Bell 412 Question

[Overwait]

Just a quick one on the Bell 412...Why is the collective raised during shutdown?

Is there a particular N1 or Nr setting that one looks for during the shutdown sequence?

Many thanks.

[Shawn Coyle]

Because of the elastomeric bearings in the head. The blades will tend to a pitch setting that is above minimum pitch anyway. On startup, you have to push the collective down once the rotor starts turning.

[Troglodita]

Is there a particular N1 or Nr setting that one looks for during the shutdown sequence?



Maintain 77% Nr (Cyclic centre light out) using recommended 70%/70% N1 during the 1 minute cool down period prior to idle stop release and engine shut down.

Re Shawn's comment - after start I personally recommend that you wait until you have accelerated to at least 65 - 70% N1 on your way to 82% min after releasing starter prior to lowering the collective (if the elastomerics have had enough time to cause it to raise) which avoids the clunk clunk that you will experience if the hydraulics have not achieved full working pressure.

Trog

[Oracle]

It might be worth mentioning that the collective should not be raised more than one to two inches of end-travel after shutdown as this defeats the object of the exercise. Many folks haul up on it like they are exhausting the hydraulic pressure in an older beast, whereas in reality this ends up loading up the flex-beam the other way and leaving the component in a 'loaded' and stressed condition after shut-down. MIL pilots seems to be addicted to this 6-inch 'pull'!

[maeroda]

Because they don't have their ass kicked by the owner if they do pull the collective as a caterpillar left steer lever!!:E:E:E:E

BTW I always do leave the collective raised for itself after shutdown without blocking it and usually wait around 65% NR or positive feedback on HYD gauges to push it down do be sure not to cause the "clunk clunk".

Ciao

Maeroda

[Overwait]

Thanks for that...very much appreciated...

[800]

Wait until the rotor system has come to a complete stop, then gently raise the collective to unload the elastomerics.

[Big Guy]

There is a warning in the flight manual not to raise the collective while the rotor is turning. Also what happens if you raise the collective to high and put stress on the bearings. Bell does not recommend raising the collective but says let it raise by it self.

[TwinHueyMan]

"There is a warning in the flight manual not to raise the collective while the rotor is turning."

Then how does it take off? :}

[TheVelvetGlove]

Now that there was funny...

[IHL]

The Bell 222 was like that as well. You raised the collective a couple of inches to unload the elastomeric bearings. ( I say was like that-I haven't flown one in nearly 20 years.)