• E387A-PT (Fig. 12.31)

• E387A-PT repeated (Fig. 12.32) .

The E387A-PT built by Bob Champine was used to compare our data with E387 data taken in other facilities. It also served as one of two calibration models used to check for measurement repeatability over the course of the six-month testing schedule.

The first data set (Fig. 12.31) was taken very early in the schedule and the second (Fig. 12.32) was taken near the end. In general the agreement is good. However, at low-lift coefficients the disagreement is larger than we found else­where. The discrepancy may be related to a spanwise twist in the model. For the first run, the twist was removed by applying an opposite twist over a two day period. No attempt was made to untwist the model for the repeated runs or for the tripped and high-turbulence runs.

• E387A-PT u. s.t. xjc = 20%, Vе = 0.17%, w/c = 1.0% (Fig. 12.33)

Figure 12.33 shows that the addition of an upper-surface trip at 20% lowers the drag over the entire range except at high lift and at 300k.

• E387A-PT high turbulence (Fig. 12.34)

To test the E387 under high turbulence conditions, a screen was placed in the test section 3 ft upstream of the model leading edge. As expected, the high turbulence leads to lower drag because the turbulence shortens the bubble in a way much like that produced by the upper-surface trip. No turbulence measure­ments were taken under these conditions as this was done merely to compare the data with that taken under the normal, low-turbulence test conditions.

• E387B-PT (Fig. 12.36)

The E387 version В data provides some measure of the need for accuracy. Since the camber of this model is substantially less than that of the prototype, large differences in performance can. been expected and were measured. An inaccurate copy of an airfoil will probably share few traits with the parent section, as this model illustrates. While it may be possible in some cases to improve an airfoil by modifying its shape, clearly if the airfoil is a good one to begin with, any modification will usually degrade its performance.

Also see: E193, SD6080, S4061, SD7037, S2091 Digitizer plot: Figs. 10.13, 10.14 Polar plot: Figs. 12.31-12.34, 12.36 Lift plot: Fig. 12.35

Thickness: 9.06% Camber: 3.80%