kochj

I have ran mine with the wings off, but you have to grap onto the wing tube, and hold it....
This takes the place of the wings... If I didn't, it would be in big trouble....

I thik you could get away with it when running WOT....but not at the lower throttle settings
and not for long even at WOT......

good info. But very surprised that in would cost 100k to make a isolation mount that works well....
Not saying it isn't true, it just seems crazzy....

Tired Old Man

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The engineering involved to produce an effective isolation mount is extreme. A couple of rubber grommets on a firewall do little more than reduce the noise generated by the vibratory effects on the fuselage. There's a tremendous difference between a REAL isolation mount and a cheap sales gimmick.

A true mount will have been subjected to a great deal of engineering and testing. There will also be a lot of various material choices involving components that work best when mated to other components. Fasteners become considerably different from whan one might normally consider for use. Then you have the interaction of the engine to the mount to the airframe and how all of that impacts engine controls.

If you work for $2.00 an hour, wrote your own CAD program, have your own CNC unit in your garage, and are adept at molding various rubber/urethane/composite components with a high level of consistency and accuracy you might be able to do it for a little less. That's just for a version for a tiny gas engine. Costs go up as engine size increases.

About the cheapest one someone might do would be similar to the Lord mounts found on full scale planes. But all that engineering has been done for them already, and based around a four stroke engine.

on_your_six

My Feedback: (11)

I thing the OP should know about Hyde mounts... this guy has been doing vibration mounts for a while.

[link=http://centralhobbies.com/Engines/mounts/hydmnts.html]http://centralhobbies.com/Engines/mounts/hydmnts.html[/link]

Merle Hyde is a good guy.. give him a call and see if he can help you out. The 50cc mount was not that outrageous as I recall. You will have additional work on the firewall as models do not anticipate this.

SJN

Mmmmmm

[youtube]http://www.youtube.com/watch?v=Mm3wPzdG8BM[/youtube]

Tired Old Man

My Feedback: (1)

Looks like that mount is doing a great job..... It's not really isolated but a very little.

Check the nose oscillations at medium RPM, then multiply by a factor of 4 for a 50cc gas engine. My hard mounted 50cc and 116cc planes don't shake as much as the one in the video.

All Day Dan

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Thank you Sonnich. That is exactly the results we have seen at my field. It has got to hurt something. Dan.

cuwaert

Hi all,


Everybody knows the pounding and shaking of high power extra light single-cil's in
extra light body 3d cells and wonders the damage that might be done to servo's
hinges, receiver...you name it.
You can just take it as it is and bolt your powerhouse firmly to the firewall, do some
other things you saw or read on the internet and bolt it back in place when it vibrates loose.
If your neighbours complain, they probably will complain anyway.
Take care electronics don't touch the cell directly and it will hold quite good, for that part .
Or you have heard a properly dampened engine run and fly and fell in love with the
quiteness and pleasantness of flying with the sound of a sawing machine.

OK there's 'as far as I know' one guy who pretty much got on top of this problem and he's called
Toni Clark.
The idea can be read on his website but it's basically something like this.
Concentrate mass of powerunit as close and as sturdy to the engine as possible. Put the engine/exhaust
on soft mounts and dampen the heavy torquemovements on iddle by shock absorbers.

Clark tries to make a solid block of engine and exhaust and softmounts this kombination to the firewall.

I think this is the most easy way to make your plane sound cute , if you have the structural room for it.

jedijody

My Feedback: (1)

I don't want my plane to sound .....cute. [&:]

cuwaert

My club neighbours do

Yes I suppose it's more a must where I live than it is in less dense populated countries, so maybe there has been
a lot more "engineering put into it" here.
And as in many cases, what you don't master yet seems to be extremely difficult and once you get the hang of it
it seems very difficult to believe you once didn't.

pe reivers

The TC system works on his scale birds and other "heavier" or well dampened constructions, using a muffler bolted firmly to the engine half of the vibratory system. It needs hydraulic dampers to keep the max amplitude of the engine in check, and it will not allow very low engine rpm. No problem for TC, because most of his engines are fitted on a belt reduction gear.
As the seismic mass of the plane gets less and less, the TC system fails to do it's job. Also, if extra power is extracted from the engine by using canisters or tuned pipes, the TC system fails to work properly and engine components start to act up (even fail).
The TC system surely is not a solve-all.

Tired Old Man

My Feedback: (1)

Pe,

I use an extremely effective iso mount for specific applications and know how well the can work, but also recognize how similar engineering just can't transfer to a model. A modeler might be able to eliminate a small amount of the airframe resonance with some simplistic components but they really would not be doing much in the way of vibration isolation. The mount in the video shows a little of the orbital effects of a running two stroke engine on an iso mount but not being very effective does not come close to illustrating the true amplitude of an extremely effective mount. There is no comparison to what occurs when using a gas two stroke. The issues are orders of magnitude greater.

The point I have been trying to make is that if people want a truly effective isolation mount they will need to do everything from the firewall forward very much differently that anything they have yet to see. Then again, if they have a real concern about noise they need to address the prop since that's the greatest noise generator on a plane. It's not the exhaust that causes grief with the neighbors.

pe reivers

That is very much true. (both vibrationwise, and prop noise wise) While still professionally active, for my firm I have initiated the use of a "shaker" to test automotive body parts. Part of the job was analizing tertz frequency waterfall diagrams taken on several part locations. Very frustrating at times.
Knowing the matter's complexity however does not keep me from using simple solutions like wellnut mounts. They prevent high frequency vibration from passing through the firewall, but do nothing to block lower frequency oscillations. To that end I sometimes use active dampers (small OIL/leadshot filled cartidges) in critical locations on the airplane. The hard part is finding the vibration bellies and nodes for their placement.

BTW, good luck with your new twin engine. Steve told me.

TimBle

Wood is a wonderful natural attenuator of noise and vibration. Where possible I try to build a wood mount for the engine. For petrol engines, standoffs mounted onto the firewall seems to work best.
'many of the anto vibration mounts are doing one simlple thing -  adding mass.
the rubber is usually showboating so you think its damping. the real attenuatio n is the extra mass they add to the model

Tired Old Man

My Feedback: (1)

Thanks Pe!

pe reivers

No, the added mass of iso mounts is not equivalent to the added mass of i.e. extra steel washers concerning vibration damping. Added mass provides no damping at all. It just reduces the vibratory deflection and resonant frequencies.
Some woods have damping properties, others don't., all depending on the woods springiness.

BTW, what is meant by "showboating"? Pls explain.

Revy

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You guys need this from Blazing Star...

All Day Dan

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Thank you Revy and Blazing Star. The engine and muffler are vibrating at their own frequency and displacement and the fuselage at another. If you rigidly connect the two, you would probably crack something around the engine and muffler. The reason Blazing Star’s strap hasn’t broken something is because it is so thin and flexible and probably isn’t providing any support to the muffler. The best thing to do is to strap the muffler to then engine. Dan.

Revy

My Feedback: (1)

You know, I asked about that when I did it and nobody chimed in that way. The mount is Blazing Star, the strap was my McGyver job. BTW , FWIW, since its been on for the past two seasons, I have had NO issues with loose bolts or cracked mufflercomponents.

Juker008

Does Blazing Star have their own site?Ican't seem to find it. Can someone post a link to more info.

Tired Old Man

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Blazing Star can be reached here: [link]http://mailto:[email protected][/link]

He goes by the handle "GravyGoodness at the big airplane site, TFC.

Revy;

Dan is right. Move the muffler strap to the lower left engine mount in order to tie the muffler to an object with the same vibration frequency. For now all that is happeneing is the screw going into the wood tearing a constantly growing hole in the engine box, with the underside of the strap compressing/fretting the wood.

TimBle

showboating: nothing to do with aquatic exhibitions. English slang for looking impressive but not doing anything of substance.

Revy

My Feedback: (1)

TOM and Dan, thanks for the heads up...where were you two when I did that in the first place!  

Tired Old Man

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You didn't ask

I hang a little here in the engine forum, but of late have a thread going in the Giant Scale and 3d forum here with a Pilot 37% Edge. The majority of the time I send at another site.

pe reivers

Here is a solution that is popular with the RC3 aerobatics crowd.

Juker008

I kinda like that, although I'm suprised that you haven't posted a pic of a gasser on hydraulic mounts .