We've Lost Our Stealth
Flying low-observable "stealth" aircraft means near-perfection in maintenance, or the aircraft aren't low-observable anymore. This has implications for a "big-boy war".
 |
| F-117 Nighthawk in flight. Image credit: USAF Staff Sgt. Aaron Allmon II |
Low-observability was a revolution in aircraft design. Since the invention of radar, air forces have sought methods to reduce their opponents' ability to see aircraft incoming. The U-2 and A-12/SR-71 spy planes in the 1950s and 1960s attempted to defeat radar through excessive altitude (it didn't work) and some coatings and shaping of the airframe. The first operational "stealth" airplane was the Lockheed F-117 Nighthawk, which first flew in 1981. The F-117 was designed to fly into the strongest air defenses available with no assets except its stealth: it was subsonic, not maneuverable, and had no air-to-air armaments. It was critical for the stealth to work.
Perfection in Maintenance
The contract for the first F-117s guaranteed a specific (extremely low) ability to be seen on radar. The technical term is "radar cross-section" and is expressed in area units (square meters, etc.). Ben Rich, who ran the Lockheed "Skunk Works" advanced development group at the time, wrote about this in his memoir:
[Emphasis added]
I was feeling particularly skittish on that score [contractually-guaranteed radar cross-section] because a few weeks before the contract negotiations began, I received an urgent call from Keith Beswick, head of our flight test operation out at the secret base.
"Ben," he exclaimed, "we've lost our stealth." He explained that Ken Dyson had flown that morning in Have Blue [the experimental predecessor to the F-117] against the radar range and was lit up like a goddam Christmas tree. "They saw him coming from fifty miles."
Actually, Keith and I both figured out what the problem was. Those stealth airplanes demanded absolutely smooth surfaces to remain invisible. That meant intensive preflight preparations in which special radar-absorbent materials were filled in around all the access panels and doors. This material came in sheets like linoleum and had to be perfectly cut to fit. About an hour after the first phone call, Keith phoned again. Problem solved. The heads of three screws were not quite tight and extended above the surface by less than an eighth of an inch. On radar they appeared as big as a barn door!
So the lesson was clear: building stealth would require a level of care and perfection unprecedented in aerospace.
Skunk Works by Ben R. Rich and Leo Janos, 1994, page 69
Over time as the US Air Force has evolved from the F-117 to the B-2, F-22, F-35, and forthcoming B-21 (plus uncrewed low-observable aircraft), the quest has been for "maintainable" stealth. The constant application of coatings for each flight on the F-117 and rapid degradation of those coatings in the field has always been an issue. The B-2 has a reputation for being hard to keep in mission-ready condition; the F-22 and the F-35 have both promised more maintainer-friendly capabilities. Some of these are chemistry: better paints and coatings that absorb radar more effectively and are also more robust. Some of the changes are design: avoid maintenance panels and instead put as many maintenance-critical items behind doors that are already open on the ground like weapons bays and landing gear bays. Those doors would also lock firmly and securely to the body of the airplane. Also from Skunk Works:
[Emphasis added]
Other Voices
Alan Brown
I was Ben's program manager. Building the stealth fighter, we had to tightrope walk between extreme care and Swiss-watch perfection to match the the low radar observability claims of our original computerized shape. We didn't have the time, money, or personnel to build a flying Mercedes. But we couldn't allow even the tiniest imperfection in the fit of the landing gear door, for example, that could triple the airplane's radar cross section if it wasn't precisely flush with the body. So we took extra steps to hold in those doors and put on an extra coating of radar-absorbing materials.
Skunk Works ibid, page 81
In my time with aircraft landing gear, landing gear doors can be "driven" several ways. The easiest is to physically attach the doors to the landing gear strut, either directly or through physical links. Those have the advantage of simplicity: if the landing gear wants to go down, it pushes the doors out of the way. If it comes up, the doors come with it. For a low-observable aircraft, the landing gear is unlikely to hold steady enough in the retracted position, and the door actuation needs to really ensure the door is flush with the rest of the skin, so I'm sure those doors have dedicated actuators.
Operational Implications
I haven't been able to find any evidence of this, but I imagine that pre-flight or pre-mission checks for low-observable aircraft must include a "can I be seen on radar?" check. The easiest way would be for an airborne or ground radar to try to "paint" the outbound aircraft, or maybe another member of the departing flight. I wonder about this though: fire-control radars are powerful and often use different frequencies than air-traffic control; is this a reasonable check? Does that mean that aircraft are sometimes revved up on the runway or even already airborne and then a mission aborts because someone says, "Hey wait, I can see you!"?
Like in manufacturing, the best quality control is as early as possible after an error might be made. Can a maintainer safely activate a radar and point it at a pre-flighted F-35 before engine start? Is that possible with the landing gear down? Is the equipment small enough and also unlikely to "cook" (literally or figuratively) anything else in the hangar? Does an aircraft carrier about to launch a strike mission have to break emissions control and broadcast its position so that the outbound aircraft can be sure that air defenses can't lock onto them?
Final Thoughts
I've discussed in other places how entering a major war would be qualitatively different for the United States (see below). Another way might be how we run missions with low-observable aircraft. Are we able to get away with fewer radar checks now because maintenance crews can check everything thoroughly and battle-damage is non-existent? Are we doing radar checks because we're in permissive environments? Maybe the various F-35 operators have already solved this problem (I hope so!).
But I wonder if an austere high-tempo F-35 base in wartime might lose a substantial fraction of its force in many missions: a bolt protrudes an eighth of an inch on one aircraft after being replaced, another aircraft has a small scratch from unnoticed battle-damage, and a third has a mis-rigged weapons bay door that doesn't quite close flush. Are maintainers and mission planners ready for an F-35 loss rate in those situations?
I just ran across Bret Devereaux using the term "A Big-Boy War" to describe these high-intensity conflicts. I've previously written about Big Boy War implications here (mostly industrial):
Comments
Post a Comment