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RPM/Pitch/Performance revisited


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Good afternoon.

I couldn't find the thread on the above but really enjoyed it.

I have a DUC Swirl three blade with the 100HP ULS engine and have been trying to get my best performance by adjusting my pitch.

My last pitch was 22* which produced 4950 on Take off with a WOT of 5350, sometimes as much at 5400.


After reading the thread I figured I was wasting fuel and may be putting a little stress on the gear box and engine at TO.

I re-pitched to 21* which proved to be to flat. I could now get 5380 at TO and well exceed red line. I was at 5800 RPM straight and level with plenty of throttle remaining. Air speed suffered 6 knots at 5200 RPM, where I like to keep it.


Went to 21.5* but still needed to add a little as I could still exceed red line. Really splitting hairs on a protractor that had 2* increments, I went to 21.75 or as close as I could measure on that scale. Just one needle width shy of 22*. That's the sweet spot on this type of prop.

I'm now getting 5350 at TO and a WOT RPM of 5750-5770.


1/4 degree just makes an incredible difference. It took 5 adjustments over the last three years to find the SPOT.

Thanks again to all who participated in the Pitch vs. RPM debate. It really was good reading.

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It will even be better to add a tad more pitch to get 5600-5650. Your 5300 rpm cruise would be my 5200 rpm cruise. Add .25 degree more. I bet you like it even better.


Yours is okay right now, but you are leaning on better climb versus cruise and fuel economy. I have set a few of the DUC props to get that 5600-5650 and the owners are happy with the results.

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Thanks Roger.

That would take me back to 22* which was the point I corrected from. I'll run it like this for a while and keep an eye on it. The warmer temps may have increased the RPM's. It was in the mid 60's when I tested the new pitch setting. Next time up I'll go to 5500 MSL and see what the WOT brings at cooler temps.

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What flap setting on take off do you use and what climb speed? Is it always the same? All flights must be operated the same way and with the same wind conditions and without any wide OAT differences.


Something's wrong with those numbers versus pitch settings. .25 degree isn't a big jump.


These numbers don't add up to me.

"4950 on Take off with a WOT of 5350, sometimes as much at 5400"  

These numbers are too close together. 4950 should be over 5500 rpm at WOT in level flight down around 5500' MSL. 5000 rpm at take off definitely should put you up around 5600-5650 at WOT in level flight.


These numbers don't seem to add up either.

"I'm now getting 5350 at TO and a WOT RPM of 5750-5770."

These numbers are too close together.


5200+ at take off should put you up to 5800 rpm WOT in level flight.



 Most take off rpms are around 4950-5000 which should give you around 5600 for WOT in flat and level flight.

.25 degree should  equal about 75 rpm. 1 degree is about 175 rpm. This is slightly different from prop to prop.

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I'm sure the conditions weren't the same, as the settings were changed at different times and seasons and never on the same day.

The two closest settings were this week a few days apart. winds and temps different, 10* flap setting at TO. After my trip south last year I re-pitched to 22* and didn't change until a week ago. 4950 was all I ever saw at TO.


Going to 21* was to flat. Like I said, I could push it way over red line. Put a half degree back in and it was still to high.

Just shy of 22* produced the best results as mentioned above.


The DUC "Swirl" has a narrow cord with very narrow (thin) leading and trailing edges. The prop acts like a constant speed prop due to its geometric design and that may be the difference. I need to fly more with this new setting to really pin it down, but, so far, this has been the best I've seen. I was also surprised that 1/4 inch made such a difference but that's what the tach was reading.


It's been set everywhere between 22.5 and 21* over the years.

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