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TRIPLE TREE AND PROPELLERS,,,
Guys, just wanted to stop the rumor mill!! For those of us in the Confederate Air Farce who fly at Triple Tree,,there is a restriction on noise. We have to run 3 blades, we have to run cans and we respect the neighbors air space. Anyone who is invited to fly for a day with us has to do the same. Pat is very serious about noise restrictions and we completely agree. I am NOT saying this applies to all the events we host at the facility.
The other facility on Smith road was lost because of noisey planes. This just won't happen at Triple Tree. IMAC contests and the Don Lowe Masters. I know for sure there is a noise restriction on the Masters. I'm assuming IMAC rules about noise apply for the IMAC meet. Stan Stockman is the man to ask. Creating a panick over next weekend's event isn't something we need to do. The three blade and can rule is for CAF members . I'm sure it will be the rule until such time as something quieter comes up. Hence the Capps brothers work on new muffler systems. Pat is very serious about reducing our noise level. To answer some thoughts before they get posted; Yes, it is way out in the country. Yes there are neighbors close by. Yes they enjoy having Triple Tree in Woodruff,,but the noise does affect them. Because that's the way the owner wants it. If I had a facility like Triple Tree and invested 9 years and countless hours/dollars I wouldn't be too keen on stuff that made the neighbors cringe while drinking coffee!! |
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Re: TRIPLE TREE AND PROPELLERS,,,
Speaking of coffee. . . I'll have my famous "minted special" on hand this weekend for your drinking pleasure Biff.
As for 3-blades, etc. being required . .common sense says "Keep it quiet". IMAC rules apply at every Meet. At the Madness this Spring I had to ask a 2-blade pilot to back off the gas a bit. . not a pleasant experience, but necessary. I have to keep MY field going too!!!! I kind of pat myself on the back sometimes because 5 years ago, at TT, I was on the forefront of the "quiet revolution". It's snowballed and gotten bigger and more able ever since then. My congratulations to the TT crew, and Especially Mr. Pat, for helping lead the way on this. |
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Re: TRIPLE TREE AND PROPELLERS,,,
Looks like I need to get to work on some silencers!
What DB level are you guys looking for and at what distance and angles to the airplane? Patty |
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Re: TRIPLE TREE AND PROPELLERS,,,
According to the diagram of how to do the sound test, on the IMAC Site, the limit is 96 dB on grass, and 98 on pavement.
http://www.mini-iac.com/Portals/57ad...gSchematic.pdf When the sound testing criteria was first instituted a few years ago, this was the standard. It was supposed to decrease in the dB level allowed, but this has never been forwarded to a lower level, that I am aware of. The Current F&JG (Flying and Judges Guide) has, in rule 5.1, a stipulation of 96 dB on Grass and 98 dB on pavement. There have been no waivers or changes Officially noted for this event. Go to: http://www.mini-iac.com/DesktopDefault.aspx?tabid=90 and download the top download for the F&JG. Without a deviation or waiver for rule 5.1, the currently stipulated sound levels should apply. |
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Re: TRIPLE TREE AND PROPELLERS,,,
Biff:
Your wish is my command. It took me about 30 minutes to draw this up. I have the header section, main cannister and divergent cone done. I have to go to a meeting right now, but when I get back, I will finish the silencer section. The silencer section will be stackable and you can add as many as needed. See you after lunch. Patty |
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Re: TRIPLE TREE AND PROPELLERS,,,
Could someone send me ID and OD dimensions for the Bud Bottle Cans please?
(we don't have them here in Richmond) I am changing my mind and going with a double wall design. I plan to use the Big Sexy can for the outer and the Bud can for the inner. I want to get the number of machined parts down. I may also spray some lightweight foam in the void between the two walls. I hope it won't melt! Thanx. Patty |
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Re: TRIPLE TREE AND PROPELLERS,,,
Quote:
Foam will do nothing except take up space and then melt when it gets too hot. . The best "muffling" of an exhaust is achieved by allowing a LARGE area for the gasses to expand, and help reduce any pressure pulses (pressure pulses make all the noise). Being able to stretch this expansion out over a long distance helps with keeping the column of exhaust heading away from the exhaust port, whereas a really huge can, right next to the port, will tend to give you reversion back into the chambe and rob some power. Tuning the baffling is easy. . go for 1/4 and 1/2 the exhaust pulse length and place your baffles at those points .. Figure. . Speed of sound (1050 fps. . about) 150 degrees of duration, and 6000 rpm for a good starting point. This would give you a total exhaust pulse length of about 52.5" at 6000 rpm, with baffles at 13" and 26", and at 39" if you wanted to get froggy. The "opening up" from the exhaust header to the Muffler section could be your first "baffle" at 13" from the exhaust port, then a divergent cone with holes in it at 26", a convergent cone at 39" and then another flat baffle with holes in it about 1" from the back wall of the pipe, thence to a 7/8-1" stinger about 6" long. This would effectively dampen your exhaust soundwaves at a Mean RPM point for the engine in flight, as well as secondary and tertiary harmonics. Sine all you are doing is silencing, you do not need divergent cones to increase exhaust scavenging. Diameter would depend on the CC's of the engine .. a 150 would require about 3" of diameter, a 100-110 would require about 2.5-2.75". Here's an idea: Copy the Greve's pipes for the DA-150, then install ACTIVE sound supression with an electronically processed reverse soundwave that attenuates the pressure pulses coming out of the exhaust stinger .. Kind of like the "Quiet Comfort" line of Bose stereo headphones that have active noise reduction to cancel out outside noises and allows the wearer to only hear either silence, or the music that they are playing on the headphones. Basically, you would dump the exhaust from the pipes into a secondary chamber, then disperse it out several ventilated exhaust tips surrounding a speaker that gives 180 degree out of phase pressure pulses at the same frequency as the exhaust. The Speaker would be moving one way, the exhaust the other,and the noise from both effectively cancels the other. A small 4-5" speaker would be all that is necessary to effectively remove 10-15 dB of "exhaust sound" from an engine, with this sort of system. It would not be totally silent, but it would sure be a lot quieter. |
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Re: TRIPLE TREE AND PROPELLERS,,,
Kris:
Thanx. An electronic inversion sine wave would work great! Patty |
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Re: TRIPLE TREE AND PROPELLERS,,,
Pale, Kris,
I like to think brilliant minds think alike as I spent half the damned day dreaming about this anti noise vs noise thing. Bose as you say Kris have hit it on the head, Heres the problem with that scenario to a guy who twists bolts and only knows that enough volts and amps can kill. Other than that you cant see the stuff so technically it dont exist. To provide enough amplification to cancel out the noise created by the engine alone is going to require some serious juice. I mean sound from an engine is a result of expended energy. To make a counter sound sufficient to cancel out the generated noise will take an equal amount of energy. Am I right or wrong here. Ok so maybe 33% of the energy of an engine escapes as noise, Thats a fair assumption I think. A DA150 produces say 15 Hp max. That means we need 5 Hp to generate the anti noise, that equates to 3730 watts of power required to equal the energy we are trying to cancel. Assume we are using an 11.1 volt battery then the darling sound system will require 3500 MaH batteries to acheive a ten minute flight with no noise except for that mongrel prop. We need another 3500 Mah approximately to kill the prop. So we now have a 7500 Mah battery on board to just kill the noise. Surely we can can reduce that by 50% if we go electric. If we can get a 50% reduction (theoretical but definitely not true) then we are at minus 50 Db without going any further. We have a silent power systen available today, we just need mass produced motors and batteries at a decent price and the noise issue is a red herring. Come on Mr Hacker. I want to see QQ or Jason win the Don Lowe or the Shootout with electric or even turbine power. AH I love the debates Kris. Bring it on mate. Kiwi |
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Re: TRIPLE TREE AND PROPELLERS,,,
Kiwi:
Very nice dissertation. Thanks for your perspective. Back in the day, we ran the exhaust through a labyrinthe. The Labyrinthe was made by sectioning off the inside of the fuse and coating the walls with polyester resin epoxy. The exhaust note was just a whisper by the time it came out the tailpipe. The romance of gasoline-internal combustion engines runs high with me. I also belong to an antique farm machinery club, but I see the writing on the wall for model airplanes. Will they ever completely go away? I hope not. I love the sound of a PAW diesel brumping around the field, or the shrill whine of a K&B torpedo whipped up on the speed circle. I think I need to go get a glass of perspective and soda. Patrick |
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Re: TRIPLE TREE AND PROPELLERS,,,
Patrick.
Now for reality. I love my 325 Hp Cummins powered Dodge. Its getting the Bullydog treatment soon. 100cc twins and better on muffs and rippin props sounds great and reminds me of the car racing days. Power and the sound of power still turns me on. Unfortunately we now live in an intolerant society that has no place for leisure or pleasure if it somehow contaminates an environment. But its very selective. I dont hear anyone demanding the coal trains stop blowing the horn all day and all night at every other level crossing in the USA. I am sure the average non RC person has no idea what it feels like to be told your still too noisy when you just dumped 300 Euros on the latest German cannister setup and now the prop is ripping a fraction more than before. Guys, Pats quest for silence at Triple Tree is truly admiarable and a worthy stance. I agree so much with what he is trying to do. Thats why I think electrics will be the next big leap in 35% and 40% planes. The technology exists, the motors are not too far off being cheap but the batteries are still a rort. Its like 42 inch plasma TV's. Today they cost 1000 bucks max, they were 3000 to 4000 when they entered the market. The same wil happen with big LiPo packs once the demand is here. Then Kris we can sleep in at the Nall without the early morning competition to be the first to rip a prop on takeoff at first light. You know it's still a nice noise to wake up to just the same. Kiwi |
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