NASA Technical Paper 2256 - CAFE Foundation

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region of the airfoil. Further observations of propeller slipstreams are made subse-
quently for the Skyrocket II and T-34C airplanes.
Gates Lear_et Model 28/29 Longhorn.- Transition locations are shown in figure 32 ....
and are listed in table 2 for the wing and winglet at M = 0.7, h d = 16 500 it,
C L = 0.12, and R = 3.08 × 106 ft -I. This test altitude was chosen to provide a
static temperature conducive to rapid sublimation of the chemicals. It isnot repre-
sentative of cruise conditions. The resulting Reynolds number was about 400 percent
higher _an typical cruise values; in this sense, the results of these experiments
are conservative.
Transition on the wing (fig. 32(a)) was (x/c) t = 40 to 45 percent. In the
figure, several turbulent wedges are seen which terminate in the natural transition
location noted. Most of the turbulent wedges were attributed to large chemical par-
ticles which adhered to the wing surface during application.
The most rearward natural transition on the winglet (fig. 32(b)) was
(x/c) t = 55 percent. Many turbulent wedges were observed emanating from chemical
particles adhering to the surface as well as from surface irregularities at the junc-
ture between the winglet leading edge and the surface skin on the suction (inner)
side. Spanwise and chordwise rows of flush-countersunk structural screwheads initi-
ated the transition.
The largest wave measured on the wing in the laminar region was h _ 0.002 in.
with k = 2.0 in. (See appendix.) For the test condition with c = 6.58 it, the
maximum allowable single wave height, as determined by using the equation in the
appendix, is 0.008 in. for k = 2.0 in. Thus, the empirically determined maximum
allowable wave height was not exceeded by waviness existing on the-wing in the lami-
nar region. On the lower span of the winglet, the measured height of an aft-facing
step near the leading edge exceeded the allowable height, and the premature transi-
tion observed on that portion of the winglet cad bg_attributed to this step. (See
fig. 32(b).)
NO spanwise contamination due to the leading-edge wing sweep A. of 17 ° was
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observed. The maximum value of attachment-line momentum thickness Reynolds number
R e at the test condition was 74.
Cessna P-210 Centurion.- Transition locations are shown in figure 33 and
are listed in table 2 for the wing upper and lower_-surfaces and the horizontal_
stabilizer for V = 139 to 154 knots, R 1.34 x 106 to 1.48 x 106 ft -I, and
C L = 0,36 to 0.32 c. Observations on the variation of the upper surface transition
locations with angle of attack_are given in the following table:
Vc, knots
1 39
149
154
C L
0.35
.28
.26
R, ft "I
1.34 × 106
1.43 × 106
1.48 × 106
(X/C)t, percen£
Figure 33(a) shows (x/c) t = 29 percent at V c = 149 knots. On the lower part
of this figure, transition of (x/c) t = 44 percent at V c = 154 knots is faintly
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