US F/A-XX and F-X 6th Gen Aircraft News Thread


anzha

Junior Member
Registered Member
I trust you meant

"... Let's face it, if something moves fast through the air, disrupts molecules and puts out heat — I don't care how cool the engine can be, it's going to be detectable. You get my point."
That sounds like it. I remembered the first part, but not the last.
 

Brumby

Major
IRST has a much shorter range and limited field of view compared to a radar and detecting an IR signal doesn't necessarily mean you can track or engage it.
Range is still the biggest issue field of view is starting to shift. F35 for sure has a EODAS and Raptors And J20 have potential for them. These are IR spectrum sensors placed around the fuselage offering 360• IRST coverage via the helmets display.
AFAIK, technology with IRST is gaining very quickly. For example, the IRST onboard the F-18 reportedly have a detection range greater than its APG-79 radar. What that actually mean is open to all forms of interpretation. For example, the detection range against a 1m2 target is different to that of a 0.1 m2 target. I have seen data that suggest the APG-79 can detect a 1m2 target at 180 kms. Translated that would be about 100 kms for a 0.1 m2 target. The IRST is intended to deal with VLO targets like the J-20 and SU-57 because of possibly their lack of IR suppression features. However the current Block 2 IRST configuration cannot present sufficient data for a firing solution. Block 3 will address that with a 2 ship triangulation. It is why the USN is pushing for Block 3. The TTNT is to ensure nil latency and the DTP-N is the processing power needed for the algorithm triangulation.
 

Brumby

Major
Analysts: Navy brass view F-35C's stealth as overrated
February 9, 2015
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This is an example of an article where the author is framing its title that is misleading in order to bait read. If you read the article, the CNO did not say the F-35C's stealth is overrated. It is the author who is making that jump. In other words, his maths is 1 plus 1 is anything but 2.

Having said that, the present and future fight in air conflict remains unchanged. It is the competition in technology between "finding" vs "hiding". In my view, as informed individuals our objective is to understand the underlying technologies and their emerging trend rather than what somebody said.

Years ago I read a USAF official stating that the next air dominance is about spectrum domination. I believe that description is valid and will remain so in the forseeable future. The obvious spectrum range in my view is IR and RF (or stealth). Since the above article has touched on IR, I think it would be appropriate to have a conversation concerning the natire of IR and IR suppression technologies.

IRSTS detection range is determined by a number of factors, including atmospheric attenuation, seeker sensitivity, sensor aperture size, target size, and the square of the difference in
target temperature and the temperature of the surrounding environment.57 The blue line in Figure 17 shows how aircraft leading-edge temperature increases with aircraft speed. Ambient
temperature between 37,000 and 80,000 feet of altitude on a standard day is -70° F. The leading edges of an aircraft flying at Mach 0.8 are heated by friction to -21° F. As aircraft speed
increases, skin temperatures rise rapidly. For example, a fighter aircraft traveling at Mach 1.8 would have leading edge temperatures of 182° F.58 Increasing leading-edge temperatures by 200 degrees increases the probability of being detected by IR sensors.
(source : CSBA Trends in Air to Air combat)
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Aircraft flying at supersonic speeds also produce shock waves of highly compressed, and therefore heated, air. Figure 18 shows how large these “Mach cones” are relative to the aircraft
creating them.

upload_2019-5-25_10-50-18.png

I remember the F-35 was heavily criticised because it could not super cruise. In the above chart, it shows speed literally kills. If an F-35 intends to penetrate contested airspace, it would be suicidal to go supersonic. Maybe, the F-35 design team knows a lot more about trade offs than the ignorant crowd.

I think the Chinese and the Russians have yet to receive the memo because it seems the idea of super cruise is still very much in their top agenda.
 

Brumby

Major
IR suppression

IR suppression for an aircraft usually starts with the engine. The signatures of hot parts are most easily suppressed by masking. The plume is shrunk primarily by enhancing the mixing of exhaust air with ambient air to reduce temperature and pressure more quickly. Common techniques include increasing engine bypass ratio and injecting cooler air, water vapor or carbon particles into the exhaust. Another method is to augment nozzles with chevrons, scallops or corrugated seals to promote radial spreading of the plume and mixing with ambient air. Chevrons along the nozzle trailing edge also create shed vortices, which accelerate mixing. These augmentations reduce sound emissions as well, which is why new airliner engines are fitted with chevron exhaust nozzles. Patents filed for these nozzles cite “substantial reduction in noise and IR signature.”

Skin emissions can be reduced by using low-emissivity materials. Theoretical studies have suggested reducing skin emissivity from 1 to 0 can halve detection range. Layering materials with different indices of refraction can make surfaces reflective at certain wavelengths and emissive in others, such as those with greater atmospheric attenuation. Of course, surface coatings on stealth aircraft must also consider their radar effects.

Panther Piss and Platypuses

IR suppression has been part of U.S. low-observability initiatives for over a half century, often integrated with efforts to reduce rear RCS. The CIA’s A-12, the first aircraft designed with signature control as a major criterion, was the first U.S. aircraft to suppress its rear RCS and reduce its vulnerability to IR-guided missiles. The aircraft’s innate rear radar and IR signatures were large, due to the round, open titanium and steel nozzles and massive exhaust plumes. Lockheed compensated by adding “Panther Piss”—later revealed in declassified CIA documents to be cesium—to the fuel. This ionized the exhaust plume, reducing the aft-quadrant RCS, while also confounding IR-guided missiles of the time, possibly by radiating so intensely in NIR and MWIR that it saturated early sensors.

With the F-117, the first aircraft to use low observability as its primary means of survivability, Lockheed made IR suppression inherent to construction. The F-117’s fuselage sloped aft from an apex above the cockpit to a broad, flat feature dubbed the “platypus.” The engine exhaust flattened to thin slots 4-6 in. deep and 5 ft. wide, divided horizontally into a dozen or so channels. The lower fuselage terminated in a lip extending 8 in. past the exhaust at a slightly upward angle. This was covered in “heat-reflecting” tiles, similar to those used on the space shuttle, that were cooled by bypass air from the engines.

The platypus shielded the hot metal parts while the flattened plume reduced IR intensity from the side and accelerated mixing with ambient air. The extended lip masked the exhaust slot and first 8 in. of plume from below, while the low-emissivity tiles limited IR absorption and emission.

With the F-117, engineers were also introduced to the difficulty of balancing radar and IR signature suppression with the demands of extreme heat and pressure tolerance. The platypus was reportedly the hardest part of the design. Heat kept causing the structure to deform and lose its faceted outer shape. Ultimately, a structures expert designed a set of “shingled” panels that slid over each other to accommodate thermal expansion.

Northrop’s B-2 stealth bomber kept many of the IR suppression techniques of the stealth fighter. Buried deep within the flying wing, the B-2’s engines are prevented from heating the outer surface. Exhaust is cooled by bypass air, including from secondary air intakes, and flattened prior to exiting over “aft deck” trenches built of titanium and covered in low-emissivity ceramic tiles. Likely containing magnetic radar-absorbent material (RAM), these extend several feet behind the nozzles, blocking the plume’s core from below and the side. Also, the engine fairings and aft deck both terminate in large chevrons, which introduce shed vortices.

This aft deck has proven one of the largest drivers of maintenance cost and time on the aircraft. By the late 1990s, B-2s were experiencing exhaust lip blistering and erosion of the magnetic RAM faster than anticipated. New tiles were developed and new coatings added to the tailpipe, but cracking in the aft deck continued. By the mid-2000s, all 21 B-2s suffered from them. Interim fixes were fielded, including thermally protective covers for the tiles, while a long-term fix was developed which by 2010 was called the Third-Generation Aft Deck.

Turbine Shields and Topcoats

For Lockheed’s
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and
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, the need for afterburning engines, supersonic flight and fighter agility, as well as the desire for less maintenance, would require some new approaches. The U.S. stealth fighters use similar IR suppression techniques for internal engine parts, tail structures and airframe coatings. They diverge most noticeably in nozzle design.

The horizontal tails of both aircraft extend well beyond the nozzles, restricting the view of the exhausts and plume core in the azimuthal plane from the side and into the rear quadrant. The engines of both also have stealthy augmenters. Aft of the low-pressure turbine are thick, curved vanes that, when looking up the tailpipe, block any direct view of the hot, rotating turbine components. Fuel injectors are integrated into these vanes, replacing the conventional afterburner spray bars and flame holders. The vanes mask the turbine and contain minute holes that introduce cooler air.

Both aircraft also feature IR-suppressive skin coatings. The final addition to the F-22’s low-observable treatment is a polyurethane-based “IR topcoat” precisely sprayed by robots. Such IR topcoats have also been included in the
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’s Have Glass signature reduction program. The F-22 may also use fuel to cool its leading edges.

Despite the RAM fiber mats in the F-35’s skin, Lockheed still finishes the aircraft with a polyurethane-based RAM coating applied by a newer robotic system. Program officials have stated this outmost layer possesses anti-friction properties; MWIR imagery of the F-35 suggests low emissivity as well. Both aircraft coatings still exhibit poor wear and temperature resistance and have needed time-intensive recoatings more frequently than desired. In 2015, the U.S. Air Force announced it was testing a new coating for the F-35 with better abrasion and temperature resistance.

The exact composition of the coatings is unknown, but polyurethane is often used as a matrix material due to its relatively high durability, adhesion and resistance to chemicals and weather. It has a natural emissivity of 0.9, but many fillers have been demonstrated to reduce the emissivity when used in composite materials. Levels as low as 0.07 have been achieved with bronze, although at the expense of higher conductivity and therefore radar reflectivity. Multilayer glass microspheres of 5-500 µm diffused at 50-70% weight can achieve low emissivity at selected wavelengths and would probably be radar-neutral. Unoxidized iron also has emissivity in the 0.16-0.28 range, and its polyurethane-matrix composites have shown emissivity below 0.5.

(Part 1)
 

Brumby

Major
Wedges and Tail Feathers

The F-22’s “non-axisymmetric,” or 2D, thrust-vectoring nozzles have upper and lower surfaces ending in wedges with blended central edges. These nozzles further mask the engine hot parts while flattening the exhaust plume and generating vortices. Minute holes are evident on their inner surfaces, likely providing bypass air for enhanced cooling.

upload_2019-5-25_11-0-30.png

The wedge nozzles are believed to be effective in signature reduction, but they are a major driver of the Raptor’s maintenance cost and workload (nozzle internal flaps are one of the most often replaced parts even on conventional fighters). Thus, when designing the Joint Strike Fighter (JSF), engine and airframe manufacturers looked for a more cost-effective approach.

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In late 1996, while the JSF competition was still ongoing, the two engine competitors tested axisymmetric designs aiming to rival the wedge nozzle’s signature while beating it on cost. Pratt & Whitney tested the Low-Observable Asymmetric Nozzle (LOAN) on an F-16C, which demonstrated significant reductions in RCS and IRSL. The LOAN was known to incorporate shaping, special internal and external coatings and “an advanced cooling system” that was expected to more than double the life of the nozzle flaps.

In early 1997,
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tested a similar Low-Observable Axisymmetric (LO Axi) exhaust system on an F-16C, achieving its signature goals. GE stated LO Axi included overlapping diamond shapes, coatings and slot ejectors inside the nozzle to provide aircraft bay cooling air. The engine-maker said improvements in RCS design and material technology allowed axisymmetric nozzles to match the signatures of 2D exhausts while weighing half and costing 40% as much.

The nozzle on the Pratt F135s that power the F-35 descends from these approaches. It comprises two overlapping sets of 15 flaps, offset so outer flaps are centered on the gaps between the inner flaps. The inner flaps are thin, have metallic exteriors and straight sides and terminate in inverted “Vs.” The sides create rectangular gaps between them with the nozzle fully diverged.

The outer flaps, which Pratt calls “tail feathers,” are thicker and covered in tiles with blended facets. They terminate in chevrons that overlap the ends of the inner flaps to create a sawtooth edge. Toward the fuselage, the tiles end in four chevrons and are covered by additional tiles that terminate fore and aft in chevrons and interlock with adjacent tiles in sawtooth-fashion.

The
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nozzle likely suppresses IR signature through multiple methods. The trailing-edge chevrons create shed vortices, shortening the plume, while their steeper axial angle likely directs cooler ambient air into the exhaust flowpath. The inner surfaces of both sets of flaps are white and incorporate minute holes similar to those on the
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, which might supply cooling air. Some reports suggest the presence of ejectors between the tail feathers and chevrons to provide even more cooling air. The tiles and inner flap surfaces are likely composed of low emissivity, RAM composites. The trailing edge of the central fuselage also terminates in small chevrons, possibly further increasing airflow vorticity.

It is hard to quantify the success of these IR suppression efforts. Periodically, IR cameras will record stealth aircraft flying at air shows, but at ranges so close the images belie the suppressive effects of atmospheric absorption. Following the start of F-22 IR signature testing in 2000, Air Force officials stated the Raptor would exhibit a “low all-aspect IR signature under sustained supersonic conditions.” Some
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suggest effective suppression of engine airframe heating and nozzle emissions. Undoubtedly, IR sensors are advancing, but they are also being met with initiatives to suppress IR signature.


(source ; an extract from part 5 of a 7 part series done by AWST on stealth)
 

Jura

General
Analysts: Navy brass view F-35C's stealth as overrated
February 9, 2015
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This is an example of an article where the author is framing its title that is misleading in order to bait read. If you read the article, the CNO did not say the F-35C's stealth is overrated. ...
Brumby inside
:
Analysts: Navy brass view F-35C's stealth as overrated
February 9, 2015
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quote,
"What does that next strike fighter look like?" Greenert asked the packed forum. "I'm not sure it's manned, don't know that it is. You can only go so fast, and you know that stealth may be overrated.
end of quote

so the CNO said "stealth may be overrated"; please elaborate on your statement
#373 Brumby, Today at 2:54 AM
:
"This is an example of an article where the author is framing its title that is misleading in order to bait read. If you read the article, the CNO did not say the F-35C's stealth is overrated. It is the author who is making that jump."

was it perhaps a difference between "may" (the modal verb the CNO used) and "is" (the verb which wasn't used) that led you to assert "It is the author who is making that jump."
??
 
Last edited:

TerraN_EmpirE

Tyrant King
“May” or “Might” or “Possibly” are wishy washy words they show no conviction.

“Is” is a assurance it shows decision.

However the CNO Speech you point is loaded with insecurities on facts.
“don’t know”
Said that once to a Drill instructor pain was my reward.
“Not Sure”
Say that in a court of law and it’s case dismissed.

Basically he said. “ What will it look like? Ask my successor when it’s ready, I have no freakin Idea.”
 

Brumby

Major
Brumby inside
:

quote,
"What does that next strike fighter look like?" Greenert asked the packed forum. "I'm not sure it's manned, don't know that it is. You can only go so fast, and you know that stealth may be overrated.
end of quote

so the CNO said "stealth may be overrated"; please elaborate on your statement
#373 Brumby, Today at 2:54 AM
:
"This is an example of an article where the author is framing its title that is misleading in order to bait read. If you read the article, the CNO did not say the F-35C's stealth is overrated. It is the author who is making that jump."

was it perhaps a difference between "may" (the modal verb the CNO used) and "is" (the verb which wasn't used) that led you to assert "It is the author who is making that jump."
??
Greenert was speaking about the next generation of fighter aircraft, but his comments could just as easily be applied to Lockheed Martin's F-35C,
Please refer to the relevant contents taken from the article. The author by his own admission made that jump. He knew that the CNO was not referring to the F-35 but he made that connection by the headline. Context is important especially when the CNO did nor refer to the F-35 in his comments, .
 

Jura

General
Please refer to the relevant contents taken from the article. The author by his own admission made that jump. He knew that the CNO was not referring to the F-35 but he made that connection by the headline. Context is important especially when the CNO did nor refer to the F-35 in his comments, .
Brumby I repeat the quote:

"What does that next strike fighter look like?" Greenert asked the packed forum. "I'm not sure it's manned, don't know that it is. You can only go so fast, and you know that stealth may be overrated.
(
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)

and I repeat your statement
#373 Brumby, Today at 2:54 AM
:
"This is an example of an article where the author is framing its title that is misleading in order to bait read. If you read the article, the CNO did not say the F-35C's stealth is overrated. It is the author who is making that jump."

while there's a semantic difference between "may" (the modal verb the CNO used) and "is" (the verb which wasn't used), the article later points to the USN F-35C "buying pattern" which is the bottom line
 

Brumby

Major
while there's a semantic difference between "may" (the modal verb the CNO used) and "is" (the verb which wasn't used), the article later points to the USN F-35C "buying pattern" which is the bottom line
Repeating does not make reinforce your claim.
Did the CNO say the following which was the headline for the article?
Navy brass view F-35C's stealth as overrated
Yes or no? Simple question.
 

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