A Practical Modification (3/19/2011)

For a full report, including an overview of the concept, test data and a simple explanation of how it works, read The Deturbulator Tape (PDF). For more information on prior Deturbulator tape experiments, see Leading-Edge-Tape-Only Performance Measurements and Effect of Leading Edge Tapes.

Saturday, March 19 was a banner day for the Deturbulator Project. After these many years of work, it appears that I have now arrived at a practical modification that does not unduely mess up the polar and offers perhaps 15% improvement. And, the icing on the cake is that it costs virtually nothing, can be installed by anyone in less than an hour and can be removed in 10 minutes. This is only a heads up notice. I'll have more to say about this later.

First a disclaimer. My glider, Standard Cirrus #60, is registered, in the United States, experimental for research and development, specifically for this kind of research. I am only reporting my results. I am not recommending that anyone follow my example nor am I suggesting that anyone violate the limitations of their registration category.

Following is the data taken on 3/19/2011:

Atmospheric conditions were not good, but after installing the new tape, I wanted an idea of whether it would work as expected. So, there is a fair amount of scatter in the data. Nevertheless, it clearly shows that the severe performance loss at all speeds with positive AOAs (1st Lower-Surface-Leading-Edge-Tape-Only Performance Measurement (1/29/2011)) was caused by placing the forward edge of that tape too close to the leading edge of the wing. It also confirmed that the characteristic performance "notch" is a top surface phenomenon after all.

After the consistency of prior leading-edge tape tests and the predictable behavior with this last change, I have every confidence that further measurements will only confirm and smooth this data. I hope that this DEturbulator tape will catch on as a better alternative to the traditional Turbulator tapes. I call it a Deturbulator tape because it functions antithetically to Turbulator tapes. I will have more to say about that later, even though it remains for professional aerodynamicits to work out the details rigorously.

Of course there will be an airfoil dependence and it's anyone's guess how this will work on modern airfoils. But, this is so easy to install and so cheap that others with the patience and skill to measure performance on other gliders should step up to the plate soon and answer the question. If you are interested, go to the Downloads page where you will find a manual on testing performance changes using your flight logger. Also, you will find a spreadsheet for reducing and plotting your results. I only request that you notify me of your work and share your results so I can use this website as a clearing house for all interested parties.

First, obtain a roll of tape equivalent to Tesa 4104. The thickness is critical. It must be very close to 76 um (.003"). Much thicker and it will trip the flow. The width needs to be around 12 mm (1/2"). This tape may be obtained from Oxford Aero Equipment.

Next, mark a guideline 45 degrees below the nose of the wing. The point of this is to ensure that at all airspeeds the relative wind sees the forward edge of the tape as a step up so it will have no significant effect. If the flow sees a step down there will be a large loss of performance.

To mark the guideline, jack up the tail until the leading and trailing edges are the same distance from the floor. Then, wrap some carbon paper around the base of an inclinometer and place it beneath the leading edge of the wing at an angle if 45 degrees as shown below. Finally, slide the inclinometer along the wing whole holding the 45 degree angle.

All that remains is to apply the tape with the forward edge along the guideline. Avoid wrinkles and bubbles. Also, of course, make sure the tape's edges are not damaged in any way. Complete the job by pressing the tape down firmly and smoothing out any roughness or sharpness on the edges. It is not necessary for the rear edge to be sharp. A rounded step works fine.

That's all there is to it.

Jim Hendrix

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