Improving Thrust

A general, non-powerplant specific, discussion on airboat technology, ie., hulls, rigging, polymer, etc..
WBS
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Improving Thrust

Postby WBS » Mon Dec 07, 2015 4:44 pm

Have engineering background, long time interest improving airboat propulsion. Have looked at a lot of tech info and not found much on actual, practical applications except re some heavy duty military and gov. apps. Have some ideas I hope to physically test on small scale. Would like to contact some individuals interested in discussing this subect.

Would be interested in serious comments.

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Re: Would like serious comment on ducted fan airboat experim

Postby jeepinocala1111 » Mon Dec 07, 2015 5:03 pm

What type of ducted fan system? Keep in mind stuff going through the prop would go through the ducted fan.

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Re: Would like serious comment on ducted fan airboat experim

Postby SWAMPHUNTER45 » Mon Dec 07, 2015 6:20 pm

I have seen a military special ops ducted fan airboat, it was bad azz but a totally different realm from where most recreational users are.
We battle weight and financial benefit where as the military has incredible power making assets and a blank check.

For most of us the weight of adding the components of a ducted system may be the first negative. That in the future could be off set with carbon fiber or injection molding of polymers. But then comes the cost factor as many of us utilize ultra light weight, inexpensive or recycled materials.

I suggest you give Water Walker props a email to discuss some of their experiences with ducted fan and Patti at Whirlwind props is always willing to discuss conceptual applications and propeller technology.

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Re: Would like serious comment on ducted fan airboat experim

Postby Hardtail » Mon Dec 07, 2015 9:52 pm

WBS wrote:Have engineering background, long time interest improving airboat propulsion. Have looked at a lot of tech info and not found much on actual, practical applications except re some heavy duty military and gov. apps. Have some ideas I hope to physically test on small scale. Would like to contact some individuals interested in discussing this subect.

Would be interested in serious comments.


I PM you with my info.

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Re: Would like serious comment on ducted fan airboat experim

Postby glades cat » Mon Dec 07, 2015 10:21 pm

As an engineer, you're probable aware of some of the advantages and disadvantages of ducted fans.
Pros:
reduced tip losses, more static thrust from same size fan, quieter, safer to some extent(duct acts as a scatter shield)…

Cons:
less efficient than prop at cruise speeds, requires very small clearances between fan and duct, requires higher rpm, turns may stall the duct and produce drag and turbulent airstream, complex design and substantial weight…

I used to race a hovercraft with a ducted fan. It was a narrow boat and the ducted fan compensated for the reduced fan diameter. The blade/duct clearance was so close the fan would "zing" when the craft landed abruptly and torqued. During aggressive turns/slide, the fan/duct would stall and loose quite a bit of thrust until you straightened out of the turn.
Airboats get ridden a bit hard sometimes :lol: , especially if hunted or driven through vegetation and that big round thing (duct) would soon enough get beat up, roughed up, tore up and knocked off.
It would work just fine in an application that it was designed and engineered for.
Just wondering how it would endure willow branches, crocs or a Natty Light can going through it. :scratch:

Would be interested in hearing about your application.
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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Mon Dec 07, 2015 10:29 pm

In the archives on this site are several discussions on ducted props ..... they were mostly created for conversations about quieting a boat down, which they do. The 'sound' of a properly muffled boat is mostly generated by the prop just as it is when you hear a light airplane overhead, because of the shock waves coming off the propeller tips.
There are even a few photos to be found there of folks who experimented with that, not for a performance benefit, but to get quieter.
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Re: Would like serious comment on ducted fan airboat experim

Postby jimbo_jwc » Mon Dec 07, 2015 11:21 pm

I liked how this would create forward lift like a wing on the outside .
https://www.youtube.com/watch?v=Cew5JF8q6eY

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Re: Would like serious comment on ducted fan airboat experim

Postby John Fenner » Mon Dec 07, 2015 11:24 pm

No real reason to reinvent the wheel, the newer engineered props with swept blades and winglets on a properly built boat with a tight powerplant will be supreme to ducted fan technology.
I never finish anyth,,,.

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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Tue Dec 08, 2015 1:09 am

John Fenner wrote:No real reason to reinvent the wheel, the newer engineered props with swept blades and winglets on a properly built boat with a tight powerplant will be supreme to ducted fan technology.

I agree John, but a boat can be made ghostly quiet with a shroud of ductile aluminum around the inside of the prop cage. I don't advance any interest in trying to increase performance with ducting, but I'm all over the idea that an airboat can be as quiet as any other water craft if the owner cares enough to want it to be. I am SO over airboaters that need to run LOUD and PROUD. They're not Harleys, people .... and we've got way too many rich Yankee's buying waterfront property down here now that don't give a damn about our heritage or our traditions. All they want to do is bi*ch about the noise that airboats make.

Would you like for your grandchildren to be able to run an airboat? Quiet yours down.
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Re: Would like serious comment on ducted fan airboat experim

Postby jeepinocala1111 » Tue Dec 08, 2015 6:55 am

Mine is quiet NGQ and a real set of mufflers :cheers:

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Re: Would like serious comment on ducted fan airboat experim

Postby Ready to ride » Tue Dec 08, 2015 7:42 am

Dude. Really????? Shut up
Vote liberal and move on. No1 is going to buy into this nor do it. Huge waste of your time and mine for even having to comment on this

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Re: Would like serious comment on ducted fan airboat experim

Postby jimbo_jwc » Tue Dec 08, 2015 10:03 am

John Fenner wrote:No real reason to reinvent the wheel, the newer engineered props with swept blades and winglets on a properly built boat with a tight powerplant will be supreme to ducted fan technology.


Are these the kind ?

http://whirlwindpropellers.com/airboats/fs-proptest/

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Re: Would like serious comment on ducted fan airboat experim

Postby John Fenner » Tue Dec 08, 2015 12:31 pm

That or NGQ from sensenich. Very quiet. And the sheet metal on inside of hoops has been done years ago, the sub sonic tip noise noise was merely disbursed in different directions and seemed amplified as well. Now a true ducted fan, as in a turbine blade setup and geared up would typically sound like the tail fan on a coast guard chopper, still noisy but a different noise.
Heck the updated Huey's that Miami Dade fire air rescue are still noisy but not like the original 2 bladed rotor wings loud repetitive wopp wopp wopp.
Bottom line is having the right designed hull for area to be run and the powerplant matched and tuned for the applicable prop that will not need to have tips go subsonic with winglets to curb the sonic booms off said tips. Plus quiet exhaust.
I never finish anyth,,,.

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Re: Would like serious comment on ducted fan airboat experim

Postby englishtribe » Tue Dec 08, 2015 1:44 pm

This is Dave from St Cloud Florida. I have developed an inexpensive Ducted Fan application that can be fitted to any Airboat Rigging. It is Patent Pending and has been tested on Airboats. The design is also very lightweight. There is a lot of performance and control improvements with My System.

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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Tue Dec 08, 2015 4:33 pm

Ready to ride wrote:Dude. Really????? Shut up
Vote liberal and move on. No1 is going to buy into this nor do it. Huge waste of your time and mine for even having to comment on this

Stupid is as stupid does. If you're unwilling to make your boat quiet then you'll be one of the first we'll all point to when the fit hits the shan and we lose more access to waterways. And the shame of it is that if you were running a good set of mufflers your engine would run a lot stronger and you could actually put more pitch in your prop. Fact.

I worked in the experimental fabrication shop for a major exhaust manufacturer many years ago. There we had a dyno room and a SBC (we all called Lucy) to test the sound levels and power production of any new muffler they were considering for production. Lucy consistently made more power and more torque (which is what turns a prop) with mufflers than she did with open headers. More, her head temperatures were lower because of something called 'anti-reversion' ..... the exhaust valves weren't sitting in a furnace without a small amount of back pressure to prevent what's called scavenging. Top Fuel dragsters run Zoomy headers because they're supercharged. Anti-reversion to hold a fuel charge in the cylinder isn't an issue, and those engines only need to live for around 5 seconds anyway.

Your attitude, and the attitude of people like you will one day be a big reason why we'll lose access to many of our beautiful waterways. Don''t bring that stuff around me 'Dude' ..... you don't know WTF you're talkin about. Are we clear?
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Re: Would like serious comment on ducted fan airboat experim

Postby Deano » Tue Dec 08, 2015 4:36 pm

WBS wrote: . . . Have some ideas I hope to physically test on small scale. Would like to contact some individuals interested in discussing this subject.
If you gave even a small description of what it is you want to test, and/or what your ideas are, you may very well get more interest and serious participation. Every possibility certainly has not been exhausted by any means, but the comments about re-inventing the wheel and so forth are fitting in some cases because in those instances, the cost/benefit analysis has already shown the attempt as having been very little more than a futile effort, if that.

As Olf Art stated, some folks are after quiet and some others point out, they don't give a shit.
Just about any parameter of what you're looking at will also generate two different camps.

I for one, am more than passively curious. But I have also already spent more time than I care
to admit re-inventing wheels to only arrive at having yet another flat tire that was of no use. :wink:

EDIT: After rereading this, I should point out that I did not mean to minimize or take away from the thoughtful, time consuming replies that a couple other airboat brothers already made. :salute: That wasn't my intent.
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Re: Would like serious comment on ducted fan airboat experim

Postby Uhairball » Tue Dec 08, 2015 7:47 pm

Olf Art wrote:
Ready to ride wrote:Dude. Really????? Shut up
Vote liberal and move on. No1 is going to buy into this nor do it. Huge waste of your time and mine for even having to comment on this

Stupid is as stupid does. If you're unwilling to make your boat quiet then you'll be one of the first we'll all point to when the fit hits the shan and we lose more access to waterways. And the shame of it is that if you were running a good set of mufflers your engine would run a lot stronger and you could actually put more pitch in your prop. Fact.

I worked in the experimental fabrication shop for a major exhaust manufacturer many years ago. There we had a dyno room and a SBC (we all called Lucy) to test the sound levels and power production of any new muffler they were considering for production. Lucy consistently made more power and more torque (which is what turns a prop) with mufflers than she did with open headers. More, her head temperatures were lower because of something called 'anti-reversion' ..... the exhaust valves weren't sitting in a furnace without a small amount of back pressure to prevent what's called scavenging. Top Fuel dragsters run Zoomy headers because they're supercharged. Anti-reversion to hold a fuel charge in the cylinder isn't an issue, and those engines only need to live for around 5 seconds anyway.

Your attitude, and the attitude of people like you will one day be a big reason why we'll lose access to many of our beautiful waterways. Don''t bring that stuff around me 'Dude' ..... you don't know WTF you're talkin about. Are we clear?


Hey OF, I agree with you 100%. But I am curious. Why don't aircraft use mufflers? And why don't you hear complaints about them?

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Re: Would like serious comment on ducted fan airboat experim

Postby WBS » Tue Dec 08, 2015 9:07 pm

Deano wrote:
WBS wrote: . . . Have some ideas I hope to physically test on small scale. Would like to contact some individuals interested in discussing this subject.
If you gave even a small description of what it is you want to test, and/or what your ideas are, you may very well get more interest and serious participation. Every possibility certainly has not been exhausted by any means, but the comments about re-inventing the wheel and so forth are fitting in some cases because in those instances, the cost/benefit analysis has already shown the attempt as having been very little more than a futile effort, if that.

As Olf Art stated, some folks are after quiet and some others point out, they don't give a ****.
Just about any parameter of what you're looking at will also generate two different camps.

I for one, am more than passively curious. But I have also already spent more time than I care
to admit re-inventing wheels to only arrive at having yet another flat tire that was of no use. :wink:

EDIT: After rereading this, I should point out that I did not mean to minimize or take away from the thoughtful, time consuming replies that a couple other airboat brothers already made. :salute: That wasn't my intent.


Comments welcomed.
Objective: Bench scale initial tests of ducted prop/fan propulsor using wide inlet inverted Clark Y type , example ; goal is 6’-7’ max width, generally rectangular shaped front, tapering smoothly to 5’ diameter circular prop/fan zone, maybe 6” to 11” . Expanding aerodynamically from circular to sharper edged rectangular outlet. Vertical height same through length of duct. The idea is to increase mass flow to try for more thrust on the order of 6 lb/hp in a quieter, safer way.. The shape would look like a short box shaped duct with aero shaped inverted airfoil inlet.
Test items include Vortex Gen inserts that are small metal or polymer shapes, about 3-4 “ size simple aluminum or polymer shapes, spaced over critical flow separation areas in inlet or after prop/fan.t . 3M even makes vortex gen tape for sailplane wings and other uses. Suggest use search engine to view examples. Another item is the use of sheet curved or conical inserts. An industrial application uses two to three inserts in commercial large air duct diffusers, wind tunnels. etc.
Another critical area is the prop or fan twist to increase pitch at outer third gradually to about 6-7 degrees more at tips over prop datum as proven in flight and stationary full size tests.
Simple 5 or so radial blade flow straightening vanes at duct end to recover significant swirl energy.
The idea is to have the duct add additional thrust to that of the prop. A theoretical goal is duct thrust double that of prop for exit diameter same as prop diameter. Proffessor Gus Raspet at Miss. State in the 60s achieved 600 lbs thrust from a 90 hp aircraft engine. 10 hp was siphoned off for inlet BLC. (Ref webs search ASME AV-14 tech report). A two blade prop with modified twist was used. In a 5.5’ inverted airfoil annular shroud. The test units were fabricated wih simple almost garage shop techniques.
The military tested Raspet prototype STOL9, (look up Marvel and Marvellete projects) and met performance specs even though the prototype was under powered and forced to use a poorly designed, gov supplied surplus prop without the important twist mods needed.
There are other areas of interest. One being that many Hovercraft guys use a Hascon or similar multiblade fan costing about 300-400 $ instead of the 2000-3000$ props made by aircraft prop firms. Tey seem to work at least as well as props for their somewhat similarpurposes. One guy in Slovenia recently sent me a youtube video link of his small engined hovercraft pulling up a water skier. (Not slalom)
Powered suction for BLC seems comple and expensive. There may be a way to use the engines poer to do this in a reasonable manner. Not ready to get into this yet and it may not be needed.
Am a believer in scimitar props but have little info on them and winglet props.
These are the priority areas of interest. Want to stick with areas that for now seem to offer the most bang for the buck. Have to be careful not let tech interest override practicality.
I feel proper integration of prop/fan support and bearings will allow close duct clearances.
There are other tweaks that literature suggests would be useful. These are minor compared to the above.

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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Tue Dec 08, 2015 9:29 pm

Uhairball wrote:Hey OF, I agree with you 100%. But I am curious. Why don't aircraft use mufflers? And why don't you hear complaints about them?

They do! And for the reasons I mentioned ..... more torque and lower cylinder temps.
I guess you don't hear complaints because they operate out of airports ..... if you buy a home near an airport you can expect to hear airplanes. Buy some fancy home on a lake in Florida and all those snowbirds expect is 'solitude'. To Hell with who or what was here first ..... nobody cares about that. :slap:
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Re: Would like serious comment on ducted fan airboat experim

Postby Afflicted » Tue Dec 08, 2015 10:29 pm

WBS wrote:
Deano wrote:
WBS wrote: . . . Have some ideas I hope to physically test on small scale. Would like to contact some individuals interested in discussing this subject.
If you gave even a small description of what it is you want to test, and/or what your ideas are, you may very well get more interest and serious participation. Every possibility certainly has not been exhausted by any means, but the comments about re-inventing the wheel and so forth are fitting in some cases because in those instances, the cost/benefit analysis has already shown the attempt as having been very little more than a futile effort, if that.

As Olf Art stated, some folks are after quiet and some others point out, they don't give a ****.
Just about any parameter of what you're looking at will also generate two different camps.

I for one, am more than passively curious. But I have also already spent more time than I care
to admit re-inventing wheels to only arrive at having yet another flat tire that was of no use. :wink:

EDIT: After rereading this, I should point out that I did not mean to minimize or take away from the thoughtful, time consuming replies that a couple other airboat brothers already made. :salute: That wasn't my intent.


Comments welcomed.
Objective: Bench scale initial tests of ducted prop/fan propulsor using wide inlet inverted Clark Y type , example ; goal is 6’-7’ max width, generally rectangular shaped front, tapering smoothly to 5’ diameter circular prop/fan zone, maybe 6” to 11” . Expanding aerodynamically from circular to sharper edged rectangular outlet. Vertical height same through length of duct. The idea is to increase mass flow to try for more thrust on the order of 6 lb/hp in a quieter, safer way.. The shape would look like a short box shaped duct with aero shaped inverted airfoil inlet.
Test items include Vortex Gen inserts that are small metal or polymer shapes, about 3-4 “ size simple aluminum or polymer shapes, spaced over critical flow separation areas in inlet or after prop/fan.t . 3M even makes vortex gen tape for sailplane wings and other uses. Suggest use search engine to view examples. Another item is the use of sheet curved or conical inserts. An industrial application uses two to three inserts in commercial large air duct diffusers, wind tunnels. etc.
Another critical area is the prop or fan twist to increase pitch at outer third gradually to about 6-7 degrees more at tips over prop datum as proven in flight and stationary full size tests.
Simple 5 or so radial blade flow straightening vanes at duct end to recover significant swirl energy.
The idea is to have the duct add additional thrust to that of the prop. A theoretical goal is duct thrust double that of prop for exit diameter same as prop diameter. Proffessor Gus Raspet at Miss. State in the 60s achieved 600 lbs thrust from a 90 hp aircraft engine. 10 hp was siphoned off for inlet BLC. (Ref webs search ASME AV-14 tech report). A two blade prop with modified twist was used. In a 5.5’ inverted airfoil annular shroud. The test units were fabricated wih simple almost garage shop techniques.
The military tested Raspet prototype STOL9, (look up Marvel and Marvellete projects) and met performance specs even though the prototype was under powered and forced to use a poorly designed, gov supplied surplus prop without the important twist mods needed.
There are other areas of interest. One being that many Hovercraft guys use a Hascon or similar multiblade fan costing about 300-400 $ instead of the 2000-3000$ props made by aircraft prop firms. Tey seem to work at least as well as props for their somewhat similarpurposes. One guy in Slovenia recently sent me a youtube video link of his small engined hovercraft pulling up a water skier. (Not slalom)
Powered suction for BLC seems comple and expensive. There may be a way to use the engines poer to do this in a reasonable manner. Not ready to get into this yet and it may not be needed.
Am a believer in scimitar props but have little info on them and winglet props.
These are the priority areas of interest. Want to stick with areas that for now seem to offer the most bang for the buck. Have to be careful not let tech interest override practicality.
I feel proper integration of prop/fan support and bearings will allow close duct clearances.
There are other tweaks that literature suggests would be useful. These are minor compared to the above.



I have no input except that hascon props explode when used in any application other than a hovercraft. They are fans not propellers. Be careful with those things, happens often

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Re: Would like serious comment on ducted fan airboat experim

Postby swamper2 » Wed Dec 09, 2015 6:04 am

Olf Art wrote:
John Fenner wrote:No real reason to reinvent the wheel, the newer engineered props with swept blades and winglets on a properly built boat with a tight powerplant will be supreme to ducted fan technology.

I agree John, but a boat can be made ghostly quiet with a shroud of ductile aluminum around the inside of the prop cage. I don't advance any interest in trying to increase performance with ducting, but I'm all over the idea that an airboat can be as quiet as any other water craft if the owner cares enough to want it to be. I am SO over airboaters that need to run LOUD and PROUD. They're not Harleys, people .... and we've got way too many rich Yankee's buying waterfront property down here now that don't give a damn about our heritage or our traditions. All they want to do is bi*ch about the noise that airboats make.

Would you like for your grandchildren to be able to run an airboat? Quiet yours down.


How wide would you make that shroud Mr. Olf art
16ft alumitech/406sbc/2.38w/3-80in.R's

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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Wed Dec 09, 2015 5:33 pm

swamper2 wrote:How wide would you make that shroud Mr. Olf art

An inexpensive way would be to cut a strip of soft aluminum sheet (softer absorbs more sound) the width of the two hoops on your prop cage, punch the edges, and Ty-rap it around the outside.
Somewhere in the gallery is a picture of a guy who did just that, and folks said his boat was spooky quiet. And that was back before we had the quiet prop technology we have today.

Another quiet technique is to get rid of the flex pipe in your exhaust system ...... solidly mount your mufflers, weld flex-mesh couplers to your headers to allow for a little heat expansion and movement, and then have a good muffler shop bend you a couple of solid pipes to put it all together. Think of flex pipe as perforated pipe. It's noisy stuff and so it wastes torque too.

Quieting a boat is easy, and done properly it doesn't have to cost you a fortune to do it. Until you've done it you probably won't understand, but being able to sit on plane on the St. Johns river at around 2,000 rpm on a 14' Gillieo with a 383 SBC behind you, a 3 blade Sensenich 'Q' prop ...... and no earmuffs ..... talking without shouting? It's amazing how cool that is. It makes you want to run all day.
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Re: Would like serious comment on ducted fan airboat experim

Postby Planeguy » Sun Dec 13, 2015 9:45 am

Uhairball wrote:Hey OF, I agree with you 100%. But I am curious. Why don't aircraft use mufflers? And why don't you hear complaints about them?


Most piston powered aircraft do have mufflers and we get complaints all the time. It has gotten so bad in some places that airports have been forced to close even though the airport was there long before those who made the complaints. Some areas have instituted noise abatement programs where you can only fly during certain times of the day or have to follow weird routing leaving the area and are encouraged to keep your RPM below 2500. Engines are loud but props are generally louder when the tips start flirting with and/or breaking the sound barrier.

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Re: Would like serious comment on ducted fan airboat experim

Postby Olf Art » Sun Dec 13, 2015 9:40 pm

Planeguy wrote: Most piston powered aircraft do have mufflers and we get complaints all the time. It has gotten so bad in some places that airports have been forced to close even though the airport was there long before those who made the complaints. Some areas have instituted noise abatement programs where you can only fly during certain times of the day or have to follow weird routing leaving the area and are encouraged to keep your RPM below 2500. Engines are loud but props are generally louder when the tips start flirting with and/or breaking the sound barrier.

All of that true. I personally think that if a person is buying a piece of real estate in the vicinity of an airport they should be required to sign an agreement that they understand that there will be the sound of air traffic.

Near an air base we used to refer to that as "the sound of Freedom".
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Re: Would like serious comment on ducted fan airboat experim

Postby blow boat » Sun Dec 13, 2015 10:38 pm

Ready to ride wrote:Dude. Really????? Shut up
Vote liberal and move on. No1 is going to buy into this nor do it. Huge waste of your time and mine for even having to comment on this



You,and the likes of you are the reason
I find it hard to spend time on this site
Any more ! Every boat builder out there
Is trying to build a quieter boat, every
Prop builder is trying to build a prop
That is quieter for a reason.If you have been sliding for any amount Of time would know this or should
Know this ,so your words show that you
Know nothing other than running your
Mouth......!


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