I'm thinking of re-pitching the prop on my 150/150. It goes to redline (and beyond) immediately when you cob the throttle in level flight down low. I think for efficiency and max utility, it should hit redline & a bit beyond but should take a minute to sorta wind up to it.
It's a Sensenich 74-54. the STC sez use a 74-58. I borrowed a 74-58 from a friend & am gonna try it out this week. If I like it, I'll have mine re-pitched the same. If it's too much, I'll guess at what I want & sorta split the difference.
I have been told that the prop shops don't want to hear about pitch in inches when you bring one in for re-pitch, they want to know how much less rpm you want to see WFO. How many inches change equals how much rpm?

Eric

Eric

All props have a certain number of inches it can be pitched. There not all the same but its the total that matters if its lets say, 4 inches then it can be re-pitched +2 if that's too much then pitching it back 2 is the end of its life.

So if its been re-pitched you may not be able to have anything done with it.

Good luck

I had my (150/150) 74" McCauley at 54 for years doing lots of back country type flying. I had it repitched to 57 and that seems to be a nice combo pitch for my all around flying now. Still climbs well but good cruise too.

Too bad there isn't an affordable light weight CS prop available for our little birds.

I had a 82 x 41 Borer repitched to 43" in July and the cost was $75 if that is what you mean by 'how much'. The 41" was too flat for an O-320 160 hp. It would pull 2700 rpm in a 500 fpm climb. The 43" is about right in my PA-18. I gained about 3-4 mph in cruise too and didn't seem to loose anything on the bottom end.

What would it take to keep the borrowed prop if you like it? Somehow or another repitching a prop sometimes isn't exactly the same as a prop pitched that way from the factory.
If they are a good prop shop, tell em what you have, then tell them what you want RPM wise, your more likely to get what you want as opposed to telling them how many inches, but I'll bet you like the 58

Danny Boy wrote:Too bad there isn't an affordable light weight CS prop available for our little birds.

Have you looked at an aeromatic prop? Sort of a non-adjustable constant speed.
I don't know if your STC would allow it or not.

a64pilot wrote:

Danny Boy wrote:Too bad there isn't an affordable light weight CS prop available for our little birds.

Have you looked at an aeromatic prop? Sort of a non-adjustable constant speed.
I don't know if your STC would allow it or not.

Yes, I'm familiar with the Aeromatic prop...it's not a pracitcal alternative. What would be nice is an IVO Magnum electrically adjustable...but only the non-certified crowd get to use that stuff.

BTW: In answer to one of the original questions: You can figure about 35 RPMs difference per inch of pitch change.

Had an interesting time working on the prop issue today. My paperwork sez I have a 74DM6S5-0-54. The "S5" stands for a 1-1/4" spacer. The borrowed prop is a 74DM6-0-58. Turns out the prop on the airplane is actually a 74DM6-0-52. It does have a 1-1/4" spacer between the prop & the aft bulkhead. The spacer has stamped on it "do not remove spacer from propeller"-- no problem there, it seems to be stuck on there pretty good. So I can't use the borrowed prop- can't install with the spacer, and it doesn't properly fit the spinner without the spacer, plus the bolts would be too long.
This airplane was in a noseover type crash in 1995 & it was rebuilt (after sitting for several years). It had a different engine installed (with proper documentation), and I had a feeling that the prop had been changed also. There isn't any logbook or other documentation for this propeller.
I'll talk to the local prop shop tomorrow about this. There is a blank space in the prop model number stamping, maybe it can be legally restamped as a "S5" prop since it does have the spacer installed. Or maybe some sort of swap if they have one with the proper model number on it.
In any event, I'm thinking a 56 or so pitch would be about right. That should let it turn up to a bit over 2700 in level flight and give me around 130 cruise at 2500, without hurting takeoff and climb too much.

Eric

Not sure if this applies to your prop, but Dominion Prop in Anchorage told me they could repitch my 69CK-52 by up to 4" for a fixed fee (I think it was about $180) any further would cost extra. I'm planning to have it pulled back to 50" this winter since I'm only getting about 2450rpm at Vy and I'd like to see 2500+.

The prop I wish I could have is Sensenich's new ground adjustable composite. But so far it's only for experimentals.

Phil

Updating this tread... I ended up buying a new 56" pitch prop last year, with the AMR&D tip mod. This is where they put an undercut trailing edge on the propeller tip (like a tiny Hoerner wingtip) -- it's supposed to let it turn up like it has 2" less pitch. I don't think it's really doing that. But at what I paid for the prop from AMR&D, they pretty much threw the tip mod in for free so I don't feel took advantage of.
It does well in cruise, but I could stand more rpm for takeoff so after running it for a year now I'm thinking about repitching slightly flatter, like maybe 54. Not much change so not sure if it's worth the trouble- both money-wise & the fact that I'd be twisting on a brand new cherry prop.

Eric

We just had our prop re-pitched on the 150 to a climb prop and overhauled by Western Propeller. It ran about $500. Can't say it really made much difference in performance but it sure looks brand spanking new with all the knicks taken out and a fresh paint job.