twin question, checking gov.

riot shields

riot shields

Well-Known Member
alright, i've gotta get something cleared up here. i've been taught too many different things, and i can't seem to find the published "correct" answer.

on a twin during run up, whats the correct way to check to ensure the governors are working? not talking about watching the manifold pressure, oil and rpm's...
now i was under the assumption that after you run the engines up to 2000 rpm's you pull the props back a little, about 1800 rpms, then advance the throttles slightly and the rpm's shouldn't go up... correct?

i've also been told to advance the throttles till the rpm's go back up to 2000, but that doesnt make sense to me, being a constant speed propeller and all..


tsk tsk for me not knowing.
 
Hopefully I'm recalling this correctly:

First I'd cycle the props
Then bring the props back until you can feel them "bite" ~about halfway
After that increase throttle by 2in. MP.
 
no one can answer that question for you unless you tell the aircraft type, and then you will still get everyone's "way" of doing it.

The specific published procedure should be in the "Expanded" run-up procedures in the POH.
 
pa-44-180 . 79 model
the expanded checklist says after cycling the props at 1500 rpms, advance the throttles up to 2000, then decrease the props 100-200 rpms. advance the throttles slightly and the rpm's shouldn't increase.... but they do. even with only about 1-2 inches of mp. so question is, is this a governor problem? or is this maybe a common thing to see in a 79 seminole ?
 
riot shields said:
now i was under the assumption that after you run the engines up to 2000 rpm's you pull the props back a little, about 1800 rpms, then advance the throttles slightly and the rpm's shouldn't go up... correct?
Click to expand...

Correct.

riot shields said:
i've also been told to advance the throttles till the rpm's go back up to 2000, but that doesnt make sense to me, being a constant speed propeller and all..
Click to expand...

Crazy incorrect. Maybe you could find some airplane somewhere that is supposed to react like this, but certainly not the bucket of bolts known as the Seminole.
 
Manifold Pressure should NEVER be set higher then your propeller RPM.

The correct way to check the governor on the Seminole, is set the throttles to 2000rpm with the props full FWD. Then pull the props back to 1800RPM. Slowly retard the throttles approx. 1-2in MP, make sure the props maintain 1800 RPM or very close to that. You do not want to advance the throttles with the props at 1800RPM because MP will exceed 18"!! You're just making sure the governor holds a specific RPM with a constant MP setting and with a slight MP change.
 
Airdale said:
Manifold Pressure should NEVER be set higher then your propeller RPM.
Click to expand...

In my Seminole Pilot Information Manual, almost every possible combination of of MP and RPM for 75% power has the MP higher than RPM.

In the turbocharged Seneca that I fly now, there are power settings in the table for 45% power that have MP higher than RPM.

The "don't have MP higher than RPM" is a good rule of thumb for training purposes, but in reality there are a lot of turbocharged and non-turbocharged piston aircraft with recommended power settings with MP higher than RPM.

the expanded checklist says after cycling the props at 1500 rpms, advance the throttles up to 2000, then decrease the props 100-200 rpms. advance the throttles slightly and the rpm's shouldn't increase.... but they do. even with only about 1-2 inches of mp. so question is, is this a governor problem? or is this maybe a common thing to see in a 79 seminole ?
Click to expand...

The RPMs may momentarily show a slight increase, but then the governor should kick in and bring the RPMs back down. At least that's the way it works in the Seneca. I can't remember what happened in the Seminole.

Mike
 
Airdale said:
Manifold Pressure should NEVER be set higher then your propeller RPM.
Click to expand...

This is an inaccurate statement. Climb out settings on the Seminole are 25" and 2400 RPM. In a turbo plane (turbocharged) cruise is 31" and props are set at 23-2400 RPM.
 
meritflyer said:
This is an inaccurate statement. Climb out settings on the Seminole are 25" and 2400 RPM. In a turbo plane (turbocharged) cruise is 31" and props are set at 23-2400 RPM.
Click to expand...

You know I don't have my POH on me right now, but I am positive our "After Take-off checklist" reads:

Power Set.........24" 2500 RPM

And our Cruise Checklist says:

Power Set.........22" 2300RPM (for local training)


Now on the cruise performance charts, I don't recall seeing a power setting higher then the props. I might be wrong but I can't look it up right now. So yes, my statement was not totally accurate and does not pertain to other aircraft.

I got screamed at during a check flight for initiating a climb by advancing full power before advancing the props and was specifically told by our head of maintenance that engine damage could result in a high power setting with a low RPM set due to engine load because of the propeller. I've never flown any twin other then the Seminole, so I can't comment on aother aircraft.
 
No worries at all. I've seen about 3 different Seminole checklists from 3 different schools and they all say different things.

It is a common teaching to avoid high manifold pressure settings along with a low RPM setting.
 
Airdale said:
was specifically told by our head of maintenance that engine damage could result in a high power setting with a low RPM set due to engine load because of the propeller.
Click to expand...

There can be some limitations in this regard, but they bear no relationship to the "oversquare" mythology. For instance, my Lycoming Operators Manual for the 360 series engine shows that any MP (up to 29 inches) is fine with RPMs 2400 and up. Below that, MP should be limited, but not in an extreme fashion. For instance, at 2100 RPM, the lowest you will likely use for cruise, the limiting MP is about 27 inches. Not much of a restriction!
 
Airdale said:
I got screamed at during a check flight for initiating a climb by advancing full power before advancing the props and was specifically told by our head of maintenance that engine damage could result in a high power setting with a low RPM set due to engine load because of the propeller. I've never flown any twin other then the Seminole, so I can't comment on aother aircraft.
Click to expand...
This is the reason you hear that you should never exceed RPM with MP.

When you go full power or several inches above rpm, you cause extreme head presures. But in accordance with cruise charts, MP can exceed rpm in certain conditions.
 
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