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SPEEDY CITATION X

Cessna's high-speed business jet Citation X is on the market. It received the FAA certification at the beginning of June. With a maximum cruise speed of Mach 0.92, the "Ten" is Mach 0.1 or approximately110 km/h faster than most other of today's airliners. Mach 0.92 is only a transient number for many military supersonic fighter aircraft, but is outdone in civil air traffic only by the Concorde.

Two Allison AE3007C turbofans with each 6400 lbs of thrust are to insure that Cessna's new flagship can reach this speed. Furthermore, the development work on the Citation X focused on >the businessjet's aerodynamical performance. The wing sweep was the center of attention. The wings of the Citation X have a high sweepback of 37 degrees which is only exceeded by the Boeing 747's wing (37,5 degrees).

The advantage of the high sweepback is the increase of the critical Mach number, allowing for a higher airspeed. The disadvantage of this wing design, however, is its unstable aerodynamical performance at low speeds, for example during take-off and landing. High lift devices, such as slats, are used to counter these harmful effects. The Citation X's slats are normally extended together with the wing flaps. However, they are also coupled to the angle of attack sensor and are automatically extended when the airspeed is in a critical regime at high angles of attack.

Furthermore, the first, inboard, sections of the wings trailing edge, where the flaps are installed, are not swept but straight, such increasing the efficiency of the flap system. The voluminous design of the aircraft belly also serves the slow but regular acceleration of the air flow, such reducing the drag.

At its maximum take-off mass of 16045 kg (including full 7371 liter fuel tanks and the full 635 kg payload) the "Ten" is supposed to offer a range of up to 3000 NM. However, the aircraft has to limit its cruise speed to Mach 0.84 to cover this distance. In order to reach the full 3300 NM range, the speed has to be further decreased to Mach 0.82. At higher cruise speeds in the Mach 0.90 region the range will probably decrease to 2500 NM. Still, this is farther than most other business jets in the mid-size category can fly.

According to Cessna, the Citation X uses 2800 lbs of fuel on a 900 NM trip, which supposedly is 18 percent less than the Hawker 800 (3400 lbs) needs and up to 37 percent less than the Falcon 50 (4500 lbs). Comparing the X with the Gulfstream GII, which is a late 1960s construction, Cessna claims that the new Citation, flying in 47.000 feet at a speed of Mach 0.80, uses 30 percent less fuel than the Gulfstream sitting with the engines in idle on the airport ramp.

The Citation X accomplishes the climb to its 51.000 feet service ceiling in two segments, beginning with a steep 20 minute climb to 45.000 feet. The remaining 6000 feet take another 15 to 18 minutes, according to Cessna test pilot Mark Schlegel. This diversion from the original climb schedule is related to the 360 kg higher take-off mass (approximately 270 kg higher structural weight and 90 kg to carry a seventh passenger at maximum payload).

According to Schlegel this weight increase does not effect the good performance of the aircraft. Cessna guarantees that its new high-performance jet can be operated at the same costs (except of the price) as the Hawker 800.

The message is clear: The Citation X innovates the definition of cruise speed, but without throwing the economical aspects out the window. This is the real achievement of Cessna's development work.

From page 32 of FLUG REVUE 9/96