when mounting a gas engine what can be done to cut down on vibration.

same things as a glow engine, except, that the gas engines vibrate less than glow engines because they have a better controlled ignition and lower compression ratio. Gas engines also tend to run at lower rpm.
Balance props well, take care of proper prop track, use iso-mounts if need be.

Could you show me an example of an iso mount and where to get 'em?

First pic is the MVVS mount the second pic is one I made myself out of MVVS parts.

Mike

Have you done any tests to determine if it actually works? I am not challenging you. I'm just curious.
I can't find anyone that has conducted tests. Even manfacturers.

Quote from MVVS thread 10 April 2007:

"Pe
You may remember I bought the MVVS isolation mounts from you some time ago, well I have now unsed them in my 2M Extra and can report that far from the popular belief that iso mounts increase vibration these are so efffective a pal of mine who is also a petrol head could not belive the lack of vibration in this instalation, In a normal hard installation the tail or wings will vibrate up and down at tick over and only smooth out when you advance the throttal, in this case the plane is smooth all through the rev range and just sits still at tick over with no vibration noticable at all, obviously the work done installing the anti vibration mounts was very worth while, none of the screws used to mount the cannopy, cowl or anything else have moved thoughout any flight, My pal was so inpresed he did not stop going on about it all day, he is now a convert."

They also reduce noise, I did start a noise reduction thread on the gas forum, but no one was interested, but for interest the difference between a Brison warp around and an MTW 75 was 7Db that is a big reduction.

MIke

In some situations you can tune most of it out, I found this out because the low end on one of my gasser's was very rough, after leaning out the low end needle there is minimal vibration now.

Mike, this is the technical side of the coin, do not expect many responses here. Where it hurts, is that sometimes models are not allowed to fly just because they are 2dB too loud. 1 dB is still considered twilight zone, and (just barely) accepted by those who know what they talk about. Nazi type field marshalls are NOT in this league.

BTW folks, and all bitter jest aside:
dB are calculated on a logarithmic scale so:
1dB is what a TRAINED ear can hear
3dB is double noice perception
10 dB is tenfold (10^1)
20 dB is 100-fold (10^2) of noise perception.
There is much more to it, but I do not want to confuse with knowledge littering. This is as KISS as I dare to go.

So the 7 dB reported by Mike is a VERY VERY LARGE noise reduction, just by using the MVVS iso mounts. Beyond that, you need to attend to airframe resonance, prop noise etc. It is the hardest noise that blankets the lower ones. Once addressed, another one pops up it's ugly head and shouts: "see to me"first!!.

Engine vibe isolation effectiveness depends a lot of airframe mass, and stabilasation by the wing (like a taut rope dancer). Large scale planes, with much frame and wing mass will not notice it much, but 3D planes will. (the engine is bolted to a seismic mass) (OK, this is not KISS, but a little advanced)

Pe

I have come to realise that trying to get some people to think about noise pollution is like either of the below.

Mike

I gotta try this sometime. I hate it when my plane shakes apart...

Mike, I do have three lovely donkeys in my back yard meadow.
They give me what they want to give, and teach me not to ask the impossible. VVBG

>They give me what they want to give, and teach me not to ask the impossible. VVBG

Is that silly critter trying to eat the truck bed? How quaint...

Are the B&B Vibra-Loc engine mounts similar to the MVVS isolation mounts?

--Bill

This may be off thread a bit but in the last year I have taken my noise deadened ears and gone electric. I don't have to worry about this anymore. Now if I can just figure out how to wipe those burned out electrons off my airplane -

Did you get into A123 power for your electrics yet?
That is another big step up.

Yes. I don't want to have lipoly's around. I have a friend that lost his garage and all of his airplanes.
I am not having a lot of success. I don't seem to get the results I read about from some people or that the spread sheets predict. The cells I have, I got out of a Dewalt pack about a year ago. I have ruined three of them.
I am trying to fly big airplanes - not foamies.
I converted a 62" Lazy Ace with 7s1p cells and a Scorpion 4025. I got some good flights with a 19-10 apc but they only lasted about 2 minutes.
I bought a Nitroplanes 80" Extra and put in 10s2p cells ( I bought some new Dewalt packs. Hopefully these are better) with a Hacker 60M (215kv) turning a 20x10 prop. Ground tests indicate 10 minutes flight with 85% throttle. We will see.
It wound up 37oz/sq ft wing loading and I am afraid to fly it. I can probably fly it OK but the landing will give me trouble. I usually fly biplanes. I am going to get Bernie Boland to fly it for me if I can get out to the field when he is there.

dirtybird,

A biplane with a wing loading of 37 ozs? Not a problem, just keep up the airspeed on final approach and don't try to dead stick it.

Elson

Old or new cells - the same on these - On the lazy ace-you were likely overproping em- - about a total draw on that 7 cell setup -full power -would be - say 50-60 amps
cruise - much much less-
I use 5 cells and a 14x7 prop and pull 50 max and cruise -I would bet -is about 25 amps on my Daimante which is a vto type model
The Extra is no featherweight but should be OK
I am an old fart - so I keep wingloadings DOWN - makes everything much easier andI LIKE easy

Are the B&B Vibra-Loc engine mounts similar to the MVVS isolation mounts?

--Bill

The MVVS mounts look like the pic below, I have no idea about the BB Vibra-Loc though.

Mike

I bet I am older than you. 81 in April.
I started with a 18x8 and 6s1p battery on the Lazy Ace. It is 22 oz/sq ft. It flew but is better with a 19x10. I added a cell and tried a 17 x10 and that didn't work at all. I need more cells but I am voltage limited by the ESC. A problem is the cells are 3.6V no load and drop to 2.6 under load. I need a 50 amp regulator. I wonder what that would cost.
Bernie flew the Extra this morning and it seemed to fly OK but he complained it was snappy.

What has this to do with vibration chaps? can we get back to the thread please.

Mike

OK;

I have read this entire thread and looked closely at the photos of the MVVS frame.

I like the concept and understand what is being done... BUT in the end all that I see is four Rubber Grommets used to isolate the engine from the airframe and dampen the vibration.

Hey if it works, I'm all for it... but I have a DA 50 mounted on 2.5" Stand offs how would you consider reducing the vibration in this situation?

Use a "HydeSoftMount" & be done with it---FWIW these are now being used by the UAV industry---

The MVVS is an integrated mounting system, whereas the B&B is an add-on rubber bushing. Photo attached.

It may be do-able. I have a Brison 4.8 Twin that I'd like to use it with, and as fate would have it, the spacing between two of the mounting bolts is 78mm ( the same as on the MVVS bracket). Are the MVVS mounts available thru a USA dealer, or should I ping Pe R?


As far as I know, the Hyde mounts are made only for the "YS" type of 4-stroke glo engines. Are the now available for gas engines?

--Bill

Yes, they are, Bill---He will custom/build for most any application---I use them on my 100cc twin & down---No more cracked cowlings-canopies-etc.---I'm a "Happy/Camper"---