More than four decades after Pan Am debuted the
Boeing
747-100, a stretched variant of the world's original Jumbo Jet is
finally plying the world's air routes. But by the time this bigger
"seven-forty-seven" arrived,
Airbus had already redefined the meaning of "Jumbo Jet" with its
A380. So the battle for that "queen of the skies" crown was on.
Boeing had spent a decade evaluating ways to create a substantially larger
747,
before decide in November 2005 not to let Airbus off the hook too
easily. Scoped under the name "747 Advanced", the stretch was launched
as the "
747-8" to reflect the naming convention around the number eight adopted for the
787 then in development.
Along with the
Dreamliner's designation came its General Electric
GEnx engines - although featuring a conventional bleed system for air-conditioning.
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Max Kingsley-Jones/Flightglobal
Lufthansa banged the drum for its new Jumbo when its first 747-8 arrived in May
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The 747-8 was originally slated for service entry in 2009, but a
series of programme delays, caused by development issues and a knock-on
from the interruptions suffered by the 787 programme, meant the first
stretched aircraft did not leave the ground until February 2010.
The new
jet finally entered service - in freighter form - with
Cargolux in October last year. The 747-8 Intercontinental passenger variant followed in June this year, debuting with Lufthansa.
The "big Boeing" is in effect a major derivative of the
747-400
that had been launched two decades earlier, which itself traces its DNA
right back to the original Jumbo developed in the late 1960s by a team
headed by industry legend Joe Sutter.
Now aged 91, Sutter has been officially retired from Boeing for more
than 25 years, but retains an office at the company's Seattle
headquarters so he can keep a watchful eye on the latest iteration of
his precious creation.
"Joe's still as sharp as ever and we talk about the airplane a lot,"
says today's 747 chief project engineer Bruce Dickinson. "I welcome
Joe's opinions and input."
Unlike some of the more ambitious studies of the 1990s, the
definitive 747 stretch does not incorporate a major fuselage extension
and enlarged wing. Instead, the fuselage has been treated with a modest
stretch, with plugs fore and aft of an effectively all-new - but
similarly sized - wing.
TYPE COMMONALITY
"About 70% by structural weight is new. In many respects, though, we
could state almost all of the airplane is new, as we have heavier gauge
materials that have similar construction as the 747-400," says
Dickinson. "We strove for a lot of commonality in general, though, as it
is a huge advantage to us for our installed fleet. You see that with a
lot of our systems, where we've tried to keep it common."
Both freighter and passenger variants feature the same-sized plugs
fore and aft, although this was not always the case. While both have
1.52m (60in) aft plugs, the 747-8I model initially had a shorter 2.03m
forward plug. A year after its launch, Boeing adopted the -8F's 4.06m
forward plug dimensions for the -8I, to further boost capacity.
This means that the stretch increases the overall length of both
models to 76.3m. On the passenger variant, this raises nominal
three-class seating capacity over the 747-400 by 51 seats to 467, while
on the freighter, it allows for two additional pairs of 96x125in pallets
on the main deck and three more pallets on the lower deck. Overall, the
747-8F has 16% more capacity than the 747-400F.
The decision to stretch the 747-8I further - which increased
passenger capacity by 17 seats, but reduced range by about 270nm (500km)
- did not have unanimous appeal.
Emirates
was evaluating the 747-8I at the time, having already ordered the
747-8F for its cargo arm, and wanted Boeing to concentrate on the range
rather than capacity.
"We have made it clear to Boeing that we prefer the [original]
stretch because of its greater range at maximum payload," said the
airline's president Tim Clark.
"With Tim's Middle East to US West Coast type [range] hunger, that's
the classic tension of trying to hit his sweet spot of the market," says
Dickinson.
Boeing's decision to go with the larger -8I was vindicated shortly
after, when Lufthansa became launch customer for the revised passenger
version, with a deal for 20 747-8Is in November 2006.
HEAVY WEIGHT
The forward plugs in the 747-8I and -8F are inserted in slightly different positions within the fuselage (
see below).
The passenger model's plug is between doors one and two to extend both
the main and upper decks, while the freighter's is inserted further aft,
closer to the front of the wing box, which avoids what would be a
pointless increase in the length of the unused upper deck.
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ALL-CHANGE ON THE INSIDE
There is a stark contrast between the experience passengers have when stepping into the new Boeing 747
family, and that of the flightcrew. While the cabin has undergone a
significant, 787-inspired makeover, the flightdeck will feel very
familiar to 747-400 pilots.
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(From top) 747-8's flightdeck has much -400 commonality; upper-deck cabin is longer; staircase has had a makeover
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The
cabin interior includes a curved, upswept architecture that provides a
greater feeling of space and comfort, and more stowage space. Boeing
says the new light-emitting diode lighting technology is designed to
create a bright airy ambience and to enable smooth transitions from
light to dark.
An important change is the elegant
sweeping staircase, which leads to the enlarged upper deck. Located
adjacent to door two, it is also designed to improve passenger flows
between the two decks during turnaround.
This change is significant as the
stretch creates an upper-deck cabin that is similar in size to the main
cabin of a 737-300/700. In a typical three-class layout, Boeing says
that 48 business class seats can be accommodated on the 747-8I's upper
deck, compared with 40 on the -400.
Adding to the ambience is a revised
passenger window design. The 747-8I's cabin windows are 388mm (15.3in)
tall and 273mm wide, giving an estimated 8% increase in the usable
viewing area. "We transitioned to a more oval-shape window and reveal,
which is modelled after that of the 777," says 747 chief product engineer Bruce Dickinson.
AT HOME
Pilots of the 747-400 will feel right at home in the -8's flightdeck, which is equipped with a Rockwell Collins avionics and display suite.
There are some revisions such as a new
Honeywell flight management computer and 777-style electronic
checklist, cursor control panel, multi-function displays and air traffic
control datalink. It also has a new maintenance terminal and a revised
central maintenance computer.
An interesting development for the 747
VIP market is the Aeroloft, designed by Greenpoint Technologies
specifically for the 747-8, which has been chosen by some customers. The
Aeroloft offers eight private sleeping berths and a changing room and
is located above the main cabin aft of the upper deck.
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The
747-8 has a much heavier weight capability than its predecessor, with a
maximum take-off weight just shy of the "1 million lb" threshold at
987,000lb (447,700kg). This puts it 51t above the -400.
The aircraft's maximum take-off weight was increased by around 6t
during testing after a flight loads survey revealed that additional
structural margin was available.
Boeing said the MTOW increase was not
aimed specifically at restoring payload/range capability lost as a
result of the growth in structural weight during development.
Boeing focused on weight reduction during the design phase through
the use of new materials.
There is extensive use of carbonfibre in
secondary structures, while the fuselage incorporates new advanced
aluminium alloys throughout its length (other than the passenger doors),
as does the wing. A weight-saving effort is expected to bring later
aircraft close to the original empty-weight target.
Aside from the stretch, there is little visual difference between the
-8 fuselage and earlier marks. But the same is not true for the wing.
"The wing is key to this airplane, combined with the GEnx engines,
and what makes it so dramatically different from its predecessors," says
Dickinson.
"There's the advanced technology airfoil with the
supercritical wing and raked wingtip designed using computational fluid
dynamics, giving it the same technology level as the 787 wing. It is
extremely efficient."
The wing shares little with the 747-400 other than its 35˚ sweep and
incorporates new materials that help reduce weight.
The design features
an optimised reloft and retwist, while the raked tip (in place of the
winglet on the -400) increases wing span by 4m to 68.4m.
"The new wing
has similar dimensions to the earlier wing, but it is quite different.
We really did not use any of the earlier aerodynamic features," says
Dickinson.
Although he declines to reveal the area of the new wing for
competitive reasons, Lufthansa quotes a figure of 554m².
The wing incorporates revised leading and trailing edge high-lift
devices while fly-by-wire outboard ailerons "enable the wing to be even
more efficient with the weight reduction, by providing manoeuvre load
alleviation, which is new for the 747. This gives us a significant
advantage for weight."
The ailerons are optimised to span-load in cruise flight and Boeing
has introduced a droop capability as a performance improvement. "We
developed this initially on the Intercontinental and have since
introduced it on the Freighter," says Dickinson.
"We realised during -8I flight-testing that we had the opportunity to
better position the aileron to optimise span-loading and discovered a
0.4% improvement, which is a pretty significant number."
WING CHANGES
The wing's major changes centre on the flaps. "Optimising the
trailing edge is a real opportunity for performance," says Dickinson.
All earlier marks (except the 747SP "shrink") incorporate
triple-slotted trailing-edge flaps, but the -8 has adopted a
double-slotted inboard and single-slotted outboard design, which extend
on redesigned tracks and new carriages.
The leading-edge variable camber
Krueger flaps have also been redesigned to incorporate a gapped
configuration. Actuation systems are unchanged. The spoilers are also
now fly-by-wire.
Boeing spent a lot of time during flight-testing optimising the flap
settings to improve on the approach speeds, which is "always a
challenge, but we did this successfully".
Dickinson says that
"fundamentally, the wing's structural design is not entirely different"
from earlier variants, although advanced aluminium alloys are
incorporated in the wing and carbon composites are used for the trailing
edge and raked tip.
During development, the changes to the 747 airfoil design created a
variety of new problems. Speaking at the time, the programme's then
chief engineer Michael Teal explained: "When we changed the wing airfoil
and ultimately changed the centre of gravity, it fundamentally shifted
how the whole aircraft balances loads.
As the loads shifted back on the
wing, the tail is the balancing load. So we changed more parts in the
tail. Then the loads in the aft body changed, so we had to change the
aft body."
The knock-on effect was that the 747-8 supply chain was thrust into
limbo as it waited to adjust tooling and this contributed to the
two-year programme delay.
"After we put that issue behind us, no follow-up was required since I joined the programme," says Dickinson.
The wing side-of-body has the same basic overall geometry and
construct to the -400, but "has been 'gauged up' to account for the
increased loads on the 747-8", Dickinson says. "The fairings are
unchanged in basic geometry. However some changes to material, gauge and
local geometry were required due to increased loads, systems changes,
increased tyre size and environmental control system [ECS] pack
temperature differences."
Dickinson says that there are no significant differences in the
primary structure of the tail section. "The materials have been updated
and gauges changed slightly. But we did adopt a double-hinged lower
rudder."
NASA TECHNOLOGY
Power comes from four GEnx-2B67 engines rated at 66,500lb-thrust
(296kN), which although derived from the 787's GEnx-1B, are optimised
for the 747-8. The engines share the same core and 80% of the line
replaceable units. The GEnx-2B incorporates a 2.67m fan, digital bleed
control and a new pre-cooler. The four engines are suspended from a new
pylon design and wrapped in nacelles that make extensive use of
carbonfibre.
The 787-style noise-reducing "saw-tooth" chevrons are incorporated
into both the trailing edge of the fan cowls and inner core engine
nozzles. These NASA-developed devices smooth the hot air as it flows
from the engine core and mixes with cooler air from the fan, reducing
the noise-creating turbulence.
The 747-8I has a 30% smaller noise footprint than its predecessor,
being approved for quota count 2 (QC2) take-offs and QC1 arrivals at the
London airports.
GE says that the GEnx-2B is designed to have 13% better fuel efficiency over the
CF6
engine, which powers the 747-400. However, the performance fell short
of the original target and GE is working on a performance improvement
package (PIP) to close the gap (
see below).
Revisions and updates were made to the 747 systems on the new family.
"We're heating and cooling slightly larger volumes and we've used
different suppliers," says Dickinson.
The aircraft features a revised ECS and changes to the electrical and
hydraulic systems. Liebherr Group's Liebherr-Aerospace Toulouse
division supplies the ECS, which takes its air from the GEnx-2Bs.
The system uses new technologies to improve performance. These
include an integrated air system controller and high-pressure water
separation which dry the air within the air cycle machine upstream of
the turbine section input. The ECS also incorporates an advanced bleed
system and subfreezing packs.
With an MTOW 13% greater than the -400's, the 747-8 is equipped with a
strengthened and revised landing gear supplied by Goodrich. The main
landing gear (MLG) struts and wheels have been strengthened and the
truck beam length revised. The wheel well has been adapted for the new
gear geometry, while the MLG has modified doors and incorporates an
alternative extend mechanism. The 18 wheels feature new tyres and
brakes.
Modification was made to the shape of the wing MLG doors after a
buffet issue was discovered following flight-testing. "Testing always
uncovers a lot of interesting things," says Dickinson.
DOOR REDESIGN
The original door was derived from the -400's, but the changes to the
wing and trailing edge created "a body/wing interface that we didn't
fully appreciate. Once the source of the aerodynamic issue was
discovered, we were able to work our way through that", he says.
The change centred on the size and position of the lower part of the door, which is now at a reduced angle to the vertical.
The door-buffet issue was resolved during flight-testing before the
first 747-8I joined the flight-test programme on 20 March 2011. The
passenger variant was awarded US Federal Aviation Administration
certification on 14 December 2011 and the first delivery - to an
undisclosed VIP customer - took place on 28 February. This marked the
first delivery of a passenger 747 for seven years.
The 747-8F has been the lead variant in both development and sales,
with total orders standing at 70 from eight customers. Since the
landmark Lufthansa deal in 2006, sales of the 747-8I to airlines have
been sluggish, with just three more customers added to date: Air China
(five), Arik Air (two) and Korean Air (five). A further nine 747-8Is
have been ordered by undisclosed customers for the VIP role (of which
four have been delivered). Russian carrier Transaero signed a
preliminary agreement for four 747-8Is last year but has yet to firm up
the deal.
Lufthansa debuted the new Jumbo on 1 June between Frankfurt and
Washington DC after taking delivery of what was the 1,443rd 747 off the
line on 25 April. And guess who was keeping a watchful eye on
proceedings at the handover in Everett? The 747-8's very proud
grandfather... Joe Sutter.
BOEING AND GE FOCUS ON PERFORMANCE BOOST
Boeing advertises the 747-8 as having 10% lower seat-mile costs than
the 747-400 and 2% lower trip costs. But maximising the new Jumbo's
efficiency has become a slog after early-build aircraft came in
overweight and the General Electric GEnx-2B missed its original
fuel-burn target by 2.7%.
Boeing, in conjunction with GE, is working on a package of engine,
aerodynamic and weight improvements to address all the issues and ensure
that the performance of 747-8s delivered from 2014 will be "within 1%"
of the original target, says chief project engineer Bruce Dickinson.
TARGETS SET
"For the current as-delivered airplanes, we are consistently seeing a
real-world fuel burn that is 1% better than our forecast. So with the
increment for the PIP [performance improvement package] engine - which
is audited to be a 1.6% improvement above today - it puts us right on
track to meet our as-promised performance," he says.
Dickinson says GE is "bullish" that it can beat the 1.6% targeted for
the PIP. Testing for the package will begin in mid-2013 and approval is
scheduled for the end of next year.
One improvement that will be incorporated in the PIP for the
freighter is a higher-thrust rating for use at hot and high airports.
"This gives up to 4% additional thrust and will provide great capability
for a number of city pairs such as Mexico City-Bogata or from airports
in China," says Dickinson.
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Max Kingsley-Jones/Flightglobal
All-new: GEnx-2B engines and redesigned wing deliver big performance gains
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In parallel with GE's PIP, Boeing has a weight-saving programme
targeting a 2,270kg (5,000lb) reduction and is working on aerodynamic
improvements. One aspect of the latter is the aileron droop, which has
already been introduced on the 747-8I.
Other efficiencies being developed include improved nacelle leakage
and rigging improvements around the aft end - primarily the rudder - to
reduce cruise drag. There are other "study items" under evaluation, says
Dickinson.
"We're always looking for minor improvements - a 10th here and a 10th
there - as the production line becomes more consistent and stable.
Virtually all the improvements can be retrofitted, although some could
be a little time-consuming to do."
One item at the top of Dickinson's to-do list is the re-activation of
the -8I's 12,500 litre (3,300 USgal) tailplane fuel tank. An analytical
model showed that in certain scenarios, a flutter condition could occur
when fuel is in the tank, so the decision was taken to disable the tank
prior to certification.
"We're on track to work our way through that and get it certified and
activated with some relatively minor changes," says Dickinson.
The other main focus of improvements is around the flight management
computer, for which a series of upgrades is being introduced.
"We rolled in the 'FMC 2.5' load around August, which addresses some
nuisance warnings but the real motivation was to activate the FMC V
speeds," says Dickinson. "'FMC 2.6' will be introduced at the end of the
year to provide a tweak to those V speeds - and is something that will
be able to be applied to the 747-400."
A major update, dubbed "FMC 3.0", is scheduled for the end of 2013
and will "complete all the different nuances that the customers have
asked for".
The upgrade will incorporate a host of new capabilities such as
required navigation performance, a quiet climb function and "other bells
and whistles features that will help the airplane operate slightly more
efficiently and bring some other features into the airplane", Dickinson
says.
Boeing will undertake a major flight-test programme in mid-2013 to
clear the GEnx PIP, FMC 3.0 update and the modifications needed to
reactivate the tail fuel tank. Approval of all these is due at the end
of next year.
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