Air Force Jets

[wireless]

Appreciate the answer.

[douglips]

*Originally posted by Monster104 *
No one knows what the top speed for the Blackbird is, but it can’t fly faster than the human body can withstand.

What does that mean? The human body can go as fast as it wants - witness the space shuttle.

I truly don’t understand what you’re trying to say.

[CurtC]

ElvisL1ves wrote:

The problem the bats have in seeing the F-117 with sonar is from the plane’s shape, not it’s materials. All those flat surfaces and straight lines reflect sound waves away from the sender as well as they reflect radio waves. That story is true too, etc.

So if bats need curved surfaces else they run into things, why aren’t they always flying into walls? I’m afraid that I would need a pretty convincing cite to believe that part.

[gabbyhayes]

I think he was referring to rapid changes in vector (delta v for appolo 13 fans). A 90-degree turn at mach 3 would turn you into a knackwurst.

[wireless]

*Originally posted by CurtC *
**
So if bats need curved surfaces else they run into things, why aren’t they always flying into walls? I’m afraid that I would need a pretty convincing cite to believe that part. **

It’s about how/where the signal reflects back to, not whether the surface is flat or not. A signal bounced off a flat wall in front of you (perpendicular - or nearly - to you) will reflect back (partly) at you (or the bat). If the angle is oblique - at an angle - then it will reflect off the surface, but not back at you where you (or the bat) can “receive” it. This is why the stealth fighter has no right-angled surfaces.

A curved surface will reflect parts of the signal back in lots of directions, pretty much assuring that some of it gets back to the source/transmitter (like the bat or the enemy radar).

Very few surfaces in nature are perfectly flat over large areas, so bats’ systems work pretty well.

[Ringo]

The site, The Lockheed F-117 Stealth Fighter, mentions the bats, but it’s not entirely clear whether the author is confirming or dismissing the tales:

The F-117 is an interesting aircraft, particularly because it gives insight into the nature of top-secret programs … the most interesting thing is how far off base most of the rumors were. Odd stories still float around about the machine – for example, soldiers guarding the aircraft in Saudi Arabia were said to have been startled by dead bats lying around the hangars. The bats had flown into the Nighthawks, which were as invisible to bat sonar as they were to human radar.

Area 51 Aircraft Database makes passing, but not necessarily convincing, mention of the bats as well.

Here’s an account of one such incident, but the source remains anonymous.

Ah! Finally a source, How “stealth” is achieved on F-117A, that gives some info on the bats and more on stealth technology.

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.

[DougC]

• • • I interpreted the question to be “why does an airplane have to have a high top speed, and be invisible to radar”. The answer is that missiles are guided by radar, and can easily be built to travel much faster (within a limited range) than airplanes. There’s nothing partiularly special about mach 2, it’s just the speed that US frontline engines are at right now: it’s a general compromise between speed and fuel efficiency.
• And I remember reading that it is sometimes possible to detect migrating swarms of insects, even on civilian radar systems. There’s a nickname pilots use for running through a swarm of airborne insects, but I forget what it is right off. - MC

[wevets]

*Originally posted by MC *

• And I remember reading that it is sometimes possible to detect migrating swarms of insects, even on civilian radar systems. There’s a nickname pilots use for running through a swarm of airborne insects, but I forget what it is right off.

I haven’t heard about the insects, but flocks of migrating birds are tracked by radar. The key word there is “flocks,” I don’t know if radar would be particularly useful in attempting to track individual birds.

The bit about the bats is suspicious, given that bats avoid other things that aren’t very radar reflective, like trees and bushes. I think beatle’s found the right answer.