Engine noise forward of engines at mach 1+?

RDoug said:
Nope. Instead of making the baseball analogy, use another wave propagation comparison — light. Even if you're traveling at .99% of the speed of light and then turn on a flashlight in the direction of travel, light still travels at the universal constant. It does not leave the flashlight at C+.99C.
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Or think of the Doppler effect...
Sound emitted from a moving vehicle changes pitch as it passes an observer because the waves are stacking up on each other. If the baseball example were correct, this wouldn't happen. The sound waves would just be traveling faster relative to the observer, and the frequency (distance between each wave) would not change.

Unlike a baseball, air particles have other air particles to run into. They are not displaced very far. Instead, the energy is transmitted from one particle to the next like a Newton's cradle or a set of billiard balls. The speed is limited by how fast the energy can be transmitted and not by the speed of the initial particle.
 
Proud Pilot said:
What if you were cruising at say, .80 Mach up at altitude and you had a 150+ kt. tailwind which put your groundspeed supersonic. Would the people on the ground hear a sonic boom?
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Supersonic groundspeed? That's nonsense.

Mach number is based on true airspeed, not groundspeed. It's the ratio of true airspeed to the speed of sound under the current ambient conditions (air density, temperature, etc). The speed of sound is actually faster at higher air temperatures.
 
Apophis said:
Supersonic groundspeed? That's nonsense.

Mach number is based on true airspeed, not groundspeed. It's the ratio of true airspeed to the speed of sound under the current ambient conditions (air density, temperature, etc). The speed of sound is actually faster at higher air temperatures.
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knot4u said:
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You're kidding me. You really must be struggling to grasp this concept.

The supersonic rocket car breaks the sound barrier because of its speed through the air, NOT THE GROUND.

Let's assume for a minute, that this car performed two separate tests, on two completely different days. One extremely cold, and one extremely hot.

On the really cold day, the car's speed over the ground when it reaches Mach 1 would be less than on the really hot day. This is because the speed of sound through air varies with things like density, pressure, temperature, etc.

This really isn't difficult to understand.
 
Clint H said:
Or think of the Doppler effect...
Sound emitted from a moving vehicle changes pitch as it passes an observer because the waves are stacking up on each other. If the baseball example were correct, this wouldn't happen. The sound waves would just be traveling faster relative to the observer, and the frequency (distance between each wave) would not change.

Unlike a baseball, air particles have other air particles to run into. They are not displaced very far. Instead, the energy is transmitted from one particle to the next like a Newton's cradle or a set of billiard balls. The speed is limited by how fast the energy can be transmitted and not by the speed of the initial particle.
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In high school my teacher demonstrated the Doppler effect by getting in his car, driving to the other side of the parkign lot then driving towards us with his horn blaring as he drove towards, then past us. So, if he was able to drive mach 1, and the horn was placed say on the trunk, not in the engine bay, would he not hear it, if it was placed on a poll so the sound couldnt be transmitted through the cars frame?

So I get that some of the engine noise would be passed through the plane itself, but in theory, sitting in front of the engines should result in some noise reduction as you travel faster?
 
Matt13C said:
So, if he was able to drive mach 1, and the horn was placed say on the trunk, not in the engine bay, would he not hear it, if it was placed on a poll so the sound couldnt be transmitted through the cars frame?
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That would be correct. The sound would never reach him.
 
Let's put it this way:

You're a speedboat traveling at 30 MPH. You're sitting in a seat in the back of the boat. You want to go talk to your friend who is sitting 20 feet ahead of you in the bow of the boat. You can swim at 3 MPH. You jump out of the boat (again, boat is traveling at 30 MPH) with the intention of swimming up to your friend. Are you going to reach him?
 
Nark said:
You'd still have to update your TAS with ATC!

That rule seems antiquated now with fancy algorithms that spit out flow control to ARTCC facilities, at least down here. Not sure if NavCanada uses a similar system.
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Flight data and arrival info is updated every 5 seconds with each sweep, however if the flight plan info is wrong, as in the TAS is way off it does mess up estimate passing within the system.

Often flights will get TAS info passed incorrectly if the issuing system grabs the flight info on departure when the flight profile is in climb (747 at 405 knots at FL350)
 
Proud Pilot said:
Learn something new everyday. My professor told me it would.
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Think of what causes the sonic boom.

Sound waves interacting with the air.

It doesn't matter what speed the whole air system it is in, is drifting, or which way it's drifting.
 
Apophis said:
You're kidding me. You really must be struggling to grasp this concept.

The supersonic rocket car breaks the sound barrier because of its speed through the air, NOT THE GROUND.

Let's assume for a minute, that this car performed two separate tests, on two completely different days. One extremely cold, and one extremely hot.

On the really cold day, the car's speed over the ground when it reaches Mach 1 would be less than on the really hot day. This is because the speed of sound through air varies with things like density, pressure, temperature, etc.

This really isn't difficult to understand.
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I understand the concept. I thought it a humorous retort to your previous post. No reason to be a condescending •.
 
Ah, cool. Sarcasm and subtle humor stump me sometimes.....okay, actually a LOT of the time. :)
 
If the speed of sound is independent of wind speed, how come sometimes I can hear people yelling far away when I am downwind of them and not hear them as well when I am upwind?
 
So if I hang my butt out the window while going just under the speed of sound and rip off a good fart, it will be a sonic boom.
 
Proud Pilot said:
If the speed of sound is independent of wind speed, how come sometimes I can hear people yelling far away when I am downwind of them and not hear them as well when I am upwind?
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The wind carries the sound waves but it doesn't change the speed at which sound travels for the given conditions.
 
How come of the B-58 Hustler supersonic bomber, it's 20mm tail gun when fired with the jet cruising supersonic, the bullets would just dribble out the barrel? How come the bullets were not going supersonic as they should be?
 
Proud Pilot said:
If the speed of sound is independent of wind speed, how come sometimes I can hear people yelling far away when I am downwind of them and not hear them as well when I am upwind?
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The speed of sound is relative to the medium through which it is propagating. If the air is moving in relation to someone at a stationary point, the speed of sound will appear to be faster going downwind and appear slower going upwind. But, if you're travelling at the same velocity as the wind, the speed of sound is in fact constant to you regardless of the direction in which the sound is propagating.
 
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