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?

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.

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.

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.

 

 

Simply because it would increase cost.

 

And weight

And weight

 

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

Have a nice day sir :-)

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..

And weight

Not to mention reduced power due to backpressure.

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:

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.

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%.

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?

 

 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.

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 ...