I seem to remember the middle bearing did not get changed at 3000hly but only the outer ball ron ends.
Actually Think I was having the cross cable under engine too tight so maybe adjusting that would help. Ian Mc Phee Box 657 Byron Bay NSW 2481 On 16 July 2015 at 10:46, Will Bignell <[email protected]> wrote: > Are your two cross braces not over tensioned or loose? I've seen them over > tightened and the rubber hangers being out of alignment leading to > vibrations. When flying at cruise I've experienced the cable go snap and it > changed the vibration pattern until I reduced power as a cautionary move as > it felt odd. Landed to find it had given out a bit. Very hard to spot if > shrouded to protect from exhaust vibrations. > > Will Bignell > > > On 16 Jul 2015, at 9:22 am, Ian Williams <[email protected]> wrote: > > Hi Laurie, > > Your prob is interesting. Could it be a dynamic resonance problem?? I > have noticed that our rocket does have specific RPM / vibration > combinations. So just adjust the RPM accordingly. Maybe the fact that the > engine is rubber mounted and uses cables to transfer the engine thrust to > the airframe attached significantly below the centre of thrust could make a > resonance problem noticeable. > > About 16 years ago I was involved with installing a 4 blade Hoffman prop > on our Pawnee (a 260Hp O-540). (Reduced noise) We had a real problem with > a dynamic resonance where the mags would fall apart, starter motors crap > out etc. A real major prob. We figured that the rotational mass of the > wooden prop was much lower than the metal prop and more blade area so it > kind of fell into place that the problem related to the lack of prop > inertia. We obtained a drawing of a large counterweight between the prop > and the hub, installed it and the problem disappeared overnight. Just like > flicking a switch. > > This may be of some help. > > > > However a question … I am doing an annual inspection on the Dimona. The > rear spring loaded pin securing the tailplane … its outer case can be > rotated .. ie is a bit loose. Has that been a problem with the other Thai > Dimona’s I have tried to see how it could be removed ... .any idea’s. > Also the middle bearings on each elevator (not threaded) are a bit loose > and “click” as they go over centre … ie as the elevator goes up and down. > May look at making new fittings they push into … again have any of you had > to sort this out. > > Best regards > > > > Ian Williams > > > > > > *From:* [email protected] [mailto:[email protected] > <[email protected]>] > *Sent:* Friday, 10 July 2015 6:47 p.m. > *To:* [email protected] > *Subject:* Re: [DOG mailing list] Vibrations at certain revs > > > > Just to ad to Rob's post. We also installed new plugs. > > > > > > > *Regards * > > *Laurie Hoffman* > > > > > > > > > ------------------------------ > > *From:* Rob Thompson <[email protected]> > *To:* "[email protected]" <[email protected]> > *Sent:* Friday, 10 July 2015, 16:38 > *Subject:* [DOG mailing list] Vibrations at certain revs > > > > G'day All, > > On our dimona with a L2000 and Hoffman prop, we have a vibration issue > which is happening at around 2950rpm in fine pitch at 60kts and 2450rpm in > course pitch at about the same speed. > > Nothing really has changed recently but the problem has developed over the > past few months. I put in new carbs but that didn't make any difference. > > At full throttle it is climbing brilliantly. > > Anyone else had a problem happen like this? Just seems strange that it > would develop with no chips or damage to the prop from grass ops. > > I am going to hire Nigel's dynamic balancer which seems like the best bet. > This unit is fantastic for getting your engine/prop running really smooth > so hopefully this will work. > > > Rob Thompson > 0429 493828 > *Please note that my new email address is [email protected] > <[email protected]>* > > > > > > > >
