It is an exciting time to be in experimental aviation from the standpoint of propellers—there are some new interesting new designs out there that are just begging to be bolted on and tested, so this week, we’re flying the new “Explorer” three-blade composite prop from Hartzell on our RV-8. If you recall, last fall we compared the latest new Whirlwind composite three-blade, the WW-300, and loved it due to excellent speed and climb performance, as well as its light weight. There is value in doing apples-to-apples comparisons, so Hartzell asked if I’d bolt their new design on to the same airplane so that we could see how it does in the same environment.
If you read our reports from our last round of testing, we found that the newer composite blade design of the Whirlwind managed to break the old rule of thumb that a three-blade prop was slower than one with two blades by pulling the airplane along at the same speed as the older design metal two-blade Hartzell. Aerodynamic knowledge has advanced in the years between the two designs, so it as not a surprise that we’d see good things from the latest computer-aided designs. So far, although our results are preliminary, we are seeing the same thing with the composite Hartzell three-blade—it beats the two-blade Hartzell metal Blended Airfoil in climb, and matches it in speed.
In addition to testing the speed of all three props at a constant density altitude of 8,000’ (the industry norm for cruise performance comparisons), we decided to take all three props to a high altitude cruise to see how they would do in the thin air. At 14,000’, what we found was that both the two-blade Hartzell and the three blade Whirlwind had their best speed peaks at 2500 RPM, with speed dropping off above and below that RPM. The Hartzell three-blade had a much more constant speed range across the range of RPMs—but it also had a slower top speed by a few knots.
Look for a complete review with numbers as we finalize our data !