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Features
Introduction
The
Lockheed L-1011 TriStar belongs to the first generation of medium to
long-range wide-bodies built in the 70s which also includes the "Jumbo"
B747 and the DC-10. Despite the lack of sales, the L-1011 was by
far the most advanced of all three aircraft. Lockheed used their
military know-how to produce a flying fortress with plenty of
redundancy. Even today, the L-1011 is a very unique aircraft. Let's
look at some of its special features.
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Official brochures from Lockheed about the TriStar
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DOWNLOAD
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Superior
design features of the Lockheed L-1011 TriStar |
Paulo Nóia |
PDF |
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L-1011-500
TriStar technical profile |
Paulo Nóia |
PDF |
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TriStar 500 |
Paulo Nóia |
PDF |
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╚► Four
anti-collision lights
The majority of commercial aircraft flying only have two
anti-collision lights (the red rotating/ blinking lights), one on the top of the fuselage and
other one under the belly. For redundancy purposes, the L-1011 has two on
the top and two under the belly. If one failed, the aircraft could
still be dispatched without delaying the flight.
Anti-collision
lights
╚► Door operation
The L-1011 doors slide up into the fuselage whether in electrical,
emergency or manual mode. This means that, in case of emergency,
no outside obstacles can prevent the doors from being opened.
Also, in electrical operation, there is no way of inadvertently
inflate a slide since the system logic wouldn't
allow the door to be opened until the selector is in the "Detach" (disarmed)
position.
In manual mode the doors are opened with a hand crank, mainly
used by maintenance.
Door mechanism
╚► Air conditioning
TriStar's air conditioning system totally renews air in the cabin
every 3 minutes, resulting in a much more enjoyable atmosphere.
Remember that the majority of other commercial aircraft (even the
modern ones) use air recirculation sacrificing
passengers' comfort for fuel efficiency purposes.
If you are curious you
might want to read this Boeing's article about
Cabin Air. They forgot to mention the L-1011 as the exception to
recirculation systems.
TriStar's air circulation
and exhaust
╚► Quiet cabin
The L-1011 has a very quiet cabin. In fact, its wing-mounted engines
are placed more distant from the fuselage.
╚► Quiet engines
When it came out, the L-1011 was known as the Whisperliner.
Its Rolls-Royce RB211 engines were innovative with their triple
shaft concept. Having one more shaft than usual, the overall engine
rotation speed could be reduced resulting in less noise. The L-1011
was the quietest wide-body of its time and still complies with Stage
III regulations without any engine modification required. The
TriStar's RB211 engines have a by-pass ratio of 5:1, driving some 70
percent of the thrust around the outside of the core.
╚► S-duct
Unlike its rival - the DC-10 - which has the engine number two mounted
in the fin, in the L-1011 the engine #2 is embedded in the rear
fuselage and is feeded by an S-duct. This design allowed a bigger and more
effective rudder (remember that airplane's height was limited by the
height of the hangars).
S-duct
╚► Hydraulic systems
The hydraulic systems power the control surfaces of an aircraft such
as ailerons, elevators, rudder, slats/flaps, etc. Without them it's
impossible to fly a large commercial aircraft. The L-1011 has 4
independant hydraulic system lines for more redundacy. The DC-10 has
only three. Only one hydraulic system is sufficient to safely fly
the L-1011. Associated with the four hydraulic lines we have a total of
eleven pumps (4 Engine Driven Pumps, 2 Power Transfer Units, 2 Air
Turbine Motors, 2 AC Motors and 1 Ram Air Turbine) which
allow for multiple system reconfigurations without losing hydraulic
fluid pressure. The L-1011 was also the first aircraft to
incorporate a Ram Air Turbine. The RAT is a small propeller stored
in the TriStar's belly which extends in the very unlikely event of
all three engine failure.
RAT - Ram Air Turbine
╚► Flying tail
When an L-1011 pilot pushes or pulls the control column, he deflects
the whole horizontal stabilizer. The function of the geared
elevators is only to increase the chamber of the surface. The main goal
of the flying tail concept is to give maximum pitch control, needed
in jet upset and mistrimed take-off configuration situations.
Flying tail
╚► Digital autopilot
The L-1011-500 was the first wide-body commercial aircraft to have a
digital auto-pilot instead of an analog system. It is still
considered one of the most accurate auto-pilots ever built. Its high
level of accuracy in conjuction with the Direct Lift Control system
led Lockheed to easily attain CAT III capability in the TriStar.
╚► Direct Lift Control
The DLC is a system particular to the L-1011 which was designed to
control inboard spoilers' deflection during final approaches to
provide vertical speed control without significant changes in pitch
attitude. In the case of the TriStar 500, when flaps are more than 30º, the 4 inner spoilers will
come up to a new neutral position of 9º. If you are above your glide
path, then the spoilers will vary from 9º to 20º, in order to "kill"
lift. If you are below your glide path they will vary between 9º and
stowed position. The DLC results in a smooth and
constant pitch attitude approach and works automatically both in
manual or
autopilot operation.
«For those who have flown
gliders, this concept is similar to the principle of using spoilers
in the final approach, controlling the rate of descent without
changing the glider's speed.»
╚► Active Control
System
The TriStar 500 is known as being a very stable aircraft even in
rough turbulence. The Active Control System contributes for this
increased stability.
While Douglas was studying and testing winglets in its DC-10
aircraft - which were eventually introduced in the MD-11 - Lockheed
believed that a more efficient way of reducing induced drag for
better fuel economy was by increasing TriStar's wingspan giving
a higher aspect ratio to the wing. However, increasing the wingspan
usually requires wing reinforcement and thus higher aircraft weight.
The solution found was to design an active system which works for
wing load alleviation.
The working principle of
ACS is very simple. Accelerometers installed in the fuselage and
wingtips of the L-1011, detect vertical accelerations induced by
turbulence or maneuvers.
1. ACS accelerometers
installation
2.
Wing bending due to vertical accelerations
The system uses the
information from accelerometers to symmetrically deflect the
outboard ailerons in order to
redistribute lift forces across the wingspan and to reduce wing bending.
3.
Symmetrical deflection of outboard ailerons
4.
Lift redistribution
5.
Wing bending reduction being achieved
The amount of deflection
of the ailerons is function of airspeed changes. The Active Control
System actuation is 100% automatic. It benefits fuel consumption and
gives the L-1011-500 the smoothest ride of all commercial aircraft.
Also, above M.65, the
Maneuvering Direct Lift Control (MDLC) is armed against excessive
vertical accelerations making use of spoilers.
╚► Performance Management System
This is another system particular to the L-1011 which is
incorporated in the Flight Management System. Lockheed noticed that
optimum cruise Mach number was unstable to keep resulting in lots of
throttle movements and corrections. In other aircrafts, many
airlines would opt for a higher Mach number which also led to higher
fuel burn. The PMS was designed to keep airspeed precisely by
changing, with small variations, the aircraft's attitude. If the
airspeed is above the selected figure, a nose-up command is sent to
the horizontal stabilizer making the aircraft rise a maximum of
50 ft and lose speed; other way,
if the airspeed falls below the selected figure, a nose-down command
is sent and the L-1011 sinks a maximum of 50 ft to gain
speed without throttle correction.
The benefits from this system were better fuel efficiency, extended
engine life and less auditory fatigue for the passengers due to
thrust variations.
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