Bell 412 Question
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Bell 412 Question
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.
Is there a particular N1 or Nr setting that one looks for during the shutdown sequence?
Many thanks.
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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.
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Is there a particular N1 or Nr setting that one looks for during the shutdown sequence?
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
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Collective lowering 412
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'!
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Because they don't have their ass kicked by the owner if they do pull the collective as a caterpillar left steer lever!!
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
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
Last edited by maeroda; 29th Jun 2008 at 23:04.
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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.
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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.)
