1、EFFECTS OF AFT-FUSELAGE-MOUNTED NACELLES ON THE SUBSONIC LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF A TWIN-TURBOJEqT AIRPLANE by Lawrence E. Putndm and Charles D. Trescot, Jr. Langley Reseurch Center Langley Station, Hampton, Vu. , , : ., . ,.p, .*/- ,. ,id. c rd .,.:. ,;c;C3 ,z, . ., .bz$Y v;y (t
2、;.; ,-.-.,7 .I . ;I i - ,. . I , ,;- -. ; ; .;r .8;:“/ il . si h / *.-a_ - NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTON, D. C. DECEMBER 1966 ) I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-TECH LIBRARY KAFB, NM NASA TN D-3781 EFFECTS
3、OF AFT-FUSELAGE-MOUNTED NACELLES ON THE SUBSONIC LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF A TWIN - TURBOJE T AIRPLANE By Lawrence E. Putnam and Charles D. Trescot, Jr. Langley Research Center Langley Station, Hampton, Va. NATIONAL AERONAUTICS AND SPACE ADMINISTRATION For sale by the Clearinghouse
4、 for Federal Scientific and Technical Information Springfield, Virginia 22151 - Price $2.50 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EFFECTS OF AFT-FUSELAGE-MOUNTED NACELLES ON THE SUBSONIC LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF A TWIN-TU
5、RBOJET AIRPLANE By Lawrence E. Putnam and Charles D. Trescot, Jr. Langley Research Center SUMMARY An investigation has been made in the Langley 26-inch transonic blowdown tunnel to determine the effects of aft-fuselage-mounted nacelles on the aerodynamic characteristics of a twin-turbojet airplane.
6、to 0.82, at Reynolds numbers (based on wing mean aerodynamic chord) from 2.79 X 106 to 3.94 X lo6, and at angles of attack from -2 to 6O. The investigation was undertaken pri- marily to determine the effects of nacelle incidence, nacelle longitudinal location, nacelle cant angle, and modifications t
7、o the local area distribution on the lift, drag, and pitching- moment characteristics of the airplane configuration. Some tests were also made in the Langley low-turbulence pressure tunnel at a Mach number of about 0.2 to determine the effects of varying the Reynolds number from 1.36 x 106 to 2.52 X
8、 106 on the high-angle-of- attack (up to 45) stability characteristics of the configuration. The tests were made over a Mach number range from 0.63 Adding nacelles and pylons to the wing-fuselage configuration caused an increase in drag coefficient of approximately 0.0021 at test Mach numbers below
9、0.76; however, the drag increment decreased with increasing Mach number until the increment was about 0.0007 at a Mach number of 0.82. The nacelles and pylons also caused a reduction in lift coefficient of about 0.09 at a given angle of attack and produced a negative increment in pitching-moment coe
10、fficient of approximately 0.04 at a given lift coefficient. Increasing nacelle incidence produced a small decrement in drag coefficient with the maximum dec- rement occurring for a nacelle incidence of about 2.5O and also caused small increases in lift and pitching-moment coefficients. ward was to i
11、ncrease lift and pitching-moment coefficient so that trim lift coefficient increased 0.07 and 0.13 at Mach numbers of 0.67 and 0.82, respectively. icant effect of canting the nacelles 3.50 (exhaust inward) was a small decrease in drag coefficient at lift coefficients above 0.20. Adding a nacelle fai
12、ring to change local area distributions of the basic configuration caused an increase in drag coefficient at Mach numbers below about 0.81; above this Mach number, as a result of favorable interference, there was a small decrease in drag coefficient. Extending the pylons of the modified nacelle conf
13、iguration caused a reduction in drag coefficient at all test Mach numbers. The primary effect of moving the nacelles rear- The only signif- Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-INTRODUCTION / i At the present time, there is considerable de
14、sign interest in turbojet airplanes having engines mounted on the rear of the fuselage. The location and alinement of the engine nacelles on the fuselage should have a considerable effect on the drag and perform- ance characteristics of this type of aircraft. Although some theoretical investigations
15、 of the effects of aft-mounted nacelles on the aerodynamic characteristics of small turbojet airplanes have been made (for example, refs. 1 and 2), evaluation of nacelle-interference effects can best be determined through experimental studies. Inasmuch as very few experimental data are generally ava
16、ilable, the National Aeronautics and Space Administration has initiated a program to investigate experimen- tally the effects of aft-fuselage-mounted engine nacelles on the aerodynamic characteris- tics of a typical twin-turbojet airplane model. The present investigation was undertaken primarily to
17、determine the effects of nacelle incidence , nacelle longitudinal location, and nacelle cant on the lift, drag, and pitching-moment characteristics of the airplane config- uration. The effects of horizontal-stabilizer deflection on the aerodynamic characteris- tics of the airplane have also been inv
18、estigated. In addition, an investigation has been made to determine the effects on the transonic drag rise of modifying the local area dis- tribution in the region of the nacelles by adding a fairing to the nacelles and by increasing the length of the pylon. The tests were made in the Langley 26-inc
19、h transonic blowdown tunnel at Mach numbers from 0.63 to 0.82 and at angles of attack from about -2O to 60. The Reynolds number (based on wing mean aerodynamic chord) was varied from 2.79 X lo6 to 3.94 x 106. Reference 3 indicates that configurations employing a high-mounted horizontal tail, such as
20、 the one on the present configuration, generally have good pitch characteristics at angles of attack prior to wing stall; at angles of attack above stall, however, the effect of - the aft-mounted nacelles on the flow over the horizontal tail can have adverse effects on - the pitch characteristics of
21、 such configurations. Since most of the available data on the problem have beenobtained at a relatively low Reynolds number, tests have been made at low subsonic speeds to determine the effects of varying the Reynolds number from 1.36 X 106 to 2.52 X lo6 on the aerodynamic characteristics of the pre
22、sent configuration at angles of attack from -4O to 45. The results of these tests, which were made in the Langley low-turbulence pressure tunnel, are presented in the appendix. SYMBOLS The forces and moments are referenced to the stability axes, which have their origin on the fuselage center line an
23、d at 20 percent of the mean aerodynamic chord of the i 1 4 wing. 4 2 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Measurements for this investigation were taken in the U.S. Customary System of Details concerning the use of SI, together with physic
24、al constants and conversion Units. Equivalent values are indicated herein parenthetically in the International System (SI). factors, are given in reference 4. wing span Drag qs drag coefficient, Lift lift coefficient, - qs Pitching moment pitching-moment coefficient, qSE stabilizer effectiveness par
25、ameter obtained over 6s range from -0.23O to -1.70 lift-curve slope per degree trim lift coefficient (that is, lift coefficient at Cm = 0) longitudinal stability parameter mean aerodynamic chord incidence angle of nacelles, positive when exhaust is downward, degrees lift-drag ratio free-stream Mach
26、number dynamic pressure Reynolds number based on E wing planform area 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Ax hCP longitudinal location of nacelle from basic position, positive rearward longitudinal location of center of pressure from mo
27、ment reference center angle of attack, degrees deflection angle of horizontal stabilizer, positive when trailing edge is down, degrees E nacelle cant angle, positive when exhaust is inward, degrees Model-component designations: B fuselage H horizontal stabilizer N1 basic nacelle NZ P1 basic pylon ba
28、sic nacelle with aft fairing added PZ extended pylon used with N2 V vertical tail W wing MODEL Drawings of the model are shown in figure 1 and photographs of the model are shown The model had a sweptback wing, sweptback horizontal and vertical tails, and as figure 2. aft-fuselage-mounted engine nace
29、lles. Modifications to the rear section of the fuselage were necessary to allow installation of the balance and sting support. A combination aft- fuselage fairing and sting shield was employed to reduce the interference effects. (See bottom photograph in fig. 2.) The gap between the fuselage and the
30、 shield was sealed. The wing, which was mounted low on the circular fuselage, had a leading-edge sweep of 330, an aspect ratio of 5.83, a taper ratio of 0.365, and fences located at 50 percent of the 4 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-
31、wing semispan. of the vertical tail and had provisions for changing the angle of incidence. The pylon- mounted engine nacelles were constructed so as to permit airflow through the circular ducts and were located as shown in figure l(a). cent of the inlet area. The all-movable horizontal stabilizer w
32、as mounted at about the midpoint The exit area of the nacelles was 95 per- Provisions were made to vary the incidence angle of the nacelles from about 00 to 4 (exhaust downward). varied from with the assumed center of gravity located at 20 percent of the wing mean aerodynamic chord, the trim lift co
33、efficient decreases from 0.29 to 0.14 at a Mach number of 0.67 and from 0.34 to 0.13 at a Mach number of 0.82. (See fig. 19.) (Compare figs. 3 and 5.) From figure 20, it can be seen that the lift decrement due to nacelle addition is slightly greater for the configuration without the vertical and hor
34、izontal tails (BW) than the configuration with the vertical and horizontal tails (BWVH). However, for the tail-off configuration, the pitching-moment-coeff icient decrement due to nacelle addition is rela- tively small. This result indicates that the center of pressure of the lift decrement is sligh
35、tly ahead of the assumed moment reference center for the tail-off configuration. Reference 2 indicates that an engine nacelle located near a wing behind and above its trailing edge would produce an appreciable reduction in the wing lift. difference in the increment in lift coefficient due to nacelle
36、 addition between the tail-off and tail-on configurations indicates that the nacelles cause a decrease in the downwash on the horizontal tail and thereby produce a small positive increment in lift on the horizontal stabilizer. As a result of the long moment arm of the tail, this positive increment i
37、n lift coefficient on the tail produces the large decrement in pitching-moment coefficient resulting from adding the nacelles to configuration BWVH. The small positive Effects of Horizontal- Stabilizer Deflection Decreasing the horizontal-stabilizer deflection angle from -0.23O to -1.70 causes an in
38、crease in pitching-moment coefficient of about 0.065 and a decrease in lift coefficient of about 0.03. (Compare figs. 4, 5, 6, and 7.) The stabilizer effectiveness parameter Cm6 is approximately -0.045 per degree for the basic configuration (BWVHNlP1). trim lift coefficient increases from 0.04 to 0.
39、32 at a Mach number of 0.67 and increases from 0.02 to 0.37 at a Mach number of 0.82 as a result of the decrease in stabilizer incidence from -0.23O to -1.70. (See fig. 21(a).) The 9 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Changing the stabil
40、izer incidence angle from -0.23O to -1.70 results in an increase in drag coefficient of approximately 0.0005 throughout the Mach number range of the pres- ent investigation. As can be seen in figure 21(b), the drag coefficient varies almost linearly with stabilizer deflection. Effects of Nacelle Arr
41、angement Variations in nacelle incidence.- At Mach numbers below approximately 0.75, increasing the nacelle incidence from 0.06O to 3.81 produces a relatively small decre- ment in drag coefficient (fig. 22); the maximum reduction in C, approximately 0.0005, occurs for a nacelle incidence of approxim
42、ately 2.5O. Above a Mach number of about 0.75, the drag decrement due to nacelle incidence is greater. The maximum decrement in drag coefficient also occurs at a nacelle incidence of approximately 2.5O in this Mach number range. For a nacelle incidence of 2.5, the drag decrement is about 0.0008 at a
43、 Mach number of 0.77 and about 0.0010 at M = 0.82 (fig. 22(b). Increasing the incidence of the nacelles from 0.060 to 3.81 generally produces positive increments in lift coefficient and pitching-moment coefficient. (Compare figs. 5, 8, 9, 10, and 11.) As a result of these positive increments, trim l
44、ift coefficient increases approximately 0.03 at a Mach number of 0.67 and approximately 0.04 at a Mach number of 0.82. (See fig. 22(a).) effect on the drag of the airplane by reducing the trim drag. This increase in trim lift coefficient can have a beneficial In order to determine whether these effe
45、cts of nacelle incidence are affected by the shape of the nacelle, the configuration with the modified nacelle BWVHNzPl was tested with the nacelles at an incidence angle of approximately Oo and at 1.85O. The effects of nacelle incidence on the aerodynamic characteristics of the basic configuration
46、BWVHNlPl (fig. 22) and the modified nacelle configuration (fig. 23) are similar; however, the magnitudes of the effects vary somewhat. Variation in nacelle longitudinal location. - Moving the nacelles rearward from Ax/C = -0.034 to 0.237 on the basic configuration BWVHNlPl generally results in a dec
47、rease in drag coefficient at a given lift coefficient for all test Mach numbers. (See fig. 24.) Moving the nacelles rearward also causes a small increase in lift coefficient at a given angle of attack and a considerable increase in pitching-moment coefficient at constant CL. (Compare figs. 5, 12, 13
48、, and 14.) These increases in CL and Cm result in a substantial improvement in trim lift coefficient (fig. 24(a) at all test Mach numbers. Moving the nacelles rearward 27.1 percent of the mean aerodynamic chord ( whereas, the modifications to the local area distribution cause small reductions in tri
49、m lift coefficient. Combining the effects on CL,trim of these geometric modifications should result in an increase in CL,trim and a corre- sponding decrease in trim drag over the values obtained for the basic configuration. Stability and Lift-Curve Slope For the present investigation, there was essentially no effect of nacelle addition, nacelle incidence an
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