Plane & Pilot
Tuesday, February 5, 2013

The Way Of Active Winglets

It’s not cheap, but it adds performance and safety to a variety of airplanes

Tamarack winglets extend wingspan on CitationJets by four feet and can improve fuel savings, range, short-field performance, climb, wing loading and more.
The airflow around winglets is complicated, however, so much so that one design definitely doesn't fit all. Cant, the angle to which the winglet diverges from vertical, and toe, the angle at which the winglet(s)' airfoils diverge from the relative wind, determine the magnitude and orientation of the lift force generated by the winglet itself.

Winglets come in a bewildering variety of shapes, some nearly vertical and severely swept, others in airfoils above and below the wing at various angles from vertical. When properly designed, winglets provide the effect of increasing aspect ratio without extending wingspan.

Trouble is, such advanced technology isn't free. Airliners have realized significant advantages for a dozen years, often benefitting by as much as a 7% lift increase, but retrofitting them on a 737 can cost as much as $800,000 installed and add over 400 pounds to empty weight. Both those costs may be tough to amortize unless the aircraft operates on long legs at high altitude.

Additionally, passive winglets can translate wing-bending moments all the way to the wing root. Turbulence only adds to the problem and demands structural beef-up.

But what can winglets do for the little guy? Tamarack's CEO Guida developed the system for initial installation on his personal Cirrus SR22, and Plane & Pilot recently flew with him in the modified aircraft out of Van Nuys Airport, Calif. Guida explained that one of the problems with winglets is they can exert additional loads on the outer wing panels. These loads aren't significant in relatively smooth air, but they can become a source of concern when the sky fills with turbulence.

Accordingly, Guida designed his ATLAS winglets to relieve gust loads any time the airplane is experiencing 1.5 Gs or more. That's a fairly major gust load, as it turns out. My first airplane was a Globe Swift that I fitted with a G-meter, expecting to see some big gust loads over the California desert in summer. I rarely saw more than 2.0 Gs and even 1.5 Gs was uncommon.

Guida's active winglets operate by deflecting up whenever the sensor registers a G-load of 1.5 Gs or more. This effectively unloads the wingtips, and virtually eliminates the possibility of any structural damage associated with the addition of winglets. The ATLAS system is automatic and reacts faster than human reactions, something like the yaw dampers that help reduce yaw instability in turbulence.

Operationally, the only function check comes during the run-up. The pilot turns the system off and looks for a warning light, and assures that the two control vanes on the outer trailing edge of each wing are in the default position. After that, there's nothing left to do but fly.


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