Air Force Jets

I saw a comercial for the Air Force that starts out innocently enough - a voice over begins with something like:

“The Air Force has a fighter that’s the most advanced Jet in the world” (please don’t shoot me for the obviously bad missquote)
“But shows up on radar as small as a humming bird - the baddest, meanest humming bird in the sky…”

My question is what good is size cloaking technology when your “humming bird” is traveling at Mach 2?

(oops hit the button too fast)

and how does the cloaking technology work?

It’s not ‘cloaking technology’. It’s a reduction of the radar cross-section of the plane by a combination of materials and design. Just as the angles of the F-117 deflect the radar waves away from the receiver, the a angled planes of the F-22 does much the same thing. There’s also a great deal of carbon fiber and other ‘exotic’ material used that generate a much lower return signal.

Also, the weapons are no longer hung on the pylons on the wing, but carried internally in a weapons bay which clears up a lot of the clutter that would normally generate returns. I don’t know if they’ve gone so far as to line the cockpit glass with a radar absorbing layer or not, but I wouldn’t be surprised.

Basically, radar equipment isn’t made to detect anything as small as a hummingbird, so it won’t see it at all. Thus, it won’t be able to notice how fast it’s going.

There’s a story, that sounds apocryphal, about the steathiness of the F22. Suppposedly when it was still in the prototype stage, one was rolled out and tested with a portable radar unit. The plane proved to be so invisible to radar that it produced no image and several people began arguing that the radar unit wasn’t being used properly. While they were doing this, the operator announced he was suddenly getting a signal off the plane but it was very small. The engineers looked at the plane and saw a bird had landed on top of it.

Little Nemo, I’ve heard the same story, only it was attributed to the F-117’s development. IIRC, bats that lived in the area(Groom Lake is desert) would frequently injure themselves by running into the parked planes. Their echolocation was useless against a few billion in stealth technology.

L. Nemo — If the Aircraft was on the ground, then its landing gear would have been extended. These are usually steel or titanium, or something like that. They are not “stealth” designed as they are retracted and covered in flight. So if nothing else, a radar aimed at the aircraft on the ground would get a very noticeable return from the L/G alone.

Wide band radar apparently can detect “stealth” aircraft. But I understand this use of wide band makes the radar source very obvious to any potential attackers or evaders.

I’d be interested in knowing from the tech wizards what all they think about the story about the bats smacking into the F-117s. Should something that reflects radar so that it doesn’t bounce back to the emitter do the same for sound? Certainly, the iron-ball paint they use won’t be too effective at absorbing sound waves.

JCH, the test LN is referring to had the aircraft mounted on a pylon out in the open, for the purpose of measuring it’s radar cross-section. The gear was up, the doors were closed, the goop was in the cracks, and so forth. The story of the detection of the bird is true, and is reported in several books.

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.

I can’t address the specifig anecdote, but it did jog a memory. IIRC, a mock-up of an F-117 was put on a pedestal and painted with radar. Since the landing gear was either retracted or not installed, the radar signature was very small. I don’t know if the pedestal was specially designed so as not to reflect the radar; or if its signature was recorded without the airframe on top first, so as to get a baseline to work from. Again, IIRC, engineers were surprised at how small the aircraft’s signature actually was.

I guess I should have waited a couple of minutes before I posted. :wink:

The hummingbird story, if I recall correctly, was relayed in great detail in the books Skunk Works : A Personal Memoir of My Years at Lockheed by Ben Rich, and Lockheed Martin’s Skunk Works by Jay Miller.

next chance you get to go to an airshow, look at the F-117 if they have one on static display. You’ll see, on each side of the aircraft, a raised, faceted bump about the size of a lemon. I noticed it and asked the pilot, and he informed me that it’s installed as a radar reflector (no radar absorbant material in the “bump”) so that FAA radar can see the plane - they’re removed when showing up on radar would be a bad thing!

Also, it turns out that every F-117 has to have constant paint touch-ups done because the nicks and abraisions on the leading edges of the wings and fuselage just from day-to-day flying cause flaws in the radar-absorbant paint and cause the plane to show up on radar.

The cockpit is coated in RAM also, because the pilot’s helmet gives a bigger radar return than the plane if they just use plexiglass like any other aircraft.

I wonder why they just don’t use a transponder?

Could be because:
Transponders transmit in a certain freqency band.
FAA/Airport radars operate in (receive at, or "look for) a certain frequency band.
No frequency band overlap = no “see”

(We’ll ignore harmonics/intermods for simplicity.)

IIRC, it’s similar to why sailboats at sea (esp. in shipping lanes) have those radar reflective stars on their masts - so the big guys see 'em, esp. at night.

Also, do military A/C typically have all the civilian systems such as transponders, etc.? (I imagine the Cargo’s do, but the Fighters’s? The Attack’s?)

Possible alternate theory:
The guy didn’t want to (or couldn’t) tell you what they really were for, so made up a B.S. answer.

F117’s regularly use transponders if they do not want to be stealthy. There was a near miss not too long ago at a major airport (Reagan?) because a pilot almost forgot to turn his on.

      • Because missiles can travel at mach 4, and turn faster than airplanes.
  • Modern air war isn’t often fought with blazing machine-guns, Red-Baron style anymore. Planes dozens of miles away from each other launch missiles without ever being in sight of either. Planes are detected, and missiles aimed, by radar. The Pentagon decided that it was easier to avoid being detected than it was to outrun whatever had detected you, so for a military jet, to not show up on radar is a good thing, generally speaking.
  • As for the mach-2 issue, it seems to be just a generally agreed-upon standard at the Pentagon. It’s just a compromise of speed and fuel efficiency, and it’s where most US fighter-engine programs are at right now. The USSR built fighters that had higher top speeds, but much poorer fuel economy (they assumed they’d be defending their home turf, or near it, and didn’t consider supplying fuel to be so much of a problem). - MC

MC, I think the point of the question about the humming bird travelling at Mach 2 was, since real humming birds don’t travel at Mach 2, no one would be fooled. A simple computer program could filter out all the bird-sized objects travelling at bird speeds, and all the stealth planes would stand out.

Of course, I think saltire is right: radar won’t detect the stealth planes at all, so their speeds are irrelevant. I think if a radar had the capacity to pick up a creature that small, processing the return signal would be a nightmare, since there are rather a lot of objects humming bird sized and larger in the air.

Yes, all military aircraft have transponders and IFF (Identify Friend or Foe) equipment. There are several modes of operation available to military A/C that may not be available to civilian A/C. And on military aircraft, there is an off button on this sort of equipment.

MC, the Russian planes you’re referring to are MiG-25 Foxbats. They’re capable of high-speed dashes up to mach 3, but the engines tend to need replacement as soon as the plane lands after one of those flights. They were built as a counter-measure to the XB-70 Valkyrie, a mach 2+ cabable bomber the US was looking into in the early '60’s that wound up being used as a high-speed test plane. Only two were built, and the sole surviving example is in the USAF Museum.

Nothing that takes off from a runway (and has been confirmed to exist) is faster than the SR-71 Blackbird, which tops out somewhere above mach 3 and currently holds the world speed record for a flight from Palmdale, CA to Washington DC in an hour and a couple of minutes. It also happens to be one of the first aircraft to use radar-absorbant materials in its construction, although it’s nowhere near as stealthy as an F-117 or an F-23. It relied on speed rather than stealth for survival, and no hostile action ever brought one down, although dozens of missiles were fired at them over the years.

As for the bump on the side of the F-117, it was three or four years ago, and i may be remembering the explanation wrong. I do remember being told that it was removed for combat missions. Makes sense that it could’ve been a transponder, except there is one on each side of the fuselage. Would they need more than one?

Actually, the Blackbird wasn’t “topped out”,that was just the faste they’ve recorded flying it. No one knows what the top speed for the Blackbird is, but it can’t fly faster than the human body can withstand. It also doesn’t rely primarily on speed, but altitude as well. The Blackbird is essentially considered to be a low-flying space-ship (The pilots wear space-type suits, btw).