Sorin F/A-22 Raptor Page
This page was last updated on 04.02.2001 07:01

Here you can find the most detailed and accurate information about the biggest fighter ever to see the light of dawn: the Lockheed-Boeing F-22A Raptor. Just read the stuff from this page. Enjoy !

Information obtained by Sorin° The F22 Raptor is the future fighter-bomber of the US Air Force, and it's incorporating the latest digital and fuselage technology. The engine of the F22 Raptor is revolutionary. Its maximum speed is Mach 2 , but the engine has an very important and revolutionary characteristic, called supercruise. The fighter is Stealth by fuselage because of the deflecting form of the fuselage, like the F117 Nighthawk, but it performs even better than F16 Fighting Falcon or an F18 Hornet in air-air and air-ground combat.

Information obtained by Sorin° The deflective fuselage, stealthy engines and reduced electromagnetical signature digital equipment make it as hard to detect as the F117 Nighthawk However, the Pratt&Whitney F119 engines with the help of thrust vectoring also make the F-22 more manoeuvrable even than the F-16 Fighting Falcon Back to Sorin Fighters Network 5.0

The F-22 Raptor incorporates a whole series of new technologies, like:
Supercruise
Stealth
Thrust-vectoring
First-sight, First-shoot, first-kill capability
AGG
...and many more

The blades of the jet engines are hidden inside the fuselage, making it harder to detect by enemy radar. It was proven that one of the most visible parts of an aircraft are the blades of its engines. Hiding them makes the radar signature of the aircraft much smaller. Also, the cockpit is surrounded by a shield of deflective titanium armor

Supercruise means that the aircraft cruises at supersonic speeds without the need for afterburners. While a normal fighter cruises at Mach 0.7, the F-22 can easily achieve speeds of Mach 1.60 in level flight without the use of its afterburners and therefore can mantain this high speed cruise for an extended period of time, also with the burning of a normal quanitity of fuel. So, same fuel consumption, but more than double speed. Besides that, the F-22's engines have Stealth characteristics, which allow them to pass almoust unobserved on enemy teritorry. But the engines are not the only things that make the F-22 a Stealthy plane. The F-22's fuselage is especially made to deflect enemy radar from any position, so the F-22 is almoust invisible on radar as well. But radar can detect the F-22, the problem is that it cannot track it, so it looses its signal. The F-22's engine has the propellers hidden inside the fuselage, and its infrared signature is reduced by special exhaust processing technology and also with the help of the elongated rhudders of the aircraft. The noise is also reduced, so the F-22 is a little bit quieter than the average fighter. The cockpit incorporates the most advanced digital technology instruments in the world, and also a userfriendly low-stress display systems using relaxing colors like blue mixed-up with relax-alert colors like green, and also the information that the pilot receives is carefully selected as well as the mode of which it is delivered to the pilot. For example, if the stress-monitoring sensors of the digital flight system decide that the pilot's level of stress has increased, information sent to the pilot by visual means (HMD, HUD, 4 digital multi-color displays, etc) starts slowly to be converted and sent to the pilot in audio-mode (female voices have been found to increase fighter pilot's attention by as much as 50% compared to male voices when coming to delivering information). Also, the F-22 Raptor's fly-by-wire system is the most advanced in the world.

F-22 Raptor over California

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F-22 over Edwards AFB

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F-22 Raptor enroute to Edwards AFB

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F-22 refueled by KC-135

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In 1981, the US Air Force requested for a replacement of its main fighter force: The F-15 Eagle.
McDonnel-Douglas, Boeing, Lockheed Martin, General Dynamics, Northrop-Grumman, North American, Republic and many other companies started a race to produce projects to fit in the Air Force's "fighter of the future" requirements.
The F19 Stealth Fighter was the first project seriousley tested. With the help of the deflective fuselage and advanced technology, the fighter was Stealthy and superior to any Soviet competitor for the next 20 years, however from the only picture of the F19 that I have right here and which I can't scan (no scanner - lack of funding eh...) I can easily say that it didn't carry enough weapons and fuel, and it wasn't a 9G aircraft. The picture was created/made sometime between 1982 and 1986.
The project was abandoned, so in 1987 a totaly new shape of what's to come was going to be introduced.
This new shape was unlike anything other the Air Force's Fighter Command had ever seen before. Looking more like the F117 Nighthawk than the F-16, two totally new, built from scrap and futuristic looking aircraft were presented and chosen for the ATF Program's competition: the YF22 Lightning II and the YF23.
US Air Force accepted the two fighters as only competitors for the ATF Program and declared that the two projects must be ready for combat trials in 1989. The programs went slower than expected and in September 1989 the US Air Force agreed to give them 6 more months to be ready.
The YF22 was the spearhead of US policy and technology, and it was first presented at the Paris Air Show, in 1991. After winning the battle against the YF23 in April 1991, the YF22 was chosen as the shape of things to come. Other projects, like the X-36 tailless Stealth Fighter, ATD (Advanced Technology Demonstrator) had also showned the importance and characteristics of this new concept, so the YF22 was aproved for more research and development. Fruther upgraded, in September the 9th, 1997, the F22 Raptor marked 001 tooked-off from Edwards AFB, CA.

World Situation at the time

But also in 1981 (coincidence ?), the europeans realized that their fighters are getting older, so they decided to work together to make a totally new one. So the EAP project was born, as countries like UK, The Federal Germany, France, Italy and Spain joined-up for the developing of the project. In 1985 the EAP is renamed Eurofighter 2000. But in 1987 (coincidence, again ?) France retriets from the project, saying that the EF2000 does not have an carrier-landing capability. France was (and still is) the only country in Europe operating steam-catapoult carriers, so an F-18-class fighter had to be developed for them. As UK operates only small carriers with VTOL aircraft, the EF2000 didn't had the capability to land on a carrier. France gave the project to D'assault, for fruther developement, so emerging the Rafale, and its Navy Version, the Rafale M. But another european country, Sweden, decided in 1981 (that year is just magnific !!!) that it needs a new fighter, small and agile, a fighter that is cost-effective and will replace the existing J-34 Draken, J-35 Draken and JA-37 Viggen fighters. The new fighter must operate from small runways near to the borders, an aircraft specific to the Northen Europe conditions. The name of this new fighter will be the SAAB JAS 39 Gripen.
But what did the Russians all this time ? They were struggling with their T-10 aka Su-27 Flanker and MiG-29 Fulcrum projects, which, after 10 years of development after their American counterparts from which they were copied and supposedly "developed", the two projects were looking very badly and their poor performances were so much lower than those of the very fighters they copied and were trying to outperform since 10 years now, the F-15 Eagle and F-16 Fighting Falcon. Bearly in 1993, the Sukhoi Design Bureau decides to upgrade a fighter (Su27 Flanker generation) to a bomber, an aviation first. The bomber is called the Su-34 SuperFlanker and in early 1999 it was still in the project phase. The year 1993 also meant the introduction of the Navy's "fighter of the future", the F/A 18 SuperHornet, which now operates in large nombers from almoust all of the big US carriers.

The US Air Force had to choose in 1991 between the YF22 and the YF23. The YF22 was an extremly good fighter, it was Stealthy, it could supercruise, it was very manoeuvrable, its maximum speed was Mach 2.2, but it could withstand only +7.5G/-4G.
The YF23, on the other hand, had the same maximum speed of Mach 2.2, but it was a lot more Stealthyer, even more stealthy than the F117 Nighthawk, it was something like the B2 Spirit, due to the 2nd generation Stealth technology used at its fabrication, meaning smooth lines like in the B-2 Spirit compared to the zig-zag lines of the 1st generation Stealth used in the F117 Nighthawk and the YF23's competitor, the YF22 Lightning II.

So, in 1991, in the Mohave Desert, California, USA, at 07:00am, 2 fighters looking a little bit strange took-off in what it would become one of the most important dogfights of the century : detearmening what would be the fighter of the future: YF22 or YF23 ?

After taking-off, above the Edwards Air Force Base, California, all day long the two fighters engaged in endless dogfights, took high G-forces, launched missiles and bombs, fired endless cannon rounds and performed air-air refueling, acrobatic maneouvres and other stuff like that. Belive it or not, they actually flew non-stop all day long, and landed only in the evening. The YF22 was piloted by Dave Ferguson, an experimented test pilot from Edwards AFB, CA.

The next day, huge bunches of press delegates and paparazzi ran at The Pentagon, the US State Department, CIA and other government agencies to ask a lot of questions, like : who won, which will be the fighter of the future for the Air Force, why it was chosen, etc, etc, but the US officials didn't gave away any clues.

But one year later, in 1992, it was becoming more and more clear of who was the Mohave Winner, as the YF22 Lightning II was flying very often and performing a lot of tests on a daily basis, and by 1993 it was clear that YF22 won against YF23

The YF23 was faster, more Stealthy, and could probably carry more weapons at a longer range and it probably was an 9G/-4G aircraft, but the YF22 and especially its huge potential just impressed the US officials.

After that hystorical day (which, btw, I don't even know when it was...), another battle started: the upgrading of the YF22 to transform it into the F-22.

And so they will come : F-22 Lightning II, F-22 Rapier, F-22 Ralier and finally, the F-22 Raptor, which was planned to enter service in november 2004.

High-Speed Research

F22 Air Dominance for the 21st Century

The industry team of Lockheed Martin and Boeing is working with the U.S. Air Force and Pratt & Whitney to develop the F-22 to replace the current F-15 beginning in 2004. First flight was September 7,1997

Lockheed Martin Aeronautical Systems
Marietta, Georgia

The 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.

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 U.S. fighter.

• The forward fuselage is just over 5.2 m (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 below.
• 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.

Composite parts

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 high-temperature resistance.

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 are 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 dimensional tolerances.

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.

Engine design

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 29,000 pounds.

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 1.6 even without firing the afterburner, which gives the fighter a greater operating range and allows for stealthier flight operation.

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 leakage.
• 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 efficiency.
• 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 durability.
• 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 F119 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 requirements.

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.

Pratt & Whitney Engines
F100-PW-220/F100-PW-220E TUBOFAN ENGINE

Engine Characteristic

This material is copyrighted to Pratt and Whitney and they retain and reserve all rights to this material.  The use of this material by the ALLSTAR network is with permission of Pratt and Whitney.  The ALLSTAR network's copyright applies to the format used in presenting this material.  Pratt and Whitney should be contacted directly for permission to use this material.

The following information was extracted from ADVANCED MATERIALS & PROCESSES 5/98 Magazine.

Aircraft Engine Thrust Calculations - Level 3

In this section, we deal with one of the forces acting on an aircraft, namely, the thrust produced by the aircraft's engine.  In the first part of this section we will look at propellers and their efficiency.  In the second part of this section, we will provide the formula for the thrust of a jet engine.

Total Propeller Efficiency

Propellers are used to drive many lightweight aircraft and were the principal means of propulsion for military aircraft until the advent of the jet engine.  As such, it is important to know how propellers work and how efficient they are.  The propeller efficiency can never reach the ideal efficiency of 100 %. This is because in the development of the propeller efficiency several concepts are ignored,

1. The friction drag of the blades.
2. The kinetic energy of the rotation of the slipstream.
3. The fact that the thrust is not uniformly distributed over the blades.

The maximun propeller efficiency is about 90 %. This is due to the combined effects of drag from the nacelle and wings upon the propeller. This combined effect drops propeller efficiency to about 87 %. From there the thrust horsepower provided by the propeller is

where:
= thrust (lb)
= velocity (ft/s)
= engine brake horsepower
550 = conversion factor from ft-lbs to horsepower
= propeller efficiency

Thrust Equation For Turbojet-Type Engines

The thrust equation for a turbojet can be derived from the general form of Newton's second law (i.e., force equals the time rate of change of momentum),

The figure below shows the inlet and exhaust flows of the turbojet. The negative thrust due to bringing the freestream air almost to rest just ahead of the engine is called momentum drag or ram drag. The resulting thrust is given by following equation,
Schematic of a turbojet engine.

where:  = is weight flow rate of the air passing through the engine.
= jet stream velocity
= static pressure across propelling nozzle
= atmospheric pressure
= propelling nozzle area
= aircraft speed

The information in this section has been extracted from several sources.  Those sources have been contacted and permission to use their material on our site is pending.   However, the format in which this material has been presented is copyrighted by the ALLSTAR network.

Aircraft Propulsion - Level 3

Gas Turbine Operation and Design Requirements

Gas Turbine Usage

In an aircraft gas turbine the output of the turbine is used to turn the compressor (which may also have an associated fan or propeller). The hot air flow leaving the turbine is than accelerated into the atmosphere  through an exhaust nozzle (Fig. la) to provide thrust or propulsion power: Figure 1a. Schematic for an aircraft jet engine Figure 1.b A land-based gas turbine.

A typical jet engine is shown in Fig. 2. Such engines can range from about 100 pounds of thrust (lbst.) to as high as 100,000 lbst. with weights ranging from about 30 to 20,000 lbs. The smallest jets are used for devices such as the cruise missile, the largest for future generations of commercial aircraft. The jet engine of Fig.2 is a turbofan engine, with a large diameter compressor-mounted fan. Thrust is generated both by air passing through the fan (bypass air) and through the gas generator itself. With a large frontal area, the turbofan generates peak thrust at low (takeoff) speeds making it most suitable for commercial aircraft.
Figure 2. A modern jet engine used to power Boeing 777 aircraft. This is a Pratt & Whitney PW4084 turbofan which can produce 84,000 pounds of thrust. It has a 112-inch diameter front-mounted fan, a length of 192 inches (4.87 m) and a weight of about 15,000 pounds (6804 kg). The nozzle has been disconnected from this engine.

A turbojet doesnot have a fan and generates all of its thrust from air that passes through the gas generator. Turbojets have smaller frontal areas and generate peak thrusts at high speeds, making them most suitable for fighter aircraft.

In non-aviation gas turbines, part of the turbine power is used to drive the compressor. The remainder, the "useful power", is used as output shaftpower to turn an energy conversion device (Fig. lb) such as an electrical generator or a ship's propeller.

A typical land-based gas turbine is shown in Fig. 3. Such units can range in power output from 0.05 MW(Megawatts) to as high as 240 MW. The unit shown in Fig. 3 is an aeroderivative gas turbine; i.e., a lighter weight unit derived from an aircraft jet engine. Heavier weight units designed specifically for land use are called industrial or frame machines. Although aeroderivative gas turbines are being increasingly used for base load electrical power generation they are most frequently used to drive compressors for natural gas pipelines, power ships and provide peaking and intermittent power for electric utility applications. Peaking power supplements a utility's normal steam turbine or hydroelectric power output during high demand periods ... such as the summer demand for air conditioning in many major cities.  
Figure 3. A modern land-based gas turbine used for electrical power production and for mechanical drives. This is a General Electric LM5000 machine with a length of 246 inches (6.2 m) and a weight of about 27,700 pounds (12,500 kg). It produces maximum shaft power of 55.2 MW (74,000 hp) at 3,600 rpm with steam injection. This model shows a direct drive configuration where the l.p. turbine drives both the l.p. compressor and the output shaft. Other models can be made with a power turbine.

Some of the principle advantages of the gas turbine are:

1. It is capable of producing large amounts of useful power for a relatively small size and weight.

   Since motion of all its major components involve pure rotation (i.e. no reciprocating motion as in a piston engine), its mechanical life is long and the corresponding maintenance cost is relatively low.

   Although the gas turbine must be started by some external means (a small external motor or other source, such as another gas turbine), it can be brought up to full-load (peak output) conditions in minutes as contrasted to a steam turbine plant whose start up time is measured in hours.

   A wide variety of fuels can be utilized. Natural gas is commonly used in land-based gas turbines while light distillate (kerosene-like) oils power aircraft gas turbines. Diesel oil or specially treated residual oils can also be used, as well as combustible gases derived from blast furnaces, refineries and the gasification of solid fuels such as coal, wood chips and bagasse.

   The usual working fluid is atmospheric air. As a basic power supply, the gas turbine requires no coolant (e.g. water).

In the past, one of the major disadvantages of the gas turbine was its lower efficiency (hence higher fuel usage) when compared to other IC engines and to steam turbine power plants. However, during the last fifty years, continuous engineering development work has pushed the thermal efficiency (18% for the 1939 Neuchatel gas turbine) to present levels of about 40% for simple cycle operation, and about 55% for combined cycle operation (see next section). Even more fuel-efficient gas turbines are in the planning stages, with simple cycle efficiencies predicted as high as 45-47% and combined cycle machines in the 60% range. These projected values are significantly higher than other prime movers, such as steam power plants.

The original article from which this section is extracted, Introduction to Gas Turbines for Non-Engineers, by Lee S. Langston, University of Connecticut and George Opdyke, Jr., Dykewood Enterprises, can be found in the ASME International Gas Turbine Institute's "Global Gas Turbine News", Volume 37, No.2, 1997, and has been used with permission.

Updated: 4 februarie 2001

Aircraft Propulsion - Level 3 Gas Turbine Operation and Design Requirements Gas Turbine Components A greater understanding of the gas turbine and its operation can be gained by considering its three major components (Figs. 1, 2 and 3 found in the three previous sections): the compressor, the combustor and the turbine. The features and characteristics will be touched on here only briefly. Compressors and Turbines: The compressor components are connected to the turbine by a shaft in order to allow the turbine to turn the compressor. A single shaft gas turbine (Fig. la and 1b) has only one shaft connecting the compressor and turbine components. A twin spool gas turbine, which is found in land- and marine-based applications, has two concentric shafts, a longer one connecting a low pressure compressor to a low pressure turbine (the low spool) which rotates inside a shorter larger diameter shaft. The shorter, larger diameter shaft connects the high pressure turbine with the higher pressure compressor (the high spool) which rotates at higher speeds than the low spool. A triple spool engine would have a third, intermediate pressure compressor-turbine spool. Gas turbine compressors are either centrifugal or axial, or can be a combination of both. Centrifugal compressors (with compressed air output around the outer perimeter of the machine) are robust, generally cost less and are limited to pressure ratios of 6 or 7 to 1. They are found in early gas turbines or in modern, smaller gas turbines. The more efficient, higher capacity axial flow compressors (with compressed air output directed along the center line of the machine) are used in most gas turbines (e.g. Figs. 2 and 3). An axial compressor is made up of a relatively large number of stages, each stage, consisting of a row of rotating blades (airfoils) and a row of stationary blades (stators), arranged so that the air is compressed as it passes through each stage. Turbines are generally easier to design and operate than compressors, since the hot air flow is expanding rather than being compressed. Axial flow turbines (e.g. Figs. 2 and 3) will require fewer stages than an axial compressor. There are some smaller gas turbines that utilize centrifugal turbines (radial inflow), but most utilize axial turbines. Turbine design and manufacture is complicated by the need to extend turbine component life in the hot air flow. The problem of ensuring durability is especially critical in the first turbine stage where temperatures are highest. Special materials and elaborate cooling schemes must be used to allow turbine airfoils that melt at 1800-1900°F to survive in air flows with temperatures as high as 3000°F. Combustors: A successful combustor design must satisfy many requirements and has been a challenge from the earliest gas turbines of Whittle and von Ohain. The relative importance of each requirement varies with the application of the gas turbine, and of course, some requirements are conflicting, requiring design compromises to be made. Most design requirements reflect concerns over engine costs, efficiency, and the environment. The basic design requirements can be classified as follows: High combustion efficiency at all operating conditions. Low levels of unburned hydrocarbons and carbon monoxide, low oxides of nitrogen at high power and no visible smoke for land-based systems. (Minimized pollutants and emissions.) Low pressure drop. Three to four percent is common. Combustion must be stable under all operating conditions. Consistently reliable ignition must be attained at very low temperatures, and at high altitudes (for aircraft). Smooth combustion, with no pulsations or rough burning. A low temperature variation for good turbine life requirements. Useful life (thousands of hours), particularly for industrial use. Multi-fuel use. Characteristically natural gas and diesel fuel are used for industrial applications and kerosene for aircraft. Length and diameter compatible with engine envelope (outside dimensions). Designed for minimum cost, repair and maintenance. Minimum weight (for aircraft applications). A combustor consists of at least three basic parts: a casing, a flame tube and a fuel injection system. The casing must withstand the cycle pressures and may be a part of the structure of the gas turbine. It encloses a relatively thin-walled flame tube within which combustion takes place, and a fuel injection system. Compared to other prime movers (such as Diesel and reciprocating automobile engines), gas turbines are considered to produce very low levels of combustion pollution. The gas turbine emissions of major concern are unburned hydrocarbons, carbon monoxide, oxides of nitrogen (NOx) and smoke. While the contribution of jet aircraft to atmospheric pollution is less than 1%, jet aircraft emissions injected directly into the upper troposphere have doubled between the latitudes of 40 to 60 degrees north, increasing ozone by about 20%. In the stratosphere, where supersonic aircraft fly, NOx will deplete ozone. Both effects are harmful, so further NOx reduction in gas turbine operation is a challenge for the 21st century. The original article from which this section is extracted, Introduction to Gas Turbines for Non-Engineers, by Lee S.Langston, University of Connecticut and George Opdyke, Jr., Dykewood Enterprises, can be found in the ASME International Gas Turbine Institute's "Global Gas Turbine News", Volume 37, No.2, 1997, and has been used with permission. Updated: 4 februarie 2001

Information about the Lockheed Martin-Northrop YF-23 prototype

YF-23   click the pics for the real size version

Name : YF23
Producer : Lockheed Martin Corporation - Nortrhop-Grumman Corporation

...more Stealthy than the F22, but has lost the battle against the YF22

...While McDonnel-Douglas-Boeing created the F22, Lockheed Martin and Northrop-Grumman created their vision of "the fighter of the future".

The YF23 is much more Stealthy than its counterpart, the YF22, because the elevators have a special form and the rhudders are pulled down to the fuselage, something like the F117, but still diffrent from that.
YF23 was considered by the american officials as "very good", it was very Stealthy, it had a powerfull engine, it could dogfight quite well, and it was faster than the YF22, but the YF22 was absolutley amazing. In early 1991, US Air Force chosed the YF22 for further upgrading and usage, due to its huge unexploited potential. But that's not such a loss for its producers, because Northrop-Grumman makes the F/A 18 SuperHornet and it will continue to do so for at least 10 years from now, and Lockheed Martin is a great and healthy corporation, and thanks to its Skunk Works Division, I think that it will never go bankroft.
Do you also like the F22 Raptor at least as much as I do ? Then don't waste any time !

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Well people, that's about it for the best fighter in the world.

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