CS Prop - Not Reaching Max 2,700 RPM

N908RV · #1 08-24-2007, 03:38 PM

Looking for any comments folks may have on this...

I have a Mattituck TMX - IO-360 with a 74" Hartzell blended airfoil CS prop and the newer MT (Jihostroj) governor. I've never been able to get more than 2,600 RPM in level flight. (Full throttle - approx 30" MAP at sea level).

I have an optical tachometer and on static run-ups I do get 2,600, which is about what I should be getting on a static test - generally 2,650 would be the upper end of what you normally get on a static test. I thought I would bump up the static RPM a bit to equally increase max RPM in flight. I adjusted the low pitch stop (on the prop) to the equivalent of an additional 100 RPM, but in static checks and in flight, I got no change. So, I returned it to the factory setting.

I double checked and made sure the prop cable allows for full max rpm (low pitch) and it hits the detent correctly on the governor. As the governor is preset at the factory (in theory) I hate to mess with their low pitch stop on the governor, although it is easy to do and easy to put back to the way it was.

But before I do that - anybody have any experience with this or comments about what RPM they are seeing with this engine/prop/gov combination?

As you can see, I've flown it quite a long time like this, but I have put it off long enough and I want to squeeze the last bit of thrust out of the engine (even though I'll barely ever use that RPM setting other than initial take-off) it would be nice to have it there if I need it.

Thanks,

Rob

asav8tor · #2 08-24-2007, 03:44 PM

The adjustment is on the front of the hub for the fine limit. Inside for the coarse limit. You can adjust the fine limit and get more RPM in the situation you describe. Do you not have a manual for your prop that explains how to do it?

dan · #3 08-24-2007, 03:58 PM

Time to mess with the governor. It's easy...I have that same Jihostroj gov'r on my RV-7/IO-360. I was only getting 2640 RPM max out of the box. A slight adjustment and now it hits 2700 every time (actually I turned it up to 2720 for those rare occasions when I need to chase Wingnut).

Ironflight · #4 08-24-2007, 04:17 PM

I second Dan's advice. Being a novice maintaining constant speed props, I researched how to set the stops on the prop, and then asked my friendly IA about it and he said "Good heavens don't touch the prop - adjust the governor!!" I pulled out the governor book, found the adjustment procedures, and in five minutes, I had it turning 2700.

Paul

N908RV · #5 08-24-2007, 06:19 PM

Just the two folks I was hoping to hear from... I know you have similar set ups.

Thanks Paul and Dan - I'll adjust the governor tomorrow - you have me convinced.

Appreciate the quick replies. Paul, look forward to seeing you next weekend at the Warrenton B-17 event.

Best,

Rob

N908RV · #6 08-24-2007, 06:34 PM

Quote:

Originally Posted by asav8tor

The adjustment is on the front of the hub for the fine limit. Inside for the coarse limit. You can adjust the fine limit and get more RPM in the situation you describe. Do you not have a manual for your prop that explains how to do it?

Thanks Mike. I have the manual for the prop and I already adjusted the prop without success, so I'm moving onto the governor - I have the manuals for both. But I didn't want to mess with the factory adjustment of the governor without hearing from other folks with similar set ups. It's an easy adjustment, but didn't want to waste time adjusting it if others haven't had any success. A friend with a Whirlwind and a McCauley governor couldn't get 2,700 after adjusting the governor and the prop, so I thought it might be the same thing with the Hartzell.

Best,

Rob

rvbuilder2002 · #7 08-24-2007, 06:41 PM

With the gov. that you have, sometimes just turning the adjustment screw isn't enough. You also need to move the control arm one position on the shaft splines. I am pretty sure the instructions supplied with the gov. mention this. They also say not to just turn the screw out all the way and allow the stop pin to hit the boss that the screw is in, but to reindex the arm so that you can still be hitting the screw when you are at your final adjustment.

N908RV · #8 08-24-2007, 10:59 PM

Thanks - I will keep that in mind. Especially since I might reach the limits of the low pitch/max RPM stop screw on the governor to achieve 2,700. It may also help the geometry some.

Thanks,

R

N908RV · #9 08-25-2007, 11:33 PM

Just wanted to say that the governor adjustment was the way to go as Paul and Dan indicated.

I adjusted it this morning. Despite what the handbook on the governor said, 4 full turns out (25 rpm a turn) on the governor stop was too much - that took it from 2600 to 2800. You'd have thought I was racing at Reno this morning.

For other folks with this problem in the future, it is approximately 50rpm for a full turn on the low pitch stop of the MT (Jihostroj) governor. In the end an 2 full turns was all it took. So, 50 rpms for a full turn.

Ironflight · #10 08-26-2007, 06:55 AM

Glad that worked for you Rob...

Just think - you have just made the cheapest Horsepower increase you will ver find for your engine!

Paul