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Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

Well, it does look pretty, doesn't it? Boeing wanted to reduce the noise generated because of jet blast of the engines. Many airports around the world are implementing new noise regulations. As ...
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51 votes

Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

I think both answers are correct, but I would like to spend some time describing the phenomena that chevrons try to reduce so that I can complement the answers already provided. So, what is happening ...
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51 votes

Are seaplanes allowed to taxi in residential areas?

A sea plane was just going around it. It was very loud and got like 10 feet from the shore. It's just going in circles and won't take off and leave. As has been pointed out in other answers and ...
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46 votes

Can I stop crop dusters repeatedly flying over my home?

In a rural area pilots can fly pretty low, and are permitted to fly even lower while carrying out a lawful activity such as crop-dusting. Even if the pilot flew at 500 feet above your house, which is ...
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43 votes
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Are seaplanes allowed to taxi in residential areas?

If you have concerns over the safety of what is going on, here is what you should do: Record a video with your phone. Try to get the N number (it should be painted in large letters on the side of the ...
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43 votes
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What is the loud noise of a helicopter when the rotors are not yet moving?

The sound you're hearing is the APU (Auxiliary Power Unit) running. Turbine (jet) engines turn at a much higher RPM than reciprocating engines. This means that an electric starter motor would have to ...
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43 votes

Will you be able to hear a supersonic aircraft flying away from you?

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 ...
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41 votes

Can I stop crop dusters repeatedly flying over my home?

I did some Pawnee flying years ago, and have fielded a bunch of complaints about ag applicators from people. Here's my experience: The FSDO will probably not care. Ag application is a different ...
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37 votes
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Why would a turboprop rev down just before going full throttle during takeoff?

Because the pilot is taxiing the airplane with the props in the beta range (turboprops turn into landsharks if you don’t do this and you end up really riding the brakes to keep the speed down), then ...
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37 votes

What could explain the fact that during 1976-80, I used to hear commercial jets make sonic booms while flying overhead?

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) ...
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36 votes
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Why don't airliners use noise cancelling?

First, some airliners do use it - the Bombardier Q400 uses a NVS (Noise and Vibration Suppression) system to reduce cabin noise. Basically, it uses devices called Active Tuned Vibration Absorbers (...
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35 votes
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Why was there a rattling noise coming from the left engine of A319?

Yes indeed, the fan blades are loose and rattle in their sockets when the fan is freewheeling in the wind. Once the engine is running, centrifugal forces will make sure they do not rattle any longer. ...
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32 votes

Are there any reported cases of noise from helicopters causing damage to property?

The article states that it's not even clear the damage was caused by the helicopters, that there is no other known incidence of such damage being caused by helicopters, and that a scientific study has ...
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32 votes

Why would a turboprop rev down just before going full throttle during takeoff?

It's because he was taxiing in DISC (discing, or flat pitch making the prop like a big disc), which is in the ground beta range, then coming out of it. Beta range is a mode where propeller blade ...
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29 votes

Is an afterburner louder than the same jet engine without it?

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
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27 votes

Why are winches not used for towing commercial planes up?

If you ever get the chance, do try a winch start in a glider. It is, to say the least, an interesting experience. I do not believe it would be accepted by the general public. So, that is one more ...
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27 votes

Why don't modern jet engines use forced exhaust mixing?

Why don't modern jet engines use forced exhaust mixing? Because there isn't as much gain to be achieved from the jet exhaust any more, and because forced mixing impacts performance. Gains. From The ...
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26 votes

Why are winches not used for towing commercial planes up?

I won't prove it's not possible, but I'd would be surprised it is. I'll develop the reasons why and provide the physical framework you can use to compute a solution to have, with some effort, a final ...
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25 votes
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Do helicopter rotor tips regularly go supersonic?

The "wop wop", usually known as blade slap, is heard when the tip of the blade passes through the vortex created by the previous one. It can be avoided. The most common flight regime when this ...
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25 votes
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Why is a Lockheed MC-130J Commando II creating such a loud droning sound?

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 $r$: $...
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24 votes

Is an afterburner louder than the same jet engine without it?

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 ...
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23 votes

Does a Mach 1 plane hear a sonic boom from a Mach 3 plane overtaking him?

To answer the question: Yes, and even more, both would be able to notice the sonic boom of the other aircraft. Why To understand why, you have to understand how sonic booms are created. Sound is ...
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23 votes
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Why do flying wires hum louder in a sideslip?

Here is one reason. It once was common for suspension wires to be flattened rather than circular in cross-section, to reduce drag. those wires were then aligned with the airflow past the wing and ...
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22 votes

Why does the Boeing 787 engine nacelle exhaust have such an unusual shape?

Actually, there were similar tricks used on Boeing aircraft before to reduce jet noise. The Rolls-Royce Conway (as used on the Boeing 707) had a scalloped exhaust which improved jet mixing and ...
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22 votes

Won't sonic booms prevent Space X's BFR intercity transport plan from being acceptable?

The only way to get anything that far that quickly is to send it into space, and that's exactly what Musk is suggesting. The BFR will launch a passenger carrying spacecraft out of the atmosphere and ...
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22 votes
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Does any of the hearing protection worn by aviation professionals use active noise reduction?

If you're talking about crew/pilot headsets then ANR is a very popular option - especially in General Aviation. The Bose A20 is probably the most popular headset, but both Lightspeed and David Clark ...
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21 votes

What causes descending aircraft to make a noise like a giant blown bottle?

Short Answer: The sound is caused by airflow across holes on the underside of the wings of certain aircraft. Long Answer: I too have noted the sound phenomenon that you describe. This video has a ...
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  • 16.1k
21 votes

What is the loud noise of a helicopter when the rotors are not yet moving?

You may be expecting the rotor to spin up in lock-sync with the engine. That's not quite what happens on a turbine helicopter. Turbine helicopter engines (turboshaft engines) have a turbojet ...
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19 votes
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Do nacelles around aircraft engines help in reducing the engine sound?

Take a modern turbofan: The tips of the fan run at approximately Mach 1.5. We know from unducted props that supersonic tips make them very noisy. The same turbofan without the shroud would be ...
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