The U.S. Air Force Air Combat Command (ACC) last week
released its 2015 strategy review, “Securing the High Ground,” primarily
a guide for updating and modernizing the existing fleet. Near the end
of the 15-page document the ACC says, “We must also continue to develop a
balanced close air support (CAS) capability across all [Global
Precision Attack] platforms, explore opportunities for a future CAS
platform, and enact specific initiatives to ensure we maintain a CAS
culture throughout the [Combat Air Force].”
This should be pretty big news to aircraft makers. The current Air
Force CAS platform is the A-10 Thunderbolt (aka, the Warthog) from
Northrop Grumman Corp. (NYSE: NOC) which entered service in 1976 with
the last one being built in 1984. The proposed replacement has been the
F-35 Joint Strike Fighter from Lockheed Martin Corp. (NYSE: LMT). And
that’s been a bone of contention among some members of Congress and Air
Force officials for some time now. An April report by the Government
Accountability Office questioned the service’s estimated $4.2 billion
saving if the A-10 is retired, saying the rationale for the estimate is
incomplete and may overstate or understate estimated savings:
Without a reliable estimate of savings, neither we nor
any other organization has a reliable basis from which it could identify
potential alternative savings and assess their relative risk, including
to air superiority and global strike. …
Nor has the USAF considered fully the implications of retiring the A-10:
Air Force divestment of the A-10 will create potential
gaps in close air support (CAS)—a mission involving air action against
hostile targets in proximity to friendly forces—and other missions, and
DOD is planning to address some of these gaps. For example, A-10
divestment results in an overall capacity decrease in the Air Force’s
CAS-capable fleet. This capacity reduction is mitigated by phasing A-10
divestment over several years and by introducing the F-35 into the
fleet, but Air Force documentation also shows that the F-35’s CAS
capability will be limited for several years. Air Force analysis shows
that divestment of the A-10 would increase operational risks in one DOD
planning scenario set in 2020.
In the strategy document released last week,
though, the Air Force appears to be saying that it is considering
requesting a new CAS plane that would replace the A-10 and, presumably,
the F-35.
Is the Air Force just tossing out a red herring that Congress will
never approve so that top commanders can say, “We did our best to
replace the A-10 with a plane specifically designed to support ground
troops, but the politicians won’t pay for it, so we’re stuck with (fill in the blank) .”
The F-35 will cost U.S. taxpayers more than $1 trillion over the next
50 years and Lockheed is scheduled to build 2,443 of the planes in
three variations: one for the Air Force, one for the Marines, and one
for the Navy. Each plane is estimated to cost more than $650 million
over its entire lifespan. The GAO said last year that it costs about
$180 million for each plane and that Lockheed expects to get that cost
down to around $85 million when production ramps up. Maintenance and
crew costs make up the balance.
The Air Force has already acquired several F-35As out of planned
purchase of more than 1,000 over the longer term. The F-35A is scheduled
to go operational in the fall of 2016.
On July 31st the Marine Corps declared the F-35B operational and
plans to buy 340 of the planes. The Marines also expect to purchase 80
of the F-35C which has been designed for carrier landings for the Navy.
The F-35C is not scheduled to be operational until 2018.
There appears to be at least some reason to believe that Lockheed
won’t build all the F-35s that the Pentagon had once hoped to buy. But
it is also a safe bet—at this point some 14 years after the Lockheed won
the contract—that the program won’t be scrapped or even re-evaluated.
As for the A-10, the Air Force has maintained that it needs to retire
the planes in order to switch its crews and maintenance programs to the
F-35. But according to the strategy document, the service is looking at
the possibility of a new CAS plane, and that could indicate that some
of the thousand or more F-35s the Air Force originally intended to be
purchased will be have to be cut back in order to launch a new CAS
program.
New airplanes are complex and expensive, and therefore a natural fit
for Congressional indecision. The next few months ought to be
instructive.
Lockheed Martin is developing a successor to the storied U-2 spy plane, Flightglobal reports.
Lockeed Martin's "Skunk Works," the office in charge of developing
the company's high-end future defense systems, is in the planning stages
for a spy plane that combines the best features of both Lockheed's U-2
and Northrop Grumman's RQ-4 Global Hawk drone.
The RQ-4 and the U-2 already perform similar operational roles. But
the Global Hawk is more difficult to detect than a U-2 and is unmanned.
Ideally, Skunk Works would combine the best features of the Global
Hawk with the U-2 to create an optionally-manned high-altitude
surveillance aircraft with the latest sensors.
The U-2 is a high-altitude manned surveillance plane.
With a service ceiling of up to nearly 85,000 feet, the plane is
capable of flying for 8 hours at a time at speeds of 500 miles per hour.
The RQ-4 is
also a high-altitude surveillance craft, although it is unmanned and
flown by a team of remote operators. It was originally designed to
complement manned surveillance craft such as the U-2, although US
military planners have long intended to replace the U-2 with the Global Hawk.
US Air Force via ReutersAn undated U.S. Air Force handout photo of a RQ-4 Global Hawk unmanned aircraft
The
Air Force has determined that its U-2s can be kept capable of flying
until 2045. But due to a shrinking budget, the U-2 is slated to be
retired by 2019. This looming deadline has prompted Lockheed to try
to develop an updated version of its iconic spy plane.
“Think of a low-observable U-2,” Lockheed’s U-2 strategic development manager, Scott Winstead, told Flightglobal. “It’s pretty much where the U-2 is today, but add a low-observable body and more endurance.”
By being optionally manned, Lockheed hopes that the U-2 successor
could offer a wider mission range than either a solely manned or
unmanned aircraft, Winstead told Flightglobal.
Wiki/The AviationistA picture of a U-2's high-altitude view.
Alongside the B-52, the U-2 is the longest serving aircraft in the US Air Force. Both planes were introduced in 1955 and have been in the US fleet ever since.
Because of the plane's ability to operate at extremely high altitudes, the Air Force maintains that the U-2 is one of the most effective
reconnaissance platforms ever built. The U-2 is generally cheaper to
operate than surveillance drones, and it has become a staple aircraft in
the monitoring of the Korean Demilitarized Zone.
For years, all the aviation world knew about Boeing’s secret stealth project from the 1960s was limited to a name and a single mysterious photo. It seemed like a relic out of time, possessing many stealthy design features that wouldn’t exist until decades later, and even then, only in highly classified black projects.
Perhaps because it was built in secret and designed to be invisible, the stealth bomber is… Read more
But Boeing just exclusively provided Foxtrot Alpha with a trove of photos and information for the very first time. After decades in the shadows, here is Boeing’s Kennedy-era “Quiet Bird.”
Even Boeing admits that there is very little known about Quiet Bird, also named Model 853, and that official records of the program were likely destroyed in 1970s.
Yet the tidbits of information that do exist about the concept paint a highly intriguing picture of an aircraft with design elements that have echoed throughout the decades that followed it.
The concept dates back to the early 1960s, with a one-half scale model of the aircraft being built sometime between 1962 and 1963. The aircraft was an exercise in utilizing specific materials and shapes to drastically reduce the radar cross-section of a tactical aircraft.
From this pioneering design, five Boeing “stealth” patents were awarded, and they only appear to have shown up in public records in the early 1990s, decades after they were officially filed.
The model of Quiet Bird was said to have been tested at Boeing’s Wichita facility in 1962-1963, all of which occurred on a radar range. No actual flight testing of Quiet Bird itself was said to have happened, though. But the tests were highly successful: they proved that it was possible to drastically decrease the radar signature of a tactical aircraft.
Still, the concept was not just designed as a shape to test radar reflectivity. Boeing had full plans to develop it into an actual aircraft. Unfortunately for them, the design ended up being too ahead of its time. Even to be adapted as a forward penetrating observation or attack aircraft, and believe it or not, the military had little interest in it.
This actually makes some sense. At the time, raw performance and increasingly advanced avionics that could allow for either all-weather high-level or low-level penetration of enemy airspace were all the rage. (See also the SR-71, U-2, A-6, and F-111). As it was, this jet wouldn’t have been much of a performer, but it very well could have been invisible to enemy sensors, and with that, who needs performance?
It would not be until about a decade later that the Pentagon would begin considering aircraft designs with low-observable technology as their primary feature set, later dubbed stealth, as a silver-bullet technology worth pursuing with fervor.
When looking at Quiet Bird, especially in these new images and schematics released to us from Boeing, it is amazing how many stealth features that are used in modern day low-observable aircraft designs existed on this 50-year-old concept. The aircraft’s chine-line that separates its smooth, shallowly curved bottom and trapezoid shaped fuselage are key tenants of stealth designs to this very day.
Nobody knows exactly where "Rat 55" lives or precisely what technology it uses to… Read more
The aircraft’s canted tails and exhaust set well forward of its trailing edge are also key features found on many modern combat aircraft that were designed with signature control in mind. This configuration not only helps with lowering radar reflectivity while still providing stability and maneuvering control, but it also shields the aircraft’s hot exhaust signature from the virtually every angle but from directly above and behind.
Even the aircraft’s gold plated canopy and use of composites structures are all major techniques widely in use today to lower a manned aircraft’s radar signature.
Quiet Bird’s unique low-observable inlet design and curved duct are meant to shield the aircraft’s highly reflective engine face from radar. A similar setup is used on the majority of stealth aircraft designs today, and Quiet Bird’s configuration is especially reminiscent of the X-47A Pegasus unmanned experimental aircraft:
In all, a stunning amount of features of Quiet Bird’s design, some of which are below its skin and detailed in these patents (1,2,3), are used to various degree on a whole slew of modern aircraft designed with signature control in mind. These include Tacit Blue, B-2, Have Blue/F-117, YF-23, X-32, F-22, Avenger, Global Hawk, and multiple unmanned combat air vehicles including Boeing’s own Phantom Ray.
Why is the F-117 Nighthawk, America's first true "stealth" aircraft, still prowling… Read more
Even stealthy cruise missiles will instantly evoke Quiet Bird’s configuration. It is almost as if Boeing spectacularly created a Rosetta Stone for stealth technology before it was even “officially” invented.
Even through they were separated by three and a half decades from one another, Bird of Prey was a reboot of sorts of Quiet Bird, meant to package a bunch of experimental low-signature and advanced manufacturing techniques together with flat out performance taking a back seat to raw innovation. They are even similar in design.
This airframe paved the way for many technologies that allowed Boeing to step into the 21st century ready to compete in the advanced military-aerospace marketplace. These included rapid prototyping, large single-piece composite structures, 3D design, disposable tooling and a host of low observable innovations.
Boeing’s Exotic Bird Of Prey technology demonstrator:
Boeing is in no way in denial of Quiet Bird’s indirect impact on many of their products, and possibly others, that followed it over the last five decades, they write:
The model and drawings do show some stealth concepts that are used in operation stealth airplanes today, so it would seem that the Boeing engineers working on this project were onto something. The lessons learned on Quiet Bird probably did influence the design of the Boeing AGM-86 Air Launched Cruise Missile
Internally Boeing continued to work on the non-metallic structures aspects that were pioneered with Quiet Bird and that work did eventually lead to the use of increasingly larger and more complex composite structures in Boeing aircraft. In the 1980s Boeing used its expertise in composite (“Stealth”) structures to build the wings and center fuselage structures of the B-2 bomber and today major structures of our commercial jets can be built from composite structures with the primary example being the 787; the first large commercial jet that is primarily made of composite materials.
Video of Lockheed’s Have Blue stealth technology demonstrator and the F-117 Nighthawk it led to:
Although other aircraft, namely the A-12 Oxcart/SR-71 Blackbird, had secondary stealth features, Quiet Bird appears to be the first concept to feature a comprehensive low-observable aircraft design. So while Lockheed largely holds the public spotlight as the harbinger of the “stealth revolution,” Boeing was miraculously there with an eerily advanced aircraft concept nearly a decade and a half before Lockheed’s Skunk Works developed its now famous “hopeless diamond” that led to the historic Have Blue technology demonstrator.
Clarence “Kelly” Johnson is the Babe Ruth of aerospace design. Aircraft programs under Johnson were … Read more
With all this in mind, Quiet Bird deserves its rightful place in history, even if only as an uncannily accurate prediction of what was to come decades later from the world of military technology and “bleeding-edge” aerospace design.
Contact the author at Tyler@Jalopnik.com.
Special thanks to Boeing’s outstanding archives and copyright departments.
All photos and drawings of Quiet Bird are Boeing copyright – credit: The Boeing Company.
WASHINGTON
— The US Air Force is about to start a deep-dive process that will
eventually decide what technologies and capabilities it will fund to
ensure air dominance in the world of 2030.
And while that includes
the potential for a sixth-generation fighter, top service officials
continue to stress that the result of the process will likely be a
family of systems approach.
Maj. Gen. Tim Ray, director of Global
Power in the service's acquisition realm, and Maj. Gen. Paul Johnson,
director for Operational Capability Requirements, told Defense News that
the Air Force will shortly stand up a team to begin researching these
decisions.
The Next-Generation Air Dominance program will be the
first pilot program for the Air Force's new Capability Collaboration
Team (CCT) structure, part of a broader strategic process unveiled by
Gen. Mark Welsh, Air Force chief of staff, at last month's Air Force
Association convention in Orlando.
The
CCT comprises a number of operational, scientific and technical experts
from an array of backgrounds, including the Defense Advanced Research
Projects Agency (DARPA), the Air Force Research Labs and the major
commands. The group will explore in depth various options that could
matter in the future, before putting out a product with two components.
The
first is a list of technologies the CCT has decided will be needed for
air superiority in 2030. The second is a road map for how to achieve
those technologies.
For example, the CCT could decide that
directed energy weapons are a key part of the strategy. It will present
to the chief and secretary a guide for what areas of directed energy
need investment, how those investments should be prioritized, and
perhaps most importantly, a timeline for when those investments would
need to pay off in order to be fielded by 2030.
Johnson said the
goal is to be able to guide limited research and development funds from
being spread to many projects — with the hope that one works out —
toward being focused on a small handful of technologies.
"It's not
about a decision to start a program, to go do x, y and z," Johnson
said. "It's not a decision to go build the next-generation fighter. It's
a set of decisions about what more do we want to learn, how do we want
to learn it, and how fast do we want to learn it? It's 'out of this set
of technologies, we want to chase these four.' "
Timewise, the CCT
will begin meeting in the next few weeks. It will spend the next three
years researching technologies before presenting a final product in
2018.
The Pentagon is littered with well-intentioned studies into
new technologies. What makes this different, Ray said, is the focus on
finding actionable items and then creating guidelines to make them real.
"This
isn't a slush fund," Ray said. "It's not just. 'hey I'm going to go
solve cold fusion, give me a couple of years and I'll get back to you.'
It's 'how do I get that power supply correct of that kind of pod to do
directed energy,' or 'how do I get this signature from this range to
that range?' "
For that to work, Ray said, industry must play a
critical role. That fits with a promise from Welsh, who in Orlando
pledged that industry would be brought in earlier in the technology
development process.
"[Right now] you have to wait until we kind
of make up our mind and give you a plan, so you can't energize your
resources, your thinking, to help us get ahead of this curve," he said
at the conference. "We're not talking to you about it. We must do that.
You should be part of this transition planning. You should be part of
the [process] in developmental planning."
At the same time, Ray
warned that industry needs to be prepared for a shift away from the days
of one prime controlling everything from development through
production.
"We have a lot of known players and we want to hear
what they have to say. The interesting part will be if we get out of the
program business, how many more voices will we get that aren't the
prime players?" Ray asked rhetorically. "Technology is moving way too
fast for us to lock down a program and say it's all got to go through
one guy."
That may lead to more focus on studying and prototyping technology without a guarantee of future production, Johnson said.
"When
I bring industry in here, industry is understandably interested in what
the program is going to look like, which is not my conversation at this
point," Johnson said. "So I've got to make it workable so when I get
ready to do some experimentation or prototyping, that industry is
willing to participate in that, knowing that at the end of the day there
may not be anything after that."
Rebecca Grant of IRIS Research
said opening another avenue of communication with industry is a net
positive for the service. And while she said the CCT brings "all the
right ingredients" together, she said the service needs to stick with
the concept to make it really work.
"The best technology
development stories come out of this mix of people and insights," she
said. "What we don't know is if you can get everyone together in a room
and just [have] the big insights. Like exercise, you need do this on a
regular basis and go for the small gains as well."
Mark Gunzinger,
a former service official now with the Center for Strategic and
Budgetary Assessments, called the CCT a "great idea" that could "help
accelerate the transition of new, potentially game-changing technologies
into the program of record." However, he also offered a word of
caution.
"Beginning these efforts by 'researching new
technologies' may take teams down the path of trying to figure out how
emerging technologies could help airmen improve how they operate today,"
he said. "I think it's also important to challenge current operational
concepts and think through how new technologies could enable airmen to
operate very differently in the future." Hints of the Future
Both generals stressed that the goal is to allow the CCT to be as open as possible as it explores future concepts.
"We
can't be prescriptive. We do have to be open," Ray said. "We have to
show them what's going on in the intel community with data management,
with cyber, with space, so they can begin to look at the tools and what
they mean and the implications of those things. It's a broader
exposure."
However, the men did drop a few hints as to what technologies they foresee the CCT considering.
Johnson
expressed confidence that the 2030 solution would not involve just the
development of a heavily advanced fighter with all-onboard capability,
noting "there is every likelihood it's going to be some sort of family
of systems, and hopefully it will be a mix of old and new.
"I
would have every expectation that it will probably be 'programs' —
that's one man's opinion," he added. "Sensors, weapons, the whole
collection of things."
That family could include a mix of
modernized versions of legacy systems in use today, working hand-in-hand
with new systems that will be online by 2030. The CCT will be on the
lookout for what Johnson called "quick wins," things like experimental
sensor upgrades that could be put onto current systems relatively
quickly.
The CCT will also look at how to build in growth for
potential future technologies, Ray said, noting "we certainly realize we
need to build in more inherent adaptability in what we do."
That
includes looking at how to build in excess power and create space for
any new system, to make sure there is the ability to add newer
technologies as they come along.
The generals casually mentioned
directed energy and signature reduction as other technologies that will
likely be looked at, which isn't news to anyone who has followed the
talk about a potential next-generation fighter.
Grant highlighted directed energy as an area that could really gain from the CCT model.
"The
time is right for demonstrating progress in directed energy," she said.
"I think all future systems from here on out, we're going to have a
discussion in directed energy on those systems. We'll be talking about
it a lot more."
While the focus now is on the family of systems,
there is confidence in industry that a major part of that will involve a
sixth-generation fighter.
The
Air Force isn't alone in looking at next-gen air dominance
technologies. The Navy has said it is looking at a next-gen fighter to
replace the F/A-18 and complement the F-35C, and Pentagon acquisition
chief Frank Kendall has launched the Aerospace Innovation Initiative, a
DARPA-led development program for X-planes to test technologies and
concepts.
Johnson said he is in regular contact with his
counterpart in the Navy, and Ray added that the lead Air Force
representative to the initiative will also be part of the CCT.
That
should create a cross-cutting of technologies between the three sides,
including, perhaps, letting the CCT test some of the technologies on a
prototype plane, then bring those results back into its research.
Industry, meanwhile, is gearing up for what could be a lucrative contract.
Northrop
Grumman has already stood up a pair of teams, dedicated to the Navy and
Air Force programs respectively, while Boeing has quietly released
several mock-ups of future fighter concepts.
Orlando Carvalho, the
head of Lockheed Martin's aerospace division, told Defense News that
the company's SkunkWorks division is working on a design, but said that
work is a natural outgrowth from the company's previous developments.
"When
it comes to next-generation air dominance, that work for us is a
continuum," he said. "We don't discretely stand up teams, disband teams
around that — that's what we do at the SkunkWorks, and it's a
continuum."
Carvalho said the Pentagon has "definitely"
communicated with companies about what future threat scenarios, tactics
and requirements may be.
Both Ray and Johnson are sympathetic to
industry's desire to know what a next-generation fighter may look like,
but insist they need this structure to prevent the proverbial cart from
leading the horse.
"The automatic question [from industry] is when
do we do the AOA [analysis of alternatives]? I don't want to hear about
an AOA," Ray said. "I want to do some learning first. I want to know
what the alternatives are before I begin to analyze those alternatives.
Right now we don't even know what the alternatives are."
http://www.ibtimes.com/
Russia’s Sukhoi T-50 PAK FA Fighter Jet Can Defuse Enemy Plane’s Stealth Capability: Report
The Sukhoi PAK FA fighter jets will reportedly go into
mass production in 2017.
Wikimedia Commons
Russia’s fifth-generation Sukhoi T-50 PAK FA fighter jet is
equipped with an advanced defense system that can neutralize an enemy
plane’s stealth capability, a report said Friday, citing a unit of
Russian state corporation Rostec. The planes, which will go into mass
production in 2017, are claimed to be capable of outperforming the F-22
and fifth-generation F-35 fighters of the U.S. Air Force.
The T-50 PAK FA fighter jet will be built with composite materials,
and come with advanced electronic systems and engines to ensure the
plane can stay mostly undetected by radars and other optical and
infrared technologies, Russia’s Sputnik News reported.
“The PAK FA is already to some degree a flying robot, where the
aviator fulfils the function not only of pilot, but is actually one of
the constituent parts of the flying apparatus,” Sputnik News quoted
Vladimir Mikheyev, the deputy head of the Concern Radio-Electronic
Technologies (KRET), a unit of Rostec, as saying.
KRET has created an advanced internal navigation system for the T-50
PAK FA jet, which autonomously processes navigation and flight
information. The system can also determine position and motion
parameters in situations when there is no satellite navigation, and make
contact with GLONASS, Russia’s satellite-based navigation system, which
works alongside the Global Positioning System.
The Russian air force will get 55 Sukhoi T-50 PAK FA jets by 2020 and
the aircraft will replace the country’s Sukhoi Su-27 fourth-generation
fighter jet. Russia is also expected to buy
at least 50 Tupolev Tu-160 “Blackjack” heavy strategic bombers, which
will be produced simultaneously with the country’s new bomber, called
PAK DA.
In April 2012, the Navy issued a formal request for information for the F/A-XX. It calls for an air superiority fighter with multi-role capabilities to replace the F/A-18E/F Super Hornet and EA-18G Growler aircraft in the 2030s, while complementing the F-35C Lightning II and UCLASS unmanned aircraft, that can operate in anti-access/area-denial environments. The aircraft must be capable of operating from Navy Nimitz-class and Gerald R. Ford-class aircraft carriers. Primary missions include air combat, ground attack, surface warfare, and close air support. Other missions can include air-to-air refueling, reconnaissance, surveillance, and target acquisition (RSTA), and electronic attack. There is consideration for manned, unmanned, and optionally manned platforms.[2]
The F/A-XX is being pursued as F/A-18 Super Hornets will reach the
end of their 9,000 hours of service life by the early 2030s. Aside from
the option of buying more F-35Cs, the F/A-XX is seeking to create a new
aircraft to replace the Super Hornet's capability and mission set. An
open architecture design is desired, so different sensors, payloads, and
weapons can be plugged in for a specific mission, and be able to be
moved around for multiple different missions on different days or
different sorties. The resulting open architecture design is likely to
take shape depending on which style of new propulsion system is
presented by the aircraft industry. Unmanned, manned, and optionally
manned systems are being considered. An Analysis of Alternatives (AOA)
was expected to begin in 2014, with a fighter to be introduced around
2030. Just as the F-35C will replace aging F/A-18 Hornets and complement
Super Hornets, the F/A-XX will replace aging Super Hornets in the 2030s
and complement the F-35C.[3]
On 9 September 2014, the Navy announced that an AoA for the F/A-XX
aircraft would begin in 2015. Meetings with industry will be held
focusing on building new aircraft to meet the requirement, developing a
family of systems (FoS) approach, and discussing mission systems,
avionics, and new next-generation weapons systems. One approach could
create a minimum cost F/A-XX that uses high cost, high performance
weapons to defeat threats; according to the Navy's Naval Integrated Fire Control-Counter Air (NIFC-CA)
battle network concept, an individual platform would not need to have a
full suite of sensors and rely on off-board data-linked information
from other platforms to provide targeting information and guide weapons
launched from the platform. The F/A-XX platforms will be made to carry
missiles, have power and cooling systems for directed energy weapons, and have sensors that can target small radar cross-section targets; cyber warfare platforms at a tactical level as part of a FoS are being explored. While the Navy is working with the U.S. Air Force
on a next-generation tactical fighter, there is significant
disagreement over the Air Force's claims that adaptive-cycle jet engine
technology, where the ratios of bypass and compression airflow can be
made variable to improve efficiency, can be scaled to benefit a
carrier-based fighter.[4][5]
Although the F/A-XX platform will be a sixth-generation fighter
aircraft, the Navy is reluctant to talk about a new aircraft because the
project is still in the very early stages of development. A range of
next-generation technologies may be explored including maximum sensor
connectivity, super cruise ability, and electronically configured "smart
skins." Maximum connectivity refers to massively increased
communications and sensor technology, such as having the ability to
connect with satellites, other aircraft, and anything providing
real-time battlefield information. Engine technologies like scramjets would enable an aircraft to cruise at supersonic speeds without needing an afterburner.
Smart skins would have sensors and electronics integrated into the
fuselage of the aircraft itself to increase the technological ability of
the sensors while reducing drag and increasing speed and
maneuverability.[6] Chief of Naval OperationsJonathan Greenert
speculated in February 2015 that the F/A-XX would not rely on speed or
stealth as much as previous generation jet fighters due to better
signature detection and proliferating high-speed anti-aircraft weapons.
Instead, the fighter would carry a new spectrum of weapons to overwhelm
or suppress enemy air defenses. Greenert favors an optionally manned
aircraft for a modular section that can either hold a pilot or more
sensors. The payload of the F/A-XX will likely match or exceed the Super
Hornet's payload.[7]
Entries
The Boeing F/A-XX concept design as of 2013.
In July 2009, Boeing unveiled a sixth-generation fighter concept the F/A-XX requirement. It was a two-seat, twin-engined tailless jet
with a blended wing. Although it has a tandem cockpit, Boeing said it
can be manned or unmanned depending on the mission. The fighter concept
is in the 40,000 lb (18,000 kg) weight class. The Northrop GrummanX-47B that was chosen for the UCAS-D program has also been proposed for the F/A-XX effort.[1][8]
In a 31 May 2011 disclosure to Congress, the Department of Defense
revealed that they were considering buying more F-35C fighters to
replace 556 Super Hornets. The DOD plans to replace the older F/A-18C/D Hornets
with 220 Lightning IIs. In March 2011, a Navy analysis of alternatives
showed that they may buy more F-35C aircraft, develop a new platform, or
do both for their NGAD fighter program.[9]
Boeing unveiled an updated F/A-XX sixth-generation fighter concept in
April 2013. The concept is a tailless twin-engine stealth fighter
available in manned and unmanned configurations. It has canards,
which usually compromises the frontal radar cross-section, but the lack
of a tail shows an emphasis on all-aspect stealth. It also has
diverterless supersonic inlets similar to the F-35. The manned version
seems to have restricted rearward visibility without the aid of a
sensor.[10]
The Pratt & Whitney F135 is an afterburningturbofan developed for the Lockheed Martin F-35 Lightning II
single-engine strike fighter. The F135 family has several distinct
variants, including a conventional, forward thrust variant and a
multi-cycle STOVL variant that includes a forward lift fan. The first production engines were scheduled to be delivered in 2009.[1]
The origins of the F135 lie with the Lockheed CorporationSkunk Works's efforts to develop a stealthy STOVL strike fighter for the U.S. Marine Corps under a 1986 DARPA program. Lockheed employee Paul Bevilaqua developed and patented[2] a concept aircraft and propulsion system, and then turned to Pratt & Whitney (P&W) to build a demonstrator engine.[3] The demonstrator used the first stage fan from a F119 engine for the lift fan, the engine fan and core from the F100-220 for the core, and the larger low pressure turbine from the F100-229
for the low pressure turbine of the demonstrator engine. The larger
turbine was used to provide the additional power required to operate the
lift fan. Finally, a variable thrust deflecting nozzle was added to
complete the "F100-229-Plus" demonstrator engine. This engine proved the lift-fan concept and led to the development of the current F135 engine.[4]
P&W developed the F135 from their F119 turbofan, which powers the F-22 Raptor, as the "F119-JSF". The F135 integrates the F119 core with new components optimized for the JSF.[5] The F135 is assembled at a plant in Middletown, Connecticut. Some parts of the engine are made in Longueuil, Quebec, Canada,[6] and in Poland.[7]
The F135-PW-600 engine with lift fan, roll posts, and rear vectoring nozzle, as designed for the F-35B V/STOL variant, at the Paris Air Show, 2007
The first production propulsion system for operational service was
scheduled for delivery in 2007. The F-35 will serve the U.S., UK, and
other international customers. The initial F-35s will be powered by the
F135, but the GE/Rolls-Royce team was developing the F136
turbofan as an alternate engine for the F-35 as of July 2009. Initial
Pentagon planning required that after 2010, for the Lot 6 aircraft, the
engine contracts will be competitively tendered. However since 2006 the
Defense Department has not requested funding for the alternate F136
engine program, but Congress has maintained program funding.[8]
The F135 team is made up of Pratt & Whitney, Rolls-Royce and Hamilton Sundstrand.
Pratt & Whitney is the prime contractor for the main engine, and
systems integration. Rolls-Royce is responsible for the vertical lift
system for the STOVL aircraft. Hamilton Sundstrand is responsible for
the electronic engine control system, actuation system, PMAG, gearbox,
and health monitoring systems. Woodward, Inc. is responsible for the fuel system.
As of 2009, P&W was developing a more durable version of the F135
engine to increase the service life of key parts. These parts are
primarily in the hot sections of the engine (combustor and high pressure
turbine blades specifically) where current versions of the engine are
running hotter than expected, reducing life expectancy. The test engine
is designated XTE68/LF1, and testing is expected to begin in 2010.[9] This redesign has caused “substantial cost growth.”[10]
P&W expects to deliver the F135 below the cost of the F119, even though it is a more powerful engine.[11]
In February 2013 a cracked turbine blade was found during a scheduled
inspection. The crack was caused by operating for longer periods than
typical at high turbine temperatures.[12]
The 100th engine was delivered in 2013.[13] LRIP-6 was agreed in 2013 for $1.1 billion for 38 engines of various types, continuing the unit cost decreases.[14]
In 2013, a former P&W employee was caught attempting to ship
"numerous boxes" of sensitive information about the F135 to Iran.[15]
In December 2013 the hollow first stage fan blisk failed at 77% of its expected life during a ground test. It will be replaced by a solid part adding 6 lb in weight.[16]
F-35 program office executive officer Air Force Lt. Gen. Christopher
C. Bogdan has called out Pratt for falling short on manufacturing
quality of the engines and slow deliveries.[17] His deputy director Rear Admiral Randy Mahr said that Pratt stopped their cost cutting efforts after "they got the monopoly".[18] In 2013 the price of the F135 increased by $4.3 billion.[19]
In July 2014 there was an uncontained failure of a fan rotor while
the aircraft was preparing for take-off. The parts passed through a fuel
tank and caused a fire, grounding the F-35 fleet.[20] The failure was caused by excessive rubbing at the seal between the fan blisk and the fan stator during high-g
maneuvering three weeks before the failure. The engine "flex" generated
a temperature of 1,900 degrees F in materials designed to fail at 1,000
degrees F. Microcracks appeared in third-stage fan blades, according to
program manager Christopher Bogdan, causing blades to separate from the
disk; the failed blades punctured the fuel cell and hot air mixing with
jet fuel caused the fire.[21][22][23]
As a short term fix, each aircraft is flown on a specific flight
profile to allow the rotor seal to wear a mating groove in the stator to
prevent excessive rubbing.[24]
In May 2014, Pratt & Whitney discovered conflicting documentation
about the origin of titanium material used in some of its engines,
including the F135. The company assessed that the uncertainty did not
pose a risk to safety of flight but suspended engine deliveries as a
result in May 2014. Bogdan supported Pratt's actions and said the
problem was now with A&P Alloys, the supplier. The US Defense
Contract Management Agency wrote in June 2014 that Pratt & Whitney’s
"continued poor management of suppliers is a primary driver for the
increased potential problem notifications." A&P Alloys stated that
it has not been given access to the parts to do its own testing but
stood behind its product. Tracy Miner, an attorney with Boston-based
Demeo LLP representing A&P Alloys said, "it is blatantly unfair to
destroy A&P’s business without allowing A&P access to the
materials in question".[25][26][27]
Design
Thrust vectoring nozzle of the F135-PW-600 STOVL variant
The F-135, a mixed-flow afterburning turbofan, was derived from the F-119 engine but was given a new fan and LP turbine.[28]
There are 3 F-135 variants with the -400 being similar to the -100,
the major difference being the use of salt-corrosion resistant
materials.[29]
The -600 is described below with an explanation of the engine
configuration changes that take place for hovering. The engine and Rolls-Royce LiftSystem make up the Integrated Lift Fan Propulsion System(ILFPS).[30]
The lift for the STOVL version in the hover is obtained from a 2-stage lift fan (about 46%[31]) in front of the engine, a vectoring exhaust nozzle (about 46%[31]) and a nozzle in each wing using fan air from the bypass duct(about 8%[31]). These relative contributions to the total lift are based on thrust values of 18,680lb, 18,680lb and 3,290lb respectively.[31] Another source gives thrust values of 20,000lb, 18,000lb and 3,900lb respectively.[32]
In this configuration most of the bypass flow is ducted to the wing
nozzles, known as roll posts. Some is used for cooling the rear exhaust
nozzle, known as the 3 bearing swivel duct nozzle(3BSD).[33]
At the same time an auxiliary inlet is opened on top of the aircraft to
provide additional air to the engine with low distortion during the
hover.[28]
The lift fan is driven from the LP turbine through a shaft extension
on the front of the LP rotor and a clutch. The engine is operating as a
separate flow turbofan with a higher bypass ratio.[34] The power to drive the fan (about 30,000 SHP[34]) is obtained from the LP turbine by increasing the hot nozzle area.[34]
A higher bypass ratio increases the thrust for the same engine power
as a fundamental consequence of transferring power from a small diameter
propelling jet to a larger diameter one.[35] The thrust augmentation for the F-135 in the hover using its higher bypass ratio is about 50%[31] with no increase in fuel flow. Thrust augmentation in horizontal flight using the afterburner is about 52%[31] but with a large increase in fuel flow.
The transfer of approximately 1/3[34]of
the power available for hot nozzle thrust to the lift fan reduces the
temperature and velocity of the rear lift jet impinging on the ground.[34]
Improving engine reliability and ease of maintenance is a major
objective for the F135. The engine has fewer parts than similar engines
which should improve reliability. All line-replaceable components (LRCs)
can be removed and replaced with a set of six common hand tools.[36]
The F135's health management system is designed to provide real time
data to maintainers on the ground, allowing them to troubleshoot
problems and prepare replacement parts before the aircraft returns to
base. According to Pratt & Whitney, this data may help drastically
reduce troubleshooting and replacement time, as much as 94% over legacy
engines.[37]
The F-35 can achieve a limited supercruise of Mach 1.2 for 150 miles.[38]
Because the F135 is designed for a fifth generation jet fighter, it
is the second afterburning jet engine to use special "low-observable
coatings".[39]
Variants
F135-PW-100 : Used in the F-35A Conventional Take-Off and Landing variant
F135-PW-400 : Used in the F-35C carrier variant
F135-PW-600 : Used in the F-35B Short Take-Off Vertical Landing variant
The Rolls-Royce LiftSystem, together with the F-135 engine, is an aircraft propulsion system designed for use in the STOVL variant of the F-35 Lightning II. The complete system, known as the Integrated Lift Fan Propulsion System (ILFPS), was awarded the Collier Trophy in 2001.[1]
The F-35B STOVL variant of the Joint Strike Fighter (JSF) aircraft is intended to replace the vertical flight Harrier,
which was the world's first operational short-takeoff /
vertical-landing fighter. A requirement of the JSF is that it can attain
supersonic flight, and a suitable vertical lift system that would not compromise this capability was needed for the STOVL variant. The solution came in the form of the Rolls-Royce LiftSystem, developed through a $1.3 billion System Development and Demonstration (SDD) contract from Pratt & Whitney.[2] This requirement was met on 20 July 2001.[3][4]
Design and development
Instead of using lift engines or rotating nozzles on the engine fan
like the Harrier, the "LiftSystem" has a shaft-driven LiftFan, designed
by Lockheed Martin and developed by Rolls-Royce,[2] and a thrust vectoring nozzle for the engine exhaust that provides lift and can also withstand the use of afterburners in conventional flight to achieve supersonic speeds.[3] The system has more similarities to the Russian Yakovlev Yak-141 and German EWR VJ 101D/E than the preceding generation of STOVL designs to which the Harrier belongs. [5]
The team responsible for developing the propulsion system includes Lockheed Martin, Northrop Grumman, BAE Systems, Pratt & Whitney and Rolls-Royce, under the leadership of the United States Department of DefenseJoint Strike Fighter Program Office. Paul Bevilaqua,[6] Chief Engineer of Lockheed Martin Advanced Development Projects (Skunk Works), invented the lift fan propulsion system.[7] The concept of a shaft-driven lift-fan dates back to the mid-1950s.[8] The lift fan was demonstrated by the Allison Engine Company in 1995-97.[9]
The U.S. Department of Defense (DOD) awarded General Electric and Rolls-Royce a $2.1 billion contract to jointly develop the F136 engine as an alternative to the F-135. The LiftSystem was designed to be used with either engine.[2] Following termination of government funding GE and Rolls-Royce terminated further development of the engine in 2011.[10]
Rolls-Royce is managing the overall development and integration
programme from its site in Bristol, UK, which is also responsible for
the LiftFan turbomachinery, 3BSM and Roll Post designs. The team in
Indianapolis, US, will provide the system’s gearbox, clutch, driveshaft
and nozzle and will conduct the build and verification testing of the
LiftFan.
Operation
Diagram of LiftSystem components and airflow
Diagram of turbojet energy for LiftSystem prototype
The three-bearing swivel module (3BSM) is a thrust vectoring nozzle at the tail of the aircraft which allows the main turbofan
cruise engine exhaust to pass either straight through with reheat
capability for forward propulsion in conventional flight, or to be
deflected downward to provide aft vertical lift.[12]
In "lift" mode for assisted vertical maneuvers, 29,000 hp[13][14][15] is diverted forward through a driveshaft from the engine's low-pressure (LP) turbine via a clutch[16] and bevel-gearbox to a vertically mounted, contra-rotating
lift fan located forward of the main engine. The fan efflux
(low-velocity unheated air) discharges through a thrust vectoring nozzle
on the underside of the aircraft, thus balancing the aft lift generated
by the 3BSM. For lateral stability and roll control, bypass air from the engine goes out through a roll-post nozzle in each wing.[17] For pitch control,
the areas of exhaust nozzle and LiftFan inlet are varied conversely to
change the balance between them while maintaining their sum, and with
constant turbine speed. Yaw control is achieved by yawing the 3BSM.[15] Forward, and even backward, motion is controlled by tilting the 3BSM and LiftFan outlet.[4]
The following indicates the component thrust values of the system in lift mode:[2]
3BSM (dry thrust)
LiftFan
Roll posts (combined)
Total
18,000 lbf (80 kN)
20,000 lbf (89 kN)
3,900 lbf (17 kN)
41,900 lbf (186 kN)
In comparison, the maximum thrust of the Rolls-Royce Pegasus 11-61/F402-RR-408, the most powerful version which is used in the AV-8B, is 23,800 pounds-force (106 kN).[18] The weight of the AV-8B is about 46% of the weight of the F-35B.
Like lift engines, the added LiftSystem components are dead weight
during flight, but the advantage of employing the LiftSystem is that its
greater lift thrust increases takeoff payload by an even larger amount.[citation needed]
Also, the fan's cool efflux reduces the harmful effects of hot,
high-velocity air which can harm runway pavement or an aircraft carrier
deck.[citation needed]
Engineering challenges
While developing the LiftSystem many engineering difficulties had to be overcome, and new technologies exploited.[19]
The LiftFan utilises hollow-bladed titanium blisks (a bladed disk or "blisk" achieved by super-plastic forming of the blades and linear friction welding to the blisk hub).[20] Organic matrix composites are used for the interstage vanes. The LiftFan must safely function[21]
at flight speeds up to 250 knots (130 m/s) This condition appears as a
crosswind to the horizontal intake and occurs when the aircraft
transitions between forward flight and hover.[22]
The clutch mechanism uses dry plate carbon–carbon technology
originally derived from aircraft brakes. Friction is only used to engage
the lift fan at low engine speeds. A mechanical lock-up is engaged
before increasing to full power.[23]
The gearbox has to be able to operate with interruptions to its oil
supply of up to a minute while transferring full power through
90 degrees to the LiftFan.[citation needed]
The Three-Bearing Swivel Module has to both support the final hot
thrust vectoring nozzle and transmit its thrust loads back to the engine
mounts. The "fueldraulic" actuators for the 3BSM use fuel pressurised
to 3,500 lbf/in2, rather than hydraulic fluid, to reduce
weight and complexity. One actuator travels with the swivel nozzle,
moving through 95 degrees while subject to intense heat and vibration.[citation needed]
Testing
During concept definition of the Joint Strike Fighter, two Lockheed
airframes were flight-tested: the Lockheed X-35A (which was later
converted into the X-35B), and the larger-winged X-35C,[24] with the STOVL variant incorporating the Rolls-Royce LiftFan module.
LiftSystem flight testing commenced in June 2001, and on 20 July that
year the X-35B became the first aircraft in history to perform a short
takeoff, a level supersonic dash and vertical landing in a single
flight. By the time testing had been completed in August, the aircraft
had achieved 17 vertical takeoffs, 14 short takeoffs, 27 vertical
landings and five supersonic flights.[3]
During the final qualifying Joint Strike Fighter flight trials, the
X-35B took off in less than 500 feet (150 m), transitioned to supersonic
flight, then landed vertically.[25]
Ground tests of the F136/LiftSystem combination were carried out at the General Electric facility in Peebles, Ohio
in July 2008. On 18 March 2010, a STOVL equipped F-35B performed a
vertical hover and landing demonstration at Patuxent River Naval Air
Station in Lexington Park, MD.[26]
Collier Trophy award
In 2001, the LiftSystem propulsion system was awarded the prestigious Collier Trophy,[27]
in recognition of "the greatest achievement in aeronautics or
astronautics in America", specifically for "improving the performance,
efficiency and safety of air or space vehicles, the value of which has
been thoroughly demonstrated by actual use during the preceding year."[3]
Two-stage contra-rotating hollow titanium blisk
fan of 50 inches (1.3 m) diameter. Uppermost fan fitted with variable
inlet guide vanes. Capable of generating more than 20,000 pounds-force
(89 kN) cold thrust[20]
Three-bearing swivel module
Able to rotate through 95 degrees in 2.5 seconds and vector 18,000
pounds-force (80 kN) dry thrust in lift mode, with reheat capability in
normal horizontal attitude
The Pratt & Whitney F119 (company designation PW5000[1]) is an afterburningturbofan engine developed by Pratt & Whitney for the Lockheed MartinF-22 Raptor advanced tactical fighter.
The engine delivers thrust in the 35,000 lbf (160 kN) class, and is
designed for supersonic flight without the use of afterburner (supercruise).
Delivering almost 22% more thrust with 40% fewer parts than
conventional, fourth-generation military aircraft engine models, the
F119 allows sustained supercruise speeds of up to Mach 1.72.[2] The F119's nozzles incorporate thrust vectoring technology. These nozzles direct the engine thrust ±20° in the pitch axis to give the F-22 enhanced maneuverability.
The F119 derivative, the F135, produces 40,000 lbf (180 kN) of thrust[3] for the Lockheed Martin F-35 Lightning II.
The AL-41F is a designation for two different families of Russian military turbofan engines. The NPO Saturn AL-41F is a Russian variable-bypass ratio turbofan engine, designed for supercruise flight for the MFI (Mnogofunktsionalni Frontovoy Istrebitel, "Multifunctional Frontline Fighter") programme, which resulted in the Mikoyan Project 1.44. It is considered by Jane's as the Russian counterpart to the General Electric YF120 engine which lost to the more conventional fixed-bypass YF-119 in the Advanced Tactical Fighter engine competition. Since the cancellation of the MFI programme, the AL-41F1S and AL-41F1 designation was assigned to highly upgraded AL-31F variants that powers the Su-35S and initial production PAK FA aircraft.
The AL-41F program was launched in 1982, and the first prototype engine flew in a MiG-25 Foxbat testbed. Originally developed for the Mikoyan Project 1.44,[1][2]
28 engines were built, however the engine did not advance beyond
prototype stage and when the MiG 1.44 was cancelled, it was also
cancelled.
The AL-41 designation was reused for heavily upgraded variants of the
AL-31 used to power the Su-35S (Izdeliye 117S / AL-41F1A) and initial
production PAK FA (Izdeliye 117 / AL-41F1) aircraft. Some of the
technologies of the original AL-41F were applied in the 117S and 117
engines.
Variants
A heavily-upgraded version of the AL-31F is being developed for the Su-35BM and PAK FA. This engine has been named the AL-41F1S and AL-41F1. It is important to note that the AL-41F1S is not considered a part of the same AL-41 line as was planned for the Mikoyan Project 1.44
because it uses the core of the AL-31F, whereas the AL-41F utilizes an
entirely new core. The designation appears to be present because the
engine approaches the projected specifications of the new AL-41F class.
It is also notable that the engine is capable of mounting 3D thrust vectoring nozzles for extra manoeuvrability.
Specifications
General characteristics
Type: Turbofan
Length: 4990 mm
Diameter: 1280 mm
Dry weight:
Components
Compressor: axial
Performance
Maximum thrust: 18,000 kgf (180,000 N; 40,000 lbf)
The Saturn AL-31 is a family of military turbofan engines. It was developed by Lyulka, now NPO Saturn, of Soviet Union, originally for the SukhoiSu-27 air superiority fighter. It produces a total thrust
of 123 kN (27,600 lb) with afterburning in the AL-31F, 137 kN
(30,800 lb) in the AL-31FM (AL-35F) and 142 kN (32,000 lb) in the
AL-37FU variants. Currently it powers all Su-27 derivatives and the Chengdu J-10 multirole jet fighter which has been developed in China.
The AL-31FP and AL-37FU variants have thrust vectoring. The former is used in the Su-30MKI export version of the Su-30 for India & Sukhoi Su-30MKM
for Malaysia . The AL-37FU can deflect its nozzle to a maximum of ±15°
at a rate of 30°/sec. The vectoring nozzle is utilized primarily in the pitch plane. The AL-31FP is built in India by HAL at the Koraput facility under a deep technology transfer agreement.
It has a reputation for having a tremendous tolerance to severely
disturbed air flow. In the twin-engined Su-27, the engines are
interchangeable between left and right. The Mean Time Between Overhaul
(MTBO) for the AL-31F is given at 1000 hours with a full-life span of
3000 hours. Some reports suggested that Russia was offering AL-31F to Iran to re-engine its F-14 Tomcat air fleet in the late 1990s.
According to Saturn`s Victor Mihailovic Chepkin, chief designer of
the 117 and 117S engines, the Chinese WS-10 was developed with the aid
of the AL-31`s maintenance technical documentation.[10] China can domestically produce most AL-31 parts for its own jet engine programs, but must import turbine blades from Russia.[11]
117S
Intended to power the Su-35BM, the izdeliye 117S (AL-41F1S) is an upgrade of the AL-31F that uses technology from the AL-41F. The engine produces 142 kN (32,000 lb) of thrust in afterburner and 86.3 kN (19,400 lb) dry.[12]
It features a fan 3% larger in diameter (932 millimetres (36.7 in)
versus 905 millimetres (35.6 in)), advanced high- and low-pressure
turbines, an all-new digital control system, and provisions for
thrust-vectoring nozzles similar to the AL-31FP. This engine will have
an assigned life of 4,000 hours and an MTBO of 1,000 hours.[13] The first flight of this engine was completed in an Su-35BM on 20 February 2008.[14] On 9 August 2010, Ufa-based company UMPO started supplying 117S engines (AL-41F1S) intended for Su-35S fighters.[15]
117
Related to the 117S is the izdeliye 117 (AL-41F1), a highly improved AL-31F derivative designed for the Sukhoi T-50 fighter. The engine features an increased diameter fan, new high and low pressure turbines, and a digital control system (FADEC).
According to Sukhoi director Mikhail Pogosyan, the 117 is a new fifth
generation engine built specifically for the PAK FA. Though the
specifics of the 117 engine remain classified, the engine's thrust was
increased by 24.5 kN (5,500 lbs) over the AL-31 while the engine weight
was reduced by 150 kg (330 lb). The new engine produces 147 kN (33,067
lbf) of thrust in afterburner and has a dry weight of 1,420 kg
(3,130 lb) and thrust-to-weight ratio of 10.5:1.[16]
Mikhail Pogosyan further mentioned that the 117 engine meets the
Russian Air Force requirements and will be installed in production
PAK-FA fighter which will be supplied to the Russian Air Force and
prospective foreign clients.[17]
The 117 is an interim engine meant for prototype and initial
production batches of the T-50. The definitive second stage for the
aircraft is designated izdeliye 30 and will eventually replace
the 117 after 2020. The new engine has increased thrust and fuel
efficiency as well as improved reliability and lower costs. Bench
testing of the new engine will start in 2014 according to the general
designer-director of the NPO Saturn Eugeny Marchuk.[18]
The People's Republic of China began development of the WS-15 in the 1990s, designed to produce a maximum 180 kN[2] thrust with afterburner, similar to the Pratt & Whitney F119 and is expected to power future 5th-Generation fighters.[2][3] The 'Core' of the WS-15 was displayed for the first time in 2010.[4][5] A high thrust turbofan for transport aircraft based on the WS-15 Core[6] has been developed. This turbofan designated SF-A[6] and is developed for the Y-20[6] military transport aircraft and the civilian C919[6] airliner.
The design and development of the WS-15 engine used many valuable experiences learned from the previous WS-10
turbofan engine program started in the early 1980s; this will
significantly help and reduce the developmental time and risks of the
WS-15 program.
General Electric began developing the YF120 for the ATF competition in the early 1980s. Unlike competitor Pratt & Whitney, GE elected against developing a conventional low bypass turbofan and instead chose to design a variable cycle engine. This decision was made as a result of the challenging ATF requirement of supercruise.
This meant the engine had to produce a large amount of dry thrust
(without afterburner) and therefore have high off-design efficiency
("design" being standard cruise conditions).[1]
The core technology used in the YF120 was developed during two
industry-government programs, the Advanced Technology Engine Gas
Generator (ATEGG) and Joint Technology Demonstration Engine (JTDE)
programs.[2]
Variable Cycle
The YF120's variable cycle system worked by varying the bypass ratio
of engine for different flight regimes, allowing the engine act like
either a low bypass turbofan or nearly a turbojet.[1] As a low bypass turbofan (like competitor F119),
the engine performed similar to comparable engines. When needed,
however, the engine could direct more airflow through the hot core of
the engine (like a turbojet), increasing the specific thrust of the engine. This made the engine more efficient at high altitude, high thrust levels than a traditional low bypass turbofan.[3]
An expected disadvantage of this variable cycle system would be
increased complexity and weight. GE claims to have combated this by
using simple pressure driven valves rather than complex mechanically
actuated valves to divert airflow. GE stated that this system resulted
in the variable cycle system adding only 10 lb to the engine.[1] Additionally a production F120 engine was expected to have 40% fewer parts than the F110 engine.[2]
Thrust Vectoring
The YF120 engine featured a two-dimensional thrust vectoring
nozzle. The nozzle allowed for vectoring in the pitch direction. This
capability gave the aircraft it was installed in a serious advantage in
pitch agility by greatly increasing the amount of nose pitching moment
available to the aircraft. The pitching moment is traditionally
generated by the horizontal stabilizer (and/or canard, if applicable),
but with a thrust vectoring nozzle that moment can be augmented by the
thrust of the engine.[citation needed]
While the YF120 engine never went into production, it was installed in the YF-22 used for the high angle of attack demonstration program as part of the ATF
competition. During this demonstration, the YF120 powered aircraft
flew, trimmed, at 60 degrees angle of attack at 82 knots. At this
attitude the aircraft was able to demonstrate controlibility. Later
analysis revealed that the aircraft could have maintained controlled,
trimmed flight up to 70 degrees angle of attack.[4]
Advanced Development
The YF120 was also proposed as the basis for a more exotic engine,
the Turbine-Based Combined Cycle (TBCC) engine that was to be used in
demonstrator aircraft like the X-43B
and future hypersonic aircraft. Specifically, the YF120 was to be the
basis for the Revolutionary Turbine Accelerator (RTA-1). The variable
cycle technology used in the YF120 would be extended to not only turn
the engine into a turbojet but also into a ramjet.
In that mode all airflow would bypass the core and be diverted into the
afterburner-like "hyperburner" where it would be combusted like a
ramjet. This proposed engine was to accelerate from 0 to Mach 4.1 (at
56,000 ft) in eight minutes.[5][6]
The General Electric/Rolls-Royce F136 was an advanced turbofan engine being developed by General Electric and Rolls-Royce plc for the Lockheed Martin F-35 Lightning II.
The two companies stopped work on the project in December 2011 after
failing to gather Pentagon support for further development.
All early F-35s were to be powered by the Pratt & Whitney F135
but it was planned that engine contracts would be competitively
tendered from Lot 6 onward. The engines selected would be either the
F135 or an engine produced by the GE/RR Fighter Engine Team and
designated the F136. The GE/RR Fighter Engine Team was a co-operation
between GE Aviation in Cincinnati, Ohio, United States (60% share) and Rolls-Royce in Bristol, United Kingdom and Indianapolis, Indiana, USA (40% share).
On 21 July 2004, the F136 began full engine runs at GE's Evendale, Ohio facility. The engine ran for over an hour during two separate runs. In August 2005, the United States Department of Defense
awarded the GE and Rolls-Royce team a $2.4 billion contract to develop
its F136 engine. The contract was for the system development and
demonstration (SDD) phase of the F136 initiative, scheduled to run until
September 2013.
The US Defense budget announced on 6 February 2006 excluded the F136 —
leaving Pratt & Whitney, maker of the F135 engine, as the sole
provider of engines for the Lockheed Martin F-35 fighters. Congress,
however, overturned this request and allocated funds for FY 2007 later
in 2006. In November 2006, the General Electric/Rolls-Royce team
successfully completed a 3-month preliminary design review by the F-35
Program Office and the prime contractor, Lockheed Martin.[1]
On 13 February 2008, the GE Rolls-Royce Fighter Engine Team
successfully completed its Critical Design Review (CDR) for the F136.
During CDR, the U.S. Government's Joint Program Office for the F-35
Lightning II validated and approved the design of the engine. Also
during the review, every aspect of the engine design was analyzed and
evaluated in order to proceed with the building of the first full
development engines. The process involved 80 detailed component and
module design reviews, involving technical experts from the JPO, General
Electric and Rolls-Royce.[2]
On 20 March 2008, the F136 successfully completed a high-altitude
afterburner testing program at the US Air Force Arnold Engineering
Development Center in Tennessee, including common exhaust hardware for
the F-35 Lightning II aircraft. All test objectives were reached as
planned using an engine configured with Conventional Takeoff and Landing
(CTOL) and Short Takeoff Vertical Landing (STOVL) common exhaust
systems. The engine configuration included a production-size fan and
functional augmenter allowing several run periods to full afterburner
operation.[3]
The GE Rolls-Royce Fighter Engine Team successfully completed Short
Take Off, Vertical Landing (STOVL) testing on an F136 engine at the GE
testing facility at Peebles, Ohio on 16 July 2008.[4]
The first complete new-build F136 engine began testing 30 January
2009, under the System Development and Demonstration (SDD) contract with
the US Government Joint Program Office for the F-35 Joint Strike
Fighter program. This marked the first complete engine assembled
following US Government validation of the F136 design in 2008. The
milestone was achieved one month ahead of schedule.[5]
Citing the Weapon Systems Acquisition Reform Act of 2009, the GERolls-Royce
Fighter Engine Team submitted an unsolicited fixed-price offer for the
F136 to the Pentagon on 28 September 2009. The fixed-price approach
would cover initial F136 engine production, beginning with the F136
second production lot. According to the GE Rolls-Royce Fighter Engine
Team, the proposal would shift significant cost risk from taxpayers to
the Fighter Engine Team until head-to-head competition begins between
the F136 and the Pratt & Whitney F135 engine in 2013.[6]
From 2006 to 2010 the Defense Department has not requested funding
for the alternate F136 engine program, but Congress has maintained
program funding.[7][8]
On 19 December 2009, U.S. Congress approved continued funding for the F136 engine program in fiscal year 2010.[9]
The U.S. Defense Department did not request FY 2010 funding for the
F136 engine program. In a report filed on 18 June 2009, the House Armed
Services Committee cited Pratt & Whitney F135 engine program cost
overruns of $1.872 billion as cause to continue funding the F136 engine.[10][11]
On 2 November 2009, the F136 team said that they would redesign a
small part of the diffuser leading to the combustor after a failure
during testing.[12] Testing resumed on January 22, 2010.[13]
The GE Rolls-Royce Fighter Engine Team is currently in the fourth year
of its System Development and Demonstration (SDD) contract with the US
Government Joint Program Office. The Fighter Engine Team has totaled
more than 800 hours of testing on pre-SDD and SDD engines. In early
2010, full afterburning thrust was reached in testing of the first
production standard engine.[14]
On 24 March 2011, the Department of Defense issued a 90-day temporary
stop work order after Congress failed to pass the defense budget. GE
declared that it would continue work on the engine program with their
own funds in spite of the stop-work order, as allowed in the order and
as had been suggested by Schwartz the previous year.[15][16][17] However GE is limited to design work only, as the stop-work prevents their use of the existing hardware.[18]
On 12 April 2011, GE reduced its team on project from 1,000 workers
down to 100, who will work on the F136 and engine technologies for
"future combat aircraft".[19][20] GE will redeploy the workers to commercial projects, but will not hire the hundreds of new engineers it was expecting.[21]
On 25 April 2011, the Department of Defense ended the contract with GE
and demanded that the engines built to date be turned over.[22]
On 5 May 2011, GE and RR offered to pay for the development through FY2012 and asked for access to the materials.[23]
By switching to self funding the cost would reduce from $480 million a
year to only $100 million, 60% to be paid by GE and 40% to be paid by
RR.[24]
After self-funding the project GE and Rolls-Royce announced on 2
December 2011, that they would not continue development of the F136
engine because it is not in their best interest.[25][26][27]
Design
The F136 produces 18,000 lbf (80.1 kN) of lift thrust in STOVL
configuration. Combined with thrust from the LiftFan (20,000 lbf or
89.0 kN) and two roll posts (1,950 lbf or 8.67 kN each), the Rolls-Royce LiftSystem produces a total of 41,900 lbf (186 kN) of thrust.[28] This compares with the maximum thrust of 23,800 lbf (106 kN) for the Harrier'sRolls-Royce Pegasus engine.
We were in a turn and climbing when one
of the inlets showed signs of instability. Shortly thereafter—KER
BLAM!—the aircraft slammed my head against the side of the cockpit and
then momentarily became unstable as it yawed, pitched, and vibrated.”
This is an account of a supersonic engine inlet failure, or
“unstart,” recalled by retired reconnaissance systems officer Roger
Jacks in SR-71 Revealed, a book by retired Lockheed SR-71 pilot Richard
H. Graham. It shows what can happen when a supersonic inlet stops
delivering the uniform stream of air upon which efficient jet engine
operation depends.
When a jet airplane is flying faster than Mach 1—beyond the speed
of sound—the air entering the engines is moving supersonically as well.
But no turbojet engine compressor—the rotating disks and blades at the
face of the engine that compress the air before it is mixed with fuel—is
capable of handling supersonic air flow. The job of an engine inlet is
to slow incoming air to subsonic speeds before it passes through the
engine.
The inlet’s job is complicated by the fact that air moving
supersonically behaves differently from subsonic air. An aircraft flying
subsonically pushes through the air ahead of it, with each molecule of
air having plenty of time to pass over its wings and fuselage. But as an
airplane approaches Mach 1, it compresses the air ahead of it into
shock waves—bands of air radiating from the airplane that are much
hotter and denser than the ambient air.
Turbojet engines cannot digest the shock waves generated by their
inlets, so a crucial role of the inlet is to keep the inevitable shock
waves positioned so that they do no harm. The SR-71 Blackbird, a
now-retired twin-engine reconnaissance aircraft, has an inlet design
based on a cone-shaped body, or spike, that generates an oblique-angled,
cone-shaped shock wave at the inlet’s entrance and a normal shock
wave—one rising at a right angle from the direction of air flow—just aft
of the internal inlet throat.
As the SR-71 increases its speed, the inlet varies its exterior
and interior geometry to keep the cone-shaped shock wave and the normal
shock wave optimally positioned. Inlet geometry is altered when the
spike retracts toward the engine, approximately 1.6 inches per 0.1 Mach.
At Mach 3.2, with the spike fully aft, the air-stream-capture area has
increased by 112 percent and the throat area has shrunk by 54 percent.
The cone shape of the spike also incrementally reduces the speed
of the incoming supersonic air without producing a drastic loss of
pressure. The farther back over the cone the air moves, the more speed
it bleeds off. As the slowed, but still supersonic, air continues to
move farther into the inlet, the normal shock wave springs up between
the inlet throat and the engine compressor—exactly where it is supposed
to be. Once there, the normal shock wave slows the air passing through
it to subsonic speeds, preparing it to enter the compressor.
It is a constant balancing act to keep the normal shock wave in
the right position. The inlet has an internal pressure sensor, and when
it detects that the pressure has grown too great, it triggers the
forward bypass doors to open, expelling excess air. The inlet also has a
set of aft bypass doors, controlled by the pilot. The forward and aft
bypass doors work in opposition to each other: Opening the aft doors
causes the forward doors to close, and when the pilot closes the aft
doors, the forward doors open in turn.
During some Blackbird flights, however, the harmonious working of
the spike and the forward and aft bypass doors broke down, and all too
quickly the inlet was filled with more air than it could handle. When
the air pressure inside the inlet became too great, the normal shock
wave was suddenly belched out of the inlet in an unstart, accompanied by
an instantaneous loss of air flow to the engine, an enormous increase
in drag, and a significant yaw to the side with the affected inlet.
Unstarts occurred “when you least expected them—all relaxed and taking
in the magnificent view from 75,000 feet,” wrote Graham in SR-71
Revealed. If the crew’s attempts to restart the inlet’s supersonic flow
failed, they would have to slow their aircraft to subsonic speeds.
With a top speed of Mach 1.6, the Lockheed Martin F-35 Joint
Strike Fighter has an inlet design that is far simpler than that of the
Mach 3-plus SR-71; the single-engine JSF inlet cannot vary its geometry.
The F-35’s engineers could get away with a less complicated design
because at vehicle speeds up to about Mach 2, the shape of the inlet
itself can slow down much of the supersonic air before it enters the
inlet. The JSF inlet is, however, a breakthrough design: It has no
diverters. Traditional fighter inlets, such as those found on the F/A-18
and F-22, have slots, slats, and moving parts to divert or channel
airflow. The F-15 inlet has ramps and doors that alter its external and
internal shape to adjust airflow as needed.
Many other currently operational
fighters also have boundary layer diverters. Air that clings to the
surface of an aircraft in flight is known as boundary layer air, and it
tends to cause turbulence in the air flowing into the engine, especially
when it interacts with shock waves. Inlet designers try to keep out as
much boundary layer air as possible, frequently positioning the inlet
several inches away from the surface of the fuselage and its boundary
layer air and employing a duct system to whisk the undesirable air away.
(The SR-71 inlet rids itself of boundary layer air by sucking it in
through slots on the spike and passing it through ducts that exit the
nacelle.)
The F-35 inlet, however, is positioned flush against the
fuselage, and just in front of the inlet opening is a raised surface, or
bump, that pushes much of the boundary layer air off to the sides and
away from the inlet. The bump serves another purpose: During supersonic
flight, it compresses and slows the air passing over it into an oblique
shock wave. The air is still moving supersonically, however, and it is
slowed down to subsonic speeds after passing through a normal shock wave
that forms at the mouth of the inlet. The simplicity of the JSF design
makes for an inlet that requires less maintenance, reduces aircraft
weight by 300 pounds, and costs $500,000 less than a traditional fighter
inlet.
"Superjet" variable cycle jet engine could power future fighter aircraft
GE Aviation is developing a revolutionary new jet engine that
aims to combine the best traits of turbojet and turbofan engines,
delivering supersonic speed capability and fuel efficiency in one
package.
The new engines are being developed under the USAF ADVENT
project, which is seeking 25 percent fuel saving which will in turn
lead to an increase in mission capability.
There are two main species of jet engines for aviation:
low-bypass turbofans, usually called turbojets, and high-bypass
turbofans. Turbojets are optimized for high-performance, pushing fighter
jets to above Mach 2 (and the SR-71 "Blackbird" to well over Mach 3),
but pay for that performance with terrible fuel efficiency. The
performance outcome of a conventional turbojet is dominated by the
operation of the high-pressure engine core (compressor, combustion,
turbine, and exhaust nozzle).
In contrast, high-bypass turbofans are the heavy lifters
of commercial aviation, being optimized for subsonic thrust and fuel
efficiency, but performing poorly at supersonic speeds. A conventional
turbofan adds lower-pressure airflow from an oversized fan which is
driven by the jet turbine. The fan airflow bypasses the combustion
chamber, acting like a large propeller.
In an ADVENT (ADaptive VErsitile ENgine Technology)
engine, the high-pressure core exhaust and the low-pressure bypass
streams of a conventional turbofan are joined by a third, outer flowpath
that can be opened and closed in response to flight conditions. For
takeoff, the third stream is closed off to reduce the bypass ratio. This
sends more of the airflow through the high-pressure core to increase
thrust. When cruising, the third bypass stream is opened to increase the
bypass ratio and reduce fuel consumption.
The extra bypass duct can be seen running along the top
and bottom of the engine. This third duct will be opened or closed as
part of a variable cycle to transform it from a strike aircraft engine
to a transport-type engine. If the duct is open the bypass ratio will
increase, reducing fuel burn, and increasing subsonic range by up to 40
percent, leading to 60 percent longer loiter times on target. If the
ducts are closed, additional air is forced through the core and high
pressure compressor, enabling thrust and speed to increase and providing
world-class supersonic performance.
GE's ADVENT designs are based on new manufacturing technologies like 3-D printing
of intricate cooling components and super-strong but lightweight
ceramic matrix composites. These allow the manufacture of highly
efficient jet engines operating at temperatures above the melting point
of steel.
Engineers also designed the new engine to be easy to fly.
“We want the engine to take care of itself and let the pilot focus on
the mission,” says Abe Levatter, project manager at GE Aviation. “When
the pilot says ‘I’m out of danger, I want to cruise home,’ the engine
reconfigures itself. We take it upon ourselves to make the engine
optimized for whatever the pilot wants.”
GE is now testing the engine’s core components and plans
to run a full test in the middle of 2013. The video below provides
additional visual description of its operation.
Source: GE Aviation
