# Tag Info

43

Yes, actually you can only hear a supersonic aircraft after it has passed over you and is now flying away from you since it is moving faster than the sound moving towards you. The sound waves will still propagate in all directions and will eventually reach you: The frequency will be shifted according to the Doppler formula: $$f = \frac{c \pm v_r}{c \pm ... 36 Note that 747's and other jumbo jets operating out of Bradley could not have produced sonic booms because they do not fly above the speed of sound (they only do 500 to 550 MPH at high altitude cruise) and, in any case, far slower than that (~250 MPH) when near the ground as for landing and takeoff. Therefore, whatever it was you heard, it was assuredly not a ... 29 This PDF indicates an increase by ~10 dB for an F-8K in afterburner versus the same aircraft in 100% dry thrust. This PDF indicates smaller increases: +5 dB for an F-15 +4 dB for F-22 and F-35 25 There are two factors reducing the volume of a sound when travelling through the air: The pressure wave expands as the surface of a sphere, which will reduce pressure as a function of distance r:$$ p(r) \sim \frac{1}{r^2} $$Since human hearing is logarithmic, we typically use Decibels (dB) as a unit for volume, rather than pressure directly:$$ L_p = ...

24

It has been around 20 years since I've been on a carrier deck, but I recall that it wasn't as dramatic of an increase as you might think. It may have gotten a little bit louder, but what I remember more is that the tone changed. The sound was more "full" when the afterburner was engaged. I realize this is a rather subjective answer.

14

I would say definitely yes, because of all the extra energy added to the exhaust flow and it's obvious to anyone who attended enough military airshows. Watch an F-16 depart with reheat on, then reduce thrust to military power (max thrust with reheat off) on the climb out, and it almost sounds like the engine flamed out. The flow out the nozzle may be ...

14

It was either not a sonic boom, or it was not a commercial jet. As Niels has pointed out, civilian aircraft are prohibited from operating faster than 250 knots Indicated Airspeed below 10,000 feet MSL in most cases. You would have to get special permission from FAA leadership (not ATC controllers) to otherwise perform such a stunt. §91.117 Aircraft speed. (...

12

If you lived near an international airport with commercial traffic, then it couldn't possibly have been sonic booms, as others have noted. What you likely have heard is jet noise. Jet noise has been known to be notoriously bad. If you google sound scale, jet noise is pretty much always near the top. That's one of the primary reasons why city airports haven't ...

10

To explain if the afterburner makes the engine louder, you must understand what the afterburner does. In the afterburner, the exhaust gases are re-heated by injecting fuel in the afterburner duct. The left oxygen is used to burn the fuel, which results in an increased exhaust gas flow. Note that the engine itself will not spool up faster: this is done by ...

9

Yes, you can definitely hear planes from that altitude. Twin turboprop regionals flying over my city at altitudes between 21000 to 25000 ft are clearly audible at pretty much any weather, so a C-130 being much larger and having two more engines would have no trouble transmitting sound down to the ground from 27000 ft.

7

This was answered by an pilot acquaintance of mine: The most recent generation of engines on the E2 comes with a geared turbofan. In the final stages of descent, the engines rotate at speeds which causes resonance in the combustion chamber. The distinct sound is that vibration. This sound can also be heard when departing the gate, when the engine experiences ...

5

What would real sonic booms have been like? The other answers do a good job of explaining how commercial airliners have gotten quieter over the years and how you were probably hearing jet noise, not sonic booms. But how do you know it wasn't a sonic boom? What would it have been like to live under regular sonic booms? Well the only way to know that for sure ...

5

You may have been hearing the Concorde reaching supersonic speed after its takeoff from the JFK and Dulles airports. I heard them frequently while on Cape Cod during the summer months. Interesting studies were done about this phenomenon and its effect on the population.

4

Yes. Most of the noise you hear from aircraft is not mechanical noise from engines but disturbances in airflow around the airframe and engine outlets and inlets. The airflow from reversing jet engine is much more turbulent than when the engine is forward pushing and thus more noisy.

4

Most supersonic aircraft have points where the cross-section suddenly changes, such as the fuselage nose, the wing root leading edge or the wing trailing edge. The points of sudden change produce sharp changes in air pressure, i.e. loud sonic booms. Concorde was one example. By designing the plane's cross-section to vary smoothly from end to end, the ...

4

Rattling that disappears after liftoff is normally associated with a vibrating tire transmitting vibrations up through the airframe, and causing some sort of interior panel that is a bit loose to rattle in sympathy. On most airliners the brake system applies the main wheel brakes momentarily, once weight-off-wheels, to prevent the usual spin down vibrations ...

3

The air attenuates high frequencies more than it does low. Thus, lower frequency sounds travel farther, so you hear them first. Also, longer wavelengths will appear to "bend" around obstacles more than ones with shorter wavelengths, so buildings around you will in many cases develop acoustic "shadow" zones for higher frequencies as those buildings' ...

2

As an additional point... the reason ADS was given its own frequencies was so that other communications would not interfere with the needed Position and Identification information sent out via that method. ADS can in many places surplant the need (though I'm not at all suggesting that it should do so) for primary radar. There are too many things that can end ...

2

Of course. I live right at the beginning of the runway 30ILS intercept area of KOAK. I hear a lot of planes, and you can usually identify an a320 variant (like a321) by its higher pitched noise compared to the 737. The 737 sounds like a hollow whooshing sound(like one you would make with your mouth). The MD-11 and DC-10 sound like the 737 but louder. 777 has ...

2

That noise is almost exclusive to turbo fan engines. If the air is right, turbo shaft engines can do it. On sudden and high power changes the big fan on the front is spinning at a different speed than the motor compressor. Since the front fan is also the first couple of stages of the engine compressor, the air doesn't move cleanly between the two when ...

1

The main objective of the engine is to generate required power $\text{P}$, which is: $$\text{F} \times \frac{D}{T}$$ where $F$ is force, $D$ is distance, and $T$ is time. Power generated by modern jets through continuous combustion of fuel dwarfs their piston predecessors. Next up is efficiency. As in wings, longer, thinner blades do a better job ...

1

From an energy standpoint, the engine produces heat, thrust, and less significantly, sound. Ignore the afterburner for a second and just consider throttling up, whether a jet or your car. The engine gets louder. That's not a law of physics, that's just what happens. There's no theoretical reason why the extra waste energy can't go 101% into heat, and -1% ...

1

Low frequencies are attenuated less over distance and by obstacles. The lower frequencies, even from the music from a dance hall or band, or that car near you playing loud music will be heard first. It may be all you hear! It is also common that as we get older, and especially those in aviation, we become high tone deaf!!

1

I found one study comparing helicopter and airplane noise levels and signatures: Aircraft source noise measurement studies summary of measurements... Unfortunately this study does not provide conclusions or any abbreviated comparison in plain language (or I just failed to notice them). It does, however, provide a near endless array of tables to shuffle ...

1

There are a number of reasons using ADS-B's frequency as a carrier for voice communications isn't a great idea. There are a few issues and factors which I believe you're not taking into consideration which, once understood should illustrate why that is not a workable or desirable solution. First, I'm not going to address this in terms of the UAT system, the ...

1

A fairly obvious point that seems to have been missed in the other answers: how fast can you cycle the winch? A busy airport might have planes departing every couple of minutes. To get to cruise altitude, your winch has to reel in a considerable length of cable. This then has to fall to the ground after the aircraft releases it, which takes a minute or ...

Only top voted, non community-wiki answers of a minimum length are eligible