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Sinha Deturbulator Progress Reports

Progress Articles
9/17/2003 First successful test of Sinha deturbulator on a glider
10/18/2003 Further drag reductions on Standard Cirrus wing
  Baseline polar for performance testing
2/8/2004 Progress Report: SSA Convention in Atlanta
2/28/2004 First outer-span test
5/27/2004 Wind tunnel goes into operation
8/31/2004 Stereolithography used for wind tunnel wing sections
12/3/2004 First success on upper surface of Standard Cirrus wing
12/12/2004 More success on upper surface of Standard Cirrus wing
2/18/2005 First Sink-Rate Measurement
(revised 3/13/2005)
2/26/2005 Second Sink-Rate Measurement: Some Encouraging Data
3/19/2005 First Parallel Flight - vs. ASW-28
3/19/2005 Measurements with Full Top Surface Deturbulation
9/12/2005 A Performance Endurance Issue
10/29/2005 It’s Deturbulation Time Again
1/9/2006 Paper Presented at AAIA Annual Conference
2/3/2006 Talk Presented at SSA Annual Convention
5/6/2006 Paper Presented at AAIA Flow Control Conference
7/1/2006 Notes on Endurance and the Temperature/Humidity Issue
10/21/2006 Measurements Show 20% Improvement!
(revised 1/3/07)
12/13/2006 Deturbulator Performance Confirmed!
1/2/2007 Calibrated Airspeeds
12/13/2006 Summary of Johnson Flight Test
(revised 2/10/2007)
12/13/2006 Details of Johnson Flight Test
(revised 12/26/2007)
12/01/2007 Johnson Effect Confirmed
(revised 12/26/2007)
06/7/2008 Third Parallel Flight - vs. Diana 1
(revised 8/3/2008)

Publications and Presentations
1/2006 Sailplane Performance Improvement Using a Flexible Composite Surface Deturbulator - Sinha
(PDF, 1174 KB)
6/2006 Drag Reduction of Natural Laminar Flow Airfoils with a Flexible Surface Deturbulator - Sinha
(PDF, 757 KB)
2/2007 Wing Surface Deturbulators - Johnson
(PowerPoint, 2140 KB)
2/2007 Revolutionary Aerodynamics - Sinha
(PDF, 856 KB)
6/2007 Optimizing Wing Lift to Drag Ratio Enhancement with Flexible-Wall Turbulence Control - Sinha
(PDF, 588 KB)
8/2007 Improving Automotive Fuel Efficiency with Deturbulator Tape - Sinha
(PDF, 1368 KB)

First success on upper surface of Standard Cirrus wing (12/3/2004)

Figure 20. Results at the 53" span station.

December 3, 2004 was another very good day for the Sinha project. After working months to resolve problems with FCSD on the top surface of the Standard Cirrus wing, we finally realized success. Furthermore, we did this at two widely separated wing stations with similar results, indicating that we are beginning to achieve the consistency we seek.

Fig. 20 shows the change in boundary layer flow at the 53" span station. Fig. 21 shows the same for the 167" station. This station is on the aileron, 3" out from the inner end. The drag probe is mounted on aileron, with the hinge gap in front of the probe. The data were taken with the hinge gap open, but with an S-seal inside and mylar on the lower surface to prevent flow through the gap. In these graphs, the dashed line shows the percent improvement, plotted against the right axis.

As usual, the differential pressure between the aircraft Pitot and the drag probe is measured and reported in volts. It is not important to convert to units of pressure for comparative measurements. Note that this is not a measure of the wings drag coefficient, but merely a measure of the change of velocity in the boundary layer near the surface. How this will affect aircraft performance will be seen when we take polar measurements with fully modified wings.

The percent change on the upper surface is roughly half that of the under side (Fig. 13). However, as Fig. 22 shows, at cruising speeds, the upper surface generates about three fifths of the drag. So, in terms of the effect on the drag coefficient, it might be reasonable to expect FCSD to have nearly equal effects on the pressure and suctuon sides. At ninty knots, this would be about 9% reduction, giving an 11% increase in L/D at that speed. Of course, this refers only to the wing, not the entire glider.

Figure 21. Results at the 167" span station.

However, there is more good news. Dr. Sinha is confident that he can get better improvements on the upper surface. He has already done better on the upper surface of the NLF-0414F laminar airfoil that resembles modern glider airfoils. With the greatest camber at the rear of the wing, these airfoils are easier to treat. The Standard Cirrus wing was a real challenge, but it forced Dr. Sinha to look into issues that will benefit every installation of FCSD and hasten time to market for this new technology.

A second source of optimism is that measurements in the wind tunnel have shown that an increase in lift comes with the drag reduction. So, this is expected to further improve L/D. Evidence of this has been noticed in test flights by the need to apply a little stick pressure toward the treated wing to keep the glider from rolling the other way.

However, my greatest optimism comes from the consistency I see in the results of two very different applications of FCSD. One near-root application and one aileron. Numerically the results are similar. Both show diminishing improvement at the lowest speeds and increasing improvement with airspeed at the highest speeds. Neigher shows an increase in drag at any speed. So, at this point, I am confident that a full span treatment of FCSD will give reasonably consistent performance at every span station and we are now able to move forward toward a full performance measurement on the glider.

Note: the baseline data (black curve) in Fig. 21 was taken in less than ideal conditions. The dips at 50 and 70 kts are likely poor data points. I think the true curve is flatter, like at the 53" station. Thus, I believe true change at 50 kts was about 5% and 8% or 9% at 70 kts.

Jim Hendrix
Oxford Aero Equipment

Figure 22. Drag from the upper vs lower surface at the 53" span station.

Airspeeds shown in graphs are instrument calibrated. The aircraft airspeed system is not calibrated. Errors in the Standard Cirrus static/Pitot system bias the data towards higher speeds. This makes polars seem better than they really are. However, this is not an issue when the purpose is only to show comparitive data on the same glider.


© Copyright 2003-2008 Jim Hendrix