McCauley Governor Adjustment

From day 1, my O-360-A1A with the Hartzell BA prop and McCauley governor has only turned about 2620-2640 RPM on takeoff. I've never been too concerned about it, because there is plenty of performance as it is. But after a couple of "hot, high and heavy" takeoffs this summer, I thought "hey, why not get that extra 10 hp or so?"

After reviewing the McCauley manual, I pulled the cowl and (fortunately) decided to do an oil change while I was in there. Getting the oil filter off gives you more room to get to the governor, and that is a big help, because doing that governor adjustment is a .... PITA! I had to saw a couple wrenches in half to get them short enough to clear the firewall, and trying to install the safety wire on the hi-rpm stop screw after I had made the adjustment was also a bear. To be safe, I also verified full travel on the prop control, and adjusted the end fitting to match the new position of the hi-rpm stop screw.

Fortunately, the "1 turn = 25 RPM" ratio for adjustment specified in the McCauley manual proved to be about right, and now I am turning 2700-2720 RPM on takeoff, and it does feel a little stronger. One thing I do notice is that when the engine is fully warm (say, after the first flight), I get slightly less RPM, say 2680-2700. Is this a common scenario - higher RPM on a "cold" engine, and a little lower once the oil is fully warmed up?

Anyway, for those of you who've not yet done this task, I recommend:

• Small size wire nippers and compact safety wire twist pliers
• Very stubby 3/8 and 5/16 wrenches
• A small, stubby screwdriver to adjust the stop screw
• Patience
• A few cold ones after the successful test flight!

[PropProfessor]

There is another way to adjust your takeoff RPM with a Hartzell Propeller. Per the Hartzell Owners Manual 115N, page 4-5 you can adjust the propellers low pitch stop. 1/4 turn out equals approximately 50 RPM increase, check the manual for the procedure. The low pitch stop on the governor is only set to give you about 100 RPM adjustment on a new unit. Used or overhauled no so much. The props preformance like the engine decreases on hot days though and there's no cure.

The low pitch stop was actually the first adjustment I had made - in fact, over the last year or so, I adjusted it a couple times to try to get the correct takeoff RPM. But it never made any difference. After doing some further research, I found that the governor can ALSO be the limiting factor here, and in fact the McCauley manual that came with the governor mentions this.

Now, the problem is that the prop low pitch stop is likely adjusted WAY too low, but I don't know in what setting that would be a problem - except maybe an engine failure where the governor loses pressure and no longer controls the prop, in which case the prop could go to a lower flat pitch than it should. But my guess is that in that case, it would just mean you are flying a slightly bigger manhole cover than otherwise

[yakdriver]

Mine does the same thing and I have the MT governor. I get 2730 when cold and exactly 2700 when oil is hot. Don

[Kevin Horton]

Originally Posted by Rutus

Now, the problem is that the prop low pitch stop is likely adjusted WAY too low, but I don't know in what setting that would be a problem - except maybe an engine failure where the governor loses pressure and no longer controls the prop, in which case the prop could go to a lower flat pitch than it should. But my guess is that in that case, it would just mean you are flying a slightly bigger manhole cover than otherwise

This will happen after an engine failure even if the governor is controlling the prop. If the actual rpm is less than the selected rpm the prop will go to full fine pitch.

If you ever do have an engine failure, you will probably wish that the prop low pitch stop was set a bit coarser, to give better glide performance. Why not make that change now?

Which is coming up in a couple months, I plan to reset the low pitch stop back to the factory setting. Hopefully no engine failure within the next 2-3 months.

This also makes me wonder about the threads that talk about pulling the prop control back to coarse pitch if you have an engine failure. Is the governor really going to have any effect at that point? Does it depend on how fast (or even if) the prop is windmilling??

All of this hopefully to remain purely hypothetical

[Kevin Horton]

Originally Posted by Rutus

This also makes me wonder about the threads that talk about pulling the prop control back to coarse pitch if you have an engine failure. Is the governor really going to have any effect at that point? Does it depend on how fast (or even if) the prop is windmilling??

It all depends on how the windmilling rpm compares to the rpm that the governor is commanding if the prop control is pulled all the way aft. If the governor can command a very low rpm, and the prop is windmilling at a faster rpm, then pulling the prop control aft should help.

I don't know what the minimum commanded rpm is for the various prop governors. I'll eventually do this test with my McCauley governor. I'll shut the engine down, establish best glide speed, then pull the prop control full aft to see what the effect is. If there is an effect, I may do a limited amount of best glide testing in this configuration.

[PropProfessor]

The propeller governor needs a minimum of 40 psi to do anything. The reason for the propeller going to low pitch is if you loose governor control, you have a fixed pitch propeller at that point, the throttle is then your control through full rpm range. If it were to go to high pitch/ high manifold pressure after a governor failure your looking for a landing site because at a high pitch your engine will be laboring to make any rpm or it could stop turning altogether. Also by going to low pitch the propeller windmills giving you a chance for an easy restart. On a Hartzell HC-C2YR-1BF/F7497(-2) Low Pitch is 13.6+- 0.2 high pitch is 35.0+-2.0, at the 30 inch station, measure from the center of your hub out in inches.

[JetA4GA]

My recollection is that the main intended functions of each of the two following systems are :

i) Governor: To prevent the propeller from exceeding the engine/propeller RPM limits (high RPM set screw) and govern the propeller at the commanded RPM,
ii) Propeller Low Pitch Stop: On propellers typically used on RVs, to reduce the probability of the propeller from exceeding the engine/propeller RPM limits and, ensure some residual thrust in the event of a governor failure where the automatic reversion mode is for the propeller to go ?FULL FINE?.

Though not applicable to RVs, reference should still be made to FAR Part 23.33, ?Propeller speed and pitch limits? (in the interest of safety, it should be complied with).

23.33 (d)(1) deals with the high speed stop screw setting.

23.33 (d)(2) deals with the propeller low pitch stops setting.

The propeller Low pitch Stops is not intended and should not be used to adjust and control the TO/governed RPM.

Propeller Low Pitch Stops: The Propeller Low Pitch Stops should normally be set with the governor removed from the engine (install the blanking plate and gasket the engine normally came with); There are other ways to do this check, but removing the governor is the only true positive means of really making sure the ?governor is not governing? the propeller (it will indeed behave like a fixed pitch propeller since the blades will be against the Low Pitch Stops). Though 103% of the engine/propeller maximum allowable TO RPM is authorized by the rule, typically they are set at around 97-99% of the engine/propeller maximum allowable TO RPM). Anyhow, adjust iaw the propeller manufacturers instructions. This adjustment should be done prior to the governor adjustment or before any flight (this is your protection if the governor fails).

Governor high RPM screw: It should be checked in flight and adjusted iaw the governor manufacturer instructions (ENSURE TO NEVER EXCEED THE ENGINE/PROPELLER LIMITS by using the propeller control A/R).

If you have set the Propeller Low Pitch Stops below 100% (recommended), with the propeller control in the ?FULL FINE? position on a zero wind TO you should initially see a lower RPM (blades against the Propeller Low Pitch Stops) and, then the RPM will rapidly regulate at the set governed maximum RPM (high RPM screw setting) the minute you get some airspeed, this is normal and, it ensures everything is working as set (this is more evidently observed if you bring the engine to TO power before brake release).


Ref.: FAR 23.33:

http://rgl.faa.gov/Regulatory_and_Gu...ighlight=23.33

If Kevin does some flight tests on this, we know they will be well organized with valid data when complete - will be interesting to see what the results are!