What Makes GA Planes So Loud?

Jay Honeck

Jay Honeck

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Jay Honeck
GA planes are incredibly loud. Is what we are hearing primarily engine noise? Or prop noise?

I'm guessing it's engine noise. Given that, is there some reason no one has marketed a plane with real mufflers placed behind the crew cabin, like an automobile?

True, this would add weight, on the order of 20 pounds (estimated), and (unless designed for it from the get go) would be ugly as sin -- but wouldn't it be nice to have an airplane as quiet as my Lexus on the freeway?

Flexibility also presents a challenge. I remember the first time I saw my engine decowled and running, and the astonishment I felt upon seeing how much the engine moved at shutdown.

Still, flexible heat pipe exists. This is not insurmountable.

I seem to remember seeing antique aircraft with long exhaust pipes, similar to what I'm describing, so apparently this has been tried. It just seems so...logical...

Another thought: Eliminate Hell's Hammers, and we might have a better chance of attracting new generations to GA. I suspect gals who have grown up in Beemers think even "modern" GA sound like Indy cars, and don't want any part of them.
 
Jim Logajan said:
Engine noise.
Click to expand...

Prop noise is the loudest. Our local C-180 is deafening when he takes off and that same engine in many planes, including a couple twins, is comparably silent. :dunno:
 
That's why ANR headsets are so popular. You should try one.

Jay Honeck said:
GA planes are incredibly loud. Is what we are hearing primarily engine noise? Or prop noise?

I'm guessing it's engine noise. Given that, is there some reason no one has marketed a plane with real mufflers placed behind the crew cabin, like an automobile?

True, this would add weight, on the order of 20 pounds (estimated), and (unless designed for it from the get go) would be ugly as sin -- but wouldn't it be nice to have an airplane as quiet as my Lexus on the freeway?

Flexibility also presents a challenge. I remember the first time I saw my engine decowled and running, and the astonishment I felt upon seeing how much the engine moved at shutdown.

Still, flexible heat pipe exists. This is not insurmountable.

I seem to remember seeing antique aircraft with long exhaust pipes, similar to what I'm describing, so apparently this has been tried. It just seems so...logical...

Another thought: Eliminate Hell's Hammers, and we might have a better chance of attracting new generations to GA. I suspect gals who have grown up in Beemers think even "modern" GA sound like Indy cars, and don't want any part of them.
Click to expand...
 
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
 
Safety has a lot to do with it too, I chase exhaust failures more often on the rather small number of cars I maintain than I do on the much larger number of planes I look after.

However if you want to know how much of the sound is the prop listen to a Robinson start up, not terribly loud at all
 
Jay Honeck said:
GA planes are incredibly loud. Is what we are hearing primarily engine noise? Or prop noise?

I'm guessing it's engine noise. Given that, is there some reason no one has marketed a plane with real mufflers placed behind the crew cabin, like an automobile?

True, this would add weight, on the order of 20 pounds (estimated), and (unless designed for it from the get go) would be ugly as sin -- but wouldn't it be nice to have an airplane as quiet as my Lexus on the freeway?

Flexibility also presents a challenge. I remember the first time I saw my engine decowled and running, and the astonishment I felt upon seeing how much the engine moved at shutdown.

Still, flexible heat pipe exists. This is not insurmountable.

I seem to remember seeing antique aircraft with long exhaust pipes, similar to what I'm describing, so apparently this has been tried. It just seems so...logical...

Another thought: Eliminate Hell's Hammers, and we might have a better chance of attracting new generations to GA. I suspect gals who have grown up in Beemers think even "modern" GA sound like Indy cars, and don't want any part of them.
Click to expand...

Airplane noise is a combination of engine and prop. Many airplanes have mufflers and some are even pretty effective but they do add weight and cost so they weren't very popular in anything designed more than 20 years ago (i.e. most of the fleet). Today you'll see significantly effective mufflers and reduced prop RPM on some airplanes, especially ones sold in Europe which as some pretty stringent noise limitations.

But you're not likely to be able to find an airplane that's as quiet (externally or internally) as a modern car for several reasons. First there's the already mentioned weight issue. Adding 25 lbs of exhaust components decreases the utility of the airplane and more often than not requires mores space than available so the drag profile gets bigger and the plane gets slower (and heavier yet for the extra structures). Similarly soundproofing the cabin adds considerable weight and either decreases interior space or increases exterior dimensions (more drag).

More importantly, cars typically run around 10-20 HP in cruise vs 100-400 for piston powered airplanes and I suspect that all else being equal, sound output is at least proportional to HP. Finally, few cars use propellers to whip the air into thrust and that's rather difficult to accomplish without making a lot of 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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Sound-deadening has a lot to do with it too, I have been told that the dodge "track pack" challengers are a few HUNDRED pounds lighter due to the absence of any sound-deadening material, and having gutted my chap little Saturn I can believe it.
 
I wouldn't call a commercial passenger jet particularly quiet either.
 
They're loud because they're running on glorified 1930s crap technology. Most of the cars on the roads today were designed in the 21st century if not the latter sliver of the 20th. :D

I would love to chuck the Lycoming IO360 in the garbage dump where it belongs and replace it with a UL Power 520iS and have the same power, less weight, and lower specific fuel consumption.
 
Goofy said:
Prop noise is the loudest. Our local C-180 is deafening when he takes off and that same engine in many planes, including a couple twins, is comparably silent. :dunno:
Click to expand...

While that is an interesting observation, consider that airplanes with electric engines of comparable power are quieter than their IC engine equivalents. In all the small single engine planes that Jay and many others fly, I believe engine noise dominates. While props cause noise too, and a poorly chosen prop can cause a lot of noise, noise from the engine appears to dominate.
 
Goofy said:
Prop noise is the loudest. Our local C-180 is deafening when he takes off and that same engine in many planes, including a couple twins, is comparably silent. :dunno:
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Supersonic prop tips. We always pull our O-540 back to 2300 RPM shortly after departure, to lessen the effect.

I'm not overly concerned about noise outside the cabin. Compared to the idiots riding straight-pipe Harleys, or driving the hopped-up turbo-diesel pickup trucks that young Texans love, a GA plane flying overhead is insignificant.
 
Geico266 said:
All aircraft should be required to have mufflers, IMHO. This is a main reason people hate GA.
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If practical noise reduction would remove non-pilot's objections to those "rich boy toys" it might be worth it. But having been through a few fights with emotional based objections to non-typical activities I seriously doubt that if we made every piston powered airplane half as noisy overnight there's be even a measurable change in complaints or hatred.
 
gismo said:
Airplane noise is a combination of engine and prop. Many airplanes have mufflers and some are even pretty effective but they do add weight and cost so they weren't very popular in anything designed more than 20 years ago (i.e. most of the fleet).
Click to expand...

My Lycoming O-540 has a muffler, but it's a joke. Not only does it do little to attenuate noise, it's so lightly (AKA: "poorly") built that it requires replacement every 350 hours or so.

I would GLADLY sacrifice ten pounds of useful load in exchange for a heavier, more effective muffler -- if for no other reason than added durability. Sound deadening would be nice, too. lol
 
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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Jim Logajan said:
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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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.
 
The prop is the predominant source of external noise. Listen to a plane fly over, and the change in amount of noise when you are on the plane of the prop vs when you are off the plane of the prop.

Also, don't discount the amount of wind noise over the aircraft body when moving at well over 100 mph. For a comparison, if you've ever been in a car at over 120-140mph, the combination of engine and wind noise is impressive.
 
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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Remember my comments at the mustang island fly-in about how it's hard to go back to a fixed pitch prop? Glad you saw the light :)
 
Fuselage sound proofing is also very poor in these spam cans. Cabin sealing is nowhere near that of modern cars. But I suspect that would also add weight to fix properly. It would certainly be a more comfortable ride for the passengers if we didn't need headsets. It's the one thing I detest about GA flying with my family. We make it happen, but it's not ideal. My earlobes are in pretty good physical pain after 3 hours of headsets and the funky arrangement of my shades at the top of the earcup in order to not disturb the passive seal is just beyond retarded.

I concur on the CS prop differences. After flogging the hell out of the Warrior at 2700 in order to eek out as much cruise speed as possible, flying behind a CS prop in bigger airplanes at 22-2300 making cruise power is significantly quieter. Definitively less fatiguing.

But I'll take noise and clunky headgear to get there 2-6 hours earlier. Driving is a hell of a lot more fatiguing than flying with noise :D
 
PilotAlan said:
The prop is the predominant source of external noise. Listen to a plane fly over, and the change in amount of noise when you are on the plane of the prop vs when you are off the plane of the prop.

Also, don't discount the amount of wind noise over the aircraft body when moving at well over 100 mph. For a comparison, if you've ever been in a car at over 120-140mph, the combination of engine and wind noise is impressive.
Click to expand...

Indeed, my big soft, muffled, sound insulated passenger car is far from quiet at 130
(Closed course trained, amature driver)
 
Geico266 said:
Europe has noise restrictions on light aircraft. One of the main reasons Rotax 912 has a efficient muffler.

All aircraft should be required to have mufflers, IMHO. This is a main reason people hate GA.
Click to expand...

I beg to differ; I believe few people hate GA, because few people know any thing at all about GA; those who hate GA because of the noise are restricted to the few who live adjacent to airports and wish them to be gone. In all likelihood, these are the same people who hate motorcycles and hate stereos and hate barking dogs and just hate anything that is not their idea.

We have a neighbor who keeps chickens, which (if you listen very closely) you might hear from time to time. Another neighbor hates chickens.

---

I note that, when the Rotax-powered Piper Sport / Sport Cruisers take off, they are vastly quieter than most other aircraft; more of a "whirring" noise than anything else. Higher-revs on the engine, lower revs on the prop.
 
gismo said:
If practical noise reduction would remove non-pilot's objections to those "rich boy toys" it might be worth it. But having been through a few fights with emotional based objections to non-typical activities I seriously doubt that if we made every piston powered airplane half as noisy overnight there's be even a measurable change in complaints or hatred.
Click to expand...

My experience is otherwise. Several attempts on building a flyin community in this area have met with objections about noise. The opposition hired a consultant to monitor the engine noise at the local airports. This data was the main reason the county board would not allow it.

The county board then passed a noise ordinance to prevent motor cross tracks on private property. One of the major problems with that law is a farmer is now breaking the law at harvest time. :yes: :lol:

Needless to say the sheriff is not gonna write tickets for harvest noise in NE. :lol:
 
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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There are some automotive exhaust failure modes you should be aware of before saying airplanes should work the same way. Exhaust is corrosive; it's essentially carbonic acid once condensed. That can make exhaust leaks (maybe loud, possible CO source if it's in the wrong spot), or it can disintegrate the muffler internally, plugging it. It can also get plugged by excessively rich mixtures. When this happens, the muffler looks fine on the outside, but the owner complains the car won't get out of it's own way. You can diagnose it easily with a vacuum or MP gauge, but bad things could happen at takeoff or go-around were you to try it in an airplane.
 
Jay Honeck said:
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.
Click to expand...

Jay, don't you have ANR headsets? If not, why not? If so, I'm wondering if yours are all that effective at reducing noise.

Another option is using foam ear plugs plus a good ANR headset.
 
MSPAviator said:
They're loud because they're running on glorified 1930s crap technology. Most of the cars on the roads today were designed in the 21st century if not the latter sliver of the 20th. :D

I would love to chuck the Lycoming IO360 in the garbage dump where it belongs and replace it with a UL Power 520iS and have the same power, less weight, and lower specific fuel consumption.
Click to expand...

:yes::yes:

My thoughts exactly! Am praying I've saved enough to make that same switch when my O-320 finally croaks. What a sweet engine they make. Would love one third more HP with less weight and modern fuel and ignition systems. :yes:
 
Bob Noel said:
Jay, don't you have ANR headsets? If not, why not? If so, I'm wondering if yours are all that effective at reducing noise.

Another option is using foam ear plugs plus a good ANR headset.
Click to expand...

Four sets of Zulus.

Why do you ask?
 
Because they're open exhaust engines running at high power settings.
 
Bob Noel said:
Why? it was right there in the post "If so, I'm wondering if yours are all that effective at reducing noise."
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Sure! I can hear a pin drop, with my Zulus on.

We're talking about making airplanes quieter, not canceling the noise that reaches our ears. For pilots, anyway, the problem of going deaf has been solved -- but it is literally just masking the underlying problem.

Surely, given 2013 technology, we can quiet the Hammers of Hell that rage inside every GA cabin.
 
For the same reason rock music is best played loud. I wuuuuv the way my IO470 sounds. ANR fixes most of the noise issue for the people inside the plane.
 
bartmc said:
For the same reason rock music is best played loud. I wuuuuv the way my IO470 sounds. ANR fixes most of the noise issue for the people inside the plane.
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It's funny, but as I get older my tolerance for loudness has diminished.

Don't get me wrong -- I will go to Austin, sit up front listening to a screaming blues guitar all night long, and relish the ringing in my ears.

But when it comes to "noise" -- like Harleys, loud pickup trucks, sirens, etc. -- it just ticks me off.

It seems to me we would be making more inroads on our quest to save GA if we actually had aircraft that didn't aggravate people. Call me crazy.
 
Jay Honeck said:
My Lycoming O-540 has a muffler, but it's a joke. Not only does it do little to attenuate noise, it's so lightly (AKA: "poorly") built that it requires replacement every 350 hours or so.

I would GLADLY sacrifice ten pounds of useful load in exchange for a heavier, more effective muffler -- if for no other reason than added durability. Sound deadening would be nice, too. lol
Click to expand...

We went to straight pipes on our O-540. Running 250HP on a fixed pitch prop.
It may be loud, headsets cover a lot. No housing community noise to worry about, we are 20 miles out from the big city in the middle of the desert.
 
I don't think they're so loud. When a plane flies over we carry on our conversation. when someone rides a harley by we have to stop talking or shout over it. That doesn't seem to dampen the enthusiasm for harleys as a hobby so i don't see why you'd think it's a concern for planes.
 
Jay Honeck said:
, loud pickup trucks, sirens, etc. -- it just ticks me off.

It seems to me we would be making more inroads on our quest to save GA if we actually had aircraft that didn't aggravate people. Call me crazy.
Click to expand...

Yup. You are getting old ............and CRAZY...:yes:;)
 
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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