Author Topic: Prop Control RPM Drop  (Read 1075 times)

Ford Hausser

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Prop Control RPM Drop
« on: December 22, 2009, 03:19:07 PM »
I fly a 1974 E-55 Baron and during the run-up, the checklist says to increase the RPM to 2200 RPM and excercise each prop to note an RPM drop.  During my run-ups at 2200 RPM, I am not seeing any drop in RPM when I bring the prop control back to the stops, but when I increase the RPM to 2400 RPM, I do see a drop in the RPM.  Is it normal that I am not seeing a drop in RPM at 2200, but do a 2400? And is this a reason to worry?

Brian Conley

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Prop Control RPM Drop
« Reply #1 on: December 22, 2009, 04:28:15 PM »
Suggest calling the ABS Techs on that one.

Our IO 520 will get a drop in a prop cycle at 1700 RPM in the Bo.

Chuck Waldrop

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Prop Control RPM Drop
« Reply #2 on: December 22, 2009, 05:18:01 PM »
Hi Ford

The IO-520C's in my BE 58 due get slight drop at 2200 provided the oil is warm. My practice is to pull it back to the stop one time @ 2200RPM and expect to see around 100 RPM drop, follow this with mags at 1700RPM and a feather check at 1500RPM.

Chuck Waldrop

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Mike Bland

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Prop Control RPM Drop
« Reply #3 on: December 23, 2009, 05:03:48 AM »
This will happen if the oil is cold.  I have seen this with freshly overhauled propellers, but returns to normal with several hours on the props.  I see an RPM drop at 1200 RPM if the oil is warm.  You might try to cycle the props a few times at 2200  and then see if you get a drop at low RPM.  I'm not sure if this is something you need to be concerned about.  My fist thought is if they work OK at 2200 and will feather OK, it is probably OK, but I am not an expert on this.

Ford Hausser

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Prop Control RPM Drop
« Reply #4 on: December 25, 2009, 04:42:30 PM »
Thanks for the reply.  My engines are IO-550's rated at 300 HP.  To clarify things more, I notice at 2200 RPM the right engine RPM drops normally, but the left engine has to be around 2400 to note any drop.  This happens even doing a runup after an hours flight.  The mags drop normally at 1700 RPM, and the feather check works at 1500 RPM.

John Collins

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Prop Control RPM Drop
« Reply #5 on: December 30, 2009, 04:58:31 AM »
 
Quote from: Ford Hausser
Thanks for the reply.  My engines are IO-550's rated at 300 HP.  To clarify things more, I notice at 2200 RPM the right engine RPM drops normally, but the left engine has to be around 2400 to note any drop.  This happens even doing a runup after an hours flight.  The mags drop normally at 1700 RPM, and the feather check works at 1500 RPM.


Ford,

My guess is that the left engine prop governor could need adjustment.

As a side note, have you checked if the left prop will feather in flight and come to a full stop?  I had a Baron where there was no RPM drop at 2200 and when I feathered the prop in flight, the prop would still rotate and not come to a complete stop.

The problem turned out to be in the governor.

If you have unfeathering accumulators that work, you can easily check the feather angle of the blades on the ground. To accomplish this, set RPM to 1500 and pull the prop control to the full rear stop. As the RPM drops thru 1000 RPM, pull the mixture to idle cutoff. Now you can check the angle of the stopped prop.  When you are finished, just push the prop control back to maximum RPM and the prop will rotate out of the feather position.