catto vs constant speed

[Reheat]

Paul your observations are correct. I do not pretend to be in the same league with you guys who design these things. The C/S curve was generated from a DOS program that Hartzell sent me some time ago when I requested propeller efficiency curves from them. I Graphed the data for sea level operation and have since lost the program when my old computer dumped. The acft was sold and I do not recall which specific propeller it was. The curves were meant to represent general FP and C/S props designed for RV's to show the basic performance differences. If you feel they are mis-representative in some way, I think we all would like to know so we can have a more acurate picture of what is going on. Perhaps the C/S would be better represented if the peak was skewed to the right a little. I seem to recall that the Hartzell peaked at .86. Your comment on the flat part of the curves has already shed some more light on the subject. Anything else you would like to add would be appreciated.

[roadrunner20]

Originally Posted by Reheat

Sorry Jon, didn't mean to be misleading. No intension of trying to sell you on the Catto. I just thought some graphic illustrations between Fixed and C/S props might be helpful to some. I do not have the where-for-all to give you a comparison between the Sensenich and the Catto. Both are good propellers, I'm sure, and I expect their performance to be similar. The Sensenich has some harmonic issues, weighs more, but is impervious to rain.

The basic physics (and the whole point, I suppose) is that there is no magic in the Catto that would allow it to perform like a C/S prop. I really like mine for its smoothness, light weight, and lack of moving parts and am willing to give up a little acceleration and rate of climb. Craig nailed the data point I gave him which was 75%/8000'/2700 rpm/200mph(175k). I did not ask for more speed so that TO/Climb could be as good as possible given the pitch of the prop.

The graphs definitely show the superior performance of a C/S prop. It's the "how much difference" I wanted to illustrate. My apologies if there was any confusion.

Chuck,
Are you running a 2 or 3 blade catto?
What pitch?

[gvgoff99]

Chuck, I apreciate your input and that, though you mention the graphs may not be perfect, I am willing to bet they are not only "in the ball park" but probably close to home plate. They give an excellent idea of the performance differences and how relatively insignificant they are (high density altitudes aside). Thanks, George
PS: I also have a Catto and except for the rain factor I like it. (I know that I would be over 2600 RPM with a Hartzell too frequently in my 160 HP Lyc.)

[David-aviator]

Thanks for the report, Chuck. Lots of good info here.

This is one I am saving to a pdf file for future reference.

[Steve Brown]

Originally Posted by L.Adamson

All depends where you live and fly, I suppose.

Out here in mountain country, we try to convince all that are still "sitting on the fence" to go with a C/S; even with the difference in cost.

Why......... because I don't know any RV owner around here, who wouldn't prefer a C/S over their fixed pitch prop, if money and engine limitations weren't of concern; especially if they've flown both for comparison. With high density altitudes, and quickly rising topography at various airfields, the C/S is amazingly different, performance wise. And that includes getting out of the airport, as well as getting in.

L.Adamson

My airport (KPAO) is so close to sea level that half the time my altimeter reads below sea level at the airport. On the other hand, my daughter lives in Littleton and I've flown the airplane out of KAPA on a hot day. Performance is obviously significantly degraded form sea level, but is also significantly better than my last airplane (1981 M20J) which had a CS prop. So, it depends on what you compare it to.
If I wanted to use even higher elevation and potentially shorter strips, with obstacles, I might be tempted to go CS. My first inclination, however, would be to address the problem with horsepower rather than CS prop. I'd rather add the pounds putting more CI under the cowling, if possible, because it doesn't add complexity in terms of maintenance or flying.
Just my preference.
My reasons for preferring FP are only tangentially related to money. I'm not a great mechanic and don't have lots of time to spend maintaining the airplane. So I put a very high value on keeping things simple. Also, I consider myself a decent IFR pilot, but I fly better IFR with fewer knobs to yank.
I'll admit that if I lived in high country my views on FP verses CS could change.

[Bugsy]

What are the rain concerns with the catto prop and what do most folks do to compensate for the condensate when IFR?

[Mel]

I've been flying my Catto for over 4 years and haven't found rain to be a problem.
Now to be honest, I don't like flying in rain anyway. When I get into rain, I pull back on power and head for the "bright spot".
I do have "prop guard" leading edge tape on mine.

[Reheat]

Dan, I am running a 66 dia / 76 pitch 3 blade.

Bugsy, Craig Catto says that if you keep the revs below 2200 then you will be ok in the rain. I haven't tried it, but I think some of the other guys have.

[Steve Brown]

Originally Posted by Bugsy

What are the rain concerns with the catto prop and what do most folks do to compensate for the condensate when IFR?

Rain usually means bumps. The RV9 has a VA of 100kts, so slowing down is a natural part of flying in rain anyway. For me that has meshed well with the RPM "limit".

I have flown in rain, but not heavy rain yet. I don't particularly like flying in heavy rain, but if it happens I'll slow to VA.

[gvgoff99]

I have flown in rain and throttle back to 2100 to be on the safe side. Even with that I still have a little rash on the first 5" or so of the leading edge. I do not have the prop guard tape and sort of wish that I did. The damage may have happened early when the rain was very light and before I pulled the power back.

Is there much, if any, loss of efficiency with the tape?