Forum: The immutable laws of physics

The recent downing of an F-117 over Yugoslavia caused us to go back to the article we authored in the December 1998 issue of Flight Journal, not so much to be sure we accurately phrased our concerns over U.S. stealth technology as to ensure we left the correct impression on our readers.

Our thesis was that no airborne platform is invisible to radar. Stealth only decreases detection range. Therefore, stealth gives its user an important but not overwhelming edge over his non-stealthy opponent in the air. After having given the article another sanity check, we feel that it would be useful to expand on those original premises.

The answers are apparently still not in, or at least not releasable as to why the airplane went down. However, considering all of the factors in this complicated environment, it is safe to assume that it was most likely shot down. The next questions are by what? and why?

We realize that we are on thin ice, but since we are already embarked on making assumptions, we project that the thing that downed the F-117 was a surface-toair missile, probably an SA-6. The parameters of the downing indicate that this is the most likely culprit of all of the surfaceto-air systems in the theater.

We have always been fascinated by the lessons to be learned from the radarrange equation. The complete equation involves the transmitter power, the antenna gain and aperture, the minimum detectable radar return signal and, last, the radar cross-section of the target. For what is to follow, we will discuss only the effect of target radar cross-section upon detection range.

A typical non-stealth fighter design might have an average radar cross-section of 1 square meter at X-band, typical for SAMs. A SAM radar could detect this target at 100n.m. Now, as we begin to "stealthily" a fighter in the same class, the radar crosssection could be driven down with greatly increased difficulty and cost, per the numbers below:

The detection range is proportional to the radar cross-section raised to the 1/4 power. This means that the detection range goes down much more slowly than does the radar cross-section. We could call this the law of high-powered diminishing returns!

The 0.001-square-meter area is about the size of a 33-cent postage stamp, and it still can be detected at 18n.m.-a reasonable SAM range, especially if the X-band fire control radar is cued on where to search by a low-frequency UHF-band surveillance system. These low-frequency radars are very effective against stealthy targets, but they are not used for fire control. The Serbians have had expert help and can be expected to use such integrated air-defense systems (IADS).

We remember in 1947, a friend who worked at Servomechanisms in Westbury, Long Island, who told of radar-tracking a needle hung from a radiosonde balloon all the way out over Jones Beach, a distance of 10 to 15 statute miles. A recent rough calculation of the radar cross-section of such a needle (Skolnik) amazingly arrived at a similar number, per the table above, more than 50 years later! The Serbians are doubtless using some older-technology SAM equipment, but the needle says the laws of physics are fairly immutable !

Some will argue that the F-117 is "different"-a "faceted" aircraft known as a "spike and fuzzball" design in which incident radiation is deflected off in narrow beams in directions away from the receiver antenna. This is true, but the fuzzball remains and is not insignificant. It is an agglomeration of tiny imperfections in fit and finish of surface pieces that get amazingly worse in service. Grumman had a demo of a single screwdriver gouge worth 10dB (x10) in radar cross-section on a small demo panel. As the needle example shows, they don't have to be very big to contribute significantly to fuzzball cross-section.

There are several conclusions we should probably draw from what we now know about the Kosovo arena:

1. The Yugos have had some help from their former Russian mentors and can be expected to have a tough IADS. It would be silly for the U.S. and NATO forces to expect to roll over the Yugoslavian IADS as we did in Desert Storm in Iraq.

2. One can't expect graceful degradation from a flying computer that is essentially unstable about all three axes. Therefore, even with its quad-redundant flight-control systems, if an F-117A is struck by almost anything thrown at it from the ground, we should expect a mission abort or an aircraft loss.

3. The B-2 is the next generation design and, except for the advantage of active stealth deception systems, the same things can be said of it as were said of the F-117. The main differences between the F-117 and the B-2 seem to be size and the astronomical cost.

The Navy has always had a tradition of naming combatant vessels after famous people, events and places; the larger and more costly the vessel, the more important the name. For example, a cruiser was always named after a city, e.g., USS Cincinnati. The larger battleships were traditionally named after states (USS New Jersey). The huge nuclear-powered aircraft carriers were named after famous national heroes and statesmen (USS Nimitz, Eisenhower, Vinson, Stennis, Truman). Maybe the U.S. Air Force should follow this example and start naming B-2s after the popes!