That is good to hear your (Nigel) explaination re Stemme and it's extra demands on a magneto.
Ian m On 7 Oct 2015 1:07 pm, "Nigel Baker" <[email protected]> wrote: > The gears are not under much load when running I agree. > However when the impulse coupling is in action the acceleration loads must > be considered and this is considered the cause of failure. > The Stemme is unusual in that you have to run the engine on the starter > till the blades are deployed then go for the ignition so they go though > points faster than we do for that reason and it is also harder on the gears > than our aircraft are. They also suffer impulse coupling (ware) failures > more than we do due to the more time running on them. > Cheers. > Nige. > > > *From:* Rob Thompson <[email protected]> > *Sent:* Monday, October 05, 2015 8:47 AM > *To:* [email protected] > *Subject:* RE: [DOG mailing list] Mag Failure > > I think I might direct a 25mm air hose through the baffle straight onto > the magneto. We have our motor very well sealed with silicon and running > cool so I think we can spare that amount of air. > > Each Rotax ignition generates 2 sparks, once when the flywheel magnet hits > the coil, second when the trailing edge of the magnet passes the coil. The > sparks are reverse polarity. > > At startup with weak sparks, a zener diode will block the normal slightly > advanced spark. This is a very unreliable way of doing it and doesn't alway > work that well. Kick backs are the worst of the problems when the Zener > doesn't block the advanced spark properly. > > Starting on one only ignition circuit will help the problem but I have a > soft start circuit diagram that your Foxbat friends might be interested in. > > Rob Thompson > 0429 493828 > *Please note that my new email address is [email protected] > <[email protected]>* > > > ------------------------------ > From: [email protected] > To: [email protected] > Date: Mon, 5 Oct 2015 10:24:31 +1300 > Subject: RE: [DOG mailing list] Mag Failure > > A couple of points of interest, > > 1) I have been doing some delivery flying and test flying of a few > Foxbat microlites which have the 100hp Rotax 912 engine. They have > electronic ignition. On start up, the engine runs like a hairy dog for a > few seconds then smooth … as the electronic pick ups are changed > automatically from the TDC start ones to the normal advance ones … maybe > a similar idea could be designed for a limbach pickup(s) > > 2) We have also had a mag failure on a Grob 109 … quite a few years > ago though. Could it be that the 109 mag cooling is simply not up to > scratch ?? Wolf Hoffman seems to have cunningly used the cooling airflow > thru oil cooler to be directed over the mag of the Dimona. While warm > air of course, it still seems to offer significant cooling > > Ian Williams > > ZK-GCB > > > > *From:* [email protected] [mailto:[email protected]] *On > Behalf Of *Rob Thompson > *Sent:* Saturday, 3 October 2015 11:08 a.m. > *To:* [email protected] > *Subject:* RE: [DOG mailing list] Mag Failure > > > > Those gear teeth don't drive much of a load except if the rotor was to jam > for some reason? > > Not easy to tell from the photo but the rotor gear teeth look OK. Maybe if > heat is a factor the stripped gear may use plastic that softens at a lower > temperature. > > Did this happen at start up? If so the gear teeth undergo some serious > acceleration as the impulse coupling kicks. > > What about at shutdown? If the engine kicks back the gear teeth also > reverse direction suddenly. > > Some serious analysis needed...I guess all will be revealed in time! > > Rob > > Rob Thompson > 0429 493828 > *Please note that my new email address is [email protected] > <[email protected]>* > > ------------------------------ > > From: [email protected] > Date: Sat, 3 Oct 2015 10:33:42 +1300 > To: [email protected] > Subject: Re: [DOG mailing list] Mag Failure > > Could well be temperature related > > Sent from my iPhone > > > On 3/10/2015, at 08:46, Ian Mc Phee <[email protected]> wrote: > > My question is why does it happen? Is it based on hours or cycles of > starts or getting too hot or something else. I can remember once at > overhaul he replaced the cog gear as it looked a little damaged > > Ian m > > On 3 Oct 2015 12:15 am, "Nigel Baker" <[email protected]> wrote: > > Attached image of what failed in Rob’s Maggy. > > The drive gear stripped/lost a tooth and took the distributor gear with it. > > Cheers. > > Nige. > > > > > > --------------------------------------------------------------------- > You are subscribed to the Dimona Owners Group mailing list. > To unsubscribe, send email to: [email protected] > >
