Prop noise vs. engine noise

A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me. Anyone
know of a website that compares prop noise and engine noise, especially when
it comes to high performance and constant speed props?

By the way I have googled til I can't read anymore!
--
Jim in NC

"Morgans" wrote in message
...
[...] Anyone
know of a website that compares prop noise and engine noise, especially
when
it comes to high performance and constant speed props?

I'm not aware of any references off the top of my head.

What I can tell you is that it's not true that the prop is *always* the
largest noise maker. It depends on prop RPM, exhaust design, and engine
power. In cruise flight, often the engine is the noisier of the two, and
something as simple as redirecting the exhaust upwards rather than down as
it usually is can significantly reduce the noise footprint on the ground.

Conversely, during takeoff and climb, the prop is often the noisier, due to
the higher RPM. The engine is louder at high power too, of course, but the
prop tips being so close to supersonic (or even exceeding it in some cases)
far surpass the noise the engine is making.

It just depends. And of course, an airplane being flown in aerobatic
maneuvers is alternately making more noise with the prop AND the engine,
depending on power and RPM setting throughout the maneuvers.

Pete

"Morgans" wrote in message
...
A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started
into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me. Anyone
know of a website that compares prop noise and engine noise, especially
when
it comes to high performance and constant speed props?

By the way I have googled til I can't read anymore!
--
Jim in NC

From a layman's perspective, noise is noise.

In article et, "Earl
Greida" wrote:

From a layman's perspective, noise is noise.

correction: unwanted sound is noise.

--
Bob Noel

"Bob Noel" wrote in message ...
In article et, "Earl
Greida" wrote:

From a layman's perspective, noise is noise.

correction: unwanted sound is noise.

Actually, there are at least three definitions:

1. Unwanted or otherwise disagreeable sound.
2. Sound in general.
3. Portions of sound that interfere with communications.

"Morgans" wrote in message
...
[...] Anyone
know of a website that compares prop noise and engine noise, especially when
it comes to high performance and constant speed props?

I'm not aware of any references off the top of my head.

What I can tell you is that it's not true that the prop is *always*
the
largest noise maker. It depends on prop RPM, exhaust design, and
engine
power. In cruise flight, often the engine is the noisier of the two,
and
something as simple as redirecting the exhaust upwards rather than
down as
it usually is can significantly reduce the noise footprint on the
ground.

Conversely, during takeoff and climb, the prop is often the noisier,
due to
the higher RPM. The engine is louder at high power too, of course,
but the
prop tips being so close to supersonic (or even exceeding it in some
cases)
far surpass the noise the engine is making.

It just depends. And of course, an airplane being flown in aerobatic
maneuvers is alternately making more noise with the prop AND the
engine,
depending on power and RPM setting throughout the maneuvers.

Pete

Page 81 of Aircraft Systems for Pilots, by Dale de Remer and
published by Jeppesen, has this to say about prop noise:

"...Propellers make a lot of noise - much more noise than does
engine exhaust. Propeller blade noise is transmitted directionally.
Noise is much greater off the tips of the propeller. Visualize
extending the propeller disk to the ground. That's where the noise
will be greatest."

Dan

A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me.

Better than any reading, take him where he can hear an SNJ (what the
Air Force mistakenly called a T-6) take off in "flat pitch" and then
reduce power. The noise will abate slightly when the trottle comes
back, but much more when the prop rpm is reduced.

vince norris

"Morgans" wrote in message
...
A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started
into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me. Anyone
know of a website that compares prop noise and engine noise, especially
when
it comes to high performance and constant speed props?

By the way I have googled til I can't read anymore!
--
Jim in NC

A P3 engine is a lot quieter to run with the prop removed.

Scet

The guy has probably forgotten by now, but...

"Morgans" wrote in message
...
A colleague and I were discussing a plane that has been practicing
aerobatics near his house, and all the noise it was making. I started
into
telling him how the prop was making most of the noise, and he seemed to
think I was crazy for thinking that.

I think I will have to show him something written, to believe me. Anyone
know of a website that compares prop noise and engine noise, especially
when
it comes to high performance and constant speed props?

I took part in a noise study some time back. A church located about a block
off (and in line with) the SW end of 06/24 was going to expand and they
planned on including enough soundrproofing to keep the sunday morning
services hearable by those attending.

The study was done off the other end of the runway as there is a shopping
center parking lot and an auto dealership just to the south of the climbout
path. Most of the high performance planes are just reaching pattern
altitude at that point.

A 210 created the highest noise level at 90 db with me a bit behind him. On
one take off I didn't get the prop RPM back quite as soon as I did on the
other take offs. The Deb was measured at 93 db, or twice as loud as the
210. The only difference was the RPM. Coming back on the MP made no
difference.

The main difference was at the higher RPM the two blade prop tips were
supersonic.


--
Roger Halstead (K8RI, EN73 & ARRL Life Member)
N833R, World's Oldest Debonair? (S# CD-2)
www.rogerhalstead.com


By the way I have googled til I can't read anymore!
--
Jim in NC