Why don't piston planes have mufflers?

[KevinAu 441]

...............

[Oracle427 45]

 

 

Most small GA airplanes do not have mufflers. The heating system uses a "muff" that fits around the exhaust pipe.

 

I know what you mean when you say that it isn't a muffler, but can you imagine how loud the Lycoming and Continental engines would actually be if they were run even without the "mufffler" shroud with short pipes like some warbird or the extremely noisy rotaries from WWI? If any of you have never heard a rotary engine in person it is most uncomfortably LOUD.

 

Here is what the stock muffler more or less looks like and it isn't much given the lack of space. http://www.aircraftexhaust.com/nav.cfm?cat=11&subcat=67&subsub=0&as_id=1&mg_id=5&sys_id=185&display=system

 

There is a restaurant at my airport with outdoor dining facing the ramp. The parked aircraft are no more than 50 feet from the tables and they face directly at the restaurant. It is noisy when they fire up but you can clearly hear motorcycles driving on a road on the other side of the runway over the airplane running at 1000 RPM just 50 feet away. Even when they are taking off from about 800 feet away, you don't have to raise your voice to be heard.

 

I will say that being in a position relatively under an airplane that is taking off will be very loud. The props make a lot of noise at high RPM and those exhaust pipes aimed downward focus the engine noise. I guess people under the path get frustrated by aircraft passing overhead every couple of minutes even though each one only lasts a few seconds. My instructor has taught me to avoid overflying homes and to be a good neighbor when it does not compromise safety. That can include dialing back the power while in the pattern and flying it a little slower or coming in for a mid field entry if traffic allows and it avoids developed areas on the other side of the field.

 

In the end, I think the benefit is tough to balance. Someone threw out a number of 30 pounds earlier for some comparisons. 30 pounds easily equates to half an hour of fuel or more in some small airplanes.

[Howellerman 104]

I am not an expert by any definition, just an observation.

 

Aircraft engines by definition are under-stressed. They need to provide "duty-cycles" over performance. They run relatively low compression ratios, they run low RPM, and they, in the grand scheme of internal combustion engines, just putt along. Made to last. A flat-four airplane engine has nothing near the brake-specific output of a Subaru.

 

Contrast that with a highly-tuned automobile or motorcycle engine - higher compression, significantly higher RPM, and lot more "bark". I have been to numerous drag races where engines, "only" 500 cubic inches in size, will rattle your fillings. And I remember reading, long ago, about someone who wanted to certify a de-tuned 350 Chevy motor as an aircraft engine. I don't think it was ever approved by the FAA. Just not enough assurance for duty-cycles.

 

So, a relatively low-power piston powered engine is not going to generate sufficient noise to warrant noise cancellation technologies. This follows Oracle's observation: just not enough bark in each bite to make it overtly noisy compared to motorcycle engines across the tarmac.

 

Besides, who in their right mind wants to quiet the sound of a rotary engine, or even better, a Merlin V-12, at full song? 

[anthony31 63]

Speaking of extremely noisy rotaries from WWII I know that in the T28 Pilots Handbook it says this about the engine:

 

"Engine exhaust outlets on each side of the cowl are designed to utilize the additional thrust available from the jet effect of the exhaust"

 

Reading the Performance book for the same plane shows about 100 extra hp* from this exhaust jet thrust (from a 1425 HP piston engine)

 

*Depends on airspeed and engine power.

[mebull 27]

I agree with the few comments on the Merlin engine sound. To my ears, not noise - music! I live near a GA airport that has a once a year air show and that is the one engine sound I will run outside just to listen and look for the Mustang or head to the airport for a look see. When I was a kid I used to get to go to the hydro plane boat races at Madison Indiana. They used the Merlin back then instead of the turbines they use now. WOW!

 

As far a the GA aircraft that fly right over town while in the pattern at about 1500ft (I Think) (mostly daytime), nobody complains, there are so many Harley Davidson riders around that you can't hear the aircraft anyway. On the other hand we do have small private jets come and go every now and then and they do rattle the china a bit. We also have a railroad yard that runs through town so as you can imagine, a GA aircraft passing over hardly gets noticed.

 

People that build homes near an airport then complain about the noise are the same types who would build on a oceanside cliff, or a foot above sea level on a beach or on the flood plain of a river then want someone else to rectify there poor choice so they don't have to suffer the responsibility.

 

I don't worry about the sound of a light aircraft flying over town. I will worry about one that isn't making any sound at all ( unless of course it is a sailplane ).

 

Regards to all,

Mel

[mgh 89]

 

 

really what's the point of a fancy muffler?

 

To stop complaints about noise and help keep small airfields open. Once an airfield's gone, it's gone for good - a point rhat seems to escape those who want to make as much noise as they wish.

[Oracle427 45]

The real threats to small airports by me are the desire to profit by redeveloping the land into commercial or high end residential properties.

 

Aircraft make noise, it's a fact of life. Some are worse than others at it. The noise complaints and any other issues are the political battles that are fought over the deed.

 

Teterboro which is one of the oldest and busiest GA airports in the US is regularly featured in the local papers. the articles go on about how dangerous the airport is and how much the locals in the surrounding towns suffer with the noise. Keep in mind this is a densely populated area in the country sitting just outside NYC. The articles go on about how the airport is only serving rich executives, etc.

 

Meanwhile, taller condos keep getting built on the outskirts of the field particularly on a ridge with great views that sits perfectly in line with one of the runways. I can guarantee that a jet will pass overhead on most days every 5 minutes.

 

I live under one of fixes for Newark. Offhand I don't know which one, but it's about 20 miles north. Those jumbos are far louder than all the props that fly overhead low to avoid the bravo airspace.

 

This is an example of one such battle over a small airport I like to visit. there is a lot of land development going on in this area and it is very obvious as you fly overhead.

 

http://www.mycentraljersey.com/article/20130702/NJNEWS20/307020038/Solberg-Airport-eminent-domain-fight-Readington-still-unresolved

[mgh 89]

 

 

The real threats to small airports by me are the desire to profit by redeveloping the land into commercial or high end residential properties.

 

That is also true but complaints about noise can influence the council's decision - "also there won't be any more noisy aircraft causing problems.

 

In the UK  agricultural land (which is essentially what a small grass airfield is) sells for about £10,000 /ha on average. However, with permission to build houses that rises to  about £2,500,000 /ha, again on average.

 

In many cases the landowner hasn't much interest in aviation and has leased the land to a flying school or club. The area of my nearest airfield is about 28 ha so the values become £280,000 or £70,000,000.  That's very tempting a for a landowner who's income from the site is merely the rent from a flying club/school . I'd take £70,000,000 any day - wouldn't everyone. Also to pu this further into context ,700 houses could be put on this airfield. At the average price for That put the total value about £210,000,000 based on an average house price 0f £300,000. That sort of money talks!

[mgh 89]

 

 

I am sorry my attitude makes me an a-hole but I will not sacrifice the safety of the people on the ground, passengers, myself, nor risk damage to property and aircraft

 

A response to that is simple. If you can't land safely without breaching the noise regulations then don't land (unless it's a real emergency). That's the safest way with no no risk  in the air or on the ground.

[pilottj 198]

Are folks there going to call up the RAF and ask them to put hush kits on their Eurofighters and Tornados?

There are a few airports here in the US where the noise abatement procedures that compromise aircraft safety. Sedona, AZ is a good example.

Sedona is a beautiful area in the desert southwest region, with many large red rock formations. The local airport happens to be built on top of one of the mesas, making for a rather exciting landing. Anyway, you can imagine this would be a popular area for tourists, so the airport is quite busy with air tour operations, not to mention a lot of sight seeing GA traffic. The airfield is uncontrolled, and due to the airport's unique location, wind conditions are a factor, not to mention high density altitudes in the summer. There is a single runway 3/21.

Now my experience in Sedona was about 8 years ago when I flew there a few times.  They wanted you to land on runway 3, and depart on 21 due to noise sensitive area off the approach end of 21. Having traffic land and depart in opposite directions already sets up a hazardous situation, especially at a popular uncontrolled airfield. The sound of two planes colliding will be a bit louder than that of a typical GA at landing power settings. I remember having lunch and watched a few aircraft make sudden avoidance maneuvers.

Either the departing aircraft or landing aircraft is invariably going to have a tailwind, which is unsafe. Local noise abatement policies at the time did state that if winds were high enough that the proper runway could be used.

My flight instructor at the time told me had previously flown a Glassair there and elected to land the proper way in order to avoid landing with a heavy tailwind. When he landed he got an earful from someone on the ground who obviously wasn't a pilot. He tried to explain to the fellow that landing a high performance airplane with a large tailwind is a bad idea.

Anyway, that is an example of noise abatement procedures turning a challenging airport into a more hazardous one. Aspen, CO is another good example.

This is taken from the Sedona Airport website noise abatement page.

Remember Runway 03 is uphill 93 feet
and Runway 21 is downhill 93 feet.
Runway 03 is preferred for landings, subject to wind conditions.
Runway 21 is preferred for take-offs, subject to wind conditions.

SAFETY ALWAYS COMES FIRST.

[mgh 89]

 

 

Sedona, AZ is a good example.

 

The Sedona Airport Administration implemented an "Aircraft Noise Incident Form" which was developed by the Sedona Citizen's Noise Abatement Committee (SNAC), a community-consensus committee formed at the request of the airport’s Board of Directors.

 

 

http://sedonaairport.blogspot.co.uk/

 

why did it do that? Because it recognised that there was a serious problem, probably exacerbated by those who disregard its noise abatement policies. on spurious safety grounds?

[pilottj 198]

Oh yes, lets throw safety out the window because Donald Trump needs to be able to hear his wind chimes play the song 'Money'. Whats it to him if two planes collide...as long as they don't crash on his property. And yes most of the folks living around Sedona are yuppies because real estate there is very expensive.

 

I think you get the impression that pilots are like teens who drive by neighborhoods blaring their super subwoofer stereos at 4AM. Just because we can buzz neighborhoods/cities in FSX doesn't mean we do it in real life. The standard regulations are fine, and we really do try to be careful with our noise footprint. If I did have to take off early in the morning, I tried to reach my cruising altitude quickly.

 

We do maintain at least 1000' AGL over populated areas per regulations. We follow established traffic pattern rules and we follow ATC instructions. A lot of pilots (myself included) like to fly at higher altitudes simply because a higher altitude means a longer gliding distance should there be an emergency. We can be very reasonable about noise abatements, provided the noise abatements are reasonable themselves.

 

Its like asking a railroad company not to blow their horns at night when going through a town, that is very reasonable. Asking them not to blow their horns during the day when a lot of traffic is crossing a track is not reasonable and would be a serious safety issue.

[ESzczesniak 128]

Not to mention reduced power due to backpressure.

 

Exactly!!!  The same reason you will never see a muffler in Formula 1 (or NASCAR for that matter...if you call that racing).

[tttocs 301]

"A response to that is simple. If you can't land safely without breaching the noise regulations then don't land (unless it's a real emergency)."
 

 

Ah, man... Yer killin' me!   Funniest thing I've read on Avsim in a long time. 

 

Uh... you did mean this to be a joke, right?  Right?  :blink:

 

Scott

[pilottj 198]

Lol if they hate hearing the sound of a Piper Cub landing, they must have really hated this Merlin symphony (with a few Griffons too)...

Seriously, anyone who phoned in to complain about that noise should have been forced to listen to bad karaoke non stop for a month LOL

 

How about some Damiler Benz music too.  It isn't a Merlin but it is still a very nice sounding engine.  You can see the BF-109's reputation as hard to land is true.  I bet if you told him or the Spitfire pilots above to land with a 15kt tailwind, they would have a few choice words in reply. :lol:

 

:Big Grin: