Stealth Technology?

Question

If a stealth plane breaks the speed of sound, will it be detectable by radar? I heard something about stealth planes not going past mach 1, and I was wondering if anyone could shed light on that...

Answer 1

You may have heard about the F-117, which is incapable of supersonic flight. As a compromose with early stealth technology, it's not designed with a good shape or powerful enough engines to break the sound barrier. Aircraft like the F-22 and F-35 can travel at supersonic speeds without any harm to their stealth cpabilities aside from more detectability from infrared tracking. Supersonic flight produces a lot of heat, which is easy to track. An interesting side note is that the first stealthy aircraft was the SR-71. It was designed to be almost undetectable by radar at it's operating altitude. Unfortunately, this was completely cancelled by an unexpected phenomenon. When the SR-71 reached it's top speed, the phenomenal heat and compression from the engines generated a trail behind the plane that was detectable on radars many miles beyond any other aircraft. This actually made the SR-71 the most easily spotted radar target in the skies. This problem was reduced by using certain fuel additives, but it was never eliminated. This doesn't occur with smaller aircraft that produce less power, but it's been theorized that a sensitive enough radar could detect shockwaves and heat created by the supersonic flight of aircraft as small as fighters. This hasn't been achieved yet, but, with more advances, may come to pass.

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EDIT: I don't like arguing, but I feel I should address the issue of exhaust plumes reflecting radar. Just so everybody knows I do know what I'm talking about.

Here's a couple of pieces. There are plenty of other sources and books to look for but I'm at work and low on time. You're all welcome to contact me if you want more info.

"Although most news reports characterize the SR-71 aircraft as `radar evading', in point of fact, however, the SR-71 was one of the largest radar targets ever detected on the FAA's long-range radars. The FAA was able to track it at ranges of several hundred miles. The explanation offered was that the radars were detecting the exhaust plume."

SOURCE:  http://www.globalsecurity.org/intell/sys...

"The aircraft was designed to minimize its radar cross-section, an early attempt at stealth design. However, the radar signature minimization did not take into account the extremely hot particles in the exhaust which reflect radar extremely well. Ironically, the SR-71 was one of the largest targets on the FAA (Federal Aviation Administration) long range radars, which were able to track the plane at several hundred miles."

SOURCE:  http://en.wikipedia.org/wiki/SR-71

Answer 2

It's mostly for infrared signatures since the plane will give off more heat due to friction, compression heating of the air, and exhaust.  

I suppose it could increase the radar signature as well.  High supersonic jet intakes are more visible to radar and the SR-71 was very visible on radar at high speeds due to its exhaust plumes (they bounced back more radar than the whole aircraft).

Answer 3

Uhhhh, exhaust plumes don't reflect RADAR signals more than even a stealthy body. ROFLMAOAM

IR cameras would detect that.

Please don't answer with information your have no clue about.

ADDED: I stand corrected on the heat plume and RADAR detection. At least I post my contact info so I can get feedback, unlike some peeps in this little universe of theirs.

Answer 4

The first and second generation of stealth aircraft the F117 and the B-2 are subsonic trading stealth or low observability for speed.  Afterburners and supersonic capability was deemed to be unnecessary and contributed to the problem of reducing the heat signature of the aircraft.  The latest generation of stealth aircraft the F22 is capable of going supersonic without afterburners.  It's called super cruise.

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Breaking the sound barrier would not necessarily call attention to aircraft as once it passes mach one it's still as stealthy as it is at lower speeds and would not make it suddenly detectable by radar.

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Answer 5

When going above mach 1, engines need to produce more thrust than normal to increase airspeed because of wave drag, a type of aerodynamic drag that is produced whenever an airplane is traveling above mach 1.

This in turn, makes more heat come out of the engine which can be detected.

Also, when going above mach 1, the air tends to be compressed and heated on the surfaces of the aircraft, even though altitude the temperatures are well below freezing. Which generates detectable amounts of heat.

There have been attempts to solve both of these problems for stealth aircraft.

1. Before the F-22, very few military aircraft can do what is known as "super cruise" or, flying supersonic without the use of afterburners. Afterburners are extremely fuel inefficient and generates a large amount of heat.

However, being able to super cruise, the engine would not produce a significant increase in heat, nor in fuel consumption. Though, it's still more fuel efficient to fly subsonic as compared to super cruise.

2. I don't know how exactly to solve the problem of external heating, but it's possible to run coolant lines around the skins of the aircraft (like oil or fuel) to cool it and reduce the IR signature.