Propulsion opportunities for future commuter aircraft

U NASA Technical Memorandum 82915

Propulsion .., pportuuxt cs for

Future Cor f i tnuter Ai rcraft

, N82-.26298 (NASA-TM-82915) PROPUL51IGN OPFORTUNISIES FUTURE COMMUTER AIRCRAFT (NASA) 27 P FOR CSCL 21B HC A 03/M F A01 Unclas G3/U7 28125 William C. Strack Lewis Research Center -.

Cleveland, Ohio Pill Prepared forjhe Eighteenth Joint Pro ulior Conference

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^^'a : , cosponsored by the AIAA, SAE, ASME ,and t~.

e Cleveland, Ohio, June 21-23, 1982 i

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PROPULSION OPPORTUNITIES FOR FUTURE COMMUTER AIRCRAFT William G. Strack National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 44135 Abstract airplane aerodynamics, structures, systems, and propulsion disciplines. These so-called Circa 1990 propulsion improvement STAT (Small Transport Aircraft Technology) concepts are discussed for 1000-5000 SHP studies were done initially by several air- frame manufacturers who assumed potential conventional turboprop powerplants including engines, gearboxes, and propellers. Cycle powerplant improvementsas Tiee mainly on selection, powerplant configurations, and judgment, To provide substantive evi- dense for these powerplant assumptions, a advanced technology elements are defined and series of complementary propulsion studies evaluated using average stage length DOC for was then Initiated by NASA with the General commuter aircraft as the primary merit Electric Company, Detroit Diesel Allison, criterion. The paper summari, ,.!os a series of and the Garrett Turbine Engine Company to five NASA-sponsored studies t,r4t addressed identify and evaluate specific engine tech- k this topic and assesses the significance of the resulting overall powerplant improvement nologies for advanced conventional turbo- potential relative to current production props.

powerplants, engines now in development, and To help focus these studies, guidelines were set forth (Table 1) that included spec- unconventional alternatives such as adia- batic diesels and regenerative turboprops. ifying the technology timeframe to be 1988 readiness--i.e., technology brought to a level that is ready for commercial develop- ment. This implies that engines using such technology could enter service in the early Text w 1990's. This was an important assumptiai

The rapi d growth of air transportation because the new generation of 1200-2500 ,HP

since the start of the jet age has wrought engines now in development will enter ser- W ever larger and faster aircraft to satisfy vice in the mid-1980's. Each company dense and long-range markets. Together with selected both a current production engine regulatory reform this trend created in- and a mid-1980's production engine as base- creasin g demand for aircraft designed spe- lines to measure the benefits of their cifically for short haul markets (fig. 1). advanced technology 1990's conceptual During the 1970's commuter passenger air engines (Table ?). All of these er;gines, traffic grew at an average annual rate of 14 whether actual or hypothetical, were scaled percent. This rapid growth is expected to during the studies to power conventional 30- continue--spurned on by the abandonment of and 50-passenger twin-engine airplanes designed to fly Mach 0.45 for 600 N.M.

air service to small communities by the However, Allison deleted the 30-passenger major airlines as a result of high fuel prices and deregulation, In 1980 commuter airplane and added a 50-passenger, Mach 0.70 airplane in order to complement Lockheed's airlines carried about 4 percent of air carrier traffic, but by 1990 the commuter STAT high-speed airplane designed for execu- portion is estimated to increase to 10 per- tive transport as well as for commuter use.

cent. Since current turbofan powered air- The required takeoff power for these appli- planes are too large and inefficient for cations ranged from 1300 to 5000 SHP. For successful sho t-haul applications, this completeness, Hamilton-Standard and McCauley market will be satisfied by increased num- investigated advanced propeller technologies.

bers a^d varieties of propeller-driven air- craft. Advanced En g ine Technologies In response to this increasing need, many new commuter airplane development pro- To enable a long list of candidate tech- grams have been launched as well as the nologies to be screened according to poten- development of several new turboprop power- tial value, 100 N.M. Dtage length DOC was plants in the 1200-2500 SHP class (e.g., selected as the single most meaningful cri- CT7, PW100, TPE 331-15). These new air- terion that properly reflects the relative planes and their powerplants will generally importance of diverse characteristics-- be somewhat larger than most of the current powerplant efficiency, weight, cost, main- commuter airplanes, utilize rather conven- tenance requirements, size, etc. On this tional configurations, and employ technology basis, fuel efficiency is the dominant advances already defined and well in-hand. driver since over 1/3 of airplane DOC is There are, of course, longer term technolog- fuel cost (fig. 2) and the sensitivity of ical opportunities that can be envisioned. both DOC and block fuel to engine weight, Such opportunities were the subject of cost, and maintenance cost is much less than recent NASA-sponsored studies that addressed for SFC (fig. 3) potential improvements in

Compressors T701.4 Items identified included: 1. Passive clearance control to reduce General Electric identified a 3 percent blade tip clearances by 15 percent 0.1 potential efficiency improvement over their percent DOC reduction) CT7-5 axi-centrifugal compressor while main- 2. Hybrid impeller rotor using HIP taining the same 17:1 overall pressure ratio bonding to attach a cast rim with blades to and reducing the number of axial stages from a forged hub which permits higher tip speeps 5 to 3. This could be accomplished by com- (-0.25t DOC).

bining four distinct technologies (figs. Garrett proposes the use of powdered 4-5): metal titanium for centrifugal impellers to 1. Highly loaded axial stages using reduce cost 25 . 40 percent witout compro- customized airfoils nising weight or performance. Garrott k. Split-blade centrifugal impellers also proposes a conprehensive parametr:t 3, Low-loss diffusers investigation of tip treatment configura- 4. Part-speed stall margin reduction tions (e,g,, slots) with the goal of improv- Advanced three-dimensional, high- spcF.,d ing compressor efficiency two points.

blade design technologies could provide the Combustors capability of accurately generating custom- ized airfoils tailored to the specific flow conditions experienced by each blade row. Combustor tochnologio y showing DOC pay- Applying these techniques to low aspect off included advanced materials for longer ratio axial blades would increase overall life, better cooling techniques, and better compressor efficiency by one point and per- fabrication methods (fig. 6). The use of an mit three stages to do the job of five. In oxide dispersion strengthened (ODS) material the split-blade impeller concept, the cen- such as 11A956 offers much higher operating trifugal stage is split into a separately temperature capability (+ 600 0P) than bladed inducer section and an impeller sec- conventional combustor materials such as Hastelloy X and HS-188, This could be tion. This permits the inducer section to handle the transonic flow more efficiently exploited to simultaneously increase life fourfold and reduce the quantity of required than a conventional continuous impeller blade by accommodating higher spanwise twist cooling air. The reduced cooling airflow gradients to better control both the blade means that more dilution air is available to loading and the passage throat contour to better control the discharge temperature avoid choking. Nigher inlet Mach numbers pattern. The more uniform temperature are permissible without causing separation p attern results in less severe cooling pro -

on the suction sid4 of the bl;.dos. In addi- lens for the high pressure turbine vanes

tion, a fresh boundary layer is initiated by and shrouds which should increase their life the impeller leading edge. The successful about 15 percent. On the other hand, ODS execution of this concept depends upon the material costs an order of magnitude more development of three-dimensional, viscous than conventional materials, incurs non- flow analysis computation methods not yet recoverable property loss in welds, and has available. A one to two point centrifugal unknown fatigue resistance. The higher stage efficiency improvement is passible. material cost would raise DOC about 1/4 The CT7-5 diffuser dumps low-speed com- percent and partially offsets the 1/2 per- pressor discharge air into a plenum, cent DOC maintenance cost savings for a nst deswirls it, then discharges it into the improvement of approximately 1/4 percent, combustor. An advanced diffuser could avoid Another approach which promises slightly the initial dump pressure loss by control better DOC improvement is the use of thermal lingthe passage contours to deswirl the barrier coatings (e.g., magnesium zirconate) applied to the hot side surface of the liner flow as it negotiates the radial-to-axial turn. This could increase the centrifugal and impingement cooling shields to increase stage efficiency one point. An additional the cooling effectiveness in the aft end one point may be achievable by reducing the section. This approach could yield a 50 diffuser throat blockage with wall bleed. percent liner life improvement and 15 per- These two sub-elements could contribute'a cent better HPT vane and shroud life with total of two points to centrifugal stage negligiable increase in engine price.

efficiency (equivalent to one point overall General Electric preferred this approach axi-centrifugal efficiency). Another con- over the ODS material technology.

cept to increase compressor efficiency (by Both Allison and Gerrett recommended 0.5 point) is the exploitation of digital transpiration cooling technology instead of electronic control system technology by conventional film cooling to increase com- adding a compressor discharge Mach number bustor life twofold. In one such scheme (M3) sensor to schedule acceleration fuel cooling passages are photoetched into sheets as a function of M3 on a closed-loop of liner material (fig. 6) which are then basis. The improved transient behavior stacked together and bonded. 4 Small could reduce the required surge margin sheets of this material are then shaped and allowance and ultimatelypernit higher com- welded to form the combustor assembly. To pressor efficiencies in the high speed oper- bring this concept to fruition, fabrication ating range (fig. 5). improvements are needed to produce lower Detroit Diesel Allison's compressor stress and temperature values in joints and evaluation also showed improved component bend radii. Conventional welding and performance relative to their PO 370-37 baseline (a turboprop version of the

forming techniques produce high local stress flow to adjust shroud dicmeter, but is rela- concentrations and restrict the cooling tively slow reacting. Neither nothod offers flow, M'`ter manufacturing methods are also a large improvement for short range comwruter r+equirod r decrease fabrication costs.

applications due to the short cruise dura- Another alternative to increase dura- tions, bility significantly (by a factor of 2) is to machine the liner which would eliminate Shafting hot spots due to shoot metal thickness tolerances and double thicknesses at overlap The pursuit of better engine efficiency ,ioints. This a? a rnative also needs more continues the trend toward high cycle pres- economical fabrication techniques since such sure ratio which dictates higher rotor a machined ring combustor would cost 50 speeds and smallor engine diameters. This percent more than one using conventional situation compounds the problem of transmit- techniques, ting torque from the power turbine through the high pressure spool to the propeller Turbines shaft, for these advanced engines it becomes impossible to use conventional Several advanced high temperature mate- forged steel shafts without incurring criti- rials were considered that would tower cool- cal speed problems (shaft speed passing ing flow penalties (e.g., cast single- through bending critical response speeds).

crystal nickel-base alloys and directionally The most promising solution to this problem solidified outectic alloys) in the core appears to be the use of metal matrix com- turbine. However, despite their increased posite shafts to increase the stiffness to engine efficiency potential of 0.71,2 per- density ratio about 40 percent (fig. g), cent, this advantage is outweighed by the This would permit subcriticai shafts thin much higher initial cost , nd maintenance enough to keep the turbine disk bore dia- costs of these materials, `5 meters small. The simular bore diamters There are DOG savings, though, asso- reduce disk stress level, enough to enable ciated with, Advanced turbine cooling tech- the higher turborrachinary rotation speeds nology, blade tip clearance control, and required to raisecomprossor anyr urbine hybrid material turbines. One recommended efficiencies with fewer stages.3- cooling improvement 1s the addition of lead- ing edge impingement film cooling passages Structure in the HPT blades rather than use the exist- ing practice of pure convective cooling Another problem aggravated by the use of (fig. 7). This could save 2 percent in r"uel fewer and more highly loaded compressor and as much as 1/2 percent in DOC for stages is the maintenance of tight rotor tip engines sized for a 50-passenger aircraft. clearances during periods of rapid thermal However, this technology is difficult to gradients and during surge and rotating apply in small engines and the DOC payoff is stall transients. It is important, there- cut in half for 30-passenger sized fore, to improve our capability to accur- engines. 3- 4 Cooling flow modulation was ately predict the tip clearance variation identified as another way to,.save fuel during periods of dynamic structural res- (0.0%) And lower DOC (0.4").0 ponse induced by rotating stall, for exam- To combat the problem of maintaining ple, (fig, 10). Current analytical techni- acceptable interstage leakage with rractical ques do not account for asymmetric effects production tolerances in these sma1 size in rotor/case coupled structural response.

engines, both passive and active blade tip These asymmetric effects include such items clearance control methods are attractive. as flanges and bleed manifolds that can be The passive seal concept (fig, 7) uses an very important to the structural dynamic abrasive blade tip coating and an abradable response.4 coated shroud to reduce the running clear- Apart from the engine itself, the use of ance without risking severe engine damaged composite nacelles rather than aluminum is during an emergency eng;no shutdown caused estimated to reduce weight 20-25 percent and by differential thermal contraction rates. reduce cost 25-30 percent. These improve- It also makes the engine more tolgrant of ments leygd to DOC reductions of 0.3-0.4 rotor offset caused by normal production percent.

tolerances, This concept has been experi- mentally verified, but needs additional Gearboxes research effort before production develop- ment,4 Improvement concepts for gearboxes are Complementing passive clearance control identified in figure 11. Split power gear- is the possible use of an active clearance trains such as the dual compound idler sys- control scheme whereby the tip shrouds are tem can reduce the number of gears signifi- moved radially inward to tighten running cantly which increases efficiency and tolerances during steady state conditions. reduces weight and cost. Externally mounted Both mechanical systems (Allison) and ther- propeller and aircraft accessories and lube mal systems (GE and Garrett) are envisioned system components, and on-condition mainte- (fig. 8). 3- 5 The mechanical system has a nance are design factors which contribute to rapid response time advantage, but is prob- less maintenance. High contact ratio gear- ably more complex and heavier than the ther- ing reduces gear tooth dynamic loads thereby mal system. The thermal system is con- producing smoother load transmission with trolled by modulating the cooling air less noise and vibration, as well as less weight.

Composite gearbox housings also Savo powered by a continuously operating blower weight. vacuum melt, high purity stools and a vaneless bleed driven ejector operated offer large improvement in bearing material At takeoff only to minimize porformance properties that could lead to weight savings losses (fig. 12). While both systems would and extendedbearing life. Bearing long iv, be quite effective in reducing FOD inci- ity can also be enhanced considerably with dents, the maintenance cost savings would advanced luMvicants exhibiting high film not offset the increased weight, cost, and strength and flat viscosity versus tempera- SFC of these devices. The powered swirl ture behavior. Collectively, these poten- vane system would incur a 2% DOC penalty tial improvements could raise gearbox effi- while the vaneless ejgctor type would cause ciency about 1/2 percent while reducing of 0.4% DOC increase. Despite these weight about 14 percent, cost 20 percent, penalties, some form of protector may never- and maintenance cost 80 percent. These theloss be necessary on the 30-passonger yield DOC reductions of 1.2-1.7 percont.3 sized engines to pass FAA requirements for bird, ice, and gravel ingestion,

Design-Features

Di n n ^ S tic Oata Recording, In addition to the advanced concepts just discussed, several design features were The current practice of scheduling considered that do not necessarily involve engine overhauls based only on the number of technology improvement, but do represent operating hours increases aggregate fleet departure from current design practice, maintenance costs since the overhaul inter- val is selected on the basis of the most Modular Construction severe duty cycle anticipated. The opposite extreme to regular overhauls is to overhauw Modular design to porn-it on-the-wing only when each life-limited part needs replacement of major componentgroups such replacement. But this alternative would as the gearbox, compressor, HP turbine, and also entail waste since the shop visit rate power turbine would facilitate easy mainte- would be needlessly high. An intermediate nance and has been frequently identified as strategy that recognizes the value of a desirable feature of any new engine. The replacing all parts approaching the and of new second generation engines, in fact, their useful life whenever a shop visit is incorporate much modularity to help reduce required is better Jhgn either of the above maintenance. Garrett and Allison incorpor- extreme strategies. It requires, how- ated modularity into their advanced engine ever, a good cycle life-prediction model and designs as well asother maintenance reduc- an on-board diagnostic systom to: (1) sense tion features such as providing extra and record the operational severity and balance material on high-speed rotors, duration for each key component, (2) compute threaded inserts to facilitate the removal individual component remaining life, and (3) of loose studs, welded assemblies rather display such data as maintenance and failure than brazed, and inserted rather than inte- alerts in the cockpit. As conceived, it gral blades. also needs the support of a ground based GE, however, reported that their modular data processing system to properly implement design actually increased DOC. Their modu- a fleet maintenance strategy (fig, 13).

lar configuration requires an extra bearing Thus it is more appropriate for larger oper- and sump in the turbine region compared to a ators who can afford this ground-based sup- non-modular configuration. This added port system.

complexity increases the part replacement cost which offsets the labor savings, Alternate Engine Ratings resulting in a small not increase in engine maintenance cost. The modular design also Several alternative rating methods were weighs more and costs more initially, and considered: (A) conventional flat rat n its overhung high-pressure turbine requires below a specified ambient tempera ure, o larger tip clearance to prevent rubs during reduce average service severity, (B) derat- maneuver load deflections (O.G't SFC penal- i1, which means installing the same sized ty). These adverse affects combine to yield engines as alternative A and having identi- a net 0.4% DOC increase. On the other hand, cal cruise power, but using less takeoff and concluding that a modular hot-end design is climb power, and (C) automatic power reserve detrimental also presumes that engine main- (APR), whereby the engine spry f sicaTly tenance can be performed overnight without downsized about 5 percent to lower cost, loss of revenue due to service interrrup- weight, and cruise SFC (higher throttle tion, Thus, it appears that airplane opera- setting) while still satisfying one-engine- tors knowledgable of their own requirements inoperative (OEI) requirements. 3 Derating and also aware of the above penalties can 10 percent reduces engine maintenance about best ,fudge the overall usefulness of modu- 1/3 due to lower turbine temperatures and is larity.

clearly advantageous (1.5% DOC improvement relative to flat rating) whenever conditions Fo r eign object Protection permit pilots to exercise this option--e.g., cold days, long runvays, low takeoff Both the frequency of major engine dam- weights, and low altitude airports. Auto- age and the rate of blade erosion due to matic power reserve involves tradeoffs bet- foreign object ingestion can be reduced with ween lower inlet protectors. Two types were Con- sidered: a swirl-vane scavenge system

,maintenance cost. This result was reported initial cost, lower engine weight, less fuel by both General Electric and Garrett who burned, but greater maintenance cost due to higher climb and cruise turbine temper- limited pressure ratio to 17. Out Allison dropped the ono-stage HPT because the high atures. The net result for APR is al,most no equivalent stag o work (44 BUM) and expan- DOC change relative to flat rating.

sion ratio (5.3) required to power the 20:1 The above examples illustrate the diver- pressure ratio single-spool compressor they sity of ideas that surfaced during the course of these studies. Tables 3 and 4 selected is too far beyond the current state-of-the-art to obtain favorable effi- provide exanple lists of selected technol- ciency compared to a more lightly loaded ogies and their fuel and DOC benefits.

two-stage core turbine.

Compressor efficiency could be increased 2.4 Turbanachinery configurations, cycles, percent, turbine efficiencies increased 1-2 percent combustor durability doubted, gear- and major characteristics of representative box efficiency increased 1/2 percent and engines are illustrated in figures 15-18.

cost reduced, nacelle weight reduced 25 All are conventional free turbine configura- percent, and so forth. None of the turbo- tions with the sole exception of GE's machinery technologies individually yields boosted free turbine configuration for their larger 2125 SHP engine. In this case, GE largo DOC benefits, but collectively they opted for 20:1 pressure ratio rather than could lower DOC by 5-6 percent and fuel consumption 8-9 percent relative to the new 17:1 to reduce DOC 1 percent. This may be achieved by driving a booster stage with the 1983 engines.

power turbine--this avoiding a second HPT Enaine Cy cles and Configurations stage (17:1 requires an expansion ratio of 4.2 which is about the upper limit for a The scope of these studies included the one-stage HPT). Cross-sections of bath the determination of appropriate thermodynamic GE 30-passenger engine and the GE 50- pas- cycles and engine configurations in addition senger engine are shown in figure 15. These two advanced engines are scaled to 1625 SHP to the identification of component Improve- to facilitate comparisons with the CT7 which ment concepts. Various engine confi.gura- tions were considered such as single shaft, is shown in the upper half on the each dia- gram.. The better cycle and higher component free turbine with single or dual-spool cores, and boosted versions of the simple efficiencies of the 50-passenger version results in greater SFC and weight Improve- free turbine layout. Different staging arrangements were also investigated includ- ments, but less maintenance cost improvement.

ing single and dual stage centrifugal, axi- The only all-axial compressor is centrifugal, and all-axial compressors, and Allison's 5025 SHP design (fig, 16) which

oneor two-stage high pressure turbines. The was reported to have a 2-percent efficiency

screening of these options was generally advantage over an axi-centrifugal arrange- carried out at the same time cycle temper- ment in this size class. Allison's 2495 SHP ature and pressure levels were selected design utilized a six-stage axi-centrifugal compressor arrangement at 20:1 pressure since these parameters are interrelated.

The overall procedure was carried out using ratio and a two-stage HPT as mentioned above projected advanced component characteristics (fig. 17). It also utilized an in-Line including maintenance cost, acquisition gearbox rather than an off-set type as used cost, size and weight as well as performance in all of the other designs.

since DOC was the main selection criterion. Garrett'stwo engines spanned a rela- Cycle and staging arrangement selections tively narrow size range (1842 to 2384 SHP) were based mainly on minimum DOC, but were which prompted their decision to retain only biased toward somewhat lower than optimum a single design. Although figure 18 shows a turbine inlet temperatures in recognition of twin-centrifugal compressor driven by a material limits and associated technical two-stage HPT, this only represents risk (fig. 14). 3 This process yielded Garrett 's initial definition which was sub- 17:1 to 20:1 compressorpressure ratios sequently revised to a one-stage HPT for use (CPR) and 2250 O F to 2500 9 F maximum tur- at 16:1 pressure ratio. They also recommend a 20:1 axi-centrifugal which requires a bine rotor inlet temperature (TRIT) which represents large improvement over existing two-stage HPT, but yields even better per- formance and lower DOC albeit at higher production engines, but lessor increases research and development cost.

relative to the new crop of mid-1980's The advanced technology STAT engines engines: Would be about 25 percent more efficient Existing Mid-1980's Future than same-sized current production engines and 8-16 percent better than the second 10-11 14-17 17.20 generation of engines now in the final CPR Max. TRIT, of 2000 2000-2300 2250-2500 development stages (fig. 19). They would also weigh 10-20 percent less than the Since SFC has much more impact on DOC second generation engines, cost within 10 than any other parameter, figure 14 nearly percent, and require significantly less maintenance (fig. 20), At 100 N.M. stage replicates that of the usual SFC versus pressure ratio type. However, whereas a lengths these improvements lead to 10-23 percent trip fuel reductions and 7-22 per- two-stage high pressure turbine (HPT) is SFC as the criterion, a one- cent DOC reductions depending on the optimum using stage HPT shows up optimum on the DOC plot selected baseline engine and engine size

due to the savings in initial cost and (fig. 21). For longer stage lengths these

benefits generally increase somewhat as right propellers can be synchrophased to figure 22, shown in within 4technically challenging one degree. Applying this source noise Propeller Technology reduction to a 30-passenger, Mach 0.45 com- muter required to meet an 05 dD OASPL cabin The smaller commuter aircraft use noise constraint would eliminate 044 pounds general aviation type propellers which are of fuselage acoustic treatment otherwise relatively simple and low performance com- needed in a wing-mounted propulsion config- pared to the more sophisticated technoloty uration. Of course, if the noise constraint employed in the larger commutor airplanes.

(D-737 cabin level) were met by mounting the The low cost propellers are typically con- powerplants onthe airplane tail this gain structed with solid aluminum blades having is absent, In fact, without a no con- circular shanks which contributes to low straint the propeller design would be reop- performance and high weight. The more timized and the fuel improvement would be sophisticated propellers, on the other hand, reduced about 2 percent as indicated in the utilize such weight-saving construction summaryfuel and DOC benefit chart (fig, 24).

techniques as aluminum spar-fiberglass shell The McCauley study of propellers blades and such performance improvements as designed for 19-seat, Mach 0,45 airplanes airfoil shanks, advanced airfoils, and low identified similar technologies, Although activity factors. the benefits were only quoted relativo to Despite the high performance levels moderate performance general aviation type currently available or in development (0.87 propellers (fig. 25), the benefits relative cruise efficiency), the STAT technology to current state-of-the-art commuter propel- studies by Hamilton-Standard and the lirs would be similar to those mentioned McCauley Division of Cessna have iddentified above, important further opportunities. 6-7 A summary of the Hamilton-Standard Complete Powerplant Benefits defined improvements is shown in figure 23 for a 30-passenger low speed design. The Figure 26 summarizes the STAT powerplant fuel savings relative to current general study results. Potential incremental aviation technology has been separated into improvements in all turboprop components low-risk and high-risk portions as viewed by plus the propeller lead to sizable total the author. "Low risk" implies that the powerplant improvements in efficiency, already avail- required technology is either, weight, maintenance, and noise, The lower could be through normal industrial able or values listed on the figure denote average R&T effort, and "high risk" implies that improvement potential relative to the second additional long-term R&T effort is needed generation engines while the higher values beyond normal industrial activities. Of the denote improvements relative current to 16.8 percent total fuel savings, 9.3 percent first generation powerplants. The conserva- is attributable to the difference between tive propeller improvements of figure 24 existing general aviation technology now were assumed (i.e., gains maasured against under development and mid-80's commuter the modern technology commuter propellers technology now under development (i.e., now in development and no credit for preci- low-risk portion), while the remaining 7.5 sion synchrophasing). The trip fuel savings percent represents high-risk future oppor- and DOC benefits are also listed in pairs tunity. For example, while the new 14 RF/SF with an identical interpretation implied.

seris propellers will utilize a new family These potential gains are large enough to of airfoils designed specifically for the conclude that the future for third genera- DeHavilland Dash 8, another 1/4 point in tion 1500-5000 SHP turboprop powerplants efficiency is thought to be obtainable holds as much promise over the new second through advanced airfoil research. Proplets generation powerplants as the second genera- are high-risk and offer nearly a 2 percent tion holds over the first generation.

fuel savings through reduced tip losses.

Toward Hi g her Increasing the number of blades improves Risk and Greater Pavoff efficiency, but requires advanced materials and construction techniques to maintain Notwithstanding the importance of the sufficient blade-retention strength in the STAT studies and the general conclusion ,lust thinner root sections. Blade activity fac- drawn, there is some evidence that consider- tors of 70 are needed to achieve this gain ably greater opportunities exist involving (the activity factor of the 14 RF/SF series revolutionary engine technologies. It is will be 91-93) which, in turn, assumes the commonly recognized that small turbine use of advanced techniques such as a steel engines have considerably lower thermal or metal matrix spar with a Kevlar or graph- efficiency than large ones. Current 1500 ite shell--possibly load-sharing and tail- SHP class turbine engines, for example, have ored to increase critical speeds. Although thermal efficiencies near 27 percent com- counter rotation offers a theoretical effi- pared to 37 percent for 20,000 SHP machines ciency improvement, the gain is too small to (fig. 27).

warrent the associated higher level of com- The fundamental reason for the poorer plexity. small engine efficiencies is the practical Experimental evidence on a T56-powered size limit (about 1/2 inch) of small turbo- P3 indicates that a 6-8 dD OASPL reduction machinery airfoils. This limit is set in cabin noise is possible if the left and partly by our inability to manufacture very

small blades with the necessary accuracy in engine, an advanced conventional cycle tur- airfoil profile, blade angle setting, and boprop could save 10 . 20 percent in fuel not intricate cooling networks, and partly by including advanced propellers or nacelles.

adverse aerod namic scaling effects such as y The fuel savings for unconventional engines disproportionately high tip clearances and are considerably greater--as much as 30-35 low Reynolds number surface roughness loss, percent for the rotary, diesel, and regoner- Together with material temperature limits, ative turbopro{ { ^ r , and 40 percent for a cer- these constraints limit cycle pressure amic, intercooied version of a regenerative ratios and turbine inlet temperatures to turboprop. Gainsof this magnitude clearly relatively modest values (fig. 27).

represent quantum Improvements and go beyond Besides striving to increase componert the customary evolutionary trend. Of efficiencies, at least two other approaches course, the particular values assigned to are apparent to mitigate these small engine the various candidates are subject to uncer- limits. One is to substantially eliminate tainty due to the iiihorent technical risk the material temperature limit and the asso- with such concepts. If necessary, this plot ciated turbine cooling penalties. This can be used to quickly redetermine the fuel might be achievable with advanced ceramic benefits for alternative engine assumptions.

technology or refractory metal matrix com- The results just quoted apply to engines posite technology. Efforts have already in the 1500 SHP class. For smaller engine started in this direction in the government sizes the unconventional engine benefits sponsored ceramic automotive engine pro- would be somewhat greater and for larger grams. To be sure, this approach is quite engines gust the reverse Is true. This risky since the technology is immature and trend occurs because the main fuel driver is the component reliability problems are very SFC and the SFC advantage of the unconven- challenging indeed. But success could raise tional engines decreases with increasing turbine temperature levels 300 . 400 OF and size (since the conventional turboprop would essentially eliminate the turbine becomes more efficient in larger sizes), cooling penalties.

The other approach is to partially Concluding Remark recover the waste heat in the exhaust flow by transferring it to the combustor inlet The principal message to be gained from airfl ow--regeneration. Regenerative cycles these studies is that several very important obtain high efficiency without the need of propulsion opportunities still exist for high compressor pressure ratios (values near commuter air transportation. Powerplant 15 are usually optimum). Hence, these technology has not been brought to a plateau cycles are especially attractive in small status or even a diminishing return status.

engine sizes. Recent Army sponsored Studies Significant improvements are feasiblein at 500 SHP show efficiency gains of 10-20 both the short term and the long term with percenj compared to the simple turboshaft risks ranging from moderate to very high.

cycle, while other military studies involving 5000 SHP engines show only 5-7 References percent gain, The main drawback of regener- ation is the extra weight required by the 1. L. J. Williams and T. L. Galloway.

heat exchanger system which is estimated at "Design for Supercoruiiruters" Astronautics and 30-50 percent of the simple cycle weight in Aeronautics, Vol. 19, No. 2, Feb. 1981.

small sixes, but perhaps 100 percent or more at 5000 SHP. The technical challenge is to 2.

L. J. Williams. "Advanced Tochnology manufacture the heat exchanger compactly and for Future Regional Transport Aircraft,' SAE leak-free, and to survive the corrosive Paper No, 82031, May 1982.

environment and thermal stresses induced by engine on-off cycling. 3. C. E. Smith, ot. al .

"Propulsion System Each of these approaches, if applied to Study for Small Transport Aircraft Technol- commuter sized powerplants, could increase ogy (STAT)," General Electric Co., Lynn, engine efficiency about 17 percent above Mass., May 1981, (NASA CR 165330).

comparable technology conventional engines (fig. 28). If both ceramic and regenerative 4, J. C. Gill, et. al, "Propulsion Study technologies were used together, substan- for Small Transport Aircraft Technology tially higher gains are possible--as much as (STAT)," Detroit Diesel Allison, Indiana- 40 percent beyond an advanced conventional polis, IN, Dec. 1980, (NASA CR 165499).

cycle, for a total gain of 55 percent beyond the new crop of mid-1980's turboprops. The S. C. F. Daerst. et. al. "Small Transport risk and resources required to establioh the Aircraft Technology (STAT)," Garrett Turbine technology is, however, considerable higher Engine Company, Phoenix, AZ, May 1982, (NASA than for the conventional engines. CR 165610).

Figure 29 shows how fuel burned varies with cruise DSFC and engine specific weight 6. I, D. Keiter. "Impact of Advanced for a typical 30-passenger, Mach 0.45 air- Propeller Technology on Aircraft/Mission plane. Spotted on this parametric plot are Characteristics of Several General Aviation the estimated values for all of the above Aircraft," SAE Paper No. 810584, April 1981.

discussed turboprop powerplants plus several advanced intermittent combustion eng^nes 7. R. G. Daigneault and D. G. Hall.

(IC) discussed in a companion paper.

Relative to the mid-1980's new

"Advanced Propellef Technology for the Novi Commuter Aircraft," SAE Paper No. 820720, May 1982.

"A Comparative Study 8, A. E. Easterling of Simple, Regenerative, and Variable Capa- city Cycles for Gas Turbine Engines," Array Aviation Research and Devotopmont Command, St. Louis, 140, USAAURADCOH-TR-81-D-1, October 1900, 9. E. A. Willis. "Development Potential of Intermittent Combustion Aircraft Engines for Commuter Applications," SAE Paper No.

820718, May 1902.

TABLE 1, - STUDY GROUNDRULES * GOO HIM. DESIGN RANGE (PLUS IFR RESERVES FOR 100 N,M, ALTERNATE AND 45 MIN, HOLD) • 4000 FT. FIELD LENGTH ON 30°F DAY AT SEA LEVEL • 250 KNOT MINIMUM IAS FROM 6000 THROUGH 10000 FEET s 180 KNOT MINIMUM IAS WITH GEAR AND FLAPS EXTENDED 93 KNOT MAXIMUM STALL SPEED IN LANDING CONFIG, AND WEIGHT • FAR 36 STAGE 3 MINUS 8 EPNDB NOISE LIMITS s 85 DB OASPL MAX. CABIN INTERIOR NOISE • TECHNOLOGY MERIT CRITERIONi DOC AT 100 N.M, STAGE LENGTH TABLE 2, - BASELINE ENGINES ,._-rALLIJU1L_._ IFNE69L.ELECTRIS_ BASE 1 BASE 2 BASE 1 BASE 2 BASE 1 BASE 2 CT7-5 CT7 .

T701 T701 CERIV. 331 -11 331-15 5 DERIV, ENGINE DESIGNATION 1979 1986 1980 1984 1983 1986 YEAR OF INTRODUCTION 2250 2250 2004 2945 2290 2390 TURBINE INLET TEMPa OF 12.7 17.7 1016 10,8 16,9 20,8 COMPRESSOR PRESSURE RATIO SEA LEVEL STATIC, 59 °F 8935 11600 1045 1712 1630 ESHP, HP .419 /HP-HR 373 .531 482 .451 -u .430 ESFC, LB

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BY CAMETT W I F, 331- 11 DA ELINE)

100-N. M. MOSION, ^1.00/GA 17U13 r c'nt' ange k er in Pe c n e 50 30 Pax nx ax ax - (gq_fGPreee_pC 1 Powdered Aluminum First- - 0,07 -0.05 -0.04 0 Stage Centrifugal 2 Powdered Titanium Se0no o - 0.22 -0.12 0 stage Centrifugal +2.07 3 Bingle-Stage 1211 +3,13 +3.86 +3.47 Centrifugal 4 Two-Stage 2011 Centrifugal -0,30 -0.40 -0.81 -0,74 5 2011 Axial-Centrifugal •0.80 -1103 -2,44 -2,28 (4 and 5 Axial Stages) -0.33 -0.62 -2,44 -2,27 6 2011 TWO -Upool Axial.- Centrifugal High-Pressure Turbine +0.33 7 single-Stags HIRT -1,21 -0,77 +0.38 +0.79 0 Uncooled 11477 K (2200$x) # +1.06 +0,44 +0$5 j CAS, 14A 6000, SC) 9 Cast Blades (SC, NASAIR- +0058 +0011 -0.29 -0,32 100) 10 Tip Treatment - 0,40 -0 . 42 -0.44 -0,46 11 Cooling Flow Modulation - 0,40 -0.42 -0.44 -0.46 Active Clearance Control -0,43 -0,35 -0.36 12 -0,48 0 +0.03 0 0 13 Net Shape PM Disk +0 11 (1500 610 Disk -0109 0 14 1089 K -0.07 0 Alloy Low-Pressure Turbine 15 Active Clearance Control -0.58 -0058 -0,64 -0.63 Titanium - + 0.33 +0.23 0 0 16 Aluminide Second Stage Single-Stage LPT +0.65 +0.60 +1.27 +1.10 Gearbox 18 Laser Hardened Gears - 0,13 -0.11 0 0 19 Roller Gears +0.51 +0.45 +0005 +0.04 20 Composite Housing +0.56 +0.39 +0.01 0 SPF/DB Gearbox +3.06 0 0 21 +3,80 Combustor + +0.02 0 0 22 Machined Ring Burner 0.02 23 Photo Etched Burner - 0.15 -0.12 0 0 TABLE 5. - DESIGN FACTOR RANKING [;ppc 30 PASSENGER 60 PASSENGER O_ VG^ A 1 _ iTEN ;1.Op/GAL ;1.50/Ga1 fl 0?/GAL j^;1.50/GAL BARK WOULAR CONSTRUCTION +.41 +.46 +.46 .50 4 VANILE°,S W +.39 +.44 +.46 +152 3 •.77 01AGN05TIC OATA RECORDING •.09 -1.01 -.85 2 10 % OCRATQ ti1.50 -1.41 •1.37 •1.22 1 r.

O F PO OR Q

tot of IRArfIc

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♦ IT IRAFfIC ""

of Us$# tote[ T a., AIAPLAN[ (^ ' K tN CI:1190ULA110 ACT r 1py^ ^t0/i641N1i Iwt4F@ ♦411,111{. AIANOIN

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^ i-' INTAO '

or TURIOPROPI ON Nit 1 TWIN 01190 49AT LINIT1 1 t e:j U

1 090

601 170 176 1Q0 YEAR Figure

1. - Commuter aircraft marketplace expanding rapidly, Passenger

traffic grew 11% per annum during 1910`s.

11011 uun FULL ANO OIL

u0%

CURRENT TECHNOLOGY COMMUTER

eaew

19 PASSENGERS

13x

ENGINE AIRFRAME MAINTENANCE MAINTENANCE 17%- 15% INOURANC AND PROPULSION RELATED REPRECIAiION

lax

TOTAL DOC a 12.3 t PER SEAT s, ml.

Figure 2. - Commuter aircraft direct operating costs -1981 dollars, $1.251gal fuel, 100 n, mi, trip.

' ' M y rJ y^ }^ In a i( '' A ^ i^

Doc

FT F +10% +10% SFC • COST WITT °' MAINTENANCE O HEIGHT -1O% -10% -10% 0 +10% -10x 0 +10Z 'INCLUM PAM B 14AINT(NAIKC Figure 3. - Stol 30 - passenger airplane sansltivities -100 n, mi,, engine and #earbox, :1, $01941, 19191, CUSTOMIZED AIRFOILS SPLIT-PLADE IMPELLER ADVANCED DIFFUSER

I

C,. y k.

V L

a TAILOR AIRFOILS FOR N SPLIT ENERGY INPJT INTO • CONTROL CONTOUR PASSAGES

AIM

LOCAL FLOW CONDITIONS TWO REGIONS TO ELIMINATE TO DESWIRL FLOW & FORM GEOMETRY CONSTRAINT RADIAL TO AXIAL 'TURN • USE WALL BLEED AT THROAT TO REMOVE BOUNDARY LAYER ACCURATE 3-D VISCOUS FLOW ANALYSES a EXPERIMENTAL DATA BASE FNARLEMEND e + 1% OVERALL EFFICIENCY • BETTER CONTROL OF BLADE w RFOUCc PRESSURE LOSS 6ENEM LOADING (+ 1% OVERALL EFFICIENCY) • FEWER STAGES (3 VS, 51 • FRESH BOUNDARY LAYER (+ 1% OVERALL EFFICIENCY) Figure b, - Compressoraerodynamicstechnology, - l:--

OtTZINAL f,'

OF POOR QUALc7l'

I.

ca^e BE:a;;^i nw

DESIGN POINT (ADVANCED) ^' auaal ^^syM^ ^ ^ ^ ) ' PRESSURE DESIGN POINT (1"0) RATIO scc; '^^c``^ IL MARG1 PART POMER FLOW —^ COPR r CTFD Figure S. - Increased compressor efficiency via reduced surge margin. Requires closed loop engine acceleration control using digital electronics and compressor exit mach number sensor.

n

-- AFT PAN(` IMPINGEMENT 'RANSPINATION COOLED \ COOLING SHIELDS

R MATERIAL ---^

e -606oF TEMP. G ► Aa1LITY e LOMER METAL TEMPERATURES I LINER LIFE QUADRUPLED e LESs COOLING AIR REa'D e BETTER HPT TEMP. PROFILE e LONGER L;FE (SOI) e EX PENSIVE n Figure 6. - Advanced combustor technologies.

ORIGINAL PAGE 18

OF POOR QUALITY'

ORMAN [ SHROUD - `_ ADRASIVF TIP CAST-IN UCLIVFRY PASSAUS TIP SCAT CONCIPT IMPINGIMINT C00II1) AIRIORS Figure 7, » Advanced luttflne technologies, TIIIVMAI "Y"TIM ON°arr vntVt POOLING We__ ^N t

r(^-lilt

c^ t I ^ t I #

ii

UNCROSS nATCnF p M11,111CR MOVIS MIAILY SIIRODU SRAIMB AT CRUiSI' OUF TO Figure R. - Active clearance control concepts for turttlnes,

.o. lial t rims IECHN41,t?i'ix QDymaE s FINITE ELI NT ANALYSIS FOR LAMINATES 40% GREATER CRITICAL SPEED • MANUFACTURING FEND FITTINGS, BIASED • REDUCED DISK BORE SIZE PLY LAYUPS) o LOWER DISK STRESS • HIGHER TIP SPEED TURBO- MACHINERY Figure 9, - Metal matrix composite shalt technology, Rotor fa Stoll lone speed Figure 10, - Rotating stall phenomenon,

OF 0 R QUALITY`

p

0^

-0

r L-- a TFC11N(11QUY, ADVANCen CURRENT TECHNOLOGY DUAL COMPOUND IDLER PINION-BULL-STAR

6 GEARS/10 BEARINGS

9 DEARS/17 BEARINGS CXTERNALLY IMOUNTED AssESSORIEs NON-MODULAR IIIGH rONTACT RATIO TOOTH PRorILES CONVENTIONAL TOOTH PROrILrs 111011 PURITY STEELS CONVENTIONAL STEELS ON-CONDITION MAINTENANCE FIXED OVERHAUL INTERVALS +Q,'ab BASE ErricieNCY -1S K AFUEL l -1,0 . 1,3 WEIGHT ABOC

COST -22 % 1 -1,2- 1,7

11II MA INTENANCE Flguro 11, -Advanced gearbox technologies, Figure 12, - Vaneless particle separatorMoreign object protector concept,

Oii; N&L P.4t

v ^

OF

P

OOR

QUALITY

141' 111 teal (ofti?a Mot yltti l.r NIfIYN / '1'NI YTIII rN 1t^.1 . /IwrlYry.l .iy rNe 4111,4111 .nY'la awl r / M Nuel 1 lInrlYvo.l ^ r 114 11411,11 hM Nf".

lrl i r%

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ll My

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Figure 13. - Powerp l ant monitoring system for reduced maintenance.

10 (-STAGE HI'T P - STAGE HPT * AD TURBINE Ir^ET TEMPERATURE 1830 'F 51 \ 1980 IF I 2900 \ 2500 If rF 2500 'F LP BOOSTER ADDED - 15 1 1-- 1 1 --1 - -' 10 IS 20 25 s0 95 COWRLSSOR PRESSURE RATIO Figure 14 - Advanced commuter engine cycle selection - 100 I n. mi. DOC. S 1 501ge1 fuel, 70 passenger, Mach 015, 1500 SHPUNG.

ORIGINAL RAG^ IS

OF POOR

QUALITY

30 PAX MH 0.45850 p AX Mn O.-A5 CTI W. TF014OLOGY

AaY9Nr.Ea r.KJ= . _

r CT7.. q V PAX c0 PAX 2290oF 23DOOF TURBINE T[MP, 2400OF 17 20 PRESSURE RATIO 1619 X46 •9x CRUISE; we -14% WEIGHT 1070 La a9% -11% COST BASE -11% -12% MAINTENANCE COST BASC -21% •17% Figure 15, - Advanced technology small transport engines, General Electric designs scaled to 1625 SNP, 90 0 F.

___ ._x ^_ u 5025 FSNP (SLSS) ESFC 1366 WEIGHT (INCL. GEARBOX) 879 2250 or TIT P/P 20 Figure M - Detroit diesel Allison engine and gearbox schematic A1ach 0,70 aircraft (50 passenger),

OF

POOU

QUALM'f

If

F S 111, firc 11103 WEIGHT (MCL, GEARBOX) 703 LU TIT P110 or P/P Figure 17, • Detroit diesel Allison engine and gearbox schematic - Mach 445alrcraft ► 50 passengers) ._- I— – I 52.5 31,0 INCHES

, I ^ ^i

0 PASSENGER AIRCRAFT 50 PASSENGER

AIRCRAFT --1 —— -- . —, Al' SHAFT I 1812: CRUISE StC Ills .41S WEIGHT UNCL, GEARBOX), 1,B 623 824 TURBINE TFMPFRAIURr, OF 2 350 COMPRESSOR PRESSURE RATIO Figure 18, - Garrett advanced technology small transport engine,

INAL

ORIG

Y

pooh QUALIT Y

OF ^'

,GO , R1Ge34 ,55 CURRENT

31.11 0=

I

Sl:$S ,50

T

LASFC, • 631 20%

, VERIvAtivE

LBAP-HR .4a cy, * C11

• °IIERIVATIVE 10%

• STAT ,40 • .

1--j-°-

1000 1500 2000 2500 '000 • 5000 5500 111E M00YN/N11C ESNP Figure 19. • Turboprop efficiency levels.

8C FIRST GENERATION

sr11 g 1u1Tn oeewuuta^^,.^

5o -0©K

EM. ru. M SECOND GENERATION k ARVANS ED TECHNOLOGY • On-CONtl1TlON OYGT:IU 0 i tUNVITION hQnl NRO • 1WROK0 PC61AOILITY

0 1 000 C1u00 30 00 4000 50

RATED SNP

Figure 20. -Maintenance cost reduction -100

n, m. stage length.

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4 L F P01r tl,u Ir

FUEL BURNED Doc

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is

to

s

GE GAr,OETT hLIGON GE GARNETT &LIGON C17.5 331.11 1701 4- PAULINC CT7 . 5 331 . 11 1701 FN }INEG COUD) Figure 21, - Advanced engine benefits summary - 30°50 nax,

Mach (145

70, TRIP LENGTH. N.H.

0 100 Roo B oo 100 Boo 000 M nuwATM

•

n FUEL 10 ,e ,.

BURM 80 PAX -Rp U0 PAX 0 100 200 Soo 100 500 1300 i O CTr it VATM DOC -5 t•1,50 `^ 00 PAX -10 50 PAX -15 -20

Figure 22. -Fuel and DOC savings » GE CT7-5 base-

line,

IS

ORIGINAL PAGE OF POOR QUALITY 90 PAX. MACH 0.47 I LOW RISK I I HIGH RISK ADVANCED AIRFOILS =3 0.6 PROPLETS ^ I.V INTEGRATED BLADES,SPINNER BETTER rIATERIALS (YT ONLY) 9.4 4.d .

MORE LOW-A F. BLADE S DESIGN OPTIMIZATION 2.s PRECISION SYNCRO11HASING 2.2 COUNTER ROTATION ::3 0.4 (OPTIONAL) 0 1 2 9 4 5 • >ti FUF^L SAVINt;S RELATIVE TO CUkkLHT TECHNOLOGY GENERAL AVIATIUN PROPELLERS Figure 71. - Commuter propeller technologies save fuel.

e

'o ADVANCED

BENEFIT

TECHNOLUGY PROPELLER MODERN TECHNOLOGY BASELINE

"UEL SAVED CUC REDUCTION

11 - Figure AAranced propeller technology benefits -'in passengers, Mach 0. 45, 100 n. mi. , 11 %/ gel fuel.

ORIGINAL PAC: IS OF POOR QUALITY T II I DI VICE S I PROPLETS BLADE SHAPL S •A4 AIRf01LS PROP/NACE LL E INl LGRATION COAAPOSI TE S SURFACE FINISH Irr r^nA r tlM: ^.^s I N1 f f RAl [ Q W41,111: nMNI G.A. l%n B1 ADI /SP INN( R Figure 2S. - Ce Nnl ffttCatjleh rdvanLed propeller technoiogiot PR(WELLERS ENGINE COMPONLNTS

r

cnw^r e.o^ I i COYNI.TOQ Lit AN AON / ^J CoNTQo1 AND AccassoQ11.

1 WOOG 'I

W W

w ^ it's-M

► m IISO% 14 "A" R Mle'illim to en T1mm"T 51111111111 141,1111% AC S an% •Aeii..

M M^ Mw.m i lg%MMIn C^•175U NM

^^

figure 26. • SW propukoon twhnologT.

ORIGINAL "k/' OF p oort ^Ijo%# - I, 0 L ADV. TV11130MACHINERY

• CERAMICS

• REGENERATION

\0k 00-000 clip s ^'l SMALL AIRFOIL LIMITS i THERMA L EFFICIENCY, TURBINE COOLING MATFRIAL a; cl i p MFG. FIDELITY TIP CLEARANCE SURFACE ROUGHNGSG lI CYCLE PRESSURE RATIn Figure 27, - Barrier and opportunities for greater efficiency. Small turbine engines, CERAMIC REGENERATIVE CYCLE INTERCOOLED ^ ^ I ► OLUTIONARY 'ECHNOLOGY PORTUNITIES ENGINE :0 t EFFICIENCY "ED 4TIONAL PROP TECHNOLOGY s=t PWI00o COMPRESSOR PRESSURE RATIO Small gas turbine engine opportunities - 15W-shp class.

Figure 28. - .

e

Of"

all, CRUISE 1001 0 INCREASED TCC NCW TURBOPROPS RISKDGY 10f13+ ADVANCED TURBOPROP FUEL BURNED _r!

ROTARY DIESEL ^'°' 0 0 HIGHLY ADVANCED I Yii' ^ f "° IC k19CINtb - - '^:•+" M M ADIABATIC L TURBOCWOUNDEO REGENERATIVE /i TURBOPROP CERAMIC REGENERATIVE/INTERCOOLED TURBOPROP

501.2

i3 ,35 140 645 150

CRUISE BSFC Figure 29. - Commuter aircraft propulsion opportunities - 30 passengers, Mach 0. 45, 15 000 ft, °1500 SNP SLSS.

F