Tuesday morning, we strapped into the left seat of Tamarack Aerospace Group’s CitationJet, S/N 525-0012, newly fitted with active winglets, to sample a technology that promises to improve runway performance, cut fuel burn and carbon emissions by up to 10%, and eliminate the excess bending loads imposed by ordinary winglets.
TAG winglets also extend span by four feet, thus the CJ’s wing has a high aspect ratio along with the induced drag reduction effect of the 35 in. winglet. The result is a more ideal elliptical distribution of wing lift from root to tip, promoting a more efficient lift-to-drag ratio.
TAG’s winglets were developed in concert with famed aerodynamicist Ian Gilchrist of Redmond, Wash.-based Analytical Methods, Inc. The key to getting all of the benefits of legacy winglets and none of the structural downside is TAG’s soon-to-be-patented Tamarack Active Control Surfaces technology to reduce lift-imposed aerodynamic loads in gusts. TACS includes a triple-channel computer with an accelerometer, which detects gust loads and sends signals to deflect the FBW control surfaces, thus reducing winglet lift and the associated wing bending moments.
VeteranCitation pilot Brian Willett, now TAG’s VP for sales and marketing, accompanied us in the right seat as demo and instructor pilot. Willett walked us around the airplane, showing us the recently attached and instrumented TAG winglets – with TACS in bright orange – for the upcoming flight test development and certification program.
Our flight plan was slated to top out at 15,000 ft., so we couldn’t soar up to the aircraft’s certified 41,000 ceiling to evaluate the drag reduction benefits of the winglets. But, even so, we easily could impose abrupt vertical loads on the aircraft at low altitudes by moving the yoke to determine how quickly the TACS could respond to simulated gusts.
No pilot inputs are required for functioning of the active load alleviation system, while the analog design eliminates the need to qualify software to Do-178C Level A integrity standards. Willett said the system will provide 10-9 probability of un-annunciated failure. If the system were to fail, the flight crew only would need slow to a reduced turbulence penetration speed.
Willett suggested we look out the left side cockpit window to watch the progressive action of the TACS. We noted that they start to deflect at loads as low as 1.25G and progressively move to full deflection at the aircraft’s 3.8G limit. Willett said TACS are so effective at load alleviation that they actually reduce overall wing bending moment below that associated with the original wing. TAG active winglets also hold promise for allowing a 350 lb. higher maximum zero fuel weight.
Subjectively, climb performance appears to be improved with the addition of the winglets. It’s likely, however, that low altitude cruise speed may drop by a few knots due to increased parasitic drag. Above FL350, the aircraft should cruise a few knots faster at max cruise thrust or achieve greater range at lower thrust. TAG believes that max range will be increased by more than 100 nmi, primarily due to substantially improved climb performance, with up to 2,000 ft. higher initial cruising altitudes. A fully loaded CitationJet without winglets cannot climb above the mid to high thirties, depending upon OAT. With winglets, it should climb routinely to FL410.
Actual performance changes associated with the TAG active winglets will be measured during the flight test program next year. The aircraft we flew has a full complement of instrumentation, including multiple strain gauges and yarn tufts to monitor flow patterns. TAG expects to earn STC certification by late 2014 and begin delivering kits. Retail prices aren’t yet available, but company officials believe it will take 80 hours to install the system, including running 28 VDC and FBW control wires from the fuselage to the TAG active winglets.
Several issues and major challenges remain. TAG must convincethat failure modes won’t jeopardize the structural integrity of the wing during peak gust conditions. And FAA will likely require an extensive fatigue analysis of the wing structure to determine the impact on maintenance inspections.
Ultimately, the success of the TAG active winglet program will be as much contingent upon getting Cessna’s endorsement as it will upon earning FAA approval or improving performance. Most CJ operators and future buyers use Cessna’s factory-owned service centers for major maintenance inspections. If Cessna refuses to endorse the modification, aircraft equipped with TAG winglets could be orphaned from the Cessna family.
When AviationWeek asked a Cessna spokesman to comment about the potential impact of TAG active winglets on warranty and admittance to factory service centers, the response was “No comment.”