Prop RPM after carb sync

by Adam Messer in 912 / 914 Technical Questions 7 years ago

Is it common to have to repitch the prop after a sync job? During my first serious post-sync flight this AM I could never get above 5200 WOT and fuel consumption and fuel consumption and oil temp were both elevated, as they have been in the past when the prop was overpitched. EGTs are close (50-100°F), CHT in range.

Re: Prop RPM after carb sync

by Roger Lee » 7 years ago

Roger Lee

127 5.22k 4.84k

You should not have to ever bother with the prop pitch after just a carb sync. Something else has changed. Is that 5200 static on the ground or at WOT in level flight? It's possible your carb sync didn't go as planned?

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Prop RPM after carb sync

by Adam Messer » 7 years ago

Adam Messer

20 29 59

WOT level flight. Guess I know what I'll be doing tomorrow...;-)

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Re: Prop RPM after carb sync

by Roger Lee » 7 years ago

Roger Lee

127 5.22k 4.84k

What was the in flight WOT rpm before a carb sync? The increased temps and fuel usage suggest the prop is over pitched.

Unless those carbs can't open all the way anymore I can't see how just a carb sync could change a WOT rpm that drastically. I try and shoot for a WOT level flight rpm of 5600-5650 for a ground adjustable prop. If I saw a 5200 WOT prop pitch I would tell the owner to reduce the pitch by 1.5 1.75 degrees and then do another flight to check it.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Re: Prop RPM after carb sync

by Adam Messer » 7 years ago

Adam Messer

20 29 59

5500+ in flight, intended to add 0.5° pitch to the Sensenich ground adjustable prop because I had to throttle back a bit from WOT.

I can't figure out how a sync job would require a prop pitch change unless I messed up and reduced the engine output. I'll check pneumatic sync and then repitch

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Re: Prop RPM after carb sync

by Roger Lee » 7 years ago

Roger Lee

127 5.22k 4.84k

If you're getting over 5500 rpm in level flight then you may want to leave it alone. 5500 is a continuous run rpm. Between 5500-5800 is 5 min. number. You do not want under 5500 rpm at WOT in level flight. Set the prop to get let's say 5600-5650 rpm and then cruise between 5100-5400. The finial cruise rpm is up to you. These numbers are just an average of what most owners run.
You don't need to run at WOT all the time if you don't want to. You may discover the additional speed gained isn't worth the additional fuel use. That's up to you. See if the rpm is over 5500 in level flight, but not over 5800 rpm. The 5600-5650 is kind of a nice balanced WOT rpm in level flight for a ground adjustable prop. You'll get a good balanced performance. If for some reason you need a better climb prop pitch then get it on up to 5700-5800. (i.e. flying on floats, short fields all the time or high DA constantly or lots of obstacles at airstrips). Defining your mission will help make this decision.
Being over pitched (under 5500 rpm at WOT) has absolutely no redeeming qualities and you'll lose climb, cruise, have higher engine temps and lose fuel economy not to mention stressing the engine.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

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Prop RPM after carb sync

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