1、NASA Technical Memorandum 8 1745 Low and High Speed Propellers for General Aviation - Performance Potential and Recent Wind Tunnel Test Results Robert J. Jeracki and Glenn A. Mitchell Lewis Research Center Cleveland, Ohio Prepared for the National Business Aircraft Meeting sponsored by the Society o
2、f Automotive Engineers Wichita, Kansas, April 7-10, 1981 i I ! Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-LOW AND HIGH SPEED PROPELLERS FOR GENERAL
3、 AVIATION - PERFORMANCE POTENTIAL AND RECENT WIND TUNNEL TEST RESULTS by Robert J. Jeracki and Glenn A. Mitchell National Aeronautics and Space Administration Lewis Research Center Cleveland, Ohio 441 35 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-
4、,-Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-THE VAST MAJORlTY OF GENERAL-AVIATION AIRCRAFT manufactured in the United States are propel- ler powered. Most of these aircraft use pro- peller designs based on technology that has not changed signif
5、icantlv since the 1940s and early 1950s. This older technology has been adequate; however, with the current world en- ergy shortage and the possibility of more stringent noise regulations, improved technol- ogy is needed. Studies conducted by NASA and industry indicate that there are a number of imp
6、rovements in the technology of general- aviation (G.A.) propellers that could lead to significant energy savings. New concepts like blade sweep, proplets, and composite materi- als, along with advanced analysis techniques have the potential for improving the perform- ance and lowering the noise of f
7、uture propel- ler-powererd aircraft that cruise at lower speeds. Current propeller-powered general- aviation aircraft are limited by propeller compressibility losses and limited power out- put of current engines to maximum cruise speeds below Mach 0.6. The technology being developed as part of NASAs
8、 Advanced Turboprop Project offers the potential of extending this limit to at least Mach 0.8. At these higher cruise speeds, advanced turboprop propulsion has the potential of large energy savings com- pared with aircraft powered by advanced turbo- fan systems. A present-day low speed G.A. airplane
9、 and a model of a possible high speed turboprop powered airplane are shown in Fig. 1. PRCPELLER PROPULSIOK SYSTEM POTENTIAL A comparison of the installed cruise ef- ficiency of turboprop-powered and turbofan- powered propulsion systems is shown in Fig. 2 for a range of cruise speeds. The installa- t
10、ion losses included with the propeller-pow- ered systems are nacelle drag and with the turbofan-powered systems the losses include fan cowling external drag and the internal fan airflow losses associated with inlet recovery and nozzle efficiency. The installed efficien- cy available with current tec
11、hnology turbo- prop-powered general-aviation aircraft is Jeracki and Ptitchell -1- “Numbers in parentheses designate Refer- ences at end of paper. SAE Paper No. 610601 1 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-about 80% at speeds up to about
12、Mach 0.5. Above this speed efficiency falls off signifi- cantly because of large propeller compressi- bility losses. These propellers are generally designed with blades of thickness to chord ratios (at 75% radius) that range from about 5 to 7%. at relatively high tip helical Mach numbers, are the ma
13、in cause of these losses. With re- ciprocating powered G.A. propulsion systems the level of installed efficiency would be slightly lower than 80% due to larger nacelle (sizes) and drag and internal cooling airflow losses (1, p. 321)“. Advanced G.A. turboprops can potentially achieve significant gain
14、s over current propel- lers with projected, installed cruise effi- ciencies of about 87% up to speeds approaching Mach 0.6. A study of advanced G.A. propeller technology (1, pp. 327-343 and 2) has indica- ted that these gains may be realized by uti- lizing composites, improved analysis methods, and
15、a number of advanced aerodynamic concepts. The advanced, high-speed turboprop shown in Fig. 2 is a new propulsion concept that has the potential of eliminating or minimizing compressibility losses at flight speeds to Mach 0.8. The level of potential installed efficiency projected for the advanced tu
16、rbo- prop is considerably higher than that avail- able with comparable technology high-bypass turbofan systems. At Mach 0.8 the installed efficiency of turbofan systems would be ap- proximately 65% compared with about 75% for the advanced turboprop. Center, McCauley Accessory Division of Cessna Airc
17、raft Company has conducted a study to evaluate the impact of advanced propeller technologies appropriate for lower speed G.A. aircraft (1, pp. 327-343 and 2). The study identified applicable advanced technologies and assessed their potential costs and bene- fits. Some of the advanced technology con-
18、 cepts included in the study are shown in Fig. 3. This figure illustrates a thin, swept, low activity factor, composite propel- ler having advanced aero/acoustic airfoil sec- These rather thick blades, when operated Under contract to NASA Lewis Research Jeracki and Mitchell tions, swept blades, and
19、NASA proplets on the blade tips. In addition, the airfoil section shapes are carried into the hub for improved bladelspinner integration and the overall de- 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-sign was evolved by improving the integrati
20、on of the propeller and nacelle. The potential benefits of these advanced technologies were assessed by McCauley in a mission analysis study of several G.A. air- craft encompassing both single and twin engine aircraft ranging in cruise speed from 120 to 295 knots. In addressing the mission analy- si
21、s, the aircraft were resized to take full advantage of the advanced technology bene- fits. Payload, range, speed, and aircraft lift to drag ratio were kept constant, and a 2 hour cruise mission was assumed. The poten- tial trip fuel savings are shown in Fig. 4. The gains shown were obtained by compa
22、ring the advanced propeller aircraft with baseline pro- peller aircraft; both meeting FAR part 36 noise limits. The data points in Fig. 4 show the results of the mission analysis calcula- tions for each aircraft while the faired curve indicates the more likely average potential gain. The application
23、 of advanced technology to lower speed G.A. propellers has the poten- tial benefit of reducing trip fuel consumed by about 10 to 15%. The larger, higher cruise speed aircraft have the larger improvements due to the higher fuel to gross weight frac- tion and higher predicted propeller perform- ance g
24、ains for these aircraft. prop propulsion system is shown in Fig. 5. The advanced propeller would be powered by a modern turboshaft engine and gear box to pro- vide the maximum power to the propeller with a minimum engine fuel consumption. Propeller efficiency would be kept high by minimizing or elim
25、inating compressibility losses. This would be accomplished by utilizing thin swept blades that would be integrally designed with an area ruled spinner and nacelle. Blade sweep would also be used to reduce noise dur- ing both take-offllanding and during high speed cruise flight (3 to 5). Aj-rcraft op
26、era- tions at high altitudes and Mach 0.6 to 0.8 requires much higher power than used on cur- rent propeller aircraft. A power loading (shaft horsepower divided by propeller diam- eter squared) about five times higher than current business turboprops would be needed to A model of an advanced high sp
27、eed turbo- minimize propeller diameter and weight. Eight or ten blades are required to increase ideal efficiency at these higher disk loadings. In addition to these advanced concepts, a modern blade fabrication technique is needed to con- Jeracki and Mitchell 3 Provided by IHSNot for ResaleNo reprod
28、uction or networking permitted without license from IHS-,-,-struct the thin, highly swept and twisted blades. by both NASA and industry to evaluate the po- tential of advanced high speed turboprop pro- pulsion for both civil and military applica- tions. Numerous references to specific stud- ies and
29、summary results are listed in Ref. (5). The trip fuel savings trend shown in Fig. 6 plotted versus operating range is a summary of these studies. Installed efficien- cy levels similar to those shown in Fig. 2 for comparable technology advanced turboprops and turbofans were used in most of these stud
30、ies. As shown in Fig. 6, trip fuel savings is de- pendent on aircraft cruise speed and range. At the bottom of the band, associated with Mach 0.8 cruise, fuel savings range from about 15 to 30% for advanced turoprop aircraft compared to equivalent technology turbofan aircraft. The larger fuel saving
31、s occurs at the shorter operating ranges where the mission is climb and descent dominated. Because of the lower operating speeds encountered during climb and descent, turboprops have an even larger performance advantage than the advan- tage at Mach 0.8 cruise conditions. In a sim- ilar manner, a lar
32、ger fuel savings is possible at Mach 0.7 cruise (represented by the top of the band in Fig. 6). At this lower cruise speed fuel savings range from about 25 to near 40;*. These fuel savings were all for advanced single rotation turboprops. A study that in- cluded co-axial counter-rotation turboprops
33、(6) has showrl that there is an additional 5 to 0% trip iusl savings at Mach 0.8 over these single rotation systems. Kith 2 dollar per gallon fuel, a Mach 0.7 advanced single rota- tion turboprop can reduce total operating cost by 207; over a comparabls high bypass ratio turbofan ( 7). A number of s
34、tudies have been conducted LOW SPEED PROPELLER TESTS As part of a program to evaluate the cap- ability of current G.A. propeller aerodynamic and acoustic analytical prediction methods, a wind tunnel test of several G.A. propeller models were conducted in the NASA Lewis 10-by-10 foot wind tunnel. A p
35、hotograph of one of these 1.524-meter (5 it diameter mod- els is shown in Fig. 7 installed on the Lewis 746 kI (1000 hp) propeller test rig (PTR). Power for this PIK is provided by a 15.0 crn Jeracki and kfitchell L Provided by IHSNot for ResaleNo reproduction or networking permitted without license
36、 from IHS-,-,-(5.9 in.) diameter air turbine using a contin- uous flow 3.1x106N/m2 (450 psi) air system routed through the support strut. Propeller aerodynamic performance was determined using a rotating balance that measured both axial force and torque. The balance was located just downstream of th
37、e propeller models inside the nacelle. The nacelle that was tested (Fig. 7) was an axi-symmetric model of the Rockwell Turbocommander 690B shown in Fig. l(a). The model and full-scale nacelle both had approximately the same cross section- al area distribution (relative to propeller diameter). To acc
38、ount for the aerodynamic interaction between the metric propeller mod- els and the nonmetric nacelle, the pressure force on the nacelle was determined based on pressure integration. The increase in nacelle drag with an operating propeller model (com- pared to the propeller removed case) was used to
39、reduce the measured propeller (apparent) efficiency to obtain a net efficiency using the well established method of Ref. (8). A small efficiency correction was also made to account for the interference between the pro- peller flow field and the tunnel wall boundary based on the method of Refs. (9 an
40、d lo, and some detailed wall pressure measurements. Four 3-blade propeller models were test- ed. These models are representative of cur- rent technology G.A. turboprop propellers de- signed for cruise near Mach 0.5. Representa- tive characteristics of the four models are shown in table 1. Activity f
41、actor (AF) per blade varied from 83 to 132 and thickness to chord ratio at 75% radius varied from about 5 to 95. Iwo of the models incorporated airfoil technology from the World War 11 era and the other two used more modern airfoil technology (ARA-D from Ref. (ll), and GAW-2) The three important ope
42、rating conditions that were in- vestigated are shown in table 11. Cruise data was obtained at Mach 0.35 rather than the higher Mach 0.5 cruise speed of the 6908 air- craft due to wind tunnel limitations. How- ever, advance ratio and power coefficient were held to the actual aircraft values. NACA 16
43、airfoil design are shown in Fig. 8 at Mach 0.35. The data are presented in the con- ventional propeller performance plot format. Net thrust efficiency and a dimensionless pow- er coefficient are plotted as ordinates. The abscissa is advance ratio which is proportion- Typical test results from the AF
44、 = 101, Jeracki and Mitchell 5 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-a1 to the ratio of flight or advance speed to blade tip speed. As tip speed increases from windmill (no power), the advance ratio de- creases and power coefficient increas
45、es. Blade angle is set and data are taken from windmill to higher power shown by the data symbols on the power coefficient plot. The blade angle (P 3/4) 3 measured at 314 of the propeller radius, becomes 90 when the chord of that airfoil section is aligned directly with the flight direction. As powe
46、r is increased the thrust increases and, as seen in the upper data curves, the net thrust efficiency in- creases, reaches a peak, and then begins to drop off. All blade angles yield similar power and efficiency curves. Power loading (P/D2) can be written in terms of propeller coefficients and free-s
47、tream conditions as: C P 00 From this relationship a line of constant power loading has been added to Fig. 8 and represents the design loading parameter cp/J3 (=0.02727) corresponding to the cruise design operating condition of J=2.234, and Cp=0.304. sign power at different propeller tip speeds. The
48、 efficiency at the design power can be found for each blade angle by locating the intersection of the design power loading line with the Cp vs J data curve for each blade angle, moving vertically up to the net effi- ciency curve (keeping the same J), and reading the efficiency. ?he design point effi
49、ciency (at design power loading - and design J) can be determined by interpolation from the resulting efficiencies obtained for each blade angle. The design efficiency for the three operating conditions of table I1 were determined using the method described above for each of the four propellers. These conditions are takeoff, clim
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