While perusing an old thread on contrails produced by stealth aircraft, a question occured to me.
Would it not be possible to detect a stealth aircraft by the sound of the engine or even it’s movement through the air?
This sort of thing was done before the development of radar
Are modern aircraft protected in some way to prevent this?
Thanks in advance
This is a severe over-simplification, but modern stealth aircraft fly faster than the speed of sound, so your detecting is going to be happening after they’ve passed.
I am no engineer, but seems like such a thing would be easy to drown out with background noise. How often are you able to hear a 747 when you are on the ground and the 747 is at 35,000 feet?
EDit: Also what **HurricaneDitka **said. Such sound detection would be of little tactical use because the stealth jet would have already “arrived.” Although many stealth aircraft fly subsonic (either because, like the B-2, they can’t go supersonic, or like other fighter jets, they might sometimes go subsonic just for fuel efficiency,) even still, you won’t get enough “notice” to do anything practical. Finally, even if you can detect the stealth jets by sound, that still doesn’t mean your missiles can lock on or that you can shoot them down.
Aside from radar (which stealth aircraft aren’t really immune from detection, but more difficult to detect via radar), infrared sensing probably offers a more fruitful avenue for detecting stealth aircraft rather than acoustic means.
A single detection device or complex could use many linked modalities - looking for radar signatures, heat, sound as you say, and probably others.
Not only would each modality be at least partially independent from the other, but their combined ‘signal’ would be strengthened and the plane more readily detected if, say, the plane was to ever fly in a straight line, or, I suppose, in any non-random path.
This is essentially what many military radar operations do.
Stealth aircraft lower their radar signature but they aren’t invisible.
Some types of radar can pick up a butterfly at a significant distance, so certain parameters are pre-set.
Size and behavior are Cheif among them.
Sufficiently sophisticated (1990’s era first world) radar can find stealth aircraft pretty well actually.
The biggest problem for radar Is actually “stealth” helicopters, since they can be designed to foil size indications and flown at speeds and paths that would likely be ignored .
At least in close ranges.
I think they can even be designed to fool radars capable of picking up the pulsating pattern created by typical rotors ( yes some radar can even look for that)
Stealth tech really just fools older systems and systems that haven’t been implemented effectively for the most part. While it does also lower the distance they can be tracked from.
For instance I know some craft like to brag about their “bumblebee sized” radar signature, but a bumblebee moving 400+ mph is pretty easily distinguished from the others.
Combining satellite visual IR detection with well implemented , up to date radar could almost fully defeat stealth tech. It’s a nice advantage but it’s not what it’s hyped up to be.
Adding to that, there are low observable target drones on the market (and have been for years), which are designed to train RADAR and AD crews to detect and engage stealth aircraft.
The radiated sound from stealth aircraft is minimized in the design to the point that even if you hear it you might not be able to identify where it is. The B-2 is incredibly quiet given its size and speed.
Also, while stealth has proven effective, they were designed to get to the target without being stopped, not necessarily to survive the aftermath. They are very good at what they were designed for.
Ever been at an air show and had an F18 or similar do a “sneak pass” from behind the crowd line? You don’t know it’s there until it’s right over the top of you, and that is at subsonic speed and very close to you. The further away it is the more distance there is between the aircraft’s actual location and the perceived sound source.
The very basic problem with using sound as a detection method is that it is incredibly slow compared to electromagnetic waves. Suitable for submarines but not so good for fighter jets.
Well, using sound to track a stealth aircraft worked in the 1982 movie Firefox.
I was a radar operator (breifly) with an AD unit
Nicely pointed out.
Also if one is interested, one could just Google some military radars and their advertised, unclassified abilities , that alone will give a clearer picture of the realities involved
I learned when the b2 was being tested you look in the opposite direction of its sound to see where it is
you learned you would see it about 30 seconds before you heard it if you caught it
Some do, some do not.
IIRC in the book the Soviets tracked the plane by infra-red, and the sound pickup was a deliberate decoy.
Aeroplane engines can be very directional noise-wise, as anyone who’s witnessed a Vulcan flypast can tell you.
Thanks for the responses.
Quote:
Originally Posted by HurricaneDitka View Post
This is a severe over-simplification, but modern stealth aircraft fly faster than the speed of sound
Supersonic or not isn’t actually the make of break for useful sound detection. A sound detector would be practically useless, for the way sound detectors were actually used, against an either slightly supersonic a/c or slightly subsonic a/c.
Basically they were used to narrow down the area in which searchlights would search to acquire targets at night. Even against a 200-300mph target as in WWII the time it took for the sound to get to the detector was significant relative to the plane’s movement. There had to be a correction for that time lag, and it had to be based on guessing the speed and altitude of the plane.
As per the example given in this US Army AA manual of the period
http://www.6thcorpscombatengineers.com/docs/FieldManualsWWII/FM%204-111%20%20Coast%20Artillery%20Field%20Manual%20Antiaircraft%20Artille.pdf
A plane directly approaching the sound locator at 4,000 yd altitude at 300mph would appear to be at an elevation angle of 470 mil (26.4 deg) when it was actually much closer at an angle of 760 mil (42.8 deg). IOW the raw sound locator output was useless for fire control. A mechanical computer corrected the output but was based on guessing the speed and altitude. That secondary rough solution was only enough to narrow down where the searchlights had to scan to pick up the plane, assuming a reasonably clear night. In clear daylight it wasn’t necessary: the aiming telescopes of the AA battery’s director would just see the plane immediately. In cloudy conditions the whole exercise was dubious: a fire control solution just based on the corrected sound locator output would probably at most give the plane crews something to think about, not necessarily a lot different than unaimed box barrages, both of which were statistically very unlikely to actually down planes.
As the speed of the plane increases, the real position at apparent angle of 26 degrees just approaches actually overhead, then actually behind the locator. There’s no point where the data suddenly becomes useless, it just goes from semi-useful at WWII speed to virtually useless as speed increases, but already essentially useless at near sonic speed. And that’s before considering that modern a/c dropping guided munitions have little reason to fly straight and level before weapon release unlike dumb bomb dropping a/c which sometimes did that even a few decades ago. Against an a/c maneuvering in three dimensions the idea of correcting the output based on guessing altitude doesn’t work at all. Keep in mind some operational AA fire control directors in WWII couldn’t deal directly with changes in a/c altitude even with direct optical or radar range measurement (though more advanced ones could).
This isn’t all historical trivia. The general idea of a potentially big difference between knowing an a/c is present and getting a fire control solution is also relevant to the debate about the effectiveness of Very Low (radar) Observables aka stealth.
I suppose they try to tune it to match ambient wind sounds, and direct it slightly upward to boot.
I’d check at the local national guard base, but all they every do is touch and goes in grey 737’s. Every once in a while we get a recon plane with that nice frisbee on top, and I’ve seen a fake Air Force One a couple of times.
Probably could drive down to Barksdale to see what their stealth B2 bombers do, but that sounds like a good method of getting arrested, or at least severely harassed.
I miss my dead-father in law’s copies of C3I. Real info has gotten progressively harder to find, and I’ll bet an Association of Old Crows patch will get a person precisely no where any more.
Heck, maybe they’ve hooked these jets up with active sound cancellation systems. That’d be something to see!
Years ago I was stationed at Andrews during their yearly airshow, and a B-2 did a flyby right overhead. I could see it plain as day, didn’t seem that stealthy to me.
They’re all based at Whiteman, in Missouri. They are loud, I can confirm.
You aren’t kidding. Several years ago one was staging for a fly by and passed over my kid’s soccer game. I watched it coming in low and eerily silent. I didn’t hear it until it went over us. You should have seen the looks on the faces of the people who were facing the other way.