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VeryBumpy

Why don't piston planes have mufflers?

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They are rather noisy flying over head. I'm sure the pilot and few pax would like it quiet. Why don't they put on a light weight muffler and reduce noise pollution?

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Others may have an "official" answer but its an interesting question; my first reaction may be weight as you suggested lightweight, even a lightweight single engine is very limited in terms of carrying capacity. Here are some real numbers from a C172

 

Empty Weight: 1720.63

3 Passengers: 540 (180lbs a passenger)

 

Without any other weight the aircraft can only carry 49.5 Gallons of fuel, this of course is not possible due to a few pounds of gear. Lets say 10 pounds per person. Now we're down to 44.5 gallons of fuel. If a muffler is added (I'm not a mx expert, simply going off a few numbers found on google) you loose another 30 lbs. This leaves 39.5 gallons of fuel, with IFR reserves of 30 plus 30 for an alternate your looking at around 2.5 - 2.8 hours of flight time. Not a huge distance at 113 TAS, vs full fuel for the C172 is 53 gallons and that will give approximately 4.1-4.2 hours of flight time.

 

Lets look at a cross country aircraft the Piper Arrow, again using real numbers.

 

Empty Weight 1848.1 lbs

3 Passengers at 180lbs 540

3 Bags at 20lbs a piece and 10 for flight gear

 

This leaves you with 49.9 gallons of fuel for the aircraft, at 11 gph your looking around 3.5 hours of trip fuel without any extra weight.

 

From real life experience in both an Arrow and Seminole, if you pull the props back to around 2200RPM with an ANR headset you can barely hear the engines and if you cruise above around 6k neither can the people on the ground.

 

Kinda a long winded answer, but I think its all about weight.

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They do have small mufflers and it does help, but the 5.7 liter engines on Cessna 172's have very short exhaust pipes and they aren't going to be quiet at full power with any amount of muffling. Even a car with that size engine and a lot more pipe and muffling is very loud at high power.

 

Once you dial back the power, the engine noise is much less noticeable from the ground IMO. You can barely hear them on downwind about .5 miles away at 1000' AGL at about 50% power.

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They are rather noisy flying over head. I'm sure the pilot and few pax would like it quiet. Why don't they put on a light weight muffler and reduce noise pollution?

 

 

Simply because it would increase cost.

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Simply because it would increase cost.

 

And weight

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And weight

 

Aircraft can be designed or adapted to handle the increase in weight. The underlying reason is still cost.

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When even an old C172 constitutes a $30,000 airfrane, a $25,000 engine, and up to $35,000 in instruments/avionics.. the cost of a muffler is a rounding error..

 

Weight is one consideration, but it's also about performance. Exhaust back-pressure can cost quite a few horses..

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And weight

Not to mention reduced power due to backpressure.

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Who says they don't have mufflers? Pretty sure there hasn't been a Cessna or Piper built in the last 50 yrs that doesn't have a muffler of some sort and I've been an A&P for 29 yrs so I've been under the cowl of a few. Where else would you get your cabin heat? Most of the noise you hear from a plane overhead comes from the prop BTW...

 

Maybe you could all argue over why dogs don't have tails :smile:

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When even an old C172 constitutes a $30,000 airfrane, a $25,000 engine, and up to $35,000 in instruments/avionics.. the cost of a muffler is a rounding error.. Weight is one consideration, but it's also about performance. Exhaust back-pressure can cost quite a few horses..

 

The correct answer.

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The correct answer.

There are no technical reasons why mufflers can't be fitted. All the aspects mentioned cann be dealt with by fitting a more powerful engine, by reducing the MTOW, or by accepting a reduced performance. There are no technical reasons why they can't be fitted simply cost.

 

Hush-kits have had to be fitted to older turbine-engined aircraft despite similar disadvantages

. For example Gulfstream hush kits weight about 300lb and can reduce range by up to 2%.

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It has to do with weight, engine efficiency and cost, but another reason is reliability. Why fit a component that is purely aesthetic in nature, even if there is low risk of it failing and then causing a serious incident?

 

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 Why fit a component that is purely aesthetic in nature, even if there is low risk of it failing and then causing a serious incident?

 

why, therefore, fit hush kits to turbine engined aircraft? The same reasoning applies.

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I don't think anybod says they can't be fitted.. the question is, why are they not fitted..

 

And of course it's not universal, as some do have a muffler, or muffler-ish component.

 

There are even aftermarket, "tuned" exhaust systems, that are muffler-ish, and actually improve performance.. and they are a cost issue.

 

It's always a trade-off.. weight/cost/performance ...

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Who would want to muffle the beautiful sound of a big V-12 or Radial...that is pure airplane music.

 

Sorry GE90, you sound great spooling up, but you cant touch a Merlin in the sound department IMHO :P

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Who would want to muffle the beautiful sound of a big V-12 or Radial...that is pure airplane music.

 

Non-aviation enthusiasts  living under its flight path certainly would - they'd say it was pure noise and annoyance.

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Are those same non aviation enthusiasts living near freeways, and usual urban noise which is frequently louder than the airplanes? We live with much more annoying urban noise than avation noise. Guys overcompensating with their big loud trucks, ghetto kids in their cars with loud stereos, construction noise, the guy who runs his lawnmower at 7AM on Saturday.

 

Do these people also move near an airport or under a flight path, know this before hand and then complain about airplane noise?

 

Prescott, AZ Airport is located about 7 miles out of town. City builds municipal golf course near airport because the land is cheap. Land developers see golf course and get the idea to build houses around it. People move into those houses, then complain about the aircraft noise. They really started to complain during the summer months when forestry aircraft were based there.

 

Some idiot there even decided to have a revival tent put up right under the departure end of the main runway, then had the gall to ask the Forestry service to suspend operations on Sunday. Maybe if the forest fires can be asked to suspend operations on Sunday, then maybe the Forestry service would LOL

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Saying people shouldn't object Is futile. The reality is that they will object and their objections will be listened to.  Burying one's head in the sand and ignoring the problem is a sure way to  reduce the extent private flying.

 

The reality is that In the UK it is becoming increasing difficult to get consent to improve any facilities at small airfields because of the objections to the increased number of movements and consequential  noise. Consent may be refused outright or, at best, granted with restrictions that effectively nullify it. The result is that airfield owners begin to look around for more profitable uses and the airfield is lost.

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Who says they don't have mufflers? Pretty sure there hasn't been a Cessna or Piper built in the last 50 yrs that doesn't have a muffler of some sort and I've been an A&P for 29 yrs so I've been under the cowl of a few. Where else would you get your cabin heat? Most of the noise you hear from a plane overhead comes from the prop BTW...

 

Bingo! Even at idle most piston planes are making as much prop noise as they do engine noise.

Maybe you could all argue over why dogs don't have tails :smile:

 

Some people would argue with a fence post.

 

Scott

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Its not like Spitfires and Hurricanes are flying over the UK every day now. I bet during WW2 those folks weren't complaining about airplane noise LOL, at least not that of Allied aircraft. Ironic, without those beautiful sounding Merlin engines 70 years ago, the people of the UK would be under a different kind of government. Do folks there really call up a place like Duxford and object to the noise of historical aircraft there?

 

I can understand why someone would object to a louder GA plane departing at 4AM over a neighborhood. However they have no basis for their complaints when the GA traffic is mixed with the daily urban noise. Sure they will complain, and it is unfortunate that their complaints carry weight with city councils. I didn't like noise abatement procedures when I was actively flying, but I did follow them as a courtesy...to a point. I would not land with a 15kt tailwind just because some yuppie didn't like the sound of a Lycoming O-360.

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Sure they will complain, and it is unfortunate that their complaints carry weight with city councils.

 

But that is the reality. Those who love near an airfield generally vote for the local councillors. Those who fly from an airfield generally don't. Which group do you think the the council will listen to?

 

I didn't like noise abatement procedures when I was actively flying, but I did follow them as a courtesy...to a point. I would not land with a 15kt tailwind just because some yuppie didn't like the sound of a Lycoming O-360.

So you did your bit to create complaints and put private aviation under threat. With friends like you who needs enemies?

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yes when safety is a factor, it always takes a major priority over some yuppie's serenity

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From memory something reminds me that a large amount of noise comes from the prop alone, org Harvard the prop tip was close to super-sonic until modified, also also when you measure db's sound is exponential

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yes when safety is a factor, it always takes a major priority over some yuppie's serenity

 

Just because you think something is unsafe mean it actually is. Also not everyone who objects to aircraft noise is a yuppie.

 

Your attitude is the sort that damages the long-term prospects for private flying..

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