Andy_R
February 12th 05, 12:37 PM
"Peter" > wrote in message
...
> Hi,
>
> I have a dual-needle RMI, the Honeywell/Bendix KI229.
>
> The instrument has seen various failures over the 3 years I've had it
> from new. Just the OBS not turning, just the needles not turning, the
> whole lot gone. The instrument has been changed and also a 400Hz
> inverter has been changed.
>
> I now have an intermittent failure which always fixes itself once the
> aircraft becomes airborne (but never on the ground) so it's probably
> vibration related. The OBS does not turn but the needles work fine.
>
> The RMI has its own 28V 400Hz inverter and the dealer reckons it is
> that (again).
>
> But surely the KI229 uses the synchro principle to rotate not just the
> OBS but also both needles, and the same inverter's failure would
> freeze the whole instrument?
>
> The HSI, from which the RMI (I am told) gets the heading data) works
> fine.
>
> I am an electronics engineer but haven't got into avionics much; also
> obtaining the schematics is a world-class challenge :)
>
> Can anyone suggest where to look?
As an electronics engineer you've probably got a lot more idea than I have.
The only things I can think of that happen in the air but not on the ground
are:
1. the engine alternator is running continually at a higher speed so there
is a decent 28v supply regardless of load.
2. the heater is on so any damp dries out
Anything more sophisticated is beyond me.
Rgds
Andy R
...
> Hi,
>
> I have a dual-needle RMI, the Honeywell/Bendix KI229.
>
> The instrument has seen various failures over the 3 years I've had it
> from new. Just the OBS not turning, just the needles not turning, the
> whole lot gone. The instrument has been changed and also a 400Hz
> inverter has been changed.
>
> I now have an intermittent failure which always fixes itself once the
> aircraft becomes airborne (but never on the ground) so it's probably
> vibration related. The OBS does not turn but the needles work fine.
>
> The RMI has its own 28V 400Hz inverter and the dealer reckons it is
> that (again).
>
> But surely the KI229 uses the synchro principle to rotate not just the
> OBS but also both needles, and the same inverter's failure would
> freeze the whole instrument?
>
> The HSI, from which the RMI (I am told) gets the heading data) works
> fine.
>
> I am an electronics engineer but haven't got into avionics much; also
> obtaining the schematics is a world-class challenge :)
>
> Can anyone suggest where to look?
As an electronics engineer you've probably got a lot more idea than I have.
The only things I can think of that happen in the air but not on the ground
are:
1. the engine alternator is running continually at a higher speed so there
is a decent 28v supply regardless of load.
2. the heater is on so any damp dries out
Anything more sophisticated is beyond me.
Rgds
Andy R