The F-117 Tested A Mirror-Like Skin Decades Before The F-22 Did

We have more on the ‘mirrored’ F-22 Raptor mystery that includes a historical connection and an official Air Force statement.

byTyler Rogoway|
F-117 photo


Since our initial reporting, Nellis Air Force Base's 'mirrored' F-22 has grabbed a ton of attention. The aircraft has been flying regular sorties, and some great additional photos and videos have emerged of it in action. That being said, we want to add a bit of important historical connective tissue to our original story, which has to do with the F-117 Nighthawk. We also have a statement from the Air Force on the Raptor's mysterious metallic coating to share.

The same mirrored F-22 is seen from different angles. The reflectivity totally changes depending on the viewing aspect., Anthony Vogel

We wrote the following about the SENIOR SPUD program earlier this year, in a story to mark the 40th anniversary of the F-117's first flight, in which we laid out all the unique paint schemes and treatments the F-117 had worn over the years:

Another oddity around the same time was the half-black, half-metallic 79-10784, another one of the FSD [full-scale development] jets, which was trialed under the SENIOR SPUD program in July 1993. Over the course of four test flights, these metallic areas were apparently used to evaluate ways of reducing infrared signature, Paul F. Crickmore records, with the jet flying together with the NKC-135A Flying Infrared Signature Technology Aircraft (FISTA). It’s not clear how successful that was, but, in terms of visual signature, the metallic panels made the jet highly conspicuous in the daytime, at least. Similar testing continues to this very day, including using other surrogate aircraft. 

The surrogate aircraft we mentioned was one of Scaled Composites' shadowy 'Son of Ares' Model 401 aircraft, which was caught flying over Naval Air Weapons Station China Lake covered in a very similar coating as what we have seen on the F-22 recently. You can read all about that revelation here. When it comes to the SENIOR SPUD program, the only image of this metallic treatment on the F-117 we knew about was included in the original article, as well as below:

In its half-metallic scheme, the coated F-117 is refueled by a KC-135., Public Domain

It turns out that there is another image, seen at the top of this story, that really helps shed light on the nature of the material applied to the F-117 under the SENIOR SPUD program. The metallic coating looks extremely similar to what the F-22 in question is wearing today. That image was posted by aviation author Peter Merlin in the forums, along with the statement:

"It looks similar to the SENIOR SPUD test project. In July 1993 an F-117A was partially coated with a reflective material in an attempt to reduce the aircraft's infrared (IR) signature. Flight testing took place with the F-117A performing various maneuvers in the vicinity of Edwards AFB including low passes over the main runway. IR measurements were taken by sensors onboard the NKC-135A Flying Infrared Signatures Technology Aircraft (FISTA).

Photos of the aircraft show what looks like some sort of diffraction grating (what we used to call "spectrum tape" or "rainbow tape" back in the 1970s). I have seen video footage of the flight tests. The coating may have reduced the IR signature, but it increased the visual signature like you wouldn't believe. When the sun struck the coated surface, it lit up like crazy."

Just like on the F-22, the coating on the F-117 is made up of a mosaic of metallic tiles and sheets, which allows it to be applied to conform to critical areas, such as the wings, and to be arrayed around moving parts and apertures. But most importantly, it is something akin to a chameleon nature, in that it looks mirror-like when viewed from some angles and matte-like and unreflective when viewed from others. 

SENIOR SPUD also had a direct relation to the F-22 program. The coating seen in a strip on the F-117's right wing was developed for the F-22 and tested aboard the F-117 under the SENIOR SPUD initiative.

It's also worth mentioning that F-117s may have donned a similar skin more recently. Images of an F-117 flying with a bizarre metallic leading edge emerged in 2019 (seen in the tweet below). As we have noted for years, F-117s still serve in a research and development role for testing low-observable treatments and new sensor systems, as well as providing low-observable adversary air support.

The idea that the F-22 program could be looking at a similar concept 30 years later isn't too surprising. Even if this material has an adverse effect on the F-22's radar cross-section, but greatly reduces its infrared signature, the trade may become well worth it in an age of rapidly advancing infrared search and track (IRST) systems, including those mounted on advanced drones. IRSTs, which are totally passive sensors that scan for aerial targets in the infrared spectrum, are fully immune to the F-22's radar-evading qualities. 

Clearly, the technology has evolved in the years since SENIOR SPUD tested its reflective material. We have received various degrees of speculation regarding exactly what this material may do and how it works, including folks thinking it carries an electric current to help mask the jet's skin temperature. Others have said the coating's unique properties — high reflectivity and low emissivity — helps decrease radiant energy, making it basically a stealth coating designed for the infrared, not radio-frequency spectrum.

Ever more capable IRSTs are being fielded on foreign fighter aircraft, and for the first time in decades, domestic fighters as well. Here we see a line of Chinese J-10s equipped with IRSTs mounted on their upper nose areas., PLAAF

As for the Air Force, the 57th Wing was kind enough to get back to us on our inquiry about the 'mirrored Raptor,' their response was quite cryptic, but at least we got one:

The F-22 is part of a material demonstration that will evaluate material suitability to improve aircraft sustainment. New materials may reduce the lifecycle management burden associated with maintaining the aircraft, and increasing the useable lifetime of aircraft is essential to optimize government resources.

Increasing the useable lifetime of the aircraft clearly makes sense, as new low-observable treatments could enhance its survivability under evolving threat circumstances. As for the rest, it isn't clear how hundreds of individual metallic tiles, sheets, and strips would help with sustainment, but it is possible this is a new coating that does help in those regards, at least partially.

The F-22's radar-absorbent coatings are notoriously maintenance-intensive. As noted earlier, trading some low observability in the RF spectrum for enhanced low observability in the IR spectrum, while also realizing a more reliable F-22 fleet, may be a worthy tradeoff. And we still don't know if the metallic cladding does reduce the F-22's stealthiness when it comes to radar detection at all. Maybe advances in material science have allowed for the best of both worlds in that regard. On the other hand, the 57th Wing's reply could be a boilerplate response for new coatings on the F-22 in general. 

We are also marching towards an age where directed energy warfare, primarily in the form of lasers, will pose an increasing risk to combat aircraft, especially in the air-to-air combat domain. It isn't clear if this material may favorably impact the survivability of an aircraft when faced with such a threat. Even relatively conservative reductions in the range at which such an aircraft is vulnerable to laser attacks of a certain power and beam quality could be a serious advantage in the decades to come.

So, the mirrored Raptor still remains something of a mystery, but it would seem that it is related, at least in some regard, to SENIOR SPUD and the F-117 program that served as a progenitor to the F-22 decades ago.

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