Os gt 33
01-01-2015, 07:58 AM
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Os gt 33
Has anyone got noise figures for the OS GT 33 using the supplied silencer? Would be happy to go to 20 * 10 prop if necessary. My club has a strict 82 db at 7 metres model held up to waist level and all 4 aspects. Would be grateful for any comments as would like to use this engine in a model.
01-05-2015, 12:48 PM
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I own one; no db figures but in comparison to any other stock muffler gasser I have or have heard, it is much quieter. I would equate the sound to a large glow engine with stock muffler. I ran a Xoar 20x6 beechwood on mine for a while; it would rip the prop a bit on wide open level passes--that was the loudest part of the noise footprint. I've switched to a Falcon 20x7 carbon, which dropped rpm from 7700+ to about 7300--only a little rip on a diving pass now. Do a search for member MTK on here; he did quite a bit of work on a piped setup for the OS33, but I can't recall if he checked noise with the stock muffler...
01-05-2015, 01:23 PM
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Here's a link to a vid with Joe Smith on a 71" Slick/OS33 with stock muffler. According to the comments, he was running a Falcon 18x9. It sounds similar to mine on the 20x6 Xoar; some prop rip, but if you listen, the muffler is quite effective. Not sure what you'll be putting it in, but if you're not looking for max thrust, a 20x8 would probably all right. I think a 20x10 would load it too much, and put it well under 7000 rpm, possibly overheating the engine as well...
https://www.youtube.com/watch?v=R8YA0bwLaBw
https://www.youtube.com/watch?v=R8YA0bwLaBw
01-06-2015, 11:07 AM
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Thanks for replying to my question. I am hoping to put the engine in an ARTF 81" DH Chipmunk and so out and out power would not be a requirement, but the use of a can would not be possible. Hence the hope that the supplied silencer would be OK. We have found during noise testing that lower RPM = less noise and so the thought of over propping the engine. Max RPM could be turned down at the tx, but we are very aware that noise could cost us our site.
01-06-2015, 12:25 PM
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I ran the APC 20.5x10 all summer with the hatori canister. It turned around 68-6900 and power was very good on a 11 lb plane. In the air it was very quiet, what it db'd at, I have no idea. 82 seems pretty low to me. A soft mount would help quiet it down also.
