MTK

This reminds of a fairly recent discovery when bench running my M38 last year. I didn't have a soft mount ready yet so I installed it on a hard mount and then put that outside on my porch's post where I do all of my bench running. The post is a 6"x6" treated lumber and extends from the ground (it's a foundation post for my porch) to belly height above the deck. It is obviously tied to the deck

Anyway, once I had the engine going I had an intense buzzing sensation (high frequency) on the soles of my feet. There is an awful lot of wood in the way, yet the vibration was quite intense. This is exactly the kind of vibration that is transmitted to an airframe when there is no isolation. Is it harmful? Probably but since I don't hard mount any of these engines on airframes, I will never know

I repeated the run after the isolation mount was installed...... Vibration transmission to the deck was nonexistent.

The type of mount I use and recommend is the Hyde style, rubber isolation mount. The front of the mount accepts the engine while the back is mounted to the firewall. Front and back are connected to one another via a rubber motorcycle inner tube. Over the years I've tried other, simpler mounts available commercially; they produced unsatisfactory results for isolating vibration. I didn't invent the mount; Merle Hyde did. I re-engineered it to accept stand offs

earlwb

Years ago, I used to use the Dubro isolation motor mounts a lot. They seemed to work quite well too. It was cool watching the engine at idle jiggling all around too. I don't know, I sort of got lazy and haven't used them too much since then though. But then it is tricky getting them installed in some planes, so I fell out of the practice of using them more.

eddieC

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Mtk,

hsukaria

What the OP is using is a very flexible mount that is supplied with the Seagull and Phoenix ARFs. They are nylon, but not the fiber-reinforced black colored mounts that Great Planes, Horizon, and other brands have. The fiber-reinforced mounts are fairly stiff. The nylon ones from Seagull and Phoenix flex quite a bit if you push up and down on the prop/spinner (when the engine is not running, of course). The first time I was exposed to one is when I was breaking in an OS 70 Surpass (4-stroke). The engine had to run super rich at first with severe vibration. The engine mount flexed so much that I thought that something broke. But as time went on (I guess I am not as consciencious as the OP), the engine smoothed out and the flexing abated. I have 2 other ARFs with those mounts, but I am running 2-stroke glow engines with no issues.

Maybe these mounts would help if an engine is vibrating a lot, but for normal use, they are not the same as rubber-isolated mounts. You could think of them as the fiber-reinforced mounts from a vibration isolation point of view. Maybe they are better for crashes?

oliveDrab

An electric motor will cause alot less vibration/flexing.

MTK

No ax to grind....Don't know where you get this crap... If you spent a moment to search you would see that everything I've post is regarding helping my fellow modelers. No reason to get you a link; it's something you can easily look up. Does this make me unhelpful or you lazy?

hsukaria

Fellas, Fellas, we should be out flying instead of mis-communicating...

eddieC

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MTK:
LOL! Really?  Arrogance, party of one, your table's ready..    I'm not 'searching' for anything, especially from one with such a 'know-it-all' approach, so hop off the high horse.

While commercial soft mounts may not work for everyone, to characterize them as 'junk' indicates a simplistic and prejudiced attitude. How do you account for their sustained popularity? I've had great success with them.

Are you  an engineer or vibration specialist?  It just so happens my flying bud's wife works in that field, and she and her coworkers have helped him dial in his pattern planes' soft mounts. So thanks, but I'll stick with quality info from actual experts. They're pretty humble too, BTW. 

IronZ

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Hahaha! That actually made me laugh!

Rocketman_

I use those black fiber filled nylon engine mounts almost exclusively for beam mounted engines and have never found them to be troublesome. But, I guess that's just one man's experience.

ahicks

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Thinkin that would be 2.....

IronZ

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The local hobby shop didn't have the aluminum mount, so I went with the Great Planes adjustable mount. I had to hack out the center, but it should be fine. Pretty much like any other two piece mount. There is a definite difference in this mount and the 'plastic' mount that came with the Ultimate. I'm pretty confident my 'flex' will not return.

Thanks again for all the input!

Z

ahicks

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Hey, Great question! Thanks for bringing it up! Best of luck on the new install. Let us know what you see when done. -Al