# Speed of airplane engine

1. Jun 3, 2010

### glennpagano

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?

2. Jun 3, 2010

### glennpagano

Bump......anyone?

3. Jun 4, 2010

### jmatejka

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.

4. Jun 4, 2010

### xxChrisxx

You can tell the speed of an engine from the sound. Don't know exactly how, but it's terribly complicated.

5. Jun 4, 2010

### Phrak

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...

6. Jun 4, 2010

### glennpagano

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.

7. Jun 4, 2010

### mender

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 occurance 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.

8. Jun 5, 2010

### Lsos

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!

9. Jun 6, 2010

### glennpagano

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. Jun 7, 2010

### mender

"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.