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%