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Fixed Pitch Prop Operation

Warbirdsolutions

Active Member
All, out of over 20,000 hrs I have zero time with fixed pitch props. Catto is asking me how I want to operate it? Over redline at cruise? How do most of you operate your fixed pitch prop? Wide open on takeoff and pull it back some for climb and cruise? Appreciate any techniques you have...
Thanks,
Brad
 
What is your average flight profile and airport environment? I'd bet most are pitching for cruise, or redline ~2700 RPM at 10k WOT. RVs perform pretty well on takeoff, even with a cruise pitched prop.

If you're dealing with shorter strips/higher density altitude, you may consider more of a climb/cruise pitch profile to get WOT at a lower density altitude, but CATTO overall has these dialed in and perform great.
 
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Fixed Prop Op

We have a carbureted 160 hp RV-6 with a Catto. Our prop is the general use propeller, a compromise between climb and cruise performance, as suggested by Nicole Catto. We run our engine using pretty much, kinda... what Lycoming calls out. We climb at full throttle of course, and I generally lean to about 150 degrees rich of peak after the initial climb, going thru, say, about 2000' above takeoff. My wife likes to run full rich. We usually cruise at about 2500 RPM and see speeds around 160 kts. If I'm really in a hurry (not often) I'll run it at redline (2700) and we go a few kts faster.
We have Flintstones engine instrumentation (for now!) Between our old timey Alcor single probe EGT, the Marvel Dribbler tractor carb and no fuel flow instrumentation, running lean of peak is a bit dicey, I think. We just lean using the EGT as a loose guide and twist the red knob out to where it jjjuuusssttt goes rough. With Slick magneto and a Lightspeed Plasma III ignition systems, we burn about 7-8 gallons an hour.
Anyway, main thing is, we don't hesitate to run at high-ish RPM. Lycoming engines seem pretty tolerant of that.
 
And A Question

Just curious. 20,000 hours and never flown a fixed pitch prop? I'll bet you have an interesting story. What types did you do your initial training in?
 
320 with Catto here. I go WOT on take off and don't come off of that until decent. I have a bit of a climb prop. I can still make 2700 at 13000'. I cruise LOP at around 2720 at 8000' and get 160 knots. I can get more if I turn 2800, but rarely do.

A lot of this depends upon the type of flying you intend to do and how often you fly economy cruise or full out ROP.

Larry
 
We have a carbureted 160 hp RV-6 with a Catto. Our prop is the general use propeller, a compromise between climb and cruise performance, as suggested by Nicole Catto. We run our engine using pretty much, kinda... what Lycoming calls out.

We usually cruise at about 2500 RPM and see speeds around 160 kts.

Anyway, main thing is, we don't hesitate to run at high-ish RPM. Lycoming engines seem pretty tolerant of that.

Flying my RV-4 with a Catto three-blade I did about the same, and turbine smooth. 2500 RPM with it leaned to the tickle seemed to be a happy spot. That O-320 is happily purring away at over 2500 hours since overhaul.
 
Thanks everyone for your input! No special story. Bit of a misrepresentation. I did fly some fixed pitch airplanes many many years ago and frankly don’t remember much about it. Thanks for all the info!
Brad
 
The flight school I went to used a plane with a constant speed prop for initial flight training. After that into twins, also with a constant speed prop. I have many classmates that have never flown a fixed pitch prop.

The types were the Zlin 242L and Piper Seminole.
 
Brad,
If you get a prop pitched to not exceed your engine limit (usually 2700 RPM), you wont have to worry about limiting your throttle, except to save fuel. I originally had a fixed pitch Sensenich metal prop on my RV4 that would turn 2900 RPM at full throttle - at any altitude up to 12,500’. I replaced that prop with a ground adjustable carbon fiber Sensenich prop that I’ve adjusted to protect my 2700 RPM Lycoming engine limitation. My takeoff roll actually is less with this prop, but my second segment, and enroute climb performance is slightly less - but still pretty good at 1500+ fpm. However, cruise performance and efficiency is better.
If your goal is short takeoff and initial climb, then a finer pitch is what you would want, with the understanding you would likely overspeed your engine in cruise at full throttle and be giving something back in cruise speed and efficiency.
Think of it like this..... do you want your airplane to be stuck in 5th gear all the time (cruise prop)?, or do you want it to be stuck in 2nd gear all the time (climb prop)? Or, do you want it somewhere in between? Catto can make you a prop that will give you whatever ‘gear’ you want to be stuck in (fixed pitch pain). My ground adjustable will allow me to change my preference - which I don’t intend to do now that I’ve found my sweet spot. The only thing you should be concerned with at this point, in my opinion, is over speeding your engine. If you are at half throttle at 3000’ and seeing 2700 RPM, and you got there in one minute, you are leaving cruise performance on the table. And that’s fine if your goal is exceptional takeoff/climb performance. If you want to go somewhere fast, get a different prop.

Also, if you have a metal Sensenich, it can be re-pitched. It takes a couple gorillas with a long bar, but an experienced prop shop can do this. They should also do a new dynamic balance for you after this change.
 
RV8 with a Superior IO360 and Catto 3 blade prop.
Just putting around and looking down, 2200 rpm, 142 ktas and less than 6 gph at 3000 da.
Cruise at 2470 rpm at 162 ktas and 8.2 gph at 6000 da.
If I want to burn some fuel, 178 ktas at 2700 rpm and 10.5 gph at 8000 da.
I have a screen shot of my EFIS at 16000 da, 178 ktas and 7.8 gph. Also have a screen shot of my EFIS at 12000 da, 158 ktas and 5.9 gph. That is over 30 statute mpg. All of the above at rich of peak.
My home grass airfield is at 150 msl. With less than half fuel, I can go from standing start to 1500 msl in 60 seconds.
What gear do you suppose I'm stuck in?
 
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