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Just a thought experiment since bats are probably not swift enough to take evasive action in the scenario described.

If a cloud of bats were to encounter a B-2, or F-35, or F-117 or any of the other stealth aircraft in stealth-mode, would they detect the airframe in time, or fly smack into the aircraft?

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These aircraft designed to minimize their radar signature (and often their active noise and IR signatures as well), but bat do their special stuff with sonar. Nor do that have to turn on some kind of "stealth mode" their construction simply is stealth in flight configuration. –  dmckee Oct 19 '12 at 19:26
    
@dmckee: Then the postulated bat/s would kill themselves flying into the airframe? –  Everyone Oct 19 '12 at 19:28
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BTW--It is a bad sign if you can't think up some decent tags for your question, especially as you have the privilege of creating new tags. You should never post a question tagged [untagged], and I have requested that it be black listed. –  dmckee Oct 19 '12 at 19:30
    
Understood. I did think of creating a tag 'radar' but the idea seemed sort of ... facetious. I'll bear it in mind for the future. –  Everyone Oct 19 '12 at 19:35
    
@dmckee: I know this is late but I just saw this post. Some stealth aircraft do actually have systems they can turn on and off to affect their visibility to radar or to covertly respond to identification systems - electronic warfare systems are an integral part of modern stealth. –  gecko Mar 11 '13 at 2:01
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1 Answer

Static stealth aircraft

If the aircraft is static (parked on the ground) the bats echolocation would enable them to "see" the aircraft and avoid it. Bats' echolocation uses sound waves at 15-100 KHz. Stealth aircraft are not designed to reduce their reflection of sound waves, they are designed to reduce reflection of electromagnetic waves (primarily radar).

Flying stealth aircraft

If bats are in the path of any aircraft flying at typical subsonic aircraft speeds (say 50-200 m/s), the bats would probably not have time to evade the aircraft. Like us, bats evolved on a planet where nothing much flew above 10-20 m/s (some hawks can dive at 50 ms or faster, but not at night when bats are active)

Note:

  • Bats fly at less than 10 m/s
  • F117s cruise at over 300 m/s

Therefore it isn't accurate to think of a collision in terms of bats flying into an airframe, the bat is relatively stationary.

Bat echolocation range

The bats reacted to insect prey at dis- tances of about 70 to 120 cm. Given the flight speed, the detection distance was estimated to about 110 to 160 cm.

http://batlab.dk/pubs/87Pkuhli.pdf

lets say a bat echolocates a cruising F117 closing at 160 cm distance, the sound echo travelling from F117 to bat at 340 m/s reaches the bat after 4 ms. The F117 arrives 1 ms later. I doubt the bat's brain has even time to register this, but if it could react in less than 0.01 ms, it can only fly a few mm before the F117 strikes it.

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It's a thought experiment. Let's assume the bats are at a distance from the aircraft, and not approaching head-on! (+: –  Everyone Oct 19 '12 at 19:57
    
Bats are delicate, before they have time to notice the aircraft their organs would be ruptured by the turbulence of the passing aircraft. See newscientist.com/article/… , bats.org.uk/pages/wind_turbines.html and fort.usgs.gov/BatsWindmills - wind turbine blades travel through the air slower than aircraft bodies. –  RedGrittyBrick Oct 19 '12 at 19:59
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