Tamarack Active Winglets Offer Weight-saving Aerodynamic Improvements

 - November 6, 2012, 5:10 AM
Tamarack Aerospace expects FAA certification of an active winglet system for the Cirrus SR22 early next year.

Tamarack Aerospace has unveiled the first of what it promises will be a series of active winglet systems designed to relieve wing bending loads caused by winglets. The company’s active technology load alleviation system (Atlas) should be certified and available for installation on Cirrus SR22 G1 and G2 piston singles early next year, but Tamarack is also testing Atlas, which includes new winglets, on a Cessna CitationJet 525. Tamarack brought the Atlas-equipped CitationJet to the NBAA Convention in Orlando and gave demonstration rides during the show.

According to Tamarack, ordinary passive winglets come with a penalty, shifting the center of pressure of the wing outboard and thus increasing the bending moment on the wing. To counteract this effect, the wing needs to be strengthened. On an Airbus A330, some 440 pounds of reinforcement had to be added, according to Brian Willett, vice president of sales and marketing. “That [bending moment] has an impact on the service life and required structural modifications,” he said. “What if you could get the benefits of winglets without the weight penalties?”

Tamarack, an engineering development firm based in Sandpoint, Idaho, has been developing Atlas for more than two years and has patented the technology. The company tested Atlas on a Vans RV-6 initially, and its entire wing was rigged with stress gauges. [See video of the SR22 Atlas here.]

The centerpiece of Atlas is the Tamarack active control surface (Tacs) actuator mounted near the winglet. The Tacs actuator drives small moveable surfaces mounted outboard on the wing trailing edge, near the winglets. These surfaces don’t intrude on space occupied by the existing ailerons. When Atlas’s sensors detect a load (change in g) they instruct the Tacs actuators to move to counteract and alleviate the load. This happens in milliseconds and the result, according to Tamarack, is that Atlas “prevents an increase in the bending moment on the wing.” The ultimate benefit is the ability to incorporate winglets without having to reinforce the wing structure, lengthening the life of the wing and, as a side benefit, “smoothing out turbulence,” Willett said. “Turbulence is a sharp spike. [With Atlas], instead of bang and bang, it’s a smoother ride.”

During testing, Tamarack engineers flew with Atlas configured in the worst-case scenario, with the Tacs deployed asymmetrically, fully deflected opposite to each other. Takeoffs and landings were accomplished safely in this configuration, according to Willett.

On the CitationJet, the Atlas winglets add two feet of length to each wing. Tamarack plans to offer Atlas on the entire CitationJet series and then on Hawker and Embraer jets. An Atlas system could be added to an airplane that already has winglets, but the full benefits aren’t available unless the winglet is large enough, Willett said. In any case, an existing winglet installation already includes the structural reinforcements that Atlas negates.

In evaluating the CitationJet wing before and after the Atlas modification, Tamarack found that, according to Willett, “some of the improvements are better than the OEM wing.” At a peak gust load of 4.4 g, the wing bending moment without a winglet (standard wing) is about 190,000 in-lbs, and with a standard winglet it climbs to 230,000 in-lbs. “With the active winglet,” he added, “we’re better than the standard wing. We’re down to 170,000 to 180,000 in-lbs. So it’s a reduced load on the wing. We expect to see an increase in wing service life due to less stress on the wing.”

The CitationJet Atlas winglets add less than 50 pounds to the airframe, Willett said. “The benefit in improved aerodynamic performance is such that with a plain-Jane CJ, you could carry a full load of fuel and one extra passenger with bags, because the wing is more efficient.” Of course, such capability would require extensive flight-testing to increase the mtow, and this is where partnering with an aircraft manufacturer would make Atlas even more attractive. In one example flight, Tamarack showed that a baseline CitationJet carrying a 1,300-pound payload flying the 863 nm from Boeing Field in Seattle to Palm Springs, Calif., could fly 850 nm, which necessitates one stop. The Atlas-equipped CJ could carry the same load and fly 1,100 nm, and thus be able to make the trip nonstop.

The FAA has imposed special conditions on certification of the Atlas winglets for the SR22, and these would apply on any Atlas modification program. The conditions mostly involve testing of failure modes of the load-alleviation system, including aerodynamic and structural implications. In the Cirrus SR22 system, failure of Atlas causes power to be removed from the system, and the Tacs move automatically to a neutral trail position, according to Tamarack. An annunciator light warns the pilot, who then needs to remain below maneuvering speed.

Willett said that Tamarack has had discussions about Atlas with several aircraft manufacturers. “[We’d like] to partner with an OEM to help make their product better,” he said.