These Images Of An F-22 Raptor's Crumbling Radar Absorbent Skin Are Fascinating
The photos are a reminder of just how much work goes into keeping the F-22's skin ready for combat and the amazing science behind its stealthy design.
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The F-22 Raptor was a highlight of this year's EAA Airventure Air Show in Oshkosh, Wisconsin. The Raptor Demo Team flew in aircraft that were from Langely AFB in Virginia, where the team is based. One of those jets showed comparatively extreme signs of corrosion on the upper nose area, right before the canopy. In fact, the section was in such poor shape, that it offered a bizarre and fascinating view of what some of the F-22's most prominent surface areas are made up of.
As you can see in the images, it's not just that the surface is corroded, it appears that areas of the radar-absorbent material (RAM) beneath it has fallen away entirely. It almost looks like there are gaping holes in the jet's upper nose, but that may not actually be the case. If you look closely, it seems like there may be a translucent coating in place over the area that creates a shell or sorts that laminates to the foam-like structure below. Still, the F-22's nose looks somewhat hollow inside.
Even the AN/AAR-56 missile launch warning system aperture appears to be at least partially 'floating' on this shell-like arrangement. If these were holes and open to the air, one would think the section would quicky rip apart while the jet was underway and cause negative aerodynamic and buffeting effects, as well as other issues. Regardless, we are looking at truly amazing material and construction science that appears downright alien when compared to that of non-stealthy fighters.
Much of what makes up and lies beneath the F-22 Raptor's silver skin remains a tightly guarded secret. The aircraft's outer mold-line is a mosaic of radar-absorbent coatings and radar transparent and radar defeating composite structures that combine to allow the Raptor to remain aerodynamically efficient while also largely invisible to fire control radars. All this takes a lot of work to maintain and many of these applications start degrading shortly after they are applied, with friction from high-speed flight, crushing G forces, and the elements accelerating that process. As such, one of the costliest aspects of operating F-22s—and flying this aircraft is extremely expensive with an average flight hour cost of about $60k—is keeping its stealthy skin up to par. This also is a major contributor to its fairly abysmal mission capable rate of around 50 percent.
For aircraft that aren't headed into combat or high-end training scenarios, maintaining the jet's stealthy skin isn't as high of a priority. There are different standards of readiness for F-22 skins to be kept at depending on the situation, with its effectiveness slipping a certain percentage before needing time-consuming reapplication.
For instance, for a jet that could see combat or is needed for high-end testing and training that will leverage its full capabilities, degradation of less than 10 percent could trigger the need to reapplication and servicing. For a jet used for training new F-22 pilots, that percentage could be far greater.
Senior Airman Joshua Moon, 192nd Fighter Wing stated the following in a USAF news item about maintaining the F-22's stealthy skin during Red Flag:
“We knew they were going to fly the hell out of the jets because this is a large-scale exercise... When the pilot flies he’ll bank real hard sometimes, which can tear or rip the radar absorbent material. If there are a lot of damages, the aircraft is easier to detect, so we try to keep those damages to a minimum to where you can’t see it on radar.
When other people have problems with a jet, it’s going to affect LO... Right now, something is wrong with a light panel on that jet. Since maintenance needs to get into that panel, we have to pick the radar absorbent material off and clean all the fasteners out so they can fix the light. Once the light is fixed we will re-bind the coating and material again to make it 100 percent ready.
At Red Flag, they’re testing our jets by hitting them with radar over the range, so that’s a lot of pressure for us – it’s really important that those jets come back undetected."
Clearly, performing at air shows doesn't require any stealth at all. In fact, the jets wear bolt-on radar-reflecting lenses so that their radar cross-section appears large on air traffic control radars. So, it makes sense to send jets that are not fresh out of low-observables servicing for such tasks and using those that are for more challenging and pressing missions.
In addition, roughly a third of the relatively tiny F-22 fleet is not combat coded at any given time. Older models that have not been upgraded to latest block configurations are used for training and in some cases testing. Once again, these aircraft would likely have a lower priority for keeping their stealth cloak in check than their front-line counterparts.
Aircraft that are based in more corrosive environments, such as humid areas or those near salty sea air, or where rain and cold are a constant reality, can see accelerated degradation of the low observable treatments. Langley sits right next to the Atlantic Ocean and would definitely challenge maintainers more than say aircraft that are based in the dry desert at Nellis AFB. But even the desert can take its toll on the Raptor's skin, especially the blowing sands of the Middle East.
The F-35 was designed with new LO skin treatments in mind that significantly reduce the time it takes to keep it in tip-top shape. But still, the newer stealth fighter gobbles up man-hours dealing with its stealth coatings and coverings. The F-22 has had new technologies and materials integrated into its skin over time, as well, including some of the advances baked in (literally in some cases) to the F-35, but it still takes a lot of work to keep the jets in their most stealthy configuration.
"Each week, LO does outer mold line inspections. This involves checking each jet's signature, which makes an aircraft appear on detection devices. A very high signature equals a very low stealth capability leaving the jet exposed to radar.
"It is extremely essential. Being invisible is priceless in combat situations," said Scott Christian, DS2 Aircraft Maintenance supervisor.
The OML helps determine where the jets sit in margin, the range of stealth capability that the aircraft need to be, and allows LO to identify the damages to the coating. When an aircraft is selected for a major signature reduction, it is in need of around 150 necessary repairs on about 30 different panels. These repairs can take up to three weeks to complete.
"We do everything from major three week repairs to what we call spike maintenance, which is just over a weekend," Sergeant Stovall said.
"The first step is always going to be to mask the aircraft, to ensure sanding debris is contained," said Staff Sgt. Armando Castellon, 325th MXS Low Observable Signatures coordinator.
This step keeps from spreading the contamination of hazardous chemicals associated with working with the LO coatings.
Next, the maintainers remove the damaged areas by sanding and then thoroughly cleaning those sanded areas to ensure a proper bonding of the coatings.
Once that is complete, LO reapplies the coatings starting with the boot layer, which is the radar absorbent material that allows for stealth capabilities. The additional top coats of paint follow. The jet is then removed from the system to avoid confusion.
One of the biggest obstacles the group face while applying the coatings is the Florida weather. Lighting within five miles of the base halts all flight line activities, including LO restorations taking place there, and the humidity and temperature levels makes it difficult to get a proper bond with the coatings, Sergeant Castellon said.
"When working with low observable material, everything deals with chemicals, and a lot of chemicals are required to stay within a certain temperature and humidity range to get the best bond," said Sergeant Stovall. "Here in Florida, we have a tremendous level of humidity. If we have one of those high humidity days when these guys are doing repairs, it is very possible there will be a disbond in the material just because environmental controls aren't where they need to be."
To counter these conditions, LO has two climate controlled bays that are the ideal location for restorations, but due to constant need of LO restoration, these bays are never empty.
During a week, the team continually work on six jets, which increases to eight to 10 during weekends. This does not include the flight line dispatch work they do."
It's amazing to think that the powerful lines of the F-22 that we have come so familiar with are really just a cloak that conceals the aircraft beneath it. As these photos prove, when it comes to the Raptor, there is so much more than meets the eye and we may never really know anywhere near all of its shrouded secrets nor much about shrouds themselves that conceal them.
Contact the author: Tyler@thedrive.com