he F-22 Raptor is an air dominance fighter with
much higher capability than current U.S. Air Force aircraft. Compared with the
F-15 it is designed to replace, the aircraft has higher speed and longer range,
greater agility, enhanced offensive and defensive avionics, and reduced
observability. Furthermore, both the air vehicle and the engine designs
emphasize reliability and maintainability of systems, and are the result of a
team approach called Integrated Product Development.
The F-22 can carry medium and short-range air-to-air missiles in internal
bays, and has an in internal 20-mm cannon and provisions for carrying precision
ground attack weapons. Pilots will have a "first-look, first-shot, first-kill"
capability because of the Raptor's stealth properties and advanced sensors. In
addition, the avionics suite is a highly integrated system that will allow the
pilot to concentrate on the mission, rather than on managing the sensors as in
Much of the increased capability is based on the materials in the engine, the
structure, and the skin. Efficient processing methods also contribute to higher
reliability, lower costs, and simplified maintenance. This article describes
some of those materials and processes.
Traditional aircraft materials such as aluminum and steel make up about 20%
of the F-22 structure by weight. Its high-performance capabilities require
significant amounts of titanium (42% of all structural materials by weight) and
composite materials (24% by weight). These are stronger and lighter than
traditional materials, and offer better protection against corrosion. Titanium
also offers tolerance to higher temperatures. In fact, titanium accounts for a
larger percentage of the structural weight on the F-22 than any other current
- The forward fuselage is just over 5.2 in (17 ft) long, slightly
more than 1.5 m (5 ft) wide at its widest point, 1.7 m (5 ft 8 in.) tall,
and weighs about 770 kg (1700 lb). Built up in two sections, the forward
fuselage is joined together by two long and relatively wide side beams and
two longerons that run the length of the assembly. The beams, which are made
of composite materials, also provide an attachment point for the "chine,"
the fuselage edge that provides smooth aerodynamic blending into the intakes
and wings. The 5.2 m (17 ft.) long aluminum longerons form the sills of the
cockpit, and the canopy rests on them.
- The canopy is about 356 cm long, 114 cm wide, 70 cm tall (140 x
45 x 27 in.), and weighs about 160 kg (360 lb). it is the largest piece of
monolithic polycarbonate material being formed today. It is made of two 0.9
cm (0.375 in.) thick sheets that are heated and fusion-bonded, then
drape-forged. It has no canopy bow, and offers superior optics throughout,
as well as the requisite stealth features.
- The mid-fuselage is also about 5.2 m (17 ft long), 2 m (6 ft)
high, and weighs about 3900 kg (8500 lb). Almost all systems pass though
this section, including hydraulic, electrical, environmental control, fuel,
and auxiliary power systems. It also includes three fuel tanks, four
internal weapons bays, and the 20-mm cannon. Only 35% of the mid-fuselage
structure is aluminum. Composites make up 23.5%, and titanium is nearly 35%.
The lower keel chord is a Ti6-22-22 alloy forging that weighs about 18 kg
(40 lb). The four bulkheads are made of titanium Ti6-4; one of these is the
largest single titanium part ever used on an aircraft.
- The aft fuselage is 67% titanium, 22% aluminum, and 11 %
composite by weight. It measures 5.8 in long by 3.6 m wide (19 x 12 ft), and
weighs 2270 kg (5000 lb). About 25% by weight of the aft fuselage is
comprised of large electronbeam-welded titanium forward and aft booms. The
largest is the forward boom, which is more than 3 m (10 ft) long and weighs
about 300 kg (650 lb). The welded booms reduce the need for traditional
fasteners by about 75%.
- The wings are composed of 42% titanium, 35% composites
(including the skin), and 23% aluminum, steel, and other materials in the
form of fasteners, clips, and other miscellaneous parts. Each wing weighs
approximately 900 kg (2000 lb) and measures 4.8 in (16 ft) on the
side-of-body, by 5.5 m (18 ft) along the leading edge. After analyzing the
results of live-fire tests that simulated severe combat damage, engineers
chose to reinforce the wing by replacing every fourth composite spar with
one made of titanium. This reinforcement ensures that the F-22 will be even
more survivable in combat situations.
- The empennage consists of the vertical and horizontal tails.
The verticals are a multi-spar configuration internally, and have a HIP'ed
cast rudder actuator housing. The edges and rudder are made of composites,
and have embedded VHF antennas. The horizontal surfaces, known as
stabilators, are made of honeycomb materials with composite edges. They are
movable assemblies, and are deflected by the composite pivot shaft described
- The main landing gear is made of Carpenter Technology's Airmet
100 steel alloy. It is one of the first applications of a steel that has
been specially heat treated to provide greater corrosion protection to the
main gear piston axle.
On the F-22, the number of parts made from thermoset composites is
approximately a 50 / 50 split between epoxy resin parts and bismaleimide (BMI)
parts. Exterior skins are all BMI, which offers high strength and
Thermoplastic composites are also highly durable materials but, unlike
thermosets, thermoplastics can be reheated and re-formed. However,
thermo-plastics proved to be more expensive and more difficult to incorporate in
the F-22 than had been hoped in the early days of the program. As a result,
although thermoset composites comprise about 24% of airframe structural
materials, thermoplastics are only about 1%. They -ire being applied on the F-22
for items such as doors for the landing gear and weapons bay, where tolerance to
impact damage is required from things such as small rocks that may be kicked up
from the runway
Resin transfer molding
The F-22 is the first aircraft to take advantage of resin transfer molding
(RTM) of composite parts. RTM is a method of composite parts fabrication well
suited to economically fabricating complex-shaped details repeatedly to tight
Large composite parts traditionally are formed by applying and pressurizing
hundreds of layers of fabric that contain a pre-embedded resin, and curing them
in an autoclave. This is a very time-consuming and labor-intensive process.
In the RTM process, fibrous preforms are first shaped under vacuum from
stacks of fabric, and then placed in metal tooling that matches the shape of the
part. The tool is then injected with heated resin under pressure. The benefit of
matching the metal tooling to RTM is a high level of part reproducibility,
consistency in assembly operations, and economies of scale.
RTM is used to fabricate more than 400 parts of the F-22 structure, ranging
from inlet lip edges to load-bearing sine-wave spars in the fighter wings. At
Boeing, RTM has reduced the cost of wing spars by 20%, and has cut in half the
number of reinforcement parts needed for in stalling the spars in the wings.
Both bismaleimide and epoxy parts are fabricated by RTM.
Composite pivot shaft
The composite pivot shaft is an application of automated fiber placement
(AFP) technology, which was combined with unique tooling approaches to produce a
lightweight composite structure that replaced titanium in a flight-critical
application - the F-22 horizontal stabilizers.
AFP technology makes possible the exact fiber positioning required to achieve
the complex geometry of the pivot shaft. It has a 25-cm (10in.) diameter
cylinder at one end, a rectangular spar about 10 cm (4 in.) wide at the other,
and an offset in the transition area. Its shape can be likened to that of an
oversized hockey stick.
It is composed of more than 400 plies of composite tow tapes ranging from 3
to 12 mm (1 / 8 to 1 / 2 in.) wide. The shaft is cured in stages to prevent
internal cracking and eliminate wrinkles, as no allowance is made for voids in
the shaft. After layup, the shafts are nondestructively inspected and tested.
Production requires up to 60 days, but weight is reduced by 40 kg (90 lb) per
shipset (two shafts) over titanium, which is an extremely large amount of weight
to take out of an aircraft at one time. Thicker tow tapes are planned for future
pivot shafts, which should greatly reduce production time.
Hot isostatic pressing
Hot isostatic pressing (HIP) is a process in which metallic castings are
subjected to very high temperatures in a static pressure environment of >70 MPa
(10 ksi). On the F-22, structural titanium castings are HIP'ed to collapse
internal shrinkage cavities and diffusion-bond the walls of the cavities. Six
large structures on the F-22 are HIP'ed: the rudder actuator housing (one for
each rudder); the canopy deck; the wing side-of-body forward and aft fittings
(four total, two for each wing); the aileron strongback (one for each aileron,
two total); and the inlet canted frame (one each for the left and right inlets).
The canted frame was originally a four-piece assembly. By switching to a
casting, mechanical joints were eliminated and machining was minimized.
Electron beam welding
Electron beam (EB) welding is helping Boeing and Aerojet, its supplier, build
lighter-weight titanium assemblies for the aft fuselage. Parts are EB Welded in
a vacuum chamber to prevent exposure to oxygen, which can create a deleterious
brittle surface. Compared with other methods, electron beam welding enables much
more reliable joints when welding titanium parts more than an inch thick.
The process also reduces the need for fasteners in some fuselage components
by up to 75%, which decreases weight, simplifies the assembly process, and
avoids the costs associated with fasteners. The reduction in the number of
fasteners also means fewer openings for possible fuel leaks.
The product of more than 40 years of research into high-speed propulsion
systems, the Pratt & Whitney F119 is proof that high-technology does not have to
be complicated. A balanced approach to the design process led to an engine as
innovative in its reliability and support as in its performance. Assemblers and
flight line mechanics participated in the F119's design from its inception. The
result is that ease of assembly, maintenance, and repair are designed into the
engine. For example, the F119 cuts requirements for support equipment and labor
by half, which also saves precious space in airlifters during combat zone
deployments. The engine will require 75% fewer ship visits for routine
maintenance than its predecessors.
The F119 has 40% fewer major parts than current fighter engines, and each
part is more durable and does its job more efficiently. Computational fluid
dynamics-airflow analyzed through advanced computers-led to the design of engine
turbomachinery of unprecedented efficiency, giving the F119 more thrust with
fewer turbine stages.
In fact, the F119-PW-100 engine develops more than twice the thrust of
current engines under supersonic conditions, and more thrust without afterburner
than conventional engines with afterburner. Each F-22 will be powered by two of
these 35,000-pound-thrust-class engines. By comparison, the engines powering the
Air Force F-15 and F-16 fighters have thrust ratings ranging from 23,000 to
Jet engines deliver additional thrust by directly injecting fuel at the
engine exhaust. The process, called afterburner, gives the aircraft a
rocket-like boost as the fuel ignites in the exhaust chamber. The tradeoff is
higher fuel consumption, a greater amount of heat, and consequently, greater
visibility to the enemy. However, the F119 engine can push the F-22 to
supersonic speeds above Mach 1.4 even without firing the afterburner, which
gives the fighter a greater operating range and allows for stealthier flight
These are some of the significant F119-PW-100 engine features:
- Integrally bladed rotors: In most stages, disks and blades are
made from a single piece of metal for better performance and less air
- Long chord, shroudless fan blades: Wider, stronger fan blades
eliminate the need for the shroud, a ring of metal around most jet engine
fans. Both the wider blades and shroudless design contribute to engine
- Low-aspect, high-stage-load compressor blades: Once again,
wider blades offer greater strength and efficiency.
- Alloy C high-strength burn-resistant titanium compressor stators:
Pratt & Whitney's innovative titanium alloy exhibits high
elevated-temperature strength and a markedly improved resistance to
sustained combustion. It increases stator durability, allowing the engine to
run hotter and faster for greater thrust and efficiency.
- Alloy C in augmentor and nozzle: The same heat-resistant
titanium alloy protects aft components, permitting greater thrust and
- Floatwall combustor: Thermally isolated panels of an
oxidation-resistant, high-cobalt alloy make the combustion chamber more
durable, which helps reduce scheduled maintenance.
Thrust vectoring nozzle
The Fll9 engine nozzle for the F-22 is the world's first full production
vectoring nozzle, fully integrated into the aircraft/ engine combination as
original equipment. The two-dimensional nozzle vectors thrust 20 degrees up and
down for improved aircraft agility. This vectoring increases the roll rate of
the aircraft by 50%, and has features that contribute to the aircraft stealth
Heat-resistant components give the nozzles the durability needed to vector
thrust, even in afterburner conditions. With precision digital controls, the
nozzles work like another aircraft flight control surface. Thrust vectoring is
an integrated part of the F-22's flight control system, which allows for
seamless integration of all components working in response to pilot commands.
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