The complete radio control model airplane FAQ.
I'm considering a soft mount for my next radio control model airplane. I noticed the price is significantly higher--are they worth it?
In a nutshell, Paul Kopp had the best answer (although there are some users):
Soft mounts originated in pattern as a means to reduce noise from the airframes. They really don't have much use elsewhere. Even 150cc TOC engines are hard mounted. On smaller engines, the soft mounts tend to just add nose weight, and the vibration of the motor reduces top end rpm. I agree with Ed - I wouldn't use one if someone gave one to me. Paul Kopp
This is what Paul was agreeing with:
No. [They aren't worth it.] In fact, I wouldn't use one if you gave it to me.
When asked why, Ed continued:
Think about it for a minute. Why would I want to carry the
extra weight of a device that is not needed? On top of that, I have to pay for it. Additionally, it stresses my engine
and voids lots of engine warranties if found out.
Of course, there are exceptions for every rule. I'm talking about sport flying model aircraft in an average flying environment. Where I live, average means that we do not have sound police patrolling the area with their sound level meters. Other places do have more stringent sound requirements, which may indeed make vibration isolation mounts almost mandatory. But not where I fly - or rather, where I used to fly. What was their phone number again? <G> Ed Cregger
I do not use any soft mounts if I do not have to. Right now I have an
engine (AirHobbies 3 inch twin) that was shipped with soft mounts as the way to attach the muffler/mount to my plane. My current plan is to have that
engine hard mounted by 01/01/01!
Why you ask? Simple, control effectiveness is enhanced and there is not that much gained from the soft mounting. I have had other gas burners soft mounted and they bounced around so much (at idle) as to break mount system (J&L).
There is a bunch of folks that will tell you that the soft mount systems tend to transfer MORE of the destructive vibration found at idle directly to your airplane AND that the high end suffers because of the soft mount adsorbing some of the energy. I cannot speak to the second issue, but I have experienced the damage generated by a gasser bouncing around at idle.
Go hard mount and balance your props. Jim Branaum
Not everybody is against soft mounting engines, though:
I have used soft mounts on nearly all of my airplanes for the past ten
years. As to why you would use them, well it depends on what your objective is. I began using them in California as a means to enhance noise reduction.
Think of your airplane as a drum. A soft mounted motor will reduce the engine noise that is made worse by the airframe.
The first soft mounts I used actually let the motor flop around a bit at idle. The motor would stop flopping around when powered up but you can also imagine that in the air it would point differently based on what maneuver you were doing. Then I went to a stiffer rubber and the flopping around ceased although there is still some deflection. The pattern people use a nose ring to reduce this deflection.
A couple of other benefits will become apparent over time. If you are not prone to crashing you will find that with a well mounted motor your airframe repairs virtually cease. I had a couple of airframes last over five years with no repairs. If the airframe lasts longer it also makes sense that the radio and servos are under less stress from destructive vibration.
Is it worth the hassle?? Are flaps, are retracts, is dropping a parachute, is anything worth the hassle?? All of us do this for both common and individual reasons. If you like to observe changes you can make through your engineering efforts, this is one area that is kind of fun.
One quick and easy way to reduce about half of the destructive frequencies is to just use a well nut. The motor will not move at all but the very high frequency vibrations will be absorbed. Will Beatty
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Revised: April 18, 2006 .