Jet Journal: An Active Approach to Better Performance

Jet Journal: An Active Approach to Better Performance

Jet Journal: An Active Approach to Better Performance

Tamarack Aero’s ATLAS Active Winglet system expands the range/payload, fuel burn and speed equation for Citation 525 line.

Sometimes the simplest ideas are the most effective.

Tamarack Aero has developed a product that is not only elegant in its simplicity, but delivers extraordinary results. The company has developed a winglet system for the Citation 525 family of light jets that allows it to fly farther, consume less fuel and lower operating costs without the weight and complexity penalty of traditional winglets.

And the numbers behind these improvements are nothing short of impressive: 20 percent fuel savings on a 2.5-hour trip vs. the stock airplane; 10 percent increase in range; climbs to altitude in under 25 minutes; maximum zero fuel weight increase of 400 pounds.

The small Sandpoint, Idaho company with the big idea has unleashed new potential in the most popular owner-flown, single-pilot jet — the 525, 525A, and 525B — allowing it to perform as well or better than its bigger brothers within the Cessna Citation line.

Winglets: Harnessing the Potential

Contrary to popular belief, winglets are not a recent invention. It has been known for more than a century that an endplate at the tip of a finite wing can reduce drag and increase wing performance. As air flows over the wing, high pressure on the wing’s lower surface and the low pressure on the top surface,  that creates lift. When flow around the wingtips streams out behind the airplane, a vortex is formed. Wingtip vortices, besides causing a wake turbulence hazard for trailing aircraft, creating an unavoidable consequence: induced drag. Angling the end of the wing upward increases the effective aspect ratio of the wing and change the pattern and magnitude of the vortex.

The concept of winglets as a drag reduction structure dates to 1897 when English engineer Frederick W. Lanchester patented wing end-plates as a method for controlling wingtip vortices. In the United States, Scottish-born engineer William E. Somerville developed the first functional winglets in 1910. Somerville installed the devices on his early biplane and monoplane designs. Another American engineer Vincent Burnelli received a patent for his “airfoil control means” in 1930.

While aerodynamicists and engineers tinkered with designs through the years, it took the energy crisis of the 1970s for researchers to get serious about winglet development and broad commercial application. NASA’s Aircraft Energy Efficiency program studied and wind-tunnel tested a range of winglet designs with the goal of improving fuel efficiency. Aeronautical engineer Richard Whitcomb published the agency’s findings in 1976, predicting that winglets deployed on transport-size aircraft could diminish drag and improve the aircraft’s lift-drag ratio by 6 to 9 percent. NASA would go on to flight test a nine-foot-high winglet on a KC-135, validating Whitcomb’s findings. (Fun fact: Whitcomb is the person credited for naming the wingtip device the “winglet.”)

In addition to drag reduction, winglets generate lift at the tip, increasing the bending moment at the wing root and requiring the structure to be beefed up. Thus, the winglet adds weight and complexity to the wing, something the original wing designer and manufacturer could have never anticipated. Winglets on a typical airline aircraft add significant weight — as much as 1,000 pounds for a typical Boeing — and deliver modest 3 to 5 percent reductions in fuel burn. If you’re an airline flying thousands of hours above FL350 on long-range flights, 3 percent can mean big savings. Traditional winglet design, however, has continued to chase the promise of 10 percent fuel burn reduction over long ranges.

Tamarack founder Nick Guida knew there had to be a better way to take advantage of the inherent benefits of winglets but without the weight and structural complexity. Guida was the kid who loved airplanes and had a natural curiosity about design and aerodynamics. As a youngster, he built his own wind tunnel to do aerodynamic testing. After getting his degree from Georgia Institute of Technology in aerospace engineering, he went to work for Boeing. After eight years, he left Boeing and accepted the chief engineering job at Aviat Aircraft, the small Wyoming company that manufactures the Husky tailwheel aircraft.

While at Aviat, Guida built an experimental plane, competed in aerobatics, and attained his Designated Engineering Representative certification for structures, loads, and fatigue. That led to a job doing contract engineering for Boundary Layer Research, which was developing aftermarket winglets for the King Air. He also worked on winglets for Hawkers and Falcons.

“All this time, I’m realizing how bad winglets are for the aircraft structurally,” he said. “All this metal we are throwing at it, all these straps and reinforcements on ailerons. It seemed silly. That’s when I had an epiphany: what if we could turn ‘off’ the winglet during higher g-force events, but still reap the aerodynamic efficiency benefits during normal 1-g phases of flight?”

That big idea was the Tamarack Active Winglet system. After proving his concept out and doing some initial testing on his own aircraft, he applied for a patent, and decided the best airframe to benefit from his new idea was the Citation 525.

“First, it’s a great aircraft, and second, there are about 1,800 of them flying. Finally, the wing is the same for the 525, 525A and 525B making certification simpler,” Guida said. “There are a lot of owner-pilots who fly the 525, and they are passionate about them. We are taking an aircraft they love and making it better.”

Tamarack successfully certified its system with the European Aviation Safety Agency (EASA) in late 2015, and received FAA STC validation for the Cessna 525, which includes the CJ, CJ1, CJ1+ and M2, last year. The company has partnered with Textron Aviation to offer the winglet system exclusively through its network of service centers. The install price is $239,900.

How the Tamarack Winglets Work

Tamarack calls their product the ATLAS Active Winglet system, which has three components: a wing extension (five feet on the Citation 525), a “powered” or active load alleviation device and the optimized winglet. The load alleviation system — called Tamarack Active Camber Surface, or TACS — is a device extension that is installed on the outboard trailing edge or the wing. The system senses increases in G-forces, such as during turbulence or maneuvers, and automatically activate to dump the load. If you look closely during maneuvers, you can see them subtly move much like you see on any other control surface. This alleviates the structural stresses that you would normally find on a conventional or “passive” wing and winglet. However, due to their relative lightweight and simplicity, there is no weight penalty trade-off and they do not require any wing reinforcement.

The TACS is completely independent of the aircraft’s flight control systems and operates autonomously. The only time the pilot needs to interact with the system is during pre-flight with a push-to-test button. Should the system lose power, the pilot will get an annunciation on the panel and will be required to slow down to a defined airspeed, similar to when flying in turbulence. With wing loading no longer a concern, the winglet itself is a highly tuned and optimized for maximum aerodynamic efficiency.

For the Citation 525 equipped with ATLAS Active Winglet system, the aircraft experiences many dramatic performance improvements. The system allows the 525 to climb quicker and get to altitude faster, shortening second segment climbs and speeds. This translates to significant fuel savings of as much as 25 percent decrease in fuel burn. On a recent CJ3 test flight from Orlando to Sandpoint, Idaho, Guida reported the Tamarack testbed saw a 10 percent increase in range (more than 200 nm)

The system also provides a maximum zero fuel weight increase — 400 pounds in the CJ3 — as well as better hot and high performance.

The winglet system increases the span and dihedral of the wing, which enhances stability at altitude and eliminates the yaw damper inop limitation. Some other benefits are that the system also improves low-speed handling, lowers stall speeds and increases the fatigue life of the wing.

Former Cessna test pilot and instructor Kirby Ortega, who has test flown the Tamarack system, said he was impressed with how the system makes a good airframe even better.

“Previously, I was never a fan of winglets, because they were never designed to deliver anything but modest improvements,” he said. “When I flew the Tamarack, the fuel savings were obvious in the first 30 minutes of the flight. The climb impressive, allowing us to go directly to FL400 in less than 25 minutes.”

He also saw an improvement in stability and ride. “Once at altitude, I switched off the autopilot and depressed a rudder pedal to see how quickly it would return to stable flight. It cycled back and forth perhaps four times before returning to straight and level. It’s a little heavier in roll, but felt solid and comfortable to hand-fly,” he added. “It makes a difference for the passengers in back, especially those who are terrified of turbulence. It dampens the turbulence and makes the ride smoother for them.”

Bern Kotelko, a CJ1+ owner-pilot based near Edmonton, Alberta, first test-flew the Tamarack Winglets in while attending the Citation Jet Pilots Association annual convention and was so blown away by performance improvements, he immediately scheduled his aircraft for installation. He has been flying the system on his own aircraft for a year now, and said the decision was “a no brainer.”

On the CJ1+, Kotelko said he now can climb directly to altitude with no step-climbs. Within 5 minutes of leveling off, the AOA decreases from 0.4 to 0.2. “Before the winglets was added, it would take 30 to 45 minutes for the aircraft to get on plane and pick up speed.”

With his typical mission being between Edmonton and southern California, he often lands with no less than IFR reserves (650 pounds), even with headwinds. He also said the lower stall speeds adds a safety cushion on days with gusty winds or wind shear on approach and landing.

“It’s the most cost-effective improvement you can make to an already great plane,” he said. “I have CJ2 range performance but the cost of the winglets is 20 percent of the cost to upgrade to the CJ2.”

What’s Next for Tamarack

With the CJ3 system expected to be certified in the fourth quarter of 2017, the company is already working on the 525A CJ2 certification program. Guida wouldn’t reveal which business jet airframes will follow the 525 series, but said the small company had some big things in store. Last fall, it was reported in Jane’s that Tamarack was interested
in working with Lockheed Martin to equip the U.S. Air Force’s fleet of C-130 Hercules transports with its active winglet technology.

“My focus is to grow the company and add three more product lines. We have some military programs underway and are talking to the airlines,” he said. “We have a lot of good stuff going on and expect to be going like
gangbusters.” 

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