FYI - probably should have chosen a better title for this thread: something like - "performance tests of Aymar Demuth vs Catto Prop" - but interested readers will find it anyway.
Test Platform is my 150hp slow build RV-8. It's not the cleanest or lightest RV-8 but it's mine
Tests using a modified version of the methodology described by Box Axsom where I chose an 8,000' reference altitude.
FYI: It turns out that simply substituting 8000 for 6000 from Bob's method actually results in a normalized test altitude of 8300 ft.
All tests were WOT and leaned aprox 100 ROP
The propellers being tested are the original 2-blade Aymar Demuth 68-71 all wood propeller with epoxy pain finish and the Catto composite wood core 2-blade with nickel leading edges.
After 6 runs with the Aymar Demuth propeller and 6 runs with the Catto propeller the average was
157.8 kts vs 161.4 kts. If I throw out the high and low from both groups, the numbers do not change much with
157.6 kts vs 161.4 kts.
The Catto was manufactured as a direct swap for the AD. This resulted in a significant gap at the backer plate as the AD propeller was much rounder than the Catto. Filling this gap may contribute to slightly better performance of the Catto but that was not part of the test.
A few interesting details ...
Craig had not previously built a 2-blade propeller for a RV-8 with only a 150hp lycoming. Based on conversations, he predicted a 2750 rpm at WOT and a 4kts speed increase. The WOT max RPM during all tests was 2750. Averaging across all tests, there is approximately
3.75 kts speed increase.
The weight is
11 lbs vs 12.5 lbs
Static is
2300 rpm vs 2025 rpm
WOT is
2725 rpm vs 2750 rpm
CHTs are slightly lower with the Catto -
likely attributed to the more refined airfoil approaching the hub.
Climb is about the same.
Fuel burn at cruise RPM is about the same.
While a little extra speed is nice, the primary reason for the propeller testing was the nickel leading edges. However, if you can get an Aymar Demuth propeller that matches your engine, its a very good performer for the price.