Category AIRFOILS AT LOW SPEEDS

• SD7062-PT {Fig. 12.141)

• SD7062-PT u. s.t. xjc = 15%, hjc = .17%, ш/с = 1.0% (Fig. 12.142)

• SD7062-PT u. s.t. xjc = 15%, hjc = .08% and. I7%,u>/c = 1.0% (Fig. 12.143)

The SD7062 is a thick (14%), highly cambered (4%) airfoil. In some ways it is comparable to the S4233, but when untripped it performs considerably bet­ter than the S4233, except at high Rn. When both airfoils are tripped (see Figs. 12.102 and 12.142), the situation reverses; the S4233 has lower drag, al­though not much. As Fig. 12.143 shows, at 200k a trip placed at 15% increases the drag with respect to the untripped case.

Also see: FX63-137, S4233, E193MOD, MB253515 Digitizer plot: Fig, 10.54 Polar plot: Figs. 12.141-12.143 Thickness: 13.98% Camber: 3.97%

• SD7043-PT (Fig. 12.138)

• SD7043-PT u. s.t. x/c = 20%, h/c = .17%,wjc = 1.0% (Fig. 12.139)

The shapes of the untripped SD7043 polars are indicative of a laminar sepa­ration bubble that would be amenable to control by a trip. This airfoil reaches a high lift coefficient which produces a low sink speed if flown just above stall speed. Due to time limitations, it was not tested with the trip at the lower Rn’s (60k, 100k, and 150k), but it is reasonable to assume that the tripped version would maintain most of this high lift while substantially decreasing the drag. If so, the SD7043 could be a good performer on small-to-medium size airplanes, but with the caveat that the stall, which is moderately abrupt, probably needs to be controlled with leading edge stall strips. (See Section 5.2.)

Also see: SPICA, E214, SD7032 Digitizer plot: Fig. 10.53 Polar plot: Figs. 12.138, 12.139 Lift plot: Fig. 12.140

Thickness: 9.13% Camber: 3.51%

• SD7037-PT (Fig. 12.136)

The SD7037 is a thinner, decambered SD7032. As would be expected, the drag is lower, the polar is shifted downward in lift, and the lift range is less. To increase the lift range, flaps would be useful.

The relatively low drag at C; near 0.3 offers good L/D performance which, together with low drag at high lift, should make the SD7037 a popular airfoil, especially for thermal-duration flying. For weak thermal conditions common to east coast soaring in the U. S., the SD7037 would make an excellent cross­country airfoil, but flaps in this case are almost essential to improve high-speed, between-thermal performance.

• SD7037-PT u. s.t. x/c = 30%,h/c = A7%,w/c= 1.0% (Fig. 12.137)

An upper-surface trip at 30% reduces the drag at lower Rn’s only slightly. Although it was not measured, one would expect the drag at 300k to be increased. As with the SD7032, trips are of little benefit.

Also see: FX60-100, SD6080, SD7032, E214 Digitizer plot: Fig. 10.52 Polar plot: Figs, 12.136, 12.137 Thickness: 9.20% Camber: 3.02%

The SD7032 is among the best of the thermal-duration type airfoils (such as the AQUILA, E214, S2091, S4061, SD6080). The design of this new airfoil incor­porates what is presently known about mitigating laminar separation problems through the use of a bubble ramp.

The data show that control of the bubble has been achieved. For example, in contrast to the untripped E214, there is little evidence of separated flow even at Rn of 60k. At moderate to high Rn’s, the performance is generally better than the E214. As compared to the E214 with a trip (which is another way to control separation), the untripped SD7032 is about the same at the lower Rn’s, but considerably better at Rn of 300k.

It should be mentioned that the angle of attack at stall decreases with Rn, and for Rn of 60k the stall is relatively sharp, as shown in Figs. 12.133. This needs to be considered primarily for wings operating at very low Rn’s, such as with hand-launch sailplanes.

• SD7032A-PT (Fig. 12.126)

• SD7032B-PT (Fig. 12.127)

• SD7032D-PT (Fig. 12.134)

There were two test sections of the SD7032 built. The first was initially covered in balsa only (version A), leaving a relatively rough aerodynamic surface. The model was then covered in Monokote (version B), and finally a 21% flap was added (version C). The flap configuration is shown in Fig. 5.6. The nominal SD7032 coordinates for the A/B/C model were modified slightly by the addition of a linear thickness increase from the leading to the trailing edge. At the leading edge the added thickness was zero and at the trailing edge it was ^ in, to give a finite trailing edge thickness. The second, more accurate model is version D. This model used the nominal coordinates.

Figs. 12.126 and 12.127 show that the balsa surface acts in a manner similar to that of a trip. The drag curves for the model A at Rn of 200k and 300k are nearly coincident which indicates premature transition at 300k. As shown in Fig. 12.127, adding the smooth Monokote covering reduces the drag by up to 20% at 300k.

For version B, the 300k polar exhibits about a 10% drag increase in the range 0.60 < C < 0.95 when compared with the SD7032D-PT. Fig. 10.50 shows that the A/B/C model has a flat spot on the upper surface near 45% which affects the laminar separation bubble. This, in turn, leads to the differences in drag at 300k. This is still another illustration of how a relatively small surface difference can affect performance. Having said that, note that both the A and В versions out-perform the D version at low to moderate Rn (with only a small penalty at high speed). This is because of the way the wing “flies through” the polars, in this case taking advantage of the low-drag areas. See Fig. 5.10.

• SD7032C-PT 6° flap (Fig. 12.128)

• SD7032C-PT 3° flap (Fig. 12.129)

• SD7032C-PT 0° flap (Fig. 12.130)

• SD7032C-PT -3° flap (Fig. 12.131)

• SD7032C-PT -6° flap (Fig. 12.132)

Flaps on the SD7032 extend the useful high-speed range. As with the E214, the flap is intended to be used only in the reflexed position. What is also of interest is that the —6° flap deflection is too much of a good thing; —3° provides lower drag at high J£n/low C.

• SD7032D-PT u. s.t. xjc = 45%, Л/с = .17%,w/c = 1.0% (Fig. 12.135)

A trip at 45% offers only marginal improvements. This is to be expected, given an airfoil that is designed with a bubble ramp. For Ci of 0.35, the drag is decreased for Rn’s less them 200k. This small improvement does not warrant the use of trips for the type of flying typically encountered.

Also see: E214, S2091, AQUILA, SD7037

Digitizer plot: Figs. 10.50, 10.51

Polar plot: Figs. 12.126-12.132, 12.134, 12.135

Lift plot: Fig. 12.133

Aircraft polar: Fig. 5.10 •

Thickness: 9.95% Camber: 3.66%

• SD7003-PT (Fig. 12.118)

• SD7003-PT repeated (Fig. 12.119)

The SD7003 was designed to have a very long and gradual upper-surface bubble ramp. In fact, it may be considered to span the entire upper surface. The resulting effect is particularly apparent in the overall smoothness of the polar which shows no trace of high drag due to a laminar separation bubble. However this does not mean there is no bubble. Rather, the bubble losses are small. At Rn’s of 60k and 100k, the drag is especially low when compared with all the other airfoils tested.

The polars shown in Fig. 12.119 axe from a second series of runs to provide a measure of the overall repeatability. Other than a few small discrepancies, the agreement is quite good and typical of repeated runs (see the E387A-PT).

• SD7003-PT u. s.t. xjc = 60%,/i/c = .I7%,iv/c = 1.0% (Fig. 12.120)

• SD7003-PT u. s.t. xjc = 70%,h/c = .17%,w/c = 1.0% (Fig. 12.121)

• SD7003-PT u. s. bumps xjc = 50%, type A (Fig. 12.122)

• SD7003-PT u. s. bumps xjc = 60%, type A (Fig. 12.123)

• SD7003-PT u. s. bumps xjc — 70%, type A (Fig. 12.124)

Several attempts were made to reduce the drag through the use of trips, but they either increased the drag or had no eifect. One is tempted to ask whether this means that the SD7003 is optimized for ramps such that no further improvements can be made. It seems unlikely, but it is an interesting question nonetheless. (See Section 5.3.)

Also see: SD8000, RG15, S3021, MILEY Digitizer plot: Figs. 10.44-10.49 Polar plot: Figs. 12.118-12.124 Lift plot: Fig. 12.125

Thickness: 8.51% Camber: 1.46%

• SD6080-PT (Fig. 12.113)

The SD6080 is an improvement over the S4061. Although the high-lift char­acteristics of the two airfoils are much alike, the SD6080 offers improvements at the low-lift end of the flight envelope.

Figures 12.94 and 12.113 show that the lower part of the SD6080 polar is extended over that of the S4061. Besides this extension, the drag over most of the polar is lower, particularly in those areas which are used by a typical RC sailplane.

• SD6080-PT u. s.t. xjc = 10%,k/c — .17%, w/c = 1.0% (Fig. 12.114)

• SD6080-PT u. s.t. xjc — 20%,k/c — .17%,wfc = 1.0% (Fig. 12.115)

• SD6080-PT u. s.t. x(c = 30%,hfc = .17%, ш/с = 1.0% (Fig. 12.116)

As shown in Figs. 12.114—12.116, trips were placed on the SD6080 at 10%,

20%, and 30% chord. Of the three cases, the trip at 30% is the best between Rn’s of 100k and 300k. As expected, the trip farthest forward is best at lower Rn’s. When the polars for the 30% trip and the untripped case are compared (Figs. 12.113 and 12.116), a 30% trip should clearly be used for Rn at and below 150k.

• SD6080-PT thickened trailing edge (Fig. 12.117)

As observed with the DAE51 and E374, the thickened trailing edge increases the overall drag on the order of 5%. It should be noted that the “thickened trailing edge* was slightly different for each of the three airfoils, but the effect of increased drag is common to all. The shape of the trailing edge is shown in Fig. 5.3.

Also see: S4061, E387, SD7037, SD7032 Digitizer plot: Fig. 10.43 Polar plot: Figs. 12.113-12.117 Thickness: 9.18% Camber: 3.74%

• SD6060-PT (Fig. 12.109)

The SD6060 was designed to be an improvement over the E374 for cross­country flying. The E374 clearly shows large drag at low RrCs due to bubble losses. To alleviate these effects, the SD6060 was designed with a longer bubble ramp than the E374.

By comparing the E374 (Fig. 12.25) with the SD6060 (Fig. 12.109), one can see the advantages of the SD6060. Almost everywhere it has lower drag than the E374, especially at the high iEn’s, which are important for cross-country flying.

• SD6060-PT u. s.t. x/c = 20%, hfc = .17%, td/c — 1.0% (Fig. 12.110)

« SD6060-PT u. s.t. x/c = 40%, h/c = .17%,u>/e = 1.0% (Fig. 12.111)

A trip placed at 40% reduces the drag at 100k by shortening the bubble. Moving the trip forward to 20% further reduces the drag at 100k, although at 200k and 300k the drag is increased.

It is not surprising to find that the SD6060 and E374 are quite similar when both are tripped at 20% (compare Figs. 12.27 and 12.110). At high-Rn/low-Ci, the E374 has a slight advantage over the SD6060, although in the same regime the plain SD6060 has the lowest drag of both airfoils, tripped or untripped.

Also see: E374, E205, NACA 2.5411, SD7090 Digitizer plot: Fig. 10.42 Polar plot: Figs. 12.109-12.111 Lift plot: Fig. 12.112

Thickness: 10.37% Camber: 1.84%

A discussion of the design philosophy used behind the SD designs is given in Chapter 4.

SD2030

• SD2030-PT (Fig. 12.104)

The SD2030 was designed for operation at speeds higher than those typically found on most RC sailplanes. For this reason it is suitable for high-wing-loading F3B and F3E type aircraft. Since the lift range is narrow, camber-changing flaps are recommended.

Also see: SD2083, S2055, RG15, S3021

Digitizer plot: Fig. 10.39

Polar plot: Fig. 12.104 ‘

Lift plot: Fig. 12.105

Thickness: 8.56% Camber: 2.25%

SD2083

• SD2083-PT (Fig. 12.106)

The SD2083 was an early and not very successful attempt at an F3B design. The airfoil suffers from a fairly large separation bubble, and there is too much camber (2.85%) for good, high-speed performance.

Also see: S2055, SD2030, SD8000, HQ2/9

Digitizer plot: Fig. 10.40

Polar plot: Fig. 12.106

Thickness: 8.96% Camber: 2.85%

SD5060

• SD5060-PT (Fig. 12.107)

For operation at Rn’s from 100k down (e. g. hand-launch RC sailplanes) the SD5060 is an improvement over the S3021. The stall characteristics of the SD5060, however, are not as benign as the S3021. In fact the airfoil stalls abruptly, much like the NACA 2.5411.

Also see: S3021, DF101, CLARK-Y Digitizer plot: Fig. 10.41 Polar plot: Fig. 12.107 Lift plot: Fig. 12.108

Thickness: 9.45% Camber: 2.30%

• S4233-PT (Fig. 12.101)

• S4233-PT u. s.t. xjc — 20%, hjc = .17%,w/c= 1.0% (Fig. 12.102)

The S4233 was designed to be an improvement over the MB253515. To date the S4233 has probably been most used by Bob Champine, retired NACA/NASA test pilot, who recently achieved his second LSF level 5 flying his “stretched” GEMINI with the S4233. His enthusiasm for this airfoil is reflected in the accuracy of the wind tunnel model which he built.

Note that the 13.6% thick S4233 has a wider lift range and lower drag than the 15% thick MB253515. As with the MB253515, the S4233 shows a bulge in the drag at a Rn of 100k, so one would expect a trip to improve matters. Fig. 12.102 shows that the low-Rn drag can indeed be reduced using a trip, but the performance with the trip is slightly worse at Rn of 300k.

Also see: MB253515, E193MOD, WB135/35, SD7062 Digitizer plot: Fig. 10.38 Polar plot: Figs. 12.101, 12.102 Lift plot: Fig. 12.103

Thickness: 13.64% Camber: 3.26%

• S4180-PT (Fig. 12.100)

The thin trailing edge of this model was wavy for the aft 25% chord along the entire span. Because of the significant three-dimensionality, nothing conclu­sive can be said about the two-dimensional airfoil characteristics. The model coordinates were not digitized because there is no representative section.

Also see: S4061

Polar plot: Fig. 12.100

Thickness: 9.77% Camber: 4.36%