What Makes GA Planes So Loud?

Turbo(s) help reduce exhaust noise.
 
RJM62 said:
Well... Anything that constricts exhaust flow will carry some performance hit, although I don't know whether it would be significant, or even measurable. Also, we'd also need to beef up the sound-deadening at the firewall, which would add weight. And none of those things would do anything about the prop noise.

If you really want to hear noise, try flying a "pusher" type trike. The fact that the air has already been disturbed by the aircraft before it even gets to the prop (not to mention that on many models, there's nothing between you and the engine / prop to deaden the sound) adds a whole 'nuther section to the orchestra.

-Rich
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I disagree. I fly a Piaggio and it's very quiet inside. I even wear Telex 5x5 pro headsets...the kind that stick in one ear and leave the other exposed. Its quiet inside and everyone talks normally. No shouting.

Putting the engines aft keeps the plane ahead of the noise. The only issue would be the 'distinctive' sound heard by people on the ground as the engine exhaust is ducted straight into the prop. The prop chops up the sound and makes it sound like a flying wood chipper.

Having the entire wing hit undisturbed air is a performance boost. If never thought of it as a source of noise. I don't think it is. The plane isn't any noisier at rotation than it is at brake release.
 
What is the distance between the crew seats and the engines?

Captain said:
I disagree. I fly a Piaggio and it's very quiet inside. I even wear Telex 5x5 pro headsets...the kind that stick in one ear and leave the other exposed. Its quiet inside and everyone talks normally. No shouting.

Putting the engines aft keeps the plane ahead of the noise. The only issue would be the 'distinctive' sound heard by people on the ground as the engine exhaust is ducted straight into the prop. The prop chops up the sound and makes it sound like a flying wood chipper.

Having the entire wing hit undisturbed air is a performance boost. If never thought of it as a source of noise. I don't think it is. The plane isn't any noisier at rotation than it is at brake release.
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Jim Logajan said:
I found the following 124 page NASA document on the CAFE Foundatio website titled:

An Assessment of Propeller Aircraft Noise Reduction Technology

http://cafefoundation.org/v2/pdf_tech/Noise.Technologies/NASA.1995.Metzger.Prop.Noise.pdf

It is long and I haven't read through it, but appears to be a review of existing literature on sources of noise and experiments on reducing noise. It seems to indicate that prop noise is indeed significant ( contrary to my own assertion, which I based on other sources) and things like reducing prop rpm can yield much reduced noise.
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Makes sense and jives with the comments I have heard from those who fly geared engines with lower prop RPMs like Twin Bos.
 
Captain said:
I disagree. I fly a Piaggio and it's very quiet inside. I even wear Telex 5x5 pro headsets...the kind that stick in one ear and leave the other exposed. Its quiet inside and everyone talks normally. No shouting.

Putting the engines aft keeps the plane ahead of the noise. The only issue would be the 'distinctive' sound heard by people on the ground as the engine exhaust is ducted straight into the prop. The prop chops up the sound and makes it sound like a flying wood chipper.

Having the entire wing hit undisturbed air is a performance boost. If never thought of it as a source of noise. I don't think it is. The plane isn't any noisier at rotation than it is at brake release.
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Well... there's a little bit of a difference between a Piaggio and an open-cockpit trike.

It's hard to describe the prop sounds of a pusher trike other than that they change with speed, attitude, wind, etc. It's kind of a cacophony of whining, chopping, whirring, and humming. On the other hand, the engine noise seems a bit more dignified (at least on the Rotax-powered birds, which have mufflers that actually muffle -- a bit).

-Rich
 
Majority is the props. Newer prop designs are quieter because of blade designs. Smaller diameter props are also quieter, but they reduce efficiency. Blade shapes will give you less noise with similar efficiency..

Engine exhaust noise is definitely part of it as well, but secondary to prop noise. You're better off going after the prop first for noise.

The 1930s technology story is a complete load of crap. Take the engine out of a new Honda, remove the exhaust system, and it will be very loud. Modern exhaust systems are complex engineering jobs. One could make an argument about adding exhausts to aircraft engines, and I think it's possible to do it safely.

But first, look at the props.
 
wabower said:
What is the distance between the crew seats and the engines?
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Maybe 25 or 30 feet. Tip to tail the whole plane is 47 feet. But it doesn't matter. The pax sit right next to the engine inlets and the sound level is fine there too. Not any louder IMO. Normal conversation level.

RJM62 said:
Well... there's a little bit of a difference between a Piaggio and an open-cockpit trike.

It's hard to describe the prop sounds of a pusher trike other than that they change with speed, attitude, wind, etc. It's kind of a cacophony of whining, chopping, whirring, and humming. On the other hand, the engine noise seems a bit more dignified (at least on the Rotax-powered birds, which have mufflers that actually muffle -- a bit).

-Rich
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Well isn't my face red. When I read "trike" I thought you were just referring to a general 'tricycle' type gear configuration. I googled what you were speaking of and I can now clearly see your point!
 
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So you're willing to testify that the noise level 3' from the engines is the same as from 20' ahead? Would you be willing to place a wager on that assertion?

What particular design of the Piaggio makes it different from all of the other turbine-powered planes?

Captain said:
Maybe 20 feet or so. But it doesn't matter. The pax sit right next to the engine inlets and the sound level is fine there too. Not any louder IMO. Normal conversation level.



Well isn't my face red. When I read "trike" I thought you were just referring to a general 'tricycle' type gear configuration. I googled what you were speaking of and I can now clearly see your point!
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Captain said:
Well isn't my face red. When I read "trike" I thought you were just referring to a general 'tricycle' type gear configuration. I googled what you were speaking of and I can now clearly see your point!
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Ah, okay. I should have used "WSC" or something like that. "Trike" is a colloquialism for a weight-shift-control aircraft. They're fun little things to fly, but it's not the quietest flying experience you'll ever have.

-Rich
 
wabower said:
So you're willing to testify that the noise level 3' from the engines is the same as from 20' ahead? Would you be willing to place a wager on that assertion?

What particular design of the Piaggio makes it different from all of the other turbine-powered planes?
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Not a thing,

From the outside they sure sound like they are at least as loud as a comparable KA, and the sound made is quite different.

Now as for why the cabin is quiet, methinks that the pressurized cabin and all the "stuff" that comes with it likely has a lot to do with it.
 
wabower said:
So you're willing to testify that the noise level 3' from the engines is the same as from 20' ahead? Would you be willing to place a wager on that assertion?
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That's my experience. I've rode in both the pilots seat and the pax seat and it's the same experience to me. Honestly can't tell a difference in sound. As far as wagers go, yes. I'll will bet that everything I've said has been my experience. 4,000+ hours in a Piaggio is what I'm drawing from.


wabower said:
What particular design of the Piaggio makes it different from all of the other turbine-powered planes?
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Well, I'm not an engineer but, I'd guess it's the fact that all the occupants sit ahead of the engines. The sound has to travel upstream to get all the ear drums...and that stream is going pretty quick too.

As a result, most of the sound that reaches the cabin is from the air going over the fuselage and vibrations coming from the engine / props.
 
denverpilot said:
Just make all of your takeoffs at half power and all approaches as engine-outs if you're worried about it, Jay. ;)
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You could also make an argument for making all your climbs at Vx to get as much altitude as possible before overflying populated areas. My SOP at ISZ was to climb fast to sufficient altitude to turn back to the airport then slightly reduce the prop RPM. My father (lives right under the departure end of what was the primary runway) reported that the drop in noise from the slight RPM drop was very noticeable. He also reported that I have a rather quiet plane flying over, my guess is the 2400rpm redline has a lot to do with that.
 
Ted DuPuis said:
The 1930s technology story is a complete load of crap. Take the engine out of a new Honda, remove the exhaust system, and it will be very loud. Modern exhaust systems are complex engineering jobs. One could make an argument about adding exhausts to aircraft engines, and I think it's possible to do it safely.
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Yup. Some of those 1930s luxury cars were almost silent. Noise has much to do with power levels, and cars just don't need to run at 75 or 100% power.

That said, prop tips exceeding 600 MPH make considerable noise, and many airplanes do that.

Dan
 
Dan Thomas said:
Yup. Some of those 1930s luxury cars were almost silent. Noise has much to do with power levels, and cars just don't need to run at 75 or 100% power.

That said, prop tips exceeding 600 MPH make considerable noise, and many airplanes do that.

Dan
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I'd wager that many of the new engines would be louder if anything, we have learned a lot about making good cams in the last 80 years and having the exhaust port open for a surprising amount of the power stroke isn't uncommon. The engine would be much quieter if the valve stayed firmly shut until the fuel air charge was done burning but that robs power and efficiency.
 
Jay Honeck said:
Recently we rejected an RV-8A after an evaluation flight. One of our main reasons for rejecting an otherwise beautiful aircraft was the fact that it did not have a constant speed prop. After having flown behind one for the last 11 years, I was amazed at how LOUD a plane with a fixed pitch prop was, when you wanted to get any speed out of the aircraft.

Not only were you increasing engine power by advancing the throttle, you were also increasing prop RPMs. This double-whammy increased noise exponentially, both in- and outside the cabin, by increasing engine AND prop noise together.

The only way to reduce noise in that plane was to reduce power/RPMs, which cost ~20 knots in cruise. The choice was "go fast/go deaf", or "go slow/be comfortable". Not acceptable.

Which is why a CS prop is the solution, of course. You can make power AND reduce prop RPMs, as desired.
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I guess I never thought about CS props that way. Since I have about 300 hours behind fixed pitch props and only about 20 behind CS props, I'll have to start paying attention to the noise increase in fixed pitch prop aircraft.
 
Skylane81E said:
You could also make an argument for making all your climbs at Vx to get as much altitude as possible before overflying populated areas. My SOP at ISZ was to climb fast to sufficient altitude to turn back to the airport then slightly reduce the prop RPM. My father (lives right under the departure end of what was the primary runway) reported that the drop in noise from the slight RPM drop was very noticeable. He also reported that I have a rather quiet plane flying over, my guess is the 2400rpm redline has a lot to do with that.
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That is my departure procedure as well. Max climb, until turn back is assured, then pull the prop back to 2300 RPM.

I figure all those folks sunbathing on the beach prolly didn't come to the island to hear a GA plane roaring overhead. Every now on then I will watch as someone departs low down the beach at max power, and cringe. Sure, you and I would think the low pass was cool -- but many would not.
 
One of the things I've been interested in doing to the 310 (dreaming, mostly) is newer style props that would be quieter. Benefits to the passengers (less noise) and the folks on the ground (less noise).
 
Ted DuPuis said:
One of the things I've been interested in doing to the 310 (dreaming, mostly) is newer style props that would be quieter. Benefits to the passengers (less noise) and the folks on the ground (less noise).
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I find that I can just pound away at 2700rpm and the cows have yet to voice a single complaint.
 
JHW said:
I find that I can just pound away at 2700rpm and the cows have yet to voice a single complaint.
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You clearly haven't tried building up enough fuel in the exhaust to cause a backfire. That gets your attention.

Besides, I'm spinning at 2850.
 
Vx climbs for noise abatement? That will work (sort of), but is it really a good idea to sacrifice forward visibility in the pattern? You'll get to higher altitude in less time with a Vy climb. Vx limits downrange, but makes it last longer.

Sorry, safety always trumps noise abatement. Every time. Midairs are much noisier than Vy climbs.
 
N801BH said:
Here is a video I made... 32f, motor was turning 4400 RPM's, prop was 3076 rpm's.. tip speed was mach.92......... well under supersonic.. Motor back then had Moroso race mufflers.. they were HEAVY and ineffective.. Plane now has Stainless Steel straight pipes.. no noisier..:no:

You need good speakers and sound card to really hear the true noise/ music the plane makes...

http://www.youtube.com/watch?v=
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The sweet sound of American Muscle. It would be intresting if the same could he done with a pr of those big mufflers from you grandmother's old 1970's Buick to compare the sound differences. I know there is a big difference in noise between a muffled big block airboat and one with open headers.
 
MAKG1 said:
Vx climbs for noise abatement? That will work (sort of), but is it really a good idea to sacrifice forward visibility in the pattern? You'll get to higher altitude in less time with a Vy climb. Vx limits downrange, but makes it last longer.

Sorry, safety always trumps noise abatement. Every time. Midairs are much noisier than Vy climbs.
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Depends

In my plane I don't spend much time climbing in the traffic pattern.

Also, on a shorter runway where you cannot land on the remaining surface after touchdown VY is probably best to spend the least time without the option of returning to the airport. Give me enough runway and I can be high enough to turn around before I run out of runway ahead, and a VX climb will help there. At VX or even VY I am not going to run anyone over in front of me and someone coming the opposite direction will be closing so rapidly they will be hard to spot regardless. One could argue that getting the hell out of there would be best.

HOWEVER this is a discussion about noise and the reply was to a tounge in cheek post about just taking off at 50% power
 
MAKG1 said:
Vx climbs for noise abatement? That will work (sort of), but is it really a good idea to sacrifice forward visibility in the pattern? You'll get to higher altitude in less time with a Vy climb. Vx limits downrange, but makes it last longer.

Sorry, safety always trumps noise abatement. Every time. Midairs are much noisier than Vy climbs.
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Yeah, I see no reason to do a Vx climb for any reason other han obstacles. My safety is more important.

Now I will do a Vy climb for the first few hundred feet before transitioning to a shallower climb at climb power.
 
Ted DuPuis said:
Yeah, I see no reason to do a Vx climb for any reason other han obstacles. My safety is more important.

Now I will do a Vy climb for the first few hundred feet before transitioning to a shallower climb at climb power.
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Where does your blue line fall WRT Vx/Vy?
 
Vx is a scam. I departed big bear and flew Vx. Summer and high in a C-152 I was getting a descent into a house. As a pre-private I knew enough to nose it over and get speed...towards the house. With speed I pulled up and climbed in a circle to clear the hills.

I'll never fly Vx again.
 
Captain said:
Vx is a scam. I departed big bear and flew Vx. Summer and high in a C-152 I was getting a descent into a house. As a pre-private I knew enough to nose it over and get speed...towards the house. With speed I pulled up and climbed in a circle to clear the hills.

I'll never fly Vx again.
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Seriously man? You're saying Vx is just some scam and you'll never fly it in any airplane based on your one event that could have been caused by a multitude of factors?
 
Captain said:
Vx is a scam. I departed big bear and flew Vx. Summer and high in a C-152 I was getting a descent into a house. As a pre-private I knew enough to nose it over and get speed...towards the house. With speed I pulled up and climbed in a circle to clear the hills.

I'll never fly Vx again.
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As a pre-private, maybe you were flying a bit slower than Vx:dunno: .As a student, I forgot to retract the flaps once during a touch & go:yikes:
 
Captain said:
Vx is a scam. I departed big bear and flew Vx. Summer and high in a C-152 I was getting a descent into a house. As a pre-private I knew enough to nose it over and get speed...towards the house. With speed I pulled up and climbed in a circle to clear the hills.

I'll never fly Vx again.
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And you wonder why folks didn't follow you in droves to your new site
 
jesse said:
Seriously man? You're saying Vx is just some scam and you'll never fly it in any airplane based on your one event that could have been caused by a multitude of factors?
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Not the least of which is that Big Bear is HIGH ALTITUDE and Vx there is higher than Vx at sea level.
 
Well, I did say I was Pre-Private.

I am very weary of the speed though (Vx). I'll take Vy any day. BTW, I had Vx nailed that day...and i was DESCENDING. I was going to be a small news story and a fiery end to a nice lake house if I didn't do what I did...speed up and miss my appointment with death.

Ya'll tell me. Whats you're VSI say at Vx an whats it say at Vy?
 
Captain said:
Well, I did say I was Pre-Private.

I am very weary of the speed though (Vx). I'll take Vy any day. BTW, I had Vx nailed that day...and i was DESCENDING. I was going to be a small news story and a fiery end to a nice lake house if I didn't do what I did...speed up and miss my appointment with death.

Ya'll tell me. Whats you're VSI say at Vx an whats it say at Vy?
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Is it possible you were flying through descending air and your application of higher lateral speed simply flew you out of that downdraft? (Edit: I assume this is what you mean when you asked about VSI.)

The vertical speed component of Vx is lower than Vy, so Vx is more likely to cause problems where air is descending.
 
Jim Logajan said:
Is it possible you were flying through descending air and your application of higher lateral speed simply flew you out of that downdraft? (Edit: I assume this is what you mean when you asked about VSI.)

The vertical speed component of Vx is lower than Vy, so Vx is more likely to cause problems where air is descending.
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Maybe. Like I said I was pre-Private and Vx was going to kill me. Learned my lesson there....speed is your friend and screw Vx.
 
Vx does increase, and Vy does decrease, with altitude. However Vy decreases a lot faster than Vx increases. POH for the 152 claims Vx is 55 KIAS from 0-10,000 feet, and Vy varies from 67 KIAS at sea level to 61 KIAS at 10,000 feet.

Señor Frog, did you take any action to lean for best power prior to departing Big Bear on a hot summer day?
 
They are loud because they are powered with the tears of 'tree-hugging-whiners.'
 
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