• RG15-PT (Fig. 12.68)

• RG15-PT u. s.t. xjc = 20%, h/c – .17%, w/с = 1.0% (Fig. 12.69)

• RG15-PT u. s.t. xjc = 40%, h/c = ,17%,u;/c = 1.0% (Fig. 12.70)

• RG15-PT u. s.t. xjc = 60%, h/c = .17%, w/c = 1.0% (Fig. 12.71)

• RG15-PT u. s.t. xjc = 70%, h/c = .17%, w/c — 1.0% (Fig. 12.72)

The RG15 was tested extensively with trips because the performance of the untripped model (shown in Fig. 12.68) was relatively good. We asked ourselves: when one starts with a “good” airfoil (the RG15-PT), can trips still make modest improvements in performance? Note that the question is specific to this airfoil and cannot be generalized.

It is instructive to begin with the trip at 70% chord shown in Fig. 12.72. At this location, it has virtually no effect since it is downstream of laminar separation. In other words, it is either inside the laminar separation bubble or immersed in the turbulent boundary layer.

At 60% chord, the trip causes the 150k and 200k curves to spread apart. At 40% chord, the trip efficiently trips the boundary layer for Rn of 150k at the lower lift coefficients. As observed before, the higher-i£n polars overlap since the boundary layer is tripped too soon, producing more drag than that found for the lower Rn’s (150k in this case).

At 20% chord, there is even more overlap at 300k. But the drag at 100k has decreased significantly from the untripped case as the trip moves forward. As is true with the HQ2/9, a trip should be employed for Rn less than 150k-200k. The location will depend on the average local chord Rn.

Also see: HQ2/9, S2048, SD8000, SD2030 Digitizer plot: Fig. 10.26 Airfoil comparision plot: Figs. 11.3, 11.6 Polar plot: Figs. 12.68-12.72 Lift plot: Fig. 12.73

Thickness: 8.92% Camber: 1.76%

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