This project was an effort to improve aircraft performance by testing a novel technique for boundary flow control
on a Standard Cirrus glider with a Wortmann airfoil.
Progress has been slow because the work was done with private funding and equipment.
This work began in 2003 as a cooperative effort by Dr. Sumon Sinha and Jim Hendrix.
However, it split into separate efforts when it became clear that the objectives of the participants were not compatible.
Until March 2011, it could only be said that we had demonstrated the viability of a new method of boundary flow control
on Wortmann wings. Now, it appears that there is a simple, cheap and practical
modification that offers up to 15%
improvement. Applicability to modern airfoils remains to be tested.
In December 2006, my glider was taken to the legendary Richard H. (Dick) Johnson
for independent testing. Johnson confirmed average improvements of 13% to 18% at 50 knots indicated airspeed.
He measured sink rates manually using his time honored methods.
Johnson summarized his report, with the conclusion that
"the new Sinha Deturbulator could be the first really significant drag-reducing aerodynamic invention
since the development of the now-common laminar-flow airfoils that were developed some 65 years ago."
A properly sized rear-facing step near the leading edge of a precision, composite wing can produce significant performance improvements.
This method (1) reduces form drag by keeping the laminar detached boundary flow close to the surface (reduces effective wing thickness),
(2) reduces surface area exposed to laminar skin friction over the front of the wing and
(3) reattaches the flow gently, at a grazing angle, for less energetic attached turbulent flow over the aft section of the wing.
On the top surface, this requires a delicate balance of conditions that is extremely effective at a precise airspeed. This
balance can be maintained manually for about 1.5 minutes by holding the airspeed constant. Beyond that, a custom designed, pitch autopilot
fed with boundary flow sensors might hold it indefinitely. This extreme performance requires non-turbulent air with relative humidity
below 75%, so
it would be practical only for high altitudes in relatively dry air. But there is no penalty when these conditions are not met.
The wing simply returns to normal, unmodified performance. The pressure side of the wing is less critical, offering up to 15%
improvement even in turbulent, relatively dry air. The glider's polar curve is lumpy though, yielding a set of prefered airspeeds.
For more information, read the Project Summary.
For more on this, see
(Leading-Edge-Tape-Only Performance Measurements).
The lower surface mod is easy and practical.
For a project overview read The Deturbulator Tape.
Sufficient data now exists to justify funded R&D efforts to
(1) model the modified flow dynamics,
(2) optimize performance characteristics,
(3) develop new airfoils to exploit this technology and
(4) to develop practical applications in aviation, wind power, ground transportation, etc.
The number of people participating in this effort is growing.
If you are an aerodynamicist or merely an interested person you are invited to take part.
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