Does a 3W 60cc engine need a isolation mount? I am putting it on a Yellow Aircraft Fiberglass fuselage P47. In general do people use anti vibration mounts with gas engines?

On my MVVS 58cc gasser the use of an isolation mount viods the warranty. You may want to check if it does on your engine.

Although isolation mounts are fairly common with 4 stroke engines and pattern aircraft, they are not commonly used with gas engines. They frequently contribute to the failure of exhaust and ignition components on gasoline engine powered aircraft. Their use will usually void all the muffler manufacturer warranties.

The 3w60 should not require an isolation mount. Vibration will be present, but the frequency is substantially different from glow engines, and the P-47 structure should be more than robust enough to carry it.

Any ideas why isolation mounts work adversely for gas engines?
It seems to go against conventional wisdom ..............[X(][X(][X(]

An improperly designed isolation mount will have adverse effects on a gas, or any other engine for that matter.
All other engines in "planes, trains and automobiles" are isolation mounted whether they are piston pounder, turbine or jet.
I use isolation mounts wherever practical and possible and I don't use ones that let the engine "jump around" nor do I mount them that firm that the isolation mount might as well not be there.
Good Luck

Merry Christmas
John

Any ideas why isolation mounts work adversely for gas engines?
It seems to go against conventional wisdom ..............[X(][X(][X(]

May be for that thing called frequency, thats the amount and size of movement waves (vibration frequency)

If I do not have an elaborate shaker test setup, how would I know whether the isolation mount is suitable or not?
And for that matter, why are isolation mounts usually bad for gas engines, but not for glow?

How about glow converted to gas?
Wonder what is the physics behind it .........
[&:][&:][&:][&:][&:][&:]

Random thought on soft mounts..If you run a twin there's no reason for an soft mount...
There are very few giant scale glow engines...Largest I can think of is the ST4500...
There is no physics behind glow VS gas..An engine will shake exactly the same no matter what fuel is used, the rotating parts don't change, you can NOT perfectly balance a single...
Some of our giant scale reaers used Q75 singles, never needed an isolation mount...
A 5.8 Sachs single will shake the muffler loose when soft mounted...
Slimline uses have an extra brace for their Pitts style mufflers and does NOT recommend soft mounts..
The Hyde soft mounts I have seen are so soft they put a ring on the front of the engine to help support it..However they seem to work well....Maybe they've since changed, it was years ago...

I see no particular reason why not to soft mount a gas engine if the exhaust system will allow it.

I use rubber mounts that allow only a tiny amount of movement (+- 0.2mm)
MVVS in their Edge video show a soft rubber mount with massive movement freedom (see picture). So how in the world can warranty be void if you use just the system they show? Beware though: The slender engine brackets are first mounted to a sturdy back plate, which in turn is used to soft-mount the complete assembly. Also observe the loops in the ignition cable, so it is allowed to move.
The only reason not to soft-mount might be, that the Walbro-type pumper carbs can become upset by the vibrations, and fail to perform properly in individual applications.

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Here is the order of preferences:

1. Well-designed isolator mount
2. Solid mount (no isolator)
3. Poorly-designed isolator mount

What is the criteria of a good isolator mount? The ability to:

1. Attenuate higher frequency vibration, such as at higher engine RPMs
2. Appear equivalent to solid mounting at lower frequencies, such as at idle.

Structurally, the airframe should be strong enough to withstand the full vibration spectrum of solid engine mounting. However, glue joints, fasteners and electornic components are much more affected by higher freq. vibration - so that's what a good isolator mount should be designed to mitigate.

Problem is, many of the commercially available isolator mount do exactly the opposite. They let the engine whip around at idle, while they may or may not islolate at higher RPM. Good designs will have the individual rubber mounts very far apart, supporting a very stiff sub-firewall. Obviously the fuselage cross section will determine how wide you can space the mounting points. If the firewall dimensions do not allow for good spacing, just solid mount the engine and let the airframe deal with it. Instead, isolate the electronic components well against vibration.

Hi
Hydro Mount is OK but costly
http://www.toni-clark.com/index_en.htm
Kris