The Boeing Company's board of directors has authorized full production go-ahead for two new longer-range 777 airplanes (-200 and -300), which it will begin delivering in September 2003. The long-range aircraft, which will be capable of flying more than 10,100 mi, could replace some of the early 747s by providing comparable capacity with twin-engine economics.
Both aircraft will be powered by a higher-thrust derivative of the GE90, which has accumulated more than one million flight hours since entering service in November 1995. GE Aircraft Engines has been working for two years to develop the GE90-115B engine (Aerospace Engineering, May 1999), which will produce the 115,000-lb thrust needed for the longer range 777-300. According to Boeing, the longer range 777s will fly at Mach 0.84,
slightly faster than some competing aircraft.
To keep costs low, many of the technologies for these longer-range 777 aircraft were carried over from its earlier versions. However, several low-risk innovations were incorporated on these new versions to improve performance, reliability, and ease of maintenance.
A semilevered gear system was developed and is being incorporated on the longer-range 777-300. During takeoff, the device moves the center of force on the landing gear to the aft two wheels, producing a lengthening effect that allows pilots to take off at a higher rotation angle. As a result, liftoff speed can be reduced and the take
off field length can be shortened by as much as
600 ft.
Another technology to be added to the new 777 versions is a supplementary electronic tailskid (SETS). This helps prevent pilots from inadvertently scraping the tail on the runway during takeoff or landing. The system resulted from a change in the flight computer's software to create a "virtual" tailskid that commands the elevators to move if the takeoff or landing attitudes exceed certain limits. SETS could also reduce further the airplane's takeoff and landing speed requirements.
Other enhancements to be made to the longer-range 777s include:
- new main landing gear and strengthened nose gear
- revised engine struts and nacelles to hold the increased thrust engines
- increased fuel capacity resulting primarily from 6.5-ft wingtip extensions and extra space that had been
reserved for an optional wing fold
- a strengthened body, wing, and empennage
- provisions for up to three optional fuel tanks in the
aft cargo compartment (longer-range -200 only).
Extending the range of the 777 further will result
in flights of up to 14-18 h,
prompting airline customers'
concerns over adequate crew rest areas. Boeing engineers responded by developing options to accommodate crews using a volume of space above the cabin, avoiding the displacement of revenue generating seats or cargo space.
The pilot rest area will be located near the flight deck at door one, with a stairway leading up to two business-class seats and two sleeping bunks. Flight attendants will be able to access their rest area at either door three or four, with modularized units accommodating from 4-11 sleeping bunks and two business-class seats. The space saved by these two crew rest areas is the equivalent of about four business-class seats and 10 economy seats or 4-6 of the large LD-3 cargo containers on the lower deck. Another proposed option is an overhead closet at door two, which is also being studied for galley cart or general storage area.
With the addition of the two new 777 models, the company will offer 25 aircraft models servicing regional, business, commercial airline, and cargo requirements. The Boeing family of airplanes ranges in size from 100 to almost 600 seats.
Frank Bokulich
Aerospace Engineering May 2000
