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Sound level and fuselage/wing resonance

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Sound level and fuselage/wing resonance

Old 06-22-2015, 09:01 AM
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JPMacG
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Default Sound level and fuselage/wing resonance

I'd like to hear what others are doing to isolate their glow engines from their air frames. The fuselage and wings of one of my airplanes seems to be resonating with the engine and contributing to the overall sound level.

Dubro makes vibration isolating engine mounts. I know that is one option. Are there other methods?

And no, I am not interested in going electric.
Old 06-22-2015, 09:09 AM
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Gtarling
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A couple of chaps in my club had a similar problem and found that stuffing cheap (poundland/dollar store) sponges, or bits of sponge, into every vacant space in the fuselage made a huge difference.
Old 06-22-2015, 05:20 PM
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Gray Beard
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I really wish I had more info but I think this is just a hard Neoprene?? It's the same stuff used in a couple of my old style anti vibe mounts. Someone left a big bunch of it at my wood workers club after cutting it up into pieces this size. I had built a Cub for a friends and his .91 four stroke required to be moved out farther from the fire wall to fit his really nice after market cowl so I put some of this on the fire wall then mounted the motor mount. It turned out to be the smoothest running four stroke I have ever seen.
Thing is I have never had a hard vibrating engine, two or four stroke. I'm also a stinker about prop balancing. I have a number of anti Vibe mounts but I almost never use them. I use more of the nylon Tower adjustable mounts then anything.
I did built a very nice CG Extra with a YS 1.40 for a friend and he asked me to use a good Anti Vibe mount so I gave the JTEC mount a try. A bit harder to use but talk about smooth!!!
For the most part vibration is just the prop out of balance and the tune not being correct. I found the DuBro balancer more useful then the Anti Vibe mounts.
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Old 06-22-2015, 08:17 PM
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jester_s1
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The only vibration that should be coming from your engine is from the torque pulses. A Hyde mount is meant to dampen those. You can buy one, or you can make your own.

http://www.ofremmi.info/HowTo/Hyde-mount/HydeMount.htm
Old 06-23-2015, 04:25 AM
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I think most engine noise is prop noise. If you're too noisey try a 3 blade prop or go with carbon fiber.
some brands of props are quieter than others. In the gass word Zoar 2 blade wood is not quiet.
Old 06-23-2015, 05:25 PM
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JPMacG
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Thanks everyone. That is good information.

I balance my props carefully using a Dubro balancer. I think I have them about as perfect as I can. I don't know about the spinner. It is a Tru-Turn, so I think it is good. I don't know how to check or balance the the spinner.

I can tell that the airframe is contributing to the noise level because I can put my hand on the wing covering and the sound level gets quieter. Its like the monokote is acting as a drum head.
I'll look into the neoprene and Hyde mounts. Stuffing the wing panels with something soft and spongy might work.
Old 06-23-2015, 08:49 PM
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Never had a glow plane do anything like you have described, did have a scratch built giant with a gas engine that had the stab bouncing like a BEE BEE in a box car at idle but that was just a combo of design and the engine used.
I don't use Mono, in plastic covering it is either Ultra or the Chinakote. It could just be the covering isn't tight enough or some odd thing like that?? Good luck with it.
Old 06-24-2015, 07:52 AM
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Balanced or not some props are noisier than others. Take a heat gun to the covering and try a different brand prop. You'll be amazed

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