Hi

I was showing my graupner extra 300 to some of the guys, and I showed them how flexible the engine mount was, by yanking it around by the spinner. It moves quite a bit, about 5mm in any direction.

Its simply the nylon/teflon or hatever it is made from that flexes.


Well, they told me that I was loosing power due to this.
Is that true ?
Would it be better to install a more ridgit engine mount ?
why do poeple use use rubber dampened mounts, if the engine looses power ?


What is your experiance?

I guess the most important thing is how do you feel about it? It's your plane.

There are differing thoughts on the soft versus rigid themes.

I had begun to think the more firm mount was best? But, everything I have is mounted rigid.

i've just never got around to the soft mounts yet because of the controversy.

Enjoy,

Jim

Hello; I figure that in every other installation of an internal combustion in the world, the engine is anti-vibration mounted. They must know something about it. Only the occasional motorcycle engine is rigidly mounted.

If the engine is turning 10.000 rpms, whether it is soft mounted or not won't prevent the air passing over the prop, or decrease the amount of power produced.

What anti-vibe mounts will do is minimize vibration damage to the airframe and radio reciever.

hehe... I feel good about it, and the plane has lots of power.
But maybe IF I installed another mount, it would be even better

Some engines that shake, will shake even worse given rubber mounts.
Have you seen one of the new Harley's with the rubber mounts at an
idle ? The engine will shake back and forth about an inch, but very little
of that vibration is going into the frame.

FBD.

I agree with Donkey Doctor regarding lost power. I have argued this with others that insist that the energy absorbed by the flexing of a soft mount is "lost" energy, that you do not get back in power, but I still disagree with that viewpoint. I like the idea of using a soft mount on larger four-strokes (1.20 & up) due to their higher vibration. I even have a Saito .72 on a soft mount (Gator brand). I think a more rigid soft mount is better than a really flexible soft mount, though. Gator tells you to add silicone RTV to the grommets to stiffen them, if you so desire. Each engine/prop combo will vibrate differently, and what shakes like heck on one setup may be smooth on another setup.

Still important to balance the prop to minimize the vibration you DO get. Donkey Dr. is dead on. Have you ever watched a full size small plane start up (172, J-3 etc)? You'd think the engine was falling off it's mounts as it first fires up. I figure ours are about the same. I use a DuBro anti vibe mount, you can wiggle the prop hub about 3-5 mm in any direction, but I doubt it has this great an excursion with the engine running, though. I can tell a difference when I pick up the running plane with the anti vibe mount as compared to my ARF with a solid mount. Both are running comparable Saitos (.56-solid mount, .65-anti vibe). But go with what you're comfortable with. I doubt that whatever power losses there are, if any, are significant enough to matter.