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Triangle engine mount question

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7 years 6 months ago #1369 by F3A-1
I have 2 projects that both have the phenolic triangle engine mounts. I see no mention of them in the plans or the plans changes. The plans call for a .250" aluminum plate.

The reason I ask is one projects has had a history of vibration. We balanced the prop (with concerns about the manufacturers quality) as best we could. The engine ran somewhat smooth until I reached 40MPH indicated at about 3,000 RPM, then a new and major vibration occurred. I closed the throttle and it immediately subsided. We are suspect of a harmonic resonance of the phenolic mount, instead of the aluminum spec. in the plans.

HAS ANYONE ELSE BEEN HERE?

Thanks for any input,

Lex

An ego is no match for gravity.

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7 years 5 months ago #1373 by F3A-1
HI all,

I went to the Q type fly-in last weekend and learned a LOT! The answer to the question I posted was "Kevlar". Terry Crouch, answered this and many other questions I had. The Kevlar fiber engine mount would not have a cycle failure as the aluminum mount would have an eventual crack/fail. The additional flexibility of the Kevlar would no doubt, also dampen vibration. THANK YOU TERRY for that answer!

We continued to adjust the carb and engine controls to get a relatively smooth and reliable range of operation. I did a couple of more runs down the runway and I feel the vibration is in the wheels/tires not the engine/prop. With the runway speed getting close to flying speed, and good engine RPM's I feel it is time to get the Quickie fully ready to fly prior to anymore tests.

Thanks again to Terry,

Lex

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