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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)

Notes on Endurance and the Temperature/Humidity Issue (7/1/2006)

In two previous articles (9/12/2005 and 10/29/2005) I reported a loss of performance over time with increasing temperature and/or humidity. It appears that this problem has been overcome by changes in the construction of the deturbulator. The humidity in the air beneath the mylar skin was condensing at high altitudes and restraining its action.

After flying one year with full-span upper-surface deturbulated wings, Dr. Sinha replaced the original deturbulators with the revised design. Although, he still has to replace several 18" strips that are not up to standards, it seems clear that the humidity issue is solved.

Meanwhile, I have resumed normal cross country soaring with newly deturbulated wings and can report that my glider is performing very well. I have no qualms about taking it on tasks that push my chances of making it back home. On long glides at low speeds and high it normally outperforms the glide slope computed by my Cambridge 302 (configured for the normal 36:1 Standard Cirrus polar).

As an example, I present a final glide on 7/1/2006 (click image on right). This flight ended with a 13 nm glide at an average airspeed of 85 kts into a 17 kt headwind. The elapsed time was 11.7 minutes and the altitude loss was 3048 ft. The average sink rate was 260 ft/min. This compares to my baseline polar at 360 ft/min, for a 25% improvement. Of course, this one case isn't conclusive since gliders always experience wild variations in sink rates depending on the air they fly through. However, I cite this case as typical of the performance I now expect.

One question that frequently comes up about the delicate Mylar outer layer of the deturbulator is "will it hold up over time in normal use?" After flying one full calendar year with the original deturbulator and half a year with the revised version, I can say that I have had no problems at all. We have not yet found it necessary to replace a panel due to damage of any kind. I should say, however, that we trailered the glider only once or twice. Additionally, deturbulator strips of similar construction have been working on Dr. Sinha's van and my truck since March 2006 despite exposure to various weather conditions and road debris.

Another question is "what is the effect of rain and ice?" I've had two experiences of that sort. In the first case, I took drag rake and sink rate measurements while flying at around 10,000 feet in icy virga. Both measurements were ugly, especially the drag. However, at lower altitudes, the wings cleared off and everything returned to normal. I was able to retake the bad data points and they fit beautifully into the overall polar.

Again, on a recent competition flight (click image on left), I was flying around the front side of a growing thunder cell when the cloud tendrils I aimed for turned out to be sleet. I put the nose down and sped away. This was followed immediately by a glide of 18 nm behind a rain cell that had just passed through. The air was absolutely smooth all the way (upper right quadrant of the image). The 302 showed a steady gain on the computed glide slope as I held 43 kts with a 10 kt quartering tailwind. So, once again the deturbulated wing cleared itself.

One thing about this flight, it ended with a landout in a soggy bean field. The glider got dirty, but the deturbulators required no maintenance except the usual cleaning before every flight. This 36 year old glider won the day with the longest flight in a field of seven competitors, some flying the latest technology. Only three got away from the home field. Granted, a task around rain cells in rapidly changing conditions is largely a question of timing and chance, but glider performance was definitely a factor.

One point should not go unmentioned. These two flights, among others, stand as clear testamony that the Sinha deturbulator does in fact work. Compare these flights to the performance one would expect of a modern composite glider modified by sticking ordinary duct tape on the upper wing surfaces from root to tip in a region that is not under the separation bubble. I would never set out on a cross country flight in such a glider. Yet, this one is obviously flies very well. Even if it were flying no better than normal, something good must be happening to overcome the drag penalty of 14 meters of tape on the wing tops. That this glider is flying with its wings so modified is common knowledge to everyone in the Memphis Soaring Society (hosts of the 2007 SSA convention). Ask anyone.

Now that we are flying with what appears to be predictable performance, we expect soon to take a good performance polar of the modified glider. If this meets expectations, we intend to have it tested independently. Meanwhile, Dr. Sinha continues to develop ways to manufacture his deturbulator with sufficient precision to ensure proper operation. Another continuing line of work is to better establish the theoretical foundation of the flow/surface interaction that produces the deturbulation action. For this we will use the LINFLOW software package together with ANSYS/ED.

Jim Hendrix
Oxford Aero Equipment


© Copyright 2003-2008 Jim Hendrix