Can I Calculate Engine Speed from Sound Frequency Inside an Airplane?

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    Airplane Engine Speed
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Discussion Overview

The discussion centers around the possibility of calculating aircraft engine speed from the sound frequency detected inside an airplane. Participants explore various aspects of sound analysis, engine types, and the relationship between sound frequency and engine RPM, with a focus on turbine engines.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires whether engine speed can be determined from sound frequency using an audio analysis program.
  • Another participant questions the type of engine (turbine or piston) and suggests that the sound characteristics may vary based on the engine type and manufacturer.
  • Some participants propose that higher pitch sounds may correlate with higher RPMs, particularly for turbine engines.
  • A participant mentions observing two frequency peaks (245.185 Hz and 632.347 Hz) and considers how these might relate to turbine speed.
  • One participant explains that the frequency peaks could correspond to pulses per minute, but emphasizes the need for knowledge about the actual engine RPM to make accurate calculations.
  • Another participant shares an anecdote about a tachometer used in a power plant that measured turbine speed based on vibrations, suggesting that similar principles might apply to aircraft engines.
  • There is a discussion about the potential for constructive interference of sound waves from various engine components affecting the observed frequencies.
  • One participant expresses interest in the method of calculating pulses per minute from frequency and notes the complexity of the relationship between sound and engine speed.

Areas of Agreement / Disagreement

Participants express varying opinions on the feasibility of calculating engine speed from sound frequency, with no consensus reached on the method or accuracy of such calculations. Multiple competing views and uncertainties remain regarding the specifics of sound analysis and engine characteristics.

Contextual Notes

Participants acknowledge limitations related to the specific engine type, the need for additional information about the engine's RPM, and the complexities of sound wave interactions within the engine.

glennpagano
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I am in the airport right now and I was wondering if there is someway to determine the speed of the aircraft engine from the sound the engine makes inside the plane. I have a audio analysis program and I can determine the frequency of the sound inside the airplane. Is there any way to determine the speed of the engine this way?
 
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What engine? Turbine or Piston? Assuming Turbine, Which Turbine Manufacturer? Which Model?

What are you "hearing"? Turbine Compressor whine? Turboprop prop wash noise?

Assuming higher pitch with higher RPM?

I'm a Private Pilot, "FAA/Military" Simulators being my only "turbine time". If I recall correctly, most turbine instrumentation reflects percentage of max rpm, not typically "actual values".

I believe the answer to your question is "yes", IF, you knew more about the specific powerplant and it's specific aircraft application.
 
You can tell the speed of an engine from the sound. Don't know exactly how, but it's terribly complicated.
 
I would say the highest frequency is the frequence obtained but the frequence of a rotor blade passing a stator. Now, if you knew how many of each...
 
I am pretty sure I would be hearing the turbine whine. When I looked at the analysis I noticed that there were 2 frequency peaks. One was 245.185 Hz and the other was 632.347 Hz. Now I am just going to try and think about how I can somehow apply these numbers to the turbine speed.
 
Your peaks correspond to 14,711 and 37,940 pulses per minute, so may represent an rpm. Without knowing the actual engine rpm, it would be hard to say though. Either or both peaks could be the result of constructive interference of the pulses generated by several parts of the engine (compressor blades, turbine blades, combustion fluctuations, etc.) leading to the occurrence of "beats" that may or may not be indicative of the engine speed. Once the ratio between the pulses and the actual engine rpm is known, it could be used to measure the rpm.
 
I worked at a power plant, and this guy had a tachometer that figured out how fast the steam turbine was spinning just based on its vibrations. It was some small magnetic thing that he placed on the turbine and BAM! there was the reading. It looked old school, too. I don't even think it was digital (although can't remember for sure). Man I was blown away by that thing!
 
mender said:
Your peaks correspond to 14,711 and 37,940 pulses per minute, so may represent an rpm. Without knowing the actual engine rpm, it would be hard to say though. Either or both peaks could be the result of constructive interference of the pulses generated by several parts of the engine (compressor blades, turbine blades, combustion fluctuations, etc.) leading to the occurrence of "beats" that may or may not be indicative of the engine speed. Once the ratio between the pulses and the actual engine rpm is known, it could be used to measure the rpm.

How did you determine the pulses per minute? I think this would be really neat if using the frequency of something to determine the speed of it. It can be used in many places. These numbers also take into account the frequencies of both engines because they were not running at the same speed. I know these because I heard a "beat" interference between the two.
 
  • #10
glennpagano said:
How did you determine the pulses per minute? I think this would be really neat if using the frequency of something to determine the speed of it.

"One was 245.185 Hz and the other was 632.347 Hz."
"The hertz is equivalent to cycles per second."

To find the number of pulses per minute, multiply the frequency as measured in hertz by 60.
 

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