R44 Starter Inhibitors

[Aucky]

Hi Guys, Does anyone know exactly how the R44 starter inhibitor circuits work?

The rotor brake 'on' is obviously one, but then the clutch and low-rpm circuits also inhibit the starter in some manner don't they? whilst still facilitating a restart in flight if necessary. Could one accidentally engage the starter/shower of sparks (and associated ignition retardation etc...) in flight, or is this protected against?

I've been looking at the Electrical diagram but can't make 100% sense of it... :8

Cheers :ok:

[Pat Cox]

To activate an R44 starter whilst on ground requires:
1. battery switch ON
2. clutch/start circuit breaker IN
3. horn/start circuit breaker IN
4. rotor brake DISENGAGED (called "released" on schematic)
5. clutch switch DISENGAGED
6. ignition switch to START

Electrical flow is:
a. from battery to battery relay
b. from battery relay thru ammeter shunt to main bus
c. from clutch/start circuit breaker on main bus thru rotor brake switch to ignition switch
d. from horn/start circuit breaker on main bus to A569 low-Nr warning unit
e. from ignition switch thru A569 warning unit to A999 master radio relay
f. from A999 radio relay to starter relay/solenoid
g. from battery thru starter solenoid to starter motor

The starter solenoid is activated by the A999 master radio relay, which in turn is activated by the A569 low-Nr warning unit. The A999 relay's control coil grounds thru either a DISENGAGED clutch switch, or thru the engine oil pressure switch when there is no engine oil pressure (if engine is producing oil pressure then the A999 relay, and thus the starter, cannot be activated in flight).

All R44-series, and R22 s/n 2115 & subsequent, have a starter lockout feature incorporated as part of the A569 low-Nr warning unit. The lockout feature allows starter activation only when:

1. Clutch switch is disengaged AND [functional] belt tension actuator is fully disengaged.
OR
2. Nr (rotor rpm) is above ~69% (to allow for in-flight restart).

Fly safely.

[Aucky]

Amazing! Thankyou so much for taking the time to write that precise and prompt response. It's occasions like this that I really appreciate this website. Especially when it's straight from Torrance :ok:

Thanks again, Aucky

p.s. I shall pass this on to my colleagues and school notice board so that we can teach the definitive explanation, that sounds convincing enough for me :)