New vibration

[RotaryWingBob]

PA28-181, just out of annual, with brand new prop.

Pre-flight, runup, takeoff roll, climb and cruise all seemed normal. However, when I reduced power to about 2,100 rpm to get under the Philly class B shelf, I suddenly got a strong vibration. Application of carb heat (I was thinking icing) had no effect, engine gauges all normal and in the green. When I increased throttle, the vibration went away above 2,250 rpm. Power output at various rpm settings seemed normal.

I decided to return to Brandywine rather than a precautionary landing at Morgantown. Throughout the pattern, landing roll, and taxi back to the hangar, I could feel the vibration, and the frequency seemed to be governed by engine rpm.

I have flown the aircraft since the new prop was installed and hadn't noticed anything like this vibration before.

Any thoughts on what might cause this?

 

[Skip Miller]

Check to see if the prop was indexed properly. Indexed = put on in the right way, i.e., with cylinder #1 at TDC, is the prop vertical, or some intermediate position. I have no direct experience but I am told it does make a difference. Check your engine maintenance manual for where it should be.

-Skip

 

[RotaryWingBob]

Check to see if the prop was indexed properly. Indexed = put on in the right way, i.e., with cylinder #1 at TDC, is the prop vertical, or some intermediate position. I have no direct experience but I am told it does make a difference. Check your engine maintenance manual for where it should be.

-Skip

I'll do that. Ironically, when I bought the plane, the pre-sale inspection showed that the old prop was misindexed.

What bothers me is that something seems to have changed in flight -- I didn't notice any vibration on the runup, for example, nor did I notice it on a flight a week ago (which was my first flight after the new prop was installed).

 

[Stache]

There are a lot of things that could cause this. Since the aircraft just came out of annual the propeller bolts were re-torqued (checked) as required. If the prop was removed it may be off one bolt hole or a bushing was left out.



However since it is a new prop it should be balanced to your engine this will cost about $200 dollars and is money well spent. When this is accomplished have them check the tack RPM calibration it may be off, most are off.



If the prop turns out okay you may other problem internal with a crankshaft damper.



Stache