The following summary is my understanding based on several emails between myself and Patrick Cox. For those who are unaware, Patrick is a technical representative for Robinson and lectures on the brilliant Safety Course at the factory in Torrance. Suffice to say, Pat is something of a guru on Robbies, falling into the "what he doesn't know about Robinsons is not worth knowing" category. He also does a very good job of promoting PPRuNe on the Factory Safety Course
The Governor change was deliberate, and came about as a result of SN-36, issued Nov 00 (as
cl12pv2s correctly pointed out). For those that don't have access, this is the reproduced text of Safety Notice 36:
Overspeeds During Liftoff
Helicopters have been severely damaged by RPM overspeeds during liftoff. The overspeeds caused a tail rotor drive shaft vibration which led to immediate failure of shaft and tailcone. Throughout the normal RPM range, tail rotor shaft vibration is controlled by damper bearing. However, damper is not effective above 120% RPM.
Mechanical correlation can cause overspeed during liftoff if RPM is increased to normal flight settings and collective raised before governor is switched on. Overspeeds can also occur if throttle is gripped too firmly during liftoff causing governor to be overridden. Inexperienced pilots, who are most likely to be nervous or distracted, are particularly susceptible to this type of overspeed.
To avoid overspeeds during liftoff:
1. Always confirm governor on before increasing RPM above 80%
2. Verify governor stabilizes engine RPM near top of green arc
3. Maintain relaxed grip on throttle allowing governor to control RPM
However, as
Grainger pointed out, we now have "Governor On" twice, once on the "Before Starting Engine" checklist and again on the "Starting Engine and Run-Up" checklist. The reason behind this is simply overkill - Robinson want the governor switched on
all the time to help prevent the many rotor and engine overspeeds
on liftoff.
You will notice that none of the checklists have you turning the Governor
off. If the governor is meant to be switched on all the time, logic dictates it should reduce the chances of operating without it. This is what Robinson are seeking to achieve. Also remembering that not all ships have the "Governor Off" warning light.
As for overspeeds on startup, the governor will probably
not prevent an engine overspeed if the throttle is open significantly; the unloaded engine just accelerates too fast.
At the risk of boring you all senseless, I would like to once again reiterate what I've mentioned earlier - the subs start at $10/year and are a great investment for anyone flying a Robinson Product - check
here for publication updates.
Thanks Patrick for taking the time out to answer my questions, and to everyone for their input on the thread
