Guy Norris /SEATTLE
Boeing has finalised the design configuration for the 777-200LR and -300ER variants, and has added an extendable nose landing gear on the latter. This will offset the potential loading problems caused by the tail-high attitude which results from the use of the semi-levered main gear on the longer version.
Firm configuration has been agreed with all six launch customers: Air France, All Nippon, EVA, GE Capital Aviation Services, International Lease Finance and Japan Airlines (JAL), which together have firm orders for 49 of the new variants. All except three of the orders are for the -300ER, major assembly of which is now set to begin in June of next year.
The situation cropped up only when the aircraft was lightly loaded and is due to increased nitrogen pre-charge pressure on the main landing gear shock strut. This is being modified on the longer -300ER nose gear where a semi-levered actuator is being added to allow the aircraft to pivot around the aft tyres on the six-wheeled truck beam. The feature was a critical element in improving the take-off performance of the 340,500kg (750,000lb) maximum take-off weight (MTOW) aircraft. The semi-levered gear increases the VMU (velocity minimum unstick) take-off angle to 10° against 8.9° for the unmodified gear. The additional angle is enough to reduce take-off distance by at least 185m (600ft), which is sufficient to allow MTOW operations from critical obstacle-limited airports such as Los Angeles.
When lightly loaded, Boeing discovered the higher main gear would produce a distinct nose down attitude which would mean having to modify cargo handling equipment to reach the higher aft cargo door sill. After various studies, it was decided to adopt a dual chamber feature on the nose gear that allowed it to extend by up to 25cm at light loads.
The feature adds around 68kg (150lb) in weight, but Boeing 777-200LR/300ER programme manager Lars Anderson says, despite this, the overall weight picture is "looking good. We are still keeping a lot of emphasis on it," he adds.
Boeing's target is an operating empty weight of 169,340kg for the -300ER and 156,175kg for the -200LR. The programme is expected to meet the 25% design release target in August. The -300ER is scheduled to make its maiden flight in January 2003, with JAL expected to be the first recipient of the aircraft, in September 2003.
Source: Flight International
