Eine Kleine Nichtmusik

Witty and pertinent observations on matters of great significance OR Incoherent jottings on total irrelevancies OR Something else altogether OR All of the above

Thursday, February 21, 2008

Squeak. Squeak. Ouch.

I was reminded by this post on Ed's World about my favourite story about F-117A fighters. I had often wondered whether it was actually true or just the kind of story that might be spread around to make servicemen feel better about their aeroplane.

So I Googled it, and found this (scroll down for the extract below):

What about the story of dead bats in the F-117A hangers?

The following article was published in Aviation Week and Space Technology, Oct 17, 1991:

"An acoustic-guided submunition call the BAT may be good against tanks, but not against an F-117. A reader who works on the stealth fighter in Saudi Arabia says bats (the natural ones) occasionally work their way into F-117 hangars. One night, a hungry bat turned right into an F-117 rudder and fell stunned to the floor. He flew away groggily, leaving behind a heightened impression of the aircraft's stealth. "I don't know what the radar return is for the vertical tails of the F-117 but I always thought it had to be more than an insect's," the reader said. "I guess I was wrong." There may be some "science" in this - the ultrasound wavelengths used by bats are roughly the same as X-band radar."

In Ben Rich's book "Skunk Works" Col. Barry Horne is quoted as saying:

"....at night the bats would come out and feed off insects. In the mornings we'd find bat corpses littered around our airplanes inside open hangers."

When I asked a pilot about this he stated:

"During the six months I lived in Saudi Arabia (Feb-Aug 91), I lived in hardened aircraft shelters with the jets. I walked by them all hours of the day and night, and never once saw a bat--let alone a dead bat."
"I knew Col. Horne well. He went to Saudi Arabia a few months before I did, so I don't know whether he saw any bats, but if the quote in Ben Rich's book is accurate, then I believe he did. I never saw even one, though, alive or dead, and (I) passed through the aircraft shelters all hours of the day and night."
"What might have really happened could have been that when the Nighthawks first got to King Khalid Air Base the Saudis exterminated bats in the hangars--the best places to roost would've been the door tracks. Or possibly poisoned the insects on which they fed."

I also asked a former F-117A crew chief who was also in Saudi Arabia after the war. He stated:

""If you think about it the bats are probably like small birds, which can't deal with the high frequency noise the engines make. It is very common for small birds to become disorientated and die from jet blast or the noise at least from dealing with jets. Especially when they are in closed confined spaces....hangars, overhangs, enclosures, flows, etc. I've seen it happen to the fine feathered friend unfortunately."

And also this:

The basic principle behind RAM coating is this: the coating contains carbonyl iron ferrite (special paint using this material is known as "iron ball" paint). When a radar wave encounters this coating, it creates a magnetic field within the metallic elements of the coating. The field has alternating polarity and dissipates the energy of a radar signal. A significant portion of radar energy is converted into heat. Such RAM coatings can be manufactured in the form of neoprene-like tiles, with application of various ferric compounds in the synthetic polymer matrix. Early versions of the F-117A employed metal-backed RAM tiles. The tiles were cut to shape and bonded directly to the aircraft's metal structure. Gaps between the tiles were filled with RAM paint. Some of the gaps between the tiles were sealed temporarily only for the duration of the mission. Current models of the F-117A are using RAM paint applied directly to the aircraft's body. The paint is applied employing robotics because the solvent used in the process is highly toxic.

Interesting incidents were observed by F-117A maintenance crews during the Gulf War. Here is a short description from At the Controls: F-117A Stealth Fighter, by Jon Lake: "The effectiveness of F-117A's RAM skin was demonstrated in an unusual manner during the Gulf War, when groundcrews started finding dead bats around the tails of hangared aircraft. The unfortunate creatures had clearly flown "full tilt" into the Black Jet's tailfins, which their high frequency 'sonar' had been unable to detect."

The story of "dead bats" in fact has nothing to do with the F-117A's "stealthy" properties. Bats use ultrasonic signals for echolocation: these are mechanical compression waves not electromagnetic waves, as in case with radars, and have certainly nothing to do with the radar absorbent paint or any geometrical properties of the F-117A. The ultrasonic signals emitted by bats are narrow and highly directional and will reflect from most surfaces, RAM or no RAM. To explain the "dead bats" phenomenon we only need to remember that the F-117As use highly toxic paint and that the aircraft were stored in hot hangars with restricted ventilation. If the maintenance crews have spent as much time in these hangars as bats did, the bodies of bats would not have been the only dead bodies found around F-117As.

I like the last sentence.


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