max prop rpx increased on new prop/engine

[david.perl]

hi

looking for some thoughts

15 hours on the new plane with lycoming IO360 and Hartzell CS prop

We set the max rpm when setting up to 1700 rpm

After 15 hours flight time, ive noticed on take off the prop is going to 1770 rpm

is this increase to be expected?

 

[noelf]

Did you intend to type 2700 rpm vs 1700rpm?

 

[david.perl]

ooops, yes, my mistake, thxs for pointing out

 

[skylor]

Fine Pitch Stop?

ooops, yes, my mistake, thxs for pointing out

There are several things that you can check that might be causing this.

1. When you initially "set the max RPM to 2700" was this done during a static ground run up? If so, it's possible that the propellor speed was being limited by the fine pitch stops of the propellor hub and not the governor itself. During actual flight, once forward airspeed is achieved the propellor blades come off the fine pitch stops and the governor takes over control of the engine speed, thus it's possible you had the governor set for a higher speed than you thought.

2. Have you verified that the propellor speed control cable firmly pushes the governor arm against the stop screw with a bit of travel to spare? If the prop cable is running out of travel prematurely then you'll have trouble withe the max RPM setting being repeatable and consistent.

Skylor
RV-8

 

[david.perl]

thxs skylor.

1 is correct, we set max rpm as a static test

2 we also checked the blue knob was fully forwarded with a 1/8 inch spare to be confident the control cable was fully against the governor stop screw.

So is the adjustment made with the governor stop screw?

 

[skylor]

thxs skylor.

1 is correct, we set max rpm as a static test

2 we also checked the blue knob was fully forwarded with a 1/8 inch spare to be confident the control cable was fully against the governor stop screw.

So is the adjustment made with the governor stop screw?

If theory 1 is correct, then yes...screw the governor screw in. You didn't say which governor you have, but on my MT/Jihostroj governor the manual indicates approximately 25 RPM change per screw revolution. In practice I've found it to be a bit more sensitive than stated.

Skylor
RV-8

 

[david.perl]

Its an MT governor

 

[Walt]

Low Pitch stop adjustment.

It takes a few seconds for the prop gov to "catch up" on the take-off run to control RPM. I like to monitor RPM (if you have peak recording tach it easy) on the takeoff run with rapid throttle movement before the gov has a chance to take over rather than strap the aircraft down. It's not unusual in my experience to have to go 2-3 turns in or more on a new Hartzell to get the RPM down into the 2700 range using the prop low pitch stop.

You can hear the "surging" of an over reving prop and then the gov catch it (rpm reduction) on the TO run pretty easily if the low pitch stop is not adjusted properly.