Hello:

     There seems to be very little interest in dampening engine vibrations in our model airplanes.  Perhaps I am looking for an answer for which there is no question.

      I have considered placing some type of soft material, rubber, between the engine lugs and the engine mounts to help stop the engine vibrations from transferring to the airplane and fuel tank.  I have seen fuel tanks with foam rubber attached to the mounting surface of the tank to help supress the tendency for fuel foaming due to engine vibration.  Why not also insulate the engine to help eliminate vibration?

     I am going to modify a profile airplane to see if I can reduce the engine vibrations.  Perhaps a piece of "soft" rubber between the engine and the mounts may help.  I will not know until I ty it.

    Has anybody attempted to do this and if so how did you do it and what were your results?

    Opinions?

                                                                                                                         Stay well,

                                                                                                                         Frank

Yes there have been 100s of people do this, most use a "soft mount" system, there are even soft mount hardware you can buy.
My VECTRA  Dreadnought use a soft mount I designed and ran very smooth, the plane is 24 years old and has no cracks from vibration, the controls are still good also, one reason for this was the soft mount, it also helps the plane to be quieter.
Simple way to do this on a profile is to use a RC type mount with rubber encased threaded mounts or use rubber standoffs

   Unfortunately, and will all due respect to their advocates, soft mounts are pretty notorious for causing uneven or inconsistent runs, too. In nearly every case, with a precious few exceptions as far as I have seen. David's PA51 example was typical, soft mount, and a new engine. He and we tried every type of engine adjustment, isolated the tank and the fuel filter, the fuel lines changed the stiffness of the rubber grommets, etc all over the place. All sorts of different engine settings, compression, pipe length, fuel and air filters, etc. Finally, put aluminum spools where the rubber went, and within 1/4 lap of takeoff it was clear that it was solved, and the engine ran perfectly.  And this is just an example of something that I have seen repeated many times. And the 51 is not known as a real shaker, certainly not as much as the 61/65/75

     If you really know what you are doing, and want to try it, make sure you have isolators of many different stiffnesses from dead soft to aluminum/steel. I would suggest starting with the engine mounted rigidly, and get it working perfectly like that. Then and only then, put in flexible isolators. This permits to reduce any problems you have to only the isolator stiffness, and not an engine setup issue. Beyond that, I have no idea how you evaluate whether they are too stiff, or too soft, or somewhere in between based on how the engine runs.

     It definitely does isolate vibration. In fact on David's airplane, it started out with a radial mount of something like 1/16 or .080 aluminum plate (held by the backplate screws), and that was fine as long as the rubber mounts where there. Once it was clear that it worked vastly better with solid mounting, the backplates started cracking. I think it went from .080 6061 to 3/32, then 3/32 steel, and maybe even 1/8 steel now. It still cracked in pretty short order. It has many cutouts for fuel tubing, etc, but still, very thick steel was cracking.

     Brett

       

My guess is that Dave Fitzgerald and Brett Buck would have had that base pretty well covered...

 "

  Unfortunately, and will all due respect to their advocates, soft mounts are pretty notorious for causing uneven or inconsistent runs, too. In nearly every case, with a precious few exceptions as far as I have seen. David's PA51 example was typical, soft mount, and a new engine. He and we tried every type of engine adjustment, isolated the tank and the fuel filter, the fuel lines changed the stiffness of the rubber grommets, etc all over the place. All sorts of different engine settings, compression, pipe length, fuel and air filters, etc. Finally, put aluminum spools where the rubber went, and within 1/4 lap of takeoff it was clear that it was solved, and the engine ran perfectly. "







Hi Brett
That is why I never used the soft mounts David did, or the ones used by Hunt  Mike Pratt  etc...  I saw a PA 61 rip the metal mounts Pratt had in his ship completely out, it just mangled them.
I also never used the "LORD MOUNTS" that bolted to the firewall then to a plate or mount. My system gave excellent runs and it was adjustable as far as how hard or soft you wanted it, It also  NEVER would be ripped out or come loose even with a 77 pulling on it.
The main problem with the soft mount most people used was the rubber kept getting softer and softer, sort of like chewing gum, the more you work it, the softer it gets.
By the way, I assumed he was talking about profiles with smaller motors, The soft mounts with a RC mount should work OK for them for a long time.  And if your using a wet 2 or 2 cycle run, there shouldn;t be any problems.

You are right , there was huge problems with soft mounts, but that was mainly on larger more powerful motors. It would work better if one replaced the rubber ones, with hard delrin, or aluminum.
It can be done, I have setup 4 planes with my design and  none have given "any "  problems at all.

and.. keep in mind I was just answering the question of has anyone  done it...  they have

Randy