On Sep 8, 3:42*pm, wrote:
On Sep 8, 3:33*pm, John H wrote:





On Mon, 8 Sep 2008 11:56:46 -0700 (PDT), wrote:
On Sep 8, 2:35*pm, wrote:
On Sep 8, 2:29*pm, wrote:

On Sep 8, 1:33*pm, (Richard Casady) wrote:

On Mon, 8 Sep 2008 08:31:27 -0700 (PDT), wrote:
Normal IC aircraft engines aren't muffled, and the back pressure has
an affect on them if you try to.

Most, maybe all, of the planes I have experience with have had
mufflers. Includes radial engines from the thirties, and the usual
Piper, Beech, and Cessna planes in use from the forties on. Still
loud, every one of them.

Casady

Expansion chambers.

They aren't really mufflers, but are designed to make some
backpressure in normally aspirated engines. My uncle was an aviation
machinist. Been around small IC engined aircraft a lot!

AHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!
COULD THEY MAKE THEM QUIETER IF THEY WANTED TO?????????

Please answer me..... * I gotta' know... sniff * - Hide quoted text -

- Show quoted text -

There is not really any reason they could not have mufflers on the
engine. *It would probably take a few mph off the top end. *But much
of the noise is from the prop. *Many simply bolt the prop to the
engine output so there is not a lot you can do with prop redesign.
More blades may allow you to run a smaller diameter but probably not a
lot smaller. *So the prop tip speeds are still going to be pretty
high.

I just spoke with a young man in Orlando. He's at Don George
Aircraft Engines & Parts
Orlando, Florida 32805 *
407.422.0188

I remembered that the airboat I rode on had a Lycoming engine, which gave
me a starting place. According to the guy I spoke with, the law in Florida
requires mufflers on *all* airboat engines. The loudness comes from the
propellor. Problem solved.- Hide quoted text -

- Show quoted text -

Sounds to me like there is not really a reasonable way to quiet the
prop, without a complete retool.. Ok, as long as they are trying I
guess most will have to live with it until noise limits are imposed
and someone works out the technology to be efficient and affordable..
Might be, it can't be done, but not everyone can own a jet either- Hide quoted text -

- Show quoted text -

Yeah, I built a hovercraft once and the push engine was a twin
cylinder two cycle rotax, The prop made more noise than the engine.

On Mon, 8 Sep 2008 08:23:21 -0700 (PDT),
wrote:

On Sep 8, 10:37*am, wrote:
On Sep 7, 10:41 pm, wrote:





On Sep 7, 10:12 pm, wrote:

On Sep 7, 10:07 pm, hk wrote:

wrote:
I was at the springs at the head of he Wacissa River this afternoon
cooling down on a hot Sept afternoon. *From far away you could hear it
coming upriver, another airboat. *I hate the damn things. *I dont hate
em for going places, I hate the noise. *So, is it the prop or engine
that makes all the noise? *Could you maybe make an effective prop that
would be less noisy?

Get a noise ordinance passed and get it enforced. That's what we did
where I lived in Florida. No airboats before or after certain hours of
the day. We also made a stink about the damned things cruising over and
cutting swaths through the wetlands.

I think they like the noise. Same sort of guys as the ones who remove
the mufflers on their motorcycles and put straight pipes on the little
Japanese cars. Big noise, small dick.

You may be right about them liking the noise. *Maybe this is a techno-
opportunity to find a way around the noise generation. *A little
searching shows that major noise is from the prop although many boats
have unmuffled engines too. I wonder if putting a cowling around the
prop would work, somebody must tried this.

Found a DTIC report (that I do not want to pay for) saying that a
cowling and redesigned multiblade prop will reduce prop noise.
Another report from the nature Conservancy discusses noise and finds
that muffling always helps some. *They also say that noise is worst at
high prop tip speeds so it is best to go with a multiblade prop.
Worst noise whn one is attempting to get underway from land or sandbar
or to get unstuck.
So, is this an opportunity for someone to make composite airboat props
with multiple blades to replace all the old ones with two blades?

I cannot jump on these airboat ppl too much for being ignorant
rednecks, partly because I ma probably related to em and partly
because airboats do have good uses. *The Wacissa is a place for em as
the water is often so shallow and covered with hydrilla. *It would
really make people like them if the noise could be significantly
reduced. *They seem to have enough power to be able to reduce noise
somehow. *Maybe radically re-think the whole concept. *At very least
put cowlings around the blades so the noise goes up or back rather
than be emitted in all directions.- Hide quoted text -

- Show quoted text -

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

OMG - waht a complete buffoon.

"Tim" wrote in message
...
I rode in an air boat once, and I do mean once. and not long. I was
invited to go, and I was sitting tight in front of a 220 hp Lycoming .
Even with ear plugs the noise was deafening. We went about 3 mi. up
the Wabash river, and I tapped the "pilot" on the shoulder and said.
"I'm getting off. he looked at me funny and kept saying A"WHAT?"
WHAT?"

I knew it was too loud. I was wearing a pretty good vest so I just
bailed off!

he circled around and shut the thing down, and I told him I'd float
back. At that moment I didn't care. He took off and I could hear him
all the way back down to the docks. A friend of mine came by in a ski
boat and picked me up.

Like I said, even with ear plugs, I had a head ache for a day and
couldn't quit hearing that fan at night.

I won't do it again.


Great story. I've never done it, but suspect my reaction would be about
the same.

Eisboch

wrote in message
...

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

----------------------------

Trust me. The engine is loud.

The prop is much, much, louder.

Eisboch

On Sep 8, 6:32*pm, "Eisboch" wrote:
wrote in message

...

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

----------------------------

Trust me. *The engine is loud.

The prop is much, much, louder.

Eisboch

Kinda' thought so... So in that case, would it be unreasonalble for a
particular jurisdiction to ban them?

On Sep 8, 5:32*pm, "Eisboch" wrote:
wrote in message

...

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

----------------------------

Trust me. *The engine is loud.

The prop is much, much, louder.

Eisboch

Yes, go to an air show sometime and listen to a PiTT Special or a
Citaborea make a low altitude fast fly-by.

BWWWWWWAAAAAAAAAAAAAAAAHHHHHHHHHH!

The noise you actually are hearing is the prop beating the air. then
after they make the pass they get a lot quieter and you hear the
engine rumble.

What's cool is if somebody comes up with an old WW2 Corsair and makes
a fly-by. Yes, you hear a tremendous noise coming fromt he prop then
when they pass you hear that marvelous "gallop:" of the Pratt 'n
Whitney radial!

On Sep 8, 7:12 pm, wrote:
On Mon, 8 Sep 2008 18:32:05 -0400, "Eisboch" wrote:

wrote in message
...

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

----------------------------

Trust me. The engine is loud.

The prop is much, much, louder.

Eisboch

Down at Wootens the make the passengers and the drivers wear ear
protection. I don't know of anyone who doesn't.
I do know a couple guys down in Everglades City who have airboats.

So, why not put a shroud round the prop, it shoudl at least silence it
some?

On Sep 8, 9:42*pm, wrote:
On Sep 8, 7:12 pm, wrote:



On Mon, 8 Sep 2008 18:32:05 -0400, "Eisboch" wrote:

wrote in message
....

WTF? Can't they put a muffler system on them, or is it the blades that
make the most noise?

----------------------------

Trust me. *The engine is loud.

The prop is much, much, louder.

Eisboch

Down at Wootens the make the passengers and the drivers wear ear
protection. I don't know of anyone who doesn't.
I do know a couple guys down in Everglades City who have airboats.

So, why not put a shroud round the prop, it shoudl at least silence it
some?

it would probably mess with the aerodynamic efficiency of the prop.

I always wondered why you couldn't mount a big "squirrel cage" fan on
a boat, those things put out a lot of air with less noise

or at least I would think so

"Eisboch" wrote in message
...

"Tim" wrote in message
...
I rode in an air boat once, and I do mean once. and not long. I was
invited to go, and I was sitting tight in front of a 220 hp Lycoming .
Even with ear plugs the noise was deafening. We went about 3 mi. up
the Wabash river, and I tapped the "pilot" on the shoulder and said.
"I'm getting off. he looked at me funny and kept saying A"WHAT?"
WHAT?"

I knew it was too loud. I was wearing a pretty good vest so I just
bailed off!

he circled around and shut the thing down, and I told him I'd float
back. At that moment I didn't care. He took off and I could hear him
all the way back down to the docks. A friend of mine came by in a ski
boat and picked me up.

Like I said, even with ear plugs, I had a head ache for a day and
couldn't quit hearing that fan at night.

I won't do it again.


Great story. I've never done it, but suspect my reaction would be about
the same.

Eisboch


Took the airboat tour out of Doc Holiday's in the Everglades. 40 passenger
twin engine V8 boats. Not that loud, and was an enjoyable tour.

On Sep 9, 12:29*am, wrote:
On Mon, 8 Sep 2008 20:02:27 -0700 (PDT), Tim
wrote:

I always wondered why you couldn't mount a big "squirrel cage" fan on
a boat, those things put out a lot of air with less noise

or at least I would think so

Aircraft engineers looked at props for over 100 years and this is what
they came up with. The guys who design wind turbine generators use the
same type of prop. There must be something attractive about this
design.

Yes, it's actually the most p-practical way to move air.

But it sure is noisy!