The shape of the winglet, as well as its size and tilt, are the keys to success. Winglet Technology calls its patented shape "elliptical" to describe the shape that transitions from the horizontal wing surface up to the winglet. Shapes are very subtle, and other designers claim equal success with winglet shapes that only an expert — or patent attorney — can tell apart. The proof of success on the X is that, with the winglets, the airplane at 34,000 pounds — just 2,100 pounds below maximum — can climb directly to 47,000 feet in 27 minutes compared with about 93 minutes to step climb without winglets. That direct climb to FL 470 adds at least 160 miles of range. With above-standard temperature conditions at cruise, the winglets can add well over 400 miles of range.
The added lift of the winglets can also get the X out of high-elevation airports on hot days when engine-out climb restrictions are the limiting factor. With winglets the X can carry 1,200 more pounds of payload on the same hot day, or can depart with the same payload as the non-winglet airplane can at a temperature 4 degrees C hotter. The net result is more than 400 miles of range increase over the standard airplane.
The winglets on the X look great. These days a jet without winglets looks, well, kind of old-fashioned. For many years winglets were thought by many to be a band-aid to improve an improperly designed wing, so some jet designers, such as those creating the Citations and Falcons, avoided them. But it is now understood that the well-crafted winglet can bring very specific benefits to any airplane, no matter how successful the design of the basic wing. Plus, an airplane with all of the exotic drag-defeating shapes of the X should have winglets to complete its ramp presence.
Winglet Technology builds the winglets from carbon epoxy laminate with polished aluminum leading edges. Cessna conducted icing tests, and there is no need to heat the leading edges of the winglets. The winglets stand 4.2 feet high and extend the tip-to-tip span of the wing 5.3 feet for a total span of 69.2 feet. A new lens covers long-life LED position lights and anti-collision lights in the winglet. The winglets look as though they were born on the X, rather than being an add-on. A non-winglet airplane looks a little stodgy in comparison.
All of the test and demonstration pilots at Cessna agree that the winglets do not change the flying qualities of the X at all. Performance, yes, but the feel of the airplane, no. To see for myself, Cessna director of flight operations Dave Nolte and I saddled up with 11,500 pounds of fuel in the X, plus one passenger, bringing takeoff weight to 34,000 pounds, pretty typical for a transcontinental trip. The winglets with their necessary structural modifications add about 150 pounds to the empty weight, but that penalty can be recovered in fuel savings on most trips of any length.
Unlike other jets in the Citation family, the X has big-airplane systems with hydraulically boosted flight controls, air starters on the engines and full-time yaw dampers. The Honeywell avionics system is one generation old and still uses CRT displays instead of flat glass, but see the companion story for information on an update there.
The X likes to fly fast, including on the runway where our V1 decision speed was 126 knots with rotation at 128 knots. Once clear of the speed restrictions, typical climb speed is 285 knots until reaching Mach .83. That means the X is flying faster in climb than most business jets can achieve in cruise.
With only a couple of brief level-offs from ATC on the way up, we were through 38,000 feet in 21 minutes with air temperature above standard the whole way up. As we climbed, the air temp cooled to standard or a little below and the X climbed smartly with an indicated Mach of .83 until we reached 45,000 feet in 28 minutes' total time. At that level we still had 10,000 pounds of fuel in the tanks, the true airspeed hit 490 knots, and total fuel flow was about 1,760 pounds per hour.
Avionics Display Swap
The new Primus Elite flat panels will be able to display Jeppesen approach charts and XM satellite weather, along with detailed moving maps that cannot be presented on the CRTs. The Citation service centers will offer the same display upgrade for existing airplanes in the second quarter of 2011.
With the flexibility of the new displays available, Cessna and Honeywell are hard at work developing synthetic vision and advanced WAAS-based approach guidance for the X. These advancements are expected to be available in 2012.
Citation X passengers will also see technological advances next year with availability of Aircells' high-speed Internet system, which will provide enough bandwidth for most functions while flying above the Aircell network that is located across the 48 states. Advanced passenger cabin displays and controls will also be part of the upgrade.
Dave told me that the rule of thumb for fuel burn in the X is 2,800 to 3,000 pounds for the first hour up to 43,000 feet, and then about 2,000 pph for additional hours, adding or subtracting 100 pounds for each 1,000 feet of added altitude lower or higher. So with the winglets, an X crew can get to FL 450 without stepping and FL 470 on most days, saving hundreds of pounds in the first couple of hours compared with the airplane without winglets. The X is certified to 51,000 feet and with the winglets can get to that altitude with well over an hour's worth of fuel, plus reserve, left.