With a supplemental type certificate (STC) secured, Winglet Technology is rolling out new “transitional” winglets for the Cessna Citation Sovereign and has already begun eying the next application for the technology—the Sovereign+. Winglet Technology obtained the STC on June 20, the culmination of a four-year development and certification program.

The result is “almost the equivalent of a new model,” said Robert “Bob” Kiser, president and managing member of Winglet Technology. “We’ve taken an airplane that has spectacular takeoff and landing performance for its class and made it an entirely different airplane at altitude. The airplane will climb to higher altitudes at heavier weights and be faster than the legacy Sovereign. We’ve made the airplane much more operationally diverse in what it can do.”

The retrofit of the transitional winglet dramatically cuts the time-to-climb to FL450, offers up to 35 knots additional speed at FL450, and extends range by 340 nm or allows up to 914 pounds' payload capability at equivalent range.

The winglets enable the aircraft fly direct to FL450 in 28 minutes, rather than the step climb required on the non-winglet model, which takes about 73 minutes. In addition, the retrofit offers an mtow increase that will bring the Sovereign in line with the Sovereign+, with an additional 475 pounds of maximum takeoff weight and 200 pounds higher zero-fuel weight. The net effect of the weight increase, Kiser said, is extra useful load that “you can spend any way you want—by filling the tank or adding passengers.”

Final results exceeded original targets of a 26-knot speed improvement at FL450, 305-nm range improvement and 350-pound gross-weight increase. Winglet Technology opted for a higher weight to ensure it matched that of the Sovereign+ and conducted a structural load analysis with the higher weights. The company also verified the improved performance through Textron Aviation’s aircraft performance data.

Designed for Varied Conditions

Kiser said the gradual transition from the horizontal wing surface to the vertical winglet surface has improved the wing's aerodynamics. “The flow coming across a gentle transition has a tendency to perform better than an abrupt vertical design,” he said, noting that a more abrupt change in surface direction causes the flow to “shock and separate at the transition. With the transitional winglet, we are trying to keep the flow attached over a broader range.” This provides a wing that is “robust and handles a wide range of operating conditions” at higher altitudes and higher weight, he said.

The flight-test program involved 170 flying hours, as well as full-scale static testing on a wing. The Wichita-based company worked on the installation with Duncan Aviation and on early proof-of-concept flight-testing with Cessna. But the bulk of the flight-testing was done from Wichita Eisenhower Airport with the use of a customer aircraft that had the interior removed and was instrumented for the program. Cessna supplied a wing. “Once we got our hands on a wing to support full-scale static testing and secured an airplane, it went pretty quickly,” Kiser noted.

Winglet Technology has already received significant interest from operators, Kiser said, noting that nearly 350 legacy Sovereigns are in service. The winglets will be offered through Textron Aviation's service center network, as well as Duncan Aviation, with a list kit price (not including installation) of $415,000. Duncan is offering an installed price of $495,000.

Winglet Technology is moving the design engineering team on to the next project, he said, which is anticipated to involve the Sovereign+. In addition to engine and avionics upgrades, the Sovereign+ has about nine feet more wingspan. The Winglet Technology project would involve removing that wing extension and adding the winglets. While the swap would shorten the span by three feet, Kiser said the result is expected to provide high-altitude benefits while preserving the short-field performance of the aircraft. He expects the Sovereign+ program to take less time than the Sovereign program, with completion in nine to 12 months once an aircraft is secured.