Figure 14. Drag change comparison: FCS on Std. Cirrus vs Turbulators on ASW-24

A common question is "how will the Sinha Deturbulator perform compared to turbulators?" For a proper answer, this should be studied on a given aircraft with the same instrumentation. But we haven't gotten around to that yet. Also, there are a lot of different gliders out there and, obviously, data from Std. Cirrus tests cannot be used to infer what Sinha FCS will do for another ship. Nevertheless, to put a comparison out there, I went back to Dick Johnson's evaluation of the ASW-24W (Soaring, May 1994) where the effect of the factory turbulators was dramatic.

Fig. 14 plots the drag measurements of both ships in kts. It also shows percent change in both cases. The green curve is the Std. Cirrus clean wing. The red curve is the Std. Cirrus wing modified with Sinha FCS. The broken red curve is the percent change for the Std. Cirrus wing, plotted against the right side scale. The blue curve is the ASW-24W clean wing. The brown curve is the ASW-24W wing with factory turbulator tape. The broken brown curve is the percent change for the ASW-24W wing, plotted against the right side scale.

Note that the data are in units of airspeed here because that's the way the they were reported by Johnson. Therefore, the percent improvement for the FCS is less than that calculated in Volts.

Since different drag rakes were used at different span stations on different wings, the drag data should not be compared directly between the two ships. A more meaningful comparison is the relative drag changes for the two cases (broken lines).

I leave it to the readers to draw their own conclusions.

Jim Hendrix
Oxford Aero Equipment