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To muffle, or not?

claycookiemonster

Well Known Member
One of the really fun things about airplane building, at least when doing so for the first time, is all the decisions I get to make with little or no foreknowledge. So, I have an Aero Sport Power IO-375 on order. Fine. At sometime I get to procure an exhaust system for it. I assume to some degree, this is no different from cars; there's LOUD and powerful, or there's Quiet and less powerful.

I don't want to be a bad neighbor. I don't want to foster angry letters to the airports I visit. I also don't want to muffle this bad girl into submission.

Planning on a Showplanes Cowl and Superior Cold Air Horizontal Sump. I will need a good heater.

Thoughts?
 
Vetterman offers an exhaust system that incorporates mufflers and fits various 4 cylinder RV's. The noise reduction is claimed as 6 DB.

Might want to give them a call to check system availability.
 
Vetterman offers an exhaust system that incorporates mufflers and fits various 4 cylinder RV's. The noise reduction is claimed as 6 DB.

Might want to give them a call to check system availability.

It's not the one we sell, but let me tell ya: The Vetterman trombone exhaust is a work of art, and it's what I have on my project airplane (which I hope to be able to spend time on again and finish one day, hah). Call Clint and talk with him about it. Lots of cabin heat is also a real side benefit of the built-in muffler/heat sink.
 
If this is a poll, I'd vote "yes, add some kind of sound reduction."

As you probably know, the sound comes from three major sources - the exhaust, the intake, and the propeller. For our engines, we can add a muffler to the exhaust, select a quiet prop (shorter length), and spin the prop slower. It's all about tip speed, obviously.

In much of Europe we are required to carry a noise certification which can affect the cost of the landing fee, so there is a financial incentive to have a piece of paper in your aircraft that says it's quiet. Most aircraft here have mufflers. Some limit max RPM. Many have 3-blade props. It makes a huge difference in the sound output, and (hopefully) goes some ways toward slowing the pace of airport closures.

Like the lead issue, we ignore the noise issue at our peril.
 
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You will be surprised that the noise is not offensive from the ground, especially if you reduce power at low altitudes when flying by. Good ANR headsets make it seem quieter than my Kitfox which has a muffler. My RV7A has Vetterman 2 into 1 exhausts. No muffs. Try that first.
 
A side note on “where does the noise come from?”

We just ran up our electric Xenos to something more than idle for the first time, and everyone at the Airpark with attended agreed that it was almost as loud as a piston airplane - and there was NO exhaust! It was all prop noise….

Paul
 
I think the RC world is quite ahead of the game here, using electrics has been a common practice for many years. And as Paul just found out, prop noise can be loud on its own.

Now, as pointed out by Mickey above, all homebuilts are now sporting some kind of muffler around here. Lest they don’t get their permit to fly…

One benefit of having a muffler, is noise reduction (sure u knew this ;)). What’s nice is to also benefit from the noise reduction inside the aircraft. I happen to fly quite a few legs of say 3 hour duration, and having a muffler will have me less tired at the end of day.
It might be age, but I sometimes wonder when reading about people here cruising 2500-2700 RPM. Once clear of the pattern, I reduce MP to my usual sedate retiree settings, but above all the RPM goes back to 2000.
Try it yourself and see how eerily quiet the flight becomes :)
 
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Too Loud, I'm Told

My A&P buddy runs a shop down at the end of the airport. He can't see the runway but says he always knows when an RV launches because they're noticeably louder than the spam cans, Citabrias and Decathlons from the local flight school. Yah, straight pipes on nearly all of the several RVs on the field. I've promised myself that when (if?) the Vetterman exhaust system on our RV-6 (O-320, two blade Catto prop) wears out, I'll install a new Vetterman system with mufflers. I THINK it will fit. Might need to tweak the cowl a bit to clear those mufflers but I'm willing to do that. I realize that much, if not most of the noise comes from the prop but every bit helps. Besides, I can use the weight up there.

As a side note, and not exclusively RV related, recently, someone in the town up the hill wrote a note on our NextDoor app, griping about those buzzy, pesky airplanes flying around. I braced for an onslaught of agreement, but was happy to be surprised at how much support we aviators got. Only a couple of letters in agreement with the OP, and about 30 from people saying how they like little airplanes, enjoy looking up and wondering where they were going, all that. Which does not relieve us of the responsibility to be good neighbors, of course. I saw this as a chance to post something positive too, so I wrote about us trying to be useful like when the airport is taken over by firefighting helicopters during our (too many) wildfires, our Open House events every month with Young Eagle rides, all that. And I pull the power back a bit when I'm over town.
 
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As a side note, and not exclusively RV related, recently, someone in the town up the hill wrote a note on our NextDoor app, griping about those buzzy, pesky airplanes flying around. I braced for an onslaught of agreement, but was happy to be surprised at how much support we aviators got. Only a couple of letters in agreement with the OP, and about 30 from people saying how they like little airplanes, enjoy looking up and wondering where they were going, all that. Which does not relieve us of the responsibility to be good neighbors, of course. I saw this as a chance to post something positive too, so I wrote about us trying to be useful like when the airport is taken over by firefighting helicopters during our (too many) wildfires, our Open House events every month with Young Eagle rides, all that. And I pull the power back a bit when I'm over town.

I feel that this is the right way - become an integral part of the community.
 
I have the Vetterman exhaust with the mufflers. If I were to do this again, I would skip the mufflers. They take up a lot of space, and need the cooling air SCAT tubing, which also takes up space. In reality, the mufflers really aren't doing much to the noise level. A good set of noise cancelling headsets is all you need. As for outside the cockpit, you really can't tell that there are mufflers.
 
While they may not do much for actual noise, Vetterman mufflers produce amazing cockpit heat for cold winter flying. There's a lot of history on VAF where folks are bemoaning their inadequate heat from a standard heat muff, but the shroud around mufflers is much larger and has much more surface area to transfer heat. I'd absolutely buy mufflers again if I needed a new exhaust.
 
It's not the one we sell, but let me tell ya: The Vetterman trombone exhaust is a work of art, and it's what I have on my project airplane (which I hope to be able to spend time on again and finish one day, hah).
What Greg said...I really like my Vetterman trombone exhaust with mufflers. I need the extra heat for Winter flying in New England and the mufflers also keep cockpit noise down a little. And while being a good neighbor might not be "cool" with some in the RV world, it's important at a lot of noise-sensitive airports around here.

ds
 
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While they may not do much for actual noise, Vetterman mufflers produce amazing cockpit heat for cold winter flying. There's a lot of history on VAF where folks are bemoaning their inadequate heat from a standard heat muff, but the shroud around mufflers is much larger and has much more surface area to transfer heat. I'd absolutely buy mufflers again if I needed a new exhaust.

Muffler or simple heat shroud? Not familiar with Vetterman products.
 
Muffler or simple heat shroud? Not familiar with Vetterman products.

Sorry I wasn't very clear. The heat shroud for cabin heat encompasses the entire muffler on my standard Vetterman exhaust (parallel valve, 4-into-2 pipes, with optional mufflers), and thus the heat shroud is larger diameter and longer, with more surface area to transfer heat, than a standard heat shroud on a non-muffled exhaust.
 
Do mufflers significantly reduce power?

My RV is a few knots slower than Vans specs while others report better than Vans specs. There could be many reasons for this but I was wondering how much power a Vetterman crossover exhaust with mufflers could reduce power compared to straight pipes, and are Vans specs determined with mufflers installed or straight pipes?

Bevan
 
Vetterman Trombone

I have the Vetterman Trombone (muffled) on the same engine you ordered.
Fits perfectly, easy to install and with one heat muff I have sufficient heat in winter down to -15C. With 2 muffs, it would be toasty warm in colder temps but I limit my winter flying to -15C or warmer.

As for the sound, well I have a couple people say that it's quieter than most RVs, and that it has a "quiet purr"...
As for power, with the IO-375 having ample of horses, don't worry, I don't think you'll notice the difference...
 
My RV is a few knots slower than Vans specs while others report better than Vans specs. There could be many reasons for this but I was wondering how much power a Vetterman crossover exhaust with mufflers could reduce power compared to straight pipes, and are Vans specs determined with mufflers installed or straight pipes?

Bevan

Mufflers tend to limit or restrict that amount of air flow into a cylinder during the intake stroke. Exhaust is open for a good amount of time when the intake is open to support cross flow. Therefore Max WOT power can be bettered by a small percentage with no restriction, though strategically placed interconnection (i.e. cross overs) can increase flow, even with a muffler. Not sure how well executed the Vetterman is, so can't speak to gains here. However, at 75% power cruise (here you are restricting the air flow into the cylinder with the throttle plate typically), there should be no meaningful difference muffled or not; Just may need the throttle plate open a hair more on the muffled engine to get the air in the cylinder. If you are at altitude and 75% power with WOT, you can expect that slightest reduction in power, but not enough to account for a few knots; Maybe a few ponies which would be under a knot.

Need to look elsewhere for the lower than book cruise speeds other than WOT.

Larry
 
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