increase pitch ?

[Selma]

Does it make sense to change propeller pitch from 79" to 81" ?

Time for OH has come. On this occasion I was thinking to increase propeller pitch a bit for a little bit more speed in the cruise

It's a RV9a, O320 D1A / FP Sensenich 70CM7S9-0-79. She climbs 1500 - 1800, which is sufficient for me and really nice .... I know it will be a bit less later on.

What do the experts think?

Thanks

[Sam Buchanan]

Originally Posted by Selma

Does it make sense to change propeller pitch from 79" to 81" ?

Time for OH has come. On this occasion I was thinking to increase propeller pitch a bit for a little bit more speed in the cruise

It's a RV9a, O320 D1A / FP Sensenich 70CM7S9-0-79. She climbs 1500 - 1800, which is sufficient for me and really nice .... I know it will be a bit less later on.

What do the experts think?

Thanks

Not an expert but based on experience with my RV-6, O-320, I would leave the prop at 79". I had mine repitched to ~80". That is a cruise prop and climb will suffer with more pitch. Sounds like you have a good combination now.

[rvbuilder2002]

Originally Posted by Selma

Does it make sense to change propeller pitch from 79" to 81" ?

Time for OH has come. On this occasion I was thinking to increase propeller pitch a bit for a little bit more speed in the cruise

It's a RV9a, O320 D1A / FP Sensenich 70CM7S9-0-79. She climbs 1500 - 1800, which is sufficient for me and really nice .... I know it will be a bit less later on.

What do the experts think?

Thanks

The answer to your question would come from you answering a different question.
Is a lot of your high speed cruising time spent in a condition that you have to pull the throttle back to something less than WOT to keep from exceeding 2600 RPM?
If so, then a little more pitch would get you a little more speed (at the altitudes that that happens) at the cost of climb perf.
If not, then all you will do is reduce your climb perf, and at some altitudes probably also reduce your cruise perf.

[flyboy1963]

well, I ain't one of those, but have the same setup, 0-320 with 79" sensi FP.
right now, I only spin about 2150 at the start of my takeoff roll....thus making 87 hp or so.
I wonder what effect another inch or two of pitch would have on the length of the roll? Once you let it accelerate to 80 kts, no doubt you will see a decent RATE of climb.....and perhaps a few kts more at the top end.

have you considered the 'total' performance gain of adding one electronic ignition? you might see the same 2 kts gain!

[chrishalfman]

I'd run it first to see where you are compared to where you want to be, along the lines of what Scott said. Then your decision isn't quite as random of a stab in the dark.

If you're thinking of upgrading the prop, I can tell you a Whirlwind GA prop can be adjusted to whatever you want.

[Jesse]

Originally Posted by flyboy1963

well, I ain't one of those, but have the same setup, 0-320 with 79" sensi FP.
right now, I only spin about 2150 at the start of my takeoff roll....thus making 87 hp or so.
I wonder what effect another inch or two of pitch would have on the length of the roll? Once you let it accelerate to 80 kts, no doubt you will see a decent RATE of climb.....and perhaps a few kts more at the top end.

have you considered the 'total' performance gain of adding one electronic ignition? you might see the same 2 kts gain!

What engine do you have? I can't imagine how you are calculating 87 HP just from rpm. Percentage HP is based on Manifold Pressure and RPM, not just a linear relationship to rpm.

[cross]

If you are often reducing power to stay below redline rpm it would make sense, but I doubt if that's happening. Twisting a prop generally makes it slightly less efficient and it should only be twisted in one direction over it's lifetime, not back and forth.
If full throttle at cruise altitude is possible without exceeding 2600rpm, any increase in pitch will likely decrease your speed. A 160hp Lycoming will produce rated power at sea level at 2700 rpm, at any lower rpm it will be producing less than rated power even at full throttle.

[Soarandtow]

Rv9 lycoming 0320 hp est 187
Selmas ? Pushes me toward the ground adjustable whirlwind without the rpm restrition of the sensenich. I also hear the Cato prop works very well. Any thoughts of which way to go here.
I just read a report of a rv4 losing a blade from the sensenich prop

[Jesse]

Originally Posted by Soarandtow

I just read a report of a rv4 losing a blade from the sensenich prop

This got my attention. I have a Sensenich ground adjustable prop. Is that what the -4 had? Does anybody have any other details?

[MRM449]

I have a Sensenich 70CM6S9-0-78, on a RV-4. Went from 150 to 160 hp. so wanted to change the pitch. I took mine to Maxwell propeller in twin cities. They said Sensenich allows 4 in. total pitch change on this prop. Add one or two inches and fly it awhile and see how you like it. If you don't like it you can pitch it back the way it was or add more at a later date.