The Vess was noisest by far, which was what we expected. We never for a moment considered the Vess viable for Pattern. That's not because there's anything wrong with a Vess, it was just a function of the diameter & pitch being wrong for the application. It's all we had handy in a Vess that day. We tested it and included the data because that prop is common for a sport or 3D setup, and up until our visit to Syssa Aircraft Performance a couple of weeks ago, Todd Syssa did not have any data to show what kind of power gains would result with that prop on a pipe. The RPMs picked up by over 1,000 with the pipe, which is huge. It was still good data for us, because it confirms a characteristic of this engine, which is what RPM range it is happiest in. When propped to run in the high 7K to low or mid 8K range, the SAP 180 does quite well on the pipe, with good throttle response. The Vess showed that it works well even up to low 9K. We would never run that high, but knowing how the engine behaves in that range is useful.

With the 18.1x10 STD blade APC, it was very well mannered in the air (with 1 flight under our belt) and on the test stand. I suspect that a 17x13 APC would be similar handling, just faster overall. We'll get around to trying several props, including a 17x12, which seems to be a light load for this engine. The 17x12 may be too noisy in the air, we'll see.

We did do some sound readings, but it wasn't really representative of what will happen in a model. We had the engine up several feet on a metal test stand, completely exposed, and the stand was attached to the back of a Dodge Caravan, which made for a nice noise reflector. But yes, the 3 blade seemed to be the quietest of the viable props. The 19x11 was real quiet, but it could only turn in the mid 6K range. No good!

The Macs header we used on the test stand was a standard OS 140 setup. I think Todd had to open up the holes to a slightly larger diameter. It's still usable on a 140RX, that's for sure.