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Old Nov 20, 2012, 12:01 PM
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United States, WI, Slinger
Joined Mar 2006
544 Posts
Question
Cox .049 Sound Level

Anyone have an idea what the sound level of a Cox .049 would be, reed valve to TD? I'm planning on scratch building several of the models popular when I got into RC years ago and am toying with the idea of doing at least one of them with a period engine. Most will certainly be electric but I still have a fondness for the buzzy little buggers, despite their shortcomings.

Problem is I fly at a field that has a strict 94dB limit. I recently sold my big one, a 1/3 scale 50cc Sig Spacewalker, partly because it was just too much of a hassle hauling it around, but mainly because it was too loud. It was checked at 100dB so it was WAY over the limit and I didn't want to mess around with trying to make it quiet enough to fly there.

I have a fairly large collection of Cox engines from the TD .010 all the way up to TD and Medallion .15's. I have a few different mufflers for the .049's but as I recall from a few years ago they don't make a tremendous difference.



Mike
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Old Nov 20, 2012, 12:39 PM
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Canada, ON, Cottam
Joined Jan 2012
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I think my TD .049 measured around 90 db at 15 ft. A B Bee would be less. There are free APP's for db meters if you have a cell phone. Someone at the field will usually have one if you don't. There are mufflers available too, but they suck power. I think the .15 will go way over without a muffler. Props make a difference too. A 5-3 will be louder than a 7-3.
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Old Nov 20, 2012, 01:07 PM
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United States, WI, Slinger
Joined Mar 2006
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The spec is 94dB @ 9 feet. I'll probably have to check it out for myself to be sure. I believe our sound level meter is kept locked up at the field and if not I'll have to check out the App. I'd rather not end up going to all the trouble to put something together with a Cox engine on it only to have to swap it out for electric after the fact. Especially since I don't need to worry about a fuel proof finish for electric. I live in an apartment so working with noxious solvent based paint is a problem.

Yeah, I would imagine the .15 or even .09 would be way more than an .049 and I am aware that mufllers don't work well at all on any engine using sub induction so that leaves out the possibility of a muffled TD.
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Old Nov 20, 2012, 09:13 PM
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Canada
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I found that the rotating throttle sleeve type throttle make a genuine noise difference, on a reedy at least. Mufflers do work.. some.. just that they reduce power so many find that unacceptable Don't be forgetting that Nitro content increases noise significantly as well.
Try a Cox on No Nitro fuel for a noise surprise. The grating scream isn't there, v nice. Add a muffler and noise is no longer an issue.
But power is down somewhat. Less than I had once thought it would be, but still reduced..
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Old Nov 20, 2012, 09:13 PM
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United States, VA, Forest
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Holy cow, I may be missing the boat, but a TD 051 turning 21,000 rpms is deafening. Have a hard time thinking it would make the DB limit????? I have never put a meter on one, but I have not heard any other motors with mufflers louder and I have heard of them not passing the DB limit. Good luck and please let us know what you find out. Get rpms as well.

John
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Old Nov 20, 2012, 09:17 PM
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United States, CA, Brentwood
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Just a guess, 108db at 9ft.
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Old Nov 21, 2012, 11:29 AM
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United States, WI, Slinger
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Quote:
Originally Posted by Bare View Post
Don't be forgetting that Nitro content increases noise significantly as well.
Try a Cox on No Nitro fuel for a noise surprise. The grating scream isn't there, v nice. Add a muffler and noise is no longer an issue.
But power is down somewhat. Less than I had once thought it would be, but still reduced..
Yes I am aware that nitro does make an engine louder. The problem I see is if I were to run low or no nitro, especially if combined with a muffler, will greatly reduce the power level. Plus low/no nitro often makes for a tricky to set needle, especially on the small Cox engines.

I'll probably just say to heck with it and just go with electric. I'm thinking about doing some glow free flight. There's a nearby club that flies free flight, the Bong Eagles. One of the sites they fly at is Bong Recreation Area and there noise shouldn't be a problem. I fly High Power rockets there and they're loud!



Mike
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Old Nov 22, 2012, 12:02 AM
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Neenah, Wisconsin, United States
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I think the TD 049/051 is the loudest of them all as I have run a TD 15 special MkII and it did not seem as loud as the TD 049 pulling 20k on a cox grey 5x3 prop. I think pitch has everything to do with it being louder.

The Cox geared twin Golden Bee I have has some bark to it.

Cox Geared Twin using Golden Bees (2 min 28 sec)
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Old Nov 22, 2012, 06:31 AM
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Hi,

We have the same problem here, still looking for a cox dragonfly to measure and confirm that its legal to fly here. ( below 94db @ 3 meter )

I'm going to test run and measure thrust, rpm and sound level etc, for killer bee (donated from a nice gentleman ) . still waiting for the parcel to arrive here. I will post it on my coming web page soon, will share with you all later.
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Old Nov 22, 2012, 11:18 AM
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Western KY
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I've read that the .049's are actually quieter than the larger engines, but the pitch generated by the higher RPM's leaves the impression that they're louder.
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Old Nov 22, 2012, 12:15 PM
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United States, SC, Columbia
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Quote:
Originally Posted by Andrew0820 View Post
I've read that the .049's are actually quieter than the larger engines, but the pitch generated by the higher RPM's leaves the impression that they're louder.
EDIT: (I stand corrected) High pitch sound travels a shorter distance.

Is there any freeware pitch meter for a desktop PC?
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Last edited by RknRusty; Nov 23, 2012 at 07:00 PM. Reason: Changed incorrect statement
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Old Nov 23, 2012, 04:02 AM
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Large gas engines are the worst in the air I think. I sure can't hear my own (1/2a) engines when they are up. I think lower frequencies travel further, while a cox engine has a more annoying sound that only a mother can love...

There are other engines that have mufflers and a far more quiet than a cox engine. The TT07GP for instance has a proper muffler and is fairly quiet in its stock version.
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Old Nov 23, 2012, 05:14 AM
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Yes, lower frequency means longer wavelength, and travel further. Elephants can communicate miles away using sub- sonic lower frequency. We fly 1/2A planes not far away as bigger planes do, thats why cox engine has a more annoying sound






Quote:
Originally Posted by surfer_kris View Post
Large gas engines are the worst in the air I think. I sure can't hear my own (1/2a) engines when they are up. I think lower frequencies travel further, while a cox engine has a more annoying sound that only a mother can love...

There are other engines that have mufflers and a far more quiet than a cox engine. The TT07GP for instance has a proper muffler and is fairly quiet in its stock version.
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Old Nov 23, 2012, 04:09 PM
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Wilson NC 27896
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Quote(The Cox geared twin Golden Bee I have has some bark to it.)

Thats MUSIC to my ears!!!......Gene
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Old Nov 26, 2012, 05:56 PM
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The nice thing about the small planes is that they don't HAVE to be flown at the club field. I think you should make at least one of your planes with a 1/2a. I recently completed a .010 Pageboy and the wow factor at the field was impressive. Now I have a Guillow's 27" Zero (new laser cut version) that is going to get a TD .020. I just love the sound of these small motors.

Tim
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