffm 
Pratt & Whitney Aircraft Group 
SUMMARY 
A new feasibility analysis screening method for predicting the airline acceptance of a pro? 
posed engine performance improvement modification has been developed for NASA by Pratt & 
Whitney Aircraft, Trans World Airlines, Boeing, and Douglas Aircraft with consultation by 
American, United, Eastern and Pan American Airlines. This method uses technical information 
derived from available test data and analytical models along with conceptual/preliminary designs 
to establish the predicted performance improvement, weight and installation characteristics, the 
cost for new production and retrofit, maintenance cost and qualitative characteristics of the per- 
formance improvement concepts being evaluated. These results are used to arrive at the payback 
period, which is the time required for an airline to recover the investment cost of concept imple- 
mentation, and to predict the amount of fuel saved by a performance improvement concept. The 
assumptions used to calculate the payback period and fuel saved are discussed. 
A summary of the results when the screening method is applied is presented for several rep- 
resentative JT8D and JT9D performance improvement concepts. An example of the input infor- 
mation used to develop the summary results is shown. 
Based on the results of the screening method, NASA has selected several performance im- 
provement concepts for development and evaluation. 
INTRODUCTION 
The general objective of the NASA-sponsored Engine Component Improvement - Perform- 
ance Improvement (EC&PI) effort at Pratt & Whitney Aircraft is to demonstrate the specific fuel 
consumption benefits of JT8D and JT9D component improvements which have a good probabi- 
lity of production incorporation. A goal of 5% fuel saving over the engine lifetime has been estab- 
lished for each engine model. As the first step in accomplishing this general objective, a feasibility 
analysis with the following specific objectives has been completed: 
0 perform conceptual design studies of candidate component improvements; 
‘0 assess the performance improvement concepts in terms of economics, airline accepta: 
bility, and probability of incorporation into existing engines (retrofit) and into future 
production of current engines; and 
0 develop plans for the introduction of promising performance improvement concepts. 
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https://ntrs.nasa.gov/search.jsp?R=19780019109 2020-03-20T13:37:22+00:00Z
The second step in accomplishing the general objective consists of rig testing, engine ground 
testing, and engine flight testing to develop the technology and demonstrate the performance im- 
provement of selected concepts. This effort has begun on three concepts.’ 
DISCUSSION 
In arriving at desirable performance improvement concepts for development under the ECI- 
PI program, a long list of potential candidates was compiled. The more promising concepts from 
reference 1, the newer ideas being explored in the development groups at P&WA, and ideas sug- 
gested by NASA and the airplane and airline companies involved in the program were all included 
on this early “shopping list”. The general areas of performance improvements represented by this 
list are summarized on figure 1. 
The long list of concepts was reduced early in the evaluation effort to 28 candidates (11 for 
JTSD engines and 17 for JTBD engines), which were subjected to a detailed evaluation process. 
The reduction was accomplished by eliminating concepts with small fuel saving potential, high 
development risk, or other practical limitations. This preliminary screening effort was based 
mostly on qualitative judgements, supplemented by quantitative evaluations of critical parame- 
ters. 
The detailed evaluation procedure, which was applied to the 28 remaining concepts, was de- 
veloped under the contract specifically for the purpose of identifying the most promising fuel 
saving concepts for development under the EC&PI program. In developing the procedure, Pratt & 
Whitney Aircraft and its subcontractors were striving to duplicate or simulate as closely as pos- 
sible the decision making process that normally occurs when the engine and airplane manufac- 
turers offer equipment modifications (improvements) to the airline operators. The procedure is 
summarized in flow chart form on figure 2. The “bottom-line” results of this procedure are pay- 
back period, percent change in fuel burned, cumulative fuel saved and contractor ranking. Pay- 
back period is the economic acceptability parameter. The change in fuel burned indicates the day- 
today effect on energy conservation to be expected from each engine or airplane equipped with 
a performance improvement concept. The cumulative fuel saving shows the effect of incorporat- 
ing the concept in any situation where it is economically acceptable, and continuing to use it for 
the life of the engine. The contractor ranking represents the combined recommendations of 
Pratt & Whitney Aircraft and its subcontractors based on the other “bottom-line” results modi- 
fied by any qualitative considerations, such as development risk and hardware commonality, 
which were judged to be significant. 
The effect of each concept on the operational and economic characteristics of a typical fleet 
of airplanes on a typical route structure was evaluated using a computerized simulation. The 
spare engines and parts provisioning requirements were estimated by airline maintenance experts. 
The results of the economic evaluation of each application of a concept was compared to an ac- 
ceptability standard (required payback period) which was established earlier on the basis of air- 
line requirements. Only those applications which met or bettered this standard were considered 
for the cumulative fuel saving estimate step of the evaluation. The evaluation procedure was de- 
veloped and applied by a team which includes the manufacturers of the JT8D and JT9D engines 
and the airplanes in which they are used, plus several major airlines which operate this equipment. 
Pratt & Whitney Aircraft defined the effects of each component improvement concept on the en- 
80 
gine characteristics using standard design, evaluation, and pricing procedures, and also provided 
overall coordination of the evaluation process. The Boeing Commercial Airplane Company defined 
the effects on the 727,737, and 747 airplanes and the Douglas Aircraft Company defined the ef- 
fects on the DC9 and DC10 airplanes, using their standard design evaluation and pricing proce- 
dures. Trans World Airlines estimated the operational and economic effects in typical fleets and 
typical route structures using a previously developed computer simulation. American Airlines and 
United Airlines, serving as consultants to P&WA, BCAC, DACO and TWA, completed the evalua- 
tion team. Their function was to insure that the overall evaluations, and the TWA evaluation in 
particular, are typical of a major portion of the U.S. airline business. Eastern Airlines and Pan 
American Airlines served as consultants to NASA on this and other programs. Their efforts in the 
ECI-PI program served to insure that the evaluation results have even broader applicability. 
The general input assumptions to the evaluation procedure are summarized on figure 3. The 
fuel prices and maintenance labor rates were selected by NASA based on the recommendations 
of the evaluation team to be consistent with the values used in related studies. Projections of the 
future sales of JT8D and JT9D engines were established for the evaluation by averaging the indi- 
vidual projections made by the Pratt & Whitney Aircraft team members. The required payback 
period, which will be discussed later, represents a consensus of the airline members of the team. 
The fleet size and route structure used with each airplane/engine model combination were defined 
by the airline members of the team to be typical of the use of this equipment in U.S. airline ser- 
vice. The annual fuel usage for each engine model represents an average of the entire U.S. airline 
industry, as reported to the Civil Aeronautics Board. 
Perhaps the best way to explain the evaluation procedure is by an example. The evaluation 
of a modification to the JTBD high pressure turbine, applied at the time of engine production 
and as a retrofit to engines already in service, is summarized on figures 4 and 5. This modification . 
requires additional steps and processes in the manufacture of the cooled turbine blades and the 
associated outer air seal ring, which will increase the price of these parts and of the complete en- 
gine. These increases combine with spare engine and spare parts requirements to increase the total 
investment cost associated with each airplane that an airline buys. The higher parts prices also re- 
sult in an increase in the cost of materials used in maintaining the engines. However, the improved 
performance provided by the modification reduces the turbine temperature required to achieve a 
given thrust level, extending the time between engine removal for maintenance, and reducing the 
maintenance labor required per engine operating hour. The performance improvement is indicated 
by the thrust specific fuel consumption (TSFC) reductions shown on the figures. The TSFC reduc- 
tions combine with any engine or installation weight changes (there were none in this case) to de- 
termine the fuel savings that will result if the concept is used in the typical fleet on the typical 
route structure. The fuel cost saving follows directly from the fuel saving, and combines with the 
maintenance cost change to produce the change in annual operating cost per airplane. Dividing 
the incremental investment cost per airplane by the incremental annual cost saving yields the pay- 
back period. This estimated payback period must be compared to the standard defined on figure 
6 to determine the acceptability of the concept in each situation being evaluated. 
The maximum acceptable payback period was calculated based on investment criteria and 
tax rule interpretations defined by the airline members of the team. While the airlines did not 
agree exactly in detail, the net result of their respective criteria and interpretations was remark- 
81 
ably close agreement on the desired capitol recovery rate and resulting maximum acceptable 
payback period. For this evaluation, the economic life of a new engine was assumed to be 15 
years. It follows that the remaining economic life of a used engine being retrofit is 15 years minus 
the age of the engine at the time of retrofit. The maximum acceptable payback period then be- 
comes a function of engine age as shown on figure 6, with the high value of 6 years for a new en- 
gine decreasing to zero (instantaneous payback) for a 15 year old engine. Applying this payback 
period standard to the estimated payback periods shown on figures 4 and 5, it may be concluded 
that the concept being evaluated should be acceptable to the airlines in new purchases of the 727, 
737, and DC9, and for retrofit in 727 engines which are 4 years old or newer. The estimated pay- 
back period for retrofit in the DC9 and 737 (7.3 years) falls outside the acceptable limits, which 
means the airlines would probably choose to operate these airplane/engine combinations without 
incorporating the modifications. A practical consideration may arise which could reverse this lat- 
ter conclusion and it is described here to illustrate the limitations of the evaluation procedure, 
and to underscore the need for direct airline participation in such an evaluation. An airline which 
operates 727 airplanes and either DC9 or 737 airplanes might choose to retrofit all of its JT8D 
engines to maintain commonality, with the accompanying benefits of parts and engine inter- 
changeability, reduced spares inventory, and simplified maintenance procedures. 
Figure 7 illustrates graphically the procedure used to estimate the cumulative fuel saving 
that will result from incorporating the concept in every situation where it is economically accept- 
able. The “engine entering service” curve is based on actual airplane sales through the year 1976, 
and represents the team consensus projection from that time onward. The “engines being retired” 
curve is the “engines entering service” curve displaced 15 years to represent the assumed 15 year 
economic life of each engine. Only the JT8D-15 and -17 models are considered here since the 
concept being evaluated applies only to these models, which have cooled high pressure turbine 
blades. The start of service date for the concept was estimated to be January 1980, based on a re- 
view of the development effort required. The “engines entering service” curve of figure 7 projects 
about 800 engines to enter service between 1980 and 1990 (the cut-off date chosen by NASA for 
the evaluation). Since the concept is economically acceptable for all of these new engines, and 
will reduce their fuel consumption until they are retired 15 years later, the shaded area between 
the curves represents the number of new engine-years that are affected. The concept is also avail- 
able for retrofit starting in 1980, and will be applied to Boeing 727 engines that entered service 
in the 4 years before 1980. For convenience, the airlines would probably choose to install the 
modified parts when the engines come into the maintenance shop for other reasons. This will 
spread the introduction of the concept over the time it takes for all engines to return to the shop, 
approximately 3 years. This analysis assumes all of these engines will be retired when they are 15 
years old regardless of when the concept was incorporated. The retrofit engine-years affected 
would be represented by the shaded area marked on figure 7 if all three airplane models were to 
be retrofitted. Since only the 727 airplane engines were found to be economically feasible for re- 
trofit, the engine-years were reduced proportionally. 
The engine-years affected are combined with the average annual fuel usage of the JT8D and 
the percent fuel saving estimated for the concept to produce the cumulative fuel savings shown 
on figures 4 and 5, which combine for a total of 340 X IO6 liters (90 X 1 O6 gallons) of fuel saved. 
The evaluation procedure was applied to ah 28 candidate concepts, and the team then 
ranked the concepts. As shown by the flow chart in figure 8, NASA combined the results of the 
82 
evaluation with development program schedule and cost information supplied by the manufac- 
turers and NASA’s own technical and funding considerations to make the final decision to include 
a concept in the ECI-PI development and demonstration effort. The concepts thus selected are 
listed in figure 9 along with a summary of the evaluation of each selected concept. NASA has 
funded development of the three concepts included in the boxes in figure 9 and work has begun 
on the programs. The others are expected to be funded and started during the next several 
months. 
CONCLUDING REMARKS 
Under the NASA sponsored Engine Component Improvement - Performance Improvement 
Program, an effective evaluation process was developed and successfully demonstrated. Using this 
process, a team formed by Pratt & Whitney Aircraft and including representatives from airframe 
manufacturers and the airlines evaluated 28 performance improvement concepts and identified 
9 that were judged to have a high probability of meeting the economic and performance require- 
ments for implementation. NASA has funded development and demonstration efforts for three 
of the nine concepts and these programs are currently in progress. 
REFERENCE 
1. Gray, D. E.,: Study of Turbofan Engines Designed for Low Energy Consumption - Final 
Report. NASA CR-l 35002, April 1976. 
83 
Considered well over 100 candidate concepts derived from: 
Improved component aerodynamics 
Improved flowpath sealing 
Blade tip clearance control 
Improved turbine cooling effectiveness 
Improved turbine materials and coatings 
Duct and nozzle aerodynamic refinements 
Nacelle aerodynamic refinements 
Forced exhaust mixers 
Advanced nacelle materials 
Advanced fuel control 
Figure l.- General areas of performance improvement considered. 
PWA TWA 
BCAC AA PAA 
OACO UAL PAL 
/ Y m 
0pGtors 
Y 
I 
I 
I I I 1 
Periormanco Weight Price % 
Required 
payback 
period 
1 
I 
Route L 
ecanamic 
Market 
projection 
f 
l- 
1 
I 
Team 
ranking 
Figure 2.- Detailed evaluation procedure flow chart. 
84 
Fuel price 
Maint. labor rate 
Spares requirements 
Market projection 
Max. acceptable payback period 
Airplane model 
Engine model 
Fleet size 
City pairs 
Flights per week 
Avg. stage length, km (NM) 
9.2q/liter (35C/galI domestic, 1 l.SC/liter 
(45C/gal) international 
3OS/hr. (fully allocated) 
Variable 
Team consensus 
Function of engine age 
DC-9-50 727-200 DClO-40 747-200 
JT8D-17 JT8D-15 JT9D-59 JT9D-7 or -70 
18 39 28 11 
82 129 45 24 
714 1418 397 138 
889(381) 1093(5901 2987f1802) 5545f2994) 
pJl JT9D 
Avg. annual fuel usage, lo6 liters(gal) 
per eng-yr 
3.8(l) 11.3(3) 
,185OblO R781WI 
Figure 3.- Summary of evaluation input assumptions. 
A Price, S/eng 
+7400 
’ A Investment cost, .I 
+35,440/+23,800 
AMaint cost, S/EOH 
Matls +0.90 
labor -0.95 
AWeight, kg/eng 
0 
A Annual cost, $/yr 
A Fuel cost,S/yr 
-8720/-4300 
ATSFC installed, % 
TO -0.20 Climb -0.23 
Cruise -0.50 
Hold 0 
0.4 I 
Engine-years affected 
12,500 
Cum fuel saving, 108 liter (gal) 
189 (50) Jt-ll mm, 
Figure 4.- Evaluation of JTBD revised IWT outer air seal for 
new buy 727-200/DC9-50. 
85 
A KIT price, S/eng _ Alnvestment cust, $ 
I +10,500 +49,200/+32,800 
I ~~ 1 
1 
AMaint cost, VEOH 
Matls +0.90 
Labor -0.95 
AAnnual cost, f/yr 
-9lOD/-4520 
laWeip:.h 
AFuel cost, S/yr 
-8720/-43DD 
It 
1 Payback period, yr 
I Climb -0.23 Cruise -0.50 r \ 
I Hold 0 I 
Cum fuel saving, 108 liters (gal) 
151 (401 
Figure 5.- Evaluation of JTBD revised HPT outer air seal for 
retrofit.727-200/DC9-50. 
Payback 
period 
w 
Tax rules 
Depreciation method 
Investment tax credit 
Debt/equity 
Economic life of en6ine 
Capital recovery rate 
before taxes IO.17 new1 
Payback period 
before taxes 
6 IO 12 14 16 
Engine age yrs 
Figure 6.- Maximum acceptable payback period determination. 
86 
JT8D-15/17 in 727/737 AND DC9 
Cumulative 
no. of 
active 
engines 
2500 
/ 
I S-Concept start of service 
1 C-Time required to retrofit 
I on “convenience” basis 
M-Maximum engine age 
1’ , for retrofit 
01’ I 4 I / 
I I I 
1970 1975 1980 1985 1990 1995 2000 2005 
Begin calendar year 
Figure 7.- Cumulative fuel savings estimate procedure. 
Fuel savings 
Payback period 
Retrofit acceptability 
Contractor recommendations I 
Development 
planning 
Development 
and 
demonstration 
Figure 8.- NASA concept selection procedure. 
87 
I lllllllllllllllllllll II I I 
Total JT8D 
Start 
of Payback period* 
Fuel saving 
service Cum, lt$- 
date New Retrofit %I liters (gall -m P 
2.7 3880 (1023) 
Revised HPT outer air seal l-15/17) l/60 3.9/5.2 5.4/7 0.4 340 190) 
Root discharge of HPT blade cooling air l-15/17) 6/61 O/O o/o 0.6 960 12591 
Abradable. trenched HPC blade tips 3/61 1.2/1.4 5.0/6 1.0 2220 15691 
DC9 reverser stang fairing l/79 -/0.7 -/0.7 0.5 320 1651 
Total JT9D 3.4 9280 (24581 
Improved HPT active clearance control l-70/59] 6/79 1.0/2.1 6 /12 0.9 1770 (4661 
3.6 aspect ratio fan (single shroud) l-7) l/60 1.6/ - lO/ - 1.5 2720 (720) 
Trenched HPC blade tips 3/61 O.l/O.l 0.7/0.3 0.4 1660 093) 
Ceramic HPT blade tip Seals l/62 0.3/0.5 0.5/0.7 0.4 1950 1516) 
Thermal barrier coating on HPT vane platform l/62 o/o o/o 0.2 960 I2591 
*727/DC9 or 747/DClO 
Figure 9.- Evaluation results for recommended concepts. 


Engine component improvement: JT8D and JT9D performance improvements

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