---------------------------------------------------------- Engines-List Digest Archive --- Total Messages Posted Tue 03/30/05: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 08:03 PM - Re: Vibration(?) problems (jerb) ________________________________ Message 1 _____________________________________ Time: 08:03:58 PM PST US From: jerb Subject: Re: Engines-List: Vibration(?) problems --> Engines-List message posted by: jerb What type of engine, gear box model, ratio and prop brand and # blades do you have? jerb At 09:10 AM 3/14/05 -0600, you wrote: >--> Engines-List message posted by: AI Nut > >Since the engine sounds smooth without the prop attached, it sounds as >if you're hitting a resonance zone. If strong enough, these can destroy >engine and prop on the ground, and cause you to crash if in flight. >Avoid that rpm range unless you can change the resonance frequency to >something above the engines upper rpm limit or down in the 300-500 rpm >range. That might be difficult in your situation. > > >Peter Cowan/Lexy Cameron wrote: > > >--> Engines-List message posted by: "Peter Cowan/Lexy Cameron" > > > > >My "proven" Rotax 912 80hp "aircraft" engine has a very annoying > >problem. At most rpm's it is fairly smooth but between 3800 to > >4000 it feels like it is running very rough. Before I did some > >updates to the gear box I described it as knocking it was that > >bad. After the updates (overload clutch, new bellvilles etc) it > >is just rough. It is not carb synch; it is not ignition. I have > >checked the balance of the prop and set the pitch on the 72" > >Warp. If I take the prop off and runn the engine it runs pretty > >smooth with just a hint of vibration at the 3800 range. > >Can anyone suggest what this means and the fix? I will double > >check prop pitch and balance and I'd like to try a three blade. > >Anyone know how significent the moment of inertia issue is which > >PowerFin props say is one of their advantages over Warp? > >And Hello ED. I'm watching the progress of a 75hp two rotor about > >to be marketed. > >Thanks > >Peter > > > > > > > > > >