rpm limit on Sensenich prop for O-320?

[Larry Brons]

I need some info...I don't remember there being an RPM limit on the metal Sensenich prop for an O-320. I noticed in the prop logbook that came with it, a placard to place in view of the pilot, "2600 RPM Limitation". Huh?

[Mel]

Yep, that limit has always been there on the O-320 prop.

[Larry Brons]

How much of an issue is it to stay below the limit?

[terrykohler]

I have the same combo on my 9A. You shouldn't be able to exceed the limit at WOT at cruise. Pay attention to RPM limit while descending.
Terry

[fliier]

Keeping below the 2600 rpm limit is not an issue on my plane. The prop pitch is selected so that it maxes out right about at the limit.

In normal flight it becomes something you are aware of, but not something that interferes with the flying. In normal cruise operations it is a non-factor. It becomes 2nd nature that when the nose goes down the throttle backs off a little.

It can become an issue in some situations, such as where you want to quickly descend while increasing or maintaining speed (such as when joining up in formation). You can find yourself running out of RPM pretty quickly.

Similarly, the prop will overspeed if you put the nose down. As Sensenich says, if you perform aerobatics you will overspeed the prop. Of course, with this airplane you'd probably overspeed the engine anyway even without the placard.

I read once that the harmonic problem is at or around 2700 RPM, therefore the limit is set at 2600 to provide a buffer. (Now, when someone on the internet says "I read once" you can flip a coin as to whether it's true or not. Since this is a pretty critical issue you will want to check with the factory yourself.)

Since the engine redlines at 2700 and it's a fixed pitch, I believe this means that static RPM is also decreased. In other words it seems intuitive to me that a prop that gives you diminished horsepower at the top end also gives it to you at all the speed ranges below it. I am no expert in props, but the static RPM of 2150 seems pretty low to me.

For my type of flying, which is cross country cruising, I find it to be an excellent propeller.


John Allen
RV-6A

[Mel]

The limit is real and should be adhered to. It is my understanding that the harmonics can occur at as low as 2675 rpm. And tachometers are notoriously inaccurate.

[az_gila]

Originally Posted by Rick of Austin

Yes that 2600 limit seemed to be an insult because now its not a 160 hp engine/prop combination. At 2600 it is maybe 150hp? I just couldnt see giving up the horsepower when its so hard and expensive to come by.
Rick

Actually, it's 157 HP at 2600 rpm per the Lycoming O-320 Operator's Manual... (98.1%)

gil in Tucson ... who likes real numbers...

[Larry Brons]

Thanks for all of your input. I'm confident it will perform fine.

[airguy]

Originally Posted by az_gila

Actually, it's 157 HP at 2600 rpm per the Lycoming O-320 Operator's Manual... (98.1%)

gil in Tucson ... who likes real numbers...

AND - it's still 157 HP on a 9A - which will take that power and fly very nicely with it, thank you.

[kcpgm]

I have the same limit on my RV-7 with the H2AD engine it has not been a problem even with a low take off rpm about 2150 it still takes off great even with full load untill now

I flew the plane for about 100 hours before paint and when i painted it (tail art section Plane crazy) i installed a sam james plenum yes i had to do alot of work to make it fit the H2AD motor but now at cruise i'm at 2650 and more with any pitch down i have to throttl back and watch carefully the RPM's

I would like to change my prop the only one taht comes to mind and is affordable is the catto but with many emails to him with no replys i dont know what to do

again the limits only became a concern once i reduced some drag

ken flying in maine