A photo coming from Edwards Air Force Base exposes some really interesting details.
Raptor 4007 (AF 91-4007) is, along with 4006, the oldest flying F-22 Raptor. The aircraft is assigned to the 411th Flight Test Squadron and F-22 Combined Test Force as serves as a “flight sciences aircraft”, a platform used to perform various tests as part of the almost continuous F-22 fleet modernization programs.
An image of the aircraft ready for flight on Apr. 1, piloted by Maj. Brandon Burfeind, 411th Flight Test Squadron, F-22 Combined Test Force, has been recently released by the Edwards Air Force Base social media team. Although we don’t know what type of test the aircraft was about to fly, the photo itself is pretty interesting as it shows two interesting details: first of all, the RAM (Radar Absorbing Material) skin of the Raptor is full of scratches, a sign that the coating has not been maintained for some time and for this reason it is corroded; second, a previously unknown (at least to this author) low-viz nose art has been applied to the right hand side of the frontal section below the canopy rail.
Team Edwards getting the test mission done #FortheWarfighter!
Maj. Brandon Burfeind, 411th Flight Test Squadron, F-22 Combined Test Force, gives a thumbs up after a ground crew gets his F-22 Raptor ready for flight, April 1. pic.twitter.com/d89ka8Zis4
— Edwards Air Force Base (@EdwardsAFB) April 3, 2020
Let’s start from the latter. The nose art shows what resembles a Mario Kart’s Bullet Bill (bullet-like projectiles in the Mario franchise) and a large number 7: indeed, the aircraft’s tail number ending in “007″ has often inspired James Bond themed references and this may be once again the case.
Dealing with the RAM coating, it’s not a secret that a lot of work is required to maintain the skin of the F-22 Raptor, that is one of the most delicate and costliest parts of the stealth aircraft.
An article written last year by Tyler Rogoway at The War Zone provides additional details about the lifecycle of the 5th Gen. aircraft’s skin.
[…] 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.
Indeed, unless it is involved in testing activities that require the LO (Low Observability) a test aircraft as 4007 may not need a pristine coating to carry out its missions. This is quite normal both within the U.S. Air Force and other air arms all around the world. On the other hand we have often highlighted how most of the training as well as combat sorties of 5th generation radar-evading aircraft fly with radar reflectors/RCS Enhancers (or Luneberg/Luneburg Lenses) along with standard radar transponders to exaggerate their real RCS (Radar Cross Section) and negate the enemy the ability to collect any detail about their LO “signature”.
Stealth aircraft, such as the F-22 Raptor or the F-35 Lightning II 5th generation jets are equipped with Luneburg (or Luneberg) lenses: radar reflectors used to make the LO (Low Observable) aircraft (consciously) visible to radars. These devices are installed on the aircraft on the ground are used whenever the aircraft don’t need to evade the radars: during ferry flights when the aircraft use also the transponder in a cooperative way with the ATC (Air Traffic Control) agencies; during training or operative missions that do not require stealthiness; or, more importantly, when the aircraft operate close to the enemy whose ground or flying radars, intelligence gathering sensors.
[…] the Russians are currently able to identify takeoffs from Israeli bases in real-time and might use collected data to “characterize” the F-35’s signature at specific wavelengths as reportedly done with the U.S. F-22s.
In fact, tactical fighter-sized stealth aircraft are built to defeat radar operating at specific frequencies; usually high-frequency bands as C, X, Ku and S band where the radar accuracy is higher (in fact, the higher the frequency, the better is the accuracy of the radar system).
However, once the frequency wavelength exceeds a certain threshold and causes a resonant effect, LO aircraft become increasingly detectable. For instance, ATC radars, that operate at lower-frequency bands are theoretically able to detect a tactical fighter-sized stealth plane whose shape features parts that can cause resonance. Radars that operate at bands below 300 MHz (lower UHF, VHF and HF radars), such as the so-called Over The Horizon (OTH) radars, are believed to be particularly dangerous for stealth planes: although they are not much accurate (because lower frequency implies very large antenna and lower angle accuracy and angle resolution) they can spot stealth planes and be used to guide fighters equipped with IRST towards the direction the LO planes might be.
F-35s deployed abroad usually feature their typical four radar reflectors. As happened during the short mission to Estonia and then Bulgaria, carried out by the USAF F-35As involved in the type’s first overseas training deployment to Europe or when, on Aug. 30, 2017, four U.S. Marine Corps F-35B Lightning II joined two USAF B-1B Lancers for the JSF’s first show of force against North Korea: the F-35Bs flew with the radar reflectors, a sign they didn’t want their actual radar signature to be exposed to any intelligence gathering sensor in the area
Back to the F-22 at Edwards AFB, the fact that the RAM coating is heavily corroded by air friction, maneuvering and lack of maintenance, should not be surprising, especially on a test article that happens to be one of the oldest aircraft in the fleet. Moreover, as already explained, stealth is not always required, not even in combat.
BTW, today, the Air Force has 183 Raptors in its inventory.
H/T @base1075 for the heads-up!