Low Rotor RPM warning systems
 

Good day to all you helicopter Pilots. I have had a question put by the CAA regarding a helicopter that I am trying to restore to flight.
Did/do the twin turbine helicopters that you fly/flew have a Main Rotor LOW RPM warning system? Or high come to that?
I seem to remember that the Bell 212 and the S-58T has, and this must be because it has Manual Fuel control of the engines on the Twin-Pac power plant. Does the 412 have this? How about all the types.
DG

I imagine that every helicopter built, regardless of the number of engines, has got a low RRPM warning system. ("RRPM is life").

Certainly all of the twins that I have flown have had low and high RRPM warnings.

Are you able to say what helicopter you are trying to restore to flight? That way you might get someone who actually flew the machine, or who is keenly interested in the make. They would be able to give you specific information.

Bravo All but the newest Schweizer 300C's dont !

S76 has no rotor warn horn, just a visual indication on IIDS equipped ships.

EC135s have both low and high audible warnings.

Bell 47's & Hiller 12's didn't have low rpm warning - neither did CH-47's, at least through the D model (haven't set foot in anything newer).

Low Rotor RPM warning systems
 

SeaKings don't. At least not a warning system. RRPM too high : Blades fly off, RRPM too low : AC-Generators trip and send the AFCS on vacation, both not the thing you want to have in an autorotation.

Having bled Nr on a Chinook (A Model) to the point the Generators dropped off line taking the SAS with it....the shrill screams coming from the Co-Pilot worked very well as a Warning.

Good thing he did as I had my eyes closed at the time waiting for the Crash that I thought was about to happen.

Not a good feeling to do that......and a learning experience at the same time.

Harry - not true ref the low Nr - the generators don't drop off line because the underfrequency protection (that would take them off) is disabled in the air as a function of the weight on wheels microswitches.

Alouette II doesn't have a low RPM warning. Not sure about A-III's and Lama's but I suspect not.

Not exactly true Crab, Westland only guarantees that while airborne the Alternators will not trip as long as Nr is higher than 92%. Below that they can trip, and they will, have done that heaps of times in testflights.

Enstrom 280 and probably older 28s have no low RPM warning system, and for that matter no governor or correlator either!. All you have are tachos and a good ear! ATG.

Without the precedence, it may be the necessity of the system that you may be looking to consider. And given the inputs above, I think the inclination is obvious.. to have the Nr warnings available (both low and high) to preclude bad situations going worse.

Harry, I do a lot of advanced single engine work with one engine in manual and I see the Nr below 92% quite a lot and the gennies have never tripped off in 12 years of doing it - it is only when the WoW switch is made that the VRSP is allowed to trip them off.

They should come on line at 94% plus or minus one or two and trip off within 2% of that IIRC from the 5M but only on the ground when the underfrequency protection is enabled.

The system is specifically designed not to drop the gennies in flight, especially not at 92% since all the flyaway procedures use 91% Nr as a target figure - it wouldn't be sensible really would it?

dg93:
Did your helicopter, as originally certifcated have an audio RRPM warnng system? If it is being rebuilt, then it must be in accordance with the applicable Certification Standard at the time of Type Certification, be that BCAR, the Defence Standard (if mil only) or whatever. If it didn't have an audio system, then however advisable it may be to incorporate one now, it can only be done as a Minor Modification...which opens a whole new can of worms...!

I believe that the S76s are now being refitted with low rotor RPM warning.
Bell 412 / 212 had low rotor warning.

Mmmmm ...

412 will ALSO flash the Rrpm warning light in an O'speed condition as well ... :eek:

Low Rotor RPM warning systems
 

Thank you gentlemen for your input and thoughts. Just to put you out of your misery the helicopter I feel is quite over powered and in forty years service it never had a Low/high rotor indicator light so realy it should not need one now. I shall see what the CAA come up with. The aircraft is of course a Wessex Mk 2. We have carried out many ground runs, the next test is the flying, fingers crossed.
DG

Did somone say Wessex?

Do post some pics, or a link to a website. :)