Basic description of Generator and Lane system operation

RW
There are no warnings about this in the 912iS operation manual. If this turns out to be the case, I would hope it’s worth of an SI or SB.  And I would think manufacturers would want to change their POH and maybe even design systems to automate the switch or at least notify the pilot the switch is on.

The installation manual does call for a momentary switch

Paul.

We are running a number of 915is engines in our Magni gyros here in NZ.

Through practical testing I can confirm the following.

Gen A failure   both lane lights flash together. With Gen B now powering the engine management system

(EMS) & the battery backup switch turned on a small amount off charge will flow to the battery.

Battery voltage still reducing though , depending on loads.

If Gen A happened to come back on line & resume powering the EMS & Gen B the airframe & battery the lane lights continue to flash until engine shut down . Next start they would act normally.

Gen B failure- No flashing lights but a decline in battery voltage can be seen. Backup power switch on & again a small charge will come to the battery from Gen A.

If Gen B failed & the backup power switch is on & then Gen A failed you will again get both lane lights flashing until shut down. Battery is now powering EMS & airframe loads.

If starting with Gen B failed then the engine will stop when the start power switch turned on is turned off

unless the engine rpm is above 2400/2500 & the EMS is now being run by Gen A.

A bit of a double up with what Jeff has posted, but this is what I have found through failing each generator and operating at various rpm.

cheers

Pete Avery.

Hi All

As noted this the call out for the type of switch is momentary, some OEM use a relay that does the same function.  

The start procedure is called out in the owner's manual and is very clear, once you starrt it should be switched off as soon as the engine is stable, 1500 or higher RPM.  Given idle is more than this on almost every injected engine that would suggest pretty much right away.  The activation for the generators to produce power is pretty much instant.  In talks with Rotax it takes only 2 crankshaft revolutions to do all its calculations for timing and crank bias readings to trigger the injectors in the correct sequence.  There is no advantage to leaving it on more than just to get it to idle. 

Cheers

Jason Fish wrote:

The installation manual does call for a momentary switch

Jason,
I see that it does call for a momentary switch, which is probably the most failsafe method. I guess if the start power switch and starter buttons were placed close together you could still operate them with one hand and leave the other free to operate the throttle. Maybe two momentary buttons right next to each other would be a good setup.

I’ve seen many SLSA manufactured with maintained switches for the start power.  And while the Rotax OM does tell you to keep the switch on “during steps 7-10 of the start sequence”, there is not a clear indication to the manufacturers that leaving it on longer can damage the alternators.  I would hope that by making this failure mode more known, it would inspire SLSA manufacturers to alert owners or possibly even prompt them to swap maintained switches for momentary.