1、NASA TECHNICAL NOTE NASA e, i -TN D-5662 4 6A 4 z EFFECTS OF GROUND PROXIMITY ON THE LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF AN UNSWEPT ASPECT-RATIO-IO WING by Arthzcr W. Curter LungZey Reseurch Center LungZey Stution, Humpton, Vu. J , .* . NATIONAL AERONAUTICS AND SPACE ADMINISTRATION WASHINGTO
2、N, D. C. FEBRUARY 1970 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-I - TECH LIBRARY KAFB,NM I111111 lllllll1lllllllllllllllllIll11111 0332472 1. Report No. 2. Government Accession No. 3. Recipients Catalog No. NASA TN D-5662 i 4. Title and Subtit
3、le 5. Report Date EFFECTS OF GROUND PROXIMITY ON THE LONGlTUDl NAL AERODYNAMIC February 1970 CHARACTERISTICS OF AN UNSWEPT ASPECT-RATIO-10 WING 6. Performing Organization Code i 7. Author(s) i 8. Performing Organization Report No. By Arthur W, Carter L-6970 110. Work Unit No.-1 721-01-11-02-239. Per
4、forming Organization Name and Address 111. Contract or Grant No.NASA Langley Research Center1i Hampton. Va. 23365 113. Type of Report and Period Covered r 112. Sponsoring Agency Name and Address I Technical Note National Aeronautics and Space Administration I Washington, D.C. 20546 14. Sponsoring Ag
5、ency Code 1 15. Supplementary Notes 16. Abstroct A wind-tunnel investigation has been made of the effects of ground proximity on the longitudinal aerody namic characteristics of an unswept wing with an aspect ratio of 10 and a taper ratio of 0.3. Data were obtained throughout a range of heights of t
6、he wing above a stationary and moving-belt ground plane with flaps retracted and with full-span double-slotted flaps deflected 300 and 500. 17. Key Words Suggested by Authorfs) 18. Distribution Statement Ground effect Unclassified - Unlimited Longitudinal aeralynamic characteristics I 19. Security C
7、lassif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price“ Unclassified Unclassified I Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-EFFECTS OF GROUND PROXIMITY ON THE LONGITUDINAL AERODYNAMIC CHARACTERISTICS OF AN TJ
8、NSWEPT ASPECT-RATIO-10 WING By Arthur W. Carter Langley Research Center SUMMARY A wind-tunnel investigation has been made of the effects of ground proximity on the longitudinal aerodynamic characteristics of an unswept wing with an aspect ratio of 10 and a taper ratio of 0.3. Data were obtained over
9、 a stationary and moving-belt ground plane with flaps retracted and with full-span double-slotted flaps deflected 30 and 50. Ground-effect data were also obtained for the model with leading-edge slats on the wing with trailing-edge flaps deflected 50. The results indicated the need for a moving-belt
10、 ground plane in order to remove the boundary-layer buildup and to predict the correct aerodynamic characteristics for a plain wing as well as for wings with trailing-edge flaps and leading-edge slats. With flaps retracted, the results indicated that a decrease in height of the wing above the moving
11、-belt ground plane produced an increase in the lift-curve slope, an increase in the angle of attack for zero lift, and a decrease in the pitching-moment-curve slope. With flaps deflected, the results indicated that a decrease in height of the wing above the ground produced decreases in the maximum l
12、ift and in the negative or nose-down pitching moments. The principal effect of ground proximity was a reduction in induced drag which resulted in an increase in lift-drag ratios as the wing approached the ground. INTRODUCTION The aerodynamic characteristics of a wing are influenced by the proximity
13、of the wing to the ground. Investigations of ground effects in wind tunnels normally are made with a fixed ground plane placed in the airstream below the model to simulate the ground. As pointed out in reference 1 for high-lift configurations at low heights above the ground, the fixed ground plane p
14、rovided incorrect simulation of the effects of ground proximity because of the thick boundary layer which developed between the airstream and the ground plane. Although this boundary layer has not created serious problems in investigations of unpowered, low-lift configurations, the ground simulation
15、 is not strictly correct, Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-especially when the model is in close proximity to the ground. In order to provide an accurate means of simulating the ground in wind-tunnel investigations, a moving-belt groun
16、d plane was installed in the 17-foot (5.18-meter) test section of the Langley 300-MPH 7- by 10-foot tunnel as described in reference 2. The purpose of the present report is to present the results of an investigation of an unswept aspect-ratio-10 wing over the moving-belt ground plane. The effects of
17、 ground proximity on the longitudinal aerodynamic characteristics were investigated for the wing with full-span double-slotted flaps deflected 30 and 50 and with the flaps retracted. Ground-effect data are also presented for the model with leading-edge slats on the wing with trailing-edge flaps defl
18、ected 50. SYMBOLS The units used for the physical quantities in this paper are given both in U.S. Customary Units and in the International System of Units (SI). Factors relating these two systems of units are presented in reference 3. wing span, feet (meters) wing chord, inches (centimeters) wing me
19、an aerodynamic chord, inches flap chord, inches (centimeters) drag coefficient, -D qtos lift coefficient, -L qoos lift-curve slope (centimeters) lift-curve slope over stationary ground plane lift-curve slope over moving-belt ground plane, VB = V, pitching-moment coefficient, Pitching moment q,SF pit
20、ching-moment-curve slope Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-D wing drag, pounds force (newtons) h height of lower surface of wing at E/4 above ground plane at (Y 0 with = wind off, feet (meters) hC height of wing corrected for angle of a
21、ttack and for sting and balance bending due to wing lift, feet (meters) K1 intercept of dCD/dCL2 at zero lift L wing lift, pounds force (newtons) qKl free-stream dynaniic pressure, pounds force/foot2 (newtons/metera) S wing area, feet2 (meters21 VB linear velocity of moving-belt ground plane, feet/s
22、econd (meters/second) VKl free-stream velocity, feet/second (meters/second) (Y angle of attack of wing, degrees s, flap deflection (positive when deflected down), degrees Subscripts: max maximum 00 free stream MODEL AND APPARATUS A drawing of the model is shown in figure 1. The wing had an NACA 4415
23、 airfoil section with an aspect ratio of 10 and a taper ratio of 0.3. The wing was mounted at the bottom of a cylindrical fuselage which had a faired nose section. Details of the full-span double-slotted trailing-edge flap arrangement and ordinates of the flap and vane are given in figure 2. The fla
24、p chord was 33.3 percent of the wing chord and the vane chord was 3 Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-Ill1 I II 111 I I II I1 I I I 1111II I I1 I1 111.1111111 I I I I, I, I I, I, 56.6 percent of the flap chord. The flap system was defle
25、cted about the hinge line indi cated in figure 2, and the relative position of the vane with respect to the flap remained the same at flap deflections of 30 and 50. Details of the leading-edge slat are given in figure 3. The leading-edge slats were used only with the 50 flap deflection. The model wa
26、s mounted on a sting-supported six-component strain-gage balance for direct measurement of the forces and moments on the model. The balance was located at the center of the fuselage with the moment center of the balance located at the 2 5-percent mean-aerodynamic-chord station of the wing. The pitch
27、ing-moment data have been transferred vertically to a moment center located at the quarter chord on the lower surface of the wing as indicated in figure 1. An electronic clinometer was located in the fuselage for use in determining the geometric angle of attack of the wing during the investigation.
28、Photographs of the sting-supported model mounted above the moving-belt ground plane in the 17-foot (5.18-meter) test section of the Langley 300-MPH 7- by 10-foot tun nel are shown as figure 4. A description of the tunnel is given in reference 4. Details of the moving-belt ground-plane system and dra
29、wings of the model-support system are presented in reference 2. TEST CONDITIONS For this investigation, the Reynolds number based on the free-stream dynamic pres sure of 5 pounds force/foot2 (239 newtons/metera) and wing mean aerodynamic chord of 1.0963 feet (0.3342 meter) was 0.45 X 106. The wing h
30、eights ranged from = 0.017 to i; = 0.683 which was the center line of the test section. This latter height was considered to be essentially out of ground effect for the present model. The heights of the model above the ground plane were measured relative to the lower surface of the model at E/4 with
31、 a! = Oo for the wind-off condition. Changes in the measured heights of the wing above the ground occurred because of sting and balance deflections due to lift and because of translation of the wing reference point due to rotation of the angle-of-attack mechanism at the various heights investigated.
32、 For the purpose of the present paper, these variations in height do not affect the relative comparisons of the data and, consequently, the heights have not been corrected. However, the height changes were calculated for each model configuration and the corrected height-to-span ratios have been plot
33、ted against angle of attack in fig ure 5 for height-to-span ratios from 0.017 to 0.283. If height corrections are desired in close proximity to the ground, the data in this figure may be used. Above = 0.283, height corrections should have no significance. 4 Provided by IHSNot for ResaleNo reproducti
34、on or networking permitted without license from IHS-,-,- . ._ A suction slot at the belt leading edge was utilized to remove the boundary layer at that point, and the boundary layer was prevented from building up over the belt by the use of a belt linear speed equal to that of the tunnel airstream.
35、Each model configuration was investigated at the lowest feasible height and at several additional heights over the moving belt. Data were also obtained at each of these heights with the ground belt stationary. When a height was reached for each configuration at which the influence of the moving belt
36、 on the data became negligible, the remaining heights were investigated only with the belt stationary. Ftl3SULTS AND DISCUSSION The basic results of the investigation are presented in figure 6. The variations of CD, a,and C, with CL show the effects of the moving-belt ground plane on the lon gitudin
37、al aerodynamic characteristics of the aspect-ratio-10 wing at several heights of the model above the ground plane. The boundary condition requiring a moving-belt ground plane for full-span high-lift configurations was presented in figure 10 of reference 1. This boundary is reproduced in figure 7 of
38、the present paper. By use of the method of reference 1, the combinations of height of the wing above the ground plane and lift coefficient which required use of the moving-belt ground plane were determined from the data of figure 6 and are shown in figure 7. These data indicate good agreement with t
39、he previously determined boundary. However, as shown in figure 7, the data for the wing with flaps retracted indicate the need for the moving-belt ground plane at all lift coefficients down to and including CL = 0 in order to predict the correct lift coefficient and lift-curve slope for height-to-sp
40、an ratios below 0.06. In theory, the velocity of the belt must be the same as the velocity of the airstream. However, as concluded in reference 1, the slope of the lift-loss curve with moving-belt velocity for high lift coefficients is such that extreme precision is not required in setting the linea
41、r velocity of the belt. As shown in figure 8, the effect of Kariations in the belt velocity between 75 and 125 percent of the airstream velocity was negligible at low lift coefficients. However, the data of figure 8 illustrate the need for removal of some of the boundary layer on the ground plane, a
42、lthough considerable variation in the belt speed appears permissible at low lift coefficients. Wing With Flaps Retracted The effects of the height of the wing above the ground and of the moving-belt ground plane on the aspect-ratio-10 wing with flaps retracted are presented in figure 9. The 5 Provid
43、ed by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-longitudinal aerodynamic characteristics over the moving-belt ground plane are shown in figure 9(a). The data at a height-to-span ratio of 0.683 which was essentially out of ground effect are shown also. Thes
44、e data indicate that the slope of the lift curve increased as the height of the wing above the ground decreased. The angle of attack for zero lift increased with decrease in height above the ground. The variation of lift-curve slope with height-to-span ratio is shown in figure 9(b) for the stationar
45、y and moving-belt ground planes. As shown in this figure, the data over the stationary ground plane incor rectly predicted the lift-curve slopes at height-to-span ratios below 0.07. At the mini mum height investigated (k = 0.017), the stationary ground plane resulted in an error of 30 percent in the
46、 slope of the lift curve (fig. 9(c). It should be pointed out that this height-to-span ratio, however, is below normal landing-gear height and would appear impractical for actual flight operations. The lift-curve slope decreased rapidly with increase in height of the model above the moving-belt grou
47、nd plane as shown in figure 9(b) and reached a constant value of 0.0833 at a height-to-span ratio of about 0.4. The lift-curve slope was calculated based on section lift data obtained from reference 5 and was corrected for aspect ratio and sweep of the 50-percent chord line in accordance with the me
48、thod of reference 6. This calculated value was 0.0833 and was in agreement with the experimentally determined value. As shown in figure 9(a), the slope of the pitching-moment curve with respect to CL increased with increase in height of the wing above the ground plane. The variation of this pitching
49、-moment-curve slope with height-to-span ratio is shown in figure 9(d). This slope increased rapidly from a value of 0.027 at a height-to-span ratio of 0.017 to a con stant value of 0.076 at a height of about one-quarter wing span above the ground. It should be pointed out that the model did not have tail surfaces. The effect of the change in downwash at the tail resultin
